SYNTHESIS AND MAGNETIC EXCHANGE PROPERTIES OF LINEAR TRINUCLEAR OXO-BRIDGED M(III)ORU(IV)OM(III) COMPLEXES (M=FE, CR, MN) FORMED BY 2-ELECTRON REDOX REACTIONS

The two-electron reductions of various porphyrin complexes Ru-VI(O)(2) (P) by Fe(II), Cr(II), and Mn(II) compounds of porphyrins and salicyla ldimines result in the formation of heterotrimetallic ore-bridged comp lexes (L)M(III)-ORuIV(P)OM(III)(L) (M = Fe(III), Cr(III), Mn(III); P i s the dianion of 5,10,15,20-tetraarylporphyrins, such as tetraphenylpo rphyrin (TPP), tetrakis(p-methoxyphenyl)porphyrin (TMP), or 2,3,7,8,12 ,13,17,18-octaethylporphyrin (OEP); L is TPP, TMP, or OEP or the diani ons of -methyl-4-azaheptane-1,7-diyl)bis(salicylaldimine) (salmah) or N,N'-ethane-1,2-diylbis(salicylaldimine) (salen). A detailed study of the temperature- and field-dependent magnetic properties of this rathe r novel series of (L)M(III)ORu(IV)(P)OM(III)(L) compounds has been mad e. The spin-states of the constituent metal centers are as follows: Ru -IV, S-Ru = 1 (d(4)); Fe-III S-Fe = 5/2 (d(5)); Cr-III, S-Cr = 3/2 (d( 3)); Mn-III, S-Mn = 4/2 (d(4)). The spin-state and coordination geomet ry of the (L)Fe-III groups were confirmed by Mossbauer spectral measur ements. Trinuclear combinations of the present kind give rise to unusu al coupled spin-state energy levels which, in the case of (L)(FeORuIV) -O-III(P)OFeIII(L) compounds, result in ''ferromagnetic-like'' plots o f magnetic moment versus temperature, particularly at low temperatures . The following best-fit values of parameters were deduced from the ma gnetic moment data, obtained in 1 T fields over the temperature range 4.2-300 K. (salmah)FeORu(TPP)OFe(salmah): g = 1.97, J(12) = -19.7 cm(- 1), J(13) = +6.5 cm(-1), alpha J(13)/J(12) = -0.33, ground-state S = 4 ; (TMP)FeORu(TPP)OFe(TMP): g = 1.95, J(12) = -23.4 cm(-1), J(13) = 5.4 cm(-1), alpha = -0.23, ground-state S = 4. (TPP)FeORu(TPP)OFe(TPP): g = 2.0, J(12) = -35.7 cm(-1), J(13) = 11.2 cm(-1), alpha = -0.31, grou nd-state S = 4, [(TPP)Fe]O-2 impurity = 13%, zero-field splitting of t he S = 4 state (D cm approximate to 5 cm(-1)). (TMP)MnORu(TPP)OMn(TMP) : g = 1.93, J(12) = -17.4 cm(-1), J(13) = 9.6 cm(-1), alpha = -0.55, g roundstate S = 3. (TPP)CrORu(TPP)OCr(TPP): g = 1.98, J(12) = -25.3 cm( -1), J(13) = -11.1 cm(-1), alpha = 0.44, groundstate S = 1. Possible r easons for the small sizes of the J(12) values, in comparison to those of related M(III)OM(III) and (RuORuIV)-O-IV compounds, are discussed.