MOSSBAUER INVESTIGATION OF HYPERFINE INTERACTIONS IN CRYSTALLINE IRON COMPOUNDS AND IRON COMPLEXES

Abstract

The MBssbauer effect i.e. the recoilless resonant absorption of gamma-rays, has been applied to study the hyperfine interactions in single crystals of FeSO4.4H20, Fe(KSO4)2.6H20 and FeTiO, and organometallic complexes of iron using the 14.4 k.e.v. gamma-rays from Co57(Pd). A mechanical velocity drive arrangement employing a constant velocity cam has been constructed as a Doppler tunning device. Continuous variable (constant) velocities in the range of 8 mm/sec were obtained by use of a friction cam, governer and sets of pullies. Argon-Methane filled proportional counter coupled with a preamplifier, a linear amplifier and a single channel analyzer has been used to detect the Mlissbauer transition giving a resolution of 4%, . Tho MOssbauer absorption of Fe57 in FeS0 WI2 0 ' ' Fe(KSO4)2.67120 and FoTiO3 monocrystals has been studied as a function of orientation of the crystal axes with respect to the direction of unpolarized gamma - ray beam. The analysis of the peak intensity area ratios of the quadrupole split doublet spectra yields the principal axis values, the asymmetry parameter and the direction consines of the Electric field gradient (EFG) with respect to the crystal axes. Furthermore it exhibits the anisotropy of the recoilless absorption probability. ii Following specifications of the EFG tensor are concluded : (A) FeS04.4H20 i. The Fe-Oq2 is the direction of g axis of the EFG where as Fe-W43 and Fe-OY4 are the X and Y faxes, respectively. ii. quadrupole coupling constant has the positive sign. iii. The asymmetry parameter 1,10 (3) Pe(KSO )6H 0 2. '2 i. The 0W9-OW9 is the direction of 2 axis of the EFG where as OW7 -Ow7 and OW8 -OW8 correspond to / and X axes respectively. ' • The .e-2 ci 4 is positive. iii. The asymmetry parameter1:z. 0.7 The ground state is orbital singlet 1XY> (C) PeTiO3 i. V zz lies along <111> direction, the spin4axis, the EFG is axially symmetric. ii. Asymmetry parameter17-.- iii. Orbital ground state is IXY > iii The MOssbauer absorption measurements have been carried out for a series of low - spin Fe(II) and Fe(III) complexes with 1.10 Phenanthroline, 2.2' bipyridyl and mixed ligands, both at 3000 and 4.2°K. The results on centre shift and quadrupole splitting have been interpreted in conjunction with magnetic data, in terms of the bonding of 1.10 Phenanthroline and 2.21 bipyridyl ligands. It is inferred that there is rt backbonding (it- 44) throughout the series. Furthermore 2.21 Bipy. is a better rt acceptor and or that it is a poorer donor, vis a vis 1.10 Phen, although the total d.-4.1 capacity is identical for both.