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Vibrational spectroscopic and force field studies of copper(II) chloride and bromide compounds, and crystal structure of KCuBr 3
Author(s) -
Stepakova Liubov V.,
Skripkin Mikhail Yu.,
Chernykh Lyudmila V.,
Starova Galina L.,
Hajba László,
Mink János,
Sandström Magnus
Publication year - 2008
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.1778
Subject(s) - chemistry , copper , halide , crystallography , bromide , raman spectroscopy , octahedron , aqueous solution , ligand field theory , crystal structure , tetragonal crystal system , inorganic chemistry , ion , physics , organic chemistry , optics
Vibrational spectroscopic and force field studies have been performed of 15 related copper(II) chloride and copper(II) bromide compounds, including hydrated salts crystallizing in ternary aqueous systems with alkali and ammonium halides. For halocuprates with distorted octahedral coordination characteristic stretching Raman wavenumbers, corresponding to symmetric stretching Cu II X modes in the equatorial plane, were found in the ranges 247–288 cm −1 for X = Cl, and 173–189 cm −1 for X = Br, while the low‐wavenumber stretching modes for the weaker axial CuX interactions varied considerably. The tetrahedral coordination for Cs 2 CuCl 4 and Cs 2 CuBr 4 leads to somewhat lower CuX symmetric stretching wavenumbers, 295 and 173 cm −1 , respectively. The assignments of the copper–ligand stretching vibrations were performed with the aid of normal coordinate calculations. Correlations between force constants, averaged CuX stretching wavenumbers and bond distances have been evaluated considering the following aspects: (1) Jahn–Teller tetragonal distortion (axial elongation) of the octahedral copper(II) coordination environment, (2) differences between terminal and bridging halide ligands (3) effects of coordinated water and the influence of outer‐sphere cations. Force constant ratios for terminal and bridging metal–halide bonds reveal characteristic differences between planar and tetrahedrally coordinated M 2 X 6 species. In the hydrated copper(II) halide complexes, the halide ligands are more strongly bound than coordinated water molecules. The crystal structure of KCuBr 3 (K 2 Cu 2 Br 6 ), which was determined to provide structural information for the force field analyses, contains stacks of planar dimeric [Cu 2 Br 6 ] 2− complexes held together by weak axial CuBr interactions. Copyright © 2007 John Wiley & Sons, Ltd.