Travis M. Anderson

Polyoxometalates on cationic silica: Highly selective and efficient O2/air-based oxidation of 2-chloroethyl ethyl sulfide at ambient temperature

Binary cupric nitrate and triflate systems catalyze the homogeneous air oxidation of the mustard (HD) simulant 2-chloroethyl ethyl sulfide (CEES) to the corresponding desired sulfoxide (CEESO) with effectively quantitative selectivity in acetonitrile under ambient conditions. This activity is enhanced when cationic silica nanoparticles coated with the anionic multi-iron polyoxometalates (POMs) are also present. The POM-coated nanoparticles are prepared by treatment of aqueous suspensions of Akzo Nobel Bindzil CAT® cationic silica nanoparticles with aqueous solutions of the POMs, K9[(FeIII(OH2)2)3(PW9O34)2] (K94) or Na12[(FeOH2)2Fe2(P2W15O56)2] (Na125).

Platinum-Containing Polyoxometalates†

Lee, Kortz, and their co-workers recently reported a Pt-containing polyoxovanadate, [H2Pt V9O28] 5 , in this journal. There are noteworthy features of this complex, and given the potential similarity of Ptand other noble metalcontaining polyoxometalates to a range of important metal-oxide supported noble-metal-based catalysts, electrodes, sensors, and other industrially significant materials, there is unquestionably interest in [H2Pt V9O28] 5 and other Ptcontaining polyoxometalates as possible tractable molecular representations of these materials. Nevertheless, there are some points many investigators will want to note. Lee, Kortz, and co-workers state: “Therefore, 1 [[H2Pt V9O28] 5 ] represents the first transition-metal-substituted decavanadate derivative...”. However, substituted decavanadates have been known for nearly two decades. See, for example, the work of Howarth, Pettersson, and co-workers on monoand di-molybdopolyvanadates or the study by Kamenar and colleagues on [(CH3)4N]4[H2MoV9O28]Cl. [3] Note that no {Mo10O28} “decavanadate” analogue exists; in the Mo-substituted decavanadates (contrary to several other polyoxometalate structure types) the Mo sites thus do not constitute addenda sites but represent genuine substituents. In addition, other substituted decavanadate motifs exist: Sasaki, Pope, and coworkers, for example, refer to their complex, [(MnV11O31)2O2] 10 , as “a manganese-substituted decavanadate” where “each half-unit may be dissected to reveal other familiar polyoxoanion structures, i.e., planar MnV6O24 (Anderson) or MnV9O28 (Mn-substituted decavanadate)”. There are also some technical concerns regarding the work reported in Ref. [1]. Lee, Kortz, and co-workers claim that the hydrogen atoms (Hb7 and Hb8) on two of the oxygen atoms (Ob7 and Ob8) bound to Pt were “actually located in the difference Fourier map and refined with the O···H separations restrained to 0.85(10) .” This is an unusual claim because hydrogen atoms on polyanion oxygen atoms bound to 5d metal centers (i.e. W or Pt) have seldom been located by X-ray analysis. The fact that the X-ray diffraction dataset was collected at high temperature (T= 293 K) makes this claim even more suspect. Without some independent confirmation of this claim, the community will be very skeptical about it. A single-crystal neutron diffraction study of this complex would provide such confirmation. We felt compelled to conduct a single-crystal neutron diffraction study of our terminal platinum oxo complex [O=Pt(H2O)(PW9O34)2] 16 [5] for precisely this reason. Without such a study, knowledgeable colleagues would have rightly questioned whether that report involved a terminal platinum oxo or platinum hydroxo unit (i.e. whether there was a hydrogen on that critical oxygen atom or not). Another serious objection with regard to the crystallographic identification of hydrogen, however, is that Lee, Kortz, and coworkers state they “placed the H atoms of the water molecules in calculated positions.” Of all the HFIX subroutines in SHELX, there is no command that will do this. In addition, Lee, Kortz, and coworkers report a Rint of “0.000” that indicates they did not collect any equivalent reflections in their data set; it is always better to have equivalent reflections, even in space group P1̄. Moreover, they state “We also prepared derivatives of 1 with different degrees of protonation, such as [HxPt V9O28] (7 x) (x = 2.5, 3, 4, 5), as shown by single-crystal X-ray analysis.” How does the latter analysis show a protonation state of 2.5 in a single molecular unit? You can have fractional occupancies (such disorder, a common phenomenon, was not mentioned in the article), but you cannot have a fractional hydrogen. Lee, Kortz, and co-workers, in reference [1] addressing our 2004 report of a terminal platinum oxo compound, state we did not show W or Pt NMR spectra. However, these investigators do not explain why we did not report these spectra (the reason was that these investigations are not possible given the lability of the platinum oxo complex in solution), but more importantly Lee, Kortz, and co-workers fail to mention that this platinum oxo complex was characterized by 10 techniques including single-crystal neutron diffraction that confirmed a terminal platinum oxo and not a platinum hydroxo unit is present. Thus W and Pt NMR, the only techniques Lee, Kortz, and co[*] Dr. R. Cao, Dr. T. M. Anderson, D. A. Hillesheim, Dr. K. I. Hardcastle, Prof. Dr. C. L. Hill Department of Chemistry Emory University Atlanta, GA 30322 (USA) Fax: (+ 1)404-727-6076 E-mail: chill@emory.edu

Stereoisomerism in polyoxometalates: structural and spectroscopic studies of bis(malate)-functionalized cluster systems

The tetrameric macrocycle [(P(mu-NtBu))2(1,4-(NH)2C6H4)]4, obtained from the reaction of the phosphazane dimer [ClP(mu-NtBu)]2 with p-phenylenediamine, has an unusual folded conformation in the solid state and contains a roughly tetrahedral arrangement of endo N-H groups for the potential coordination of anions.

Manganous heteropolytungstates. Synthesis and heteroatom effects in Wells–Dawson-derived sandwich complexes

A tetranuclear manganous Wells–Dawson sandwich-type polyoxometalate has been synthesized by the reaction of α-Na12(As2W15O56) with an aqueous solution of MnCl2·4H2O. The structure of this complex, αββα-Na16(MnIIOH2)2MnII2(As2W15O56)2·55H2O (Na1), was determined by single-crystal X-ray crystallography (a = 14.5230(12) A, b = 14.7104(13) A, c = 19.8927(17) A, α = 84.326(2)°, β = 81.709(2)°, γ = 65.584(2)°, triclinic, R1 = 6.2%, based on 26721 independent reflections) and is similar to the phosphorus analogue, αββα-Na16(MnIIOH2)2MnII2(P2W15O56)2 (Na2). Magnetization studies confirm that both Na1 and Na2 show antiferromagnetic coupling of the four Mn(II) centers. Despite the structural similarities, electrochemical studies reveal that the presence of arsenic shifts the Mn waves to more positive potentials. Catalytic studies confirm that 1 is a significantly better catalyst than 2 for the H2O2-based epoxidation of cis-cyclooctene, cyclohexene, and 1-hexene.

Semi-vacant Wells–Dawson anions. Synthesis of tri-tungsten-vacant derivatives and crystallographic studies of [αββα-(CuIIOH2)2(CuII)2(AsW15(OH2)3(OH)O52)2]12−

The tri-tungsten-vacant polyoxometalate, [alpha-AsW15(OH)4O52]13-, derived from the semi-vacant Wells-Dawson complex [alpha-AsW18(OH)4O58]7-, reacts with the late-transition metal cations, Cu(II) or Zn(II), to form sandwich-type species; the X-ray crystal structure of [alphabetabetaalpha]-(Cu(II)OH2)2(Cu(II))2(AsW15(OH2)3(OH)O52)2]12-, prepared by the acidification of [alphabetabetaalpha]-(Cu(II)OH2)2(Cu(II))2(AsW15(OH)4O52)2]18-, reveals that the missing heteroatoms are distal to the central Cu4 unit and the vertices of the vacant tetrahedron are occupied by one OH- and three OH2 groups.