A study of cation-dependent inverse hydrogen bonds and magnetic exchange-couplings in lanthanacarborane complexes

Ten lanthanacarborane complexes were synthesized to study the rare B-H^δ-∙∙∙Mⁿ⁺ inverse hydrogen bonds (IHBs). The average bonding energy of B-H^δ-∙∙∙Ln³⁺ is theoretically determined to be larger than 24 kJ/mol, which is comparable to moderately strong hydrogen bonds (21-56 kJ/mol). In addition to NMR and IR, magnetometer was used to study the exchange-coupling interaction via such B-H^δ-∙∙∙Ln³⁺ IHBs in detail, and the coupling constant is determined to be -2.0 cm^-1, which is strong enough to compare with single-atom bridged dysprosium(III) complexes. Two imidazolin-iminato incorporated complexes have shown energy barrier for magnetization reversal larger than 1000 K, and the exchange-biasing effects are evident. Moreover, the bonding strengths of B-H^δ-∙∙∙Mⁿ⁺ IHBs are cation-dependent. If M = Na, the B-H^δ-∙∙∙Na⁺ bonding energy is reduced to 14 kJ/mol, and the dimerization process is no longer reversible. The exchange-biasing effect is also disappeared. We believe such a finding extends our knowledge of IHBs.