Syntheses and Properties of New Layered Alkali-Metal/Ammonium Vanadium(V) Methylphosphonates: M(VO(2))(3)(PO(3)CH(3))(2) (M = NH(4), K, Rb, Tl). Single-Crystal Structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2)

The hydrothermal syntheses of a family of new alkali-metal/ammonium vanadium(V) methylphosphonates, M(VO(2))(3)(PO(3)CH(3))(2) (M = K, NH(4), Rb, Tl), are described. The crystal structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) have been determined from single-crystal X-ray data. Crystal data: K(VO(2))(3)(PO(3)CH(3))(2), M(r) = 475.93, trigonal, R32 (No. 155), a = 7.139(3) ?, c = 19.109(5) ?, Z = 3; NH(4)(VO(2))(3)(PO(3)CH(3))(2), M(r) = 454.87, trigonal, R32 (No. 155), a = 7.150(3) ?, c = 19.459(5) ?, Z = 3. These isostructural, noncentrosymmetric phases are built up from hexagonal tungsten oxide (HTO) like sheets of vertex-sharing VO(6) octahedra, capped on both sides of the V/O sheets by PCH(3) entities (as [PO(3)CH(3)](2-) methylphosphonate groups). In both phases, the vanadium octahedra display a distinctive two short + two intermediate + two long V-O bond distance distribution within the VO(6) unit. Interlayer potassium or ammonium cations provide charge balance for the anionic (VO(2))(3)(PO(3)CH(3))(2) sheets. Powder X-ray, TGA, IR, and Raman data for these phases are reported and discussed. The structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) are compared and contrasted with related layered phases based on the HTO motif.     

Synthesis,crystal structure,and solid state NMR spectroscopy of NH(4)[(V(2)O(3))(2)(4,4'-bpy)(2)(H(2)PO(4))(PO(4))(2)].0.5H(2)O,a mixed-valence vanadium(IV,V) phosphate with a pillared layer structure

A mixed-valence vanadium phosphate, NH(4)[(V(2)O(3))(2)(4,4'-bpy)(2)(H(2)PO(4))(PO(4))(2)].0.5H(2)O, has been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group C2/c (No. 15) with a = 12.6354(8) A, b = 9.9786(6) A, c = 23.369(1) A, beta = 92.713(1) degrees, and Z = 4 with R(1) = 0.0389. The structure consists of dimers of edge-sharing vanadium(IV,V) octahedra that are connected by corner-sharing phosphate tetrahedra to form layers in the ab-plane, which are further linked through 4,4'-bipyridine pillars to generate a 3-D framework. Magnetic susceptibility confirms the valence of the vanadium atoms. The (31)P MAS NMR spectrum shows a resonance centered at 80 ppm with a shoulder at ca. 83 ppm in an intensity ratio close to 1:2, which correspond to two distinct P sites. The observed large downfield (31)P NMR shifts can be ascribed to magnetic exchange coupling involving phosphorus atoms. The unpaired electron spin density at the phosphorus nucleus was determined from variable-temperature (31)P NMR spectra. The (1)H MAS NMR spectrum was fitted to six components in accordance with the structure as determined from X-ray diffraction.     

Two new hybrid organic/inorganic copper(II)-oxovanadate(V) diphosphonates: [Cu2(phen)2(O3PCH2PO3)(V2O5)(H2O)] x H2O and [Cu2(phen)2(O3P(CH2)3PO3)(V2O5)] x C3H8. Synthesis, structure, and magnetic properties

Two new hybrid organic/inorganic copper oxovanadium diphosphonates [Cu2(phen)2(O3PCH2PO3)(V2O5)(H2O)] x H2O (1) and [(Cu2(phen)2(O3P(CH2)3PO3)(V2O5)] x C3H8 (2) have been obtained by hydrothermal synthesis. The compounds are monoclinic, and they crystallize in the space group P2(1)/n with cell parameters of a = 11.788(2) A, b = 17.887(3) A, c = 14.158(2) A, and beta = 93.99(0) degrees and in the space group C2/c with cell parameters of a = 11.025(1) A, b = 18.664(2) A, c = 15.054(2) A, and beta = 90.06(0) degrees, respectively. Both compounds present two-dimensional frameworks built up from infinite chains of corner-sharing vanadium tetrahedra and diphosphonate groups connected by copper tetramers for (1) and copper dimers for (2). The remarkable feature of (2) is the encapsulation of propane molecules, stabilized by strong hydrogen bonding between the layers. The magnetic properties of the compounds have been investigated showing antiferromagnetic coupling with Tmax = 64 K for (1) and Curie-like paramagnetic behavior for (2).     

Adsorption Mechanism and Structure of the Montmorillonite Complexes with (CH(3))(2)XO (X=C, and S), (CH(3)O)(3)PO, and CH(3)-CN Molecules

The formation of complexes with different ligands in the interlayer space of montmorillonite saturated in Na(+), Mg(2+), Ca(2+), Co(2+), Cu(2+), Ni(2+), Fe(3+), and Cr(3+) was studied. Acetone, acetonitrile, dimethyl sulfoxide, and trimethylphosphate were used as ligands. The nature of the complexes was studied by means of X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, microcalorimetry, and ab initio quantum mechanical methods. In all cases, the organic ligands penetrate into the interlayer space at room temperature, forming complexes stable in vacuum with the interlayer cations. The ligand-cation ratio depends on the valence of the saturating cation. The cation-ligand interaction in these complexes has an ion-dipole electrostatic nature. The complexes are formed by the direct interaction of the oxygen or nitrogen atom of ligand and the interlayer cation. Using the quantum mechanical approach, allow us to determine the disposition of the ligand in these complexes. In all cases, only one layer of ligands is present in the stable complexes. Copyright 2000 Academic Press.     

Synthesis and structure of the framework scandium methylphosphonates ScF(H2O)CH3PO3 and NaSc(CH3PO3)2.0.5H2O

Two framework scandium methylphosphonates have been prepared hydrothermally and their structures solved. ScF(H(2)O)CH(3)PO(3) is a non-porous solid built up from -ScF- chains linked by methylphosphonate groups. The ScO(4)F(2) octahedra are completed by a coordinated water molecule. NaSc(CH(3)PO(3))(2).0.5H(2)O was solved ab initio from high-resolution synchrotron X-ray powder diffraction data. It has a fully connected, negatively charged scandium phosphonate framework where ScO(6) octahedra share vertices with PO(3)CH(3) groups. The solid contains charge balancing sodium cations, coordinated by a water molecule, which may be reversibly removed and adsorbed. The structure of the perdeuterated, dehydrated solid has been refined against neutron powder diffraction data collected at 2.5 K, showing the CD(3) groups in a fully staggered orientation with respect to the phosphonate oxygen atoms.     

Synthetic Strategies To Obtain V-P-O Open Frameworks Containing Organic Species as Structural Directing Agents. Crystal Structure of the V(IV)-Fe(III) Bimetallic Phosphate [H(3)N(CH(2))(2)NH(3)](2)[H(3)N(CH(2))(2)NH(2)][Fe(III)(H(2)O)(2)(V(IV)O)(8)(OH)(4)(HPO(4))(4)(PO(4))(4)].4H(2)O

A general synthetic approach to rationalize the solution preparative chemistry of oxovanadium phosphates containing organic species as structural directing agents is presented. Careful attention is payed to the hydrolysis and condensation processes involving the ionic species in solution, and a simple restatement of the partial charge model (PCM) has been used in order to organize the experimental results. The structure of a new V(IV)-Fe(III) bimetallic oxovanadium phosphate, [H(3)N(CH(2))(2)NH(3)](2)[H(3)N(CH(2))(2)NH(2)] [Fe(III)(H(2)O)(2)(V(IV)O)(8)(OH)(4)(HPO(4))(4)(PO(4))(4)].4H(2)O, has been determined by X-ray single crystal diffraction methods. This compound crystallizes in the monoclinic system, space group P2(1)/n and the cell dimensions are as follows: a = 14.383(3) ?, b = 10.150(2) ?, c = 18.355(4) ?, and beta = 90.39(3) degrees (Z = 2). The existence of a complex intercrossing channel system, including a very large channel of 18.4 ? of diameter (in which both water molecules and ethylenediamine species are located), is the more interesting feature of this structure. Thermal decomposition, including the dehydration/rehydration process, has been studied by thermal analysis and variable temperature X-ray powder diffraction techniques. A complementary SEM study of the different intermediate decomposition products is presented.     

Synthesis,X-ray powder structure,and magnetic properties of layered NiII methylphosphonate, [Ni(CH3PO3)(H2O)], and NiII octadecylphosphonate, [Ni(CH3-(CH2)17-PO3)(H2O)

[Ni(CH(3)PO(3))(H(2)O)] (1) and [Ni(CH(3)-(CH(2))(17)-PO(3))(H(2)O)] (2) were synthesised by reaction of NiCl(2).6 H(2)O and the relevant phosphonic acid in water in presence of urea. The compounds were characterised by elemental and thermogravimetric analyses, UV-visible and IR spectroscopy, and their magnetic properties were studied by using a SQUID magnetometer. The crystal structure of 1 was determined "ab initio" from X-ray powder diffraction data and refined by the Rietveld method. The crystals of 1 are orthorhombic, space group Pmn2(1), with a=5.587(1), b=8.698(1), c=4.731(1) A. The compound has a hybrid, layered structure made up of alternating inorganic and organic layers along the b direction of the unit-cell. The inorganic layers consist of Ni(II) ions octahedrally coordinated by five phosphonate oxygen atoms and one oxygen atom from the water molecule. These layers are separated by bilayers of methyl groups and van der Waals contacts are established between them. A preliminary structure characterisation of compound 2 suggests the crystallisation in the orthorhombic system with the following unit-cell parameters: a=5.478(7), b=42.31(4), c=4.725(3) A. The oxidation state of the Ni ion in both compounds is +2, and the electronic configuration is d(8) (S=1), as determined from static magnetic susceptibility measurements above 50 K. Compound 1 obeys the Curie-Weiss law at temperatures above 50 K; the Curie (C) and Weiss (theta) constants were found to be 1.15 cm(3) K mol(-1) and -32 K, respectively. The negative value of theta indicates an antiferromagnetic exchange coupling between near-neighbouring Ni(II) ions. No sign of 3D antiferromagnetic long-range order is observed down to T=5 K, the lowest measured temperature. Compound 2 is paramagnetic above T=50 K, and the values of C and theta were found to be 1.25 cm(3) K mol(-1) and -24 K, respectively. Below 50 K the magnetic behavior of 2 is different from that of 1. Zero-field cooled (zfc) and field-cooled (fc) magnetisation plots do not overlap below T=21 K. The irreversible magnetisation, DeltaM(fc-zfc), obtained as a difference from fc and zfc plots starts to increase at T=20 K, on lowering the temperature, and it becomes steady at T=5 K. The presence of spontaneous magnetisation below T=20 K indicates a transition to a weak-ferromagnetic state for compound 2.     

Cl(3)V(mu-S(CH(3))(2))(3)VCl(3)(2)(-): a first-row,face-shared bioctahedral complex with multiple metal-metal bonding

Density functional theory calculations have been used to investigate the structure and bonding of the d(3)d(3) bioctahedral complexes X(3)V(mu-S(CH(3))(2))(3)VX(3)(2)(-) (X = F(-), Cl(-), OH(-), SH(-), NH(2)(-)). According to geometry optimizations using the broken-symmetry approach and the VWN+B-LYP combination of density functionals, the halide-terminated complexes have a V-V bond order of approximately 2, while complexes featuring OH(-), SH(-), or NH(2)(-) as terminal ligands exhibit full triple bonding between the vanadium atoms. The tendency toward triple bonding in the latter complexes is consistent with an increased covalency of the vanadium-ligand bonds, and the influence of bond covalency is apparent also in the tendency for V-V bond elongation in the complexes with OH(-) and NH(2)(-) terminal ligands. Detailed examination of the composition of molecular orbitals in all of the thioether-bridged V(II) complexes substantiates the conclusion that the strong antiferromagnetic coupling which we have determined for these complexes (-J > 250 cm(-)(1)) is due to direct bonding between metal atoms rather than superexchange through the bridging ligands. As such, these V(II) complexes comprise the first apparent examples of multiple metal-metal bonding in first-transition-row, face-shared dinuclear complexes and are therefore of considerable structural and synthetic interest.     

Hydrothermal Synthesis, Structure, and Solid State (19)F NMR Study of ULM-17: (H(3)O)(2)[V(4)(HPO(4))(PO(4))(3)O(6)F](2)[NC(7)H(14)](6)

(H(3)O)(2)[V(4)(HPO(4))(PO(4))(3)O(6)F](2)[NC(7)H(14)](6) (labeled ULM-17) has been hydrothermally synthesized (150 degrees, 24 h, autogeneous pressure). It is monoclinic (space group P2(1)/c (No. 14)) with a = 21.4747(6) ?, b = 17.7223(5) ?, c = 20.1616(6) ?, beta = 94.329(1) degrees, and Z = 4. The structure consists in the hexagonal close packing of discrete hydronium cations, protonated quinuclidine and molecular anions [V(4)(HPO(4))(PO(4))(3)O(6)F](4)(-) (1) The structure presents two kinds of octameric anions built up from the tetrahedral arrangement of V(V)O(5)F octahedra sharing edges and vertices, capped by phosphorus tetrahedra. The stability of the solid is ensured via strong hydrogen bonds between the oxygens of the polyanions and the hydrogens of both hydronium and quinuclidinium cations. The particuliar location of fluorine at the center of the molecular anion 4-fold coordinated by V(V) was studied by solid state NMR.     

Synthesis, crystal structure, and solid-state NMR spectroscopy of a new open-framework aluminophosphate (NH(4))(2)Al(4)(PO(4))(4)(HPO(4))xH(2)O

A new three-dimensional open-framework aluminophosphate (NH(4))(2)Al(4)(PO(4))(4)(HPO(4)).H(2)O (denoted AlPO-CJ19) with an Al/P ratio of 4/5 has been synthesized, using pyridine as the solvent and 2-aminopyridine as the structure-directing agent, under solvothermal conditions. The structure was determined by single-crystal X-ray diffraction and further characterized by solid-state NMR techniques. The alternation of the Al-centered polyhedra (including AlO(4), AlO(5), and AlO(6)) and the P-centered tetrahedra (including PO(4) and PO(3)OH) results in an interrupted open-framework structure with an eight-membered ring channel along the [100] direction. This is the first aluminophosphate containing three kinds of Al coordinations (AlO(4), AlO(5), and AlO(6)) with all oxygen vertexes connected to framework P atoms. (27)Al MAS NMR, (31)P MAS NMR, and (1)H --> (31)P CPMAS NMR characterizations show that the solid-state NMR techniques are an effective complement to XRD analysis for structure elucidation. Furthermore, all of the possible coordinations of Al and P in the aluminophosphates with an Al/P ratio of 4/5 are summarized. Crystal data: (NH(4))(2)Al(4)(PO(4))(4)(HPO(4))xH(2)O, monoclinic P2(1) (No. 4), a = 5.0568(3) A, b = 21.6211(18) A, c = 8.1724(4) A, beta = 91.361(4) degrees , V = 893.27(10) A(3), Z = 2, R(1) = 0.0456 (I > 2 sigma(I)), and wR(2) = 0.1051 (all data).     

Sandwich-type phosphotungstates: structure,electrochemistry, and magnetism of the trinickel-substituted polyoxoanion [Ni(3)Na(H(2)O)(2)(PW(9)O(34))(2)](11-)

The novel nickel-substituted, dimeric phosphotungstate [Ni(3)Na(H(2)O)(2)(PW(9)O(34))(2)](11-) (1) has been synthesized and characterized by IR spectroscopy, elemental analysis, and electrochemistry. X-ray single-crystal analysis was carried out on Na(11)[Ni(3)Na(H(2)O)(2)(PW(9)O(34))(2)].21.25H(2)O, which crystallizes in the triclinic system, space group P1, with a = 12.2467(6) A, b = 16.6031(7) A, c = 22.4017(12) A, alpha = 73.9870(10) degrees, beta = 87.6060(10) degrees, gamma = 79.344(2) degrees, and Z = 2. The polyanion consists of two lacunary B-alpha-[PW(9)O(34)](9-) Keggin moieties linked via three nickel(II) centers and a sodium ion. The structure of 1 is composed of two fused Keggin fragments that represent different Baker-Figgis isomers (alpha- vs beta-type). Electrochemical studies show that 1 exhibits a stable and reproducible voltammetric pattern, with a first wave featuring a chemically reversible four-electron/four-proton process. An investigation of the magnetic properties indicates that the three nickel centers exhibit ferromagnetic exchange interaction.     

Cd(2+) Complexation with P(CH(2)OH)(3), OP(CH(2)OH)(3), and (HOCH(2))(2)PO(2)(-): Coordination in Solution and Coordination Polymers

The coordination of Cd(2+) with P(CH(2)OH)(3) (THP) in methanol was followed by (31)P and (111)Cd NMR techniques. A cadmium-to-phosphine coordination ratio of 1:3 has been established, and effective kinetic parameters have been calculated. Air oxidation of THP in the presence of CdCl(2) at room temperature produces coordination polymer (3)(∞)[Cd(3)Cl(6)(OP(CH(2)OH)(3))(2)] (1). The same oxidation reaction at 70 °C gives another coordination polymer, (∞)[CdCl(2)(OP(CH(2)OH)(3))] (2). Complexes 1 and 2 are the first structurally characterized complexes featuring OP(CH(2)OH)(3) as a ligand that acts as a linker between Cd atoms. The addition of NaBPh(4) to the reaction mixture gives coordination polymer (∞)[Na(2)CdCl(2)(O(2)P(CH(2)OH)(2))(2)(H(2)O)(3)] (3) with (HOCH(2))(2)PO(2)(-) as the ligand. Coordination polymers 1-3 have been characterized by X-ray analysis, elemental analysis, and IR spectroscopy.     

Nanoscale Hemispheres in Novel Mixed-Valent Uranyl Chromate(V,VI), (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6)

The structure of a novel mixed-valent chromium uranyl compound, (C(3)NH(10))(10)[(UO(2))(13)(Cr(12)(5+)O(42))(Cr(6+)O(4))(6)(H(2)O)(6)](H(2)O)(6) (1), obtained by the combination of a hydrothermal method and evaporation from aqueous solutions with isopropylammonium, contains uranyl chromate hemispheres with lateral dimensions of 18.9 × 18.5 ?(2) and a height of about 8 ?. The hemispheres are centered by a UO(8) hexagonal bipyramid surrounded by six dimers of Cr(5+)O(5) square pyramids, UO(7) pentagonal bipyramids, and Cr(6+)O(4) tetrahedra. The hemispheres are linked into two-dimensional layers so that two adjacent hemispheres are oriented in opposite directions relative to the plane of the layer. From a topological point of view, the hemispheres have the formula U(21)Cr(23) and can be considered as derivatives of nanospherical cluster U(26)Cr(36) composed of three-, four-, and five-membered rings.     

A comparison of the magnetic structures of KMn(4)(PO(4))(3) and KCo(4)(PO(4))(3) based on the connectivity of the coordination polyhedra

The crystal structures of KMn(4)(PO(4))(3) and KCo(4)(PO(4))(3) have been determined by neutron diffraction at room temperature. Both compounds are orthorhombic with similar cell parameters, but they crystallize in different space groups, Pnam for the Mn phosphate and Pnnm for the Co analogue. On the basis of the metal cation polyhedra and their connectivity, the crystal structures have been rationalised, which allow interpretation of the main magnetic interactions between them. Magnetic measurements show ferromagnetic behaviour for the Co compound, whereas in the Mn derivative antiferromagnetism is observed. Both magnetic structures are described and qualitatively analysed in terms of superexchange and super-superexchange interactions.     

Excited-state properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py)

The photophysical properties of Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF = tetrahydrofuran, PPh(3) = triphenylphosphine, py = pyridine) were explored upon excitation with visible light. Time-resolved absorption shows that all the complexes possess a long-lived transient (3.5-5.0 micros) assigned as an electronic excited state of the molecules, and they exhibit an optical transition at approximately 760 nm whose position is independent of axial ligand. No emission from the Rh(2)(O(2)CCH(3))(4)(L)(2) (L = CH(3)OH, THF, PPh(3), py) systems was detected, but energy transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to the (3)pipi excited state of perylene is observed. Electron transfer from Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) to 4,4'-dimethyl viologen (MV(2+)) and chloro-p-benzoquinone (Cl-BQ) takes place with quenching rate constants (k(q)) of 8.0 x 10(6) and 1.2 x 10(6) M(-1) s(-1) in methanol, respectively. A k(q) value of 2 x 10(8) M(-1) s(-1) was measured for the quenching of the excited state of Rh(2)(O(2)CCH(3))(4)(PPh(3))(2) by O(2) in methanol. The observations are consistent with the production of an excited state with excited-state energy, E(00), between 1.34 and 1.77 eV.     

Metal coordination to the formal P=N bond of an iminophosphorane and charge-density evidence against hypervalent phosphorus(V)

The iminophosphorane Ph(2)P(CH(2)Py)(NSiMe(3)) (1) was treated with deprotonating alkali metal reagents to give [(Et(2)O)Li[Ph(2)P(CHPy)(NSiMe(3))]] (2), [[Ph(2)P(CH(2)Py)(NSiMe(3))]Li[Ph(2)P(CHPy)(NSiMe(3))]] (3) and [[Ph(2)P(CH(2)Py)(NSiMe(3))]Na[Ph(2)P(CHPy)(NSiMe(3))]] (4). We report their coordination behaviour in solid-state structures and NMR spectroscopic features in solution. Furthermore, we furnish experimental evidence against hypervalency of the phosphorus atom in iminophosphoranes from experimental charge-density studies and subsequent topological analysis. The topological properties, correlated to the results from NMR spectroscopic investigations, illustrate that the formal P=N double bond is better written as a polar P(+)--N(-) single bond. Additionally, the effects of metal coordination on the bonding parameters of the iminophosphorane and the related anion are discussed.     

Pillared layered structures based upon M(III) ethylene diphosphonates: the synthesis and crystal structures of M(III)(H(2)O)(HO(3)P(CH(2))(2)PO(3)) (M = Fe, Al, Ga)

A three-dimensional iron(III) diphosphonate, Fe(III)(H(2)O)(HO(3)P(CH(2))(2)PO(3)), I, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Pbca (no. 61) where a = 9.739(5) A, b = 9.498(5) A, c = 15.940(8) A, V = 1474.4(1) A(3), Z = 8, and R(1) = 0.0380. The structure consists of inorganic sheets pillared by the 1,2-ethylenediphosphonate groups. The sheets are composed of Fe(H(2)O)O(5) octahedra connected through PO(3)C tetrahedra. The corresponding isostructural aluminum (II) and gallium (III) compounds were also synthesized and indexed: II, a = 9.534(1) A, b = 9.255(2) A, c = 15.724(1) A, V = 1387.5(1) A(3); III, a = 9.670(1) A, b = 9.357(2) A, c = 15.862(4) A, V = 1435.4(1) A(3).