μ-(2,2′-Bipyrimidine)-bis[dichloridopalladium(II)] dimethylformamide monosolvate

In the title compound, [Pd2Cl4(C8H6N4)]·C3H7NO, the two Pd2+ cations have a distorted square-planar coordination sphere and are bridged by a bis-bidentate 2,2′-bipyrimidine ligand. Two terminal chloride anions are also bonded to each of the Pd2+ cations. The dinuclear complex and the dimethylformamide solvate molecule lie on the intersection of a twofold rotation axis and a mirror plane, with disorder present in the solvate molecule. There is a slight distortion from the square-planar metal geometry, as indicated by the bite angles of 81.77 (13)° and 91.63 (5)°. The C and O atoms of the solvent molecule are disordered over two sets of sites of equal occupancy.

In the title compound, [Pd 2 Cl 4 (C 8 H 6 N 4 )]ÁC 3 H 7 NO, the two Pd 2+ cations have a distorted square-planar coordination sphere and are bridged by a bis-bidentate 2,2 0 -bipyrimidine ligand. Two terminal chloride anions are also bonded to each of the Pd 2+ cations. The dinuclear complex and the dimethylformamide solvate molecule lie on the intersection of a twofold rotation axis and a mirror plane, with disorder present in the solvate molecule. There is a slight distortion from the square-planar metal geometry, as indicated by the bite angles of 81.77 (13) and 91.63 (5) . The C and O atoms of the solvent molecule are disordered over two sets of sites of equal occupancy.

Experimental
Financial assistance from the University of the Free State, NRF(THRIP) and Sasol is gratefully acknowledged, while Theunis Muller is thanked for the data collection. Although a wide variety of metals are used in catalysis today, the platinum group metals show the most promising catalytic properties (Van Leeuwen (2004). Unfortunately, knowledge surrounding the actual catalysis process on a molecular level is minimal. Various platinum group metals which find application in heterogeneous catalysis are dispersed onto supports with little control. Consequently, this study was undertaken to explore the possibility of using bridging ligands ensure that metals are well dispersed in a controllable fashion. The insight gained by exploring bridged platinum group metals could contribute to ongoing homogeneous catalyst models of the metal complex. (Meij et al. (2005), Otto et al. (2003) Steyn et al. (1997)).
The compound crystallizes in a monoclinic C2/m space group with Z = 2. Both palladium atoms are situated on a twofold rotation axis and three carbon atoms, namely C11, C13 and C22 lie on a mirror plane. O22 of the DMF solvate molecule is situated on a twofold rotation axis and N22 on both a mirror plane and a rotation axis, which essentially gives N22 an occupation of 25%. As a result of the symmetry in the molecule there are only twelve atoms, including the hydrogen atoms, in the asymmetric unit. The geometry of the palladium centers is slightly distorted from the square planar geometry. This is illustrated by the N1-Pd01-N1c and Cl11-Pd01-Cl11c angles which are 81.77 (13)° and 91.63 (5)° respectively. The bond lengths and angles for the title compound are comparable to those in literature (Inagaki et al. (2007), Maekawa et al. (1994)). The palladium-nitrogen bonds of 2.05 Å are marginally longer than the monocoordinated palladium complex (Hudgens et al. (1997)) which has a bond length of 1.99 Å. The Pd-Pd intra-molecular bond distances of 5.47 Å, is slightly shorter than the 5.62 Å for the platinum counterpart (Kawakami et al. (2006)).

Experimental
The title compound was prepared by the modification of the published procedure by Boyle et al. (2004). PdCl 2 (0.

Refinement
The aromatic, methine, and methyl H atoms were placed in geometrically idealized positions (C-H = 0.93-0.98) and constrained to ride on their parent atoms with U ιso (H) = 1.2U eq (C) for the aromatic protons. The highest residual electron density was located 0.55 Å from C13 and was essentially meaningless.

Figure 1
Diamond representation of the title compound, showing the numbering scheme and displacement ellipsoids (50% probability).

Refinement
Refinement on F 2 Least-squares matrix: full R[F 2 > 2σ(F 2 )] = 0.028 wR(F 2 ) = 0.059 S = 1.11 1108 reflections 68 parameters 0 restraints Primary atom site location: structure-invariant direct methods Secondary atom site location: difference Fourier map Hydrogen site location: inferred from neighbouring sites H-atom parameters constrained w = 1/[σ 2 (F o 2 ) + (0.0172P) 2 + 2.5414P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.75 e Å −3 Δρ min = −0.79 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s involving l.s. planes. 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 > 2σ(F 2 ) is used only for calculating R-factors(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.