A nuclear magnetic resonance investigation of bis(OO′-diethyl dithiophosphato)-complexes of the lanthanoids: separation of contact and pseudo-contact contributions to the chemical shifts

Abstract

Measurements of ¹H and ³¹P chemical shifts have been made at 26 and –40 °C for [AsPh₄][Ln{S₂P(OEt)₂}₄](Ln = La–Lu, excluding Pm and Gd). The results show that there are two structure types in solution, La–Dy and Ho–Lu. In both series the ¹H shifts are dipolar in origin, but the ³¹P shifts have a large contact contribution. A new approach to the determination of the contact contribution has been developed, and hyperfine coupling constants of 1.52 and 0.86 MHz obtained for the two structure types. This is interpreted as a covalent contribution to the bonding.