Gas Adsorption of Mixed-Valence Trinuclear Oxothiomolybdenum Glycolates

Trinuclear oxothiomolybdenum(IV) glycolates (H₂glyc, glycolic acid) with 2-methylimidazole (2-mim), 4-methylimidazole (4-mim), and sulfite, Na₂[Mo^IV₃(μ₃-S)(μ₂-O)₃(glyc)₃(2-mim)₃]·1.5H₂O (1), (4-Hmim)₆[Mo^IV₃(μ₃-S)(μ₂-O)₃(glyc)₃(4-mim)₃]₂[Mo^VIO₂(glyc)₂] (2), and Na₃(4-Hmim)[Mo^IV₃(μ₃-S)(μ₂-O)₃(SO₃)(glyc)₃(4-mim)]·8H₂O (3), have been isolated in reduced media, where 4-methylimidazole trinuclear oxothiomolybdenum(IV) glycolates in 2 coprecipitate with dioxomolybdenum(VI) glycolate, exhibiting unusual mixed valences of 4+ and 6+. Large downfield shifts of glycolates have been observed in solid-state and solution ¹³C (¹H) NMR spectra with coordination to Mo, indicating obvious dissociation of soluble 1 and 3 in solution. Investigations of the coordination modes and conversions among the three complexes give insight into the reactivities of trinuclear oxothiomolybdenum(IV) complexes. Channels with 3.1 × 7.0 Ų diameters exist in 2, showing reversible O₂ absorption of 65.03 mg at 29.9 bar compared with little or no adsorption of N₂, H₂, CO₂, and CH₄ at room temperature, respectively. Moreover, trinuclear 2- or 4-methylimidazole oxothiomolybdenum(IV) glycolates 1 and 3 show only a few adsorptions for O₂ under the same conditions.