Titanium and manganese complexes supported by a xanthene-bridged bis(tripodal N2O2) ligand: isomerization, intramolecular hydrogen bonding and metal-binding ability.

A new bis(N2O2) ligand, L(4-), in which two tripodal diamine-bis(phenolate) moieties are bridged by a xanthene backbone, was prepared. The reaction of H4L with 2 equiv. of [Ti(O(i)Pr)4] produced C2 and Cs symmetrical isomers of the dititanium(IV,IV) complex [Ti2(L)(O(i)Pr)4]. The isolated C2 isomer was slowly converted to the Cs isomer via Ti-N bond cleavage to form a 3 : 2 mixture in equilibrium. A similar dimanganese(III,III) complex [Mn2(L)(OMe)2(MeOH)2] was synthesized from a 1 : 2 mixture of H4L and manganese(II) perchlorate in the presence of triethylamine. An X-ray analysis of [Mn2(L)(OMe)2(MeOH)2] revealed that two Mn-N2O4 octahedrons are connected by intramolecular hydrogen bonds as well as a xanthene bridge to form a C2 symmetrical structure. The dimanganese(III,III) complex further reacted with manganese(II) acetate to form the mixed-valence trimanganese(III,II,III) complex [Mn3(L)(μ-OMe)2(μ-OAc)2]. Electrochemical data of the trimanganese(III,II,III) complex indicated that the xanthene-bridged dimanganese(III,III) unit effectively binds a Mn(II) ion in solution.