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Article

Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb)

1
N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 31 Leninsky Prosp., 119991 Moscow, Russia
2
L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 Prosp. Nauki, 03028 Kiev, Ukraine
3
V. V. Voevodsky Institute of Chemical Kinetics and Combustion, 3 Institutskaya Str., 630090 Novosibirsk, Russia
4
Novosibirsk State University, 2 Pirogova Str., 630090 Novosibirsk, Russia
5
P. N. Lebedev Physical Institute, Russian Academy of Sciences, 53 Leninsky Prosp., 119991 Moscow, Russia
6
Academic Department of Innovational Materials and Technologies Chemistry, Plekhanov Russian University of Economics, 117997 Moscow, Russia
*
Author to whom correspondence should be addressed.
Deceased.
Molecules 2021, 26(14), 4296; https://doi.org/10.3390/molecules26144296
Submission received: 30 April 2021 / Revised: 25 June 2021 / Accepted: 28 June 2021 / Published: 15 July 2021

Abstract

:
A series of heterometallic carboxylate 1D polymers of the general formula [LnIIICd2(piv)7(H2O)2]n·nMeCN (LnIII = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of CdII instead of ZnII under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with LnIIIZn2 cores. All complexes 17 are isostructural. The luminescent emission and excitation spectra for 24 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 35 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.

1. Introduction

The design and synthesis of new coordination compounds with two or more different physical properties that are promising for practical application, as well as the search for the ways to modify the physical properties (including their reversible change) are urgent problems of modern coordination chemistry and physical chemistry [1,2,3]. Such properties may include a combination of non-trivial magnetism and luminescence [4,5] or conductivity [6,7,8], a combination of magnetism and rotation of polarized light [9,10], sensitivity of magnetic properties to irradiation [11], or thermochromic properties [12], electrochromism [13], the ability to convert mechanic deformation into voltage and vice versa [14] to display thermoelectric behavior [15] or magnetocaloric effect [16]. A change in the physical properties of a compound in comparison with the known prototype can be achieved by fine-tuning its structure by changing the synthesis conditions [17] or by an irreversible post-synthetic reaction [18,19], while a reversible change in the property can be caused by interaction with a certain substrate [20].
The choice of LnIII compounds for this study was caused by the unique properties of such ions, i.e., their ability to exhibit slow magnetic relaxation (the so-called Single-Molecule Magnetism, SMM, or Single Ion Magnetism, SIM) [21] along with luminescence [22]. A lot of coordination polymers, containing only LnIII ions as paramagnetic centers, exhibit SMM properties (in particular, slow relaxation of magnetization) [23,24,25], however, in many cases, the role of the exchange coupling between LnIII ions (if any) in the occurrence of SMM properties was not clear. In some cases, it was shown that exchange interactions between paramagnetic ions can facilitate magnetic relaxation via the mechanism of quantum tunneling of magnetization (QTM) [26], but the opposite effect was also found: QTM was quenched due to the CrIII···DyIII coupling compared to the analog containing diamagnetic CoIII [27]. More interesting effects were found for magnetically diluted Ln complexes, characterized by slow magnetic relaxation [23,28]. In addition, long-range magnetic ordering was found in the LnIII coordination polymers [29].
Thus, the main goal of this study was to reveal the effect of diamagnetic dilution of LnIII ions with CdII on the magnetic properties. Dilution of paramagnetic complexes inside an isostructural diamagnetic matrix reduces dipolar interactions and suppresses QTM, allowing examining the individual behavior of a metal ion in a particular environment [30,31,32]. Notably, it was shown that diamagnetic ions can induce a change in the magnetic properties of LnIII due to a change in the distortion of its coordination polyhedron [4,33]. A direct effect of CdII on the LnIII luminescence is not expected; there was no reason to expect the suppression of luminescence due to the incorporation of Cd. Thus, the second goal of this study was to reveal the fine effects of Cd incorporation, which could manifest themselves in the luminescent properties (including luminescence quantum yields and lifetimes). Finally, the development of new ways for assembling coordination polymers has also been challenging. It is known that, in many cases, stable polynuclear cores are formed due to the self-assembly of metal cations and ligand anions, for example, FeIII2MII (MII = Mn, Fe, Co, Ni and other) [34,35,36,37,38]. It has recently been shown that the combination of CdII ions with EuIII leads to the formation of compounds containing LnCd/LnCd2/Ln2Cd2 cores [39,40,41,42,43]. It was attractive to extend this methodology to the synthesis of the LnIII-Cd coordination polymers.
In this paper, we report on the synthesis, X-ray diffraction analysis, luminescence properties, as well as experimental and quantum chemical studies of magnetic properties of a series of coordination polymers [LnIIICd2(piv)7(H2O)2]n·nMeCN, where LnIII = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7).

2. Results and Discussion

2.1. Synthesis and Structural Study of Complexes 17

The reaction of cadmium(II) trimethylacetate [Cd(H2O)2(piv)2] with lanthanide(III) nitrates in the ratio Cd:Ln = 2:1 in MeCN produced 1D polymeric complexes [LnIIICd2(piv)7(H2O)2]n·nMeCN (LnIII = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7)). Upon addition of a stoichiometric amount of 2,4-lutidine to complex 2, unchanged starting compound 2 was isolated. In contrast, the use of chelating N-donor ligands (1,10-phenantroline (phen), 2,2′-bipyridine (bpy)) caused the destruction of the heterometallic metal core and the formation of complexes [Eu2(piv)6(bpy)2], [Eu2(piv)6(phen)2] [44]. It should be noted that the metal core did not undergo rearrangement upon replacement of the pivalate anion by the dianion of 1,4-naphthalenedicarboxylic acid leading to the formation of a metal-organic framework structure [45].
Complexes 14, 6 and 7 were characterized by single-crystal X-ray diffraction analysis. All the compounds were isostructural (Table S1), so only their general structure is presented and the main geometrical parameters are compared (Table 1). The complexes crystallize as solvates with one acetonitrile molecule per formula unit. In 1D polymeric chains, one can distinguish trinuclear linear fragments {LnCd2}, which play the role of monomeric fragments (Scheme 1, Figure 1a). In such units, metal centers are linked by carboxylate bridges from piv anions. The transition from SmIII to YbIII is accompanied by a change in the geometry of the LnO8 polyhedron. The coordination environment of the SmIII ion in 1 has the geometry of a biaugmented trigonal prism, the environment of EuIII ion in 2 can be described as both a triangular dodecahedron and a biaugmented trigonal prism with a minimal deviation from an ideal polyhedron among 13 types of known 8-vertex polyhedra (Figure 1b). The geometry of the LnO8 polyhedron in 3, 4, 6, 7 corresponds to a triangular dodecahedron (Table S2). Cadmium metallocentres are bound to oxygen atoms of bridging and chelate-bridging carboxylate groups as well as of one water molecule. The Cd1 ion is located in a pentagonal bipyramidal (D5h) CdO7 environment, where the atoms O1, O2, O5, O6, and O14 are located in the equatorial plane. The geometry of the Cd2 ion’s environment (CdO6) corresponds to both the trigonal prism (D3h) and octahedron (Oh). Hydrogen atoms of coordinated water molecules participate in the formation of H-bonds with the O atoms of the carboxylate groups (inside the polymer chain) and the N atom of the MeCN solvate molecule. Thus zigzag polymer chains are formed, the minimal distance between Ln ions (>10 Å) in the crystal corresponds to the distance in the polymer chain, while the shorter distance between Ln ions of neighboring chains is more than 11 Å (Figure 1b,c).
It was previously shown that the combination of LnIII with ZnII ions gives molecular complex [EuZn2(piv)6(MeCN)2] under the same conditions that are used herein for assembling LnIII–CdII coordination polymers [46]. The zinc(II)-lanthanide(III) analog [EuZn2(piv)6(MeCN)2] has a trinuclear metalcore with a central EuIII atom, which is similar to the crystallographically-independent unit of complex 2 (taking into account that positions of ZnII were occupied by CdII in 2). All six piv anions in the compound have a bridging type of coordination and bind EuIII to ZnII atoms. Only one acetonitrile molecule is coordinated with both zinc(II) atoms in the terminal position and completes the formation of the molecular compound. The difference in ionic radii of ZnII and CdII (r(Zn2+) = 0.88 Å, r(Cd2+) = 1.09 Å) [47] may be responsible for the difference in the structure of Ln-Zn and Ln-Cd complexes. As a consequence, the cadmium ion can have higher coordination numbers (CN = 5–7) compared to the zinc ion (CN = 4–6), and the CdII ions can coordinate the oxygen atoms of neighboring trinuclear fragments {LnCd2(piv)6}. Thus, cadmium ions induce the polymerization of Cd2Ln fragments with the formation of polymeric Ln-Cd pivalates. A similar situation was previously observed for complexes [Ln2M2(pfb)10(phen)2] (Ln = Eu, Gd, Tb, Dy; M = Zn, Cd; pfb- is the anion of pentafluorobenzoic acid): Ln2Zn2 complexes had a discrete molecular structure, while the Ln2Cd2 species were molecular or 1D polymers as a result of changes in the functionality of bridging carboxylate groups and π-π interactions between aromatic fragments (pfb anion and phen ligand) of neighboring tetranuclear fragments [48]. Similarly, 1D polymer [CdEu2(pfb)8(Etypy)(H2O)2]n (Etypy = 3-ethynylpyridine) was reported, where CdII ion adopted coordination number 7 and could be bound in the chain [39].
In all these examples, as in the present study, the high ionic radius of CdII and its ability to form a large number of coordination bonds at least contributed to the polymerization of CdxLn2 (x = 1 or 2) moieties and, in some cases, were the main driving force behind the formation of coordination polymers. As expected, molecular complexes with CdxLny pivalate cores were formed upon the addition of “capping ligands”, which blocked the coordination sites of CdII ions and prevented the formation of coordination bonds between these ions and pivalate oxygen atoms from the neighboring units [39,41,43,48,49,50]. Among the heterometallic Cd-Ln carboxylates that do not contain specific capping ligands, only the compound [Cd2Eu(bzo)6(NO3)(MeCN)2(THF)2] (bzo = 3,5-di-tert-butylbenzoate anion) had a molecular structure, and the coordination positions of the terminal CdII ions were blocked by coordinated THF and MeCN molecules [51]. Notably, this compound differs from all previous examples like the carboxylate ligand. Most likely, the formation of a molecular compound, in this case, is caused by the lower donor ability of O atoms of bzo- compared to pivalate, however, other effects (such as the energy of the crystal lattice) cannot be excluded.
Complexes 17 are stable when stored in air, their phase purity and isostructurality were determined using PXRD (Figures S1–S7).
IR spectra of the synthesized complexes 17 are similar. The observed absorption bands correspond to symmetric (s), asymmetric (as), deformation (δ), and skeleton (γ) vibrations of methyl groups in piv-anions, as well as valence (ν) vibrations of C-H bonds and carboxy groups. These bands are located at the wavenumber ranges 2961–2966 cm−1, 2921–2929 cm−1, 2864–2903 cm−1 (three bands ν(CH3)), 1530–1563 cm−1as(COO)), 1480–1486 cm−1as(CH3)), 1416–1427 cm−1s(COO)), 1377–1380 cm−1, 1360–1365 cm−1 (two bands δs(CH3)), 1220–1228 cm−1 (γ(CH3)). The difference Δν = νas(COO) − νs(COO) is 135–166 cm−1, which indicates the presence of both coordination types of the carboxylic groups—Chelate and bridging [52], which is consistent with the data of X-ray diffraction analysis.

2.2. Photoluminescence Properties of 24

Figure 2, Figure 3 and Figure 4 display the excitation and emission spectra of polycrystalline samples of compounds 24, measured at ambient temperature. Compounds exhibit bright luminescence in the red (2) or green (3 and 4) regions of the spectrum. The absence of broad bands of the ligands in the excitation spectra indicates the inability of sensitization through ligands. The high triplet level of the piv ligand (determined earlier as 27,470 cm−1 [46] does not promote the energy transfer to lanthanide ions, nevertheless, the characteristic red and green emission of Eu3+ and Tb3+ ions can be observed with the naked eye under ultraviolet excitation.
The emission spectrum of complex 2 demonstrates characteristic narrow bands at 579, 590, 616, 651, and 700 nm associated with the 5D07FJ (J = 0–4) transitions of Eu3+, respectively. The most intense 5D0-7F2 transition, named hypersensitive, is highly dependent on changes in the EuIII ion environment. In contrast, the probability of the 5D07F1 magnetic dipole transition in the first approximation can be considered constant, therefore, this transition is often used as a measure of the luminescence intensity. The ratio of the integrated intensities I(5D07F2)/I(5D07F1) is 4.8 for 2 and indicates the absence of an inversion center at the Eu3+ position [53]. The single symmetric line of the 5D07F0 transition, as well as the monoexponential decay of the luminescence, indicate the presence of a unique crystal site of EuIII. These data agree with the single-crystal X-ray diffraction data.
The emission spectrum of 3 (Figure 3) demonstrates the typical TbIII luminescence bands at 486, 542, 585, and 620 nm associated with transitions from the 5D4 excited state of Tb3+ to the 7FJ multiplets (J = 6–3), respectively. The 5D44F2 transition demonstrates low intensity at 640 nm. The most intense band corresponds to the 5D47F5 transition; its intensity is about 62% of the total integrated intensity.
The emission spectrum of 4 consists of three lines at 480, 575, and 665 nm, corresponding to the 4F9/26H15/2, 4F9/26H13/2, and 4F9/26H11/2 transitions of Dy3+, respectively (Figure 4). The 4F9/26H13/2 transition is dominant; its intensity is about 64% of the total intensity.
The excitation spectra of complexes 2, 3, and 4 (Figure 2, Figure 3 and Figure 4) demonstrate a series of narrow bands corresponding to the 4f–4f transitions of lanthanide ions and the absence of the broad absorption bands of the ligands. The excitation spectrum of 3 features a strong broadband with a maximum at ~31,000 cm−1, which is absent in the spectra of 2 and 4 and may belong to the 4f–5d parity allowed transition of TbIII.
The luminescence decay curves for 2 and 3 are well fitted by monoexponential functions (Table 2). The lifetimes of the metal-centered luminescence were long due to the absence of low-lying energy levels contributing to the depopulation of the 5D0 (EuIII) and 5D4 (TbIII) excited states, as well as the lack of efficient quenchers in the closest surrounding of lanthanide ions. The ligand environment prevents the coordination of solvent molecules to the lanthanide ion, which leads to a low rate constant of the non-radiative decay of the EuIII excited state.
The intrinsic quantum yield ( Q L n L n ) calculated for 2 turned out to be higher than for Eu(NO3)3·6H2O [54], and is comparable with that of aromatic carboxylate complexes of EuIII (Table 2). The lifetimes of the excited state (τobs) of complexes 2 and 3 are comparable to those for the LnIII-Zn and LnIII-Cd heterometallic complexes with aromatic carboxylate ligands, as well as for the LnIII pivalate complexes with coordinated aromatic N-donors, in which radiative decay prevails over nonradiative (for EuIII-containing complexes) (Table 2). These results confirm that the presence of “antenna” ligands and the absence of water molecules in the coordination sphere of the LnIII ion contribute to an increase of the lifetime, effective sensitization of emission, as well as a high quantum yield.

2.3. Magnetochemical Measurements and Modeling

Direct current (dc) magnetic susceptibilities in 5000 Oe dc-field were measured for compounds 3 (TbCd2), 4 (DyCd2), 5 (HoCd2), and 7 (YbCd2) in the temperature range of 2–300 K (Figure 5). The χMT values at room temperature were 11.6, 14.0, 13.3, and 2.4 cm3·K·mol−1 for 3, 4, 5, and 7, respectively. These values are in a good agreement with the expected values for one isolated TbIII (S = 3, L = 3, g = 3/2, 7F6, χT = 11.82 cm3·K·mol−1), DyIII (S = 5/2, L = 5, g = 4/3, 6H15/2, χT = 14.17 cm3·K·mol−1), HoIII (S = 2, L = 6, g = 5/4, 5I8, χT = 14.07 cm3·K·mol−1), and YbIII (S = 1/2, L = 3, g = 8/7, 2F7/2, χT = 2.57 cm3·K·mol−1) [64]. With a temperature decrease, the χMT values for 4 remain almost constant up to 100 K and then decrease with further lowering the temperature, reaching a value of about 8.5 cm3·K·mol−1 at 2 K. The χMT values for 3, 5, and 7 decreases with decreasing temperature over the entire temperature range, reaching minimum values of 6.3, 4.8 and 0.64 cm3·K·mol−1, respectively, at 2 K. Such magnetic behavior may be the result of depopulation of the excited Stark sublevels, corresponding to a number of crystal-field (CF for 3, 6) or Kramers (KD for 4 and 7) doublets [65]. χMT vs. T dependencies of 3, 4, 5, and 7 could be simulated using a model based on the Hamiltonian (1), similarly to reported cases [65,66,67,68,69].
H ^ = Δ Ln J z 2
where ΔLn is the parameter of electronic levels splitting by crystal field of axial symmetry, and Jz is the operator of the full angular momentum of LnIII ion. Consideration of the molecular field (zJ term) [69] improved the fit in all cases. The simulation was performed using Mjollnir software [69,70,71,72] as described previously [37].
The best correspondence between the experimental and calculated χMT vs. T curves was achieved at ΔTb = −15.9 cm−1, zJ = −0.04 cm−1 for 3 (gTb = 3/2, R2 = 6.1 × 10−4, which is defined as R2 = Σ(χTcalc − χTobs)2/Σ(χTobs)2), ΔDy = 3.9 cm−1 for 4 (gDy = 4/3, R2 = 6.7 × 10−4), ΔHo = 10.0 cm−1, zJ = −0.18 cm−1 for 5 (gHo = 5/4, R2 = 3.1 × 10−3) and ΔYb = 125 cm−1, zJ = −0.73 cm−1 for 7 (gYb = 8/7, R2 = 2.8 × 10−4) (Figure S8). The values of ΔLn are quite close to the values, reported previously for Dy [37] and Ho [69], however, the correspondence between the experimental and calculated χMT vs. T curve for 5 was not very good (R2 > 3 × 10−3). Thus, simple model based on the above Hamiltonian cannot describe magnetic properties of these two complexes adequately.
We also used the SINGLE_ANISO code and the results of SA-CASSCF/SO-RASSI calculations for model clusters 4m and 7m to simulate the χMT temperature dependences for 4 and 7 (see Section 3.6, Figures S9 and S11, Supplementary material). Indeed, our ab initio modeling, which takes into account the temperature-dependent population of Kramers doublets of isolated model clusters (Table 3), is in good agreement with experiment for 7 and in reasonable agreement—For 4 (Figure 5).
To investigate the magnetization dynamics, alternating current (ac) magnetic susceptibility measurements were performed for polycrystalline samples of 35 and 7. The studied complexes did not demonstrate the presence of slow magnetic relaxation in the zero magnetic field. The application of dc-magnetic field made it possible to observe non-zero values of the imaginary component of magnetic susceptibility for 4 and 7. Such a change in the magnetic behavior in the presence of an external magnetic field usually indicates a rather strong contribution of quantum tunneling of magnetization (QTM) to the relaxation process, which significantly accelerates the rate of relaxation. For 3 and 5, the deviation from zero of the χ″ value was within the instrument error range even in non-zero dc-magnetic fields (Figures S13 and S14). The high efficiency of QTM in complexes 4 and 7 is due to their insufficiently high magnetic axiality, as evidenced by the rather high values of gx, gy (Table 3), which leads to large values of the corresponding matrix elements between components of KDs of the transversal magnetic moment (Figures S10 and S12) [64].
For the most effective neutralization of the QTM effect, it is necessary to determine the optimal field at which the relaxation time is the longest. Measurement of the ac-magnetic susceptibility in the dc-field range from 0 to 5000 Oe at 2 K made it possible to determine the optimal field value, at which the maximum values of the imaginary component of the ac-susceptibility are shifted to the lowest frequencies; these field values were equal to 1000 Oe for both 4 and 7 (Figure 6).
The results of measuring the ac-magnetic susceptibility of complex 4 in the optimal dc-field are shown in Figure 7. The relaxation time τ0 = 1/2πνmax was determined by processing the dependences χ′(ν) and χ″(ν) using the generalized Debye model. Approximation of the high-temperature part of the τ(1/T) dependence using the Arrhenius equation (Orbach relaxation mechanism, τOrbach = τ0expEeff/kBT}) led to an evaluation of the effective energy barrier of magnetization reversal and the characteristic relaxation time, ΔEeff/kB = 15 K and τ0 = 5.6·10−7 s, respectively (Figure 8).
For compound 7, the maxima on the frequency dependence of χ″ were observed in an optimal field of 1000 Oe in the temperature range 2–4 K (Figure 6). The τ values were evaluated as in the previous case. ΔEeff/kB and pre-exponential factor (τ0) were determined by approximation of the high-temperature data using the Arrhenius law and found to be 13 K and 5.7 × 10−7 s, respectively (Figure 9). To approximate the experimental data in the entire temperature range the sum of Orbach, Raman, and direct mechanisms were used. The following values of the parameters were obtained: ΔEeff/kB = 7.2 K, τ0 = 7.1 × 10−6 s, CRaman = 2.8 K−7s−1, nRaman = 7, Adirect = 1.8 × 10−9 s−1 Oe−4 K−1, ndirect = 4, R2 = 0.99996, where R2 was determined using formula.
R 2 = E x p l a i n e d var i a t i o n T o t a l var i a t i o n = T S S R S S T S S = 1 R S S T S S
On the other hand, it should be borne in mind that the Orbach process does not always contribute to the relaxation process, which has already been observed for some Er and Yb complexes [73]. The absence of such a contribution can be evidenced by the ab initio prediction of the energy of the first excited state, which exceeds the effective barrier by two times for 4 and by an order of magnitude for 7 (Table 3), as well as by sufficiently large values of τ0. The relaxation times characteristic of the over-barrier magnetization reversal corresponding to the Orbach mechanism should be ~10−10–10−12 s. For 4 and 7, the values of τ0 are very far from these limits. Thus, we tried to explain the experimental data excluding the Orbach regime from the analysis of relaxation processes according to ref. [74].
For 4, the sum of Raman (τRaman−1 = CRamanTn_Raman) and temperature independent (τQTM−1 = A) terms described well the experimental τ vs. 1/T dependence over the entire temperature range (Figure 8, red line) with the following parameters: CRaman = 31 ± 2 Kn_Ramans−1, nRaman = 5.00 ± 0.06, A = 2970 ± 40 s−1, R2 = 0.99996. Furthermore, the data fitting by the sum of the direct and Raman relaxation mechanisms also provided satisfactory results with the following parameters: Adirect = (1.700 ± 0.005) × 10−9 K−1Oe−4s−1, ndirect = 4 (fixed for Kramers ions), CRaman = 11 ± 3 Kn_Ramans−1, nRaman = 6.1 ± 0.2, R2 = 0.99986. The fits with other sets of mechanisms led to over-parameterization.
Similar to the case of 4, the approximation of the temperature dependency of the relaxation time for 7 (Figure 10) was performed with sufficient confidence, taking into account the direct and Raman mechanisms of relaxation with the following parameters: CRaman = 1040 ± 100 K−n_Ramans−1, nRaman = 2.9 ± 0.1, Adirect = (7.4 ± 1.0) × 10−12 K−1Oe−4s−1, ndirect = 4, R2 = 0.9959. Thus, we propose that the magnetization relaxations in compounds 4 and 7 take place predominantly by the direct and Raman mechanisms.
A large number of DyIII complexes exhibit SMM properties, but the search for conditions leading to the formation of a certain geometry of the coordination environment of a metal ion and its isolation from other paramagnetic ions is a rather difficult task. The proposed method of incorporating DyIII into a polymeric chain of CdII ions and pivalate ligands made it possible to isolate metal ions from each other, but the geometry of the coordination environment did not favor to slow magnetic relaxation by the Orbach mechanism. The creation of a certain geometry of the coordination environment is apparently governed by the unpredictable action of several factors. For example, diamagnetic dilution of DyIII ions by ZnII in the heterometallic trinuclear {DyZn2} complex with a Schiff-base and carboxylate ligands was associated with the formation of DyO8 polyhedron with the geometry of square antiprism (Dy···Dy 9.736 Å) [75]. This {DyZn2} complex possessed a field-induced slow magnetic relaxation with ΔEeff/kB ≈ 12.3 K (2 kOe) [75]. On the other hand, in the case of 1D-polymer [Dy2(piv)5(OH)(H2O)]n based on tetranuclear fragment {Dy4(piv)63-OH)2} [76], the field-induced slow relaxation of magnetization was revealed using the ac-magnetic data analysis, but the barrier was much lower (ΔEeff/kB ≈ 4.5 K), this lower value was presumably caused by intramolecular exchange interactions between DyIII ions (Dy···Dy 3.790−4.175 Å). The same paper [76] reported on the binuclear complex [Dy2(piv)6(phen)2] (Dy···Dy 5.391 Å), for which the field-induced slow magnetic relaxation was also observed and the barrier was estimated using the Arrhenius equation as ≈ 28.4 K.
A direct comparison of the magnetic properties of heterometallic complexes of lanthanides with ZnII or CdII cations is hampered by the small number of such complexes with similar geometric parameters. Since the ZnII and CdII ions are diamagnetic, the difference in their effect on the magnetism of the Zn-Ln and Cd-Ln compounds is exclusively due to their influence on geometric characteristics. As noted above, the larger ionic radius of the CdII cation and, accordingly, its higher possible coordination numbers in comparison with ZnII are the main sources of differences in geometric characteristics. For the above zinc complexes, in one case, two relaxation pathways were observed, which is quite typical for heterometallic DyIII complexes. The existence of two relaxation pathways can be associated with several asymmetric units and, possibly, with low-temperature isomers/conformers or Ln-Ln interactions, which perturb the electronic structure of some LnIII ions. In the CdLn complexes, we observed only one relaxation pathway, which indicates that, in this particular case, the Cd-based structure was more symmetric and/or rigid in view of the changes caused by temperature (as shown in [37]). In Cd-Ln complexes, the higher separation of LnIII ions may be responsible for their better magnetic isolation and the absence of disturbing interactions. However, there are currently insufficient data to formulate general conclusions.

3. Experimental and Computational Details

3.1. Materials and Methods

The compounds were synthesized in the air using commercial MeCN solvent (˃99%). Commercial Sm(NO3)3·6H2O (99%), Eu(NO3)3·6H2O (99%), Tb(NO3)3·6H2O (99%), Dy(NO3)3·5H2O (99%), Ho(NO3)3·5H2O (99%), Er(NO3)3·5H2O (99%), Yb(NO3)3·6H2O (99%), were used without additional purification. Starting compound [Cd(H2O)2(piv)2] was synthesized from Hpiv (99%, Merck, Darmstadt, Germany) and Cd(NO3)2·4H2O (>99%, Acros Organics, Waltham, MA, USA) according to the known procedure [77]. Elemental analysis was carried out on an EA1108 Carlo Erba automatic CHNS-analyzer. IR spectra of the compounds were recorded on a Perkin Elmer Spectrum 65 spectrophotometer equipped with a Quest ATR Accessory (Specac, Orpington, UK) by the attenuated total reflectance (ATR) in the range 400–4000 cm−1. Luminescent spectra were measured with a Perkin Elmer LS-55 spectrofluorometer.

3.2. Synthesis of the Compounds

0.28 mmol Ln(NO3)3·xH2O (x = 5 for Ln = Dy, Ho, Er and 6 for Ln = Sm, Eu, Tb, Yb) was added to a solution of 0.20 g [Cd(H2O)2(piv)2] (0.57 mmol) in 20 mL of MeCN. The reaction mixture was stirred for 20 min at 80 °C, cooled to room temperature, and filtered. The solution was kept at room temperature and colorless crystals of complexes precipitated after 72 h. The crystals were filtered off, washed with cold MeCN (t = −5 °C), and dried in air at t = 20 °C.

3.2.1. [SmCd2(piv)7(H2O)2]n·nMeCN (1)

Yield: 0.21 g (63% counting per Sm(NO3)·6H2O). Calc. for C37H70NO16Cd2Sm (%): C 38.0; H 6.1; N 1.2. Found (%): C 38.3; H 6.2; N 1.6. IR (ν, cm−1): 3391 m, 2966 m, 2161 w, 1670 w, 1592 m, 1482 s, 1418 s, 1378 s, 1307 m, 1226 s, 1080 w, 1032 w, 900 m, 806 m, 789 m, 603 m, 541 m, 421 m.

3.2.2. [EuCd2(piv)7(H2O)2]n·nMeCN (2)

Yield: 0.28 g (86% counting per Eu(NO3)3·6H2O). Calc. for C37H70NO16Cd2Eu (%): C 38.3; H 6.1; N 1.2. Found (%): C 38.1; H 6.7; N 1.0. IR (ν, cm−1): 3352 w, 2961 w, 1594 m, 1534 s, 1511 s, 1480 s, 1460 m, 1416 s, 1362 s, 1224 m, 1031 w, 900 w, 805 w, 789 w, 602 m, 562 w, 540 m, 414 w.

3.2.3. [TbCd2(piv)7(H2O)2]n·nMeCN (3)

Yield: 0.26 g (78% counting per Tb(NO3)3·6H2O). Calc. for C37H70NO16Cd2Tb (%) C 38.0; H 6.0; N 1.2. Found (%): C 37.7; H 6.1 N 1.2. IR (ν, cm−1): 3381 w, 2963 m, 2871 w, 1597 m, 1535 s, 1514 s, 1481 s, 1461 m, 1418 s, 1378 s, 1362 s, 1225 s, 1032 w, 939 w, 901 m, 806 m, 789 m, 604 s, 564 m, 542 m, 458 w, 450 w, 440 w, 421 m, 407 m.

3.2.4. [DyCd2(piv)7(H2O)2]n·nMeCN (4)

Yield: 0.26 g (78% counting per Dy(NO3)3·5H2O). Calc. for C37H70NO16Cd2Dy (%): C 37.9; H 6.0 N 1.2. Found (%): C 37.6; H 6.3; N 1.0. IR (ν, cm−1): 3337 m, 3256 m, 2961 w, 1704 w, 1612 s, 1563 s, 1486 s, 1428 s, 1378 s, 1360 s, 1200 s, 1030 w, 899 m, 824 w, 809 w, 791 w, 672 w, 598 m, 560 m, 453 w, 418 w.

3.2.5. [HoCd2(piv)7(H2O)2]n·nMeCN (5)

Yield: 0.17 g (55% counting per Ho(NO3)·5H2O). Calc. for C37H70NO16Cd2Ho (%): C 37.8; H 6.0; N 1.2. Found (%): C 37.5; H 6.4; N 1.4. IR (ν, cm−1): 2962 m, 1704 w, 1585 m, 1539 s, 1483 s, 1462 m, 1427 s, 1379 m, 1362 s, 1032 w, 903 m, 811 m, 791 m, 594 m, 563 m, 543 m, 492 w, 450 w, 441 w, 419 m.

3.2.6. [ErCd2(piv)7(H2O)2]n·nMeCN (6)

Yield: 0.18 g (53% counting per Er(NO3)·5H2O). Calc. for C37H70NO16Cd2Er (%): C 37.7; H 6.0; N 1.2. Found (%): C 37.8; H 6.2; N 1.5. IR (ν, cm−1): 2964 m, 2162 w, 1673 w, 1531 s, 1483 s, 1457 m, 1381 s, 1365 s, 1231 s, 1032 w, 937 w, 902 m, 790 m, 587 s, 566 s, 492 w, 436 w, 419 m.

3.2.7. [YbCd2(piv)7(H2O)2]n·nMeCN (7)

Yield: 0.21 g (62% counting per Yb(NO3)·6H2O). Calc. for C37H70NO16Cd2Yb (%): C 37.6; H 6.0; N 1.2. Found (%): C 37.4; H 6.3; N 1.4. IR (ν, cm−1): 2964 m, 2162 w, 1673 w, 1531 s, 1483 s, 1457 m, 1381 s, 1365 s, 1231 s, 1032 w, 937 w, 902 m, 790 m, 587 s, 566 s, 492 w, 436 w, 419 m.

3.3. X-ray Diffraction Studies

Single crystal X-ray studies of crystals 14, 6 and 7 were carried out on a Bruker Apex II diffractometer equipped with a CCD detector (MoKα, λ = 0.71073 Å, graphite monochromator) [78]. A semiempirical adjustment for absorption was introduced for all complexes [79]. Using Olex2 [80], the structures of the compounds obtained were solved by direct methods and refined in the full-matrix least-squares anisotropic approximation using the SHELX software complexes [81]. The hydrogen atoms in the ligands were calculated geometrically and refined in the “riding” model. The crystallographic parameters and the structure refinement statistics are shown in Table S1. CCDC numbers 2044967 (for 1), 2044968 (for 2), 2044970 (for 3), 2044972 (for 4), 2044971 (for 6), 2044969 (for 7) contains the supplementary crystallographic data for the reported compounds. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk/data_request/cif (accessed on 14 July 2021).
The polyhedron geometry of metals was calculated using the SHAPE 2.1 software [82].
Powder X-ray diffraction data were collected using a Bruker D8 Advance diffractometer (CuKα, λ = 1.54 Å, Ni-filter, LYNXEYE detector, geometry reflection).

3.4. Magnetic Measurements

Magnetic susceptibility measurements were performed with a Quantum Design susceptometer PPMS-9. This instrument works between 1.8 and 400 K for DC applied fields ranging from −9 to 9 T. For AC susceptibility measurements, an oscillating AC field of 1 or 5 Oe with a frequency between 10 and 10,000 Hz was employed. Measurements were performed on polycrystalline samples sealed in polyethylene bags and covered with mineral oil to prevent field-induced orientation of the crystallites. The paramagnetic components of the magnetic susceptibility χ were determined taking into account the diamagnetic contribution evaluated from Pascal’s constants as well as the contributions of the sample holder and mineral oil.
The magnetization relaxation times τ = 1/2πνmax and the α factors, which account for the distribution in relaxation processes, were obtained by fitting the χ′(ν) and χ″(ν) plots using the generalized Debye model (see SI).

3.5. Photo-Physical Measurements

Luminescent measurements were performed with a Horiba-Jobin-Yvon Fluorolog FL 3-22 (Horiba Scientific, Kyoto, Japan) spectrometer, which has a 450 W xenon arc lamp as an excitation source for steady state measurements and a 150 W xenon pulse lamp for kinetic experiments. An R-928 PMT tube (Hamamatsu Photonics K.K, Hamamatsu, Japan) was used as a detector. The spectra were corrected for instrumental responses. Lifetimes were measured with the same instrument using a xenon flash lamp. The quantum yield measurements were carried out on solid samples with a Spectralone-covered G8 integration sphere (GMP SA, Renens, Switzerland) under ligand excitation, according to the absolute method. Each sample was measured several times under slightly different experimental conditions. The estimated error for quantum yields was ±10%. All complexes studied were powdered before measurements.

3.6. Details of Quantum Chemical Calculations

Coordination polymers were divided into smaller structural fragments of individual spin centers, which then could be treated by ab initio computational methods. Calculations were performed for DyCd2 and YbCd2 clusters using the truncated XRD geometry with the trBu groups substituted by Me groups in the piv ligand (hereinafter referred to as 4m, 7m, Supplementary Materials, Figures S8 and S10). The SA-CASSCF/SO-RASSI approach [83,84,85], implemented in the MOLCAS 8.2 suite of programs [86], was used for calculations. The ANO-RCC-VTZP relativistic basis sets for lanthanides and oxygen atoms with the smaller ANO-RCC-VDZ for other atoms were employed [87]. The scalar relativistic effects were taken into account using the DKH2 Hamiltonian [88]. For the dysprosium complex, 21 sextet, 128 quintet, and 130 doublet states (the energy region up to ~50,000 cm−1) were taken into account with the active space consisted of 9 electrons distributed on 7 f-orbitals. For the ytterbium complex, seven singlet and seven triplet states were accounted with the active space consisted of 13 electrons on 7 f-orbitals.
The g-tensors for Kramers doublets, their orientations in the molecular axes, and temperature dependence of the molar magnetic susceptibility were evaluated using results of the SA-CASSCF/SO-RASSI calculations and SINGL_ANISO code [89].

4. Conclusions

A series of new LnCd2 heterometallic 1D polymers [LnCd2(piv)7(H2O)2]n·nMeCN (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb) with pivalic acid anions were synthesized and characterized by various methods. Due to the larger ionic radius of CdII and its ability to have higher coordination numbers in comparison with ZnII, the trinuclear units LnCd2 undergo polymerization, forming 1D chains, in contrast to the discrete Zn2Ln analogs. The polymers [LnCd2(piv)7(H2O)2]n·nMeCN are isostructural; according to the single-crystal X-ray data, the geometry of the LnO8 polyhedron changes from a biaugmented trigonal prism for Ln = Sm and Eu to a triangular dodecahedron for Ln = Tb, Dy, Er, and Yb. In the polymeric chain, lanthanide ions are isolated from each other by two Cd ions (the minimal Ln···Ln distance is more than 10 Å) and coordinates only the oxygen atoms of the bridging carboxylate groups. This type of the closest coordination environment, where efficient quenching groups are absent, gives rise to higher values of the intrinsic quantum yield of luminescence for 2 (EuCd2 core) than for Eu(NO3)3·6H2O, and the quantum yield comparable to that for EuIII aromatic carboxylate complexes. The excited state lifetimes for 2 and 3 (EuCd2 and TbCd2 cores) are comparable to the similar lifetimes of the Ln-Zn and Ln-Cd heterometallic carboxylates. Complexes 4 and 7 (DyCd2 and YbCd2 cores) exhibit the properties of field-induced SMMs. Based on the analysis of the relaxation of magnetization and the results of high-level ab initio calculations, the contribution of the Orbach relaxation mechanism was excluded. The sum of the Raman and QTM mechanisms was dominant in the magnetization relaxation for 4, and the sum of the direct and Raman processes was the dominant relaxation mechanism in the case of 7.

Supplementary Materials

The following are available online. Tables S1 and S2 (structural data), Figures S1–S7 (PXRD data), Figures S8, S13, and S14 (magnetic data), Figures S9–S12 (computation data).

Author Contributions

Conceptualization, validation—A.A.S. and I.L.E.; methodology—M.A.S., I.S.E., N.V.G., and R.A.P.; formal analysis—M.A.S., I.V.T., P.N.V., and N.N.E.; investigation—M.A.S. and E.A.V.; calculations—N.P.G. and A.A.D.; writing—original draft preparation—M.A.S. and S.V.K.; writing—review and editing—M.A.K., S.V.K., and N.P.G.; funding acquisition—I.L.E. All authors have read and agreed to the published version of the manuscript.

Funding

M.A.S., N.V.G., P.N.V., N.N.E., A.A.S., M.A.K., and I.L.E. thank the Ministry of Science and Higher Education of the Russian Federation, grant number 075-15-2020-779.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available in this article and Supplementary Materials.

Acknowledgments

X-ray diffraction analysis, CHN and IR-spectral analyzes, as well as magnetochemical studies, were performed using the equipment at the Center for Collective Use of the Kurnakov Institute RAS, which operates with the support of the state assignment of the IGIC RAS in the field of fundamental scientific research. Photo-physical measurements were carried out with financial support from the Ministry of Science and Higher Education of the Russian Federation using the equipment of the center for molecular composition studies of INEOS RAS. S.V.K. thanks to VolkswagenStiftung, Trilateral Partnership project “Multifunctional molecular materials-bridging magnetism and luminescence” (grant no. 90343) for support. A.A.D. and N.P.G. acknowledge the Supercomputer Centre of Novosibirsk State University for computational resources.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Samples of the compounds 17 are available from the authors.

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Scheme 1. Schematic structure of 17.
Scheme 1. Schematic structure of 17.
Molecules 26 04296 sch001
Figure 1. The fragment of the polymer chain (a); Methyl-groups and solvent molecules are omitted, the dashed line corresponds to H-bond, atom index: ½ − x, ½ + y, ½ − z (A); ½ − x, -½ + y, ½ − z (B)), the EuO8 polyhedron (b) and crystal packing (c,d); H atoms at carbon atoms are omitted, the interatomic distances Eu···Eu are indicated by arrows) of 2.
Figure 1. The fragment of the polymer chain (a); Methyl-groups and solvent molecules are omitted, the dashed line corresponds to H-bond, atom index: ½ − x, ½ + y, ½ − z (A); ½ − x, -½ + y, ½ − z (B)), the EuO8 polyhedron (b) and crystal packing (c,d); H atoms at carbon atoms are omitted, the interatomic distances Eu···Eu are indicated by arrows) of 2.
Molecules 26 04296 g001aMolecules 26 04296 g001b
Figure 2. Excitation (blue line, λem = 616 nm) and emission (red line, λex = 394 nm) spectra of 2 (solid sample, RT).
Figure 2. Excitation (blue line, λem = 616 nm) and emission (red line, λex = 394 nm) spectra of 2 (solid sample, RT).
Molecules 26 04296 g002
Figure 3. Excitation (blue line, λem = 543 nm) and emission (green line, λex = 370 nm) spectra of 3 (solid sample, RT).
Figure 3. Excitation (blue line, λem = 543 nm) and emission (green line, λex = 370 nm) spectra of 3 (solid sample, RT).
Molecules 26 04296 g003
Figure 4. Excitation (blue line, λem = 575 nm) and emission (yellow line, λex = 365 nm) spectra of 4 (solid sample, RT).
Figure 4. Excitation (blue line, λem = 575 nm) and emission (yellow line, λex = 365 nm) spectra of 4 (solid sample, RT).
Molecules 26 04296 g004
Figure 5. Temperature dependences of χMT for 35 and 7 (H = 5000 Oe). Solid lines are the results of modeling based on high-level quantum chemicals.
Figure 5. Temperature dependences of χMT for 35 and 7 (H = 5000 Oe). Solid lines are the results of modeling based on high-level quantum chemicals.
Molecules 26 04296 g005
Figure 6. Frequency dependences of the imaginary χ″ components of magnetic susceptibility of complex 4 (a) and 7 (b) in various applied fields at 2 K.
Figure 6. Frequency dependences of the imaginary χ″ components of magnetic susceptibility of complex 4 (a) and 7 (b) in various applied fields at 2 K.
Molecules 26 04296 g006aMolecules 26 04296 g006b
Figure 7. Frequency dependences of the real (χ′, (a)) and imaginary (χ″, (b)) components of ac-magnetic susceptibility for complex 4 in the dc-field (1000 Oe). The lines are the best fit by the generalized Debye model.
Figure 7. Frequency dependences of the real (χ′, (a)) and imaginary (χ″, (b)) components of ac-magnetic susceptibility for complex 4 in the dc-field (1000 Oe). The lines are the best fit by the generalized Debye model.
Molecules 26 04296 g007aMolecules 26 04296 g007b
Figure 8. The dependence of the relaxation time τ on the reciprocal temperature 1/T for 4. The points are obtained by approximating the frequency dependence of χ″ by the generalized Debye model. The magenta dashed line represents the result of the fit by the Arrhenius equation, the red solid line corresponds to the sum of Raman and QTM processes, the blue dashed line corresponds to Raman and direct processes.
Figure 8. The dependence of the relaxation time τ on the reciprocal temperature 1/T for 4. The points are obtained by approximating the frequency dependence of χ″ by the generalized Debye model. The magenta dashed line represents the result of the fit by the Arrhenius equation, the red solid line corresponds to the sum of Raman and QTM processes, the blue dashed line corresponds to Raman and direct processes.
Molecules 26 04296 g008
Figure 9. Frequency dependences of the real (χ′, (a)) and imaginary (χ″, (b)) components of the ac-magnetic susceptibility for complex 7 in the 1000 Oe dc-field. The lines are the best-fits by the generalized Debye model.
Figure 9. Frequency dependences of the real (χ′, (a)) and imaginary (χ″, (b)) components of the ac-magnetic susceptibility for complex 7 in the 1000 Oe dc-field. The lines are the best-fits by the generalized Debye model.
Molecules 26 04296 g009
Figure 10. The dependence of the relaxation time τ on the reciprocal temperature 1/T for 7. The points are obtained by approximating the frequency dependence of χ″ by the generalized Debye model. The magenta dashed line represents the result of the fit by the Arrhenius equation, the red line corresponds to the sum of Raman, direct, and Orbach relaxation processes, blue dashed line corresponds to the sum of the direct and Raman relaxation processes.
Figure 10. The dependence of the relaxation time τ on the reciprocal temperature 1/T for 7. The points are obtained by approximating the frequency dependence of χ″ by the generalized Debye model. The magenta dashed line represents the result of the fit by the Arrhenius equation, the red line corresponds to the sum of Raman, direct, and Orbach relaxation processes, blue dashed line corresponds to the sum of the direct and Raman relaxation processes.
Molecules 26 04296 g010
Table 1. Selected bond lengths, the shortest interatomic distances [Å], and angles [°] for compounds 14, 6, and 7.
Table 1. Selected bond lengths, the shortest interatomic distances [Å], and angles [°] for compounds 14, 6, and 7.
123467
Cd···Ln3.6716(4), 3.6910(4)3.6615(4), 3.6749(4)3.6554(2), 3.6652(2)3.6496(2), 3.6513(2)3.6370(5), 3.6415(4)3.6253(5), 3.6383(5)
Cd···Cd4.1634(5)4.1556(5)4.1576(3)4.1529(3)4.1529(6)4.1480(6)
Ln···Lnmin10.40510.37610.36210.32610.31310.296
Cd-O(O2CR)2.218(3)–2.720(3)2.213(4)–2.722(4)2.214(2)–2.718(2)2.216(2)–2.703(2)2.210(3)–2.711(3)2.217(3)–2.711(4)
Cd-O(H2O)2.269(3), 2.309(3)2.267(4), 2.308(4)2.273(2), 2.305(2)2.271(2), 2.306(2)2.279(4), 2.305(3)2.280(4)–2.297(5)
Ln-O(O2CR)2.309(3)–2.560(3)2.300(3)–2.553(3)2.273(2)–2.537(2)2.261(2)–2.534(2)2.241(3)–2.523(3)2.213(4)–2.515(4)
Cd-Ln-Cd153.954(9)153.890(10)153.617(6)153.420(5)153.324(9)153.061(13)
Cd-Cd-Ln142.387(10), 149.957(10)142.508(11), 149.818(11)142.526(8), 149.706(7)142.463(6), 149.219(6)142.535(11), 149.411(10)149.232(16)
SQ(Cd1O7), D5h2.4282.4272.4212.4032.4132.414
SQ(Cd2O6), C5v/Oh6.075/6.5586.174/6.5346.210/6.6146.329/6.4966.355/6.6256.269/6.812
SQ(LnO8), D2d/C2v3.314/3.2733.157/3.1483.028/3.1012.941/3.0192.791/2.9712.633/2.868
H···O(O2CR)1.81–1.931.82–1.911.88–1.931.86–1.971.82–1.951.93–1.98
O(H2O)···O(O2CR)2.695–2.8282.696–2.8162.701–2.8072.697–2.8082.708–2.7982.700–2.810
O-H-O154.6, 167.8157.5, 168.4158.9, 167.2156.5, 165.4155.3, 164.9156.7, 157.9
H···N(MeCN)2.142.022.132.072.032.14
O(H2O)···N(MeCN)2.8832.8932.8972.8932.8912.881
O-H-N146.3168.4163.3169.1163.8145.4
Table 2. Lifetimes (τobs), rate constants of radiative (Arad) and non-radiative (Anrad) decay, intrinsic ( Q L n L n ), and overall ( Q L n L ) quantum yields.
Table 2. Lifetimes (τobs), rate constants of radiative (Arad) and non-radiative (Anrad) decay, intrinsic ( Q L n L n ), and overall ( Q L n L ) quantum yields.
Complexτobs, msArad, s−1Anrad, s−1 Q L n L n ,   % Q L n L ,   % Ref.
21.634927656 This work
32.1 This work
Eu(NO3)3·6H2O 18 [54]
Tb(NO3)3·6H2O0.65 [54]
[Eu(NO3)3(H2O)3]·2L0.2529037107 [55]
[Eu(pfb)3(H2O)n]0.65 6515[56]
[Tb(pfb)3(H2O)n]1.36 38[56]
[EuCd(pfb)5(phen)]n1.923251956236[48]
[Eu2Zn2(pfb)10(phen)2]1.904251008141[48]
[TbCd(pfb)5(phen)]n2.09 63[48]
[Tb2Zn2(pfb)10(phen)2]1.83 45[48]
[Eu2Cd2(4-TBA)10(bpy)2]1.8 8113[49]
[Eu2(piv)6(bpy)2]1.47 60 [44]
[Eu2(piv)6(phen)2]1.51 60 [44]
[Eu(tpc)3(Htpc)2]n1.10310598 34[57]
[Tb2(CH3COO)6(H2O)4]·4H2O1.03 [58]
[{Tb(pyr)3(H2O)2}·H2O]n0.79 10.6[59]
[Eu(fbz)3(H2O)2]21.03 2550[60]
[Eu(f2bz)3(H2O)2]n0.66 7510[60]
[Eu(f3bz)3(H2O)]n1.30 7570[60]
[Eu(f4bz)3(H2O)2]2.20 4535[60]
[Tb(fur)3(H2O)3]n0.82 23.812.8[61]
[Eu(fur)3(H2O)3]n 7.37.2[61]
[Tb(FBA)3(H2O)4]n·nH2O1.08 41[62]
[Eu(FBA)3(H2O)4]n·nH2O0.42 14[62]
[EuCd2(bzo)6(NO3)(H2O)2(EtOH)2]1.3143033556 [50]
[EuCd2(bzo)6(NO3)(MeCN)2(THF)2]1.04440520461[51]
[EuCd2(bzo)6(NO3)(pz)(H2O)2]n0.85480700417[51]
[EuCd2(bzo)6(NO3)(pz)2(EtOH)2]2.05320170667[51]
[Eu(phbz)3]n1.14604505014[63]
[Tb(phbz)3]n0.75 24[63]
pfb is pentafluorobenzoate, bzo is 3,5-di-tert-buthylbenzoate, phbz is 4-phenylbenzoate, 4-TBA is trifluoromethylbenzoate, tpc is thiophene-2-carboxylate, pyr is pyrrol-2-carboxylate, fbz is 2-fluorobenzoate, f2bz is 2,5-difluorobenzoate, f3bz is 2,3,6-trifluorobenzoate, f4bz is 2,3,4,5-tetrafluorobenzoate, FBA is 4-fluorobenzoate, phen is 1,10-phenantroline, pz is pyrazine, py is pyridine, lut is 2,3-lutidine, bpy is 2,2′-bipyridine.
Table 3. Calculated at the SA-CASSCF/SO-RASSI level energies, corresponding g-tensors, and crystal field wave functions for Kramers doublets (KDs) of the ground state multiplets: the 6H15/2 of DyIII in 4m and 2F7/2 of YbIII in 7m.
Table 3. Calculated at the SA-CASSCF/SO-RASSI level energies, corresponding g-tensors, and crystal field wave functions for Kramers doublets (KDs) of the ground state multiplets: the 6H15/2 of DyIII in 4m and 2F7/2 of YbIII in 7m.
ComplexKDsKD Energies, cm−1gxgygzCrystal Field Wave Functions
4m101.073.6415.1750%|± 15 2 〉 + 19%|± 13 2
222 (31.7 K)1.151.8813.8421%|± 13 2 〉 + 19%|± 1 2
3591.832.9414.9626%|± 1 2 〉 + 25%|± 3 2
41000.944.0210.9435%|± 13 2 〉 + 19%|± 1 2
51579.177.160.849%|± 11 2 〉 + 13%|± 5 2
62041.081.9714.5125%|± 7 2 〉 + 23%|± 9 2
72181.413.6911.5626%|± 9 2 〉 + 22%|± 5 2
83680.050.0919.2922%|± 1 2 〉 + 20%|± 7 2
7m100.22.25.2764%|± 7 2
2960.321.685.5938%|± 5 2 〉 + 34%|± 7 2
32234.482.670.8542%|± 1 2 〉 + 25%|± 5 2
43011.222.145.939%|± 3 2 〉 + 33%|± 1 2
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Shmelev, M.A.; Polunin, R.A.; Gogoleva, N.V.; Evstifeev, I.S.; Vasilyev, P.N.; Dmitriev, A.A.; Varaksina, E.A.; Efimov, N.N.; Taydakov, I.V.; Sidorov, A.A.; et al. Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb). Molecules 2021, 26, 4296. https://doi.org/10.3390/molecules26144296

AMA Style

Shmelev MA, Polunin RA, Gogoleva NV, Evstifeev IS, Vasilyev PN, Dmitriev AA, Varaksina EA, Efimov NN, Taydakov IV, Sidorov AA, et al. Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb). Molecules. 2021; 26(14):4296. https://doi.org/10.3390/molecules26144296

Chicago/Turabian Style

Shmelev, Maxim A., Ruslan A. Polunin, Natalia V. Gogoleva, Igor S. Evstifeev, Pavel N. Vasilyev, Alexey A. Dmitriev, Evgenia A. Varaksina, Nikolay N. Efimov, Ilya V. Taydakov, Aleksey A. Sidorov, and et al. 2021. "Cadmium-Inspired Self-Polymerization of {LnIIICd2} Units: Structure, Magnetic and Photoluminescent Properties of Novel Trimethylacetate 1D-Polymers (Ln = Sm, Eu, Tb, Dy, Ho, Er, Yb)" Molecules 26, no. 14: 4296. https://doi.org/10.3390/molecules26144296

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