Halogen-bonded network of trinuclear copper(II) 4-iodopyrazolate complexes formed by mutual breakdown of chloroform and nanojars

Abstract

Crystals of bis(tetrabutylammonium) di-μ3-chlorido-tris(μ2-4-iodopyrazolato-κ2N:N′)tris[chloridocuprate(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)}nCO3] (n= 27–31) nanojars in chloroform/1,4-dioxane. The decomposition of chloroform 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 CuIIions and free 4-iodopyrazole. CuIIions, in turn, act as catalyst for the accelerated decomposition of chloroform, 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 molecules, which create further bridgesviaC—H...Cl hydrogen bonds with terminal chlorido ligands of the trinuclear complex not involved in halogen bonding.