PREPARATIVE, STRUCTURAL, AND MAGNETIC STUDIES OF 2-HYDROXYPYRIDINATE COMPLEXES OF DIRUTHENIUM(II)

Three new compounds each containing the Ru2 4+core bridged by four 6-X-2-hydroxypyridinate anions (mhp-, X = CH3; chp-, X = Cl; bhp, X = Br) have been prepared in good yields (60-90%) from Ru2(O2CCH3)4, and each one has been characterized by X-ray crystallography and magnetic susceptibility measurements from ca. 5 to ca. 300 K. (1) Red-brown Ru2(mhp)4crystallizes in space group Pbca with a = 16.165 (3) Å, b = 18.638 (5) Å, c = 15.745 (3) Å, V = 4744 (3) Å3, and Z = 8; (2) brown [Ru2(chp)4]2-CH2Cl2crystallizes in space group PĪ with a = 14.489 (7) Å, b = 15.514 (10) Å, c = 11.703 (2) Å, α = 101.13 (3)°, β = 103.60 (3)°, γ = 100.03 (4)°, V = 2452 (4) Å3, and Z = 2; (3) dark-red Ru2(bhp)4crystallizes in space group P21c with a = 14.996 (5) Å, b = 13.464 (6) Å, c = 16.130 (5) Å, β = 109.22 (3)°, V = 3075 (4) Å3, and Z = 4. The structure of Ru2(mhp)4has Ru-Ru = 2.235 (1) Å and a torsion angle of 6.2°, with a symmetrical ligand arrangement placing like atoms (i.e., N's or O's) trans at each end. The Ru2(bhp)4molecule is very similar, with Ru-Ru = 2.259 (1) Å and a torsion angle of 1.17°. The chp compound has tetranuclear molecules consisting of two approximately (but not rigorously) identical halves bonded by axial O-Ru bonds. Within each half, three chp ligands are oriented in the same direction. Both Ru-Ru distances are 2.247 (1) Å, and the twist angles are 19.9° and 20.8°, respectively. All three compounds show essentially the same magnetic behavior, indicating that they have a spin-triplet/orbital-singlet ground state derived from a δ*2Π*2electron configuration. Zero-field splitting of the state to give a lower singlet (Ms= 0) causes the magnetic moment to aproach zero as T → 0 K. © 1990, American Chemical Society. All rights reserved.