Structural motif-dependent magnetic diversity observed in three-dimensional tetrazolyl-based MMOFs: synthesis, structures and magnetism

Abstract

Three extended three-dimensional (3D) magnetic metal–organic frameworks (MMOFs), {[Mn₃(H₂O)₂(atz)₄Cl₂]·2CH₃OH}_n (1), {[Mn₂(H₂O)(atz)₂(ip)]·C₂H₅OH}_n (2) and {[Mn₂(H₂O)₂(atz)(btc)]·3H₂O·0.7CH₃OH}_n (3) (atz⁻ = 5-aminotetrazolate, ip²⁻ = isophthalate and btc³⁻ = 1,3,5-benzenetricarboxylate), were respectively obtained by varying the coligands with different numbers of functionalities and molecular topology, and structurally and magnetically characterized. Complex 1 exhibits an eight-connected 3⁶·4¹⁸·5³·6 topological network with linear Mn^II₃ subunits periodically linked by ditopic atz⁻ connectors. Complex 2 possesses a pillared-layer framework constructed from undulated {Mn₂(atz)₂} layers and bidirectional ip²⁻ spacers. By contrast, 3 consists of bent one-dimensional (1D) {Mn(atz)} ribbons, which are crosslinked through the carboxylate groups of tripodal btc³⁻ connectors to generate a 3D architecture. Structural analysis reveals that the interesting motifs of 1–3 and their diverse linkages are significantly dominated by the cooperate coordination of the mixed ligands to the octahedral Mn^II ion. Magnetically, 1 displays ferrimagnetic behavior resulting from the periodic arrangement of the net moment in the Mn^II₃ subunit, which is scarcely observed in the homometallic azolate systems. Complex 2 features unusual coexistence of spin-canted antiferromagnetic behavior and field-induced spin-flop transition due to the asymmetric magnetic superexchange within the two-dimensional (2D) {Mn₂(atz)₂} sublayer. By contrast, only antiferromagnetic ordering is observed in the 1D {Mn(atz)} ribbon of 3. These interesting results suggest that the diverse structural motifs by the cooperate coordination of octahedral Mn^II ion with the N-rich tetrazolyl group can more significantly direct the magnetic behaviors and could be hopefully utilized upon the construction of novel MMOFs.