Magnetic properties and superexchange in single chloride-bridged copper(II) chain compounds

A novel and reliable method for the synthesis of polybis(p-pyrazolato-N,N ')copper(II), [ C~( p z )~] , (where pz = N2C3H3), is presented. Single crystals of the polymer suitable for X-ray study have been grown under carefully controlled conditions. Crystals of polybis(p-pyrazolato-N,N1)copper(II) are orthorhombic, a = 7.917(1), b = 11.491(2), c = 7.778(1) A, Z = 4, space group lbam. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.029 and R, = 0.038 for 507 reflections with 1 2 3u(1). The crystal structure consists of infinite double-bridged polymeric chains. The Cu atom has a D2 distorted tetrahedral coordination geometry with Cu-N = 1.957(2) A and N-Cu-N Mots clks : structure cristalline, chaine polymCrique de pyrazolato-cuivre(II), Cchange antiferromagnktique.[Traduit par la revue] Introduction As part of our continuing interest in metal pyrazolate complexes and magnetic exchange effects in transition metal coordination polymers we have initiated a comprehensive study of binary transition metal pyrazolate compounds. Earlier studies in this area have been reviewed by Trofimenko (I) and the intractable nature of the polymeric species noted. Our primary interest in these materials stems from the expectation that they will provide examples of infinite-chain polymers with the bridging pyrazolate ligands acting as pathways for strong magnetic exchange between metal centres. By varying the substituents on the pz (pz = pyrazolyl) rings and studying different metal systems it should be possible to examine systematically how electronic and structural factors affect the magnetic and other properties of these materials. We present here a novel method for the synthesis of the [ C u ( p~)~] . polymer and provide evidence that the methods (2) employed in previous attempts to prepare this compound in fact yield a different product. In addition, the new route described provides excellent crystals of the binary copper(I1) pyrazolate polymer enabling us to report the first X-ray crystal structure determination of this type of complex. We also describe electronic and vibrational spectroscopic, variable temperature magnetic susceptibility (4.2 to 299 K), and thermal studies on this novel material. Experimental SynthesisCopper metal shot was cleaned by washing first in 12 M HCl, ther! water and finally acetone. A magnetic stir bar, 10.0 g (147 rnmol) of pyrazole and 8.13 g (78.2 rnmol) of cleansed copper shot were placed in a 100 mL round bottom flask fitted with a reflux condenser. The reaction mixture was heated, with stining, to llO°C and air was bubbled into the molten pyrazole via a Pyrex tube lowered through the condenser. A green solid appeared almost immediately. The mixture was allowed to react for 18 h during which time sublimed pyrazole was periodically scraped back into the reaction mixture. The mixture, which had solidified on cooling, was then washed with 4 X 100 mL portions of CH2C12, 100 mL of high boiling petroleum ether and then suction filtered. [ C u (...

Section: Resultsmentioning

confidence: 81%

Metal pyrazolate polymers. Part 1. Synthesis, structure, and magnetic properties of the [Cu(pz)₂]_x polymer

Ehlert¹,

Rettig²,

Storr³

et al. 1989

“…( l), we have analyzed the magnetic data according to the isotropic Heisenberg model for exchange coupled linear chains employing the polynomial developed by Hall and others (9,10). Computer fits to the model using experimental data over the 2 to 300 K range were made for all five compounds and the best fit values of J , g, and % paramagnetic impurity are given in Table 5.…”

Section: Magnetic Propertiesmentioning

confidence: 99%

Metal pyrazolate polymers. Part 2. Synthesis, structure, and magnetic properties of [Cu(4-Xpz)₂]_x polymers (where X = Cl, Br, Me, H; pz = pyrazolate)

Ehlert¹,

Rettig²,

Storr³

et al. 1991

. 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-...

“…This increase in susceptibility at the lowest temperatures is indicative of the presence of paramagnetic monomer impurity. As before (3), the magnetic data were analyzed according to the isotropic Heisenberg model for exchange coupled linear chains employing the polynomial expression for the magnetic susceptibility developed by Hall (22,23). Computer fits were made to the susceptibility data with J, g, and percent paramagnetic impurity as variables.…”

Section: Magnetic Propertiesmentioning

confidence: 99%

“…The low temperature magnetic susceptibility data (4.2-100 K) were fit to theory employing the polynomial expression of Baker et al for ferromagnetically coupled S = 112 chains (23,24). Attempts to include paramagnetic impurity produced no improvement in agreement between experiment and theory in these cases.…”

Section: Magnetic Propertiesmentioning

confidence: 99%

Magnetic concentration and polymorphism in di-n-octyl-, di-n-decyl-, and di-n-dodecylphosphinates of copper(II)

Haynes¹,

Oliver²,

Thompson³

1985

. Can. J. Chem. 63, I1 l l (1985). Phosphinates of copper(l1) of the type C U ( R~P O~)~ where R is n-octyl, n-decyl, and n-dodecyl have been synthesized and characterized by differential scanning calorimetry, vibrational and electronic spectroscopy, and variable temperature (300 to 4.2 K) magnetic susceptibility studies. Each of these compounds was obtained in distinct a and P structural forms. All materials appear to have the double phosphinate bridged extended chain structure and the magnetic data have been successfully analyzed according to the isotropic Heisenberg model for linear chains. The a forms exhibit antiferromagnetic behaviour with J values of -25, -29, and -29 cm-' for the octyl, decyl, and dodecyl derivatives respectively. The P forms are ferromagnetic and have corresponding J values of 1.8, 2