COMPOUNDS CONTAINING LINKED, MULTIPLY-BONDED DIMETAL UNITS .1. TETRAKIS(MU-6-CHLORO-2-HYDROXYPYRIDINATO)DIRUTHENIUM(II,III) CATIONS LINKED AXIALLY BY PYRAZINE - COMPARISON WITH A SINGLE MOLECULE AXIALLY COORDINATED BY PYRIDINE

The tetranuclear compound [{Ru2(chp)4}2(pyz)](BF4)2 and the dinuclear compound [RU2(chp)4(py)](BF4) were prepared by substitution of an axial chloride ligand of Ru2(chp)4Cl with pyrazine and pyridine, respectively. Each compound has been characterized by X-ray crystallography and by magnetic susceptibility measurements from ca. 5 to ca. 300 K. [{Ru2(chp)4}2(pyz)](BF4)2 crystallizes with four solvent molecules in space group P2(1)/c (No. 14). With (CH2Cl2)2 and (pyz)2 the unit cell has a = 12.414 (3) angstrom, b = 16.083 (5) angstrom, c = 17.812 (4) angstrom, beta = 97.915 (2)-degrees, V = 3522 (2) angstrom, and Z = 2. With (CH2Cl2)4, the very similar unit cell has a = 12.081 (4) angstrom, b = 16.469 (4) angstrom, c = 17.209 (3) angstrom, beta = 98.28 (2)-degrees, V = 3390 (2) angstrom3, and Z = 2. [Ru2(chp)4(py)](BF4) crystallizes in a triclinic cell with a = 13.907 (3) angstrom, b = 16.322 (3) angstrom, c = 9.168 (1) angstrom, alpha = 106.09 (1)-degrees, beta = 99.89 (2)-degrees, gamma = 76.88 (2)-degrees, V = 1934 (1) angstrom3, and Z = 2. The pyrazine ligand bridges two diruthenium species in the [{Ru2(chp)4}2(pyz)]2+ cation, and the pyridine ligand coordinates to one axial position in the [Ru2(chp)4(py)]+ ion. The pyridine or pyrazine nitrogen atoms are in all cases attached to the ruthenium atoms that are coordinated by oxygen atoms. The two complexes show similar magnetic behavior; they exhibit Curie-Weiss behavior, and the decrease in moment at low temperatures results primarily from zero-field splitting effects. There is no significant magnetic exchange interaction between the two dinuclear species in the [{Ru(Chp)4}2(pyz)]2+ ion.