Synthesis and reactivity of (benzoxazol-2-ylmethyl)phosphonic acid.

An efficient three step synthesis of (benzoxazol-2-ylmethyl)phosphonic acid (6-H(2)) is described along with IR, mass spectrometry (MS), and (1)H, (13)C, and (31)P NMR spectroscopic characterization data, and a single crystal X-ray diffraction structure determination. 6-H(2) is unstable in acidic aqueous solutions (pH < 4) undergoing ring-opening to give [(2-hydroxyphenylcarbamoyl)methyl] phosphonic acid (7-H(2)) that is characterized by IR, MS, and NMR methods. The protonation constants (pK(a)) for 7-H(2) have been measured, and crystal structure determinations for (NH(4))(7-H) and K(7-H)·DMF are described. Reactions of NaOH and KOH with 6-H(2) in MeOH/H(2)O solutions led to isolation and crystal structure determinations of the salts [Na(6-H)·H(2)O](2), K(6-H), Na(3)(6)(6-H)·H(2)O, and [K(2)(6)](2)·3H(2)O. The complexation reactions of 7-H(2) with La(III), Nd(III), and Gd(III), as a function of pH, were also examined by titrametric methods, and a model for the 1:1 anion binding with Ln(III) cations is proposed.

Synthesis and lanthanide coordination chemistry of trifluoromethyl derivatives of phosphinoylmethyl pyridine N-oxides.

A synthetic route for the formation of 2-[bis(2-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1c) and 2-[bis(3,5-trifluoromethylphenyl)phosphinoylmethyl]pyridine N-oxide (1d) was developed and the new ligands characterized by spectroscopic methods and single-crystal X-ray diffraction analyses. The coordination chemistry of 1c was examined with Yb(NO3)3 and the molecular structure of one complex, [Yb(1c)(NO3)3(DMF)].DMF.0.5H2O, was determined by single-crystal X-ray diffraction methods. The ligand is found to coordinate in a bidentate fashion, and this is compared against lanthanide coordination chemistry observed for the related ligand, [Ph2P(O)CH2] C5H4NO.

Frequency-switching inversion-recovery for severely hyperfine-shifted NMR: evidence of asymmetric electron relaxation in high-spin Co(II).

A new method for reliably measuring longitudinal relaxation rates for severely hyperfine-shifted NMR signals in aqueous solutions is presented. The method is illustrated for a well-defined cobalt tetracysteinate, with relevance to cobalt-substituted metalloproteins. The relaxation measurements are indicative of asymmetric electronic relaxation of the high-spin Co(II) ion.