In:
European Journal of Inorganic Chemistry, Wiley, Vol. 2003, No. 7 ( 2003-04), p. 1340-1354
Kurzfassung:
The protonation and metal complex formation of the branched pentaamine ligand 2,2,6,6‐tetrakis(aminomethyl)‐4‐azaheptane (ditame, L) with Co II , Co III , Ni II , Cu II , Zn II , and Cd II have been studied. The crystal structures of [Ni(ditame)(EtOH)]Br 2 , [Co 2 (ditame) 2 (O 2 )]Cl 4 ·4H 2 O, and [Co 2 (ditame) 2 (O 2 )]Cl 2 [ZnCl 4 ][ZnCl 3 (H 2 O)]·H 2 O 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 (N sec ) apical. This geometry enforces a relatively short M−N sec bond. Complex formation in aqueous solution was evaluated by potentiometric titration. The ditame ligand forms a surprisingly stable Ni II complex with log K NiL = 17.8 (25 °C, 0.1 M KNO 3 ), and formation of protonated species [Ni(H n ditame)] ( n +2)+ ( n = 1, 2) is not significant. Different behavior is evident for Zn II and Cd II , with which protonated species are extensively formed, while the stability of [ML] 2+ is relatively low. Complex formation between ditame and Cu II in the range 3 〈 pH 〈 7 resulted in the formation of [Cu(H 2 ditame)] 4+ . In slightly alkaline solution, the dinuclear [Cu 2 (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 Cu II ··· Cu II 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 Ni II/III and Co II/III couples. For the dinuclear peroxo/ superoxo‐bridged Co III complexes, quasi‐reversible electron transfer corresponding to oxidation/reduction of the O 2 2− /O 2 − bridge was observed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Materialart:
Online-Ressource
ISSN:
1434-1948
,
1099-0682
DOI:
10.1002/ejic.v2003:7
DOI:
10.1002/ejic.200390174
Sprache:
Englisch
Verlag:
Wiley
Publikationsdatum:
2003
ZDB Id:
1475009-0
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