BA2(NI1-XLIX)NI2N2 - A LOW-VALENCY NITRIDONICCOLATE WITH PUCKERED LAYERS 2-INFINITY-[(NIN2/2)-(NI1-XLIX)-(NIN2/2)]

Ba2(Ni1-xLix)Ni2N2 is obtained by reaction of lithium-barium-melts (molar ratios Li:Ba between 1:1 and 3:1) with nitrogen (1 atm.) in nickel-crucibles within a period of 15 h. Single crystals with a dark-metallic lustre are formed by cooling the melt to room temperature with a rate of 10-degrees-C/h (orthorhombic, Cmca; a = 713.3(2) pm, b = 1027.4(7) pm, c = 752.2(4) pm; Z = 4; D(XR) = 5.50 g/cm3 with x = 0.43). The crystal structure contains nearly linear 1 infinity [NiN2/2]-chains (N-Ni-N: 178.5(7)-degrees, Ni-N-Ni 173.4(7)-degrees; Ni-N: 178.6(1) pm), running parallel to the [100] direction, which are interconnected via (Ni1-xLi(x))-sites (linear units (N-(Ni1-xLix)-N); bond-lenths: 194.5(12) pm with x = 0.43) to form puckered layers 2 infinity [(NiN2/2)-(Ni1-xLix)-(NiN2/2)]. Barium is in a distorted trigonal-planar coordination by nitrogen atoms (Ba-N: 281.1(11) pm - 285.5(11) pm). The nitrogen-coordination corresponds to a distorted octahedron, NBa3(Ni1-xLix)Ni2, with nickel in trans-position. The crystal structure of Ba2(Ni1-xLix)Ni2N2 is closely related to the Li3N-type structure: Li2[LiN] <--> Ba{(Ni1-xLix)0.5-square-0.5}[NiN]. Furthermore, this structure enlarges the scope of barium-nitrido-niccolates which up to now were found to contain merely 1 infinity [NiN2/2]-chains (BaNiN: planar zigzag-chains; Ba8Ni6N7: helical zigzag-chains)