The Preparation, Structural Characteristics, and Physical Chemical Properties of Metal-Nitrosyl Complexes

Abstract

The preparation and characterization of a representative group of novel non-heme metal nitrosyl complexes that have been synthesized over the last decade are discussed here. Their structures are examined and classified based on metal type, the number of metal centers present, and the type of ligand that is coordinated with the metal. The ligands can be phosphorus, nitrogen, or sulfur based (with a few exceptions) and can vary depending on the presence of chelation, intermolecular forces, or the presence of other ligands. Structural and bonding characteristics are summarized and examples of reactivity regarding nitrosyl ligands are given. Some of the relevant physical chemical properties of these complexes, including IR, EPR, NMR, UV–vis, cyclic voltammetry, and X-ray crystallography are examined.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

“…These bands exist in the visible region (above 400 nm); excitation weakens π-back-bonding to the NO ligand and facilitates electron transfer from the metal center to NO + , which is then liberated as a neutral NO molecule. 1252 Transition metal complexes releasing NO have been reviewed by Ford 77 − 79 , 98 , 107 Mascharak, 63 and Liu 1253 and their co-workers.…”

“…The oldest and best known NO donors are pentacyano­nitrosylmetallates such as disodium pentacyano­nitrosylferrate (sodium nitroprusside), which has been known since the mid-19th century. − The M–NO bond is readily cleaved by excitation into the MLCT (d M → π* NO ) band of an organometallic complex. These bands exist in the visible region (above 400 nm); excitation weakens π-back-bonding to the NO ligand and facilitates electron transfer from the metal center to NO + , which is then liberated as a neutral NO molecule . Transition metal complexes releasing NO have been reviewed by Ford − ,, Mascharak, and Liu and their co-workers.…”

Transition Metal Nitrosyls: Statistics, Charge Estimates via CDVR, and Studies of Tetradentate Chelate Diamides (pddi)M and (pddi)MNO (M = Cr, Fe, and Co)

“…The equation of charge for CO is shown in eq , where c CO is the resultant charge and ν(CO) is the average stretching frequency. Assessment of different ligands can be obtained from [M( CO ) x L y ] p complexes − ,− using eq , where p is the complex ion charge, c M c CO = ( ν false( CO false) − 2207 cm − 1 ) / 475 p = c normalM + x CO c CO + y normalL c normalL + z normalL ′ normalc normalL ′ + ... is the CDVR metal charge (for this work: Cr(+2.6), Fe(+2.0), Co(+1.6)), x CO is the number of CO ligands, c CO is the corresponding charge, and y L is the number of L, the ligand of interest. In the simplest case of CO and L, solving for c L affords the average charge of L.…”

“…The research above serves to augment the long history of the nitrosyl ligand in organometallic and inorganic chemistry and hopefully continues to dispel notions that electron counting methods of the former are electronically realistic, as plenty of previous investigators have also intimated. − ,− ,− , Reliance on valence bond theory and formal oxidation states plays into the difficulties in assessing an appropriate charge to an NO ligand that is intrinsically electronegative in comparison to its metal binder. It is probably best to consider NO as neutral or anionic when linear and anionic when bent in conforming to the estimated atomic number (EAN) rule, that is, the 18 e – rule.…”

“…Bound NO, being attached to a Lewis acid in the simplest sense, is not the same as gas phase NO, and clearly (NO) + is an unrealistic limiting portrayal even though it may be a convenient e – -counting model. Researchers in nitrosyls have understood this conundrum − but often stick with convention, presumably since the lexicon of organometallic chemistry and its counting schemes are convenient.…”