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Metal Complexes with Macrocyclic Ligands. Part XXXVIII . Steric effects in the copper(II) and nickel(II) complexes with tetra‐ N ‐alkylated 1,4,8,11‐tetraazacyclotetradecanes
Author(s) -
Oberholzer Martin R.,
Neuburger Markus,
Zehnder Margareta,
Kaden Thomas A.
Publication year - 1995
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19950780220
Subject(s) - chemistry , steric effects , metal , nickel , alkyl , copper , square pyramidal molecular geometry , ligand (biochemistry) , medicinal chemistry , alkylation , metal ions in aqueous solution , tetrahedral molecular geometry , stereochemistry , aqueous solution , crystallography , organic chemistry , catalysis , biochemistry , receptor
A series of tetra‐ N ‐alkylated 1,4,8,11‐tetraazacyclotetradecanes have been synthesized and their complexation potential towards Ni 2+ and Cu 2+ studied. In the case of sterically demanding alkyl substituents, such as i‐Pr, PhCH 2 , or 2‐MeC 6 H 4 CH 2 , no metal complexes are formed, whereas for substituents such as Me, Et, and Pr, the metal ion is incorporated into the macrocycle. The spectroscopic properties of the Ni 2+ and Cu 2+ complexes in aqueous solution indicate that, depending on the sterical hindrance of the N ‐substituents, the complexes are either square planar or pentacoordinated. All these Ni 2+ and Cu 2+ complexes react with N 3 −to give ternary species, the stability of which have been determined by spectrophotometric titrations. The tendency to bind N 3 −decreases with increasing steric hindrance of the alkyl substituents. The X‐ray studies of the Ni 2+ complex with the macrocycle 11 , substituted by two Me and two Pr groups, and that of the Cu 2+ complex with the tetraethyl derivative 8 show that in the solid state, the metal ions exhibit square planar coordination with a small distortion towards tetrahedral geometry.