Helical-Chain Copper(II) Complexes and a Cyclic Tetranuclear Copper(II) Complex with Single Syn−Anti Carboxylate Bridges and Ferromagnetic Exchange Interactions

Abstract

Tridentate Schiff-base carboxylate-containing ligands, derived from the condensation of 2-imidazolecarboxaldehyde with the amino acids beta-alanine (H2L1) and 2-aminobenzoic acid (H2L5) and the condensation of 2-pyridinecarboxaldehyde with beta-alanine (HL2), D,L-3-aminobutyric acid (HL3), and 4-aminobutyric acid (HL4), react with copper(II) perchlorate to give rise to the helical-chain complexes [[Cu(mu-HL1)(H2O)](ClO4)]n (1), [[Cu(mu-L2)(H2O)](ClO4).2H2O]n (2), and [[Cu(mu-L3)(H2O)](ClO4).2H2O]n (3), the tetranuclear complex [[Cu(mu-L4)(H2O)](ClO4)]4 (4), and the mononuclear complex [Cu(HL5)(H2O)](ClO4).1/2H2O (5). The reaction of copper(II) chloride with H2L1 leads not to a syn-anti carboxylate-bridged compound but to the chloride-bridged dinuclear complex [Cu(HL1)(mu-Cl)]2 (6). The structures of these complexes have been solved by X-ray crystallography. In complexes 1-4, roughly square-pyramidal copper(II) ions are sequentially bridged by syn-anti carboxylate groups. Copper(II) ions exhibit CuN2O3 coordination environments with the three donor atoms of the ligand and one oxygen atom belonging to the carboxylate group of an adjacent molecule occupying the basal positions and an oxygen atom (from a water molecule in the case of compounds 1-3 and from a perchlorate anion in 4) coordinated in the apical position. Therefore, carboxylate groups are mutually cis oriented and each syn-anti carboxylate group bridges two copper(II) ions in basal-basal positions with Cu...Cu distances ranging from 4.541 A for 4 to 5.186 A for 2. In complex 5, the water molecule occupies an equatorial position in the distorted octahedral environment of the copper(II) ion and the Cu-O carboxylate distances in axial positions are very large (>2.78 A). Therefore, this complex can be considered as mononuclear. Complex 6 exhibits a dinuclear parallel planar structure with Ci symmetry. Copper(II) ions display a square-pyramidal coordination geometry (tau = 0.06) for the N2OCl2 donor set, where the basal coordination sites are occupied by one of the bridging chlorine atoms and the three donor atoms of the tridentate ligand and the apical site is occupied by the remaining bridging chlorine atom. Magnetic susceptibility measurements indicate that complexes 1-4 exhibit weak ferromagnetic interactions whereas a weak antiferromagnetic coupling has been established for 6. The magnetic behavior can be satisfactorily explained on the basis of the structural data for these and related complexes.

Crystal structures and magnetic properties of a set of dihalo-bridged oxalamidato copper(ii) dimers

“…Therefore, the resulting sign depends on the amplitude of that overlap. 52 The above correlation rule is valid only for complexes with square-pyramidal arrangement of type II (pyramids share one base-to-apex edge with parallel basal planes) 29 .…”

Crystal Structure of [Bis(L-Alaninato)Diaqua]Nickel(II) Dihydrate

“…Transition metal complexes with Schiff-base ligand containing the carboxylate group have been of great interest due to their importance as essentially biologically active [1][2][3] models for metalloproteins [4] and their various geometry aspects [5]. Metals bound to amino acids are essential for the catalytic function of certain enzymes, and their chemistry has received a great deal of research interest due to their significant interaction with enzymes and with different organic ligands which enables a better understanding of the antitumor/viral activities of this class of compounds and for modeling substrates involved in enzyme inhibition [6,7].…”

Crystal structure of dichloro ((N-(N ',N '- dimethylammonio) ethyl) - 2,4 - dichlorosalicylaldiminato-N ,O) copper(II) ,Cu(C11H14Cl2N2O) Cl2

“…Metal complexes of Schiff bases have been extensively studied, and copper(II) complexes play a major role in both synthetic and structural research [1][2][3]. Schiff base metal complexes are one of the most important stereochemical models in transition metal coordination chemistry with their easy preparation and structural variation [4][5][6].…”