Elektronendichte-verteilungen in metallorganischen verbindungen. Wechselnde struktur- und bindungsverhältnisse in dimeren metallorganischen nickel-hydriden mit ionenpaar-beziehungen zu den hauptgruppen-metallen natrium und lithium

Abstract

The compounds [[(C 2H 4) 2Ni] 2H][Na(TMEDA) 2] (I) and [[(C 2H 4) 2Ni] 2H][Li(CH 3 2NCH 2CH 2N(CH 3) CH 2CH 2N(CH 3 2] (II) have been investigated by high resolution X-ray techniques. Compound I is found to exist as distinct ions which are well-separated in the unit cell, while II shows an ion pair contact between the lithium ion part and one nickel atom, one ethene group, and the hydride in the anion. This latter interaction has little effect on the geometry of the anion, which is similar in both compounds. Each nickel atom is surrounded by a trigonal-planar coordination geometry comprising two ethene groups and the bridging hydrige. The NiHNi bridge is non-linear and the angle at the hydrogen atom is 131 and 111°, respectively. The unusual geometry adopted by the anion is explained in terms of an interaction between the two nickel atoms involving the empty p-orbital on one metal with the filled d-orbitals on the other. The bonding situation obtained from semi-empirical molecular orbital calculations is in accord with the observed electron density distributions.