Bis(2,2′-bipyrimidine-κ2 N 1,N 1′)palladium(II) bis(tetrafluoroborate) acetonitrile monosolvate

The reaction of [Pd(MeCN)4](BF4)2 with 2,2′-bipyrimidine (bpm) in MeCN–CHCl3 afforded the title compound, [Pd(C8H6N4)2](BF4)2·C2H3N. The asymmetric unit contains two half complexes, with the PdII atoms both lying on a twofold axis. Each metal atom adopts a tetrahedrally distorted square-planar geometry. In the crystal, [Pd(bpm)2] dications are linked by C—H⋯N hydrogen bonds, forming chains parallel to the b axis. The chains are further linked by C—H⋯F and C—H⋯N interactions involving the tetrafluoroborate anions and acetonitrile molecules. In this way, each chain interacts with six surrounding chains to generate the observed three-dimensional structure.

The reaction of [Pd(MeCN) 4 ](BF 4 ) 2 with 2,2 0 -bipyrimidine (bpm) in MeCN-CHCl 3 afforded the title compound, [Pd(C 8 H 6 N 4 ) 2 ](BF 4 ) 2 ÁC 2 H 3 N. The asymmetric unit contains two half complexes, with the Pd II atoms both lying on a twofold axis. Each metal atom adopts a tetrahedrally distorted square-planar geometry. In the crystal, [Pd(bpm) 2 ] dications are linked by C-HÁ Á ÁN hydrogen bonds, forming chains parallel to the b axis. The chains are further linked by C-HÁ Á ÁF and C-HÁ Á ÁN interactions involving the tetrafluoroborate anions and acetonitrile molecules. In this way, each chain interacts with six surrounding chains to generate the observed three-dimensional structure.
Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) andMaterials Studio (Accelrys, 2002); software used to prepare material for publication: UdMX (Maris, 2004) and publCIF (Westrip, 2010 The title compound was obtained and characterized in the course of a study of complexes of Pd(II) with chelating heterocyclic ligands (Duong et al., 2011). In the crystal structure, each Pd II center is coordinated by two 2,2′-bipyrimidine (bpm) ligands to form two different distorted square-planar complexes ( Figure 1). Distortions in such complexes arise because a normal square-planar geometry, which is inherently preferred by d 8 metals, is opposed by steric interactions of the two ligands. As a result, related complexes of 2,2′-bipyridine (bpy) typically adopt one of two characteristic conformations: a so-called twisted geometry (involving a tetrahedral distortion of the metal center) and a bow-step deformation of the ligands themselves, as described by Constable (1989) and Milani et al. (1997). In the title compound, each of the two observed complexes incorporates approximately planar bpm ligands (maximum r. m. s. deviation 0.089 Å), and the geometry of coordination is twisted, with angles α of 21.52 (16)° and 25.80 (18)° between the N-Pd-N planes of the ligands. These values of α are similar to those found in analogous dicationic Pd II (bpy) 2 complexes with twisted geometries, as reported by Chieh (1972), Geremia et al. (1992), Hinamoto et al. (1972), Milani et al. (1997), Stoccoro et al. (2002), and Wehman et al. (1994). In addition, the average Pd-N distance is normal [2.030 (2) Å] (McKenzie, 1971).
The structure consists of chains of Pd II (bpm) 2 dications linked along the b-axis by C-H···N hydrogen bonds involving uncoordinated atoms of nitrogen (mean C-H···N distance: 3.348 (4) Å; Table 1), as shown in Figure 2. Within each chain, adjacent dications are arranged in an approximately orthogonal way (the dihedral angle between the N 4 coordination cores is 89.01 (6)°). The tetrafluoroborate counterions are located between the chains and bridge them via weak C-H···F contacts to create the three-dimensional packing. Included molecules of MeCN are located close to the Pd II centers, fill remaining volume, and engage in additional C-H···N interactions ( Figure 3).

Experimental
Solid [Pd(MeCN) 4 ](BF 4 ) 2 (71 mg, 0.16 mmol) was added at 25 °C to a stirred mixture of MeCN (2.5 ml) and CHCl 3 (2.5 ml) containing 2,2′-bipyrimidine (50 mg, 0.32 mmol). The resulting mixture quickly turned yellow, and a yellow solid began to precipitate. After the suspension had been stirred for 2 h, volatiles were removed by evaporation under reduced pressure, and the residual yellow solid was washed with MeCN. Crystals of the title complex were obtained in 70% yield by allowing vapors of MeCN to diffuse slowly into a solution of the yellow solid in DMSO.

Figure 1
Molecular structure of the title compound, with atomic labels and 50% probability displacement ellipsoids for nonhydrogen atoms. Hydrogen atoms are drawn as a sphere of arbitrary radius. Unlabelled atoms in the cationic complexes are related by the symmetry operations 1 -x, y, -z + 1/2 for Pd1 and -x, y, -z + 1/2 for Pd2.

Figure 2
View along the a-axis of a chain of cationic complexes, with C-H···N interactions shown as broken lines.   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 1.07 e Å −3 Δρ min = −0.75 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.000355 (19) Special details Experimental. X-ray crystallographic data for I were collected from a single-crystal sample, which was mounted on a loop fiber. Data were collected using a Bruker Platform diffractometer, equipped with a Bruker SMART 4 K Charged-Coupled Device (CCD) Area Detector using the program APEX2 and a Nonius FR591 rotating anode equipped with Montel 200 optics. The crystal-to-detector distance was 5.0 cm, and the data collection was carried out in 512 x 512 pixel mode. The initial unit-cell parameters were determined by a least-squares fit of the angular setting of strong reflections, collected by a 10.0 degree scan in 33 frames over four different parts of the reciprocal space (132 frames total). One complete sphere of data was collected to better than 0.80 Å resolution. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l. s. planes) were estimated using the full covariance matrix. The cell e.s.d.'s were taken into account individually in the estimation of e.s.d.'s in distances, angles, and torsion angles; correlations between e.s.d.'s in cell parameters were only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s was used for estimating e.s.d.'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 and 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 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.