The coordination chemistry of the pentadentate 2,2,6,6-tetrakis(aminomethyl)-4-azaheptane (ditame)

Hegetschweiler, K; Maas, O; Zimmer, A; Geue, R; Sargeson, A; Harmer, J; Schweiger, A; Buder, I; Schwitzgebel, G; Reiland, V; Frank, W

Journal article

The coordination chemistry of the pentadentate 2,2,6,6-tetrakis(aminomethyl)-4-azaheptane (ditame)

Abstract:: The protonation and metal complex formation of the branched pentaamine ligand 2,2,6,6-tetrakis(aminomethyl)-4-azaheptane (ditame, L) with CoII, CoIII, NII, CuII, ZnII, and CDII have been studied. The crystal structures of [Ni(ditame)(EtOH)] Br2, [CO2(ditame)2(O2)Cl4 ·4H2O, and [Co2-(ditame)2(O2)]Cl2 [ZnCl4][ZnCl3(H2O)]·H2O were determined by X-ray diffraction analyses. The metal complexes showed octahedral coordination geometries with exclusive formation of six-membered chelate rings, the four primary amino groups being in equatorial positions and the secondary amino group (Nsec) apical. This geometry enforces a relatively short M-Nsec bond. Complex formation in aqueous solution was evaluated by potentiometric titration. The ditame ligand forms a surprisingly stable NiII complex with logKNiL = 17.8 (25 °C, 0.1 M KNO3), and formation of protonated species [Ni(Hnditame)](n+2)+ (n = 1, 2) is not significant. Different behavior is evident for ZnII and CdII, with which protonated species are extensively formed, while the stability of [ML]2+ is relatively low. Complex formation between ditame and CuII in the range 3 < pH < 7 resulted in the formation of [Cu(H2ditame)]4+. In slightly alkaline solution, the dinuclear [Cu2(ditame)2]4+ appears to be formed. The structural assignment of this dimer is based on its UV/Vis and EPR characteristics, with the EPR data indicating a CuII···CuII separation of about 5.9 Å. The redox behavior of the Ni and Co complexes was investigated by cyclic voltammetry. The mononuclear species showed quasi-reversible electron transfer for the NiII/III and ColII/III couples. For the dinuclear peroxo/superoxo-bridged CoII/III complexes, quasi-reversible electron transfer corresponding to oxidation/reduction of the O22-/O2- bridge was observed. (© Wiley-VCH Verlag GmbH and Co. KGaA, 69451 Weinheim, Germany, 2003).

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APA Style

Hegetschweiler, K., Maas, O., Zimmer, A., Geue, R., Sargeson, A., Harmer, J., Schweiger, A., Buder, I., Schwitzgebel, G., Reiland, V., & Frank, W. (2003). The coordination chemistry of the pentadentate 2,2,6,6-tetrakis(aminomethyl)-4-azaheptane (ditame). EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, 2003(7), 1340–1354.

MLA Style

Hegetschweiler, K., et al. “The Coordination Chemistry of the Pentadentate 2,2,6,6-Tetrakis(Aminomethyl)-4-Azaheptane (Ditame).” EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, vol. 2003, no. 7, 2003, pp. 1340–54.

Chicago Style

Hegetschweiler, K, O Maas, A Zimmer, R Geue, A Sargeson, J Harmer, A Schweiger, et al. 2003. “The Coordination Chemistry of the Pentadentate 2,2,6,6-Tetrakis(Aminomethyl)-4-Azaheptane (Ditame).” EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2003 (7): 1340–54.
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