Ca4Ni3C5, a Carbide with an One-Dimensionally Infinite Nickel-Carbon Polyanion, and CaPd3C, a Perovskite Carbide

Abstract

The new carbides Ca4Ni3C5 and CaPd3C were prepared from the elemental components by arc melting and subsequent annealing at 700 °C. The structure of Ca4Ni3C5 was determined from single-crystal X-ray data. It crystallizes in the monoclinic space group C2/m, a = 1108.7(3) pm, b = 377.1(1) pm, c = 983.9(2) pm, β = 112.58(2)°, Z = 2. Powder data show CaPd3C to have the cubic perovskite structure with a = 414.1(2) pm. While the carbon atoms in CaPd3C are isolated from each other, they form C2 pairs in Ca4Ni3C5 with the typical triple bond C-C distance of 120(2) pm. In addition to the C2 pairs there are isolated carbon atoms in distorted octahedral coordination of four Ni atoms forming a square, which is augmented by two Ca atoms. In the one-dimensionally infinite polyanion [Ni3C5]n 8n- these CNi4 squares are condensed by sharing two Ni atoms at opposite corners of the squares. A C2 pair is attached to each of the other Ni atoms in an end-on configuration. Chemical bonding within this polyanion is briefly discussed on the basis of the 18- and 8-electron rules for the Ni and C atoms, respectively. Ca4Ni3C5 is diamagnetic with a susceptibility of χ = – 12(± 5) × 10-9 m3/mol.