Theoretical Investigation of the Apparently Irregular Behavior of Pt−Pt Nuclear Spin−Spin Coupling Constants

• Published in: Journal of the American Chemical Society 2003-01, Vol.125 (4), p.1028-1032
• Main Authors: Autschbach, Jochen, Igna, Ciprian D, Ziegler, Tom
• Format: Article
• Language: English
• Subjects: Atomic and molecular physics; Exact sciences and technology; Molecular properties and interactions with photons; Nuclear resonance and relaxation; Physics
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja027931q

One-bond Pt−Pt nuclear spin−spin coupling constants J(Pt−Pt) for closely related dinuclear Pt complexes can differ by an order of magnitude without any obvious correlation with Pt−Pt distances. As representative examples, the spin−spin couplings of the dinuclear PtI complexes [Pt2(CO)6]2+ (1) and [Pt2(CO)2Cl4]2- (2) have been computationally studied with a recently developed relativistic density functional method. The experimental values are 1 J(195Pt−195Pt) = 5250 Hz for 2 but 551 Hz for 1. Many other examples are known in the literature. The experimental trends are well reproduced by the computations and can be explained based on the nature of the ligands that are coordinated to the Pt−Pt fragment. The difference for J(Pt−Pt) of an order of magnitude is caused by a sensitive interplay between the influence of different ligands on the Pt−Pt bond, and relativistic effects on metal−metal and metal−ligand bonds as well as on “atomic orbital contributions” to the nuclear spin−spin coupling constants. The results can be intuitively rationalized with the help of a simple qualitative molecular orbital diagram.