Factors affecting the magnetic properties of dimeric copper(II) complexes

The electronic matrix element coupling a ground and charge-transfer excited state can be calculated from the energy intensity of the appropriate charge-transfer transition. An expression for the electronic coupling element widely used for this purpose is based on equations derived by Mulliken and Hush for an effective two-state model and is frequently assumed to be valid only in the perturbation limit. This expression is shown to be exact within a two-state model. Provided that overlap can be neglected and that the spectroscopic transition is polarized along the donor—acceptor axis, it can be applied to system ranging from those which are very weakly coupled to those which are very strongly coupled. Application of the Mulliken—Hush expression to (NH3)5RuL2+ complexes, for which metal—lingand backbonding is important, yields metal—lingand coupling elements of 5000–6000 cm−1 with pyridyl lingands (donor—acceptor separation 3.5 A), in very good agreement with estimates obtained from a molecular orbital analysis of the band energies. With use of the superexchange formalism, the metal—lingand coupling elements were used to calculate metal—metal coupling elements for binuclear mixed-valence complexes. Comparison of these values with those obtained from the Mulliken—Hush expression applied directly to the metal-to-metal charge-transfer transition yields agreement within a factor of two or better.

Metal—lingad and metal—metal coupling elements

Organonitrile complexes of transition metals

The coordination chemistry of TCNE, TCNQ and related polynitrileπ acceptors

Tetracyanoethylene (TCNE) undergoes numerous reactions and is reported to exist in many structural motifs. Identification of these forms and motifs can be challenging. Nonetheless, the number of nu(CN) absorptions and their frequencies provide insight with respect to the specific forms and charge on the TCNE fragment. Particularly informative is the average of the fundamental nu(CN) bands, as well as the length of the central C-C bond. This Review discusses the assignment of structure and formal charge for TCNE-containing compounds. Scrutiny of previous assignments reveals some discrepancies which are discussed, and provides a basis for further study of TCNE structure-function relationships. Several multimetal complexes with bridging [TCNE](z) units exhibit mixed valency and extensive delocalization. The scarcity of suitable model compounds, especially those with M(d(pi-pi*)) backbonding to the CN groups, have thwarted the detailed description of these valence ambiguous compounds; thus, new well-characterized polynuclear compounds are needed.

Tetracyanoethylene (TCNE): the characteristic geometries and vibrational absorptions of its numerous structures.

Benzonitrile and acetonitrile complexes of ruthenium ammines

Cyanopyridine complexes of pentaammineruthenium(II)

Spectroscopic characterization of pentaammineruthenium complexes of acrylonitrile

Syntheses of cis- and trans-tetraamminedichlororuthenium(iii) chloride

Benzonitrile complexes of ruthenium(II) and ruthenium(III): analogues of the molecular nitrogen complex ion Ru(NH3)5N22+

Richard E. Clarke

Papers

Benzonitrile and acetonitrile complexes of ruthenium ammines

Cyanopyridine complexes of pentaammineruthenium(II)

Spectroscopic characterization of pentaammineruthenium complexes of acrylonitrile

Syntheses of cis- and trans-tetraamminedichlororuthenium(iii) chloride

Benzonitrile complexes of ruthenium(II) and ruthenium(III): analogues of the molecular nitrogen complex ion Ru(NH3)5N22+