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IntroductionWe recently reported on a number of metal pyrazolate coinplexes containing copper or zinc ( 1-6). Particular emphasis was placed on studies of the magnetic properties of copper(I1) oligometallic and polymeric systems (1,(4)(5)(6), studies in which it was demonstrated that pyrazolate and substituted pyrazolate ligands are efficient mediators of antiferromagnetic exchange between copper centres.As part of our investigations of binary metal pyrazolates, generally, we have synthesized a number of polymeric cobalt(I1) pyrazolates (7). In the course of this work, two 3,5-dimethylpyrazolate-bridged complexes, the dimeric [Co(drnp~)~(Hdmpz)]~ and the trimetallic [Co(dmpz),Cl-(Hdmpz)],Co, were isolated in crystalline form suitable for single crystal X-ray diffraction studies. The structures and magnetic properties of these complexes, together with some studies on a dimeric-oligometallic material with the empirical formula C~( d m p z )~. 0.344(Hdmpz), form the basis of this communication. These materials provide important in-

A moderately high-yield, high temperature synthesis of the title compound is reported. Crystals of tris [(3,5-dimethylpyrazolato-N',~2)copper(~)] are triclinic, a = 12.360(4), b = 14.637(4), c = 12.358(4) A, a = 105.29(2), P = 119.83(2), y = 93.99(3)", Z = 4 (trimers, two per asymmetric unit), space group P i . The structure was solved by heavy atom methods and was refined by full-matrix least-squares procedures to R = 0.034 andR,, = 0.038 for 3877 reflections with1 2 3a(4. The structure consists of trimeric molecules with an unusually short average Cu-N distance of 1. et Z = 4 (deux trimbes par unite asymktrique). On a affint la structure par la mtthode des atomes lourds et on l'a affinee par la mtthode des moindres canes jusqu'a des valeurs respectives de R = 0,034 et R,, = 0,038 pour 3877 reflexions avec I 3 o Q . La structure est formte de molCcules trimtres dans lesquelles la distance moyenne Cu-N, 1,852 A, est anormalement courte. Les cycles centraux a neuf chafnons de Cu3N6 sont plans a moins de 0,07 A. Des interactions Cu...Cu faibles, de distance moyenne 2,946 A, retiennent les unites de trimere par paires autour de centres de symttrie.Mots clks : trimere pyrazolato-cuivre (I), pyrazolat de cuivre (I).[Traduit par la revue]

The reaction of ferrocene with molten imidazole at 150 °C yielded pale yellow crystals of composition [Fe3(imid)6(imidH)2] x . Crystals of [Fe3(imid)6(imidH)2] x are monoclinic, a = 10.5912(9), b = 12.958(2), c = 10.617(1) Å; β = 92.696(9)°; Z = 2; space group P21/c. The structure was solved by Patterson methods and refined by full-matrix least-squares procedures to R = 0.033 and R w = 0.031 for 2260 reflections with I ≥ 3σ(F 2). The structure consists of chains of tetrahedral iron centers cross-linked via octahedral iron ions to generate a 3-D array. All of the iron centers are bridged to four other metal centers via imidazolate ions, the two remaining (trans) coordination positions of the octahedral centers being occupied by neutral imidazole molecules. Magnetic susceptibilities on powdered samples were measured over the temperature range 2−300 K and at fields ranging from 0 to 55 000 G. The compound exhibits antiferromagnetic coupling along chains of tetrahedrally coordinated iron centers. A canted spin structure leads to weak ferromagnetism at temperatures below a magnetic phase transition temperature of 17 K. Upon cycling the applied magnetic field between +55 000 and −55 000 G at 4.8 K, a hysteresis loop was obtained with a remnant magnetization of 2500 cm3 G mol-1 and a coercive field of 200 G.

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 (...