Transition-metal polyhydride complexes

Publisher Summary This chapter discusses the chemistry of nitrogen fixation and models for the reactions of nitrogenase The interest in nitrogen fixation for the inorganic chemist is to try to understand, using simple compounds, what nature does so comparatively effortlessly within the enzyme, nitrogenase This is of particular value considering the increasing demand for nitrogenous fertilizers, and the vast industrial expenditure of energy in producing ammonia The literature of chemical nitrogen fixation, even excluding that related to the Haber process, is now considerable The mechanisms of reaction of coordinated dinitrogen are a matter of dispute There are several proposals extant, chemical and biological, and these are espoused by their progenitors with varying degrees of fervor However, there is now sufficient chemistry available for us to make preliminary judgments concerning the validity of the various proposals

The Chemistry of Nitrogen Fixation and Models for The Reactions of Nitrogenase

The hydride route to the preparation of dinitrogen complexes.

A detailed investigation on the properties of the high-temperature and low-temperature modifications of the iron(II) spin-crossover complex [FeL1(HIm)2] (1) and its isotopic deuterium-labelled analogue [FeL1(DIm)2] (1D), and the pair [FeL2(azpy)]·MeOH/[FeL2(azpy)]·CD3OD/[FeL2(azpy)] (2·MeOH/2·CD3OD/2), in which L1 and L2 are tetradentate N2O22–-coordinating Schiff base like ligands, L1 = {diethyl(E,E)-2,2′-[1,2-phenylbis(iminomethylidyne)]bis[3-oxobutanoate](2–)-N,N′,O3,O3′}, L2 = {2,2′-[1,2-phenylbis(iminomethylidyne)]bis[1-phenylbutane-1,3-dione](2–)-N,N′,O3,O3′},HIm = imidazole, and azpy = 4,4′-azopyridine, is presented. All complexes except 2 show a cooperative spin transition with hysteresis widths between approximately 5 K (1LT and 1LTD), 70 K (1HT[9] and 1HTD, around room temperature), and 80 K (2·MeOH and 2·CD3OD). In all cases, an influence of the H/D exchange on the transition temperature and the hysteresis width is observed. For 1HT, first-order reversal curves (FORCs) have been recorded, and a statistical analysis gives the interaction parameter J = 560 K, indicating strong intermolecular interactions. X-ray structural analysis of the different samples (1HT[9] and 1HTD: HS; 1LT and 1LTD: LS; and 2·MeOH and 2·CD3OD: HS) gives a deeper insight into the molecular packing in the crystals and helps explain the increase of cooperative interactions during the spin transition. In all cases, one hydrogen bond involves an oxygen atom of the Schiff base like ligand that serves as a donor for the iron centre. The influence of this hydrogen bond on the ligand field strength of the iron centre is discussed and a new model is developed to explain the observed connection between hydrogen bonds and exceptionally wide hysteresis loops for the complexes presented in this work and other examples from the literature.

Influence of Hydrogen Bonding on the Hysteresis Width in Iron(II) Spin-Crossover Complexes

The non-template synthesis of novel non-symmetrical, tetradentate Schiff bases. Their nickel(II) and cobalt(III) complexes

The crystal structure of bis[N-(2-aminoethyl)salicylaldiminato] iron (III) chloride monohydrate, a low spin oron(III) complex stabilized by lattice water ☆

A.A. Diamantis

Papers

The crystal structure of bis[N-(2-aminoethyl)salicylaldiminato] iron (III) chloride monohydrate, a low spin oron(III) complex stabilized by lattice water ☆

Flash photolysis of a tungsten-dinitrogen complex. An intermediate in the formation of carbon-nitrogen bonds