Abstract
The title compound is obtained in high yield from a two-step reaction of K with Si in sealed tantalum and then of that product with As in silica at 800-900°C. Ion exchange with NaI at 500°C gives the sodium derivative. The structure of the purple KSi <sub>3</sub> A <sub>3</sub> crystals has been established by X-ray diffraction means at room temperature (orthorhombic, space group Pbam, Z = 4, a = 10.010 (4) Å, b = 19.139 (8) Å, c = 3.664 (1) Å, R = 0.044 for 674 reflections, 2θ < 55°). The <sup>2</sup> <sub>∞</sub> [Si <sub>3</sub> As <sub>3</sub> ] <sup>-</sup> anion layers may be generated by Si-Si bonding between puckered Si <sub>3</sub> As <sub>3</sub> (As) rings to form chains followed by side-by-side condensation of these to sheets. The structure may be derived from the layered structure of SiAs in a concerted way through reductive ring opening and Si-Si bond formation. Comparisons are also made with more reduced Si-As anion chains and clusters and with the closely related Li <sub>3</sub> NaSi <sub>6</sub> . K <sub>2</sub> SiAs <sub>2</sub> has also been synthesized and shown to be isostructural with K <sub>2</sub> SiP <sub>2</sub> . © 1987 American Chemical Society.