New molecular assemblies of redox isomers, [CrIII(X4SQ)3-n(X4Cat)n]-n (X = Cl and Br; n=0, 1, and 2), with metallocenium cations, [MIIICp2]+ (M = Co and Fe):: X-ray crystal structures and physical properties

A series of redox isomers of [Cr-III(X(4)SQ)(X(4)Cat)(2)](2-) , [Cr-III(X(4)SQ)(2)(X(4)Cat)](-), and [Cr-III(X(4)SQ)(3)](0) (X = Cl and Sr, SQ = semiquinonate, and Cat = catecholate) have been synthesized and characterized as charge-transfer (CT) compounds with metallocenium cations: ((CoCP2)-C-III)(2)[Cr-III(Cl(4)SQ)(Cl(4)Cat)(2)] (1), ((CoCp2)-Cp-III)(2)[Cr-III(Br(4)SQ)(Br(4)Cat)(2)] (2), ((FeCp2)-Cp-III) [Cr-III(Cl(4)SQ)(2)(Cl(4)Cat)].C6H6 (4), ((FeCp2)-Cp-III) [Cr-III(Br(4)SQ)(2)(Br(4)Cat)]. CS2 (5), and ((FeCp2)-Cp-III)[Cr-III(Cl(4)SQ)(2)(Cl(4)Cat)][Cr-III(Cl(4)SQ)(3)] (6). First, the oxidation states of the chromium complexes are strongly dependent on the redox potentials of the metallocenes used. The (CoCp2)-Cp-II, exhibiting stronger reduction power than (FeCp2)-Cp-II, is useful for two-electron reduction of the [Cr-III(X(4)SQ)(3)](0), affording [Cr-III(X4SQ) (X(4)Cat)(2)](2-) (1 and 2), which are first isolated and crystallographically characterized in the solid state. In contrast the reaction with (FeCp2)-Cp-II affords only [Cr-III(X(4)SQ)(2)(X(4)Cat)](-) (4 and 5). Second, solvents influence crystal structures of these compounds. The solvent set of C6H6/CS2 gives 1:1:C6H6 compound 4 with unique charged anions, [Cr-III(C(4)SQ)(2)(Cl(4)Cat)](-), while the other set, n-C6H12/CS2, affords 1:2 compound 6 including the two redox isomers, [Cr-III(Cl(4)SQ)(2)(Cl(4)Cat)](-) and [Cr-III(Cl(4)SQ)(3)](0). The [Cr-III(X(4)SQ)(X(4)Cat)(2)](2-) anions in 1 and 2 show no significant interconnection between them (discrete type), while the [Cr-III(X(4)SQ)(2)(X(4)Cat)](-) anions in 4-6 show one- dimensional column-type structures with the aid of intermolecular stacking interactions of the ligand moieties. The anions in 4 show additional stacking interaction with the [(FeCp2)-Cp-III](+) to form one-dimensional ...[D][A][S][D][A]...(D = [(FeCp2)-Cp-III](+), A = [Cr-III(Cl(4)SQ)(2)(Cl(4)Cat)](-), and S = C6H6) type mixed-stack arrangements similar to that of previously reported ((CoCp2)-Cp-III)[Cr-III(Cl(4)SQ)(2)(Cl(4)Cat)].C6H6 (3) Compound 6 forms a two-dimensional sheet structure where the two redox isomers, [Cr-III(Cl(4)SQ)(2)(Cl(4)Cat)](-) and [Cr-III(Cl(4)SQ)(3)](0), are included. The sheet is regarded as a mixed-valence molecular assembly. Two types of the anions, [Cr-III(X(4)SQ)(X(4)Cat)(2)](2-) (1 and 2) and [Cr-III(X(4)SQ)(2)(X(4)Cat)](-) (4-6), exhibiting an intramolecular mixed-valence state, show intramolecular intervalence CT transition (IVCT) from the Cat to the SQ at near 5800 and 4300 cm(-1), respectively, both in the solution and in the solid states. The intermolecular mixed- valence state of 6 was characterized by absorption spectroscopy, electric conductivity, and SQUID magnetometry. Interestingly, this mixed-valence state of the chromium module is dependent on the redox active nature of the coordinated ligands.