✍ Scribed by Olaf Reckeweg; H.-Jürgen Meyer
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Single crystals of the lanthanoide nitrido borates Ln 3 B 2 N 4 (Ln = La±Nd) and La 5 B 4 N 9 have been obtained from reactions of lanthanoide metal powder, lanthanoide nitride powder, and hexagonal boron nitride in calcium chloride melts. The isotypic compounds Ln 3 B 2 N 4 belong to the space group Immm (#71), Z = 2, with the lattice parameters for La 3 B 2 N 4 : a = 362.94(3), b = 641.25(6), c = 1097.20(8) pm; Ce 3 B 2 N 4 : a = 356.20(3), b = 631.90(6), c = 1071.91(8) pm; Pr 3 B 2 N 4 : a = 353.46(4), b = 630.04(13), c = 1079.04(23) pm and Nd 3 B 2 N 4 : a = 351.52(4), b = 627.01(15), c = 1075.59(23) pm. The structure of La 5 B 4 N 9 has been determined in the space group Pbcm (#57), Z = 4, with a = 988.25(5); b = 1263.48(7), c = 770.33(4) pm.
These two structure types resemble three kinds of nitrido borate anions, the oxalate analogue B 2 N 4 of Ln 3 B 2 N 4 , and the carbonate analogue BN 3 together with the six-membered ring system B 3 N 6 of La 5 (BN 3 )(B 3 N 6 ). In contrast to the valence compound La 5 B 4 N 9 the compounds (Ln 3+ ) 3 (B 2 N 4 ) 8± (e ± ) contain one electron in the conduction band, yielding temperature independent paramagnetism for La 3 B 2 N 4 . The calculated electronic structure is developed through the formation of B 2 N 4 8± ions by dimerisation of two BN 2 units.
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