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},] *
