Electronic Structures of Reduced and Superreduced Ir_2(1,8-diisocyanomenthane)_4^(n+) Complexes

Abstract

Molecular and electronic structures of Ir_2(1,8-diisocyanomenthane)_4^(n+) (Ir(dimen)^(n+)) complexes have been investigated by DFT for n = 2, 1, 0 (abbreviated 2+, 1+, 0). Calculations reproduced the experimental structure of 2+, ν(C≡N) IR, and visible absorption spectra of all three oxidation states, as well as the EPR spectrum of 1+. We have shown that the two reduction steps correspond to successive filling of the Ir–Ir pσ orbital. Complexes 2+ and 1+ have very similar structures with 1+ having a shorter Ir–Ir distance. The unpaired electron density in 1+ is delocalized along the Ir–Ir axis and over N atoms of the eight C≡N– ligands. The second reduction step 1+ → 0 changes the Ir(CN−)_4 coordination geometry at each Ir site from approximately planar to seesaw whereby one −N≡C–Ir–C≡N– moiety is linear and the other bent at the Ir (137°) as well as N (146°) atoms. Although complex 0 is another example of a rare (pσ)2 dimetallic species (after [Pt_2(μ-P_2O_5(BF_2)_2)_4]^(6–), J. Am. Chem. Soc. 2016, 138, 5699), the redistribution of lower lying occupied molecular orbitals increases electron density predominantly at the bent C≡N– ligands whose N atoms are predicted to be nucleophilic reaction centers.

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