High steric constraints and molecular distortion in methyl-substituted amide-based paracyclophanes and the binuclear Cu2+ complexes: X-ray structures, NMR and absorption spectra

Michiko B. Inoue*, Motomichi Inoue, Rocio Sugich-Miranda, Lorena Machi, Enrique F. Velazquez, Quintus Fernando

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Scopus citations

Abstract

Chelating paracyclophanes that are sterically constrained to a great extent have been synthesized and characterized by X-ray crystallography and NMR spectroscopy: the macrocycles studied are 2,9,18,25-tetraoxo-4,7,20,23-tetrakis(carboxymethyl)-1,4,7,10,17,20,23,26- octaaza[10.10]paracyclophane, abbreviated as (Lpd)H4, and its 2,5-dimethyl-p-phenylene and tetramethyl-p-phenylene derivatives, abbreviated as (Ldmpd)H4 and (Ltmpd)H4, respectively. Steric interaction between tetramethylphenylene and amide groups in the tetramethyl derivative defines the conformation of the macrocyclic cavity, and causes unusual spectroscopic and chemical properties including the extreme line-broadening of 1H NMR signals and the low basicity of amino nitrogen; such properties are not observed for the other macrocycles, in which steric interaction between phenylene and amide groups is less effective. The complexation of the highly strained ligand (Ltmpd)H4 with Cu2+ ions has been studied by X-ray crystallography and solution electronic spectroscopy. The macrocycle forms a binuclear complex of [Cu2(LH-4)]4- type in which four amide nitrogen atoms are deprotonated and each metal ion is coordinated to two amide nitrogen atoms and two amino nitrogen atoms. In the binuclear chelate molecule, the severe contraction of the macrocyclic ring forces the phenylene groups distorted to a boat form, due to the steric effect of the tetramethyl substituents. As a result, the metal-ligand charge-transfer interaction in the binuclear complex differs from that in the mononuclear chelate of the same macrocycle.

Original languageEnglish
Pages (from-to)181-189
Number of pages9
JournalInorganica Chimica Acta
Volume317
Issue number1-2
DOIs
StatePublished - 28 May 2001

Bibliographical note

Funding Information:
The X-ray studies were carried out by using an X-ray diffractometer provided by the National Science Foundation (Grant No. CHE9610374) to the Molecular Structure Laboratory at the University of Arizona.

Keywords

  • Binuclear complexes
  • Copper complexes
  • Crystal structures
  • Macrocyclic complexes

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