Unexpected structural and electronic effects of internal rotation in diruthenium paddlewheel complexes containing bulky carboxylate ligands

Raquel Gracia, Harry Adams, Nathan J. Patmore

Research output: Contribution to journalArticle

8 Citations (Scopus)


A series of Ru2II,III complexes containing the bulky carboxylate ligand 2,4,6-triisopropylbenzoate (TiPB) of type trans-[Ru2(TiPB) 2(O2CCH3)2X] [X = Cl (1), PF 6 (2)] and [Ru2(TiPB)4X] [X = Cl (3), PF 6 (4)] have been synthesised. The corresponding Ru2II,II complexes trans-[Ru2(TiPB)2(O2CCH3) 2] (5) and [Ru2(TiPB)4] (6) were also isolated. Magnetic susceptibility measurements indicate that the diruthenium cores have the expected three (1-4) or two (5 and 6) unpaired electrons consistent with σ2π4δ21π 1)3 and σ2π4δ 2δ2π2 electronic configurations. Compounds 1-4 and 6 were structurally characterised by X-ray crystallography, and show the expected paddlewheel arrangement of carboxylate ligands around the diruthenium core. The diruthenium cores of complexes 3, 4 and 6 are all distorted to minimise steric interactions between the bulky carboxylate ligands. The Ru-Ru bond length in the Ru2II,II complex 6 [2.2425(6) ] is the shortest observed for a diruthenium tetracarboxylate and, surprisingly, is 0.014 shorter than in the analogous Ru2II,III complex 4, despite an increase in the formal Ru-Ru bond order from 2.0 (6) to 2.5 (4). This is rationalised in terms of the extent of internal rotation, or distortion, about the diruthenium core. This was supported by density functional theory calculations on the model complexes [Ru2(O2CH)4] and [Ru2(O 2CH)4]+, that demonstrate the relationship between Ru-Ru bond length and internal rotation. Electrochemical and electronic absorption data were recorded for all complexes in solution. Comparison of the data for the 'bis-bis' (1, 2 and 5) and tetra-substituted (3, 4 and 6) complexes indicates that the shortening of the Ru-Ru bond length results in a small increase in energy of the near-degenerate δ1 and π1 orbitals.

Original languageEnglish
Pages (from-to)3856-3864
Number of pages9
JournalInorganica Chimica Acta
Issue number14
Early online date16 Jul 2010
Publication statusPublished - 25 Nov 2010
Externally publishedYes


Cite this