Synthesis and Structure of (Bis(1-propylbenzimidazol-2-yl)-trans-1,2-cyclohexane)copper(II) Dichloride and the Structure of a Novel, Unexpected By-Product

Abstract  

Two structures containing the novel ligand bis(1-propylbenzimidazol-2-yl)-trans-1,2-cyclohexane, L, are reported. The first structure, (bis(1-propylbenzimidazol-2-yl)-trans-1,2-cyclohexane)copper(II) dichloride, Cu(II)(L)Cl₂ 1, crystallized in the monoclinic space group P 2₁/n with a = 10.992(4) ?, b = 13.576(5) ?, c = 18.047(7) ?, β = 106.909(8) and V = 2576.7(16) ?³ and Z = 4. Complex 1 exhibits a D _2d-flattened tetrahedral Cu(II)N₂Cl₂ coordination geometry, for which the four-coordinate geometry index τ₄ of 0.59 lies almost midway between the ideal geometry values of zero (square-planar) and 1 (tetrahedral). The second and unexpected structure, (bis(1-hydro-3-propylbenzimidazol-1-ium)-trans-1,2-cyclohexane)(μ⁴-oxo-hexa-(μ²-chloro)-tetra(chloro-copper(II)) di(nitromethane) solvate, 2[H₂L]²⁺[Cu₄OCl₁₀]⁴⁻·(CH₃NO₂)₂, 2, consists of three dimensionally hydrogen bonded bis(benzimidazolium) dications and tetra-copper(II)-oxo-chloride tetra-anions, interspersed with nitromethane solvate molecules. A balanced equation for the formation of the byproduct suggests that it forms via an acid–base reaction in the presence of water in the reaction mixture. The complex crystallized in the triclinic space group P −1 with a = 13.696(3) ?, b = 13.819(3) ?, c = 16.797(4) ?, α = 89.480(4), β = 87.308(4)°, γ = 89.434(4) and V = 3175.3(12) ?³ and Z = 2. Ligand L contains two stereogenic centers, each of the same handedness, and, since the space groups determined for structures 1 and 2 are centrosymmetric, both structures are racemates.