Structure determination, magnetic and optical properties of a new chromium(II) thioantimonate, [Cr((NH2CH2CH2)3N)]Sb4S7

The chromium(II) antimony(III) sulphide, [Cr((NH2CH2CH2)3N)]Sb4S7, was synthesised under solvothermal conditions from the reaction of Sb2S3, Cr and S dissolved in tris(2-aminoethyl)amine (tren) at 438 K. The products were characterised by single-crystal X-ray diffraction, elemental analysis, SQUID magnetometry and diffuse reflectance spectroscopy. The compound crystallises in the monoclinic space group P21/n with a=7.9756(7), b=10.5191(9), c=25.880(2) Å and β=90.864(5)°. Alternating SbS33− trigonal pyramids and Sb3S63− semi-cubes generate Sb4S72− chains which are directly bonded to Cr(tren)2+ pendant units. The effective magnetic moment of 4.94(6)μB shows a negligible orbital contribution, in agreement with expectations for Cr(II):d4 in a 5A ground state. The measured band gap of 2.14(3) eV is consistent with a correlation between optical band gap and framework density that is established from analysis of a wide range of antimony sulphides.