Binuclear, tetranuclear and hexadecanuclear thio-oxomolybdenum(v/iv) glycolates with selective adsorptions of gases

Abstract

By adjusting the pH values of the solutions, binuclear, tetranuclear and hexadecanuclear glycolato thio- and oxomolybdenum(V/IV) complexes [Mo^V₂O₂(μ₂-O)(μ₂-S)(Hglyc)₂(Hpz)₂]·H₂O (1, H₂glyc = glycolic acid, Hpz = pyrazole), (Hdpa)[Mo^V₂O₂(μ₂-S)₂(Hglyc)(glyc)(H₂O)] (2, dpa = 2,2′-dipyridylamine), (Hdpa)₄[Mo^V₄O₄(μ₃-O)₂(μ₂-S)₂(glyc)₂(S₂O₃)₂] (3) and Na₂[Mo^IV₄Mo^V₁₂O₁₂(μ₂-O)₆(μ₂-OH)₂(μ₃-O)₁₂(glyc)₄(Hpz)₄(pz)₈]·28H₂O (4) have been obtained successfully. Here the glycolates existed in varying aggregates with different degrees of protonation and deprotonation in 1–4. The stable formations of 1 and 2 are attributed to strong hydrogen bonds formed between the molecules. In particular, the asymmetric unit in 2 is a tetramer linked by hydrogen bonding [2.574(9) Å] between α-hydroxy and α-alkoxy groups for further construction of unsaturated penta-coordination environments. Moreover, deprotonated glycolates act as bridging ligands to form tetra- and hexadecanuclear compounds 3 and 4, respectively. The smallest unit in 4 exhibits mixed valences of 4+ and 5+ simultaneously, where its gas adsorption experiments manifest that 4 is obviously beneficial for O₂ and CO₂ compared with no adsorption of N₂, CH₄ and H₂ at different pressures.