Different magnetic responses observed in Co-4(II), Co-3(II) and Co-1(II)-based MOFs

Four magnetic MOFs with anisotropic Co-II ions, {[Co-5(H2O)(2)(mu(3)-OH)(2)(atz)(2)(stp)(2)]center dot 1.5H(2)o}(n) (1), {[Co-5(H2O)(2)(mu(3)-OH)(2)(trz)(2)(stp)(2)]center dot 1.3H(2)O}(n) (2), {[Co-5(H2O)(6)(mu(3)-OH)(2)(trz)(2)(stp)(2)]center dot 2.5CH(3)OH}(n) (3) and {[Co-3(H2O)(4)(Hdatrz)(2)(stp)(2)]center dot 3H(2)O}(n) (4) (stp(3-)= 2-sulfoterephthalate, trz(-) = 1,2,4-triazolate, atz(-) = 3-amino-1,2,4-triazolate and Hdatrz = 3,5-diamino-1,2,4-triazole) were solvothermally isolated by varying the substituent groups appended on the N-heterocyclic triazole and structurally and magnetically characterized. Structural analyses indicate that the former two complexes are crystallographically isostructural, exhibiting pillared-layer frameworks with mixed triazolyl and carboxylate extended Co-4(II) + Co-1(II) layers supported by rigid stp(3-) connectors. Complex 3 is built from butterfly-shaped CoII 4 cluster-based layers, which are interconnected with single cobalt(II) octahedra by ditopic stp(3-) bridges. By contrast, complex 4 consists of linear {Co-3(mu-N1,N4-Hdatrz)(2)} subunits, which are extended by 3-connected stp(3-) linkers into a stable 3D framework. Magnetically, 1 exhibits ferromagnetic ordering below 2.7 K due to the well-organized alignment of the non-compensated resultant moment from octahedra and tetrahedral cobalt(II) carriers, while 3 is in a non-zero paramagnetic state above 2.0 K resulting from the coexistence of intermetallic ferromagnetic and antiferromagnetic interactions. The magnetic competition between weak inter-subunit antiferromagnetic interactions and the external magnetic field makes 4 behave as a field-induced metamagnet with a critical field of 27.5 kOe. These interesting magnetostructural results suggest that the anisotropy of the moment carrier and the interlayer/intersubunit separations significantly dominate the magnetic responses in extended MOFs, providing an informative platform for the further development of interesting magnetic materials, both of academic and industrial interest.