The use of conductivity measurements in organic solvents for the characterisation of coordination compounds

Publisher Summary This review is concerned with the neglected class of inorganic compounds, which contain ions of the same element in two different formal states of oxidation. Although the number of references cited in our review show that many individual examples of this class have been studied, yet they have very rarely been treated as a class, and there has never before, to our knowledge, been a systematic attempt to classify their properties in terms of their electronic and molecular structures. In the past, systems containing an element in two different states of oxidation have gone by various names, the terms “mixed valence,” nonintegral valence,” “mixed oxidation,” “oscillating valency,” and “controlled valency” being used interchangeably. Actually, none of these is completely accurate or all-embracing, but in our hope to avoid the introduction of yet another definition, we have somewhat arbitrarily adopted the phrase “mixed valence” for the description of these systems. The concept of resonance among various valence bond structures is one of the cornerstones of modern organic chemistry.

Mixed Valence Chemistry-A Survey and Classification

Publisher Summary This is one of two articles in this volume that is concerned with the borane-carborane structural pattern. In the other, Williams has shown how the pattern reflects the coordination number preferences of the various atoms involved. The purpose of the present article is to note some bonding implications of the pattern, and to show its relevance to a wide range of other compounds, including metal clusters, metal-hydrocarbon 7∼ complexes, and various neutral or charged hydrocarbons. Boranes and carboranes may be regarded as cluster compounds in the sense defined by Cotton; they contain a finite group or skeleton of atoms held together entirely, mainly, or at least to a significant extent by bonding directly between those atoms, even though some other atoms may be associated intimately with the cluster. Examples of their structural pattern, however, can be found far beyond the confines of what is normally regarded as cluster chemistry, so this survey includes many systems not commonly referred to as clusters.

Structural and Bonding Patterns in Cluster Chemistry

Sub-nanometre sized metal clusters, with dimensions between metal atoms and nanoparticles, have attracted more and more attention due to their unique electronic structures and the subsequent unusual physical and chemical properties. However, the tiny size of the metal clusters brings the difficulty of their synthesis compared to the easier preparation of large nanoparticles. Up to now various synthetic techniques and routes have been successfully applied to the preparation of sub-nanometre clusters. Among the metals, gold clusters, especially the alkanethiolate monolayer protected clusters (MPCs), have been extensively investigated during the past decades. In recent years, silver and copper nanoclusters have also attracted enormous interest mainly due to their excellent photoluminescent properties. Meanwhile, more structural characteristics, particular optical, catalytic, electronic and magnetic properties and the related technical applications of the metal nanoclusters have been discovered in recent years. In this critical review, recent advances in sub-nanometre sized metal clusters (Au, Ag, Cu, etc.) including the synthetic techniques, structural characterizations, novel physical, chemical and optical properties and their potential applications are discussed in detail. We finally give a brief outlook on the future development of metal nanoclusters from the viewpoint of controlled synthesis and their potential applications.

Sub-nanometre sized metal clusters: from synthetic challenges to the unique property discoveries

Layered double hydroxides (LDH) intercalated with metal coordination compounds and oxometalates

The Electronic Structures of Tetrahedral Cobalt(II) Complexes

The structures of the STAM/sub 6/X/sub 8/!/sup 4+/, M=Mo, W(?), STAM/sub 6/Cl/sub 12//sup 2+/, M = Nb, Ta, and STAM/sub 3/X/sub 12/!/sup 3-/, M= Re, species, which contain clusters of heavy transition metal atoms are compared; and the occurrence of approximately square MX/sub4/ units is noted as a common feature. The metal-metal bonding within the clusters is treated by a simple molecular orbital method, and it is shown that in this way all the general aspects of the electronic structures can be straightforwardly accounted for. Clues provided as to other possible metal ion cluster compounds are discussed. (auth)

A Molecular Orbital Treatment of the Bonding in Certain Metal Atom Clusters

The electronic spectra of eight tetrahedral complexes of nickel(II), viz., STANiCl/sub 4/!/sup 2-/, STANiBr/sub 4/!/sub s/sup -/, STANiI4>i!/sup 2/ s, STANi(Ph/sub 3/PO)/sub 2/Cl/sub 2/!' STANi(Ph/sub 3/PO)/sub 2/Br/sub 2/!, STANi(Ph/sub 3/PO)/sub 2/I/sub 2/!, STANi(Ph/sub 3/AsO)/sub 2/Cl i!, and STANi(Ph/sub 3/AsO)/sub 2/Br/sub 2/!, were carefully studied in the region of the two highest energy, spin-allowed bands, nu /sub 3/ and nu /sub 2/. It is shown that the tetrahalo ions are very sensitive to solvolysis, even by nitromethane and acetonitrile, and that the spectra of the solvolyzed species, most probably STANiX/sub 3/solvent!/sup -/, especially in the region of nu /sub 2/, are quite different from the true spectra of the STANiX/sub 4/!/sup 2-/ ions. The true spectra were obtained by measuring solid compounds either by reflectance ( nu / sub 3/ only) or using mulls. It was then found that if excess X/sup -/, in the form of soluble salts of R/sub 4/P/sup +/ or R/sub 4/N/sup +/ cations, was added to the solutions the bands of the solvolyzed species could be completely, or almost completely suppressed and the true STANiX/sub 4/!/sup 2-/ spectra obtained. From these spectra the values of DELTA snd B were calculated using Liehr and Ballhausen' smore » complete theory. The order of DELTA values was STANiI/sub 4/!/ sup 2-/ - STANiBr/sub 4/!/sup 2-/ < STANiCl /sub 4/!/sup 2-/. The flve ndxed ligand complexes were not so readily subject to solvolysis. Their spectra in the nu /sub 3/ and nu /sub 2/ regions are also reported and analyzed to yield DELTA and B values. The oscillator strengths of the bands are reported and discussed. Some remarks on the relatively low magnetic moment of STANiI/sub 4/!/ sup 2-/ are also given. (auth)« less

Electronic Spectra of Some Tetrahedral Nickel(II) Complexes

The compound STACo(Ph/sub 3/P)/sub 2/(SCN)/sub 2/! was studied magnetically and spectroscopically. The data lead to the following conclusions: (1) the compound is tetrahedral; (2) the SCN groups are bound to Co via the sulfur atoms; (3) the position of S-bonded thiocyanate ions in the spectrochemical series is between Cl/sup -/ and Br/sup -/ as previously shown by Schaffer. Several salts of the STACo(NCS)4!/sup 2-/ anion were studied magnetically and spectroscopically. A number of importart parameters pertaining to the electronic structure and ligand field were evaluated and the effect of bonding the S atom to Hg(II) in moving the -NCS- ion to a stronger position in the spectrochemical series, as observed by Schaffer, was confirmed. The compound STACo(Ph/sub 3/PO)/sub 2/(NCS)/sub 2/! has been prepared. Comparison of spectral and magnetic data for the compound with similar data for its chloride and bromide analogs shows that in this case the thiocyanate ions are coordinated through the nitrogen atoms. (auth)

F. A. Cotton

Papers

The Electronic Structures of Tetrahedral Cobalt(II) Complexes

A Molecular Orbital Treatment of the Bonding in Certain Metal Atom Clusters

Electronic Spectra of Some Tetrahedral Nickel(II) Complexes

Magnetic studies of high-spin cobaltous compounds. vii. some thiocyanate complexes

Preparation and Magnetic and Spectral Studies of Some Cobalt(II) Complexes of Benzimidazole