indicates that the oxidation product is diamagnetic and that all three ligands are equivalent. Diamagnetism must result either from strong spin-spin coupling between the paramagnetic metal and radical ligand or from charge delocalization within the cationic complex. This observation further suggests that the positively charged complex, which may form initially in the hydrolysis reaction between M 0 4 -and catechol in reaction 1, is the Tc(V1) species TcV1( DBSQ) ( DBCat)2f rather than TcV"( DBCat) 3+. Given the negative value of the DBSQ/DBCat couple, catecholate reduction of Tc(VI1) to Tc(V1) would be quite favorable. DiscussionTwo unusual examples of Tc(V1) have been obtained from the reaction between NH4Tc0, and 3,5-di-tert-butylcatechol. Other well-characterized complexes of Tc(V1) are confined to the nitrido anions TcNX4-(X = C1, Br, TCF6) and the polymeric oxyhalides TcOX4 (X = F, Cl).10315*16 In the reaction, catechol serves as an acid to hydrolyze oxo ligands of the pertechnetate ion, as a chelating agent with the metal, and as a reducing agent for Tc-(VII). Both Tc(DBCat), and T C ( D B C~~)~( D B A P )show wellresolved IO-line EPR spectra in solution at room temperature. Electrochemical characterization has been used to show the stability of the neutral Tc(V1) complexes relative to Tc(V) and Tc(IV) forms and to evaluate the accessibility of cationic forms of the complexes.Empirical studies have shown that complexes with a single positive charge are particularly effective as heart-imaging agents. Spheroidal complexes appear to bind most effectively with myocardial receptors and the hexakis(isonitrile)technetium(I) complexes are among the most effective myocardial-imaging agents." The tert-butylisonitrile complex T C (~-B U N C )~+ provides high-quality images but accumulates in the liver, blocking exposure to the heart. Derivatives with methoxy substituents have shown lower liver accumulation and higher miocardia1 specificity. Abstract:The in situ oxidation of niobium and tantalum in HS0,F by bis(fluorosulfury1) peroxide, SzO6F2, results in the formation of solvated Lewis acids M(SO,F),, M = Nb or Ta. Both solutes behave as moderately strong, monoprotonic acids, based on electrical conductivity measurements over the concentration range 0-0.05 m and on conductometric titrations against KS03F. These measurements suggest a general order of acidity, Au(S03F), > Ta(SO,F), 2 SbFS > Nb(S0,F)5 > NbF5, all giving rise to monoprotonic acids. Supporting evidence comes from 'H, I9F, and 93Nb NMR spectroscopy and the successful isolation and characterization of complexes of the type CS,[M(SO,F)~+,], with M = Nb or Ta and n = 1 or 2, from these solutions.
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...
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