Chiral, three-dimensional supramolecular compounds: Homo- and bimetallic oxalate- and 1,2-dithiooxalate-bridged networks. A structural and photophysical study

In analogy to the [M(II)(bpy)(3)](2+) cations, where M(II) is a divalent transition-metal and bpy is 2,2'-bipyridine, the tris-chelated [M(III)(bpy)3(+) cations, where M(III) is Cr-III or Co-III, induce the crystallization of chiral, anionic three-dimensional (3D) coordination polymers of oxalate-bridged Cu-ox) metal complexes with stoichiometries [M(2)(II)(ox)(3)](2n-)(n) or [M(I)M(III)(ox)3](2n-)(n). The tripositive charge is partially compensated by inclusion of additional complex anions like ClO4-, BF4-, or PF6- which are encapsulated in cubic shaped cavities formed by the bipyridine ligands of the cations. Thus, an elaborate structure of cationic and anionic species within a polymeric anionic network is realized. The compounds isolated and structurally characterized include [Cr-III(bpy)(3)][ClO4] [NaCrIII(ox)(3)] (1), [Cr-III(bpy)(3)][ClO4][Mn-2(II)(ox)(3)] (2), [Cr-III(bpy)(3)][BF4] [Mn-2(II)(ox)(3)] (3), [Co-III(bpy)(3)][PF6][NaCrIII(ox)(3)] (4). Crystal data: 1, cubic, P2(1)3, a = 15.523(4) Angstrom, Z = 4; 2, cubic, P4(1)32, a = 15.564(3) Angstrom, Z = 4; 3, cubic, P4(1)32, 15.553(3) Angstrom, Z = 4; 4, cubic, P2(1)3, a = 15.515(3) Angstrom, Z = 4. Furthermore, it seemed likely that 1,2-dithiooxalate (dto) could act as an alternative to the oxalate bridging ligand, and as a result the compound [Ni-II(phen)(3)][NaCoIII(dto)(3)]. C3H6O (5) has successfully been isolated and structurally characterized. Crystal data: 5, orthorhombic, P2(1)2(1)2(1), a = 16.238(4) Angstrom, b = 16.225(4) Angstrom, c = 18.371(5) Angstrom, Z = 4. In addition, the photophysical properties of compound 1 have been investigated in detail. In single crystal absorption spectra of [Cr-III(bpy)(3)][ClO4][NaCrIII(ox)(3)] (1), the spin-flip transitions of both the [Cr(bpy)(3)](3+) and the [Cr(ox)(3)](3-) chromophores are observed and can be clearly distinguished. Irradiating into the spin-allowed (4)A(2) --> T-4(2) absorption band of [Cr(ox)(3)](3-) results in intense luminescence from the (2)E State of [Cr(bpy)(3)](3+) as a result of rapid energy transfer processes.