Second-sphere coordination in hexaamminecobalt(III) salt with organic sulphonate anion: Synthesis, characterisation and X-ray crystal structure of [Co(NH3)6](CH3SO3)3

Reaction of hexaamminecobalt(III) chloride with the silver salt of methanesulphonic acid in aqueous medium (1:3 molar ratio) forms hexaamminecobalt(III) methanesulphonate, [Co(NH₃)₆](CH₃SO₃)₃, in high yield. This cobalt(III) complex has been characterized by spectroscopic techniques (UV/visible, IR and NMR) and its solubility product determined. The X-ray crystal structure shows that the [Co(NH₃)₆]³⁺ cations interact at the second sphere by sharing edges with the anions, via N–H  O hydrogen bonds. The structure is related to that of [Co(NH₃)₆]Cl(CH₃SO₃)₂, but is modified to accommodate additional anions in place of Cl⁻.     

Voltammetric Reduction of alpha- and gamma-[S2W18O62]4- and alpha-, beta-, and gamma-[SiW12O40]4-: isomeric dependence of reversible potentials of polyoxometalate anions using data obtained by novel dissolution and conventional solution-phase processes

Comparative studies on the voltammetric reduction of the alpha and gamma isomers of Dawson [S(2)W(18)O(62)](4)(-) and alpha, beta, and gamma forms of Keggin [SiW(12)O(40)](4)(-) polyoxometalate anions have been undertaken. For the six reversible one-electron [S(2)W(18)O(62)](4)(-)(/5)(-)(/6)(-)(/7)(-)(/8)(-)(/9)(-)(/10)(-) processes in acetonitrile, reversible potentials (E(0)(')) were found to be independent of isomeric form within experimental error (+/-5 mV). However, because both the alpha and gamma* isomers of [Bu(4)N](4)[S(2)W(18)O(62)] are insoluble in water, solid-state voltammetric studies with microcrystals adhered to electrode surfaces in contact with aqueous Et(4)NCl and Bu(4)NCl electrolyte media were also possible. Although no isomeric distinction was again detected in the solid-state studies, it was found that reduction of adhered solid by four or more electron equivalents led to rapid dissolution. When Et(4)NCl was the electrolyte, this dissolution process coupled with potential cycling experiments enabled conventional solution-phase data to be obtained in water for the analogous six one-electron reduction steps previously detected in acetonitrile. A strong medium effect attributed to Lewis acidity effects was apparent upon comparison with E(0)(') data obtained in water and acetonitrile. In contrast, with the [SiW(12)O(40)](4)(-) system, E(0)(') values for the [SiW(12)O(40)](4)(-)(/5)(-)(/6)(-)(/7)(-) processes in acetonitrile exhibited a larger (about 70 mV) dependence on isomeric form, and the isomerization step, [gamma-SiW(12)O(40)](6)(-)--> [alpha-SiW(12)O(40)](6)(-), was detected on the voltammetric time scale. The influence of isomeric form on reversible potential data is considered in terms of structural and charge density differences exhibited in the [S(2)W(18)O(62)](4)(-) and [SiW(12)O(40)](4)(-) systems studied in this paper and published data available on the alpha, beta, gamma, and gamma isomers of [As(2)W(18)O(62)](6)(-) and [P(2)W(18)O(62)](6)(-) Dawson anions and Keggin systems.     

Reactions of 1,4-bis(tetrazole)benzenes: formation of long chain alkyl halides

The reactions of 1,4-bis[2-(tributylstannyl)tetrazol-5-yl]benzene with α,ω-dibromoalkanes were carried out in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazole. This led to the formation of several alkyl halide derivatives, substituted variously at N1 or N2 on the tetrazole ring. The crystal structures of 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (2-N,2-N′), 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (1-N,2-N′) and 1,4-bis[(2-(8-bromooctyl)tetrazol-5-yl)]benzene (2-N,2-N′) are reported. Further discussion involves the structure of 1,4-bis[2-(6-bromohexyl)-2H-tetrazol-5-yl]benzene (2-N,2-N′) previously reported.     

Exo-metal coordination by a tricyclic [(P(mu-N-2-NC5H4))2(mu-O)]2 dimer in [(P(mu-N-2-NC5H4))2(mu-O)]2(CuCl x (C5H5N)2)4 (2-NC5H4 = 2-pyridyl, C5H5N = pyridine)

The in situ reaction of the phosphazane dimer [CIP(mu-N-2-NC5H4)]2 (2) with CuCl in the presence of CsH5N/H2O gives the title complex [(P(mu-N-2-NC5H4))2(mu-O)]2(CuCl x (C5H5N)2)4 (1), containing a tricyclic [(P(mu-N-2-NC5H4))2(mu-O)]2 ligand which is isoelectronic with species of the type [(P(mu-NR))2NR]2.     

(Z)-3-p-tolylsulfinylacrylonitrile as a chiral dienophile: diels-alder reactions with furan and acyclic dienes

The behavior of (Z)-3-p-tolylsulfinylacrylonitrile (1) as a chiral dienophile has been evaluated from its reactions with furan and acyclic dienes. Electrostatic interactions of the cyano group with the sulfinyl one restrict the conformational mobility around the C-S bond, thus controlling the pi-facial selectivity, which is almost complete in all cases, the approach of the diene from the less-hindered face of the dienophile (that bearing the lone electron pair) in the predominant rotamer being the favored one. The regioselectivity is also completely controlled by the cyano group. Additionally, the reactivity of compound 1 as well as its endo-selectivity are both higher than those observed for the corresponding (Z)-3-sulfinylacrylates, thus proving the potential of sulfinylnitriles as chiral dienophiles.     

Oxidation processes at mercury electrodes for tetraphenyllead and related compounds in dichloromethane

Two oxidation waves are observed at mercury electrodes for tetraphenyllead in dichloromethane. The mechanisms of the oxidation processes have been investigated by dc and differential pulse polarography. The first wave is a broad two-electron step and represents the summation of a number of processes related to mercury exchange and halide abstraction. The exchange reactions are as follows: 2 Φ₄Pb + Hg→2Φ₃Pb⁺ + Φ₂Hg+2e^? 2 Φ₃Pb⁺ + Hg→2Φ₂Pb²⁺ + Φ₂Hg+2e^? Dichloroethane and HgCl₂ are identified as products of controlled potential electrolysis experiments as well as Φ₂Hg and Φ₂PbCl₂ implying that the coordinatively unsaturated Φ₃Pb⁺ and/or Φ₂Pb²⁺ react with the solvent dichloromethane and abstract chloride. The second oxidation process is the two electron step. Φ₂Hg+Hg→2 ΦHg⁺ + 2e^?Tetraalkyllead compounds (tetramethyl, tetraethyl, tetrabutyl) also give rise to related electrode processes at mercury electrodes and polarographic techniques may form the basis of a method for their analytical determination if separated chromatographically prior to detection.     

Synthesis and molecular structure of a plutonium(IV) coordination complex: [Pu(NO3)2(2,6-[(C6H5)2P(O)CH2]2C5H3NO)2](NO3)2x1.5H2Ox0.5MeOH

The trifunctional ligand 2,6-[(C6H5)2P(O)CH2]2 C5H3NO (1), in a mixed EtOH/MeOH solvent system, when combined with an aqueous nitric acid solution of Pu(IV), produces a 2:1 coordination complex, [Pu(1)2(NO3)2](NO3)2. A single crystal of [Pu(NO3)2(2,6-[(C6H5)2P(O)CH2]2C5H3NO)2](NO3)2x1.5H2Ox0.5MeOH was characterized by X-ray diffraction analysis. The crystal is monoclinic, space group P2(1)/n, with a = 19.1011(9) A, b = 18.2873(9) A, c = 21.507(1) A, alpha = gamma = 90 degrees, beta = 108.64(1) degrees, and Z = 4. Two neutral ligands (1) are bonded to the Pu(IV) ion in a tridentate fashion. Two nitrate ions also occupy inner sphere coordination positions, while two additional NO3- ions reside in the outer sphere. Comparison of the solution optical absorbance and solid diffuse reflectance spectra shows the same Pu(IV) chromophore exists in both solid and solution states.