Synthesis, structure and properties of Nd2BC containing the trans-dibora–(1,3)-butadiene [C=B–B=C]8–-unit

Abstract

Abstract The crystal structure of Nd2BC, synthesized by arc melting of the element mixture, repeated in a high frequency furnace and subsequent annealing at 1070 K, has been determined from single crystal X-ray diffraction data. It crystallizes in a new structure type in the monoclinic space group C2/m (a = 12.732(2) Å, b = 3.6848(4) Å, c = 9.398(2) Å, β = 130.43(1)°, R1 = 0.038 (wR2 = 0.091) for 596 reflections with I o > 2σ (I o)). Characteristic building units are C—B—B—C entities with the distances d C—B = 1.51(2) Å and d B—B = 1.65(2) Å. These units are embedded in a framework of neodymium atoms resulting from the stacking of slightly corrugated two-dimensional square nets of Nd. Within the ionic limit Nd2BC can be described as (Nd2+)4[C—B—B—C]8– or (Nd3+)4[CBBC]8– · 4 e– with [C=B—B=C]8– units, which are isoelectronic to 1,3-butadiene. The measured magnetic moment of 3.65μ B per Nd atom in Nd2BC is in good agreement with the expected value of 3.62μ B for 4f3 configuration. LMTO band structure calculations show that Nd2BC is metallic and the extra electrons occupy mainly bonding Nd-5d and antibonding π* states within the C—B—B—C units.