Ternary Copper(II) Coordination Compounds with Nonpolar Amino Acids and 2,2′-Bipyridine: Monomers vs. Polymers

Abstract

Reactions of copper(II) sulfate with 2,2′-bipyridine (bipy) and amino acids with nonpolar side chains (l-alanine (HAla), l-valine (HVal), or l-phenylalanine (HPhe)) were investigated under different solution-based and mechanochemical methods. Five new ternary coordination compounds were obtained by a solution-based synthesis and three of them additionally by the liquid-assisted mechanochemical method: {[Cu(μ-l-Ala)(H2O)(bipy)]2SO4·2H2O}n (1a·2H2O), {[Cu(μ-l-Ala)(H2O)(bipy)][Cu(l-Ala)(H2O)(bipy)]SO4·2.5H2O}n (1b·2.5H2O), {[Cu(μ-l-Val)(H2O)(bipy)][Cu(l-Val)(H2O)(bipy)]3(SO4)2·4H2O}n (2·4H2O), [Cu(l-Phe)(H2O)(bipy)][Cu(l-Phe)(SO4)(bipy)]∙8H2O (3·8H2O), and [Cu(l-Phe)(H2O)(bipy)][Cu(l-Phe)(SO4)(bipy)]∙9H2O (3·9H2O). The compounds were characterized by single-crystal and powder X-ray diffraction, infrared spectroscopy, and a thermal analysis. Structural studies revealed two structural types, monomeric in 3·8H2O and 3·9H2O, polymeric architectures in 1a·2H2O, and mixed structures (monomeric and polymeric) in 1b·2.5H2O and 2·4H2O. The copper(II) ion is either pentacoordinated or hexacoordinated, with an observed Jahn–Teller effect. The crystal structures are based on an intensive network of hydrogen bonds and π interactions. 1a·2H2O and 2·4H2O showed substantial in vitro antiproliferative activity toward human hepatocellular carcinoma (HepG2) and moderate activity toward human acute monocytic leukemia cell lines (THP-1).

Keywords

• 2,2′-bipyridine
• amino acids
• coordination polymers
• copper
• crystal structures
• mechanochemistry