No abstract

The Mossbauer spectra of the mono-, di-, tri-, and tetra-nuclear iron carbonyl anions and carbonyl hydride anions are reported and compared with the known spectra of the neutral binary carbonyls.Increase in anionic charge in the sequence 0, -1, -2 results in progressively lower values of chemical isomer shift 6 for each series. In addition, there is a systematic increase in 6 as the co-ordination number of iron increases from 4 to 7. These trends are interpreted in terms of changes in the bonding in these compounds. Systematic variations in the quadrupole splitting A are also discussed.The effects on 6 and A of substituting carbon monoxide by tertiary phosphines are investigated and the structure and bonding in the unusual new compound [(OC)3FePMe2Ph]3 are discussed.The Mossbauer spectra of the tetrameric species i are also investigated.

Abstract

Qualitative rules governing carbon and bridge-hydrogen placement permit the prediction of the most stable isomeric structures for the various carboranes. Seventy-three isomeric boron hydride and carborane structures, from B(6)H(9)(-) to C(4)B(2)H(6), were computed at the ab initio MP2(fc)/6-31G level to determine their relative stabilities quantitatively. Specific architectural features, recognized to be unfavorable, were assigned "energy penalty" values that allow the projection of comprehensive thermodynamic stability values via a simple additivity procedure. These values match the ab initio results with surprising precision. Our study includes Siebert's nido-2,3,5-C(3)B(3)H(7) and Wrackmeyer's nido-2,4-C(2)B(4)H(8) nido-6 carboranes, which contain "unusual" CH-B-bridge hydrogens.