Pyridinderivate als Komplexbildner. XI. Die Thermodynamik der Metallkomplexbildung mit Bis‐, Tris‐ und Tetrakis[(2‐pyridyl)methyl]‐aminen

Helvetica Chimica Acta - Tập 60 Số 1 - Trang 123-140 - 1977
G. Anderegg1, Egon Hubmann1, Nitya G. Podder1, F. Wenk1
1Laboratorium für Anorganische Chemie, ETH, Universitätsstrasse 6, CH–8092 Zürich

Tóm tắt

Pyridine Derivatives as Complexing Agents XI. Thermodynamics of Metal Complex Formation with Bis‐, Tris‐ and Tetrakis[(2‐pyridyl)methyl]‐amines.The equilibria between H+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Cd2+, Pb2+, Hg2+ and Ag+, and the ligands bis(2‐pyridylmethyl)‐amine (=DPA), tris(2‐pyridylmethyl)‐amine (=TPA), tris(6‐methyl‐2‐pyridylmethyl)‐amine (=TLA) and N,N,N′,N′‐tetrakis(2‐pyridylmethyl)‐ethylenediamine (=TPEN) have been studied. Only the stability constants of DPA and TLA with almost all these cations were obtained using the pH method. For the other ligands, the complexes are already formed in acid solutions and only the use of different ligand‐ligand or metal‐metal exchanges as well as of pM methods were successful.The protonation constants indicate that for DPA the protonation occurs firstly at the aliphatic nitrogen atom whereas in all other cases only the pyridine groups can be protonated. The thermodynamic functions of protonation are in agreement with this interpretation.The stability constants of the complexes are often similar in magnitude to those of the analogous aliphatic amines, in spite of the much lower basicities of the pyridine derivatives. The Fe(II)N6 species of DPA and TPEN are appreciably more stable than those of the corresponding aliphatic ligands. This is due to the formation of low‐spin complexes with an unexpected ΔH value. Comparison of the thermodynamic data of formation of the complexes with TPA and TLA shows the effect of the three bulky methyl groups of the second ligand. As a consequence of steric hindrance and of the major dehydration, ΔH and less ΔS are more positive for M(TLA)2+ than for M(TPA)2+. Therefore M(TLA)2+ is normally much less stable than M(TPA)2+. The data for MnTPA2+ and ZnTPA2+ appear to indicate that in these complexes the coordination number of the metal ion is seven and four respectively. In addition to the complexes ML2+, with these two ligands hydroxo complexes ML(OH)+ are formed at remarkably low pH. Further TPEN seems to be sexidentate in the 1:1 complexes with Mn2+, Co2+ and Ni2+ but quinquedentate in those with Cu2+ and Zn2+, also in agreement with the spectra in solution and of the solid complex salts. The reaction: M(DPA)22+ + TPEN → M(TPEN)2+ + 2DPA is for all metal ions favoured by ΔH and ΔS, whereas in the case of the corresponding aliphatic ligands only by the second term. This result is explained in terms of a different magnitude of hydration of the two sexidentate ligands as a consequence of the presence of the hydrophobic aromatic rings in TPEN.

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Tài liệu tham khảo

10.1080/00958977508075911

10.1002/hlca.19550380509

Rossotti F. J. C., 1960, Modern Coordination Chemistry

10.1002/hlca.19600430153

10.1002/hlca.19650480425

Anderegg G., 1971, Helv., 51, 224

10.1021/je60033a018

Rossotti F. J. C., 1961, The determination of stability constants

10.1002/hlca.19610440624

10.1002/hlca.19600430611

10.1002/hlca.19570400625

E.Hubmann Dissertation ETH Nr. 4422 (1970).

10.1351/pac196306020125

J. O.Ljenzin K.Vadasdi&J.Rydberg Trans. Roy. Institute Technology Stockholm No 280 (1972).

Näsanen R., 1960, Suomen Kem., 33, 9

S. M.Nelson&J.Rodgers J. chem. Soc. (A)1968 272.

L.Sacconi P.Paoletti&M.Ciampolini J. chem. Soc.1964 5046.

M.Ciampolini P.Paoletti&L.Sacconi J. chem. Soc.1960 4553.

10.1002/hlca.19630460740

P.Paoletti M.Ciampolini&L.Sacconi J. chem. Soc.1963 3589.

10.1021/ic50052a048

M.Ciampolini P.Paoletti&L.Sacconi J. chem. Soc.1961 2994.

A.Vacca&P.Paoletti J. chem. Soc. (A)1968 2378.

10.3891/acta.chem.scand.10-0887

10.3891/acta.chem.scand.09-1362

M. M.da Mota J.Rodgers&S. M.Nelson J. chem. Soc. (A)1969 2036.

Schläfer H. L., 1970, Einführung in die Ligandenfeldtheorie

10.3891/acta.chem.scand.09-1362

S. M.Nelson&J.Rodgers J. chem. Soc. (A)1968 272.

10.1002/9780470132425.ch16

10.1021/ic50090a017

10.1063/1.1723943

D. P.Madden M. M.da Mota&S. M.Nelson J. chem. Soc. (A)1970 790.

10.1021/ja01500a009

10.1039/qr9641800295

Bühler H., 1970, Chimia, 24, 433

H.Bühler Dissertation ETH Nr. 4796 Zürich1972.

Ashcroft S., 1970, Thermochemistry of transition metal complexes

10.1021/j100825a031

Paoletti P., 1963, Ricerca Sci., 33, 405

10.1021/ic50061a022

10.1021/ic50064a018

F.Holmes&D. R.Williams J. chem. Soc. (A)1967 1702.

10.1002/hlca.19710540209

10.1002/hlca.19500330428

10.1002/hlca.19500330426

10.1002/hlca.19530360309

10.1002/hlca.19500330427

10.1038/249773a0

10.1021/ja01512a005

Arnek R., 1970, Arkiv Kem., 32, 55

10.1016/0020-1650(75)80022-5

10.1021/ja01477a045

L.Sacconi P.Paoletti&M.Ciampolini J. chem. Soc.1961 5115.

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Helvetica Chimica Acta

Tập 60 Số 1

123-140

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