μ-Pyrazine-2,5-dicarboxylato-bis[chlorido(η6-p-cymene)ruthenium(II)] tert-butanol disolvate

A new tert-butanol solvate of [{(iPrC6H4Me)RuCl}2{μ-2,5-pyz(COO)2}] (pyz = pyrazine) has been crystallized and structurally characterized. The solvate, [Ru2(C10H14)2(C6H2N2O4)Cl2]·2C4H10O, contains one half-molecule of the ruthenium(II) complex and one molecule of tert-butanol in the asymmetric unit. The complex molecule lies on an inversion centre with the two chlorides trans. In contrast, the previously reported structure was solvent-free. Similar metric parameters are found between the butanol solvate and the solvent-free form and an intermolecular O—H⋯O hydrogen bond exists between μ-pyrazine-2,5-dicarboxylato-bis[chlorido(η6-p-cymene)ruthenium(II)] and the tert-butanol molecule.


S1. Comment
There has been considerable interest in the chemistry of areneruthenium(II) complexes for a variety of purposes. These range from their interesting and varied coordination chemistry (Cadierno et al., 2002;Drommi et al., 1995) including DNA binding studies (Dorcier et al., 2005) to applications in areas including supramolecular chemistry, as highly selective receptors and catalysis (Dann et al., 2006;Ganter, 2003;Grote et al., 2004;Ion et al., 2006). These organometallic ruthenium(II) fragments have also been used in the synthesis of chiral half-sandwich compounds (Ganter, 2003;Pinto et al., 2004). Pyrazine polycarboxylic acids are excellent ligands for metal coordination (Konar et al., 2004;Ma et al., 2004). Complexes of ruthenium(II) with pyrazine carboxylic acids are known and their redox behaviour has been studied by voltammetric methods (Govindaswamy et al., 2007). We report here the molecular structure of a new tert-butanol solvate of the ruthenium(II) complex [{(η 6 -p-i PrC 6 H 4 Me)RuCl} 2 {µ-2,5-pyz(COO) 2 }]\. t BuOH 1. The solvent free structure, 2, which contains one molecule with a trans configuration of the two chloro ligands and a second molecule with twofold symmetry that has two chloro ligands disposed in a cis configuration, has recently been reported (Govindaswamy et al., 2007).
The molecular structure of 1 is shown in Figure 1 and shows a typical piano-stool geometry at each ruthenium(II) centre with each metal bonded to an η 6 -p-i PrC 6 H 4 Me arene [Ru-C centroid 1.6689 (16) (7) Å respectively] and with those of other related three-legged piano-stool ruthenium(II) complexes (Carter et al., 1993;Gemel et al., 2000;Lahuerta et al., 1988). The N(1)-Ru(1)-O(2) bite angle in 1 [77.29 (12)°] is broadly as expected for this type of five-membered chelating ligand. The η 6 -p-i PrC 6 H 4 Me arene ring is essentially planar with C-C bond lengths in the range 1.392 (6)-1.435 (6) Å. The Ru complex is hydrogen-bonded to a t BuOH molecule through a strong intermolecular O-H···O interaction.

S2. Experimental
Crystals of compound 1 were obtained unexpectedly from the experimental procedure outlined here. Boronic acid (0.004 g, 0.007 mmol) in warm t BuOH (10 ml) was added dropwise to a solution of [{(η 6 -p-i PrC 6 H 4 Me)RuCl} 2 {µ-2,5pyz(COO) 2 }] (0.023 g, 0.0325 mmol) in CH 2 Cl 2 (10 ml) affording an orange-red solution. The solution was stirred at room temperature for 3 h and the volume was concentrated to 2-3 ml. Suitable X-ray quality crystals of 1 were obtained supporting information by slow vapour diffusion of diethyl ether into the concentrated CH 2 Cl 2 / t BuOH solution.

S3. Refinement
H atoms were placed in geometric positions (C-H distance = 0.95 Å for aryl H; 0.98 Å for methine, 1.00 Å for methyl H; and 0.84 Å for O-H) using a riding model. U iso values were set to 1.2U eq (C) (1.5U eq (C/O)for methyl H and OH atoms respectively).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are 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 are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is 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 , 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq