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

The asymmetric unit of the title compound, [Pd2(C9H12NSe)2Cl2]·0.5CH2Cl2, contains two half-molecules, each lying on a twofold 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 15.02 (5) and 14.91 (5)°. This hinged cis arragement also allows the two molecules to form pairs linked by secondary interactions between the Pd and Se atoms [3.4307 (9) and 3.4317 (9) Å] of adjoining molecules, leading to an overall tetrameric structure. During the refinement stages, it was noticed that there were dichloromethane solvent molecules present disordered about a twofold axis. After unsuccessful attempts were made to model this, they were removed using SQUEEZE.

The asymmetric unit of the title compound, [Pd 2 (C 9 H 12 NSe) 2 Cl 2 ]Á0.5CH 2 Cl 2 , contains two half-molecules, each lying on a twofold 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 15.02 (5) and 14.91 (5) . This hinged cis arragement also allows the two molecules to form pairs linked by secondary interactions between the Pd and Se atoms [3.4307 (9) and 3.4317 (9) Å ] of adjoining molecules, leading to an overall tetrameric structure. During the refinement stages, it was noticed that there were dichloromethane solvent molecules present disordered about a twofold axis. After unsuccessful attempts were made to model this, they were removed using SQUEEZE.
HBS acknowledges the DST, New Delhi, for financial support. TC acknowledges the CSIR, New Delhi, for a fellowship. RJB acknowledges the NSF-MRI program (grant CHE-0619278) for funds to purchase the diffractometer.

Comment
The coordination chemistry of transition metal complexes with both organoselenide and organotelluride 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) 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 arrangemnt the possibility of chirality exisits. 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 arrangment of ligands about the bridging plane (Kaur et al., 2009;Oilunkaniemi et al., 2000). However, in no previous case has this resulted in a chiral structure.
C 18 H 24 Cl 2 N 2 Pd 2 Se 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 (Fig. 1). For this hinged dimeric structure the angles between the two coordination planes in each molecule are 15.02 (5) and 14.91 (5)° respectively. This hinged cis arragement also allows the two molecules to form pairs linked by secondary interactions between the Pd and Se of an adjoining molecule (Fig. 2) leading to a tetrameric overall structure. Apart from this the Pd-Se, Pd-Cl and Pd-N bond lengths are in the normal ranges.

Experimental
The ligand and complex were prepared using previously reported methods (Chakraborty et al., 2011). Crystallization of the selenolate was done at ambient temperature from dichloromethane/hexane (2:1).

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H distances of 0.95 -0.97 Å [U iso (H) = 1.2U eq (CH, CH 2 ) [U iso (H) = 1.5U eq (CH 3 )]. During the refinement stages it was noticed that there were disordered solvent molecules present. The solvent molecule is CH 2 Cl 2 and it is disordered about a 2-fold axis. After unsuccessful attempts were made to model this, it was removed using the SQUEEZE routine from PLATON (Spek, 2009 Fig. 1. The structure of one of the two molecules of the asymmetric unit showing the hinged cis arrangement of the two Pd coordination planes. The two halves of the molecule are related by 1 -x, 1 -y, z.

Special details
Experimental. The structure of the Te analog was also determined, but at low temperature. This compound is isostructural and isomorphous with the Se compound but in this case the solvent was ordered. An Acta E submission for this structure has been made and it is currently under review (jj2116). 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.  (11) 117. Symmetry codes: (iv) x+1/2, −y+1/2, −z+2; (v) −x+1/2, y−1/2, −z+1.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
supplementary materials sup-9