trans-Dichloridotetrapyrazineruthenium(II) dichloromethane disolvate

In the title compound, [RuCl2(C4H4N2)4]·2CH2Cl2, the RuII atom occupies a position of 222 symmetry and the C atom of the solvent molecule occupies a site with twofold symmetry. The RuII atom has a slightly distorted octahedral geometry. The pyrazine rings are propeller-like and rotated 45.1 (1)° from the RuN4 plane. In the crystal, the complex and solvent molecules are bridged by weak C—H⋯N hydrogen bonds along the c axis. Weak intermolecular C—H⋯Cl contacts link the complexes in the ab plane, forming a network.


Related literature
The synthesis of the title complex and its use as a building block in coordination networks are described by Carlucci et al. (2002) and Coe (2004). For related structures using pyridine and varying trans ligands, see: Coe et al. (1995); Desjardins et al. (1999).
We thank Austin College (Cullen Funds) for supporting innovative undergraduate education and the Welch Foundation (AD-0007) for a chemistry department grant furthering undergraduate research. We also recognize the work of Jessie H. Berger, Tehreem Bilal, Michela L. Brumfield, Raven M. Clark, Edward J. Selvik, Jacob B. Smith, and Hans H. Yoon, who, as fellow students with WK and AER in an advanced inorganic lab, synthesized and attempted to grow crystals of the title compound.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK5139).  (Coe et al., 1995 and references therein). The terminal chloride atoms on the Ru(pz) 4 Cl 2 complexes are 2.86 -2.94 Å from the four hydrogen atoms belonging to neighboring pyrazine groups (Fig. 2). This additional interaction enhances the stability of the propeller-like structure.
The Ru-Cl bond length is 2.3920 (5) Å and the Ru-N bond length is 2.0620 (14) Å. These distances are on the low side of the narrow range of bond lengths when this complex is used in supramolecular assemblies (Carlucci et al., 2002), indicating very little influence on bond distance upon further coordination of this metal-based building block. Ru-N distances in tetrakis(pyridine)RuL 2 , are 2.09 Å (L = 2-chlorophenylcyanamide) (Desjardins, et al., 1999), or 2.08 Å (L = one chloride and one benzonitrile) (Coe et al., 1995).
H-bonds and intermolecular contacts form a network in the crystal. Atom Cl1 has an intermolecular contact with a hydrogen atom on two pyrazine ligands on a neighboring complex ( Fig. 3 and Table 1). At the same time, the hydrogen atoms of the dichloromethane solvate have weak hydrogen bonds between two terminal N-atoms on the pyrazine ligands of two separate Ru(pz) 4 Cl 2 complexes ( Fig. 4 and Table 1). Additionally, the solvent chloride atom is 3.383 (3) Å from the C2 atom near the uncoordinated nitrogen on the pyrazine ligand.

Experimental
The ruthenium complex was synthesized by the student co-authors in the laboratory component of Austin College's advanced inorganic course according to procedures by Carlucci et al. (2002) and Coe (2004). Crystals of the title compound were grown from a slow diffusion of hexanes into a solution of the ruthenium complex dissolved in dichloromethane.

Refinement
The H atoms attached to C atoms of the pyrazine molecules were placed in idealized positions (C-H = 0.95 Å) and allowed to ride on their parent atoms. Their positions were constrained so that the U iso (H) was equal to 1.2U eq of their respective parent atoms. The solvent molecule, CH 2 Cl 2 , occupies a special position in the unit cell so the H atom was located using a difference map and was refined with a constrained U iso (H) equal to 1.2U eq of its parent atom.
The maximum and minimum residual electron density peaks of 1.01 and 0.37 eÅ -3 , respectively, were located 1.44 Å and 0.76 Å from the H4A and Ru1 atoms, respectively, with the large residue most likely due to imperfect absorption corrections frequently encountered in heavy-metal atom structures.

Figure 1
View of the title compound with 50% probability displacement ellipsoids.     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 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.