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

The hexaanion of mellitic acid, mel = (C<sub>6</sub>(CO<sub>2</sub>)<sub>6</sub>)<sup>6−</sup>, links metal ions into extensively connected magnetic coordination polymers. Reaction of alkali metal mellitate salts, M<sub>6</sub>(mel) (M = K, Rb), with M′Cl<sub>2</sub> 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<sub>2</sub>[M′<sub>2</sub>(mel)(OH<sub>2</sub>)<sub>2</sub>] (M/M′ = K/Mn (<b>1a</b>); K/Co (<b>1b</b>); K/Ni (<b>1c</b>); Rb/Mn (<b>2a</b>); Rb/Co (<b>2b</b>); Rb/Ni (<b>2c</b>)). 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<sup>2+</sup> material with NH<sub>4</sub><sup>+</sup> cations, (NH<sub>4</sub>)<sub>2</sub>[Co<sub>2</sub>(mel)(OH<sub>2</sub>)<sub>2</sub>] (<b>3</b>), produced by reaction of H<sub>6</sub>mel with [Co(NH<sub>3</sub>)<sub>6</sub>]Cl<sub>3</sub> is also presented. The magnetic susceptibility data for <b>1a</b>−<b>c</b>, <b>2a</b>−<b>c</b>, and <b>3</b> 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.