Y7I12C2N - A COMPOUND WITH UNITS OF 2 Y-6 (C-2) OCTAHEDRA AND A Y6N2 DOUBLE TETRAHEDRON

The new compounds Y7I12C2N and Ho7I12C2N have been prepared by reactio n of stoichiometric amounts of the metals (RE), REI(3), REN and C in c losed Ta capsules at 1150 and 1120 K, respectively. Pure samples of th e compounds were obtained after 5 days annealing time. The crystals wi th xenomorphic shape are olive-green (Y7I12C2N) or red-brown (Ho7I12C2 N) in colour and sensitive to air and moisture. Y7I12C2N crystallizes in the space group P (1) over bar: (No. 2) with lattice constants a = 971.24(7), b = 1030.38(7), c = 1673.58(11) pm and alpha = 101.366(5), beta = 92.758(5), gamma = 112.799(5)degrees. According to Guinier phot ographs Ho7I12C2N is isotypic with the lattice constants a = 968.8(3), b = 1028.7(3), c = 1667.8(5) pm and alpha = 101.31(2), beta = 92.78(2 ), gamma = 112.80(1)degrees. In the structure the C atoms are present as C-2 units with a C-C distance of 144 pm. These C-2 units are octahe drally coordinated by Y atoms (o(1)). The N atoms are in the center of Y-4 tetrahedra, which are linked via a common edge to form double tet rahedra (t(2)). By condensation of N-centered double tetrahedra (t(2)) with a C-2-centered Y octahedron (o(1)) the characteristic units o(1) t(2)o(1) are formed. The I atoms coordinate all free edges and corners of these units and connect them via I-i-I-a contacts parallel [100] a nd [001]. The compounds are semiconducting. Ho7I12C2N exhibits Curie-W eiss behaviour with theta = 15(1) K and mu(eff) = 10.5(1) mu(B).