Coexistence of ferromagnetism and metallic conductivity in a molecule-based layered compound

Crystal engineering-the planning and construction of crystalline supramolec ular architectures from modular building blocks-permits the rational design of functional molecular materials that exhibit technologically useful beha viour such as conductivity and superconductivity(1), ferromagnetism(2) and nonlinear optical properties(3). Because the presence of two cooperative pr operties in the same crystal lattice might result in new physical phenomena and novel applications, a particularly attractive goal is the design of mo lecular materials with two properties that are difficult or impossible to c ombine in a conventional inorganic solid with a continuous lattice. A promi sing strategy for creating this type of 'bi-functionality' targets hybrid o rganic/inorganic crystals comprising two functional sub-lattices exhibiting distinct properties. In this way, the organic pi -electron donor bis(ethyl enedithio)tetrathiafulvalene (BEDT-TTF) and its derivatives, which form the basis of most known molecular conductors and superconductors(1), have been combined with molecular magnetic anions, yielding predominantly materials with conventional semiconducting or conducting properties(4,5), but also sy stems that are both superconducting and paramagnetic(6,7). But interesting bulk magnetic properties fail to develop, owing to the discrete nature of t he inorganic anions. Another strategy for achieving cooperative magnetism i nvolves insertion of functional bulky cations into a polymeric magnetic ani on, such as the bimetallic oxalato complex [(MnCrIII)-Cr-II (C2O4)(3)](-), but only insoluble powders have been obtained in most cases(8-12). Here we report the synthesis of single crystals formed by infinite sheets of this m agnetic coordination polymer interleaved with layers of conducting BEDT-TTF cations, and show that this molecule-based compound displays ferromagnetis m and metallic conductivity.