The Synthesis and Static Magnetic Properties of First-Row Transition-Metal Compounds with Chain Structures

Can. J. Chem. 63, 1055 (1985. The dimethylphosphinate of manganese(ll), Mn[(CH3)zP02]2, and its dihydrate have been prepared and studied using magnetic susceptibility, differential scanning calorimetry, and electronic and vibrational spectroscopic methods. The dihydrate was obtained in crystalline form and a single crystal X-ray diffraction study revealed a polymeric structure.Crystals of~poly-bis(p-dimethylphosphinato)diaquomanganese(l1) are monoclinic, o = 20.722(3), b = 4.8652(2), c = 11.0689(14) A, P = 102.209(7)", Z = 4, space group C2/c. The structure was solved by conventional heavy-atom methods and was refined by full-matrix least-squares procedures to R = 0.030 and R,,. = 0.033 for 983 reflections with I 2 3u(I). The structure consists of infinite centrosymmetric chains of Mn(ll) atoms linked by double phosphinate bridges and extending along the crystallographic b axis. The water molecu!es are involved in both interchain and bifurcated intrachain hydrogen bonding (0.--0 = 2.734(2), 2.899(3) and 3.120(3) A). The coordination about Mn is slightly distorteG octahedral with librationcorrected bond lengths Mn-O(phosphinato) = 2.156(2) and 2.212(2), Mn-OH2 = 2.247(2) A. Magnetic susceptibility studies on the dihydrate from 300 to 4.2 K reveal a magnetic moment of -5.9 BM over most of the range and give no evidence for significant magnetic exchange. The anhydrous compound, which is considered on the basis of indirect evidence to retain the double phosphinate bridged structure exhibited by the dihydrate, shows relatively strong antiferromagnetic behaviour. The data have been analyzed according to two theoretical models both of which employ the isotropic Heinsenberg Hamiltonian. The scaling model of Wagner and Friedberg gives J = -2.94 cm-' and g = 2.02 and the interpolation scheme of Weng gives J = -2.69 cm-' and g = 2.01. The magnitude of the exchange coupling is considered in relation to that observed in related manganese compounds and possible reasons for the observed damping of the exchange on hydration are discussed. Les etudes de susceptibiliti magnttique, rCalisCes avec I'hydrate double ii des temperatures allant de 300 a 4,2 K, rtvklent la presence d'un moment magnttique de 5.9 BM environ sur presque tout I'intervalle considtrk. Le compose anhydre, qui, d'aprts des preuves indirectes, conserverait la structure pontCe double phosphinate qui existe dans le dihydrate, exhibe un comportement antiferromagnktique relativement fort. On a analysC les donntes selon deux modtles thkoriques qui utilisent I'Hamiltonien isotrope de Heinsenberg. Le modble proportionnt de Wagner et Friedberg permet de prtdire des valeurs de J = -2,94 cm-' et g = 2,02 alors que le schema d'interpolation de Weng conduit a des valeurs de J = -2,69 cm-' et g = 2,01. On considkre I'amplitude du couplage d'echange en rapport avec celui observe avec des composes apparentes du mangankse et on discute des raisons qui pourraient expliquer le fait que I'tchange accompagnant I'hydratation est amoindri.[Traduit par le journal] Introduction The po...

Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 99%

Magnetic properties of anhydrous and hydrated dimethylphosphinates of manganese(II). The crystal and molecular structure of poly-bis(μ-dimethylphosphinato)diaquomanganese(II)

Cicha¹,

Haynes²,

Oliver³

et al. 1985

“…Accordingly the strongest antiferromagnetic exchange observed previously is in the a-forms of copper(I1) n-decyl-and n-dodecylphosphinate where I J I values of 29 cm-' have been reported (3). The neutral pyrazine (1,4-diazine, C4H4N2) ligand is also known to bridge copper centres and form linear chain polymers (15)(16)(17). An examination of the exchange coupling constants reported for Can.…”

Section: Resultsmentioning

confidence: 88%

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

Ehlert¹,

Rettig²,

Storr³

et al. 1989

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 (...

“…4. The magnitude of J is small and, particularly since zero field splitting effects can account for minor decreases in moment at low temperatures (14), not too much quantitative significance should be attached to it. Clearly though, the results place an upper limit of 0.017 cm-I on the magnitude of the exchange coupling constant in 1 and show that antiferromagnetic exchange in the compound, if it exists at all, is very weak.…”

Section: Resultsmentioning

confidence: 99%

Extended chain 2,3-pyrazinedicarboxylate complexes of manganese(II) and cadmium(II); synthesis and structure and magnetic properties

Mao¹,

Rettig²,

Thompson³

et al. 1996