SYNTHESIS, CRYSTAL-STRUCTURES, MOSSBAUER, SUSCEPTIBILITY, AND EPR STUDIES OF A SERIES OF SPIN EXCHANGE COUPLED COMPLEXES CONTAINING THE (MU-OXO)BIS(MU-ACETATO)RUTHENIUMMETAL CORE AND ITS HYDROXO-BRIDGED ANALOG (METAL = V, CR, MN, FE, CO)

Co hydrolysis of equimolar amounts of the mononuclear complexes L'RuCl3.H2O and LMCl3 (M = Co(III), V(III), Mn(III), Fe(III)) in methanol solutions which contain an excess of sodium acetate affords the asymmetric, heterodinuclear complexes [L'Ru(mu-O)(mu-CH3CO2)2ML]2+ (M = Co (1), V (2), Mn (4), Fe (5)) which have been isolated as crystalline bis(hexafluorophosphate) salts by addition of NaPF6. The same reaction using L'CrBr3 and LRuCl3 yields [LRu(mu-O)(mu-CH3CO2)2CrL'](PF6)2 (3) (L = 1,4,7-triazacyclononane, C6H15N3; L' = 1,4,7-trimethyl-1,4,7-triazacyclononane, C9H21N3). Complexes 1-5 are electrochemically reversibly oxidized by one electron. Chemically, the oxidized species [L'Ru(mu-OH)(mu-CH3CO2)2ML](PF6)3 (M = Mn (6), Fe (7)) have been generated by oxidation of 4 and 5 in H2O with Na2S2O8. The oxo bridges in 1, 3, and 5 are protonated reversibly in acidic solution and the mu-hydroxo complexes [L'Ru(mu-OH)(mu-CH3CO2)2ML](PF6)3 (M = Co (8), Fe (10)) and [LRu(mu-OH)(mu-CH3CO2)2CrL'](PF6)3 (9) have been isolated. The acidic dissociation constants have been determined spectrophotometrically in aqueous solution at 20-degrees-C (pK(a) values: (8) 8.0, (9) 7.5, (10) 4.0). The crystal structures of 4, 8, the bisperchlorate hexafluorophosphate salt of 6, and the trisperchlorate monohydrate salt of 7 have been determined by X-ray crystallography: 4, orthorhombic, Pbca, a = 18.985 (4) angstrom, b = 14.311 (3) angstrom, c = 24.511 (3) angstrom, z = 8; (6)(ClO4)2(PF6), monoclinic P2(1)/m, a = 11.483 (2) angstrom, b = 9.754 (2) angstrom, c = 16.307 (4) angstrom, beta = 110.30 (1)-degrees, Z = 2; (7)(ClO4)3.H2O, monoclinic P2(1)/m, a = 11.472 (3) angstrom, b = 9.752 (2) angstrom, c = 16.623 (2) angstrom, beta = 110.33 (1)-degrees, Z = 2; 8, monoclinic P2(1)/m, a = 11.986 (3) angstrom, b = 10.010 (2) angstrom, c = 16.383 (4) angstrom, beta = 111.20 (1)-degrees, Z = 2. Complexes 4, 6, and 7 contain a (mu-oxo)bis(mu-acetato)rutheniummetal core where the Ru ions are capped by the tridentate macrocycle L' and the first-row transition metals by L; 8 contains a mu-hydroxo bridge. From temperature-dependent (4-295 K) susceptibility measurements on powdered samples of 1-8 nearly temperature-independent magnetic moments have been calculated which indicate the following electronic ground states: (1), S = 1/2; (2), S = 1/2; (3), S = 1; (4), S = 3/2; (5), S = 2; (6) S = 1; (7), S = 3/2; (8), S = 1/2. Low-temperature EPR measurements confirm these electronic states. The mu-hydroxo species 9 and 10 have temperature-dependent magnetic moments; weak antiferromagnetic spin exchange coupling has been observed. The assignment of oxidation states in these heterodinuclear complexes proved to be not trivial. Mossbauer spectra of 5, 7, and 10 indicate the presence of an octahedral high-spin ferric ion in each case. 5 is therefore formulated as [RuIIIOFeIII]2+, 7 as [RuIVOFeIII]3+, and 10 as [RuIII(OH)FeIII]3+. From the combined physical data the oxidation states in the other complexes are assigned: (1) [RuIIIOCoIII]2+; (2) [RuIIOVIV]2+, (3) [RuIIIOCrIII]2+, (4) [RuIIIOMnIII]2+, (6) [RuIIIOMnIV]3+, (8) [RuIII(OH)CoIII]3+, and (9) [RuIII(OH)CrIII]3+. A model to interpret the very strong spin exchange coupling in complexes 2-7 is presented.