Solvent effects on the structures and magnetic properties of two doubly interpenetrated metal–organic frameworks

Abstract

Two doubly interpenetrated coordination polymers [Co₂(BDC)₂(bpt)₂]·nSolvent based on dimeric secondary building units and crystallizing with distinct solvent molecules (1-H₂O and 2-MeOH for nSolvent = 2H₂O and MeOH·H₂O, respectively) were obtained by employing 1,4-benzenedicarboxylate (BDC) and 1H-3,5-bis(4-pyridyl)-1,2,4-triazole) (bpt) as linkers. The structures consist of a square grid of dimers bridged by BDC and pillared by bpt. Thermogravimetry and PXRD indicate that the frameworks are stable and are retained up to 400 °C, but the structures are modified irreversibly. 1-H₂O, high-symmetry Pna2₁, exhibits antiferromagnetic coupling within the dimer, while 2-MeOH, low-symmetry P2₁/n, exhibits ferromagnetic coupling. Upon desolvation, the 1-de and 2-de couplings are antiferromagnetic but reduced. Subsequent resolvation to 1′-H₂O and 2′-MeOH resulted in a slight increase of the antiferromagnetic coupling without attaining the virgin states. The interesting difference of magnetic properties between 1-H₂O and 2-MeOH, the solvated/desolvated phases, particularly at low temperature, indicates that there is a prominent solvent effect.