Ancillary Ligand Effect on the Properties of “Mg(thd)2” and Crystal Structures of [Mg(thd)2(ethylenediamine)]2, [Mg(thd)2(tmeda)], and [Mg(thd)2(trien)]1

Complexes [Mg(thd)2(A)] (Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione; A = ethylenediamine, en (2); N,N'-dimethylethylenediamine, dmeda (3); N,N'-diethylethylenediamine, deeda (4); N,N,N',N'-tetramethylethylenediamine, tmeda (5); diethylenetriamine, dien (6); triethylenetetra-amine, trien (7); 1,2-ethanediol (8)) and [Mg(thd)2(EtOH)]2(1,3-propanediol) (9) were prepared and characterized by NMR spectroscopy, mass spectrometry, and thermal analysis. Crystal structures of compounds 2, 5, and 7 are presented. In all structures, Mg exhibits distorted six-coordination, with four shorter distances between Mg and keto-oxygens and two longer distances between Mg and nitrogen atoms (2, 5, 7). The structure of 2 consists of two monomeric complexes which form an asymmetric unit. The structure of 7 is similar to 2, but the trien molecule has coordinated through one terminal and one vicinal N atom to Mg. All complexes containing amines evaporated almost completely, but the complex 8, which contained 1,2-ethanediol, was thermally unstable and decomposed when heated. At temperatures below the dissociation temperature, all adducts of diamines appeared to evaporate intact.