Combined experimental and theoretical studies of some uranium(VI) complexes derived from imidazole-based carbenes

Abstract

A series of bidentate, viz., 1,1'-(1,2-ethylene)-3,3'-dimethyldiimidazoline-2,2'-diylidene (L1), 1-methyl-3-(2-pyridylmethyl)-imidazoline-2-ylidene (L2) and tridentate, viz., 1,3-bis(2-pyridyl)-imidazoline-2-ylidene (L3) ligands have been obtained from their corresponding imidazolium salts through deprotonation reactions. Treatment of UO₂Cl₂(THF)₃ with one equivalent L3 produces air-stable U(VI)-carbene complex 3, characterized by elemental analysis, FTIR, NMR spectroscopy as well as extended X-ray absorption fine structure (EXAFS) analysis. EXAFS result indicates that the ligand is bonded through one C and two N-atoms to the uranium atom. Attempts to synthesize uranyl complexes derived from L1 and L2 were also successful but these complexes are decomposed quickly within one hour at room temperature. 3 produces pure UO₂ powder when heated under an argon atmosphere from room temperature to 600 °C with constant heating rate of 5 °C/min. The solid-state UV–Vis spectrum of the compound shows absorption peaks at 332 and 450 nm. The excitation spectrum of 3 (at λ_em = 520 nm) exhibits two almost symmetrical peaks at 273 and 368 nm. Density functional theory-based quantum mechanical calculations indicate that a partial covalent interaction exists between the carbene C and U while a weak non-covalent interaction exists between carbene N and U atoms.

Keywords:

• Uranium complex
• organometallic compounds
• N-heterocyclic carbene
• uranyl
• imidazole based carbene

Acknowledgements

Sincere thanks are due to Computer Centre, BARC for providing ANUPAM parallel computational facility. DD is thankful to Dr. S. N. Jha, Shri Akhil K. Dubey, Shri Kamal P Chaudhari, Dr. Nisha Kushwah, Dr. Manojkumar Pal and Dr. Aditi Chakrabarty Patra, BARC for their various analytical support at different stages of study. DD would also like to acknowledge Dr. A. S. Pente, Dr. Amar Kumar, Dr. K.C. Pancholi, Shri Anand Gangadharan, and Smt. Smitha Manohar for their continuous support and encouragement for the work.

Disclosure statement

No potential conflict of interest was reported by the authors