New molybdenum(V) complexes based on the {Mo 2O 4} 2+ structural core with esters or anions of malonic and succinic acid

Abstract

A series of malonato complexes of molybdenum(V) was prepared by reacting (PyH) 5[MoOCl 4(H 2O)] 3Cl 2 or (PyH) n [MoOBr 4] n with malonic acid (H 2mal) or a half-neutralized acid, hydrogen malonate (Hmal −), at ambient conditions: (PyH) 3[Mo 2O 4Cl 4(μ 2-Hmal)] · CH 3CN ( 1), (PyH) 3[Mo 2O 4Br 4(μ 2-Hmal)] · CH 3CN ( 2), (PyH) 2[Mo 2O 4Cl(η 2-mal)(μ 2-Hmal)Py] ( 3), (3,5-LutH) 2(H 3O) [Mo 2O 4(η 2-mal) 2(μ 2-Hmal)] ( 4), (PyH)[Mo 2O 4Cl 2(μ 2-Memal)Py 2] ( 5), (3,5-LutH)[Mo 2O 4Cl 2(μ 2-Memal)(3,5-Lut) 2] ( 6), (PyH)[Mo 2O 4Cl 2(μ 2-Etmal)Py 2] ( 7), (3,5-LutH)[Mo 2O 4Cl 2(μ 2-Prmal)(3,5-Lut) 2] ( 8) and [{Mo 2O 4(μ 2-Memal)Py 2} 2(μ 2-OCH 3) 2] ( 9) (where Py = pyridine, C 5H 5N; PyH + = pyridinium cation, C 5H 5NH +; 3,5-Lut = 3,5-lutidine, C 7H 9N; 3,5-LutH + = 3,5-lutidinium cation, C 7H 9NH +; mal 2− = malonate, −OOCCH 2COO −; Memal − = monomethyl malonate, −OOCCH 2COOCH 3; Etmal − = monoethyl malonate, −OOCCH 2COOC 2H 5 and Prmal − = monopropyl malonate, −OOCCH 2COOC 3H 7). The complex anions of compounds 1– 8 have a common structural feature: a dinuclear, singly metal–metal bonded {Mo 2O 4} 2+ core with the carboxylate moiety of the malonato ligand coordinated in a syn– syn bidentate bridging manner to the pair of metal atoms. The remaining four coordination sites of the {Mo 2O 4} 2+ core are occupied with halides in 1 and 2, with halides/pyridine ligands in 5– 8, with a pair of bidentate malonate ions in 4 and with the combination of all in 3. The neutral molecules of 9 consist of two {Mo 2O 4} 2+ cores linked with a pair of methoxide ions into a chain-like, tetranuclear cluster. An esterification of malonic acid was observed to take place in the reaction mixtures containing alcohols. Solvothermal reactions with malonic acid carried out at 115 °C produced anionic acetato complexes as found in (PyH)[Mo 2O 4Cl 2(μ 2-OOCCH 3)Py 2] · Py ( 10), (PyH)[Mo 2O 4Cl 2(μ 2-OOCCH 3)Py 2] ( 11), (3,5-LutH)[Mo 2O 4Cl 2(μ 2-OOCCH 3)(3,5-Lut) 2] ( 12) and (4-MePyH) 3[Mo 2O 4Cl 2(μ 2-OOCCH 3)(4-MePy) 2] 2Cl ( 13) (4-MePy = 4-methylpyridine, C 6H 7N). The acetate coordinated in the syn– syn bidentate bridging mode in all. Reactions of (PyH) 5[MoOCl 4(H 2O)] 3Cl 2 with succinic acid (H 2suc) at ambient conditions resulted in a complex with a half-neutralized acid, (PyH)[Mo 2O 4Cl 2(μ 2-Hsuc)Py 2] · Py ( 14) (Hsuc − = hydrogen succinate, −OOC(CH 2) 2COOH), while those carried out at 115 °C in a tetranuclear succinato complex, (4-MePyH) 2[{Mo 2O 4Cl 2(4-MePy) 2} 2(μ 4-suc)] ( 15) (suc 2− = succinate, −OOC(CH 2) 2COO −). The tetranuclear anion of 15 consists of two {Mo 2O 4} 2+ cores covalently linked with a tetradentate succinato ligand. The compounds were fully characterized by infrared vibrational spectroscopy, elemental analyses and X-ray diffraction studies.