A structurally perfect S = 1/2 metal-organic hybrid kagomé antiferromagnet.

Geometric spin frustration occurs when the structural arrangement of spins precludes the simultaneous satisfaction of all nearestneighbor interactions.1,2 The corner-sharing equilateral triangles of a kagomé lattice present an excellent construct on which to study spin frustration; spin liquid physics can result when the kagomé lattice features S ) /2 spins on lattice vertices.3-5 However, compounds bearing the kagomé structural motif are rare,6-10 and exceptionally so when an organic moiety is a structural constituent of the kagomé triangles.11-14 Previous studies of spin frustration on metal-organic hybrid kagomé compounds have been complicated by long exchange pathways,15,16 triangulated17,18 or interpenetrating structures,19 and spin centers composed of dimers displaying intradimer exchange interactions.20-23 There are some structurally distorted metal-organic hybrid kagomés with isolated metal ions (Co-Zn-Cd) on the vertices11 and fewer structurally perfect systems (In, V, Zn);12-14 none are composed of S ) /2 magnetic ions. We report herein the synthesis and magnetic characterization of the first structurally perfect metal-organic hybrid kagomé with a spin of S ) /2 on lattice vertices. We recently employed a hydrothermal approach to prepare the first structurally perfect S ) /2 kagomé all-inorganic antiferromagnet, herbertsmithite ZnCu3(OH)6Cl2. This remarkable material shows no long-range ordering to 50 mK,24 despite having strongly antiferromagnetic nearest-neighbor superexchange, as evidenced by ΘCW ) -314 K. We have subsequently sought to generalize the S ) /2 kagomé lattice by discovering new systems that can be prepared in crystalline form. Initial treatment of Cu(OH)2 with isophthalic acid (1,3-bdcH2) under hydrothermal conditions led to the formation of a novel metal-organic hybrid kagomé, Cu(1,3-bdc) (1), according to the condensation reaction below: