Structure and Mesomorphism of Neodymium(III) Alkanoates

The structural and thermal behavior of all members of the homologous series of neodymium(III) alkanoates,
ranging from neodymium(III) butyrate to neodymium(III) eicosanoate are described. Neodymium(III) butyrate
monohydrate, Nd(C3H7COO)3·H2O crystallizes in space group P1̄ (No. 2), Z = 2. The lattice parameters are a =
9.824(2) Å, b = 11.974(2) Å, c = 14.633(2) Å, α = 86.21(2)°, β = 75.92(2)°, γ = 77.97(2)°. The crystal
structure consists of ionic layers of neodymium ions, separated by bilayers of butyrate anions. In the ionic layers,
the neodymium ions are connected by bridging tridentate carboxylate groups to zigzag chains, whereas the chains
are connected among themselves by bridging bidentate carboxylate groups. The two crystallographically different
neodymium ions are both having coordination number 9, with a geometry close to a monocapped square antiprism.
The structure of the higher homologues can be derived from the structure of neodymium butyrate by extending
the alkyl chains. These compounds have a lamellar bilayer structure with planes of neodymium(III) ions coordinated
to the carboxylate groups and with the alkyl chains in an all-trans conformation. All homologous compounds
from neodymium(III) pentanoate to neodymium(III) pentadecanoate display a thermotropic mesophase, which
was identified by high-temperature X-ray diffraction as a smectic A phase. For the series from neodymium(III)
pentanoate to neodymium(III) undecanoate an additional high viscosity mesophase is present between the crystalline
state and the smectic A mesophase.