On the theory of N.M.R. screening constants in t₂¹ and t₂⁵ transition metal ion complexes—The pseudocontact contribution

Abstract

The pseudocontact contribution to the N.M.R. shift arising from the interaction of the electron spin and orbital angular momenta with the N.M.R. nucleus is calculated for the case of a d ¹ transition metal ion in a crystal field of octahedral symmetry and for a d ⁵ transition metal ion in a strong crystal field of octahedral symmetry. The results are applicable for not only long-range dipolar coupling but for short-range coupling including the special case when the N.M.R. nucleus is the transition metal ion. Also, the pseudocontact contribution to the N.M.R. shift is calculated for two cases when the crystal field has a specific tetragonal and a trigonal component. Bonding effects are examined for the case of a d ⁵ transition metal ion and the ¹⁴N N.M.R. results for the Fe(CN)₆ ^3- ion are interpreted as arising dominantly from the interaction with the nitrogen nucleus of the unpaired electrons in the nitrogen p-orbital of the ² T ₂ molecular orbital.