The first lead perrhenate crown ether complex, [Pb(12-Crown-4)(H2O)(ReO4)2]: from rotation of the ReO4 tetrahedra in the (3+1)-D space using constrained Legendre functions to the rotation in the 3D space

Abstract

A unique lead perrhenate crown ether complex, [Pb(12-Crown-4)(H2O)(ReO4)2], exhibits an incommensurately modulated crystal structure at 101 K. Therein, the apical oxygens of the ReO4 tetrahedra rotate in (3+1)D space. Describing their continuous rotation required introducing several constraints into the Legendre polynomials describing displacive modulation of these atoms. At 296 K, the rotation of these tetrahedra is characterized by jumps between certain "stationary" positions. The average structure is monoclinic, P21/c with Z = 4; it can be described as comprised of [Pb(C8H16O4)(ReO4)2(H2O)] ribbons. One half of the Pb2+ coordination sphere is occupied by crown ether ligand while the other, by the oxygen atoms of water molecules and the perrhenate groups. The latter play two crystallographic roles, one bridging the PbO8 polyhedra, the other terminal with a very rare monodentate (K 1 ) coordination. This is probably the reason of the nearly free rotation of these terminal ReO4 groups along the Pb–O–Re axis. The structural chemistry of lead crown ether complexes, even those with relatively simple counteranions, is expected to yield a wide variety of unique and complex structures.