Structure and Properties of Magnesium Complexes with Bulky β-Diketones: 2,2,6,6-Tetramethylheptane-3,5-dione and Its Methoxy-Substituted Derivative

In order to study the effect of bulky terminal substituents in the β-diketonate ligand on the structure and properties of volatile magnesium compounds, complexes with 2,2,6,6-tetramethylheptane-3,5-dione (HThd) and, for the first time, with 2-methoxy-2,6,6-trimethylheptane-3,5-dione (HZis) were obtained. The complexes [Mg₂(L)₄] (L = Thd (I), Zis (II)), the synthesis intermediates [Mg(H₂O)₂(L)₂] (L = Thd (III), Zis (IV)), and aqua derivative [Mg₂(H₂O)(Zis)₄] (V) were characterized by elemental analysis and IR spectroscopy. The structures of binuclear complexes and the synthesis by-product [Mg₇(Zis)₆(μ-OH)₆]Cl₂·5CHCl₃ (VI) were established by X-ray diffraction (CCDC nos. 2424128 (Ia, a new polymorph), 2424130 (II), 2424129 (V), 2424126 (V·1/2CHCl₃), 2424127 (VI) ). Both [Mg₂(L)₄] molecules are characterized by asymmetric environment of metal centers (the Mg coordination number (C.N.) is 5, 6), but in I, three μ,κ²:¹-ligands occupy bridging positions, while in II, two ligands have different coordinations (μ,κ²:κ¹ and μ,κ²(O,O'):κ²(O',O_OMe)). The inclusion of water in II to give V is not associated with any significant structural rearrangement, but C.N. of the unsaturated metal center changes from 5 to 6. Thermogravimetric analysis showed that complex I is more volatile and low-melting than II.