Syntheses for 2-(pyridyl N-oxide) methylphosphonic acid, 1-H, and 2-(pyridyl N-oxide) hydroxymethylphosphonic acid, 4-H, are described, and the crystal structures of both ligands are presented. Combination of these ligands with freshly prepared erbium hydroxide results in the formation of the isostructural complexes Er(L(-))(3)(LH).8H(2)O. The crystal structure determinations of the complexes show that extensive hydrogen bonding links the individual eight coordinate Er(L(-))(3)(LH) molecular units into a 3-D structure.

A multistep synthesis for 2-(2-pyridyl-N-oxide) ethylphosphonic acid 6-H2 is described along with its spectroscopic (IR, NMR) data and a single-crystal X-ray diffraction structure analysis. Combination of the ligand with Nd(OH)3 results in the formation of a complex Nd(6-H)3. Single-crystal X-ray diffraction analysis reveals a three-dimensional crystal network generated by hydrogen-bonded chains along the crystallographic c axis. The hydrogen bonds are formed between phosphonic acid anion (6-H)(-1) protons on one chain and pyridyl N-oxide oxygen atoms in neighboring chains. The asymmetric unit contains 1/3[Nd(6-H)3] and there are two unique Nd(III) atoms, each with point symmetry. As a result, each Nd(III) ion is bound to six (6-H)(-1) ligands and the symmetry about the Nd(III) ion is octahedral with each vertex occupied by a phosphonate oxygen atom. The Nd-O bond lengths are essentially identical: Nd(1)-O(3), 2.336 (1) A; Nd(2)-O(4), 2.340 (1) A. The monoanionic ligand (6-H)(-1), therefore, serves to bridge the unique Nd(III) centers.

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