Structure of a diorganotelluroxonium(IV) cation, {[2,6-(CH2NMe2)2C6H3Te(μ-O)]2}2+, with the trichlorido(dimethyl sulfoxide)platinum(II) anion

In the structure of the salt [C24H38N4O2Te2]2+ [PdCl3(DMSO)]− 2, the phenyl rings in the [C24H38N4O2Te2]2+ cation are in a cis arrangement to enable this species to participate in Te⋯Cl cation–anion interactions.


Chemical context
After the initial discovery (Moulton & Shaw, 1976) and seminal contributions from various research groups, the coordination chemistry of pincer ligands has become an important field in coordination chemistry (Peris & Crabtree, 2018). One pincer ligand scaffold that has recently attracted considerable attention with respect to its interesting structural features and reactivity, is the NCN pincer ligand, [2,6-(Me 2 NCH 2 ) 2 C 6 H 3 ] (HL).
Of particular interest are the group 16 derivatives of these ligands where, due to the presence of intramolecular N!M interactions from the two coordinating auxiliary arms, their compounds show interesting reactivity and have been used in the formation of selenium cations (Fujihara et al., 1995;Poleschner & Seppelt, 2004Gupta et al., 2017;Pop et al., 2014;Varga et al., 2010;Rani et al., 2018). It is worth noting that, compared to the selenenium cation of ligand L, studies on their higher congener i.e., tellurenium cations, are relatively scarce in the literature and this was the initial impetus for this work. Furukawa and co-workers reported the synthesis of a tellurenium cation by the reaction of heteroleptic diorganotelluride LTeR (where R = n-butyl) with Br 2 /K[PF6] (Fujihara et al., 1995). However, the structural elucidation of the tellurenium cation of the ligand L remained elusive until Silvestru and co-workers reported the first structural characterization of a tellurenium cation (Beleaga et al., 2011).
It is interesting to note that the related tin(II) cations of ligand L, containing one lone pair of electrons, have been used as ligands to isolate heterobimetallic complexes 4a,b (Martincová et al., 2011(Martincová et al., , 2012. However, no such coordination chemistry has been explored for the selenenium(II) and tellurenium(II) cations of ligand L, which have two such pairs of electrons. A notable work is that by Lin & Gabbaï (2013) where they used Te IV cations having one lone pair of electrons as ligands for isolating complex 5 where the Te IV center acted as a -acceptor (Z-type) ligand.

Structural commentary
The title structure represents a rare example of a structurally characterized diorganotelluroxonium(IV) cation and key geometrical data are listed in Table 1 The molecular structure of the [C 24 H 38 N 4 O 2 Te 2 ] 2+ cation, showing the cis arrangement of the phenyl rings with respect to the Te 2 O 2 core. Atomic displacement parameters are drawn at the 30% probability level. Table 1 Selected geometric parameters (Å , ). is in contrast to that observed in the structure of [2,6-(CH 2 NMe 2 ) 2 C 6 H 3 Te(-O)] 2 + ÁPF 6 À , wherein the cation lies on a center of inversion and thus the aryl groups are in a trans configuration (Kobayashi et al., 2000). Each Te atom is in a five-coordinate geometry with the phenyl rings occupying the apical position. An analysis of this geometry using the continuous shape measurement (CSM) method (Cirera et al., 2005;Llunell et al., 2013) and using the four appropriate reference shapes [vacant octahedron, C 4v ; trigonal bipyramid, D 3h ; square pyramid, C 4v ; and Johnson trigonal bipyramid, D 3h ] showed that the closest fit was the vacant octahedron. The Te-N bond distances, lying in the range from 2.450 (2)-2.495 (2) Å for 2, are in good agreement with the values observed in [2,6-(CH 2 NMe 2 ) 2 C 6 H 3 Te(-O)] 2 + ÁPF 6 À [2.475 (5)-2.486 (5) Å ] (Kobayashi et al., 2000). In 2, the dihedral angle between the two aryl groups is 6.2 (2) and those between the Te 2 O 2 plane and the aryl rings are 88.77 (8) and 85.00 (8) , indicating that the two aryl groups are not coplanar, and are too far apart to formstacking interactions (the closest contact is between C1 and C1A at 3.672 Å ). Thus, the driving force for the adoption of this sterically unfavorable cis conformation appears to be the formation of TeÁ Á ÁCl cation-anion interactions, which would not be possible if the trans conformation were adopted. In this case, there is a short Te2Á Á ÁCl3 contact of 3.386 (1) Å and longer contacts of 3.833 (1) Å (Te2Á Á ÁCl2) and 3.991 (1) Å (Te1Á Á ÁCl5) (see Fig. 2). In contrast, in the case of [2,6-(CH 2 NMe 2 ) 2 C 6 H 3 Te(-O)] 2 + ÁPF 6 À , no such cation-anion interactions are present and hence the more sterically favorable trans conformation is adopted. In the other two related structures containing the Te 2 O 2 2+ core dication, the same cis configuration is adopted to allow the formation of interionic TeÁ Á ÁO interactions (Hupf et al., 2017;Deka et al., 2020).

Figure 3
Packing diagram showing how the TeÁ Á ÁCl cation-anion interactions, C-HÁ Á ÁO interactions involving the DMSO ligands, and numerous cationanion and anion-anion C-HÁ Á ÁCl interactions linking these moieties into a complex three-dimensional array (all interactions shown as dashed lines).

Database survey
There are only three reports available containing a cation with the Te 2 O 2 2+ core. The first report on the molecular structure of a diorganotelluroxonium(IV) cation was made by Furukawa and co-workers (Kobayashi et al., 2000

Synthesis and crystallization
To a solution of 1 (0.10 g, 0.20 mmol) in CCl 4 (3 ml), a solution of SO 2 Cl 2 (0.03 g, 17.76 mL, 0.22 mmol) in CCl 4 (2 ml) was added dropwise at 273 K under an N 2 atmosphere. After stirring the reaction mixture for 1 h, hexane (10 ml) was added, resulting in the formation of a white precipitate. The precipitate was washed with hexane (2 Â 5 ml) and dissolved in THF (20 ml

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. A riding model was used for the H atoms with atomic displacement parameters = 1.2U eq (C) [1.5U eq (CH 3 )] and C-H distances ranging from 0.95 to 0.99 Å .

Funding information
HBS wishes to acknowledge the DST for the award of a J. C. Bose fellowship. RJB thanks the United States-India Educational Foundation for the award of a Distinguished Chair Fulbright Fellowship to India from January-May 2019. Computer programs: CrystalClear-SM Expert (Rigaku, 2012), SHELXT (Sheldrick, 2015a), SHELXL2018/3 (Sheldrick, 2015b) and SHELXTL (Sheldrick, 2008).

κS)platinate(II)]
Crystal data (C 24  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.72 e Å −3 Δρ min = −0.95 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.