  New equiatomic nickel germanides MgNiGe, SrNiGe, and BaNiGe have been
synthesized from the elements in sealed tantalum tubes using a high-frequency
furnace. The compounds were investigated by X-ray diffraction both on powders
and single crystals. MgNiGe crystallizes with TiNiSi structure type, space
group Pnma, Z = 4, a = 6.4742(2) A, b = 4.0716(1) A, c = 6.9426(2) A, wR2 =
0.033, 305 F2 values, 20 variable parameters. SrNiGe and BaNiGe are isotypic
and crystallize with anti-SnFCl structure type (Z = 4, Pnma) with a = 5.727(1)
A, b = 4.174(1) A, c = 11.400(3) A, wR2 = 0.078, 354 F2 values, 20 variable
parameters for SrNiGe and a = 5.969(4) A, b = 4.195(1) A, c = 11.993(5) A, wR2
= 0.048, 393 F2 values, 20 variable parameters for BaNiGe. The increase of the
cation size leads to a reduction of the dimensionality of [NiGe] polyanions. In
the MgNiGe structure the nickel and germanium atoms build a three-dimensional
3D-[NiGe] network with magnesium atoms in the channels. In contrast, in
Sr(Ba)NiGe one-dimensional 1D-[NiGe] ribbons, running parallel to the b-axis,
are separated by strontium/barium atoms. The crystal chemistry and chemical
bonding in equiatomic alkaline-earth nickel germanides AeNiGe (Ae = Mg, Ca, Sr,
Ba) is discussed. The experimental results are reconciled with electronic
structure calculations performed using the tight-binding linear muffin-tin
orbital (TB-LMTO-ASA) method.
