Discrete Dinuclear Cyano-Bridged Complexes

The cyano-bridged complexes [L¹⁴Co^IIINCFe^II(CN)₅]^-, [L¹⁴Co^IIINCFe^III(CN)₅], [L¹⁵Co^IIINCFe^II(CN)₅]^-, and [L¹⁵Co^IIINCFe^III(CN)₅] (L¹⁴ = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine, L¹⁵ = 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine) are prepared and characterized both structurally and spectroscopically. In each complex, the pendant amine is trans to the bridging CN ligand, as determined by spectroscopy and X-ray crystallography:  Na{trans-[L¹⁴Co^IIINCFe^II(CN)₅]}·8H₂O, monoclinic space group P2₁/c, a = 15.58(1) Å, b = 19.797(4) Å, c = 19.830(6) Å, β = 91.62(4)°, Z = 8; trans-[L¹⁴Co^IIINCFe^III(CN)₅]·4H₂O, monoclinic space group P2₁/m, a = 9.9690(9) Å, b = 13.316(1) Å, c = 10.1180(8) Å, β = 90.720(6)°, Z = 2; [L¹⁵Co^IIINCFe^III(CN)₅]·4H₂O, triclinic space group P1, a = 9.454(1) Å, b = 9.778(1) Å, c = 9.865(2) Å, α = 60.37(1)°, β = 62.60(1)°, γ = 65.82(1)°, Z = 1. A precursor to the 14-membered macrocyclic complexes is prepared for the first time, and its crystal structure is also reported: trans-I [CoL¹⁴Cl](ClO₄)₂, orthorhombic space group Pbca, a = 11.833(3) Å, b =13.363(2) Å, c = 26.015(2) Å, Z = 8. These compounds form part of a novel series of discrete CN-bridged dinuclear compounds. The mixed-valent Co^III−Fe^II compounds exhibit metal-to-metal charge-transfer (MMCT) transitions in the region 510−530 nm.