The chemistry of transition-metal-NO complexes,
or metal nitrosyls, has taken on added significance
in recent years because of the important role that
nitric oxide has been found to play as a signaling
molecule in biological systems Recent work has also
established that the characteristic chemistry of nitrosyl
complexes is often markedly different from that
exhibited by their isoelectronic carbonyl analogues
It has been almost 10 years since these complexes
were last reviewed in the book Metal Nitrosyls,1 and
so it seemed to us that an update of this rapidly
expanding field would be appropriate at the present
time Consequently, this article picks up where Metal
Nitrosyls left off and summarizes comprehensively
the literature dealing with nitrosyl complexes from
1991 to mid-2001 Some particularly relevant work
reported in late 2001 has been included where
appropriate during the final stages of revising and
polishing the text As outlined in the table of contents,
the pertinent information concerning the compounds
themselves is first partitioned in terms of the
position of the central transition metal in the periodic
table and then in terms of the ligands other than NO
present in the complexes In the interests of keeping
the article to a manageable size, most of the routine
preparative and characterization data for individual
compounds are simply referenced rather than being
presented and discussed in detail The review concludes
with a general section that applies, in principle,
to all classes of transition-metal-NO complexes,
namely the characteristic reactivities of bound
NO groups Whenever possible, emphasis is placed
on the unique physical and chemical properties
imparted to nitrosyl complexes by the presence of the
strongly electron-withdrawing NO ligands If not
specified otherwise, the abbreviations employed
throughout are those summarized in the ACS Style
Guide

Nitrogen NMR spectroscopy of metal nitrosyls and related compounds

The 14N nuclear quadrupole coupling (NQC) constants (χ) and asymmetry parameters (η) for a series of small nitrogen-containing imidazole derivatives are investigated, by using density functional theory (DFT), in three clearly distinct environments:  as free molecules, in the solid state, and in solution. The spectroscopic characterization is also extended to coenzyme B12 and cob(II)alamin systems. The main findings can be summarized as follows:  (i) Deviations in the calculated χ for the two nitrogen sites in the free imidazole molecule are small enough to allow quantitatively accurate predictions for isolated molecules of substituted benzimidazole compounds. (ii) Asymmetry parameters, however, are difficult to reproduce with accuracy; only trends along a series of compounds can be taken as informative. (iii) Shifts of the NQC parameters on going from gas phase to solid state are reasonably well reproduced at a qualitative level by using a trimer model; to reach similar levels of accuracy in the case of η...

Calculation of Nuclear Quadrupole Parameters in Imidazole Derivatives and Extrapolation to Coenzyme B12. A Theoretical Study

The calculations of the electric field gradients were performed in the different basis sets at the selected ab initio, density functional theory (DFT), and ECP levels of the theory. The most reliable QCC and η values were obtained within the DFT and with the use of B3LYP functional and middle 6-31G* or extended 6-311G* basis sets. The universality of the B3LYP/6-31G* method was checked by comparing the experimental and calculated Up values as only such a comparison enables assessment of the quality of the results obtained for different (heavy and light) nuclei. The NQR parameters obtained with the use of all-electrons (AE) and pseudopotential (ECP) methods for a group of halogens or nitrogen-containing compounds were compared and the former were found to be close to the experimental values. The explanation of so extremely small values of EFG calculated with the use of pseudopotential was proposed. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

J. A. S. Smith

Papers

Nuclear quadrupole interactions in solids