Complexes with substituted 2,5-dihydroxy- p-benzoquinones: A neutron diffraction study on BaC 6(C 6H 5) 2O 4·4H 2O

Abstract

Orthorhombic crystals of BaC 6(C 6H 5) 2O 4·4H 2O were grown from aqueous silica gel. Lattice constants: a = 1791.7(4)pm, b = 926.5(2)pm, c = 1121.2(2)pm, Z = 4, space group Pbcn. Anisotropic refinement of neutron diffraction data converged at R w = 0.0305 . Ba 2+ has CN 8. It is surrounded by four oxygen atoms of the bis-chelating polyporate dianions and four water molecules in a distorted, dodecahedral fashion. The connection of Ba 2+ with the dianions leads to folded, infinite chains extending along [001]. Adjacent chains are interlinked by asymmetric hydrogen bonds thus forming layers parallel (100). Only one hydrogen atom of each of the two crystallographically independent water molecules is involved in hydrogen bonding. The polyporate dianion is centrosymmetric with phenyl rings inclined to the quinone ring plane. Only the oxygen atom of the quinone ring which is less strongly bound to Ba 2+ acts as proton acceptor. However, the resulting C O and C C bond lengths do not indicate a system of alternating double bonds in the quinone ring; rather, they indicate extensively delocalized π-electrons.