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The pnictides RE(2)Mn(3)Cu(9)Pn(7) (Pn = P, As) have been prepared by stoichiometric reaction of the elements at 800 °C. They are quaternary ordered variants of the hexagonal Zr(2)Fe(12)P(7)-type structure (Pearson symbol hP21, space group P6, Z = 1; a = 9.6444(3)-9.5970(7) Å, c = 3.9027(1)-3.7761(3) Å for RE(2)Mn(3)Cu(9)P(7) (RE = La-Nd, Sm, Gd-Dy); a = 9.9376(6)-9.9130(3) Å, c = 4.0194(2)-3.9611(1) Å for RE(2)Mn(3)Cu(9)As(7) (RE = La-Nd)). Of the four possible sites available for the transition metal, the square pyramidal site (CN5) is occupied preferentially by Mn atoms, whereas the three tetrahedral sites (CN4) are occupied by Cu atoms. On proceeding to smaller RE members in the RE(2)Mn(3)Cu(9)Pn(7) series, one of the transition-metal-centered polyhedra (Cu1) tends to become less distorted, while the remaining three (Cu2, Cu3, Mn4) become more distorted. Band structure calculations on La(2)Mn(3)Cu(9)P(7) confirm that Mn-P and Cu-P contacts provide the strongest bonding interactions. Electrical resistivity measurements on Ce(2)Mn(3)Cu(9)P(7) reveal metallic behavior with transitions at 165 and 18 K, probably of magnetic origin.

The title compounds are prepared from the elements (800 °C, 10 d) and characterized by powder and single crystal XRD, electrical resistivity measurements, and TB-LMTO-ASA band structure calculations.

The quaternary rare-earth phosphides REMnCu(4)P(3) (RE = Gd-Ho) were obtained from direct reactions of the elements at 800 °C. They are the first examples in which ordering of two different transition-metal atoms takes place within the orthorhombic YCo(5)P(3)-type structure [Pearson symbol oP36, space group Pnma, Z = 4; a = 12.667(2)-12.6489(4) Å, b = 3.8119(7)-3.7755(1) Å, and c = 10.895(2)-10.8632(4) Å for RE = Gd-Ho]. Columns of trigonal prisms centered by P atoms are connected in propellor-shaped units in zigzag arrangements to generate square-pyramidal (CN5) sites that are occupied by Mn atoms and tetrahedral sites (CN4) that are occupied by Cu atoms. Spin-polarized band-structure calculations predict that the hypothetical compound YMnCu(4)P(3) will exhibit magnetic ordering. Electrical resistivity measurements on TbMnCu(4)P(3) indicate a poor metal.

The pnictides Ln2Mn3Cu9P7 (Ln: La—Nd, Sm, Gd—Dy) and Ln2Mn3Cu9As7 (Ln: La—Nd) are prepared from stoichiometric mixtures of the elements (800 °C, 14 d).