Dinuclear copper (I) complexes derived from three benzimidazole-containing binucleating ligands are described within the context of synthetic models for deoxyhemocyanin and carbon monoxyhemocyanin. The neutral, potentially septadentate ligand HL-Et, which contains bis((1-ethyl-2-benzimidazolyl) methyl) moieties at both ends of a 2-hydroxypropylenediamine spacer, forms the CO complex [Cu 2 (HL-Et)(CO) 2 ][CF 3 SO 3 ] 2 (1) and the acetonitrile complex [Cu 2 (HL-Et)(MeCN) 2 ] [CF 3 SO 3 ] 2 (2). The related tetrakis (1-methylbenzimidazole)-containing ligand HCAB-Me, having a 2,6-disubstituted cresol spacer, forms the acetonitrile complex [Cu 2 (HCAB-Me)(MeCN) 2 ][CF 3 SO 3 ] 2 (3). The unalkylated benzimidazole analogue of HL-Et, HL-H, forms the acetonitrile complex [Cu 2 (HL-H)(MeCN) 2 ][ClO 4 ] 2 1 / 3 Et 2 O (4) and the CO complex [Cu 2 (HL-H)(CO) 2 ][BF 4 ] 2 (5). Complexes 1-4 have been characterized by X-ray crystallography. Crystal data: 1, C 47 H 50 N 10 O 9 Cu 2 F 6 S 2 , triclinic, P1, a = 16.616 (8) A, b = 11.884 (5) A, c = 15.131 (4) A, α = 106.69 (3)˚, β = 83.25 (3)˚, γ = 110.75 (4)˚, Z = 2; 2, C 49 H 56 N 12 O 7 Cu 2 F 6 S 2 , orthorhombic, Pbcn, a = 15.473 (5) A, b = 16.369 (9) A, c = 44.178 (17) A, Z = 8; 3, C 51 H 51 O 7 Cu 2 F 6 S 2 , triclinic, P1, a = 14.20 (1) A, b = 13.39 (1) A, c = 15.31 (1) A, α = 104.52 (6)˚, β = 76.08 (7)˚, γ = 90.71 (8)˚, Z = 2; 4, C 39 H 40 N 12 O 9 Cu 2 Cl 2 1 / 3 C 4 H 10 O, monoclinic C2/c, a = 28.710 (9) A, b = 7.600 (2) A, c = 21.857 (9) A, β = 114.23 (3)˚