Synthesis and Crystal Structure of KLa[C(CN)3]4·H2O containing a Shielded Potassium Ion

KLa[C(CN)3]4·H2O was crystallized from an aqueous solution containing La(NO3)3·6H2O and K[C(CN)3]. The crystal structure was solved and refined from X-ray single crystal data (P4/n, Z = 2, a = b = 12.379(1) A, c = 6.5695(8) A, V = 1006.7(2) A3). Solid KLa[C(CN)3]4·H2O forms a framework structure with bridging tricyanomethanide ions, each of them connecting two La3+ ions and one K+ ion. Potassium is apparently situated in a tetrahedral environment with four K–N distances of 2.741(3) A, shielded by four other tricyanomethanide ions. Each La3+ has a square antiprismatic coordination of nitrogen atoms from eight [C(CN)3]– ions, and this antiprism is mono-capped by one water molecule.