A study of the magnetic properties of copper(II) pyrazinamide complexes

Abstract

The magnetic susceptibilities of the compounds [Cu(pyzA), CI,].[Cu(pyzA), Br,]. and [(Cu(pyzA),(CIO,),),] (where pyzA = pyrazine-2-carboxamide) were measured between 1-7 and 280 K. The perchlorate complex exhibits Curie-Weiss behaviour to low temperatures. The susceptibilities of the halide complexes maximize at 17 K for the chloride and at ca. 31 K for the bromide. The experimental results are described by the Heisenberg model for a one-dimensional chain exhibiting antiferromagnetic interactions. Consistent with i.r. observations reported previous to this work, the observed susceptibilities of the halide complexes are indicative of a halogenbridged infinite-chain structure for these species.COPPER( 11) complexes of pyrazine-2-carboxamide (hereafter referred to as pyrazinamide, pyzA) were initially reported by Sekizaki and Yamasaki.l There are many structures that can be proposed for copper(I1)-pyrazinamide complex compounds because this potentially multidentate ligand can interact with a metal ion in several ways. Based upon the normal room temperature magnetic moments and the i.r. spectra of these complexes, Sekizaki and Y amasaki proposed squareplanar monomeric structures for the complexes A subsequent crystal-structure determination of [{Cu(pyzA),(C10,),},1 revealed that the copper ions of this complex are actually six-co-ordinate and are linked together through the pyrazinamide ligands to form an infinite two-dimensional polymeric molecular framework. I n the perchlorate complex, pyrazinamide is tridentate, bonding to one copper atom through the carbonyl oxygen of the amide group and the aromatic nitrogen ortho to the amide function, while weakly interacting with a neiglibouring copper ion through the ring nitrogen atom iiseta to the carboxamide moiety.-4 large number of copper complexes of the type [CuL,X,J (where L is an aromatic nitrogen-containing ligaiid and X is a halogen) are known and some have been structurally char act erized. The molecular s t ructures of the parent complexes of this series, [Cu-(pyridine),Cl,] and [Cu(pyridine),Br,], have been deterinined t o be halide-bridged one dimensional The structures of the related compounds [Cu(4-vinylpyridine),ClJ and [Cu(4-ethylpyridine),ClJ have been shown t o possess structures analogous to the copper halide-pyridine compounds. By way of contrast, [Cu (Z-picoline),C1,] and [Cu (2-picoline) 2Br2] are halogenbridged dirner~.'.~ In addition to these known structures, the magnetic [cu ( PYZA) Zc121 , [cu ( p3'ZA),Br2] 9 and [(cu( pYZA)2 ( c104)2},] *

Synthesis and NMRD studies of gadolinium(3+) complexes of macrocyclic polyamino polycarboxylic ligands bearing .beta.-benzyloxy-.alpha.-propionic residues

“…The observed water proton longitudinal relaxation rate is given by the sum of three contributions: (1) where Rlw is the gadolinium-free water relaxation rate, Rl: represents the contribution due to the exchange of water molecules from the inner coordination sphere of the metal ion to the bulk water and RIPm is the contribution of the water molecules diffusing in the outer coordination sphere of the paramagnetic center. The inner-sphere relaxation rate is described in terms of the following set of equations: H.…”

“…The rapid development of nuclear magnetic resonance imaging techniques has stimulated the interest in studies of magnetic relaxation of solvent protons by complexes of paramagnetic lanthanide ions, because of their potential utility as contrast agents. 1 The anionic complexes Gd(DTPA)2" (diethylenetriaminepentaacetic acid-gadolinium complex)2 and Gd(DOTA)" (1,4,7,10-tetraazacyclododecane-7VK/vyV",7V/"-tetraacetic acid-gadolinium complex)3 are those studied most extensively and have now entered into clinical practice because of their low toxicity and their ability to significantly alter the water proton relaxation times. Currently the search for new contrast agents for MRI is directed toward the synthesis of Gd3+ complexes of functionalized derivatives of DTPA4"6 and DOTA7 ligands without altering their chelating abilities.…”

Magnetic susceptibility of the chloro(2-diethylaminoethanolato)copper(II) tetramer

“…species and the radical produced by its reduction by ascorbic acid may be expected to be fully protonated. (17) In addition to the uncertainties associated with a structureless model for precursor formation,5 one would also have to contend with typical standard deviations of ±1.5 kcal mol"1 and ±7 cal deg"1 mol"1 in the activation enthalpies and entropies for reduction of CoOH2+(aq) by benzenediols, which are somewhat higher than are those for ascorbic acid (present work).…”

Structure and magnetic exchange in poly-bis(pyrazine)bis(methanesulfonato-O)-copper(II). One-dimensional exchange in a two-dimensional polymer

“…(where pyzA is pyrazine-2-carboxamide), the pyrazine rings lie in the xy plane (34) resulting in orthogonal overlap and a magnetically-dilute system (35). These previous studies and the X-ray structure results for C U ( P Y Z )~( C H~S O~)~ suggest that the equatorially bound pyrazine group in the methanesulfonate compound, which is canted out of the xy plane by 28.5", is suitably oriented to present a T-pathway for magnetic interactions between copper centres.…”