Formation, Characterization, and Bonding of cis- and trans-[PtCl2{Te(CH2)6}2], cis-trans-[Pt3Cl6{Te(CH2)6}4], and cis-trans-[Pt4Cl8{Te(CH2)6}4]: Experimental and DFT Study

[PtCl2{Te(CH2)6}2] (1) was synthesized from the cyclic telluroether Te(CH2)6 and cis-[PtCl2(NCPh)2] in dichloromethane at room temperature under the exclusion of light. The crystal structure determination showed that in the solid state, 1 crystallizes as yellow plate-like crystals of the cis-isomer 1cis and the orange-red interwoven needles of 1trans. The crystals could be separated under the microscope. NMR experiments showed that upon dissolution of the crystals of 1cis in CDCl3, it isomerizes and forms a dynamic equilibrium with the trans-isomer 1trans that becomes the predominant species. Small amounts of cis-trans-[Pt3Cl6{Te(CH2)6}4] (2) and cis-trans-[Pt4Cl8{Te(CH2)6}4] (3) were also formed and structurally characterized. Both compounds show rare bridging telluroether ligands and two different platinum coordination environments, one exhibiting a cis-Cl/cis-Te(CH2)6 arrangement and the other a trans-Cl/trans-Te(CH2)6 arrangement. Complex 2 has an open structure with two terminal and two bridging telluroether ligands, whereas complex 3 has a cyclic structure with four Te(CH2)6 bridging ligands. The bonding and formation of the complexes have been discussed through the use of DFT calculations combined with QTAIM analysis. The recrystallization of the mixture of the 1:1 reaction from d6-DMSO afforded [PtCl2{S(O)(CD3)2}{Te(CH2)6}] (4) that could also be characterized both structurally and spectroscopically.

The current contribution is the continuation of our systematic investigation of the synthesis of the series of telluroether heterocycles [Te(CH 2 ) m ] n (n = 1-4; m = 3-7) [29] and the coordination complexes of telluroethers (see refs.[35][36][37][38][39] for some recent publications).Monotelluroethers Te(CH 2 ) m are liquid in ambient conditions, but species with higher Te contents are solid.The molecular structures and the packing of seven macrocyclic aliphatic telluroethers have been explored [29].Te(CH 2 ) 6 was one of the monotelluroethers that was synthesized and characterized through NMR spectroscopy, but since it is a liquid at room temperature with a low melting point, its crystal structure determination could not be carried out.It was thought that the reaction with [PtCl 2 (NCPh) 2 ] should enable it to coordinate with the platinum center, and the resulting complex would be crystalline.Its crystal structure determination would establish the molecular structure of Te(CH 2 ) 6 .The monodentate also ligand avoids the formation of coordination polymers.It turned out that the reaction produced not only the expected cisand trans-[PtCl 2 {Te(CH 2 ) 6 } 2 ] (1 cis and 1 trans , respectively), but small amounts of cis-trans-[Pt 3 Cl 6 {Te(CH 2 ) 6 } 4 ]•1 1 /4CH 2 Cl 2 ) (2•1 1 /4CH 2 Cl 2 ) and, depending on the molar ratio of the reagents, also cis-trans-[Pt 4 Cl 8 {Te(CH 2 ) 6 } 4 ]•4CDCl 3 (3•4CDCl 3 ).The attempts to produce the polynuclear complexes in better yields involved the use of d 6 -dimethyl sulfoxide as the crystallization solvent, in which case crystals of the mononuclear [PtCl 2 {S(O)(CD 3 ) 2 }{Te(CH 2 ) 6 }] (4) were obtained.The crystal structures of 1 cis and2-4, the isomerization of 1 cis to 1 trans , and the bonding features and formation of 2 and 3 are discussed in this paper.
The current contribution is the continuation of our systematic investigatio synthesis of the series of telluroether heterocycles [Te(CH2)m]n (n = 1-4; m = 3-7) the coordination complexes of telluroethers (see refs.[35][36][37][38][39] for some recent tions).Monotelluroethers Te(CH2)m are liquid in ambient conditions, but spec higher Te contents are solid.The molecular structures and the packing of seven m clic aliphatic telluroethers have been explored [29].Te(CH2)6 was one of the mo roethers that was synthesized and characterized through NMR spectroscopy, but is a liquid at room temperature with a low melting point, its crystal structure det tion could not be carried out.It was thought that the reaction with [PtCl2(NCPh)2 enable it to coordinate with the platinum center, and the resulting complex would talline.Its crystal structure determination would establish the molecular stru Te(CH2)6.The monodentate also ligand avoids the formation of coordination poly turned out that the reaction produced not only the expected cis-and [PtCl2{Te(CH2)6}2] (1cis and 1trans, respectively), but small amounts of c [Pt3Cl6{Te(CH2)6}4]•1¼CH2Cl2) (2•1¼CH2Cl2) and, depending on the molar ratio o agents, also cis-trans-[Pt4Cl8{Te(CH2)6}4]•4CDCl3 (3•4CDCl3).The attempts to prod polynuclear complexes in better yields involved the use of d6-dimethyl sulfoxid crystallization solvent, in which case crystals of the mono [PtCl2{S(O)(CD3)2}{Te(CH2)6}] (4) were obtained.The crystal structures of 1cis and isomerization of 1cis to 1trans, and the bonding features and formation of 2 and 3 cussed in this paper.

General
The reaction of two equivalents of Te(CH2)6 with one equivalent of cis-[PtCl2(N in dichloromethane produces cis-and trans-[PtCl2{Te(CH2)6}2] (1cis and 1trans) (see 1).The 1 H, 125 Te{ 1 H}, and 195 Pt{ 1 H} NMR spectra recorded in CDCl3 indicate that th isomer is the main isomer in CDCl3, as discussed in Section 2.2.Small amounts o ble, likely polymeric products were also formed.The syntheses of platinum and palladium complexes using related telluracyclopentane Te(CH 2 ) 4 have been reported to give [MX 2 {Te(CH 2 ) 4 } 2 ] (M = Pt, Pd; X = Cl, Br, I) [30].The [PtCl 2 {Te(CH 2 ) 4 } 2 ] was deduced to be the cis isomer in the solid state on the basis of IR spectroscopy, but the complex was reported to exist as a mixture of cisand transisomers in solution in the respective concentration ratio of, ca.1:2.The palladium complex [PdCl 2 {Te(CH 2 ) 4 } 2 ] exists only as a trans isomer [30].
The crystallization of the product of the reaction of Te(CH 2 ) 6 and cis-[PtCl 2 (NCPh) 2 ] from dichloromethane/pentane gave a mixture of yellow plates and orange-red needles.The yellow plate-shaped crystals were suitable for the determination of the crystal structure, which showed them to be cis-[PtCl 2 {Te(CH 2 ) 6 } 2 ] (1 cis ) (see Section 2.3).The orange-red needles were intergrown and proved to be unsuitable for X-ray structure analysis.However, the NMR and mass spectroscopic information indicated them to be trans-[PtCl 2 {Te(CH 2 ) 6 } 2 ] (1 trans ).
Small amounts of both yellow and orange-red crystals were manually separated under the microscope.They were dissolved in CDCl 3 for the recording of the NMR spectra (see Section 2.2).An additional small crop of red plate-shaped crystals was identified under the microscope and could be manually isolated based on their different crystal habits.The crystal structure was determined as cis-trans- Section 2.3).Because of the very small amount of 2, no bulk analysis could be carried out.
The synthesis was repeated by using equimolar amounts of cis-[PtCl 2 (NCPh) 2 ] and Te(CH 2 ) 6 .Thin-layer chromatography indicated mostly the formation of cisand trans-[PtCl 2 {Te(CH 2 ) 6 } 2 ] (1 cis and 1 trans ) together with the presence of the starting materials.After recording the NMR spectra in CDCl 3 , red well-shaped crystals grew in the NMR tube.The crystal structure determination showed these crystals to be cis-trans- During the attempts to crystallize 3 in larger amounts, the recrystallization in dimethyl sulfoxide was attempted.It yielded almost colorless crystals of [PtCl 2 {S(O)(CD 3 ) 2 }{Te(CH 2 ) 6 }] (4) (see Section 2.3).

NMR Spectroscopy
The crystals of cis-[PtCl 2 {Te(CH 2 ) 6 } 2 ] were dissolved in deuterochloroform for recording the 125 Te{ 1 H} NMR and 195 Pt{ 1 H} NMR spectra (see Figure 1).All spectra can be interpreted in terms of a mixture of 1 cis and 1 trans .The NMR spectroscopic information of 1 cis and 1 trans is compared with those of related species in Table 1.
The syntheses of platinum and palladium complexes using related telluracyclopentane Te(CH2)4 have been reported to give [MX2{Te(CH2)4}2] (M = Pt, Pd; X = Cl, Br, I) [30].The [PtCl2{Te(CH2)4}2] was deduced to be the cis isomer in the solid state on the basis of IR spectroscopy, but the complex was reported to exist as a mixture of cis-and trans-isomers in solution in the respective concentration ratio of, ca.1:2.The palladium complex [PdCl2{Te(CH2)4}2] exists only as a trans isomer [30].
The crystallization of the product of the reaction of Te(CH2)6 and cis-[PtCl2(NCPh)2] from dichloromethane/pentane gave a mixture of yellow plates and orange-red needles.The yellow plate-shaped crystals were suitable for the determination of the crystal structure, which showed them to be cis-[PtCl2{Te(CH2)6}2] (1cis) (see Section 2.3).The orange-red needles were intergrown and proved to be unsuitable for X-ray structure analysis.However, the NMR and mass spectroscopic information indicated them to be trans-[PtCl2{Te(CH2)6}2] (1trans).
Small amounts of both yellow and orange-red crystals were manually separated under the microscope.They were dissolved in CDCl3 for the recording of the NMR spectra (see Section 2.2).An additional small crop of red plate-shaped crystals was identified under the microscope and could be manually isolated based on their different crystal habits.The crystal structure was determined as cis-trans-[Pt3Cl6{Te(CH2)6}4]•1¼CH2Cl2 (2•1¼CH2Cl2) (see Section 2.3).Because of the very small amount of 2, no bulk analysis could be carried out.
The synthesis was repeated by using equimolar amounts of cis-[PtCl2(NCPh)2] and Te(CH2)6.Thin-layer chromatography indicated mostly the formation of cis-and trans-[PtCl2{Te(CH2)6}2] (1cis and 1trans) together with the presence of the starting materials.After recording the NMR spectra in CDCl3, red well-shaped crystals grew in the NMR tube.The crystal structure determination showed these crystals to be cis-trans- During the attempts to crystallize 3 in larger amounts, the recrystallization in dimethyl sulfoxide was attempted.It yielded almost colorless crystals of [PtCl2{S(O)(CD3)2}{Te(CH2)6}] (4) (see Section 2.3).

NMR Spectroscopy
The crystals of cis-[PtCl2{Te(CH2)6}2] were dissolved in deuterochloroform for recording the 125 Te{ 1 H} NMR and 195 Pt{ 1 H} NMR spectra (see Figure 1).All spectra can be interpreted in terms of a mixture of 1cis and 1trans.The NMR spectroscopic information of 1cis and 1trans is compared with those of related species in Table 1.Based on the trends in the 125 Te and 195 Pt chemical shifts that have been reported previously [30,40,41], the tellurium resonance at 352 ppm has been assigned to the cis isomer 1 cis and that at 399 ppm to the trans isomer 1 trans .It can also be seen in Table 1 that the magnitudes of the 1 J TePt coupling constants in the cis-isomers are almost double compared to those of the corresponding trans-isomers.These relative values, as well as the trends in both the 125 Te and 195 Pt chemical shifts, reflect the stronger trans-influence of the tellurium donors compared to that of the chlorido ligand and support the assignments.
The cis -> trans isomerization of [PtCl 2 {Te(CH 2 ) 6 } 2 ] was monitored using 1 H NMR spectroscopy (see Figure S1 in Supplementary Materials).The crop of crystals of 1 cis from which the crystal structure determination was carried out (Section 2.3) was dissolved in CDCl 3 , and the spectra were recorded at room temperature for 30 s after the dissolution and again after 1.2 h.In solution, the trans-isomer 1 trans quickly became the dominant species.Already in the first spectrum (Figure S1a) recorded almost immediately after the dissolution of the crystals, the trans-isomer can be observed, and in the second spectrum (Figure S1b), it is clearly the predominant species.The assignment of the 1 H chemical shifts was verified by recording the 1 H NMR spectrum of the redissolved orange needles.Immediately after the dissolution, the resonances marked as trans in Figure S1 were the major signals in the spectrum and remained so throughout prolonged monitoring of the solution.
After 1.2 h, the cis:trans ratio was estimated from the integrated intensities of the resonances to be 1:1.8,which is very close to the ratio of 1:2 that Kemmitt et al. [30] estimated for the related [PtCl 2 {Te(CH 2 ) 4 } 2 ] in dichloromethane.The intensity distribution in the 125 Te{ 1 H} and 195 Pt{ 1 H} NMR spectra (see Figure 1) bears semiquantitative agreement with the inferences from the 1 H spectrum in Figure S1b.
The 125 Te{ 1 H} NMR spectrum of the solidified and redissolved reaction mixture prior to separation of the products is shown in Figure S3 of Supplementary Materials.In addition to the resonances of 1 cis and 1 trans , two weak signals at 489 ppm and 598 ppm were observed.The qualitative comparison of their relative signal intensities and the chemical shifts might indicate the presence of the trinuclear complex cis-trans-[Pt 3 Cl 6 {Te(CH 2 ) 6 } 4 ] (2), but this assignment remains tentative at best.The former resonance could be due to the terminal Te(CH 2 ) 6 ligand, and the latter due to the bridging ligand (see Section 2.3).
In addition to 1cis and 1trans, a few red, plate-shaped crystals of the trinuclear cis-trans-  S1 and S2 in Supplementary Materials).The asymmetric unit of 2•1 1 /4CH 2 Cl 2 contains two independent complexes (denoted A and B) with virtually the same conformations and bond parameters.There are also 2 1 /2 solvent molecules in the asymmetric unit.Some Te(CH 2 ) 6 ligands exhibit orientational disorder.Since the structures of both discrete complexes in the asymmetric unit are closely similar, only complex A is shown in Figure 3a.In the case of 3•4CDCl 3 , the asymmetric unit contains only half of the tetranuclear complex, with the other half being completed through symmetry.The geometry of 3 is closely related to that of 2, as shown in Figure 3b.
Both complexes 2 and 3 show the simultaneous occurrence of very slightly distorted square-planar cisand trans-PtCl 2 Te 2 coordination environments.In the cis-moieties, the Pt-Te bonds range from 2.5045 (7)  The asymmetric unit of 2•1¼CH2Cl2 contains two independent complexes (denoted A and B) with virtually the same conformations and bond parameters.There are also 2½ solvent molecules in the asymmetric unit.Some Te(CH2)6 ligands exhibit orientational disorder.Since the structures of both discrete complexes in the asymmetric unit are closely similar, only complex A is shown in Figure 3a.In the case of 3•4CDCl3, the asymmetric unit contains only half of the tetranuclear complex, with the other half being completed through symmetry.The geometry of 3 is closely related to that of 2, as shown in Figure 3b.
Both complexes 2 and 3 show the simultaneous occurrence of very slightly distorted square-planar cis-and trans-PtCl2Te2 coordination environments.In the cis-moieties, the Pt-Te bonds range from 2.5045(7) to 2.5226(6) Å and the Pt-Cl bonds range from 2.309(3) to 2.331(5) Å.In the trans-PtTe2Cl2 moieties, the Pt-Te and Pt-Cl range from 2.5546(6) to 2.5774(15) Å and from 2.302(2) to 2.326(6) Å, respectively.The relative magnitudes of these metrical values demonstrate the stronger trans-influence of tellurium compared to chlorine.
The molecular structure of [PtCl2{S(O)(CD3)2}{Te(CH2)6}] ( 4) is shown in Figure 4 together with the labeling of atoms and selected bond parameters.S2), in the case of the latter polynuclear complexes, they are intra-molecular (see Figure 5).Similar linking of the square-planar MX2E2 (M = Pt, Pd; E = Se, Te) coordination spheres into dimers has also been observed  S2), in the case of the latter polynuclear complexes, they are intra-molecular (see Figure 5).Similar linking of the square-planar MX 2 E 2 (M = Pt, Pd; E = Se, Te) coordination spheres into dimers has also been observed in other chalcogenoether complexes provided that the steric bulk of the organic group

General
We carried out PBE0-D3/def2-TZVP calculations to study the bonding, secondary bonding interactions, as well as energetics of the cis-trans isomerization of [PtCl2{Te(CH2)6}2] and the formation of tri-and tetranuclear complexes.

General
We carried out PBE0-D3/def2-TZVP calculations to study the bonding, secondary bonding interactions, as well as energetics of the cis-trans isomerization o [PtCl2{Te(CH2)6}2] and the formation of tri-and tetranuclear complexes.

Density Functional Theory (DFT) Computations 2.4.1. General
We carried out PBE0-D3/def2-TZVP calculations to study the bonding, secondary bonding interactions, as well as energetics of the cis-trans isomerization of [PtCl 2 {Te(CH 2 ) 6 } 2 ] and the formation of tri-and tetranuclear complexes.

Optimized Geometries
The PBE0-D3/def2-TZVP optimized geometries of [PtCl 2 {Te(CH 2 ) 6 } 2 ] (1 cis and 1 trans ), cis-trans-[Pt 3 Cl 6 {Te(CH 2 ) 6 } 4 ] (2), and cis-trans-[Pt 4 Cl 8 {Te(CH 2 ) 6 } 4 ] (3) agree well with the experimental information despite the fact that the experimental information is from the crystalline state and the computational data are calculated in vacuum.The PBE0-D3/def2-TZVP-optimized coordinates are shown in Table S3 and the computed geometries are shown in Table S4 in Supplementary Materials.The total energies in vacuum are presented in Table S5 and those in dichloromethane in Table S6.

Chalcogen Bonding and Metallophilic Interactions
The QTAIM analysis of the secondary bonding Te•••Cl and Pt•••Pt interactions are shown in Table 2.The Pt-Te bond lengths and experimental close contacts in the crystals have been included for comparison.The use of QTAIM in the characterization of metalmetal bonding has recently been reviewed [55].In addition to the classical descriptors of electron density (ρ) and the Laplacian (∇ 2 ρ) at the bond critical point that are expected to be large and negative, respectively, for covalent bonds, the relative magnitudes of the kinetic G b and the potential V b energy densities have been used to classify bonds.The relative magnitudes have been examined either via the electronic energy density (H b = G b + V b ) [56,57] 2) are much closer to the limit of closed-shell interactions.The low level of electron sharing in the Pt•••Pt interactions is reflected by the ρ values 0.122, 0.172, and 0.202 e Å −3 and the DI values 0.18, 0.26, and 0.30 for 1 cis , 2, and 3, respectively.By comparison, the QTAIM analysis in a recent study on platinum complexes of phenylpyridine, triazolyl-phenylpyridine, and imidazolyl-phenylpyridine that form head-to-tail dimers via the Pt•••Pt interactions in the solid state show the ρ values of 0.132-0.150e Å -3 that are between those of 1 cis and 2 [62].The |V b |/G b ratios of Pt•••Pt interactions of 1.08-1.10are also very similar to those found in this contribution.In both cases, the metallophilic Pt•••Pt interactions show weak covalence.The weak Te•••Cl contacts are classified as closed-shell interactions by the positive H b values of 0-3, as shown in Table 2.This is also reflected by the small values of ρ (0.061-0.074 e Å −3 ) and DI (0.06-0.10).They can be compared to the intermolecular Te•••Te chalcogen bonds in solid macrocyclic telluroethers and are of the same order of magnitude [29].The relative strengths of the Pt•••Pt and Te•••Cl interactions can be qualitatively estimated using E int calculated from V b [63], although some caution should be exercised when drawing conclusions, as the reliability of the relationship has been questioned [64].Comparison of the E int values shows that in all complexes 1 cis , 2, and 3, the metallophilic Pt•••Pt interactions (E int = −16-(−31) kJ mol -1 bohr -3 ) are stronger than single Te•••Cl interactions (E int = −6-(−7) kJ mol -1 bohr -3 ).The stronger attraction between the Pt centers compared to that between Te and Cl could explain the observation that in all three complexes, the square-planar coordination plane is slightly concave with Pt•••Pt showing the closest distance between these distorted planes (see Figure S4).However, there are four Te•••Cl interactions in each complex structure compared to one Pt•••Pt interaction, suggesting that the total stabilization of the complexes due to Te  3) that could be identified and structurally characterized through X-ray diffraction.The total PBE0-D3/def2-TZVP energies of all species in dichloromethane (see Table S6) can be used to calculate Gibbs energy changes in the formation of complexes 1 cis , 2, and 3 from cis-[PtCl 2 (NCPh) 2 ] and Te(CH 2 ) 6 that are shown in Table S7.One possible route for the formation of the polynuclear complexes is shown in Scheme 2 together with the Gibbs energy changes in the individual reaction steps.The relative Gibbs energies of the reaction products and intermediates with respect to cis-[PtCl 2 (NCPh) 2 ] are also shown in Scheme 2.

General Procedures
All manipulations involving air-and moisture-sensitive materials were conducted under a nitrogen atmosphere using Schlenk techniques.Dichloromethane and chloroform were distilled over CaH2 and hexane over Na/benzophenone under a nitrogen atmosphere prior to use.Ethanol was degassed by bubbling nitrogen through the solvent for at least 15 min.Semiconductor-grade tellurium was freshly ground.All other reagents were used as purchased without further purification.The preparation of Te(CH2)6 has been reported earlier [29].

General Procedures
All manipulations involving air-and moisture-sensitive materials were conducted under a nitrogen atmosphere using Schlenk techniques.Dichloromethane and chloroform were distilled over CaH 2 and hexane over Na/benzophenone under a nitrogen atmosphere prior to use.Ethanol was degassed by bubbling nitrogen through the solvent for at least 15 min.Semiconductor-grade tellurium was freshly ground.All other reagents were used as purchased without further purification.The preparation of Te(CH 2 ) 6 has been reported earlier [29].

NMR Spectroscopy
1 H, 13 C{ 1 H}, 125 Te{ 1 H}, and 195 Pt{ 1 H} NMR spectra of 1 cis and 1 trans were recorded in CDCl 3, and those of 4 in d 6 -DMSO were recorded on a Bruker Avance III 400 spectrometer operating at 400.13, 100.61, 126.24, and 86.02 MHz, respectively.The respective pulse widths were 13.0, 9.70, 6.0, and 10.0 µs, and the corresponding relaxation delay was 2.0 s for each nucleus.The deuterated solvent was used as the 2 H lock.All resonances were indirectly referenced by using the deuterium signal of the solvent for the lock to the frequency that relates to the resonance frequency of the TMS protons at exactly 400.130000MHz.Chemical shifts for the 125 Te resonances are given relative to dimethyl telluride through indirect referencing (the tellurium resonance ν 0 (Te) was calculated by using the ratio Ξ = ν 0,H (Te)/ν 0 (TMS) = 31.549769%[61]).Chemical shifts for 195 Pt are given relative to Na 2 [PtCl 6 ] (1.2 M in D 2 O) also through indirect referencing (Ξ = ν 0,H (Pt)/v 0 (TMS) = 21.96784%)[65].The 1 H and 13 C are reported relative to tetramethyl silane TMS [66].

Mass Spectrometry
Electron ionization mass spectra were recorded on Finnigan MAT SSQ 710 and Finnigan MAZ95XL spectrometers.The energy of the electrons was 70 eV.

X-ray Diffraction
The crystals of 1-4 were coated with Paratone oil and mounted in a nylon CryoLoop, and the intensity data were collected on a Bruker Nonius Kappa CCD diffractometer at 133 K using graphite monochromated Mo Kα radiation (λ = 0.71073 A; 55 kV, 25 mA) [67,68].Crystal data and the details of structure determinations are given in Table S1.The data were corrected for Lorenz and polarization effects, after which semi-empirical absorption correction was applied to net intensities using SADABS [69].The structures were solved through direct methods using SHELXT [70] and refined using SHELXL-2018 [71].After the full-matrix least-squares refinement of the non-hydrogen atoms with anisotropic thermal parameters, the hydrogen atoms were placed in calculated positions in the CH 2 groups (C-H = 0.99 A).In the final refinement, the hydrogen atoms were riding with the carbon atoms they were bonded to.The isotropic thermal parameters of the hydrogen atoms were fixed at 1.5 times that of the corresponding carbon atoms.The scattering factors for the neutral atoms were those incorporated with the program.Some Te(CH 2 ) 6 ligands and solvent molecules in 2•1 1 /4CH 2 Cl 2 and 3•4CDCl 3 were disordered.The disorder was resolved through appropriate restraining of the anisotropic displacement parameters and some bond lengths.Some parts of the disorder model were introduced by utilizing the program DSR [72].

Computational Details
All calculations were performed using the Gaussian 16 program [73] by employing the PBE0 hybrid functional [74][75][76] together with the def2-TZVP basis sets [77,78].The combination of the PBE0 functional and the def2-TZVP basis set has been shown to be suitable for computational characterization of compounds of heavy p-block elements (see the discussion in ref. [79]).Implicit C-PCM solvent model was applied to treat the solvation effects [80,81], and dispersion forces were treated by using the D3BJ version of Grimme's empirical correction with Becke-Johnson damping parameterized for the PBE0 functional [82][83][84].Full structure optimization was carried out for each species considered in this work and the frequencies were calculated for the optimum geometries to ascertain the nature of the stationary points.The quantum theory of atoms in molecules (QTAIM) was used to study inter-molecular interactions in the [PtCl 2 {Te(CH 2 ) 6 }] (1 cis , 1 trans ), as well as intra-molecular interactions in the cis-trans-[Pt 3 Cl 6 {Te(CH 2 ) 6 } 4 ] (2) and cis-trans-[Pt 4 Cl 8 {Te(CH 2 ) 6 } 4 ] (3) structures [85].AIMAll software was used for the QTAIM calculations [86].Te(CH 2 ) 6 (46.2 mg, 0.218 mmol) was dissolved in 50 mL CH 2 Cl 2 and crystalline cis-[PtCl 2 (NCPh) 2 ] (50.0 mg, 0.106 mmol) was added.The mixture was stirred under exclusion of light for 20 h.The solvent was removed under reduced pressure and the crude product was extensively dried at 40 • C and 1 mbar to remove any benzonitrile, yielding 71.7 mg (theoretical: 74.4 mg) of an odorless yellow solid with few orange crystals in it.TLC analysis (silica, chloroform) showed two spots at Rf = 0.89 and 0.25 corresponding to trans-[PtCl 2 {Te(CH 2 ) 6 } 2 ] (1 trans ) and cis-[PtCl 2 {Te(CH 2 ) 6 } 2 ] (1 cis ) beside a very faint spot at Rf = 0.58 and few minor spots at Rf < 0.25.The substances corresponding to the latter were mostly removed through column chromatography (silica, chloroform), yielding 54.5 mg of substance.The product was dissolved in CH 2 Cl 2 /pentane and, upon slow evaporation, both 1 trans and 1 cis crystallized, with the former giving orange to red, heavily intergrown the formation of tri-and tetranuclear complexes.A significantly larger excess of the cis-[PtCl 2 (NCPh) 2 ] reagent might improve their yields, but that is the subject for a future study.
addition to 1cis and 1trans, a few red, plate-shaped crystals of the trinuclear cis-trans-[Pt3Cl6{Te(CH2)6}4]•1¼CH2Cl2 (2•1¼CH2Cl2) could be manually separated from the reaction mixture after the crystallization from CH2Cl2/pentane.The crystals of tetranuclear cistrans-[Pt4Cl8{Te(CH2)6}4]•4CDCl3 (3•4CDCl3) could be obtained upon recrystallization from CDCl3 in the NMR tube after the recording of the NMR spectra of the equimolar reaction of the reagents.The molecular structures of 2•1¼CH2Cl2 and 3•4CDCl3 are shown in Figure 3 (for details of the structure determination and the list of selected bond parameters, see Tables
be manually separated from the reaction mixture after the crystallization from CH2Cl2/pentane.The crystals of tetranuclear cistrans-[Pt4Cl8{Te(CH2)6}4]•4CDCl3 (3•4CDCl3) could be obtained upon recrystallization from CDCl3 in the NMR tube after the recording of the NMR spectra of the equimolar reaction of the reagents.The molecular structures of 2•1¼CH2Cl2 and 3•4CDCl3 are shown in Figure 3 (for details of the structure determination and the list of selected bond parameters, see Tables
or the |V b |/G b ratio [58].The Laplacian for the bonds between heavy atoms tends to give positive values regardless of the bond type [59].Therefore, the energy densities have been good additional descriptors for defining metal bonding.The negative H b values have been taken as a sign of covalent bonding and the positive values as indicators of closed-shell interactions [60].The |V b |/G b ratio further distinguishes the regions of shared-shell interactions with |V b |/G b > 2, intermediate regions corresponding to 1 < |V b |/G b < 2, and closed-shell interactions with |V b |/G b < 1 [55].The intermediate region includes metal-metal and donor-acceptor interactions [59].In the case of complexes 1 cis , 2, and 3, the calculated ∇ 2 ρ for Pt•••Pt, Pt-Te, and Te•••Cl are all positive, as can be expected for interactions between the heavy atoms.For the Pt-Te bonds, the values of H b are negative and |V b |/G b ratios are in the intermediate region between 1.64 and 1.75, consistent with the donor-acceptor bonds.The electron densities at bond critical points (ρ) and the delocalization indices (DIs) that are close to the single bond values [61] corroborate this classification of the coordinative bonds.Because of the trans-influence, the Pt-Te bonds are slightly longer than single bonds and cause the delocalization indices of the Pt-Te(trans) bonds to be smaller than those of the Pt-Te(cis) bonds.By comparison, H b of the Pt•••Pt interactions are still negative but |V b |/G b ratios that fall between 1.06 and 1.15 (see Table

Table 1 .
NMR spectroscopic information of some telluroether complexes of platinum a .

125 Te), ppm 1 J PtTe , Hz δ( 195 Pt), ppm Ref.
The cis-designation refers to the relative positions of the two chloride ligands. a