New pyridine carboxamide ligands and their complexation to copper(ii). X-Ray crystal structures of mono-, di, tri- and tetranuclear copper complexes

Abstract

Seven new pyridine dicarboxamide ligands H2L(1-7) have been synthesised from condensation reactions involving pyridine-2,6-dicarboxylic acid (H2dipic), pyridine-2,6-dicarbonyl dichloride or 2,6-diaminopyridine with heterocyclic amine or carboxylic acid precursors. Crystallographic analyses of N,N'-bis(2-pyridyl)pyridine-2,6-dicarboxamide monohydrate (H2L8 x H2O), N,N'-bis[2-(2-pyridyl)methyl]pyridine-2,6-dicarboxamide and N,N'-bis[2-(2-pyridyl)ethyl]pyridine-2,6-dicarboxamide monohydrate revealed extensive intramolecular hydrogen bonding interactions. 2,6-Bis(pyrazine-2-carboxamido)pyridine (H2L6) and 2,6-bis(pyridine-2-carboxamido)pyridine (H2L7) reacted with copper(II) acetate monohydrate to give tricopper(II) complexes [Cu3(L)2(mu2-OAc)2]. X-Ray crystallography confirmed deprotonation of the amidic nitrogen atoms and that the (L6,7)2- ligands and acetate anions hold three copper(II) ions in approximately linear fashion. H2L8. Reacted with copper(II) tetrakis(pyridine) perchlorate to give [Cu(L8)(OH2)]2 x 2H2O, in which (L8)2- was tridentate through the nitrogen atoms of the central pyridine ring and the deprotonated carboxamide groups at one copper centre, with one of the terminal pyridyl rings coordinating to the other copper atom in the dimer. The corresponding reaction using H2L7 gave [Cu3(L7)2(py)2][ClO4]2, which transformed during an attempted recrystallisation from ethanol under aerobic conditions to a tetracopper(II) complex [Cu4(L7)2(L7-O)2].

Template synthesis of novel carboxamide dinuclear copper (II) complex: spectral characterization and reactivity towards calf-thymus DNA

“…A medium intensity sharp band was observed in the region 1,704-1,713 cm -1 assigned to t(C=O) of carboxamide linkage (Jain et al 2004). Previous reports on carboxamide ligand also support these assignments (Alcock et al 2005) and confirm the non-involvement of [C=O group in coordination with the metal ion.…”

Rare and Diverse Binding Modes Introduced through Mechanical Bonding

“…[4] We were intrigued to find that upon protic demetalation of the complex to give H 2 1, the 1 H NMR spectrum in CDCl 3 indicated significant intercomponent hydrogen bonding between the amide groups of the macrocycle and the pyridine nitrogen atom of the rotaxane thread (the protons of the amide groups in the macrocycle appear 1.7 ppm downfield relative to the corresponding protons in the free macrocycle). Such a binding motif, which requires essentially orthogonal pyridine rings with the nitrogen atoms bridged by bifurcated hydrogen bonds, is extremely rare (a search of the Cambridge Crystallographic Database reveals only one other example [5] ) but is somewhat reminiscent of the hydrogen bonding that occurs at 908 to the plane of the lone pairs of amide groups in threads seen extensively in other hydrogen-bonded rotaxanes. [6] Slow cooling of a hot, saturated solution of H 2 1 in acetonitrile/chloroform (10:1) yielded single crystals that were of sufficient quality to confirm the interaction in the solid state by X-ray crystallography (Figure 3 a, b) but were inadequate to confidently characterize the interaction in detail.…”

Porphyrin‐Based Switchable Molecular Turnstiles

“…Dimesylate 13 was prepared in two steps. The reaction [34a] of diacylchloride derivative 6 [36] with the commercially available aminoglycol 7 at room temperature and in the presence of Et 3 N afforded in about 72 % yield the diol 11, which was subsequently transformed into the dimesylate 13 in about 72 % yield upon treatment with methanesulfonyl chloride in the presence of triethylamine in dry THF at room temperature.…”