The crystal structure of [Mg(dmso)][BPh] and the formation mechanism of the conformer on the basis of conformational analysis

The crystal structure of a new magnesium( ii ) complex, [Mg(dmso) 6 ][BPh 4 ] 2 ( 1 ) (dmso: dimethylsulfoxide), was determined, and the reason for the observed structure was clarified by conformational analysis. For a dmso-ligand arm, three conformations, α, β, and γ, are possible. The α-arm is the most energetically favourable and is suitable for reducing the steric repulsion between the arms; the β-arm is less energetically favourable, but can be stabilized by interaction with surroundings ( e.g. CH π interaction); the γ-arm is not energetically favourable, but is effective in reducing the size of the complex cation. From the conformational analysis, the most stable conformer of the [Mg(dmso) 6 ] 2+ complex cation was found to be the α 6 conformer, and the complex cation in dmso solution was predicted to exist as a mixture of α 6 , α 5 β, and trans -α 4 β 2 species. On the contrary, in the crystal structure, the trans -β 2 γ 4 species, considered to be unstable, was observed. From the conformational analysis in the tetraphenylborate surroundings, the trans -β 2 γ 4 structure was found to become more stable, due to its small size suitable for crystal packing with bulky tetraphenylborate anions. The crystal structure of a new magnesium( ii ) complex, [Mg(dmso) 6 ][BPh 4 ] 2 ( 1 ) (dmso: dimethylsulfoxide), was determined, and the reason for the observed structure was clarified by conformational analysis.