Structural and spectroscopic studies of some copper(i) halide tert-butyl isocyanide adducts

Abstract

Single-crystal structural characterizations confirm the existence of the unusual 1 : 4 copper(I) halide : unidentate ligand adducts [Cu(CNt-Bu)₄]X for X = Cl, Br (two forms), I (the chloride and one form of the bromide being solvated) with crystal packing dominated by stacks of interleaving cations. Cu–C range between 1.941(2) and 1.972(4) Å. The structure of the 1 : 2 chloride complex is also recorded, being [ClCu(CNt-Bu)₂], with the copper(I) atom environment trigonal planar, while CuCN : (CNt-Bu) (1 : 1) is a single-stranded polymer which spirals about a crystallographic 3-axis (CN scrambled), the ligands being pendant from the …CuCNCuCN… string. The ⁶⁵Cu static broadline NMR spectra of [Cu(CNt-Bu)₄]I and [Cu(CNt-Bu)₄]Br·H₂O in the solid state exhibit dominant, narrow −1/2 ↔ +1/2 central transition resonances and associated ±1/2 ↔ ±3/2 satellite transition resonances which are characteristic of first-order quadrupole broadened systems, while associated high-resolution ⁶⁵Cu MAS NMR data provide accurate measurement of the ⁶⁵Cu isotropic chemical shifts. Both approaches provide complete data on the quadrupole and chemical shift interactions which contribute to these spectra. Far-IR spectra of products of reactions involving a range of CuX : t-BuNC ratios reveal the existence of 1 : 1.5 adducts for X = Br, I. Metal–carbon and metal-halogen bands are assigned in the far-IR spectra, which indicate a binuclear double halogen-bridged structure for the 1 : 1.5 complexes.