Chiral cadmium–amine complexes for stimulating non-linear optical activity and photoluminescence in solids based on aurophilic stacks

The design of high-performance optical materials can be realized using coordination polymers (CPs) often supported by non-covalent interactions, such as metallophilicity. The challenge is to control two or more optical effects, e.g., non-linear optics (NLO) and photoluminescence (PL). We present a new strategy for the combination of the NLO effect of second-harmonic generation (SHG) and the visible PL achieved by linking dicyanidoaurate(i) ions, which form luminescent metallophilic stacks, with cadmium(ii) complexes bearing chiral amine ligands, used to break the crystal's symmetry. We report a family of NLO- and PL-active materials based on heterometallic Cd(ii)–Au(i) coordination systems incorporating enantiopure propane-1,2-diamine (pda) ligands (1-S, 1-R), their racemate (2), and enantiopure trans-cyclopentane-1,2-diamine (cpda) ligands (3-S, 3-R). Due to acentric space groups, they exhibit the SHG signal, tunable within the range of 11–24% of the KDP reference, which was correlated with the dipole moments of Cd(ii) units. They show efficient blue PL whose energy and quantum yield, the latter ranging from 0.40 to 0.83, are controlled by Cd(ii) complexes affecting the Au–Au distances and vibrational modes. We prove that chiral Cd(ii)–amine complexes play the role of molecular agents for the stimulation of both the NLO and PL of the materials based on aurophilic stacks.

Comment to Fig. S2: The IR spectra of 1-S, 1-R, 2, 3-S, and 3-R are very similar.In all samples, the wide absorption above 2850 cm −1 , as well as the extensive area of absorption bands in the 1500-700 cm −1 range is related to the stretching and skeletal vibrations of amine ligands.Moreover, the N-H bending vibration of primary amines is observed in the region of 1615−1565 cm −1 .In the range of 2220−2120 cm −1 , characteristic peaks related to stretching vibrations of cyanido ligands can be observed.The higher energy bands above 2145 cm −1 can be attributed to vibrations of Cd II -N≡C-Au I cyanido bridges, while the lower energy peaks to terminal cyanido ligands.More absorption bands in this range for 3-S and 3-R are associated with a greater number of various molecular bridging modes as their crystal structures include both bent (weaker) and almost linear (stronger) cyanido bridges (Fig. 2), appearing in the lower and higher energy ranges, respectively.Due to the presence of almost linear Cd II -N≡C-Au I modes in 3-S and 3-R, the related stretching vibrations are shifted towards higher energies when compared to 1-S, 1-R, and 2, in which only one kind of bent molecular cyanido bridges can be observed.The gathered spectroscopic results are in line with structural models of the respective materials (Fig. 1 and 2) and previous works on related dicyanidoaurate(I)-based compounds.S1-S3 Fig. S3.Thermogravimetric (TG) curves collected in the temperature range of 20-390 o C for 1-S (a), 1-R (b), 2 (c), 3-S (d), and 3-R (e).The steps related to the loss of diamine ligands are depicted.
Comment to Fig. S3: All presented compounds are stable with heating up to ca. 200 o C when the gradual decrease of the sample mass is detected.The two-step weight loss in 1-S, 1-R, and 2 can be assigned to the removal of two pda ligands per the {Cd II Au I 2} unit (theoretical values are 9.8% for one and 19.5% for two pda molecules).A similar two-step decrease in 3-R can be attributed to the removal of the two cpda ligands, while in 3-S there is a single abrupt decrease corresponding to the removal of two cpda molecules per the {Cd II Au I 2} unit (theoretical values are 12.4% for one and 24.7% for two cpda molecules).
Table S1.Crystal data and structure refinement parameters for 1-S and 1-R for the SC-XRD measurements performed at 100(2) and 300(2) K.             Comment to Tables S7 and S8 S9.Inside the left panel, the photos of the observed SHG light from the respective samples under the 1040 nm laser irradiation are also presented.S9.Inside the left panel, the photos of the observed SHG light from the respective samples under the 1040 nm laser irradiation are also presented.The resulting dipole moment is oriented along the c crystal.direction with a magnitude of 1.168(±0.023)D The resulting dipole moment has a magnitude of 2.562(±0.055)D (orientation presented in Fig. S15) The resulting dipole moment has a magnitude of 2.419(±0.055)D (orientation presented in Fig. S15)   S10) in the crystal structures of 1-S (a), 2 (b), and 3-S (c), and the schematic presentation of the directions of dipole moment vectors of all metal complexes as well as favorable and unfavorable dipoledipole interactions (Tables S10 and S11) in the crystal structures of 1-S (d) and 2 (e).The best-fit parameters, as well as the CIE 1931 chromaticity parameters, are gathered in Table S12.S12.

Cd
S35 The best-fit parameters, as well as the CIE 1931 chromaticity parameters, are gathered in Table S12.Additional comment on the observed values of emission lifetimes and their relation to the emission mechanism.One can consider a thermally activated delayed fluorescence (TADF) as a potential luminescence mechanism in the reported systems.To investigate whether the radiative process in our systems is phosphorescence or a TADF process, we studied the temperature dependence of the decay.
In the TADF process, the delayed fluorescence is heavily suppressed when the sample is cooled, indicating that the delayed component arises from a thermally activated process.On the other hand, the long-lived phosphorescence shows the opposite trend, being present at low temperatures but suppressed when the sample is warmed to RT.In the submitted work, we measured the luminescence lifetime at room (300 K) and liquid nitrogen (77 K) temperature.As presented in Table S12 above, with increasing temperature, the lifetime decreased twofold, which rather indicates phosphorescence as an emission mechanism.Moreover, theoretical calculations and experimental investigations on similar types of compounds containing aurophilic interactions support the interpretation of the observed emission from the triplet excited state (please see the section Photoluminescence and other optical properties of the main article).

Fig. S4 .
Fig. S4.The representative views of the coordination framework of 1-S (left panel, i.e., a, c, and e parts) and 1-R (right panel, i.e., b, d, and f parts) for the crystal structures determined at 100(2) K, presented along the main a, b, and c crystallographic axes (parts a-b, c-d, and e-f, respectively).Hydrogen atoms were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

Fig. S5 .
Fig. S5.The representative views of the coordination framework of 1-S (left panel, i.e., a, c, and e parts) and 1-R (right panel, i.e., b, d, and f parts) for the crystal structures determined at 300(2) K, presented along the main a, b, and c crystallographic axes (parts a-b, c-d, and e-f, respectively).Hydrogen atoms were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

Fig. S6 .
Fig. S6.Detailed structural views of 1-S (left panel, i.e., a and c parts) and 1-R (right panel, i.e., b and d parts) at 100(2) K (upper part, i.e., a and b parts) and 300(2) K (bottom part, i.e., c and d parts), including the detailed presentation of cyanido-bridged {Cd II Au I }-based chains with a demonstration of the Cd(II) coordination sphere (i.e., cis-Λ/Δ-[Cd II (µ-NC)2(S-/R-pda)2]), the visualization of Au⋯Au metallophilic interaction pattern with depicted intermetallic distances, and the asymmetric unit with the labeling scheme for selected symmetrically independent atoms.Thermal ellipsoids for the asymmetric unit are presented at the 50% probability level.Hydrogen atoms in some views were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

Fig. S7 .
Fig. S7.The representative views of the coordination framework of 2 at 100(2) K (left panel, i.e., a, c, and e parts) and 300(2) K (right panel, i.e., b, d, and f parts), presented along the main a, b, and c crystallographic axes (parts a-b, c-d, and e-f, respectively).Hydrogen atoms were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

Fig. S8 .
Fig. S8.Detailed structural views of 2 at 100(2) K (a) and 300(2) K (b), including the detailed presentation of the cyanido-bridged {Cd II Au I 2} trimetallic molecules (two types, with S-pda and R-pda ligands, shown on left and right sides, respectively), being alternately arranged with supramolecular layers consisting of cis-Λ-[Cd II (µ-NC)2(S-pda)2] or cis-Δ-[Cd II (µ-NC)2(R-pda)2] complexes (left and right sides, respectively), the visualization of Au⋯Au metallophilic interaction pattern with depicted intermetallic distances, and the asymmetric unit with the labeling scheme for selected symmetrically independent atoms.Thermal ellipsoids for the asymmetric unit are presented at the 50% probability level.H-atoms in some views were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

Fig. S9 .
Fig. S9.The representative views of the coordination framework of 3-S (left panel, i.e., a, c, and e parts) and 3-R (right panel, i.e., b, d, and f parts) for the crystal structures determined at 100(2) K, presented along the main a, b, and c crystallographic axes (parts a-b, c-d, and e-f, respectively).Hydrogen atoms were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

Fig. S10 .
Fig. S10.The representative views of the coordination framework of 3-S (left panel, i.e., a, c, and e parts) and 3-R (right panel, i.e., b, d, and f parts) for the crystal structures determined at 300(2) K, presented along the main a, b, and c crystallographic axes (parts a-b, c-d, and e-f, respectively).Hydrogen atoms were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

Fig. S11 .
Fig. S11.Detailed structural views of 3-S (left panel, i.e., a and c parts) and 3-R (right panel, i.e., b and d parts) at 100(2) K (upper part, i.e., a and b parts) and 300(2) K (bottom part, i.e., c and d parts),including the detailed presentation of cyanido-bridged {Cd II Au I }-based mixed inorganic-organic layers (I 1 O 1 ) with the demonstration of the metal-organic and inorganic connectivities within the layers, the visualization of Au⋯Au metallophilic interaction pattern with depicted intermetallic distances, and the asymmetric unit with the labeling scheme for selected symmetrically independent atoms.Thermal ellipsoids for the asymmetric unit are presented at the 50% probability level.Hydrogen atoms in some views were omitted for clarity.Colors: green with various hues = Cd centers with amine ligands attached to them, orange with various hues = Au centers with cyanido ligands.

:
Fig. S12.Experimental (T = 300(2) K) and calculated powder X-ray diffraction patterns of 1-S, 1-R, 2, 3-S, and 3-R presented in the broad 2Θ range of 5-50 o (a) and the limited low-angle region of 6-22 o (b).Experimental data were compared with the patterns calculated from the respective structural models obtained from the single-crystal X-ray diffraction (SC-XRD) structural analysis (T = 100(2) K and T = 300(2) K).

Fig. S13 .
Fig. S13.The wavelength-dependences of the SHG signal (left panel, i.e., a, c, and e parts) and the dependences of the SHG light intensity on the excitation light intensity (right panel, i.e., b, d, and f parts) for the reference of potassium dihydrogen phosphate (KDP; a, b) and the indicated compounds 1-S (c, d) and 1-R (e, f).In the right panel, the coloured points represent the experimental results while the solid lines represent the best-fit curves according to the quadratic function indicating the second-harmonic nature of detected light.The resulting parameters are gathered in TableS9.Inside the left panel, the

Fig. S14 .
Fig. S14.The wavelength-dependences of the SHG signal (left panel, i.e., a, c, and e parts) and the dependences of the SHG light intensity on the excitation light intensity (right panel, i.e., b, d, and f parts) for the indicated compounds 2 (a, b), 3-S (c, d), and 3-R (e, f).In the right panel, the coloured points represent the experimental results while the solid lines represent the best-fit curves according to the quadratic function indicating the second-harmonic nature of detected light.The resulting parameters are gathered in TableS9.Inside the left panel, the photos of the observed SHG light from the respective Fig. S15.The directions of dipole moment vectors (red arrows) in the {CdN6} distorted octahedrons (TableS10) in the crystal structures of 1-S (a), 2 (b), and 3-S (c), and the schematic presentation of the

Fig. S16 .
Fig. S16.The dependence of SHG intensities generated by the investigated samples of 1-S, 1-R, 2, 3-S, and 3-R as a percentage of the KDP reference sample on the estimated dipole moment calculated for the {CdAu2} unit (a), and the comparison of estimated dipole moment and the results of Continuous Shape Measure analyses for Cd(II) and Au(I) complexes in 1-S, 1-R, 2, 3-S, and 3-R materials (Tables S7−S11) (b).

Fig. S19 .
Fig. S19.Selected curves of solid-state photoluminescent properties of 2, including the comparison of low-and high-temperature (77 and 300 K, respectively) emission (a) and excitation (b) spectra collected under indicated wavelengths, emission colors presented on the CIE 1931 chromaticity diagram (c), and comparison of low-and high-temperature (77 and 300 K, respectively) emission decay profiles (d).The best-fit parameters, as well as the CIE 1931 chromaticity parameters, are gathered in TableS12.

Fig. S20 .
Fig. S20.Selected curves of solid-state photoluminescent properties of 3-S (left panel, i.e., a, c, e, and g parts) and 3-R (right panel, i.e., b, d, f, and h parts), including the comparison of low-and hightemperature (77 and 300 K, respectively) emission (a, b) and excitation (c, d) spectra collected under indicated wavelengths, emission colors presented on the CIE 1931 chromaticity diagram (e, f), and comparison of low-and high-temperature (77 and 300 K, respectively) emission decay profiles (g, h).

Table S2 .
Crystal data and structure refinement parameters for 2 for the SC-XRD measurements

Table S3 .
Crystal data and structure refinement parameters for 3

Table S7 .
Results of Continuous Shape Measure (CShM) analyses for Cd(II) complexes in

Table S9 .
Comparison of the SHG intensities generated by the investigated samples of 1-S, 1-R, 2, 3-S, and 3-R with the SH intensity generated by the potassium dihydrogen phosphate (KDP) reference sample (see Fig.S13and S14 for detailed characteristics).

Table S10 .
Results of dipole moment calculations of Cd(II) complexes in the crystal structures of 1-S, 1-R, 2, 3-S, and 3-R measured at 300(2) K. Details of the calculations are described in the comment below.The resulting direction of the dipole moment vectors is presented in Fig.S15.

Table S11 .
Results of dipole moment calculations of Au(I) complexes in the crystal structures of 1-S, 1-R, 2, 3-S, and 3-R measured at 300(2) K. Details of the calculations are described in the comment below.The resulting direction of the dipole moment vectors is presented in Fig.S15.

Table S12 .
Selected spectroscopic parameters of the solid-state photoluminescent properties of 1-S, at 77 and 300 K (Fig.S18−S20), including the position of an emission pattern maximum, the CIE 1931 chromaticity parameters, the best-fit parameters for the emission decay profiles to the mono-exponential function, and the absolute quantum yield.

Table S13 :
the radiative (kr) and nonradiative (knr) decay rate constants are based on the relationship kr= φem/τ and φem=kr/(kr+knr) in which τ values are luminescence lifetimes and the φem is the related absolute quantum yield.S9,S10