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Article

Coordination Polymers in Dicyanamido-Cadmium(II) with Diverse Network Dimensionalities

by
Franz A. Mautner
1,*,
Patricia V. Jantscher
1,
Roland C. Fischer
2,
Ana Torvisco
2,
Klaus Reichmann
3,
Nahed M. H. Salem
4,
Kenneth J. Gordon
5,
Febee R. Louka
5 and
Salah S. Massoud
4,5,*
1
Institut für Physikalische and Theoretische Chemie, Technische Universität Graz, Stremayrgasse 9/II, A-8010 Graz, Austria
2
Institut für Anorganische Chemie, Technische Universität Graz, Stremayrgasse 9/V, A-8010 Graz, Austria
3
Institut für Chemische Technologie von Materialien, Technische Universität Graz, Stremayrgasse 9/I, A-8010 Graz, Austria
4
Department of Chemistry, Faculty of Science, Alexandria University, Moharam Bey, 21511 Alexandria, Egypt
5
Department of Chemistry, University of Louisiana at Lafayette, P.O. Box 43700, Lafayette, LA 70504, USA
*
Authors to whom correspondence should be addressed.
Crystals 2021, 11(2), 181; https://doi.org/10.3390/cryst11020181
Submission received: 30 January 2021 / Revised: 7 February 2021 / Accepted: 9 February 2021 / Published: 12 February 2021
(This article belongs to the Special Issue A 10 Years Journey: Chemical, Physical, and Biological Properties and Applications of Crystals)
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Versions Notes

Abstract

:
The synthesis and structural characterization of six dicyanamido-cadmium(II) complexes are reported: catena-[Cd(μ1,3-dca)(μ1,5-dca)(3-ampy)] (1), catena-[Cd3(μ1,3,5-dca)2(μ1,5-dca)4(pyNO)2(H2O)2] (2), catena-{Cd(H2O)2(μ1,5-dca)2](2,6-lut-NO)} (3), catena-[Cd(Me2en)(μ1,5-dca)2] (4), catena-[Cd(Me4en)(μ1,5-dca)2] (5), and [Cd(1,8-damnp)2(dca)2] (6), where dca = dicyanamide anion, 3-ampy = 3-aminopyridine, pyNO = pyridine-N-oxide, 2,6-lut-NO = 2,6-lutidine-N-oxide, Me2en = N,N-dimethyl-ethylenediamine, Me4en = N,N,N′,N′-tetramethyl-ethylenediamine, and 1,8-damnp = 1,8-diaminonaphthaline. The coordination polymers have different dimensionalities: 1 and 5 form 3D networks structures; 3 and 4 form polymeric 1D chains and 1DD double chains, respectively. Ribbons of three fused polymeric chains are observed in 2. In 6, the mononuclear complex units form a hydrogen-bonded supramolecular 3D network. In the coordination polymer compounds, the dca linkers display three bonding modes: the most common μ1,5-dca and the least popular μ1,3- and μ1,3,5-dca bonding. The luminescence emission and thermal properties of the complexes were investigated.

Graphical Abstract

1. Introduction

Cadmium(II) ion forms complexes with phosphates, amino acids, peptides, nucleobases, nucleotides, and nucleic acids ([1] (a,b)). The most common coordination geometry in cadmium(II) complexes is octahedral, but tetrahedral and five-coordinate geometries were also formed, depending on the steric coordination environment [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]. The interaction of small pseudo halides (N3−, NCS−, and NCO−) and the longer dicyanamide, dca (dca = N(CN)2−) with the divalent metal(II) ions and co-ligands, are considered to be the most studied pseudohalide compounds. These anions have the capability of assembling metal ions, leading to the formation of bridged dinuclear and polynuclear, as well as coordination polymers (CPs) with various architecture topologies [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] and interesting potential applications [17,18,19,20,21,22,23]. One of the most obvious reasons for the formation of these compounds is their wide range of coordination bonding modes. With the focus on the relatively less-studied bent-shaped dca system, the anion can display two terminal bonding sites (end-to-end), or two sites of the same atom (end-on) [5,7,14,15,24,25,26,27], in addition to the central amide nitrogen [28,29]. The various coordination bonding modes of dca have been previously summarized [30,31], and they are illustrated in Scheme 1.
One of the very important property associated with (n−1)d10 metal ions such as Cd(II) is their tendency to produce photoluminescence emission [5,15,24,25,32], a phenomenon which can possibly be used in photochemical devices [32,33,34,35] and in the catalytic activity of some organic reactions, such as Knoevenagel condensation [36]. In addition, cadmium(II) coordination chemistry and coordination polymers, as well as metal organic framework materials, were successfully employed in the crystal engineering architecture, for the design of many interesting compounds, which showed diverse structural properties and promising applications [33,34,35,36,37,38,39,40].
Herein, we examine the interaction of Cd(II) and dca in the presence of a wide range of auxiliary N-donors ligands with variable skeletons simple monodentates, such as N-pyridyloxide (ONpy) and 2,6-lutidine-N-oxide (ON-2,6-lut); bidentate ligands, N,N-dimethyl-(Me2en) and N,N,N′,N′-tetramethyl-ethylenediamine (Me4en); and 1,8-diaminonaphthalene (1,8-damnp), in addition to the ambidentate 3-aminopyridine ligand (3-ampy), which possibly can act as a bridging ligand, too. The structural formulas of these ligands are shown in Scheme 2. The selected ligands should provide vacant coordination sites at the cadmium center and, hence, allow its interaction with the dca linker(s) to propagate the formation of bridging coordination polymers. The photoluminescence emission and thermal properties of the complexes were also investigated.

2. Experimental

2.1. Materials and Physical Measurements

Sodium dicyanamide was purchased from TCI, and 3-aminopyridine was purchased from Aldrich. All other materials were reagent-grade quality. Infrared spectra of the solid complexes were performed on a Bruker Alpha P (platinum-ATR-cap) or Cary 630 (ATR-IR) spectrometer. Thermal analyses were measured on solid samples, using NETSCH STA (N2 atmosphere; heating rate, 10 °C/min). PXRD measurements of the microcrystalline bulk material were performed with a Bruker D8 Advance powder diffractometer. Emission spectra were recorded with a Perkin-Elmer Lamda LS55 spectrofluorometer. Elemental CHN microanalyses were carried out with an Elementar Vario EN3 analyzer and by the Atlantic Microlab, Norcross, GA, USA.

2.2. Preparation of the Compounds

Catena-[Cd(3-ampy)(μ1,3-dca)(μ1,5-dca)] (1): Cadmium(II) nitrate tetrahydrate, Cd(NO3)2·4H2O (0.345 g, 1 mmol), sodium dicyanamide (0.18 g, 2 mmol), and 3-aminopyridine (0.19 g, 1 mmol) were dissolved in 80 mL H2O/MeOH (1:2 v:v). The solution was heated up to 85 °C and stirred for 30 min. This was then filtered, and the clear solution was allowed to stand at ambient temperature. After about one week, brown-tinted needle-shaped crystals were obtained (yield: 0.28 g, 83%). These were collected by filtration and dried in air. Analytical Calculated for C9H6CdN8 (338.63 g/mol): 31.9% C, 1.8% H, and 33.1% N. Found: 31.7% C, 1.7% H, and 33.3% N. IR (ATR, cm−1): 3224 (w) ν(N-H); 2926 (w), 2888 (w), and 2838 (m) ν(C-H); 2293 (m), 2229 (s), and 2162 (s) ν(C-N, dca); 1629 (s), 1581 (m), 1492 (w), 1449 (m), 1356 (m), 1305 (m), 1269 (m), 1194 (m), 1140 (m), 1054 (w), 922 (w), 889 (m), 853 (w), 796 (m), 694(m), 646 (m), 599 (m), 514 (s), and 413 (w).
Catena-[Cd3(μ1,3,5-dca)2(μ1,5-dca)4(pyNO)2(H2O)2] (2): This complex was prepared, using a similar procedure to that described for 1, except pyridine-N-oxide (0.032 g, 0.34 mmol) was used instead of 3-ampy. The isolated colorless needle-shaped crystals were collected by filtration (yield: 0.23 g, 72%). Analytical Calculated for C22H14Cd3N20O4 (959.72 g/mol): 27.5% C, 1.5% H, and 29.2% N. Found: 27.3% C, 1.6% H, and 29.4% N. IR (ATR, cm−1): 3571 (w), 3400 (m,br) ν(O-H); 3107 (w), 3065 (w) ν(C-H); 2312 (m) 2284 (m), 2286 (s), 2256 (m), 2226 (m), 2190 (m), 2166 (s), and 2128 (s) ν(C-N, dca); 1905 (w), 1667 (w), 1468 (m), 1360 (m), 1342 (m), 1320 (m), 1318 (m), 1240 (m), 1207 (m), 1168 (m), 1071 (m), 1016 (w), 947 (w), 818 (m), 771 (m), 675 (m), 660 (m), 547 (w), 514 (s), 487 (m), and 448 (m).
Catena-{[Cd(H2O)2(μ1,5-dca)2](2,6-lut-N-oxide)} (3): This complex was prepared, using a similar procedure to that described for 1, except 2,6-lutidine-N-oxide (0.123 g, 1 mmol) was used instead of 3-ampy. Colorless needle-shaped crystals were obtained (yield: 0.31 g, 77%). Analytical Calculated for C11H13CdN7O3 (403.69 g/mol): 32.7% C, 3.2% H, and 24.3% N. Found: 32.5% C, 3.1% H, and 24.4% N. IR (ATR, cm−1): 3570 (w), 3343 (m,br) ν(O-H); 3075 (w), 2928 (m,br) ν(C-H); 2285 (s), 2229 (m), 2168 (s), and 2148 (m) ν(C-N, dca); 1686 (w), 1579 (m), 1496 (w), 1457 (m), 1419 (m), 1377 (m), 1338 (s), 1210 (s), 1162 (m), 1100 (w), 1034 (w), 930 (w), 863 (m), 830 (w), 785 (m), 668 (m), 602 (m), and 520 (s).
The three dicyanamido complexes 4–6 were synthesized by using a general procedure: An aqueous solution of Nadca (0.091 g, 1 mmol in 5 mL H2O) was added to a mixture containing Cd(NO3)2·4H2O (0.155 g, 0.5 mmol), and the corresponding ligand (0.5 mmol) dissolved in MeOH (15 mL). The resulting solution was heated for 5–10 min, on a steam-bath, filtered through celite, and then allowed to crystallize at room temperature.
Catena-[Cd(Me2en)(μ1,5-dca)2] (4): The colorless single crystals, which were obtained after one week, were collected by filtration and dried in air (yield 41%). Characterization: Analytical Calculated for C8H12CdN8 (332.47 g/mol): C, 28.89%; H, 3.64%; and N, 33.69%. Found: C, 28.89%, H, 3.51%; and N, 33.58%. IR bands (ATR, cm−1): 3282 (w) ν(N-H); 3077 (vw), 2989 (vw), 2955 (vw), 2922 (vw), 2877 (vw) ν(C-H); 2287 (s), 2234 (m), 2157 (vs) ν(C-N, dca); 1443 (w), 1430 (s), 1281 (w), 1140 (w), 1095 (w), 1074 (m), 1003 (m), 925 (s), 841 (s), 821 (m), and 668 (m).
Catena-[Cd(Me4en)(μ1,5-dca)2] (5): The long colorless needles, obtained on the following day, were collected by filtration and dried in air (yield 76%). Characterization: Analytical Calculated for C10H16N8Cd (360.70 g/mol): C, 33.30%; H, 4.47%; and N, 31.07%. Found: C, 33.45%, H, 4.44%; and N, 30.77%. IR bands (ATR, cm−1): 3058 (vw), 2880 (vw), 2840 (vw) ν(C-H); 2285 (m), 2227 (m), 2154 (vs) ν(C-N, dca); 929 (s), 833 (s), and 794 (m).
[Cd(1,8-damnph)(dca)2] (6): This complex was isolated as off-white-colored crystals after two days of standing at room temperature. Crystals were collected and dried in air (yield 47%). Characterization: Analytical Calculated for C24H20CdN10 (560.89 g/mol): C, 51.39%; H, 3.59%; and N, 24.97%. Found: C, 50.99%; H, 3.66%; and N, 25.00%. IR bands (ATR, cm−1): 3255 (m) ν(N-H) stretching; 3153 (m), 3064 (vw) ν(C-H); 2257 (s), 2219 (s), 2156 (s) (vs) ν(C-N, dca); 1620 (m), 1573 (s), 1396 (s),1330 (s), 1280 (s), 1049 (vs), 988 (vs), 908 (m), 812 (s), and 754 (vs).

2.3. Single-Crystal Structure Determination

Suitable single crystals of the six title compounds were mounted on a Bruker-AXS APEX II CCD diffractometer and measured at 100(2) K with Mo-Kα radiation (λ = 0.71073 Å). Table 1 summarizes refinement and data collection features and crystallographic data. The following program packages were used for data processing, LP and absorption corrections, structure solution and refinement (F2 full-matrix least-squares), and visualization and analysis: APEX [41], SADABS [42], SHELX program library [43,44], Mercury [45], PLATON [46], and ToposPro [47]. Depository codes: CCDC 1982387 (for 1) and CCDC 2059063-2059067 (for 2–6).

3. Results and Discussion

3.1. Synthetic Aspects and IR Spectra of the Complexes

With the high tendency of Cd(II) ion to predominantly form six-coordinate complexes, one expects that its interaction with the long dicyanamide anion (NCNCN)− (dca), in the presence of small non-sterically hindered mono- or bi-dentate co-ligands, to generate coordination polymeric compounds. With this hypothesis in mind, the reaction of a methanolic mixture containing Cd(NO3)2.4H2O and ligands such as 3-ampy, NO-py, Me2en, and Me4en and an aqueous solution of Nadca in the stoichiometric ratio 1:1:2 afforded the expected CPs: catena-[Cd(3-ampy)(μ1,3-dca)(μ1,5-dca)] (1), catena-[Cd3(μ1,3,5-dca)2(μ1,5-dca)4(pyNO)2(H2O)2] (2), catena-[Cd(Me2en)(μ1,5-dca)2] (4), and catena-[Cd(Me4en)(μ1,5-dca)2] (5), respectively. Interestingly, the corresponding reactions with the sterically planar molecules of 2,6-lut-NO and 1,8-damnph yielded the CP catena-{[Cd(H2O)2(μ1,5-dca)2](2,6-lut-NO)} (3) and the discrete mononuclear complex [Cd(1,8-damnph)(dca)2] (6), respectively. The former complex constitutes a CP, in which the 2,6-lutidine-N-oxide is not encountered in the coordination sphere of the complex, whereas, in 6, the dca is acting as a monodentate ligand. The purity of the isolated complexes was checked by X-Ray Powder Diffraction and the XRD method, and the graphs of these patterns are depicted in Supplementary Materials Figures S1–S6 for complexes 1–6, respectively. The complexes were structurally characterized by single-crystal X-ray crystallography, as well as elemental microanalyses and IR spectroscopy.
The IR spectra of the complexes reveal the general characteristic features of the dicyanamide group. In general, the complexes display three medium–strong intense bands over the vibration ranges 2290–2260, 2230–2220, and 2160–2150 cm−1 regions. The later band is attributable to νs(C≡N), and the former two vibrational bands are attributable to νas(C≡N) and νs + νas(C≡N), respectively [3,4,5,6,7,14,26,27,28,29,48,49]. These bands are clearly pronounced in the complexes 1, 4, 5, and 6. The observed split of bands in complexes 2 and 3 is most likely attributed to the involvement of the aqua ligands in hydrogen bonds of the type O-H···N to N2 and/or N5 atoms of the adjacent dca groups (see Section 3.2). The further split of the bands in catena-[Cd3(μ1,3,5-dca)2(μ1,5-dca)4(pyNO)2(H2O)2] (2) results from two dca coordination bonding modes. These two complexes also display medium broad bands over the range 3570–3340 cm−1 assigned for the ν(O-H) stretching frequency of the coordinated aqua molecules [50]. The weak–medium intense band(s) located over the 3280–3220 cm−1 region is/are due to the ν(N-H) stretching frequencies in complexes 1, 4, and 6. The weak ν(C-H) stretching frequencies were shown for all complexes over the 3100–2840 cm−1 region [50]. Representative IR spectra of compounds 1–3 are shown in Supplementary Materials Figures S7–S9.

3.2. Description of the Structures

3.2.1. Catena-[Cd(μ1,3-dca) (μ1,5-dca)(3-ampy)] (1)

A molecular plot of the title compound 1 is given in Figure 1 and bond parameters are listed in Supplementary Materials Table S1. The Cd(II) is octahedrally coordinated by 4 N donor atoms of the dicyanamide anions, and two N donor atoms of the μ2-bridging 3-aminopyridine ligand in cis-configuration. The Cd-N bond lengths are in the range from 2.297(3) to 2.392(4) Å. The dicyanamide anions reveal two different bonding modes μ1,3- and μ1,5-bridging, to form a 3D network structure, together with the μ2-bridging 3-ampy ligands with their metal–metal bridging distances of 6.1863(5), 7.1006(5), and 7.2195(7) Å, respectively. The μ2-bridging 3-ampy and μ1,3-bridging dca anions form a 2D sub-lattice extended along the b- and c-axis directions, consisting of square layers with rings of type [-Cd-μ1,3-dca-(Cd-μ2-3-ampy)2-Cd-μ1,3-dca-], which are further linked by the μ1,5-dca anions, to generate the 3D network (Figure 1).
Topological investigations show that the uninodal six-connected network of 1 has rob topology (point symbol: 48.66.8). The Cd-dca bridges have the following bond parameters: Cd-N-C, from 116.4(3) to 160.2(3)°; N-C-N, 172.1(4) to 174.4(5)°; C-N-C, 119.4(4) and 123.6(4)°; C-N(nitril), from 1.150(5) to 1.160(5) Å; and N-C (amin), 1.305(5) to 1.332(6) Å. The amino group forms hydrogen bonds (H-bonds) of the type N-H···N to the non-ligated N4 and N8 atoms of the dca anions (Supplementary materials Figure S10 and Table S2). Non-covalent π···π ring···ring interactions are found between neighboring aromatic rings with a separation of their centers of gravity (Cg) of 3.760(2) Å, which further stabilizes the network structure.
Metal complexes containing both types of μ1,3- and μ1,5-bridging dca ligands have been published, e.g., for M(dca)2 [51] or mixed ligand compounds [52]. However, only one Cd(II) complex containing μ1,3- and μ1,5-bridging dca and additional bridging co-ligand (μ2-2,2′-bis(4-pyridylmethoxy)-1,1′-biphenylene) has been described [53]. The catena-[M(3-ampy)2(μ1,5-dca)2] (M = Cd(ii), Zn(ii), Mn(ii), Co(ii) and Cu(ii)) complexes form 1D chain systems, where the 3-ampy acts as a terminal ligand [54].

3.2.2. Catena-[Cd3(μ1,3,5-dca)2(μ1,5-dca)4(pyNO)2(H2O)2] (2)

Two crystallographic independent metal centers exist in 2, and both have CN 6 (Figure 2). Each Cd1 center is octahedrally ligated by two oxygen atoms of terminal aqua and pyridine-N-oxide molecule in trans positions and by four N donor atoms of the dicyanamide bridging ligands, with two acting in the -μ1,5-dca and the other two in -μ1,3,5-dca bridging mode. The Cd1-N/O bond lengths vary from 2.2916(16) to 2.332(2) Å. The axially elongated octahedron around each Cd2 that has site symmetry −1 is formed by six N atoms of dca groups only. The equatorial positions are occupied by N7 and N9 donor atoms of four -μ1,5-dca bridging ligands [Cd2-N7 = 2.274(2), Cd2-N9 = 2.3041(19) Å], and the axial sites by N5 atoms of two -μ1,3,5-dca bridging groups [Cd2-N5 = 2.3858(19) Å]. Thus, each Cd2 center is linked to 4 Cd1 centers by two -μ1,3,5-dca bridging groups.
The resulting coordination polymer of compound 2 may be described as “ribbons” consisting of three polymeric trans-Cd-bis(-μ1,5-dca) 1D chains, where the central polymeric [Cd2] chains are crosslinked to the two external polymeric [Cd1] chains by the N5 atoms of the -μ1,3,5-dca (Figure 2). The ribbons are running along the b-axis direction. The Cd···Cd separations within the ribbons are 6.2840(14), 6.4363(14), and 7.7098(17) Å. The bond parameters of Cd-dca bridges are as follows: Cd-N-C, from 119.32(14) to 159.13(19)°; N-C-N, 172.7(3) to 174.7(2)°; C-N-C, 119.17(19) to 121.0(2)°; C-N(nitrile), from 1.150(5) to 1.160(5) Å; and N-C(amine), 1.301(3) to 1.320(3) Å. H-bonds between O2 of aqua ligand to adjacent N2 of dca group and O1 of pyridine-N-oxides form a supramolecular 2D system (Supplementary Materials Figure S11 and Table S2).

3.2.3. Catena-{[Cd(H2O)2(μ1,5-dca)2](2,6-lut-NO)} (3)

Compound 3 consists of two crystallographic independent polymeric [Cd(dca)2(H2O)2] 1D chains and non-coordinated two-fold disordered 2,6-lutidine-N-oxides (Figure 3). Each Cd(ii) with site symmetry −1 is ligated by two O atoms of terminal aqua ligands in trans positions and four N atoms of μ1,5-bridging dca anions. The Cd-O bond lengths are 2.279(3) and 2.284(3) Å, and the Cd-N bond lengths vary from 2.314(3) to 2.331(3) Å. The bond parameters of Cd-dca are as follows: Cd-N-C, from 140.2(3) to 164.1(3)°; N-C-N, 173.0(4) to 174.6(4)°; C-N-C, 120.2(3) and 120.6(3)°; C-N(nitrile), from 1.150(5) to 1.154(5) Å; and N-C(amine), 1.311(4) to 1.319(4) Å. The Cd···Cd intra-chain separations are 7.6936(4) and 7.7130(4) Å. The aqua ligands form H-bonds of the type O-H···N to N2 and N5 of neighboring dca groups and H-bonds of type O-H···O, to link the [Cd(dca)2(H2O)2] polymeric chains with O3 atom of non-coordinated 2,6-lutidine-N-oxide molecules, to create a supramolecular 3D network structure (Supplementary Materials Table S2).

3.2.4. Catena-[Cd(Me2en)(μ1,5-dca)2] (4)

In this complex, each Cd(ii) center is ligated by two N of the chelating Me2en in cis positions and four N of μ1,5-bridging dca anions. Centrosymmetric pairs of CdN6 polyhedra are linked by bis(μ1,5-bridging) dca groups, to form dimeric subunits. Furthermore, these subunits are connected by four single μ1,5-bridging dca anions, to create 1D double chains running along the a-axis direction (Figure 4). The Cd-N(dca) bond distances vary from 2.2916(11) to 2.3545(11) Å, and the Cd-N(en) bond lengths are 2.2938(11) and 2.4523(10) Å. The bond parameter of Cd-dca bridges are as follows: Cd-N-C, from 126.04(9) to 161.76(10)°; N-C-N, 172.64(14) to 174.28(13)°; C-N-C, 119.49(11) and 121.36(11)°; C-N(nitrile), from 1.1550(17) to 1.1668(16)°; and N-C(amine), 1.3040(15) to 1.3397(16)°. The amino function forms H-bonds of the type N-H···N to the non-ligated N4 and N8 atoms of the dca anions (Supplementary Materials Table S2 and Figure S12).

3.2.5. Catena-[Cd(Me4en)(μ1,5-dca)2] (5)

Crystals of compound 5 have orthorhombic space group Pnma (no 62). Cd1 and ordered dicyanamide group (dca1: N1/C1/N2/C2/N3) have site symmetry m. The second dicyanamide group (dca2: N4/C4/N5/C4/N6) and the Me4en molecule are located on general positions and show two-fold disorder. The distorted CdN6 octahedra are generated by the two donor atoms of chelating Me4en molecule in cis-position and four terminal N of dca groups. The Cd-N bond distances vary from 2.267(9) to 2.3907(6) Å. The μ1,5-dca bridging anions link each Cd1 center with four neighboring ones, to create a 3D network structure (Figure 5). Cd1 and dca1 groups on mirror planes at y = 0.25 and 0.75 form “polymeric chains” running along the a-axis direction. These “polymeric chains” are further “cross-wise” linked by alternating zig-zag chains of dca2 groups, to create the 3D network. The bond parameters of the Cd-dca bridges are affected by the partial disorder (Supplementary Materials Table S1).

3.2.6. [Cd(1,8-damnph)2(dca)2] (6)

In the centrosymmetric mononuclear complex 6, [Cd(1,8-damnph)2(dca)2] (Figure 6), the Cd(ii) center is forming a compressed octahedron by ligation of four amine-N donor atoms of two trans-coordinated 1,8-diaminonaphthalene molecules and of two terminal dicyanamide anions. The Cd1-N(dca) distance is 2.3655(9), and the Cd1-N(amine) distances are 2.3051(9) and 2.3565(10) Å, respectively. The N1-Cd1-N5 bite angle is 74.19(3), and the N1-Cd1-N5 bond angle is 105.81(3)°, whereas the other N-Cd-N cisoid bond angles deviate less than 3.1° from rectangular angle. The naphthalene-rings are inclined by 57.9° to the mean CdN4 (amine) plane. The bond parameters of the terminal dca anions are as follows: Cd-N-C, 162.29(8)°; N-C-N, 172.23(11) and 172.70(11)°; C-N-C, 121.82(9)°; C-N(nitrile), 1.1588(14) and 116.08(13) Å; and N-C (amine), 1.3075(13) and 1.3196(13) Å. H-bonds of type N-H···N form a supramolecular 3D network structure with bcu topology (Supplementary Materials Table S2, and Figure 6).

3.3. Luminescence Emission

The photoluminescence emission of solid Cd-dca complexes were examined at room temperature. Unfortunately, the complexes 3–6 did not show any significant luminescence, whereas enhancement fluorescence emissions were observed in complexes 1 and 2, compared to their parent ligands and Nadca. Excitation of the two complexes at 366 nm revealed single emission maxima at 460 and 445 nm for 1 and 2, respectively. The corresponding ligands 3-ampy in 1 (Supplementary Materials Figure S13) and pyNO in 2 (Supplementary Materials Figure S14) showed a maximum intensity band at 429 and 454 nm, respectively. While a red shift was observed in the former complex, a small blue shift was detected in 2. The observed fluorescence enhancement in complexes 1 and 2 is most likely attributed to the increase of the conformational rigidity of the ligand upon coordination. The strong the overlap in the Cd-N (3-ampy) or Cd-O (pyNO) bond reduces the non-radiative decay within the intra-ligand (n–π*) excited state, hence enhancing the fluorescence intensity [6,7,55]. Thus, the non-radiative processes in complexes 3–6 are superior.

3.4. Thermal Analyses

The heating curves (TG and DSC) of the title compounds are presented in the Supplementary Materials section (Figures S15–S20), for 1–6, respectively. The heating curve of 2 shows a first step of weight loss of 3.51% (DSC signal at 121.0 °C), which corresponds to release of aqua ligand (Calculated 3.75%). The anhydrous product of 2 shows an explosive decomposition at 332.6 °C. The heating curve of 3 exhibits three narrow steps of weight loss, namely −2.52, −2.45, and −3.07% (sum 8.34%), with two resolved DSC peaks at 103.6 and 136.4 °C. These three steps of weight losses can be attributed to the release of the aqua ligands (Calculated 8.93%). The anhydrous title compounds show first steps of weight loss of 11.77, 0.83, 17.48, and 6.47%, with sharp DSC signals at 204.1, 194.7, 197.9, and 185.3 °C, for compounds 1 and 4–6, respectively. The subsequent steps of weight loss at higher temperatures are accompanied by deflagration.

4. Conclusions

In the studied Cd-dca complexes 1–6, we demonstrated that four types of dca coordination bonding modes were observed: terminal, μ1,5-dca, μ1,3-dca, and μ1,3,5-dca (Scheme 1). In complex 1, three different linkers build the 3D network μ1,5-dca, μ1,3-dca, and μ2-3-ampy, whereas, in 5, only μ1,5-dca-bridges exist. Unique ribbons of three 1D polymeric chains were observed in 2 that had never been reported in transition metal-dca complexes. In addition, 1DD double chains were found in 4 with mono-(μ1,5-dca) and bis-(μ1,5-dca) polymeric chains, which are quite common in these class of compounds. Moreover, the catena-{[Cd(H2O)2(μ1,5-dca)2](2,6-lut-NO)} (3) complex revealed the presence of 1D chains via bis(μ1,5-dca) and non-coordinated two-fold disordered 2,6-lutidine-N-oxide molecules. However, it is interesting to note that an aqua ligand containing [M(H2O)2(μ1,5-dca)2] chain was only reported once in the corresponding Mn(II) complex with non-coordinating tetrametylpyrazine-N,N′-dioxide by A. L. Rheingold and J. S. Miller, CSD Communication (Private Communication: 2019, CCDC Refcode: NOZZIO). On the other hand, the mononuclear complex [Cd(1,8-damnph)2(dca)2] (6) with terminal dca-bonding forms a supramolecular 3D network structure through N-H···N hydrogen bonds. One of the crucial key steps in designing coordination polymers is the use of mono-dentate or less sterically hindered bidentate ancillary ligands in conjunction with suitable linkers, such as pseudohalides and polycarboxylates.

Supplementary Materials

The following are available online at https://www.mdpi.com/2073-4352/11/2/181/s1, Supplementary data: bond parameters (Table S1), hydrogen bond systems (Table S2), and XRD powder pattern (Figures S1–S6) for compounds 1–6, respectively; IR spectra (Figures S7–S9) for 1–3; packing plots (Figures S10–S12) for 1, 2, and 4; luminescence spectra (Figures S13 and S14) for compounds 1 and 2, and thermal analysis plots (Figures S15–S20) for compounds 1–6, respectively.

Author Contributions

F.A.M., R.C.F. and A.T. performed the X-ray structural analysis. S.S.M., P.V.J., K.J.G., F.R.L., and N.M.H.S. contributed to the synthesis and spectral characterization of the designed compounds. F.A.M. and K.R. contributed to studying the thermal and luminescence properties of the complexes. F.A.M., S.S.M., F.R.L., K.J.G., and N.M.H.S. contributed to the writing of the manuscript. All authors have read and agreed to the published version of the manuscript.

Funding

Financial support of this work came from the department of chemistry at UL Lafayette by S.S.M. Open Access Funding by Graz University of Technology.

Informed Consent Statement

Not applicable.

Acknowledgments

F.A.M. thanks K. Gatterer (TU Graz) for assistance. S.S.M. and F.R.L. thank the department of chemistry (UL Lafayette) for funding this work.

Conflicts of Interest

The authors declare no conflict of interest.

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Crystals 11 00181 sch001 550
Scheme 1. Bridging modes of dicyanamide anion.
Scheme 1. Bridging modes of dicyanamide anion.
Crystals 11 00181 sch001
Crystals 11 00181 sch002 550
Scheme 2. The structural formulas and abbreviations of ligands used in this study.
Scheme 2. The structural formulas and abbreviations of ligands used in this study.
Crystals 11 00181 sch002
Crystals 11 00181 g001 550
Figure 1. Coordination (left) and 3D network (right) of complex 1. (Color code: yellow, Cd; blue, N; black, C.)
Figure 1. Coordination (left) and 3D network (right) of complex 1. (Color code: yellow, Cd; blue, N; black, C.)
Crystals 11 00181 g001
Crystals 11 00181 g002 550
Figure 2. Ribbons consisting of three 1D chains in complex 2. (Color code: yellow, Cd; red, O; blue, N; black, C.)
Figure 2. Ribbons consisting of three 1D chains in complex 2. (Color code: yellow, Cd; red, O; blue, N; black, C.)
Crystals 11 00181 g002
Crystals 11 00181 g003 550
Figure 3. Coordination (left) and 1D system (right) of complex 3. Dotted lines indicate H-bonds. (Color code: yellow, Cd; red, O; blue, N; black, C; gray, H.)
Figure 3. Coordination (left) and 1D system (right) of complex 3. Dotted lines indicate H-bonds. (Color code: yellow, Cd; red, O; blue, N; black, C; gray, H.)
Crystals 11 00181 g003
Crystals 11 00181 g004 550
Figure 4. One-dimensional double chains in complex 4. (Color code: yellow, Cd; blue, N; black, C.)
Figure 4. One-dimensional double chains in complex 4. (Color code: yellow, Cd; blue, N; black, C.)
Crystals 11 00181 g004
Crystals 11 00181 g005 550
Figure 5. The 3D Cd-dca network in 5. The C and H atoms of Me4en and one orientation of disordered dca2 group were omitted for clarity. (Color code: yellow, Cd; blue, N; black, C.)
Figure 5. The 3D Cd-dca network in 5. The C and H atoms of Me4en and one orientation of disordered dca2 group were omitted for clarity. (Color code: yellow, Cd; blue, N; black, C.)
Crystals 11 00181 g005
Crystals 11 00181 g006 550
Figure 6. Coordination (left) and H-bonded network with bcu topology (right) of complex 6. Dotted lines indicate H-bonds. (Color code: yellow, Cd; blue, N; black, C; gray, H).
Figure 6. Coordination (left) and H-bonded network with bcu topology (right) of complex 6. Dotted lines indicate H-bonds. (Color code: yellow, Cd; blue, N; black, C; gray, H).
Crystals 11 00181 g006
Table
Table 1. Crystallographic data and processing parameters of 1–6.
Table 1. Crystallographic data and processing parameters of 1–6.
Compound123
Empirical formulaC9H6CdN8C22H14Cd3N20O4C11H13CdN7O3
Formula mass338.62959.76403.69
SystemMonoclinicTriclinicTriclinic
Space groupCcP-1P-1
a (Å)14.3557(7)6.6636(12)7.4407(4)
b (Å)11.0239(6)7.7098(17)7.6936(4)
c (Å)7.3916(4)16.035(3)15.6387(8)
α (°)9077.982(9)88.291(2)
β (°)104.588(2)78.672(9)86.251(2)
γ (°)9086.459(12)61.252(2)
V (Å3)1132.05(10)789.9(3)783.22(7)
Z412
Dcalc (Mg/m3)1.9872.0181.712
θ max (°)26.99230.30930.040
Data collected254701542922948
Unique refl./Rint2441/0.06574675/0.04414564/0.0455
Parameters/Restraints169/4231/0212/10
Goodness-of-Fit on F21.0361.1621.333
R1/wR2 (all data)0.0176/0.04140.0261/0.06060.0388/0.0921
Residual extrema (e/Å3)0.517/−0.6030.936/−1.3520.744/−1.168
Compound456
Empirical formulaC8H12CdN8C10H16CdN8C24H20CdN10
Formula mass332.67360.72560.90
SystemMonoclinicOrthorhombicMonoclinic
Space groupP21/cPnmaP21/n
a (Å)7.4137(3)16.8193(7)7.6234(3)
b (Å)13.8858(5)11.9291(6)11.1927(4)
c (Å)12.2685(5)7.6217(3)13.3631(5)
α (°)909090
β (°)90.251(2)9099.803(2)
γ (°)909090
V (Å3)1262.97(9)1529.21(12)1125.90(7)
Z442
Dcalc (Mg/m3)1.7501.5671.656
θ max (°)33.27430.54933.303
Data collected10744797158106749
Unique refl./Rint4849/0.08522444/0.05094323/0.0642
Parameters/Restraints164/0130/0176/0
Goodness-of-Fit on F21.0421.1081.050
R1/wR2 (all data)0.0190/0.04910.0244/0.06180.0192/0.0517
Residual extrema (e/Å3)0.792/−0.9341.084/−0.6570.800/−0.694
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Mautner, F.A.; Jantscher, P.V.; Fischer, R.C.; Torvisco, A.; Reichmann, K.; Salem, N.M.H.; Gordon, K.J.; Louka, F.R.; Massoud, S.S. Coordination Polymers in Dicyanamido-Cadmium(II) with Diverse Network Dimensionalities. Crystals 2021, 11, 181. https://doi.org/10.3390/cryst11020181

AMA Style

Mautner FA, Jantscher PV, Fischer RC, Torvisco A, Reichmann K, Salem NMH, Gordon KJ, Louka FR, Massoud SS. Coordination Polymers in Dicyanamido-Cadmium(II) with Diverse Network Dimensionalities. Crystals. 2021; 11(2):181. https://doi.org/10.3390/cryst11020181

Chicago/Turabian Style

Mautner, Franz A., Patricia V. Jantscher, Roland C. Fischer, Ana Torvisco, Klaus Reichmann, Nahed M. H. Salem, Kenneth J. Gordon, Febee R. Louka, and Salah S. Massoud. 2021. "Coordination Polymers in Dicyanamido-Cadmium(II) with Diverse Network Dimensionalities" Crystals 11, no. 2: 181. https://doi.org/10.3390/cryst11020181

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