The magnetic behaviour of cubic-field 4 T 1g terms in lower symmetry

Abstract

The behaviour of the magnetic properties of the *TI, term under simultaneous perturbation by spin-orbit coupling and an axial ligand-field is presented. The theory is applied to the variation with temperature of fifteen octahedral cobalt(1i) complexes in the range 80--300°K. The values of k, the orbital reduction factor, deduced for the present complexes are determined mainly by the absolute magnitudes of the mean susceptibilities, while those of the axialfield splitting, A, and spin-orbit coupling coefficient are determined more by the temperature variation of the moments. It is found that for these compounds, where the variation of the magnetic moment with temperature is not large, there is usually uncertainty concerning the magnitude, and even the sign, of A.IN previous papers it has been shown that the theory of the magnetic properties of the cubic-field 2T2,1 5T2,2 and 3T1,3 terms under perturbation by spin-orbit coupling and a tetragonal or trigonal ligand-field component can be useful in accounting for the magnetic behaviour of complexes in which they are the ground terms. In this paper we now report the results of a similar treatment on the remaining orbital triplet groundterm which can arise for transition-metal complexes, namely 4T1.t The data has been applied to a number of six-co-ordinate cobalt (11) complexes and estimates of the values of the axial ligand-field component, A, the spinorbit coupling constant, A, and the amounts of t,, orbital reduction have been made.The treatment and parameters are identical to those for the 3T1 terms3 The matrices of 4T1, under the combined action of spin-orbit coupling and an axial ligand-field component, are given in the Appendix. As in previous papers 1-3 A is defined as the splitting of the orbital degeneracy of the 4T1 term by the asymmetric ligand-field component, in the absence of any spint The term is 4T,, in the octahedral and *TI in the tetrahedral case, but in order to simplify the text, we will use 4T, as the name of the term.1 See ref. 4 and 5 for further discussion of k and A.

Syntheses, Crystal Structures and Magnetic Properties of Cr(NCNH2)4Cl2 and Mn(NCNH2)4Cl2

“…The best fit results of the magnetic parameters are given in Table 2, in good agreement with the EHCF values and the molecular field parameter λ mf indicating antiferromagnetic coupling. For the Co 2+ complex the orbital reduction factor κ is equal to 0.75, nicely in line with data of Co complexes in the literature [28]. The ratios B 2 2 /B 2 0 = 0.53 and B 4 4 /B 4 0 = 0.12 were fixed at the values of the EHCF calculations.…”

Magnetic and Spectral Studies on Cobalt(II) and Copper(II) Salts of Methylsulfuric, Trifluoromethylsulfuric, and Paratolylsulfuric Acids

“…The interelectron repulsion parameter, B, also provides a measure of covalent character in metal-ligand bonds and a similar reduction in B on going from Co(FSO,), and CO(CF,SO,)~ to CO(~-CH,C,H,SO,)~ is indicated by the analysis of the spectral data as discussed above. The values of k obtained for the four cobalt salts are all relatively high and the lack of correlation with h is, according to Figgis et al (22), not unexpected. These authors point out that the k values do not, in fact, provide a good measure of the degree of covalent bonding.…”

“…The effects of electron delocalization and low symmetry ligand fields on the magnetic properties of complexes with 4T1g ground terms have been examined by Figgis et al (22). These authors have calculated theoretical magnetic moments from expressions involving four parameters: h, spin-orbit coupling constant; k, the orbital reduction factor which allows for a reduction in the orbital contribution to the magnetic moment due to electron delocalization; v, the distortion parameter which is equal to A/h where A is the magnitude of splitting of the 4T1g(F) term by fields of axial symmetry, and A, which allows for the admixture of the higher lying 4~, , (~) term into the ground 4~, g ( F ) term by the primary cubic field.…”

Magnetic and Spectral Studies on Cobalt(II) Fluorosulfate

“…The parameter A allows for the admixture of the higher lying 4T1,(P) into the ground Tl,(F) term by the primary cubic field and may be obtained from a knowledge of the parameters Dq and B (16). From the values of Dq and B determined in the present work A is calculated to be 1.43 for cobalt(I1) fluorosulfate.…”