Premium
Synthesis, Crystal Structures, and Solution Properties of N ‐Methylene(phenyl)phosphinic Acid Derivatives of Cyclen and Cyclam
Author(s) -
Rohovec Jan,
Kývala Mojmír,
Vojtíšek Pavel,
Hermann Petr,
Lukeš Ivan
Publication year - 2000
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/(sici)1099-0682(200001)2000:1<195::aid-ejic195>3.0.co;2-6
Subject(s) - chemistry , protonation , cyclen , cyclam , conformational isomerism , methylene , moiety , crystallography , nmr spectra database , hydrogen bond , nuclear magnetic resonance spectroscopy , crystal structure , ligand (biochemistry) , stereochemistry , dissociation constant , acid dissociation constant , stability constants of complexes , medicinal chemistry , metal , aqueous solution , molecule , ion , organic chemistry , spectral line , biochemistry , physics , receptor , astronomy
Two phenylphosphinic acid derivatives of tetraaza macrocycles, (1,4,7,10‐tetraazacyclododecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid) [(H 4 L 1 ) and (1,4,8,11‐tetraazacyclotetradecanetetrayl)tetrakis(methylene)tetrakis(phenylphosphinic acid)] (H 4 L 2 ), were synthesised and the crystal structures of H 4 L 2 and its bis(1‐adamantylammonium) salt were determined. In both the structures, the ring conformation is virtually the same and is stabilised by hydrogen bonds. Protonation constants of the acids and stability constants of their Zn 2+ and Cd 2+ complexes were determined pH‐metrically at 25 °C and at an ionic strength of 0.1 mol dm –3 (KNO 3 ). The p K A values found for both the compounds are lower than those for their carboxylic analogues and correspond to the expected electron‐withdrawing ability of the –P(Ph)O 2 H moiety. The value p K 1 of the last dissociation constant of H 4 L 1 is surprisingly high. The complexes of Zn 2+ and Cd 2+ with (L 1 ) 4– and (L 2 ) 4– are less stable than those with other similar ligands, which is in accordance with lower overall basicity of H 4 L 1 and H 4 L 2 . A pronounced drop in the stability of the complexes of H 4 L 2 can be explained by partial coordination of the ligand to the metal ions. The solution properties of the ligands were also investigated by 31 P‐NMR spectroscopy. The spectra observed suggest stable (on the NMR time scale) conformations of the protonated ligands in solution. A comparison of NMR spectra in solution and CP/MAS‐NMR spectra indicates that the structures of the conformers roughly correspond to the structures observed in the solid state. The conformations are stabilised by intramolecular hydrogen bonds and by hydrophobic interactions of phenylphosphinic moieties. The conformers are stable even at 90 °C, but not in the presence of complexing metal ions.