Search

Flash memory devices--that is, non-volatile computer storage media that can be electrically erased and reprogrammed--are vital for portable electronics, but the scaling down of metal-oxide-semiconductor (MOS) flash memory to sizes of below ten nanometres per data cell presents challenges. Molecules have been proposed to replace MOS flash memory (1), but they suffer from low electrical conductivity, high resistance, low device yield, and finite thermal stability, limiting their integration into current MOS technologies. Although great advances have been made in the pursuit of molecule-based flash memory (2), there are a number of significant barriers to the realization of devices using conventional MOS technologies (3-7). Here we show that core-shell polyoxometalate (POM) molecules (8) can act as candidate storage nodes for MOS flash memory. Realistic, industry-standard device simulations validate our approach at the nanometre scale, where the device performance is determined mainly by the number of molecules in the storage media and not by their position. To exploit the nature of the core-shell POM clusters, we show, at both the molecular and device level, that embedding [[[(Se(IV)[O.sub.3]).sub.2]].sup.4-] as an oxidizable dopant in the cluster core allows the oxidation of the molecule to a [[Se[(V).sub.2][O.sub.6]].sup.2-] moiety containing a {Se(v)-Se(v)} bond (where curly brackets indicate a moiety, not a molecule) and reveals a new 51 oxidation state for selenium. This new oxidation state can be observed at the device level, resulting in a new type of memory, which we call 'write-once-erase'. Taken together, these results show that POMs have the potential to be used as a realistic nanoscale flash memory. Also, the configuration of the doped POM core may lead to new types of electrical behaviour (9-11). This work suggests a route to the practical integration of configurable molecules in MOS technologies as the lithographic scales approach the molecular limit (12)., To engineer the flash memory devices, we selected a core-shell POM 'Dawson-like' archetype as the functional part of the switching node with the general formula [[[M.sub.18][O.sub.54][(X[O.sub.n]).sup.2]].sup.m-] (where M = Mo [...]

Pentacoordinate complexes of the divalent metal ions [M.sup.2] = [Mn.sup.II] (S = 5/2), [Ni.sup.II] (S = 1) and [Cu.sup.II] (S = 1//2) with the pentadentate bispidine ligands [L.sup.1] and [L.sup.2] are useful building blocks for the assembly of trinuclear cyanide-bridged complexes based on hexacyanometalates. The absence of single-molecule magnetic behavior in all spin clusters is due to the large angular distortion of the [[Fe[(CN).sub.6]].sup.3-] center and the concomitant quenching of orbital angular momentum of the [Fe.sup.III] ([super 2][T.sub.2g]) ground state.

We report a {Cu16} embedded within a {W44} cluster containing four cubane-like [Cu4O4] units within an isopolyoxotungstate (isoPOT) in a {Na4Cu4[(H2W11O38) (CH3COO)(OH)3]}4·88H2O (1) and a polyanion Cu-linked {W11} chain Na6Cu2[(H2W11O38)(CH3COO)(OH)]·26H2O (2). Electronically, the redox properties show that both compounds 1 and 2 undergo irreversible reductions resulting in the demetalation of the compounds, whilst the magnetic behavior of 1 and 2 shows a weak antiferromagnetic and a stronger ferromagnetic coupling, respectively. [ABSTRACT FROM AUTHOR]

By incorporating phosphorus(III)-based anions into a polyoxometalate cage, a new type of tungsten-based unconventional Dawson-like cluster, [W18O56(HPIIIO3)2(H2O)2]8−, was isolated, in which the reaction of the two phosphite anions [HPO3]2− within the {W18O56} cage could be followed spectroscopically. As well as full X-ray crystallographic analysis, we studied the reactivity of the cluster using both solution-state NMR spectroscopy and mass spectrometry. These techniques show that the cluster undergoes a structural rearrangement in solution whereby the {HPO3} moieties dimerize to form a weakly interacting (O3PH⋅⋅⋅HPO3) moiety. In the crystalline state the cluster exhibits a thermally triggered oxidation of the two PIII template moieties to form PV centers (phosphite to phosphate), commensurate with the transformation of the cage into a Wells-Dawson {W18O54} cluster. [ABSTRACT FROM AUTHOR]

The article discusses a study on the polyoxomethane {W18O56XO6} clusters with localized redox active inner-cluster templates, which can adopt to different oxidation stress. It says that cyclic voltammetry and electron paramagnetic resonance (EPR) spectroscopy were used with experimental comparison to a control embedded Dawson-like cluster. Results show that polyoxometalates (POMs) are configured as a new type of inner-sphere electron transfer device or reagent.

Two near isomeric clusters containing a novel {Mn8W4} Keggin cluster within a [W36Mn10Si4O136(OH)4(H2O)8]24− cluster are reported: K10Li14 [W36Si4O136MnII10(OH)4(H2O)8] ( 1) and K10Li13.5Mn0.25[W36Si4O136MnII10(OH)4(H2O)8] ( 1′). Bulk characterization of the clusters has been carried out by single crystal X-ray structure analysis, ICP-MS, TGA, ESI-MS, CV and SQUID-magnetometer analysis. X-ray analysis revealed that 1′ has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two 'intermediate' types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X-ray analysis and revealed to be novel clusters K4Li22[W36Si4Mn7O136(H2O)8]⋅56 H2O ( 2) and Mn2K8Li14[W36Si4Mn7O136(H2O)8]⋅45 H2O ( 3). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X-ray crystallography directly facilitated understanding the means by which a POM assembled. [ABSTRACT FROM AUTHOR]

The reaction of the hexacyanometalates K3[M¹(CN)6] (M¹ = CrIII, FeIII, CoIII) with the bispidine complexes [M²-(L¹)(X)]n+ and [M²(L²)(X)]n+ (M² = MnII, NiII, CuII; L¹ = 3-methyl-9-oxo-2,4-di-(2-pyridyl)-7-(2-pyridylmethyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylic acid dimethyl ester; L² = 3-methyl-9-oxo-7-(2-pyridylmethyl)-2,4-di-(2-quinolyl)-3,7-diazabicyclo[3.3.1]nonane-1,5-dicarboxylic acid dimethyl ester; X = anion or solvent) in water-methanol mixtures affords trinuclear complexes with cis- or trans-arrangement of the bispidine-capped divalent metal centers around the hexacyanometalate. X-ray structural analyses of five members of this family of complexes (cis-Fe[CuL²]2, trans-Fe[CuL¹]2, cis-Co[CuL²]2, trans-Cr[MnL¹]2, trans-Fe[MnL¹]2) and the magnetic data of the entire series are reported. The magnetic data of the cyanide bridged, ferromagnetically coupled cis- and trans-Fe[ML]2 compounds (M = NiII, CuII) with S = 3/2 (CuII) and S = 5/2 (NiII) ground states are analyzed with an extended Heisenberg Hamiltonian which accounts for anisotropy and zero-field splitting, and the data of the CuII systems, for which structures are available, are thoroughly analyzed in terms of an orbital-dependent Heisenberg Hamiltonian, in which both spin-orbit coupling and low-symmetry ligand fields are taken into account. It is shown that the absence of single-molecule magnetic behavior in all spin clusters reported here is due to a large angular distortion of the [Fe(CN)6]3- center and the concomitant quenching of orbital angular momentum of the FeIII (²T2g) ground state. [ABSTRACT FROM AUTHOR]

A high-nuclearity polyoxopalladate compound, [PdII2⊂{H7PdII15O10(PO4)10}]9- {PdII17}, comprising a {Pd15} host occupied by a {Pd2} guest and the parent pristine "empty" [H7PdII15O10(PVO4)10]13- {Pd15} cluster have both been prepared and characterized by single-crystal X-ray crystallography, 31P NMR, CSI-MS, and XPS. The encapsulated {Pd2} has a short PdII-PdII distance within the {Pd15} host. Solution studies indicate that the empty host and filled guest complex are in equilibrium with each other, and UV titrations revealed a binding constant of ca. 103 for the guest PdII ions, with a binding stoichiometry of almost 2. [ABSTRACT FROM AUTHOR]

We report a {Cu 16 } embedded within a {W 44 } cluster containing four cubane-like [Cu 4 O 4 ] units within an isopolyoxotungstate (isoPOT) in a {Na 4 Cu 4 [(H 2 W 11 O 38 ) (CH 3 COO)(OH) 3 ]} 4 ·88H 2 O (1) and a polyanion Cu-linked {W 11 } chain Na 6 Cu 2 [(H 2 W 11 O 38 )(CH 3 COO)(OH)]·26H 2 O (2). Electronically, the redox properties show that both compounds 1 and 2 undergo irreversible reductions resulting in the demetalation of the compounds, whilst the magnetic behavior of 1 and 2 shows a weak antiferromagnetic and a stronger ferromagnetic coupling, respectively.

By incorporating phosphorus(III)-based anions into a polyoxometalate cage, a new type of tungsten-based unconventional Dawson-like cluster, [W18O56(HP(III)O3)2(H2O)2](8-), was isolated, in which the reaction of the two phosphite anions [HPO3](2-) within the {W18O56} cage could be followed spectroscopically. As well as full X-ray crystallographic analysis, we studied the reactivity of the cluster using both solution-state NMR spectroscopy and mass spectrometry. These techniques show that the cluster undergoes a structural rearrangement in solution whereby the {HPO3} moieties dimerize to form a weakly interacting (O3PH⋅⋅⋅HPO3) moiety. In the crystalline state the cluster exhibits a thermally triggered oxidation of the two P(III) template moieties to form P(V) centers (phosphite to phosphate), commensurate with the transformation of the cage into a Wells-Dawson {W18O54} cluster., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We explore the concept that the incorporation of polyoxometalates (POMs) into complementary metal oxide semiconductor (CMOS) technologies could offer a fundamentally better way to design and engineer new types of data storage devices, due to the enhanced electronic complementarity with SiO2, high redox potentials, and multiple redox states accessible to polyoxometalate clusters. To explore this we constructed a custom-built simulation domain bridge. Connecting DFT, for the quantum mechanical modelling part, and mesoscopic device modelling, confirms the theoretical basis for the proposed advantages of POMs in non-volatile molecular memories (NVMM) or flash-RAM., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Two near isomeric clusters containing a novel {Mn(8)W(4)} Keggin cluster within a [W(36)Mn(10)Si(4)O(136)(OH)(4)(H(2)O)8](24-) cluster are reported: K(10)Li(14)[W(36)Si(4)O(136)Mn(II)(10)(OH)(4)(H(2)O)(8)] (1) and K(10)Li1(3.5)Mn(0.25)[W(36)Si(4)O(136)Mn(II)(10)(OH)(4)(H(2)O)(8) ] (1'). Bulk characterization of the clusters has been carried out by single crystal X-ray structure analysis, ICP-MS, TGA, ESI-MS, CV and SQUID-magnetometer analysis. X-ray analysis revealed that 1' has eight positions within the central Keggin core that were disordered W/Mn whereas 1 contained no such disorder. This subtle difference is due to a differences is how the two clusters assemble and recrystallize from the same mother liquor and represents a new type of isomerism. The rapid recrystallization process was captured via digital microscopy and this uncovered two "intermediate" types of crystal which formed temporarily and provided nucleation sites for the final clusters to assemble. The intermediates were investigated by single crystal X-ray analysis and revealed to be novel clusters K(4)Li(22)[W(36)Si(4)Mn(7)O(136)(H(2)O)(8)]·56H(2)O (2) and Mn(2)K(8)Li(14)[W(36)Si(4)Mn(7)O(136)(H(2)O)(8)]·45H(2)O (3). The intermediate clusters contained different yet related building blocks to the final clusters which allowed for the postulation of a mechanism of assembly. This demonstrates a rare example where the use X-ray crystallography directly facilitated understanding the means by which a POM assembled., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)