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The Coordination Chemistry of 1,4‐Diazepan‐6‐amine
Author(s) -
Romba Jens,
Kuppert Dirk,
Morgenstern Bernd,
Neis Christian,
Steinhauser Stefan,
Weyhermüller Thomas,
Hegetschweiler Kaspar
Publication year - 2006
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200500690
Subject(s) - chemistry , ligand (biochemistry) , protonation , amine gas treating , steric effects , aqueous solution , single crystal , potentiometric titration , crystallography , yield (engineering) , diamine , nuclear magnetic resonance spectroscopy , crystal structure , coordination complex , medicinal chemistry , stereochemistry , metal , polymer chemistry , organic chemistry , ion , biochemistry , materials science , receptor , metallurgy
The new, tridentate, facially coordinating ligand 1,4‐diazepan‐6‐amine (daza) has been prepared from ethane‐1,2‐diamine and 2,3‐dibromo‐1‐propanol in a seven‐step procedure with an overall yield of 22 %. The conformation of the free ligand has been elucidated by pH‐ and temperature‐dependent 1 H NMR spectroscopy and by a single‐crystal X‐ray structure analysis of H 3 dazaCl 3 · H 2 O. A twisted chair with a predominantly equatorial orientation of the primary amino group has been established for daza and its protonation products H x daza x + (1 ≤ x ≤ 3). The formation constants of [M(daza)] 2+ and [M(daza) 2 ] 2+ have been determined in aqueous solutions for M = Ni II , Cu II , Zn II , Cd II , and Co II by potentiometric and spectrophotometric measurements, and a remarkably high stability has been found for the bis complexes ML 2 in comparison to the mono complexes ML. This effect is discussed in terms of the particular steric requirements of the daza ligand. [Cu(daza)Cl 2 ], [Ni(daza) 2 ]Cl 2 · 3.2H 2 O and [Zn(daza) 2 ]SO 4 · 5H 2 O have been characterized by single‐crystal X‐ray analyses. Aerial oxidation of Co 2+ in the presence of daza results in the formation of the inert[Co(daza) 2 ] 3+ , which was isolated as a mixture of the cis and trans isomers. These two isomers were separated by chromatographic methods and identified by NMR spectroscopy and single‐crystal X‐ray structure analysis of cis ‐[Co(daza) 2 ][ZnBr 4 ]Br · H 2 O and trans ‐[Co(daza) 2 ] 3 [ZnBr 4 ] 2 Br 5 · 4H 2 O. The redox potentials of [Ni(daza) 2 ] 3+/2+ (1.04 V vs. NHE) and [Co(daza) 2 ] 3+/2+ (–0.21 V vs. NHE) were determined by cyclic voltammetry. The values are slightly more positive than for corresponding complexes with related cyclic triamines. This effect is again discussed in terms of the particular steric requirements of these ligands.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)