Bis{μ-2-[(dimethylamino)methyl]benzenetellurolato}bis[chloridopalladium(II)] dichloromethane hemisolvate

The asymmetric unit of the title compound, [Pd2(C9H12NTe)2Cl2]·0.5CH2Cl2, contains two half-molecules, each lying on a twofold rotation axis; each molecule is chiral and of the same enantiomer. This is only possible as the molecule has a hinged cis arrangement about the Pd2+ coordination spheres. For this hinged dimeric structure, the angles between the two coordination planes in each molecule are 21.59 (4) and 22.10 (4)°. This hinged cis arrangement also allows the two molecules to form pairs linked by secondary interactions between the Pd and Te atoms of an adjoining molecule, leading to a tetrameric overall structure. C—H⋯Cl interactions consolidate the crystal packing.

The asymmetric unit of the title compound, [Pd 2 (C 9 H 12 NTe) 2 Cl 2 ]Á0.5CH 2 Cl 2 , contains two half-molecules, each lying on a twofold rotation axis; each molecule is chiral and of the same enantiomer. This is only possible as the molecule has a hinged cis arrangement about the Pd 2+ coordination spheres. For this hinged dimeric structure, the angles between the two coordination planes in each molecule are 21.59 (4) and 22.10 (4) . This hinged cis arrangement also allows the two molecules to form pairs linked by secondary interactions between the Pd and Te atoms of an adjoining molecule, leading to a tetrameric overall structure. C-HÁ Á ÁCl interactions consolidate the crystal packing.

Related literature
For related structures of bridged dimers of palladium mediated by Se, see: Brown & Corrigan (2004); Chakraborty et al.  Oilunkaniemi et al. (1999Oilunkaniemi et al. ( , 2001. For Se/Te-bridged Pd dimeric structures which exhibit either a hinged or cis arrangement of ligands about the bridging plane, see: Kaur et al. (2009);Oilunkaniemi et al. (2000); Chakravorty et al. (2012). For the synthesis of the title compound, see: Chakraborty et al. (2011).

Comment
The coordination chemistry of transition metal complexes with both organoselenato and organotellurato ligands is a rapidly growing area due to the ability of the resulting complexes to find applications in materials science (Morley et al., 2006;Ford et al., 2004), and investigations of oxidation additive to low valent transition metal centers. In addition to this, organotellurium compounds have been used in catalytic carbon-carbon formation. Bridged dimers of palladium mediated by Se (Nakata et al., 2009;Chakraborty et al., 2011;Oilunkaniemi et al., 1999;Oilunkaniemi et al., 2001;Brown & Corrigan, 2004;Dey et al., 2006,) or Te (Oilunkaniemi et al., 2000;Kaur et al., 2009;Dey et al., 2006;Chakravorty et al., 2012) have been previously reported. Such dimers involving two square planar coordination spheres can adopt either a coplanar or hinged arrangement. The arrangement of the donor ligands with respect to the bridging plane can be cis or trans. In the case of a hinged cis arrangement the possibility of chirality exists. While the majority of previously determined Se/Te bridged Pd dimeric structures are both coplanar and trans, there have been a small number which exhibit either a hinged or cis arrangement of ligands about the bridging plane (Kaur et al., 2009;Oilunkaniemi et al., 2000, Chakravorty et al., 2012.
Of these, only that by Chakravorty et al., 2012, which is the Se analog of the title complex, has resulted in a chiral complex.
The title compound, bis[µ-2-tellurolatobenzyldimethylaminochloropalladium(II)], hemi(dichloromethane) solvate, C 18 H 24 Cl 2 N 2 Pd 2 Te 2 0.5(CHCl 2 ), crystallizes in the chiral orthorhombic space group, P2 1 2 1 2. The asymmetric unit contains 2 half molecules, each lying on a 2-fold axis and each molecule is chiral and of the same enantiomer. This is only possible as the molecule has a hinged cis arrangement about the Pd coordination spheres. For this hinged dimeric structure the angles between the two coordination planes in each molecule are 21.59 (4) and 22.10 (4)° respectively. This hinged cis arrangement also allows the two molecules to form pairs linked by secondary interactions between the Pd and Te of an adjoining molecule leading to a tetrameric overall structure. This hinged cis arrangement also allows the two molecules to form pairs linked by secondary interactions between the Pd and Te of an adjoining molecule ( Fig. 2) leading to a tetrameric overall structure. Apart from this the Pd-Te, Pd-Cl and Pd-N bond lengths are in the normal ranges.
A previous polymorph of the title compound has been previously published (Kaur et al., 2009). While this crystallized in the non-centrosymmetric space group, P-42 1 c, it did not result in an enantiomerically pure compound as the symmetry of the space group generated the other enantiomer. Thus this is the first example of a chiral dimeric tellurium bridged palladium compound to be structurally characterized. In both instances, however, the asymmetric unit is chiral. We believe that it is the desire of the dimers to associate which then requries the molecule to adopt the cis hinged structure which has lead to this inherent chirality.

Experimental
The ligand and complex were prepared using previously reported methods (Chakraborty et al., 2011). The reaction time for the synthesis of the tellurolate complex was 2 h and it was crystallized from chloroform/hexane as reported earlier. However, supplementary materials sup-2 when the reaction was run for 30 min following the reported procedure and crystallized from dichloromethane/hexane (2:1) at ambient temperature the complex crystallized in a different space group which is chiral.

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H distances

Special details
Geometry. All e.s. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.