Nuclear Magnetic Resonance Spectroscopy

BY B. E. MANN

1 Introduction

Following the criteria established in earlier volumes, only books and reviews directly relevant to this chapter are included, and the reader who requires a complete list is referred to the Specialist Periodical Report 'Nuclear Magnetic Resonance', where a complete list of books and reviews is given. Reviews which are of direct relevance to a section of this report are included in the beginning of that section rather than here. Papers where only 1H n.m.r. spectroscopy is used are only included when the 1H n.m.r. spectra make a non-routine contribution, but complete coverage of relevant papers is still attempted where nuclei other than the proton are involved.

Only one relevant book has appeared during 1980, namely 'E.P.R. and N.M.R. in the Chemistry of Coordination Compounds'. Numerous reviews have appeared, including 'Correlations in Nuclear Magnetic Shielding, Part II', 'N.M.R. Spectroscopy of Organometallic Compounds of the f-Elements; Practical Applications', 'N.M.R. for Rare Earth Complexes; Theory', 'N.M.R. of Other Nuclei', 'Application of N.M.R. in the Structure Elucidation of Coordination Compounds: Metal Nuclei', 'Nuclear Magnetic Resonance of the Less Common Quadrupolar Nuclei', 'Carbon-13 and Nitrogen-15 N.M.R. Studies in Organic and Organometallic Chemistry', σ,π-Conjugation in Organometallic Systems', 'Dynamic and Stereochemical Studies by Phosphorus-31 N.M.R. Spectroscopy on Polyphosphine Complexes of Heavy Metals', 'Phosphorus-31 N.M.R. Studies of Catalytic Systems Containing Rhodium Complexes of Chelating Diphosphines', 'Model Compounds as Aids in Interpreting N.M.R. Spectra of Haemoproteins', 'High Resolution N.M.R.', a review of n.m.r. properties of metal nuclei in metallo-proteins, 'Nuclear Magnetic Resonance Spectroscopy of Diamagnetic Porphyrins', 'Biophysical Applications of N.M.R. to Phosphoryl Transfer Enzymes and Metal Nuclei of Metalloproteins', 'Multinuclear N.M.R. Studies of Crown and Cryptand Complexes', 'Synthesis, Molecular Dynamics, and Reactivity of Mixed-Metal Clusters', and 'Nuclear Magnetic Resonance in Molten Salts and Molten Metal–Salt Mixtures. I. Chemical Shift'.

A number of papers have been published which are too broadly based to fit into a later section and are included here. J(15N, 13C) and 15N/14N isotope effects on 13C chemical shielding have been reported for [Cu(CN)4,]3-, [Ni(CN),]2-, [Pt(CN),]2-, [Cd(CN)4]2-, and [Hg(CN)4]2-. The isotope shifts, 0.02 — 0.04 p.p.m, are comparable to recently reported 16O/18O isotope effects on 13C chemical shielding in metal carbonyl derivatives. The H chemical shifts of 2-hydroxy-1,3-propanediamine-NNN'N'-tetra-acetic acid and 1,3-propanediamine- NNN'N'-tetra-acetic acid in 1:1 complexes with diamagnetic metal ions have been investigated as a function of the metal ion charge z and crystal ionic radius r. The chemical shifts correlate with z/r linearly. 1H and 31P n.m.r. spectra have been recorded for complexes of ATP with MgII, CaII, SrII, ZnII, CdII, SnII, PbII, HgII, AgI, and TlI. Each of these ions, except HgII, affected the 13P n.m.r. of ATP, usually shifting all three resonances to high frequency and decreasing J(31P,31P). PbII exerted the greatest shifts, whereas MgII caused the greatest change in coupling constant. In 13C n.m.r. spectroscopy the intensities of different signals become almost equal on adding Cr(acac)3 as a relaxation reagent.

15N n.m.r. spectra of nitrogen-containing crown ethers, cryptand ligands, and other ligands with pyridine-type nitrogens and their complexes with alkali, alkaline-earth, AgI, and TlI ions have been reported. An analytical LCAO MO theory of the Fermi contact term, 1K (A, 19F), has been developed for substituted planar-trigonal AF3 - n Ln and tetrahedral AF4 - n Ln fluorides of main-group elements. This treatment was extended to octahedral cases. For melts of transition, alkali, and alkaline-earth metal fluorides a theory about the effect of outer-sphere cations on the chemical shift of the 19F nucleus entering into the [MF4]n - 4 complex ion has been developed. The changes in the chemical shift of a central-atom nucleus during successive substitution of ligands in the AXk-nYn-type molecular systems have been explained.

2 Stereochemistry

This section is subdivided into ten parts which contain n.m.r. information about lithium, magnesium, and transition-metal complexes, presented by Groups according to the Periodic Table. Within each Group, classification by ligand type.

Complexes of Group IA and IIA. — The 3J (13C, 1H) and 1J(13C 13C) in EtM, Pr1M, and ButM (M = alkali metal or halogen) have been determined. The substituent electronegativity dependence of 3J(13C,1H) shows that the influence exerted by a β-Me substituent on 3J(13C,1H) and 2J (13C,1H) is not constant. The σ- vs. π-character of R2CR1=CR3CH 2M (M = Li, K, or MgBr) has been studied via13C n.m.r. spectroscopy.

INDO molecular-orbital calculations have suggested that 1J (13C, 7Li) in methyl-lithium monomer should be 16 Hz. The 13C n.m.r. shifts in straight-chain alkyl-lithium compounds in ether and cyclopentane are linear with those of the corresponding hydrocarbons, indicating that the whole series of compounds studied have similar electronic structures about the bridged carbon-lithium bonds. The C1, 13C n.m.r. resonance in PrLi broadens with decreasing temperature, indicating the operation of interaggregate bond exchange as well as lithium quadrupole relaxation. 13C n.m.r. spectra of allyl-lithium-1-d have been reported which are consistent with a symmetric rather than a rapidly equilibrating unsymmetric structure. 1H and 13C n.m.r. spectra of a series of para-substituted α-methyl-α-neopentylbenzyl-lithium indicate a Hückel charge distribution. For some 9-alkyl-10-lithio-9, 10-dihydroanthracenes the para n.m.r. shift has been investigated as a function of solvent.

The magnetic moment of 24mNa is 1.930(3) nuclear magnetons (uncorrected). The Na n.m.r. spectrum of Na{CH(PPh2CHPh)2} (thf) shows an asymmetric ligand arrangement with a 2200 Hz linewidth. 1H, 13C, and 31P n.m.r. spectra were also recorded. The 13C n.m.r. spectrum of C5H7 K has also been reported. The 31P skeleton of...