Ternary and higher order phases comprising a rare earth metal, boron, and carbon show a particularly rich and varied structural chemistry. These structure types can be classified in three different families according to the dimensionality of the boron-carbon sublattice: two-dimensional (2D) networks, one-dimensional (ID) zigzag chains, or finite, linear units of various lengths."] Such compounds are attractive not only as new materials with interesting physical properties, but also simply as solid-state analogues of molecular organic and organometallic compounds containing all-carbon ligands. ['] Finite boron -carbon units stabilized in metallic lattices are rather scarce and limited in length to three or four atoms as demonstrated in the metal-and carbon-rich compounds Sc,BC2
Ce,B,C6,f41 La,BC,Br,, and Ce,B2C3Br3 .I5] We report herein on the characterization of chains with up to 13 atoms that are contained in new cerium, lanthanum, and neodynium boride carbide materials. Lai5B,,C,9, MioB,Ci2 (M = La, Ce, Nd), and Ce,B,C, are obtained as lustrous black pellets by arc melting and subsequent annealing of the elements for several days.@] In all compounds, the metallic sublattice can be described as resulting from an irregular stacking of slightly corrugated 2D square nets, which gives rise to a three-dimensional (3D) framework with metal-metal separations between 3. 40 and 4.10 A.19] This leads to the formation of small channels of different sizes in which roughly linear B,C, units are inserted (Fig. 1). Two kinds of eleven-membered units, B,C7 and B,C6, are embedded in the structure of La,,B,,C,,, corresponding to the formula contains a thirteen-membered B,C, chain (the longest so far observed in these materials) and an eight-membered B,C, chain, corresponding to the Ceio(B5C,)-(B,C,) formula. Ce,B,C, con-.ce tains eight-membered B,C, and O C six-membered B3C3 units, in addition to single C atoms and the already known BC, group, giving rise to the formula Ce,,(B,C,)-