Two spin isomers or spinomers of [{Mn(H2O)(phen)}(2)(mu-2-ClC6HCOO)(2)(mu-O)](ClO4)(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 center dot H2O, shows a spin ground state S = 0. Compound 1 exhibits ferromagnetic behavior, with J = 2.7 cm(-1), vertical bar D-Mn vertical bar = 2.06 cm(-1), vertical bar E-Mn vertical bar = 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 vertical bar D-4 vertical bar = 0.51 cm, 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.H2O 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-ClC6H4COO bridging ligand.