The crystal structure of [Mg(dmso)(6)][BPh4](2) and the formation mechanism of the conformer on the basis of conformational analysis

摘要

The crystal structure of a new magnesium(ii) complex, [Mg(dmso)(6)][BPh4](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, alpha, beta, and gamma, are possible. The alpha-arm is the most energetically favourable and is suitable for reducing the steric repulsion between the arms; the beta-arm is less energetically favourable, but can be stabilized by interaction with surroundings (e.g. CH pi interaction); the gamma-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 alpha(6) conformer, and the complex cation in dmso solution was predicted to exist as a mixture of alpha(6), alpha(5)beta, and trans-alpha(4)beta(2) species. On the contrary, in the crystal structure, the trans-beta(2)gamma(4) species, considered to be unstable, was observed. From the conformational analysis in the tetraphenylborate surroundings, the trans-beta(2)gamma(4) structure was found to become more stable, due to its small size suitable for crystal packing with bulky tetraphenylborate anions.