Cu 4 TiTe 4 : Synthesis, Crystal Structure, and Chemical Bonding.

A new compound Cu 4 TiTe 4 in the Cu-Ti-Te ternary system is prepared using high-temperature solid-state synthesis and characterized by single-crystal X-ray diffraction and energy-dispersive X-ray spectroscopy. The average structure of Cu 4 TiTe 4 crystallizes in the cubic space group P 4̅3 m ( cP 9; a = 5.9484(1) Å) and adopts the Cu 4 TiSe 4 structure type. Like Cu 4 TiSe 4 , it shows positional disorder in one of the two Cu sites. The three-dimensional structure of Cu 4 TiTe 4 is viewed as a cubic close-packed (ccp) array of Te, where half of the tetrahedral holes are orderly occupied by three Cu and one Ti and the disordered Cu atoms effectively occupied 1/4 of the octahedral holes. The calculated density of states (DOS) discerns that the compound is a narrow-bandgap semiconductor, and the crystal orbital Hamilton population (COHP) analysis shows that though the individual Cu-Te short contact is relatively weak compared to the Ti-Te contact, Cu-Te bonds largely contribute toward the overall stability. Due to the unique atomic arrangements, some Te atoms in the unit cell have unsaturated coordination, which presents 5s 2 lone pairs on the Te atoms. This has been confirmed by the density of states (DOS) and electron localization function (ELF) calculations.