Solvent-controlled structural diversity observed in three Cu(II) MOFs with a 2,2′-dinitro-biphenyl-4,4′-dicarboxylate ligand: Synthesis, structures and magnetism

Three extended three-dimensional Cu^II-based metal-organic frameworks (MOFs) have been separated successfully from reactions of 2,2′-dinitro-biphenyl-4,4′-dicarboxylate (H₂dnpdc) and Cu(NO₃)₂ under controllable solvothermal conditions. The resulting structures of the MOFs are highly dependent on the solvent used during the synthesis. Compound 1, [Cu(dnpdc)(H₂O)]_n·(DMA)₄(H₂O)₂, is a two-fold interpenetrated three-dimensional framework with NbO topology based on a binuclear [Cu₂(O₂C)₄] "paddle-wheel" secondary building unit. In compound 2, [Cu₉(dnpdc)₆(OH)₆(H₂O)₂]_n·{(DMF)₈(EtOH)₃(H₂O)₁₂}_n, the complicated one-dimensional [Cu(OH)(OCO)]_n chains are cross-linked into three-dimensional frameworks by the dnpdc^2- ligands. Compound 3, {Cu₄(dnpdc)₃(OH)₂(py)₄}_n, displays three-dimensional nets with pcu topology based on 6-connected [Cu(μ₃-OH)₂(OCO)₄] tetracopper clusters. Magnetically, compound 2 exhibits homo-spin topological ferrimagnetic behavior. Compound 3 features antiferromagnetic interactions mediated by μ₃-OH and syn-syn-OCO heterobridges between the Cu^II ions.