Sodium-europium bis-nitrilo-tris(methylenephosphonate)

F. F. Chausov^abc, V. G. Petrov^b, M. A. Shumilova^b, R. M. Zakirova^a, D. K. Zhirov<sup>b

a</sup> Udmurt State University, Izhevsk, Russia
^b Institute of Mechanics, Ural Branch of the Russian Academy of Sciences, Izhevsk, Russia
^c Physical-Technical Institute, Ural Branch of the Russian Academy of Sciences

Abstract: New coordination compound of Europium - Sodium-Europium Bis-Nitrilo-tris(Methylenephosphonate) (hereinafter referred to as the EuNTP$_2$) was synthesized. To 10 cm$^3$ of water suspension of 0.001 mol of Eu(OH)3, freshly precipitated from solution of Eu(NO$_3$)$_3$ by double stoichiometric excess of NaOH and washed out to pH = 6-7, have added 15 cm$^3$ of water solution of 0.002 mol of Nitrilo-Tris(Methylenephosphonic) acid (double recrystallized, no more than 0.3 % of PO$_4^{3-}$) and 0.008 mol of NaOH. The reaction mixture was heated to 95-100 $^{\circ}$C at continuous vigorous stirring, cooled to room temperature and filtered. At slow evaporation of water EuNTP$_2$ crystallizes from solution in the form of small colorless triclinic crystals.
IR-spectra (Fourier-spectrometer FSM-1201, pellets, mg: substance 1, KBr 250) and Raman-spectra (Centaur U-HR microscope-microspectrometer, 473 nm laser excitation, double monochromator with 600 mm$^{-1}$ grating) confirm low symmetry of a coordination environment of metal atoms in structure of EuNTP$_2$. Bands in the range of 170 - 230 cm$^{-1}$ relate to oscillations of $\nu$(Eu-O); splitting indicate to non-equivalence of PO$_3$-group coordinating Eu atom. Bands about 400 cm$^{-1}$ belong to oscillations of bonds in Na-O-clusters. The structure of a ligand is characterized by bands (cm$^{-1}$): 570 $\delta$(O-P-O(M)), 600-710 $\delta$(O-P-O), 770-930 $\delta$(N-C-P), 970-1150 $\nu$(P-O). Splitting of bands in each group indicate to non-equivalence of CH$_2$PO$_3$-group because of strong distortion of structure of molecules of a ligand. Band 1230 cm$^{-1}$ indicate to existence in the PO$_3$ groups of the localized multiple bonds P=O. All characteristic bands of the molecules NTP are present both at Raman-spectra, and at IR-spectra, that confirms asymmetric conformation of molecules of a ligand.
DSC of EuNTP2 (Shimadzu DTG-60H, Argon atmosphere, 3 $^{\circ}$C/min) indicate to the elimination of water with the endothermic effect in range 40-115 $^{\circ}$C. At 115-190 $^{\circ}$C on dm/dt-curve observed broad peak of mass loss without observable thermal effect related to removal one CH$_2$PO$_3$-group with the formation of Sodium hydrogen phosphate or phosphite. In broad range 190-418 $^{\circ}$C there is a mass loss corresponding to the elimination of one water molecule, apparently due to intra- or intermolecular condensation of the groups P-OH with the formation of the bridge P-O-P. At 418-441 $^{\circ}$C 1/2 H$_2$O is lost and the molecule N$_2$ with the strong exothermic effect, that indicate to the destruction of the bonds C-N in the ligand molecule. The exothermic effect is probably due to the destruction of highly strained chelate cycles. Upon further heating in the range 441-483 $^{\circ}$C eliminated 1/2 H$_2$O with a small exothermic effect.

Keywords: europium, coordination compounds, nitrilo-tris(methylenephosphonic) acid, spectral analysis, IR-spectra, raman-spectra, differential scanning calorimetry.

UDC: 547.1