. Can. J. Chem. 69, 432 (1991).Novel and reliable methods for the synthesis of the polymers [C~(4-Xpz)~], (where X = H, C1, Br, and Me; pz = pyrazolate) are presented. The X = C1 compound was obtained as green and brown forms. Single crystals of the polymers with X = Me and X = C1 (green form) suitable for X-ray analysis have been obtained. [C~(4-Mepz)~], and [C~(4-Clpz)~], are isomorphous, crystallizing with four formula units per unit-cell in the orthorhombic space group Ibam, a = 9.7436(6), 9.155(4), b = 12.6106(8), 12.968(6), and c = 7.7482(6), 7.717(5) A, respectively, for the 4-Me and 4-C1 derivatives. The structures were refined by full-matrix least-squares procedures to R = 0.027 and 0.041 for430 and 246 reflections with 1 2 3u(l), respectively. Magnetic susceptibility studies over the temperature range 2 to 300 K have revealed that all the polymers exhibit very strong antiferromagnetic exchange between copper(I1) centres in the extended linear chains. Discontinuities displayed in the susceptibility versus temperature plots suggest the presence of phase transitions at -133 and -108 K in the X = C1 (green form) and x = Br materials, respectively. The four compounds, X = H, Br, Me, and C1 (green form) also exhibit thermochr6mism over the 77 to 176 K region. ' The magnetic data have been analyzed employing an isotropic Heisenberg model for antiferromagnetic exchange in extended chain polymers. Values of the exchange coupling constant, J, for the room temperature forms of these materials are determined as -81, -105, -96, -104, and -88 cm-' for 4-X = H, Br, Me, C1 (green form), and Cl (brown form), respectively. The magnitude of the exchange coupling is discussed in relation to structural parameters for the X = H, Me, and Cl (green form) compounds.Key words: copper(I1) 4-substituted pyrazolate polymers, crystal structures, magnetic exchange. Ibam, avec a = 9,7436(9), 9,155(5), b = 12,6106(8), 12,968(6) et c = 7,7482(6), 7,717(5) A, respectivement pour les dCrivCs 4-Me et 4-C1. On a affint les structures par la mCthode des moindres carrCs jusqu'i des valeurs respectives de R = 0,027 et 0,041 pour 430 et 246 reflexions avec I 2 3u(I). Des Ctudes de susceptibilit6 magnCtique effectuCes de 2 i 300 K ont rCvClC que tous les polymkres presentent un Cchange antiferromagnCtique trks fort entre les centres cuivre(I1) des chaines IinCaires allongCes. Les discontinuitCs obsen6es dans la courbe de susceptibilitC en fonction de la ternpkrature suggtrent la prtsence de transitions de phase 2 1 respectivement -133 K et -108 K dans les composCs avec X = Cl (forme verte) et X = Br. Les quarte composts, X = H, Br, Me et C1 (forme verte) prCsentent aussi de la thermochromie entre 77 K et 176 K. On a analysC les donntes magnttiques i I'aide du modtle isotrope de Heisenberg pour 1'Cchange antiferromagnttique dans les chafnes Ctendues de polymtres. On a dCterminC que les valeurs de la constance de couplage, J , pour les formes de ces matCriaux existant a la temperature ambiante, sont respectivement -81, -105, -96, -104 et -88 cm-...