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)](infinity) chains into an oblique two-dimensional network. Both compounds show anti ferromagnetic 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/k(B) = - 16.03(3) K, D/k(B) = 86.2(4) K), while 2 is a candidate Haldane antiferromagnet (g = 2.194(2), J/k(B) = -39.3(1), E-g/k(B) = 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.