Structural and Electronic Investigation of Tetrachalcogenidomolybdate Dianions

Abstract

Four compounds with tetrachalcogenidomolybdate dianions were examined under identical conditions by single crystal Xray diffraction and density functional theory (DFT) calculations. Structural comparisons of bond lengths and angles were made looking at effects of counter-cations and type of chalcogenide (S or O). Ultimately, bond lengths and angles were found to be fairly regular for each anion and in good agreement with computational results, with exceptions likely stemming from close contacts in the crystal packing. A trend of increasing bond lengths was observed with increasing cation size. The most notable structural deviation occurred in [MoO 2 S 2 ] 2À , where the theoretical structure has a smaller OÀMo-O angle and a larger SÀMo-S angle, which was opposite in the crystal structure. This is likely attributed to NÀH-S and NÀH-O interactions. Both experimental and computational results suggest that uniform charge delocalization in all four structures. The HOMO-LUMO gap increases significantly with increasing number of oxygen atoms and electronic transitions were determined to be all ligand to metal charge transfer (LMCT).[a] A.