On the crystal chemistry of Tm2Ni1.896(4)In, Tm2.22(2)Ni1.81(1)In0.78(2), Tm4.83(3)Ni2In1.17(3), and Er5Ni2In

The rare earth-nickel-indides Tm2Ni1.896(4)In, Tm2.22(2)Ni1.81(1)In0.78(2), Tm4.83(3)Ni2In1.17(3), and Er5Ni2In were synthesized from the elements by arc-melting and subsequent annealing for the latter three compounds. Three indides were investigated by X-ray powder and single crystal diffraction: Mo2FeB2 type, P4/mbm, Z=2, a=731.08(4), c=358.80(3) pm, wR2=0.0201, 178 F2 values, 13 variables for Tm2Ni1.896(4)In, a=734.37(7), c=358.6(1) pm, wR2=0.0539, 262 F2 values, 14 variables for Tm2.22(2)Ni1.81(1)In0.78(2), and Mo5SiB2 type, I4/mcm, a=751.0(2), c=1317.1(3) pm, wR2=0.0751, 317 F2 values, 17 variables for Tm4.83(3)Ni2In1.17(3). X-ray powder data for Er5Ni2In revealed a=754.6(2) and c=1323.3(5) pm. The Mo2FeB2 type structures of Tm2Ni1.896(4)In and Tm2.22(2)Ni1.81(1)In0.78(2) are intergrowths of slightly distorted CsCl and AlB2 related slabs, however, with different crystal chemical features. The nickel sites within the AlB2 slabs are not fully occupied in both indides. Additionally In/Tm mixing is possible at the center of the CsCl slab, as is evident from the structure refinement of Tm2.22(2)Ni1.81(1)In0.78(2). The Mo5SiB2 type structures of Tm4.83(3)Ni2In1.17(3) and Er5Ni2In can be considered as an intergrowth of distorted CuAl2 and U3Si2 related slabs in an ABA'B' stacking sequence along the c-axis. Again, one thulium site shows Tm/In mixing. The U3Si2 related slab has great structural similarities with the Mo2FeB2 type structure of Tm2Ni1.896(4)In and Tm2.22(2)Ni1.81(1)In0.78(2). The crystal chemical peculiarities and chemical bonding in these intermetallics are briefly discussed