Two-Dimensional Metal−Organic Frameworks: A System with Competing Chelating Ligands

We report the synthesis, structure, and magnetism of two coordination polymers with a designed network topology. These isostructural materials are hydrothermally crystallized having a composition of M(en)(ox) (en = ethylenediamine, ox = oxalate, M = Co(II) 1 and Ni(II) 2). The structures show a rare bridging mode of ethylenediamine which links linear [M(ox)]∞ chains into an oblique two-dimensional network. Both compounds show antiferromagnetic interactions behaving as one-dimensional magnets. The magnetism of 1 is consistent with an S = 3/2 chain affected by spin−orbit coupling (g = 2.814(2), J/kB = −16.03(3) K, D/kB = 86.2(4) K), while 2 is a candidate Haldane antiferromagnet (g = 2.194(2), J/kB = −39.3(1), Eg/kB = 16.5 K). We discuss the use of models for S = 3/2 antiferromagnetic chains and present our own polynomial for Heisenberg S = 3/2 antiferromagnetic chains.