Cross-linking of cyanide magnetic coordination polymers by rational insertion of formate, cyanide or azide

Abstract

Carefully selected molecular bridging ligands formate, cyanide and azide, that are known to transmit strong magnetic interactions, have been successfully inserted into the {[Mn^II(H₂O)₂]₂[Nb^IV(CN)₈]·4H₂O}_n (Mn₂Nb) ferrimagnetic parent framework, resulting in the additional molecular bridging of the two Mn^II centres in three new coordination polymers: {(NH₄)[(H₂O)Mn^II-(μ-HCOO)-Mn^II(H₂O)][Nb^IV(CN)₈]·3H₂O}_nMn₂NbHCOO, {(NH₄)[(NH₃)Mn^II-(μ-CN)-Mn^II(H₂O)][Nb^IV(CN)₈]·2H₂O}_nMn₂NbCN and {(NH₄)[(H₂O)Mn^II-(μ-N₃)-Mn^II(H₂O)][Nb^IV(CN)₈]·3H₂O}_nMn₂NbN₃. The extra bridging ligands cross-linking the two Mn^II centers strongly influence the long-range ferrimagnetic order of the Nb^IV–CN–Mn^II parent framework by introducing competing antiferromagnetic interactions. The values of the J_MnMn constants were obtained by fitting the magnetic properties of the Mo^IV congeners {(NH₄)[(H₂O)Mn^II-(μ-HCOO)-Mn^II(H₂O)][Mo^IV(CN)₈]·3H₂O}_nMn₂MoHCOO, {(NH₄)[(NH₃)Mn^II-(μ-CN)-Mn^II(H₂O)][Mo^IV(CN)₈]·2H₂O}_nMn₂MoCN and {(NH₄)[(H₂O)Mn^II-(μ-N₃)-Mn^II(H₂O)][Mo^IV(CN)₈]·3H₂O}_nMn₂MoN₃, where the paramagnetic Nb^IV was substituted by the diamagnetic Mo^IV, thus disabling the long-range magnetic ordering of the CN-framework. Our strategy demonstrates how chemists can control the magnetic behavior of molecular magnets by subtle and rational structural modification based on chemical knowledge.