NOVEL POLYNUCLEAR COMPOUND OF EUROPIUM WITH N-PHOSPHONOMETHYLGLYCINE - SPECTROSCOPY AND STRUCTURE

Phosphonic acid analogues of amino acids display interesting biologica l activities, the possible applications of which range from medicine t o agriculture. Aminophosphonates are found in tissues as free compound s but their most frequent forms of occurrence include complex structur es, such as lipids, proteins and polysaccharides [1]. For the first ti me, to our knowledge, lanthanide compounds with N-phosphonomethylglyci ne were obtained and analyzed by X-ray diffraction methods. The compou nd is polynuclear, with unexpected architecture, and crystallizes in t he P2(1)/c space group (cell parameters a = 17.788(4) Angstrom, b = 10 .706(2) Angstrom, c = 18.560(4) Angstrom, beta = 113.37(3)degrees, Z = 4). Two nonequivalent metal sites exist in the structure. Both carbox yl and phosphonate groups of the ligand are involved in metal ion coor dination forming two centrosymmetric dimers: one by the carboxyl (simp le and chelating) bridges, and one by phosphonate groups. Moreover, in the latter dimer, coordination of metal ion is completed by three wat er molecules and one oxygen of perchlorate ion, thus the coordination number is 8. In the former dimer, additional water molecules are bonde d and the coordination number of Eu becomes 9, with a little different distortion. The M-M distances are 4.012 and 5.940 A for carboxyl and phosphonic dimers, respectively. The compound was characterized by IR and electron spectroscopy methods. Absorption, excitation and emission spectra were measured down to 77 K. Electron transition probabilities and splitting of levels were analyzed and compared to the structural data. Assignment of the vibronic components in electronic transitions, which obey the selection rule Delta J = 0.2 was made on the basis of IR spectra. (C) 1998 Elsevier Science S.A.