Axial binding of 2-methylimidazole to the tetraarylcarboxylatodiruthenium (II,III) core: X-ray crystal structure of [Ru2(O2CC6H4-p-OMe)4 (2-mimH)2](ClO4). 1.75CH2Cl2.H2O

Diruthenium (II,III) complexes of the type [Ru2(O2CAr)4 (2-mimH)2](ClO4) (Ar=C6H4-p-X: X=OMe.1; X=Me.2: 2-mimH=2- methylimidazole) have been isolated from the reaction of Ru2Cl(O2CAr)4 with 2- mimH in CH2Cl2 followed by the addition of NaClO4. The crystal structure of 1. 1.75CH2Cl2.H2O has been determined. The crystal belongs to the monoclinic space group p2l/c with the following unit cell dimensions for the C40H40N4O16ClRu2.1.75CH2Cl2.H2O (M=1237.0): a=12.347 (3)A.b=17.615(5).c=26.148(2)A.β=92.88(1)o. v=5679(2)A3, Z=4, Dc=1.45 g cm-3. λ(Mo-Kα) = 0.7107 A. μ(Mo-Kα) = 8.1 cm-1, T=293 K, R=0.0815 (wR2=0.2118) for 5834 reflections with 1 > 2 σ(1). The complex has a tetracarboxylatodiruthenium (II,III) core and two axially bound 2-methylimidazole ligands. The Ru-Ru bond length is 2.290(1)A. The Ru-Ru bond order is 2.5 and the complex is three-electron paramagnetic. The complex shows an irreversible Ru2(II,III) →Ru2(II,II) reduction near -0.2 V vs SCE in CH2Cl2-0.1 M TBAP. The complexes exemplify the first adduct of the tetracarboxylatodiruthenium (II,III) core having N-donor ligands. (author)