Cobalt Phosphonates: An Unusual Polymeric Cobalt Phosphonate Containing a Clathrated Phosphonate Anion and a Layered Bisphosphonate

Novel cobalt phosphonates [Co(H2O)4(H4L)][H2L]·2H2O, 1, and Co2(H2O)2(L), 2, have been synthesized from 1,8-octylenediphosphonic acid (H4L). 1 has been fully characterized by X-ray single-crystal data, TGA, IR spectroscopy,
and chemical analysis. The compound crystallizes in the triclinic space group P1̄ with a = 5.5415(8) Å, b =
8.6382(8) Å, c = 16.794 (2) Å, α = 87.694(2)°, β = 80.859(2)°, γ = 76.005(2)°, V = 770.11(19) Å3, and Z =
1. A cobalt atom lies in the center of symmetry and is octahedrally coordinated by two oxygen atoms from two
undissociated diphosphonic ligands H4L and four molecules of water. The cobalt atom and undissociated ligand
H4L are combined to form polymeric chains along the c-axis, resulting in the formation of a one-dimensional framework.
The positive charge on the cobalt atom remains upon coordination and is balanced by a negatively charged
uncoordinated ligand (H2L) found as a clathrate in the lattice. Two lattice water molecules, hydrogen-bonded with
the coordinated and uncoordinated ligands, complete the structure. The metal phosphonate chains are held together
and bridge the uncoordinated anionic ligands by a number of strong hydrogen bonds, which make the structure
possible. Cobalt phosphonate 2 has been characterized by TGA measurements, IR spectroscopy, and chemical
analysis. The compound has a layered structure with an interlayer spacing of 14.26 Å. Metal phosphonate layers
are cross-linked by hydrocarbon chains. The water molecules are coordinated to the metal atom. According to IR
data, compound 2 contains two equivalent PO bonds and one different PO bond, which may be a result of the
different types of Co−O−P connectivity within one phosphonic group.