Mixed Alkali Metal/Transition Metal Coordination Polymers with the Mellitic Acid Hexaanion: 2-Dimensional Hexagonal Magnetic Nets

Abstract

The hexaanion of mellitic acid, mel = (C(6)(CO(2))(6))(6-), links metal ions into extensively connected magnetic coordination polymers. Reaction of alkali metal mellitate salts, M(6)(mel) (M = K, Rb), with M'Cl(2) precursors (M' = Mn, Co, Ni) under mild (473 K) hydrothermal conditions yields an extensive family of isostructural 3-dimensional mixed alkali metal/transition metal polymers of general formula M(2)[M'(2)(mel)(OH(2))(2)] (M/M' = K/Mn (1a); K/Co (1b); K/Ni (1c); Rb/Mn (2a); Rb/Co (2b); Rb/Ni (2c)). These materials incorporate distorted 2-dimensional magnetic hexagonal nets with a honeycomb topology that are exclusively based on metal-carboxylate-metal bridging interactions. A further isostructural alkali metal-free Co(2+) material with NH(4)(+) cations, (NH(4))(2)[Co(2)(mel)(OH(2))(2)] (3), produced by reaction of H(6)mel with [Co(NH(3))(6)]Cl(3) is also presented. The magnetic susceptibility data for 1a-c, 2a-c, and 3 are presented. The susceptibility data for the Mn(II)- and Ni(II)-containing phases have been analyzed using a simple Mean Field Theory approach, and have been modeled using a high temperature series expansion. The comparative magnetism of the Co(II) phases is also presented, and is more complicated because of significant spin-orbit coupling effects.