Halogen-bonded network of trinuclear copper(II) 4-iodo-pyrazolate complexes formed by mutual breakdown of chloro-form and nanojars.

Abstract

Crystals of bis-(tetra-butyl-ammonium) di-μ3-chlorido--tris-(μ2-4-iodo-pyrazolato-κ2N:N')tris-[chlorido-cuprate(II)] 1,4-dioxane hemisolvate, (C16H36N)2[Cu3(C3H2IN2)3Cl5]·0.5C4H8O or (Bu4N)2[CuII3(μ3-Cl)2(μ-4-I-pz)3Cl3]·0.5C4H8O, were obtained by evaporating a solution of (Bu4N)2[{CuII(μ-OH)(μ-4-I-pz)} n CO3] (n = 27-31) nanojars in chloro-form/1,4-dioxane. The decomposition of chloro-form in the presence of oxygen and moisture provides HCl, which leads to the breakdown of nanojars to the title trinuclear copper(II) pyrazolate complex, and possibly CuII ions and free 4-iodo-pyrazole. CuII ions, in turn, act as catalyst for the accelerated decomposition of chloro-form, ultimately leading to the complete breakdown of nanojars. The crystal structure presented here provides the first structural description of a trinuclear copper(II) pyrazolate complex with iodine-substituted pyrazoles. In contrast to related trinuclear complexes based on differently substituted 4-R-pyrazoles (R = H, Cl, Br, Me), the [Cu3(μ-4-I-pz)3Cl3] core in the title complex is nearly planar. This difference is likely a result of the presence of the iodine substituent, which provides a unique, novel feature in copper pyrazolate chemistry. Thus, the iodine atoms form halogen bonds with the terminal chlorido ligands of the surrounding complexes [mean length of I⋯Cl contacts = 3.48 (1) Å], leading to an extended two-dimensional, halogen-bonded network along (-110). The cavities within this framework are filled by centrosymmetric 1,4-dioxane solvent mol-ecules, which create further bridges via C-H⋯Cl hydrogen bonds with terminal chlorido ligands of the trinuclear complex not involved in halogen bonding.