Two spin isomers or spinomers of [{Mn(H(2)O)(phen)}(2)(mu-2-ClC(6)H(4)COO)(2)(mu-O)](ClO(4))(2) have been synthesized, characterized, and theoretically analyzed. The thermodynamically most stable, compound 1, shows a spin ground state S = 4, while the kinetically most favorable, compound 2.H(2)O, shows a spin ground state S = 0. Compound 1 exhibits ferromagnetic behavior, with J = 2.7 cm(-1), |D(Mn)| = 2.06 cm(-1), |E(Mn)| = 0.69 cm(-1), and zJ' = -0.11 cm(-1). Because of the anisotropy of the Mn(III) ions, the ground state S = 4 shows zero-field splitting (ZFS) with |D(4)| = 0.51 cm(-1), appreciably smaller than the D value for the single ion (D(Mn)), due to the relative orientations of the Jahn-Teller axes of both Mn(III) ions, which are quite perpendicular (102 degrees ). Compound 2.H(2)O shows antiferromagnetic coupling, with J = -12.6 cm(-1) (H = -JS(1).S(2) for both compounds). The formation of two spinomers has been explained by density functional theory (DFT) studies, which show that the stability of these compounds and their magnetic interaction are very sensitive to the rotation of the phenyl ring with respect to the carboxylate group of the 2-ClC(6)H(4)COO bridging ligand.