Antiferro- and Ferromagnetic Interactions in Mn(II), Co(II), and Ni(II) Compounds with Mixed Azide−Carboxylate Bridges

A series of transition metal coordination polymers with azide and flexible zwitterionic dicarboxylate ligands was synthesized and structurally and magnetically characterized. These compounds are formulated as [M2(L1)(N3)4] (L1 = 4,4′-trimethylenedipyridinio-N,N′-diacetate and M = Mn, 1; Co, 2; and Ni, 3) and [ML2(N3)6(H2O)2] (L2 = 4,4′-dipyridinio-N,N′-diacetate and M = Mn, 4; Co, 5). The isomorphous compounds 1−3 consist of two-dimensional coordination layers in which the anionic uniform chains with mixed triple bridges (two end-on (EO) azides and a syn−syn carboxylate) are cross-linked by the flexible cationic 4,4′-trimethylenedipyridinium spacers, while the isomorphous compounds 4 and 5 consist of alternating chains with triple (two EO azides plus a carboxylate) and double (two end-to-end azides) bridges, the 4,4′-dipyridinium spacers serving as side bridges along the chain. Magnetic studies demonstrated that the triple bridge transmits antiferromagnetic coupling in the Mn(II) compounds (1 and 4) but ferromagnetic coupling in the Co(II) and Ni(II) species (2, 3, and 5). The differences have been discussed in terms of the collaboration or competition between the carboxylate and azide pathways. Compound 4 exhibits alternating antiferromagnetic interactions, while alternating ferromagnetic−ferromagnetic−antiferromagnetic interactions with spin canting are suggested for 5.