Electric‐field gradients and magnetic hyperfine parameters of square‐pyramidal [M(CN)₅]³⁻ (M = Co, Rh, and Ir) complexes

Abstract

rnDensity functional self-consistent spin-polarized calculations with the discrete variational method were performed to obtain the electronic structure of the paramagnetic complexes [CO(CN)S]~-, [R h(CN)5I3-, and [ II-(CN)~]~-of square-pyramidal geometry. All electrons were kept in the variational space. Electric-field gradients and magnetic hyperfine parameters at the metal site were computed with the molecular charge and spin densities obtained and compared with experimental values derived by electron paramagnetic resonance. It was found that the Fermi interaction is critically dependent on the angle between the axial and equatorial CN ligands. 0

Density Functional Calculations ofgValues and Molybdenum Hyperfine Coupling Constants for a Series of Molybdenum(V) Oxyhalide Anions

“…The methodology outlined below and in the Supporting Information provides a means of more completely defining electronic structure/EPR parameter correlations for these and other complexes. Similar computational studies have been carried out for several other transition metal complexes [36][37][38] but few involving fourth-or fifth-row elements and none for molybdenum-containing systems.…”

“…Similar conclusions have been reached for [M(CN) 5 ] 3-(M ) Co, Rh, Ir) species in terms of the effects of small changes in the C ax -M-C eq bond angles on the Fermi contact term. 37 The origin of the large differences in A F between the aqua species with the same halides but different orientations of the water remains unclear. It is, however, apparent that for similar geometries A F is dominated by polarization of the 4s shell and is correlated with the ground state metal character of the SOMO.…”

“…25,27,32,35 Only recently have attempts been made to calculate EPR parameters of transition metal complexes by direct evaluation of the relevant matrix elements over complete molecular wave functions. [36][37][38] This has been made possible by the development of reasonably reliable and efficient density functional methods for electronic structure calculations of transition metal complexes. 39 We report herein the results of such calculations on the highsymmetry, well-characterized molybdenum(V) oxyhalide series [MoOF 5 ] 2-, [MoOCl 4 ] -, [MoOCl 4 (H 2 O)] -, and [MoOBr 4 (H 2 O)] -.…”

“…There have been a number of computational attempts to determine the relationship between experimental EPR parameters and electronic structure for a variety of transition metal complexes. Previous studies on molybdenyl complexes have tended to use bonding coefficients from separate calculations in approximate LCAO expressions for g values. ,,, Only recently have attempts been made to calculate EPR parameters of transition metal complexes by direct evaluation of the relevant matrix elements over complete molecular wave functions. − This has been made possible by the development of reasonably reliable and efficient density functional methods for electronic structure calculations of transition metal complexes …”

Ab Initio Calculations of Electric Field Gradients in Cadmium Complexes

“…This is not, with present-day computer power, possible for reasonably large cadmium complexes. Only a few calculations have been done on heavier elements, for example, Mn, Fe, Co, Ni, Cu, Zn, Br, Rh, Cd, Sn, I, Kr, and Hg. − …”