ChemInform Abstract: 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]ₙ⁸ⁿ⁻ 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.