Original scientific paper

Heptacarbonyldiosmium and Hexacarbonyldiosmium: Two Highly Unsaturated Binuclear Osmium Carbonyls

Bing Xu ; aInstitute of Chemical Physics, Beijing Institute of Technology, Beijing 100081, China
Qian-Shu Li ; aInstitute of Chemical Physics, Beijing Institute of Technology, Beijing 100081, China
Yaoming Xie ; Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA
Bruce King ; Center for Computational Quantum Chemistry, South China Normal University, Guangzhou, 510631 China
Henry F. Schaefer III ; Department of Chemistry and Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA

Abstract

A total of nine singlet structures for Os₂(CO)₇ and 15 structures (nine singlet and six triplet) for Os₂(CO)₆ have been found by density functional theory thereby indicating very complicated energy surfaces. The global minimum for Os₂(CO)₇ is a doubly carbonyl bridged structure Os₂(CO)₅(μ-CO)₂ with an Os=Os distance of 2.67 Å suggesting a formal double bond and hence a 16-electron rather than an 18-electron configuration for one of the osmium atoms. However, at only slightly higher energy (3.2 kcal mol−1) lies an unbridged Os₂(CO)₇ structure with a shorter Os≡Os distance of 2.54 Å, corresponding to a formal triple bond and an 18-electron configuration for each osmium atom. The global minimum for
Os₂(CO)₆ can be derived from that of Os₂(CO)₇ by removal of a carbonyl group while retaining the Os=Os double bond and the two bridging carbonyl groups. Slightly higher energy Os₂(CO)₆ structures at ≈3 kcal mol−1 or more above the global minimum have short Os-Os quadrupole bond distances around 2.4 Å, consistent with the formal quadruple bonds necessary to give both osmium atoms the favored 18-electron configuration. None of the 24 structures for Os₂(CO)₇ and Os₂(CO)₆ found in this work has a four-electron donor η2-μ-CO bridging carbonyl group.

Keywords

DFT calculations; organometallic compounds; osmium carbonyls

Hrčak ID:

38649

URI

https://hrcak.srce.hr/38649

Publication date:

30.6.2009.

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