RAMAN SPECTROSCOPY OF TRANSITION METAL COMPLEXES: MOLECULAR VIBRATIONAL FREQUENCIES, PHASE TRANSITIONS, ISOMERS, AND ELECTRONIC STRUCTURE

Abstract

Raman spectroscopy is less commonly used than infrared absorption spectroscopy for the vibrational characterization of inorganic compounds, but its applications have significantly increased over the past decade due to high-performance instrumentation. This Comment describes the use of Raman spectroscopy for the characterization of inorganic compounds. We illustrate the application of Raman techniques with the spectra of a series of classic transition metal complexes recorded at variable temperature and pressure. Illustrative examples include [Ni(NH₃)₆]X₂ compounds (X˭Cl⁻ or [NO₃]⁻), thermochromic square-planar or tetrahedral [CuCl₄]²⁻ complexes, the cis and trans [Cu(glycinato)₂] · H₂O complexes, square-planar [Pt(dithiocarbamate)₂] and [Pd(dithiocarbamate)₂] complexes, as well as metal-oxo and trans-dioxo complexes of metals with the d² electron configuration, such as molybdenum(IV), rhenium(V), and osmium(VI). The variation of the symmetric metal-ligand stretching frequencies with temperature or pressure is presented. Resonance Raman spectroscopy provides a detailed characterization of the electronic structure for the [Ru(BQDI)(NH₃)₂Cl₂] complex with the observation of overtones and combination bands at the excitation wavelength of 488 nm. Time-dependent theoretical calculations for the [Ru(BQDI)(NH₃)₂Cl₂] complex are used to rationalize the resonance Raman intensities and to determine excited-state properties. Molecular lanthanide clusters are used to illustrate the applications of Raman spectroscopy to polymetallic complexes.

Keywords:

• lanthanide clusters
• phase transition
• polymetallic complexes
• Raman spectroscopy
• resonance Raman spectroscopy
• thermochromism
• transition metal complexes
• variable pressure spectroscopy
• variable temperature spectroscopy

ACKNOWLEDGMENT

We thank all group members for contributing to the work presented in this Comment and Dr. Kelly Akers (Prospect Scientific) for encouraging us to compile many of the spectroscopic results presented here for an invited lecture at the 94th Canadian Chemistry Conference and Exhibition (Montreal, 2011). Financial support from the Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged.

Notes

Ligand abbreviation: DEA = diethylammonium and DMA = dimethylammonium.

*A = active and I = inactive.

DEA = diethylammonium; PDTC = pyrrolidine-N-dithiocarbamate; en = N,N,N′,N′-ethylenediamine; tmen = N,N,N′,N′-tetramethylethylenediamine and dppe = 1,2-diphenylphosphinoethane.