Li0.44Eu3[B3N6] was synthesized from the metathesis reaction of Li3[BN2] and EuCl3 at 850°C. Li0.44Eu3[B3N6] crystallizes in the trigonal space group (No. 167) with a=12.0225(2)Å, c=6.8556(2)Å and Z=6. In the crystal structure, isolated, planar cyclic [B3N6]9− units are charge-balanced by the mixed-valence Eu3+/Eu2+ and Li+ cations. Li+ occupies partially (44%) the Wyckoff site 6b and is sandwiched between the [B3N6]9− anions. Mössbauer spectroscopy results show the resonance lines of Eu2+ and Eu3+, respectively, indicating the heterogeneous mixed valency of the Eu atoms. X-Band ESR investigations between 5 and 300K reveal an intense signal over the whole temperature range originating from Eu2+. Magnetic susceptibility measurements indicate a Curie–Weiss behavior with an experimental effective magnetic moment of μ eff=8.28μB per formula unit. [ABSTRACT FROM AUTHOR]