Ruthenium intermetallics grown from La-Ni flux: synthesis, structure, and physical properties.

Crystals of three new intermetallic compounds were grown from reactions of ruthenium with other elements in La(0.8)Ni(0.2) eutectic flux. The new boride LaRu(2)Al(2)B crystallizes in a filled CeMg(2)Si(2) structure type (P4/mmm, a = 4.2105(5) A, c = 5.6613(8); Z = 1, R(1) = 0.014), with Ru atoms forming a planar square net; B atoms center alternating Ru squares, which is an unusual coordination of boron by transition metals. Al atoms connect the Ru(2)B layers, forming large voids where La ions reside. The chemical bonding analysis using the electron localization function (ELF) reveals two-center covalent bonding between Al atoms, an absence of direct Ru-Ru interactions, and three-centered bonds between Ru and B or Al atoms. The band structure calculation shows LaRu(2)Al(2)B to be metallic, which is in agreement with the observed temperature independent paramagnetism and heat capacity data. The crystal structure of La(2)Ni(2-x)Ru(x)Al (HT-Pr(2)Co(2)Al-type; x = 0.21(1) and x = 0.76(1); C2/c; a = 9.9001(3) A, b = 5.7353(1) A, c = 7.8452(2) A, beta = 104.275(1); Z = 4, R(1) = 0.016 for x = 0.76(1)) features infinite [Ni(2-x)Ru(x)Al] spiral-twisted chains composed of Al(2)M(2)-rhombic units (M = Ni/Ru) seen in many La-Ni-Al intermetallics. The structure of La(6)SnNi(3.67)Ru(0.76)Al(3.6) (Nd(6)Co(5)Ge(2.2)-type; P6m2, a = 9.620(1) A, c = 4.2767(9) A; Z = 1, R(1) = 0.015) is composed of a three-dimensional Ni(3.67)Ru(0.76)Al(3.6)(infinity) network with large hexagonal channels accommodating interconnected tin-centered lanthanum clusters Sn@La(9).