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Molecular structure of lanthanide complexes of 2-aminothiazole
SPECTROCHIMICA ACTA PARTA ELSEVIER
Spectrochimica Acta Part A 52 (1996) 705 706
Short Note
Molecular structure of lanthanide complexes of 2-aminothiazole B. Singh*, Praveen K. Singh Department 0[' Chemistry, Banaras Himh~ Unit:ersi(v. Varanasi-221 005, hTdia
Received 23 September 1995: accepted 21 October 1995
Molecular addition complexes [Ln(amth)2C12] C1, (where Ln(III) is La, Pr, Nd, Sm, Eu, Gd, Tb or Dy; amth is 2-aminothiazole) have been prepared by reacting an ethanol solution of the lanthanide chlorides (1 mmol) and 2-aminothiazole (2 mmol) containing 0.05 ml concentrated hydrochloric acid. The chemical composition of the complexes has been established by analytical and molar conductance data. The molar conductance values are consistent with 1:1 electrolytic [1] nature of the complexes. The complexes melt in the temperature range 115 160°C, except that of Pr(III) which decomposes at 210°C. The complexes are soluble in MeOH, EtOH, DMF and DMSO. The monomeric nature of the complexes has been indicated by the fast atom bombardment mass spectrum of the terbium(Ill) complex. The base peak at m / z 385 in the spectrum is assigned to the fragment
/~
N - - Tb - - N - - ~ S
A peak at m / z 463 is attributed to the molecular ion (M+). The bonding and stereochemistry of
* Corresponding author.
the complexes were investigated by emloying infrared, electronic and emission spectra and magnetic susceptibility data. The room temperature magnetic moments of the complexes except for Sm(III) and Eu(III) show little deviation from Van Vleck values [2] indicating little participation of 4f electrons in bonding. The relatively high/~r values obtained for Sm(III) and Eu(III) complexes are attributed to low J - J separation [3]. Bonding of 2-aminothiazole to the metal ions through the cyclic and amine nitrogen is adduced from shift of bands due to ring skeletal v~(NH) and v(CN)ex~, vibrations to the lower frequencies. The lowering in energy of the hypersensitive transition (4192--.465,2, 2G7,2) at 17182 cm ~ in the electronic spectrum of the Nd(III) complex compared to the aqua metal ion is indicative of a partial covalent character of the metal ligand bond. This is also consistent with the increase in oscillator strength (P) [4] of the absorption bands of this complex compared to the aqua ion. The higher value of P for the transition 419~2 ---~4F52 may be due to lowering in symmetry of the complex. The shape of the hypersensitive band suggests coordination number six around the metal ion as reported by Karraker [5]. The spectral parameters [6,7], viz. nephelauxetic (fl), bonding (b j 2), covalency (q) and the Sinha parameter
0584-8539/96/$15.00 © 1996 Elsevier ScienceB.V. All rights reserved SSD1 0584-8539(95)01613-9
706
B. Singh, P.K. Singh / Spectrochimica Acta Part A 52 (1996) 705 706
(~5 %) are indicative of interaction of amth with the lanthanide ions. Emissions from the non-degenerate emitting level (SDo) of the Eu 3+ ion to various 7F 3 levels are useful for interpretation of the site symmetry and geometry around the metal ion [8]. The room temperature emission spectrum of [Eu(amth)2Cl2]Cl exhibits a single band at 692 nm due to the 5Do ~ 7F 4 transition. The spectrum at liquid nitrogen temperature shows bands at 590, 616 and 692 nm which are attributed to the SDo--* 7F 1, SDo ~ 7F 2 and 5Do--* 7F 4 transitions, respectively, the last transition having the highest intensity. The 5Do--. 7F o and 5D0--* 7F 3 transitions are absent at both room and liquid nitrogen temperatures. The higher intensity of the electricdipole allowed transition (SD 0--, 7F2) compared to the magnetic-dipole allowed transition (SDo ---, 7F I ) at liquid nitrogen temperature suggests low symmetry for the complex [9] and the absence of an inversion centre. The appearance of the 5Do ~ 7F 3 transition and the unsplit nature of 5Do ~ 7F~ and 5D0---, 7F2 transitions correspond to an absence of a centre of inversion consequent upon a symmetry lowering from D3h to D 3 [10]. The Tb(III) complex shows strong emission when excited with 310-350 nm radiation. The 5D 4 "* 7F 5 and 5D 4 --* 7F 6 transitions are observed to be most populated at 546 and 494 nm, respectively. The 5D4-,VF 4 and 5D4-*TF 3 transitions observed at 588 and 624 nm, respectively, are less intense. All the transitions are broad without splitting and suggest a high symmetry [11] for the electrostatic field around terbium(Ill) ion. No lines are common in the X-ray powder diffraction pattern of amth and [Pr(amth)2Cl2]Cl, indicating that the latter is a pure compound. The indexing [12] of the pattern suggests a tetragonal lattice with parameters a = b = 11.25/k, c = 16.22
/k, z = 4, Px-r~y = 1.45 g cm 3 and Pexp = 1.46 g cm 3 for [Pr(amth)~C12]C1 and a = b = 9.32 /~ and c = 14.43 ft. for amth.
Acknowledgements We wish to thank RSIC, Bose Institute, Calcutta, for recording emission spectra and the Departments of Metallurgical and Chemical Engineering, I.T., B.H.U., for recording X-ray powder diffraction spectra and T G A / D T A data, respectively. Recording of fast atom bombardment mass spectra by CDRI, Lucknow, is also gratefully acknowledged.
References [I] W.J. Geary, Coord. Chem. Rev., 7 (1971) 81. [2] J.H. Van Vleck and A. Frank, Phys. Rev., 34 (1929) 1494, 1625. [3] B.N. Figgis and J. Lewis, Tech. Inorg. Chem., 4 (1965) 137. [4] W.T. Carnall, P.R. Fields and K. Rajnak, J. Chem. Phys., 49 (1968) 4412. [5] D.G. Karraker, lnorg. Chem., 6 (1967) 1863. [6] J.L. Rayan and C.K. Jqbrgensen, J. Phys. Chem., 70 (1966) 2845. [7] M. Singh, S.N. Mishra and R.D. Verma, J. Inorg. Nucl. Chem., 40 (1978) 1939. [8] J.H. Forsberg, Coord. Chem. Rev., 10 (1973) 195. [9] G. Blasse, in K.H. Gschneidner, Jr. and L. Cyring (Eds.), Handbook on Physics and Chemistry of Rare Earths, North Holland, Amsterdam, 1979, Chapter 34. [10] G. Blasse, A. Brill and W.C. Nieuwpoort, J. Phys. Chem. Solids, 27 (1966) 1587. [! 1] A. Musumeci, R.P. Bonomo, V. Cucinotta and A. Seminara, Inorg. Chim. Acta, 59 (1982) 133. [12] L.V. Azaroff and M.J. Buerger, The Powder Method in X-ray Crystallography, McGraw Hill, New York, t958, p. 119.
Spectrochimica Acta Part A 52 (1996) 705 706
Short Note
Molecular structure of lanthanide complexes of 2-aminothiazole B. Singh*, Praveen K. Singh Department 0[' Chemistry, Banaras Himh~ Unit:ersi(v. Varanasi-221 005, hTdia
Received 23 September 1995: accepted 21 October 1995
Molecular addition complexes [Ln(amth)2C12] C1, (where Ln(III) is La, Pr, Nd, Sm, Eu, Gd, Tb or Dy; amth is 2-aminothiazole) have been prepared by reacting an ethanol solution of the lanthanide chlorides (1 mmol) and 2-aminothiazole (2 mmol) containing 0.05 ml concentrated hydrochloric acid. The chemical composition of the complexes has been established by analytical and molar conductance data. The molar conductance values are consistent with 1:1 electrolytic [1] nature of the complexes. The complexes melt in the temperature range 115 160°C, except that of Pr(III) which decomposes at 210°C. The complexes are soluble in MeOH, EtOH, DMF and DMSO. The monomeric nature of the complexes has been indicated by the fast atom bombardment mass spectrum of the terbium(Ill) complex. The base peak at m / z 385 in the spectrum is assigned to the fragment
/~
N - - Tb - - N - - ~ S
A peak at m / z 463 is attributed to the molecular ion (M+). The bonding and stereochemistry of
* Corresponding author.
the complexes were investigated by emloying infrared, electronic and emission spectra and magnetic susceptibility data. The room temperature magnetic moments of the complexes except for Sm(III) and Eu(III) show little deviation from Van Vleck values [2] indicating little participation of 4f electrons in bonding. The relatively high/~r values obtained for Sm(III) and Eu(III) complexes are attributed to low J - J separation [3]. Bonding of 2-aminothiazole to the metal ions through the cyclic and amine nitrogen is adduced from shift of bands due to ring skeletal v~(NH) and v(CN)ex~, vibrations to the lower frequencies. The lowering in energy of the hypersensitive transition (4192--.465,2, 2G7,2) at 17182 cm ~ in the electronic spectrum of the Nd(III) complex compared to the aqua metal ion is indicative of a partial covalent character of the metal ligand bond. This is also consistent with the increase in oscillator strength (P) [4] of the absorption bands of this complex compared to the aqua ion. The higher value of P for the transition 419~2 ---~4F52 may be due to lowering in symmetry of the complex. The shape of the hypersensitive band suggests coordination number six around the metal ion as reported by Karraker [5]. The spectral parameters [6,7], viz. nephelauxetic (fl), bonding (b j 2), covalency (q) and the Sinha parameter
0584-8539/96/$15.00 © 1996 Elsevier ScienceB.V. All rights reserved SSD1 0584-8539(95)01613-9
706
B. Singh, P.K. Singh / Spectrochimica Acta Part A 52 (1996) 705 706
(~5 %) are indicative of interaction of amth with the lanthanide ions. Emissions from the non-degenerate emitting level (SDo) of the Eu 3+ ion to various 7F 3 levels are useful for interpretation of the site symmetry and geometry around the metal ion [8]. The room temperature emission spectrum of [Eu(amth)2Cl2]Cl exhibits a single band at 692 nm due to the 5Do ~ 7F 4 transition. The spectrum at liquid nitrogen temperature shows bands at 590, 616 and 692 nm which are attributed to the SDo--* 7F 1, SDo ~ 7F 2 and 5Do--* 7F 4 transitions, respectively, the last transition having the highest intensity. The 5Do--. 7F o and 5D0--* 7F 3 transitions are absent at both room and liquid nitrogen temperatures. The higher intensity of the electricdipole allowed transition (SD 0--, 7F2) compared to the magnetic-dipole allowed transition (SDo ---, 7F I ) at liquid nitrogen temperature suggests low symmetry for the complex [9] and the absence of an inversion centre. The appearance of the 5Do ~ 7F 3 transition and the unsplit nature of 5Do ~ 7F~ and 5D0---, 7F2 transitions correspond to an absence of a centre of inversion consequent upon a symmetry lowering from D3h to D 3 [10]. The Tb(III) complex shows strong emission when excited with 310-350 nm radiation. The 5D 4 "* 7F 5 and 5D 4 --* 7F 6 transitions are observed to be most populated at 546 and 494 nm, respectively. The 5D4-,VF 4 and 5D4-*TF 3 transitions observed at 588 and 624 nm, respectively, are less intense. All the transitions are broad without splitting and suggest a high symmetry [11] for the electrostatic field around terbium(Ill) ion. No lines are common in the X-ray powder diffraction pattern of amth and [Pr(amth)2Cl2]Cl, indicating that the latter is a pure compound. The indexing [12] of the pattern suggests a tetragonal lattice with parameters a = b = 11.25/k, c = 16.22
/k, z = 4, Px-r~y = 1.45 g cm 3 and Pexp = 1.46 g cm 3 for [Pr(amth)~C12]C1 and a = b = 9.32 /~ and c = 14.43 ft. for amth.
Acknowledgements We wish to thank RSIC, Bose Institute, Calcutta, for recording emission spectra and the Departments of Metallurgical and Chemical Engineering, I.T., B.H.U., for recording X-ray powder diffraction spectra and T G A / D T A data, respectively. Recording of fast atom bombardment mass spectra by CDRI, Lucknow, is also gratefully acknowledged.
References [I] W.J. Geary, Coord. Chem. Rev., 7 (1971) 81. [2] J.H. Van Vleck and A. Frank, Phys. Rev., 34 (1929) 1494, 1625. [3] B.N. Figgis and J. Lewis, Tech. Inorg. Chem., 4 (1965) 137. [4] W.T. Carnall, P.R. Fields and K. Rajnak, J. Chem. Phys., 49 (1968) 4412. [5] D.G. Karraker, lnorg. Chem., 6 (1967) 1863. [6] J.L. Rayan and C.K. Jqbrgensen, J. Phys. Chem., 70 (1966) 2845. [7] M. Singh, S.N. Mishra and R.D. Verma, J. Inorg. Nucl. Chem., 40 (1978) 1939. [8] J.H. Forsberg, Coord. Chem. Rev., 10 (1973) 195. [9] G. Blasse, in K.H. Gschneidner, Jr. and L. Cyring (Eds.), Handbook on Physics and Chemistry of Rare Earths, North Holland, Amsterdam, 1979, Chapter 34. [10] G. Blasse, A. Brill and W.C. Nieuwpoort, J. Phys. Chem. Solids, 27 (1966) 1587. [! 1] A. Musumeci, R.P. Bonomo, V. Cucinotta and A. Seminara, Inorg. Chim. Acta, 59 (1982) 133. [12] L.V. Azaroff and M.J. Buerger, The Powder Method in X-ray Crystallography, McGraw Hill, New York, t958, p. 119.