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 salicylaldimines result in the formation of heterotrimetallic oxo-bridged complexes (L)M(III)ORu(IV)(P)OM(III)(L) (M = Fe(III), Cr(III), Mn(III); P is the dianion of 5,10,15,20-tetraarylporphyrins, such as tetraphenylporphyrin (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 dianions of N,N'-(4-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 rather novel series of (L)M(III)ORu(IV)(P)OM(III)(L) compounds has been made. The spin-states of the constituent metal centers are as follows: Ru(IV), SRu = 1 (d(4)); Fe(III), SFe = 5/2 (d(5)); Cr(III), SCr = 3/2 (d(3)); Mn(III), SMn= 4/2 (d(4)). The spin-state and coordination geometry of the (L)Fe(III) groups were confirmed by Moessbauer spectral measurements. Trinuclear combinations of the present kind give rise to unusual coupled spin-stateenergy levels which, in the case of (L)Fe(III)ORu(IV)(P)OFe(III)(L) compounds, result in "ferromagnetic-like" plots of magnetic moment versus temperature, particularly at low temperatures. The following best-fit values of parameters were deduced from the magnetic moment data, obtained in 1 T fields over the temperature range 4.2-300 K. (salmah)FeORu(TPP)OFe(salmah): g = 1.97, J12 = -19.7 cm**-1, J13 = +6.5 cm**-1, α = J13/J12 = -0.33, ground-state S = 4; (TMP)FeORu(TPP)OFe(TMP): g = 1.95, J12= -23.4 cm**-1, J13 = 5.4 cm**- 1, α = -0.23, ground-state S = 4.(TPP)FeORu(TPP)OFe(TPP): g = 2.0, J12 = -35.7 cm**-1, J13 = 11.2 cm**-1, α = -0.31, ground-state S = 4, [(TPP)Fe]2O impurity = 13%, zero-field splitting of the S = 4 state (D ~ 5 cm**-1). (TMP)MnORu(TPP)OMn(TMP): g = 1.93, J12 = -17.4 cm**-1, J13 = 9.6 cm**-1, α = -0.55, ground-state S = 3. (TPP)CrORu(TPP)OCr(TPP): g = 1.98, J12 = -25.3 cm**-1, J13 = -11.1 cm**-1, α = 0.44, ground-state S = 1. Possiblereasons for the small sizes of the J12 values, in comparison to those of related M(III)OM(III) and Ru(IV)ORu(IV) compounds, are discussed.