Theoretical Chemistry Accounts

, Volume 130, Issue 2–3, pp 393–400 | Cite as

Unsaturation in homoleptic tetranuclear iridium carbonyls: a comparison of density functional theory with the MP2 method in metal cluster structures

  • Qing Kui Chi
  • Qian-shu Li
  • Yaoming Xie
  • R. Bruce King
  • Henry F. Schaefer III
Regular Article


The lowest energy Ir4(CO)12 structure is predicted by density functional theory to be a triply bridged structure analogous to the experimental structures for its lighter congeners M4(CO)9(μ-CO)3 (M=Co, Rh). The experimental unbridged structure for Ir4(CO)12 is predicted to lie ~6 kcal/mol above the triply bridged structure. However, the MP2 method predicts the unbridged structure for Ir4(CO)12 to be the lowest energy structure by ~9 kcal/mol over the triply bridged structure. The lowest energy Ir4(CO)11 structure is predicted to be a doubly bridged structure with a central tetrahedral Ir4 unit. A higher energy Ir4(CO)11 structure at ~18 kcal/mol above this global minimum is found with an unusual μ4-CO group bridging all four atoms of a central Ir4 butterfly. This Ir4(CO)8(μ-CO)24-CO) structure is analogous to the lowest energy Co4(CO)11 structure found in a previous theoretical study, as well as Rh4(CO)4(μ-CO)4(PBu 3 t )2(PtPBu 3 t )(μ4-CO), which has been synthesized by Adams and coworkers. The Ir4 tetrahedron is remarkably persistent in the more highly unsaturated Ir4(CO) n (n = 10, 9, 8) structures with relatively little changes in the Ir–Ir distances as carbonyl groups are removed. This appears to be related to the spherical aromaticity in the tetrahedral Ir4 structures.


Iridium Metal carbonyls Metal clusters Density functional theory Møller–Plesset second-order perturbation theory 



We are indebted to the Scientific Research Fund of State Key Laboratory of Explosion Science and Technology (2DkT10-01a) and the Research Fund for the Doctoral Program of Higher Education (20104407110007) of China as well as the U. S. National Science Foundation (Grants CHE-0716718 and CHE-1054286) for support of this research.

Supplementary material

214_2011_1005_MOESM1_ESM.pdf (275 kb)
Tables S1–S17: Theoretical harmonic vibrational frequencies for the Ir4(CO) n (n = 12, 11, 10, 9, and 8) structures using the BP86 and MPW1PW91 methods; Tables S18–S34: Theoretical Cartesian coordinates for the Ir4(CO) n (n = 12, 11, 10, 9, and 8) structures using the BP86 method; Table S35: Wiberg bond indices for the Ir–Ir interactions in selected Ir4(CO) n structures (n = 12, 11, 10, 9, and 8) using the three DFT methods; Complete Gaussian reference (reference 32). (PDF 275 kb)


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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  1. 1.Center for Computational Quantum ChemistrySouth China Normal UniversityGuangzhouPeople’s Republic of China
  2. 2.Institute of Chemical PhysicsBeijing Institute of TechnologyBeijingPeople’s Republic of China
  3. 3.Department of Chemistry and Center for Computational ChemistryUniversity of GeorgiaAthensUSA

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