Complexes of 2,6-bis[N-(2′-pyridylmethyl)carbamyl]pyridine: formation of mononuclear complexes, and self-assembly of double helical dinuclear and tetranuclear copper(ii) and trinuclear nickel(ii) complexes

Abstract

The potentially pentadentate ligand 2,6-bis[N-(2'-pyridylmethyl)carbamyl]pyridine (H2L1), readily prepared from reaction of a diester of pyridine-2,6-dicarboxylic acid (H2dipic) and 2-aminomethylpyridine (ampy), shows limited tendency to form 1:1 M:L complexes with labile metal ions, although [CuL1] and [NiL1] were observed as minor species, the latter characterized by a crystal structure analysis. A mononuclear complex formed with inert Co(III) was characterized by a crystal structure as the neutral 1:2 complex [Co(L1)(HL1)] with two ligands acting as tridentate ligands, one coordinated by the central pyridine and its two flanking deprotonated amido groups, and the other by the central pyridine, one amido and one terminal pyridine group, with the remaining poorly coordinating protonated amide remaining unbound along with other terminal pyridine groups. Fe(III) is known to form a symmetrical 1:2 complex, but that complex is anionic due to binding of all four deprotonated amido groups; the unsymmetrical neutral Co(III) complex converts into a symmetrical anionic species only on heating for hours in aqueous base in the presence of activated carbon. The most remarkable tendency of H2L1, however, is towards the formation of robust double helical complexes: a dinuclear Cu(II) complex [Cu2L1(2)] forms, as well as a trinuclear Ni(II) complex [Ni(3)(L1)2(OAc)2(MeOH)2]. Moreover, in the presence of added H2dipic, the tetranuclear complex [Cu4(L1)2(dipic)2(OH2)2] is obtained. All helical complexes have been characterized by X-ray crystal structure analyses, and all crystals feature a racemic mixture of left- and right-handed double helices stabilized by inter-ligand pi-stacking (inter-ring distances of 3.2-3.8 A) of ligands which each span several metal ions. Using the chelating ligand pentane-2,4-dione (acac), each of the two pairs of adjacent monodentate ligands in [Ni3(L1)2(OAc)2(OH2)2] have been shown to be available for substitution without destroying the helical structure, to form [Ni3(L1)2(acac)2], also characterized by a crystal structure.

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. Additionally, signals at *1,394, *2,877, and *2,933 cm -1 were attributed to t (C-N), t(CH 2 ), and aromatic t(CH) vibrations, respectively.…”

Synthesis and Biophysical Studies of Bis‐Macrocyclic Cobalt/Copper(II) Complexes Having a Pyridine Spacer with CT DNA and 5′‐GMP

“…To further elucidate the structure of the bis-macrocyclic complexes, the diamagnetic complex 2 was characterized by 1 H-and 13 C-NMR spectroscopy, showing characteristic aliphatic and aromatic signals with chemical shifts in accordance with the proposed structure. The aromatic region of the spectrum of 2 was consistent with the presence of a doublet at d(H) 7.85 and a well-resolved triplet at d(H) 7.14 due to equivalent and non-equivalent H-atoms from the pyridine spacer [35] 2 þ , respectively. The peaks occurring at m/z 149 and 77 corresponding to the 1,8-diamino-3,6-diazaoctane and pyridine groups, respectively, further confirm this fragmentation pattern.…”

An [{Fe(mecam)}2]6− Bridge in the Crystal Structure of a Ferric Enterobactin Binding Protein

“…[25] Another remarkable feature of the structure of the (CeuE) 2 -{Fe(mecam)} 2 assembly is the chirality of the Fe centers. Both [Fe(catecholate) 3 ] 3À recognition sites in the crystal structure of [{Fe(mecam)} 2 ]…”

“…[1] In particular, the exploration of interstrand p interactions to determine the nuclearity of helical metal complexes is currently attracting a lot of attention. [2,3] Here we present the crystal structure of the periplasmic ferric enterobactin binding protein CeuE of Campylobacter jejuni bound to L,L-[{Fe(mecam)} 2 ]…”