Determination of the changes of the basic structures of silica species in dependence on the concentration of sodium chloride by FAB-MS

The chemical species of silica in NaCl solutions of different concentrations were identified by FAB-MS (fast atom bombardment mass spectrometry). The basic structures of silica species, such as cyclic pentamer (Si5 (OH)9O6-), linear pentamer (Sis(OH)11O5-), cyclic hexamer (Si6(OH)9O8-, Si6(OH)11O7-) and linear hexamer (Si6(OH)14 O6-), were identified, in addition to dimer (Si2(OH)5O2-), trimer (Si3(OH)7O3-) and cyclic tetramer (Si4(OH)7O5-). The patterns of changes of the peak intensities of the silicate complexes relative to the dimer with increasing NaCl concentration were classified into two types: that represented by linear silicate complexes and the other by cyclic silicate complexes. The differences in the type of chemical species and their changes according to the NaCl concentration reflect the number of bonds necessary for polymerization and hydrolysis of the silica complexes. The differences between the linear and the cyclic silicate type have some implications on the dissolution mechanism of silicate complexes, the hydration of the molecules and the equilibrium between solubility, hydrolysis, polymerization and the salting-out effect in NaCl solution.     

Characterization of silicate monomer with sodium,calcium and strontium but not with lithium and magnesium ions by fast atom bombardment mass spectrometry

Fast atom bombardment mass spectrometry (FABMS) was applied to the direct detection of silica species dissolved in LiCl, NaCl, MgCl(2), CaCl(2) and SrCl(2) solutions in order to investigate its dissolution process in solution. Several species of dissolved silicate complexes in the solution were directly detected by FABMS. The peak intensities of [SiO(2)(OH)(2)Na](-), [SiO(3)(OH)Ca](-) and [SiO(3)(OH)Sr](-) increased with increasing concentrations of NaCl, CaCl(2) and SrCl(2), whereas the peak intensities of [SiO(2)(OH)(2)Li](-) and [SiO(3)(OH)Mg](-) did not increase with increasing concentrations of LiCl and MgCl(2). These results indicte that silicate and cation bind in the solution not after but before ionization. The isotope pattern of Sr(2+) confirmed the existence of the silicate-Sr complex not only with increase of the concentration of silica but also the mass numbers of Sr. The silicate complexes formed with Na(+), Ca(2+) and Sr(2+) showed high stability in chloride solution. This is in good accordance with the fact that Na(+), Ca(2+) and Sr(2+) accelerate the dissolution of silica to form complexes during solution equilibrium. Considering that the stability constant was examined and reported in other papers, this new findings that Mg(2+) does not form a complex with silicic acid (Si(OH)(4)) is very important.     

Altering the inclusion properties of CTV through crystal engineering: CTV, carborane, and DMF supramolecular assemblies

The complexes [Na(CTV)2(OH)(H2O)](H2O)(DMF)2(o-carborane) (3; CTV = cyclotriveratrylene), [K(OH)(CTV)(DMF)]2(o-carborane) (4), [(DMF)(CTV)]2(H2O)4(o-carborane) (5), and (o-carborane)(CTV)(DMF)2 (6) all form as crystalline inclusion complexes from N,N'-dimethylformamide (DMF) solution. Complexes 3 and 4 are the first reported examples of CTV acting as a chelating ligand, with two CTV molecules coordinating cis to the six-coordinate M+ centers (M=Na, K). The extended structures of complexes 3-5 are similar, forming extended coordinate and/or hydrogen-bonding interactions and all feature intracavity complexation of DMF by CTV, while the complex 6 forms an assembly of (o-carborane) intersection of two sets (CTV) ball-and-socket supermolecules with DMF as a channel-type included guest.     

Intra and intermolecular magnetic interactions in a series of dinuclear Cu(II)/hxta complexes [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: correlation of magnetic properties with geometry

Nine dinuclear copper(II) complexes with hxta5- ligands [H5hxta = N,N'-(2-hydroxy-1,3-xylylene)-bis-(N-carboxymethylglycine)]: [Cu2(MeO-hxtaH)(H2O)2] x 4H2O (1), [Na(micro-H2O)2(H2O)6][Cu2(Cl-hxta)(H2O)3]2 x 6H2O (2), [Cu(H2O)6][Cu2(Me-hxta)(H2O)2](NO3) x 2H2O (3), [Cu2(R-hxtaH)(H2O)3] x 3H2O [R = Cl (4), CH3 (5), and MeO (6)], [Cu2(MeO-hxtaH2)(micro-X)(CH3OH)] x 3CH3OH [X = Cl (7), Br (8)] and K5Na(micro-H2O)10[Cu2(micro-CO3)(Me-hxta)]2 x 4H2O (9), have been synthesized and structurally characterized. In complexes 4-7, the dinuclear units are linked via novel pairwise supramolecular interactions involving the ligand carboxylate groups. The intra- and intermolecular magnetic interactions have been quantified, and the coupling constants have been related to the structural geometries.     

Self-assembly of hybrid organic-inorganic polyoxovanadates: functionalised mixed-valent clusters and molecular cages

Herein we report the intra- and inter-molecular assembly of a {V(5)O(9)} subunit. This mixed-valent structural motif can be stabilised as [V(5)O(9)(L(1-3))(4)](5-/9-) (1-3) by a range of organoarsonate ligands (L(1)-L(3)) whose secondary functionalities influence its packing arrangement within the crystal structures. Variation of the reaction conditions results in the dodecanuclear cage structure [V(12)O(14)(OH)(4)(L(1))(10)](4-) (4) where two modified convex building units are linked via two dimeric {O(4)V(IV)(OH)(2)V(IV)O(4)} moieties. Bi-functional phosphonate ligands, L(4)-L(6) allow the intramolecular connectivity of the {V(5)O(9)} subunit to give hybrid capsules [V(10)O(18)(L(4-6))(4)](10-) (5-7). The dimensions of the electrophilic cavities of the capsular entities are determined by the incorporated ligand type. Mass spectrometry experiments confirm the stability of the complexes in solution. We investigate and model the temperature-dependent magnetic properties of representative complexes 1, 4, 6 and 7 and provide preliminary cell-viability studies of three different cancer cell lines with respect to Na(8)H(2)[6]·36H(2)O and Na(8)H(2)[7]·2DMF·29H(2)O.     

Synthesis, crystal structure, and solution stability of Keggin-type heteropolytungstates (NH4)6NiII0.5[alpha-FeIIIO4W11O30NiIIO5(OH2)].nH2O, (NH4)7Zn0.5[alpha-ZnO4W11O30ZnO5(OH2)].nH2O, and (NH4)7NiII0.5[alpha-ZnO4W11O30NiIIO5(OH2)].nH2O (n approximately 18)

Reaction of acidified (pH approximately 7) sodium tungstate solutions with transition metal cations (Fe(3+), Ni(2+), Zn(2+), Co(2+)) leads to the formation of transition-metal-disubstituted Keggin-type heteropolytungstates with 3d-metal ions distributed over three different positions. A detailed investigation of the synthesis conditions confirmed that the complexes could equally be obtained using aqueous solutions of either Na(2)WO(4).2H(2)O (sodium monotungstate) at pH approximately 7, Na(6)[W(7)O(24)]. approximately 14H(2)O (sodium paratungstate A), or Na(10)[H(2)W(12)O(42)].27H(2)O (sodium paratungstate B) as starting materials. Three complexes, (NH(4))(6)Ni(II)(0.5)[alpha-Fe(III)O(4)W(11)O(30)Ni(II)O(5)(OH(2))].18H(2)O, (NH(4))(7)Zn(0.5)[alpha-ZnO(4)W(11)O(30) ZnO(5)(OH(2))].18H(2)O, and (NH(4))(7)Ni(II)(0.5)[alpha-ZnO(4)W(11)O(30)Ni(II)O(5)(OH(2))].18H(2)O were isolated in crystalline form. X-ray single-crystal structure analysis revealed that the solid-state structures of the three compounds consist of four main structural fragments, namely [MO(4)W(11)O(30)M'O(5)(OH(2))](n-) (Keggin-type, alpha-isomer) heteropolytungstates, hexaquo metal cations, [M'(OH(2))(6)](2+), ammonium-water cluster ions, [(NH(4)(+))(8)(OH(2))(12)], and additional ammonium cations and water molecules. The 3d metals occupy the central (tetrahedral, M) and the peripheral (octahedral, M') positions of the Keggin anion, as well as cationic sites (M') outside of the polyoxotungstate framework. UV-vis spectroscopy, solution ((1)H, (183)W) and solid-state ((1)H) NMR, and also chemical analysis data provided evidence that the 3d-metal-disubstituted Keggin anions do not exist in solution but are being formed only during the crystallization process. Investigations in the solid state and in solution were completed by ESR, IR, and Raman measurements.     

Silsesquioxane models for geminal silica surface silanol sites. A spectroscopic investigation of different types of silanols

The incompletely condensed monosilylated silsesquioxanes (c-C5H9)7Si7O9(OSiRR'2)(OH)2 (SiRR'2 = SiMe3, SiMe2C(H)CH2, SiMePh2) were reacted with SiCl(4) in the presence of an amine which yielded the dichloro compounds (c-C5H9)7Si7O9(OSiRR'2)O2SiCl2 (1-3). These compounds could be hydrolyzed into the corresponding silsesquioxanes containing geminal silanols, (c-C5H9)7Si7O9(OSiRR'2)O2Si(OH)2 (4-6). At elevated temperatures, the geminal silsesquioxanes 4 and 5 undergo condensation reactions and form the closed-cage silsesquioxane monosilanol, (c-C5H9)7Si8O12(OH). The more sterically hindered geminal silsesquioxane 6 undergoes in solution intermolecular dehydroxylation, yielding the thermodynamically stable dimeric disilanol, [(c-C5H9)7Si7O9(OSiMePh2)(O2Si(OH)-)]2-(mu-O) (7). NMR and FT-IR studies show that the two silanols of the geminal silsesquioxanes 4-6 are different from each other with respect to hydrogen bonding, both in solution and in the solid state. Hydrogen bonding of the geminal silanol-containing silsesquioxanes was examined and compared to hydrogen bonding in silsesquioxanes possessing vicinal or isolated silanol groups. The relative Br?nsted acidity of the geminal silanols was determined using pK(ip) (ion-pair acidity) measurements in THF with UV-vis. These acidities were compared with those of other silsesquioxanes containing silanol groups. Acidities of 4-6 were found to be among the lowest known for silsesquioxanes.     

Determination of the equilibrium formation constants of two U(VI)-peroxide complexes at alkaline pH

The formation of uranyl-peroxide complexes was studied at alkaline media by using UV-Visible spectrophotometry and the STAR code. Two different complexes were found at a H(2)O(2)/U(VI) ratio lower than 2. A graphical method was used in order to obtain the formation constants of such complexes and the STAR program was used to refine the formation constants values because of its capacity to treat multiwavelength absorbance data and refining equilibrium constants. The values obtained for the two complexes identified were: UO(2)(2+) + H(2)O(2) + 4OH(-) UO(2)(O(2))(OH)(2)(2-) + 2H(2)O: log β°(1,1,4) = 28.1 ± 0.1 (1). UO(2)(2+) + 2H(2)O(2) + 6OH(-) UO(2)(O(2))(2)(OH)(2)(4-) + 4H(2)O: log β°(1,2,6) = 36.8 ± 0.2 (2). At hydrogen peroxide concentrations higher than 10(-5) mol dm(-3), and in the absence of carbonate, the UO(2)(O(2))(2)(OH)(2)(4-) complex is predominant in solution, indicating the significant peroxide affinity of peroxide ions for uranium and the strong complexes of uranium(VI) with peroxide.     

Synthesis and characterization of mesoporous silica from selectively acid-treated saponite as the precursors

Mesoporous silicas were synthesized by hydrothermal treatment of selectively acid-treated saponite (an ideal structural formula: Na(1/3)Mg(3)(Si(11/3)Al(1/3))O(10)(OH)(2)), having a 2:1 type layered structure as the silica source and its porous properties were examined and compared with that from kaolinite (an ideal structural formula: Al(2)Si(2)O(5)(OH)(4)), having a 1:1 type layered structure. Synthetic saponite was selectively leached in H(2)SO(4) solutions with various concentrations (0.05-1 M) at 70 degrees C for 0.5 h. The resulting products (precursors) were mixed with cetyltrimethylammonium bromide (CTABr), NaOH and H(2)O, hydrothermally treated at 110 degrees C and removed the CTABr by calcining at 560 degrees C. A hexagonal mesoporous phase was obtained with higher Si/(Al(+Mg)) ratios of the resulting precursors. The XRD patterns of these products show the peaks assigned by a hexagonal lattice with a(0)=4.0-4.6 nm and the crystallinity becomes higher with higher Si/(Al(+Mg)) ratios of the precursors. The specific surface area (S(BET)) values of the present mesoporous silicas range from 800 to 1100 m(2)/g at CTABr/precursor=0.1 and although they are not as high as those from precursors prepared from calcining and acid-treatment of kaolinite (1420 m(2)/g), they are increased to 1400-1500 m(2)/g by increasing the ratio CTABr/precursor 0.2. The reason for the difference in the optimum preparation conditions between saponite and kaolinite may be attributed to the difference in the linkage of the SiO(4) tetrahedra in these precursors (i.e. layered or framework structures), which result in great differences in the selective leaching rates and structures of the resulting silica-rich products.     

Structural and spectroscopic evidence for the formation of trinuclear and tetranuclear vanadium(III)/carboxylate complexes of acetate and related derivatives in aqueous solution

The formation of vanadium(III) complexes with nuclearity greater than two is believed to occur in aqueous solution on the basis of potentiometric, electrochemical, and/or UV-vis spectroscopy titration measurements, although structural evidence for this is limited. Upon the addition of 1-2 equiv of acetate, propionate, chloroacetate, trifluoroacetate, or bromoacetate to an aqueous, acidic solution of vanadium(III), trinuclear and tetranuclear complexes are formed. The structures of [V4(mu-OH)4(mu-OOCCF3)4(OH2)8]Cl4.7.5H2O (1), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.CH3COOH.12H2O (2), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.3H2O (3), [V3(mu3-O)(mu-OOCCH2Br)6(OH2)3]CF3SO3.H2O (4), [V3(mu3-O)(mu-OOCCH2CH3)6(OH2)3]Cl.2H2O (5), [V3(mu3-O)(mu-OOCCH3)6(OH2)3]Cl.3.5H2O (6), and [V3(mu3-O)(mu-OOCCH2Cl)6(OH2)3]CF3SO3.H2O (7) have been determined by X-ray diffraction. Importantly, electrospray mass spectrometry and 1H NMR measurements suggest that these complexes are not purely solid-state phenomena but are also present in solution. For the vanadium(III)/acetate and vanadium(III)/propionate systems, two paramagnetic 1H NMR signals corresponding to two distinct complexes (species A and B) are observed in the 40-55 ppm region for 0.20 mol equiv of acetate or propionate, at pD 3.44. No corresponding signals are observed for the vanadium(III)/bromoacetate and vanadium(III)/chloroacetate systems under the same conditions or for the vanadium(III)/ trifluoroacetate system using 19F NMR spectroscopy. UV-vis spectra suggest that species B are structurally analogous for the vanadium(III)/acetate and vanadium(III)/propionate systems, whereas structurally different complexes are the major species for the other systems. Diffusion coefficients of species B for the vanadium(III)/acetate and vanadium(III)/propionate systems determined by pulsed-field-gradient spin-echo NMR spectroscopy measurements are (3.0 +/- 0.1) x 10-6 and (3.23 +/- 0.01) x 10-6 cm2 s-1, respectively, and are most consistent with species B being trimeric, rather than tetranuclear, complexes.     

A dodecanuclear Zn cluster sandwiched by polyoxometalate ligands

A dodecazinc silicotungstate K(20)Na(2)[Zn(6)(OH)(7)(H(2)O)(Si(2)W(18)O(66))](2)·34H(2)O (1) has been synthesized and characterized by X-ray crystallography, elemental analysis, infrared, UV-vis spectroscopy, cyclic voltammetry, acid-base titration, and DFT calculations. The twelve zinc atoms between the two [Si(2)W(18)O(66)](16-) frameworks make this complex more stable hydrolytically than the heteropolytungstate ligands, [Si(2)W(18)O(66)](16-), themselves. The structurally unique central Zn(12) core is formed by the fusion of two [Zn(6)(OH)(7)(H(2)O)](5+) units through two edge-sharing Zn6 atoms. DFT B3LYP calculations give HOMO-LUMO and (HOMO - 1)-LUMO energy gaps of ～3.65 and 3.91 eV, respectively, as compared to the band gap in ZnO of 3.35 eV.     

Interactions of silicate ions with zinc(II) and aluminum(III) in alkaline aqueous solution

We present (29)Si, (27)Al, and (67)Zn NMR evidence to show that silicate ions in alkaline solution form complexes with zinc(II) (present as zincate, Zn(OH)(3)(-) or Zn(OH)(4)(2-)) and, concomitantly, with aluminate (Al(OH)(4)(-)). Zincate reacts with monomeric silicate at pH 14-15 to form [(HO)O(2)Si-O-Zn(OH)(3)](4-) and with dimeric silicate to produce [HO-SiO(2)-O-SiO(2)-O-Zn(OH)(3)](6-). The exchange of Si between these free and Zn-bound sites is immeasurably fast on the (29)Si NMR time scale. The cyclic silicate trimer reacts relatively slowly and incompletely with zincate to form [(HO)(3)Zn{(SiO(3))(3)}](7-). The concentration of the cyclic trimer becomes further depleted because zincate scavenges the silicate monomer and dimer, with which the cyclic trimer is in equilibrium on the time scale of sample preparation. Identification of these zincate-silicate complexes is supported by quantum chemical theoretical calculations. Aluminate and zincate, when present together, compete roughly equally for a deficiency of silicate to form [(HO)(3)ZnOSiO(2)OH](4-) and [(HO)(3)AlOSiO(2)OH](3-) which exchange (29)Si at a fast but measurable rate.     

Cationic assembly of metal complex aggregates: structural diversity,solution stability,and magnetic properties

The tetradentate imino-carboxylate ligand [L](2)(-) chelates the equatorial sites of Ni(II) to give the complex [Ni(L)(MeOH)(2)] in which a Ni(II) center is bound in an octahedral coordination environment with MeOH ligands occupying the axial sites. Lanthanide (Ln) and Group II metal ions (M) template the aggregation of six [Ni(L)] fragments into the octahedral cage aggregates (M[Ni(L)](6))(x)(+) (1: M = Sr(II); x = 2,2: M = Ba(II); x = 2, 3: M = La(III); x = 3, 4: M = Ce(III); x = 3, 5: M = Pr(III); x = 3, and 6: M = Nd(III); x = 3). In the presence of Group I cations, however, aggregates composed of the alkali metal-oxide cations template various cage compounds. Thus, Na(+) forms the trigonal bipyramidal [Na(5)O](3+) core within a tricapped trigonal prismatic [Ni(L)](9) aggregate to give ((Na(5)O) subset [Ni(L)](9)(MeOH)(3))(BF(4))(2).OH.CH(3)OH, 7. Li(+) and Na(+) together form a mixed Li(+)/Na(+) core comprising distorted trigonal bipyramidal [Na(3)Li(2)O](3+) within an approximately anti-square prismatic [Ni(L)](8) cage in ((Na(3)Li(2)O) subset [Ni(L)](8)(CH(3)OH)(1.3)(BF(4))(0.7))(BF(4))(2.3).(CH(3)OH)(2.75).(C(4)H(10)O)(0.5), 8, while in the presence of Li(+), a tetrahedral [Li(4)O](2+) core within a hexanuclear open cage [Ni(L)](6) in ((Li(4)O) subset [Ni(L)](6)(CH(3)OH)(3))2ClO(4).1.85CH(3)OH, 9, is produced. In the presence of H(2)O, the Cs(+) cation induces the aggregation of the [Ni(L)(H(2)O)(2)] monomer to give the cluster Cs(2)[Ni(L)(H(2)O)(2)](6).2I.4CH(3)OH.5.25H(2)O, 10. Analysis by electronic spectroscopy and mass spectrometry indicates that in solution the trend in stability follows the order 1-6 > 7 > 8 approximately 9. Magnetic susceptibility data indicate that there is net antiferromagnetic exchange between magnetic centers within the cages.     

Cobalt(III) complexes of monodentate N9-bound adeninate (ade-), [Co(ade-kappaN9)Cl(en)2]+ (en = 1,2-diaminoethane): syntheses, crystal structures, and protonation behaviors of the geometrical isomers

In acidic aqueous solution, a cobalt(III) complex containing monodentate N(9)-bound adeninate (ade(-)), cis-[Co(ade-kappaN(9))Cl(en)(2)]Cl (cis-[1]Cl), underwent protonation to the adeninate moiety without geometrical isomerization or decomposition of the Co(III) coordination sphere, and complexes of cis-[CoCl(Hade)(en)(2)]Cl(2) (cis-[2]Cl(2)) and cis-[Co(H(2)ade)Cl(en)(2)]Cl(3) (cis-[3]Cl(3)) could be isolated. The pK(a) values of the Hade and H(2)ade(+) complexes are 6.03(1) and 2.53(12), respectively, at 20 degrees C in 0.1 M aqueous NaCl. The single-crystal X-ray analyses of cis-[2]Cl(2).0.5H(2)O and cis-[3]Cl(2)(BF(4)).H(2)O revealed that protonation took place first at the adeninate N(7) and then at the N(1) atoms to form adenine tautomer (7H-Hade-kappaN(9)) and cationic adeninium (1H,7H-H(2)ade(+)-kappaN(9)) complexes, respectively. On the other hand, addition of NaOH to an aqueous solution of cis-[1]Cl afforded a mixture of geometrical isomers of the hydroxo-adeninato complex, cis- and trans-[Co(ade-kappaN(9))(OH)(en)(2)](+). The trans-isomer of chloro-adeninato complex trans-[Co(ade-kappaN(9))Cl(en)(2)]BF(4) (trans-[1]BF(4)) was synthesized by a reaction of cis-[2](BF(4))(2) and sodium methoxide in methanol. This isomer in acidic aqueous solution was also stable toward isomerization, affording the corresponding adenine tautomer and adeninium complexes (pK(a) = 5.21(1) and 2.48(9), respectively, at 20 degrees C in 0.1 M aqueous NaCl). The protonated product of trans-[Co(7H-Hade-kappaN(9))Cl(en)(2)](BF(4))(2).H(2)O (trans-[2](BF(4))(2).H(2)O) could also be characterized by X-ray analysis. Furthermore, the hydrogen-bonding interactions of the adeninate/adenine tautomer complexes cis-[1]BF(4), cis-[2](BF(4))(2), and trans-[2](BF(4))(2) with 1-cyclohexyluracil in acetonitrile-d(3) were investigated by (1)H NMR spectroscopy. The crystal structure of trans-[Co(ade)(H(2)O)(en)(2)]HPO(4).3H(2)O, which was obtained by a reaction of trans-[Co(ade)(OH)(en)(2)]BF(4) and NaH(2)PO(4), was also determined.     

Lanthanide-tungstobismuthate clusters based on [BiW9O33]9- building units: synthesis, crystal structures, luminescent and magnetic properties

The reaction of Na(12)[Bi(2)W(22)O(74)(OH)(2)]·44H(2)O, Na(9)[BiW(9)O(33)]·16H(2)O, lanthanide chloride and Na(2)CO(3) in aqueous solution at a pH value of about 7.0 resulted in the three unprecedented giant lanthanide-tungstobismuthate clusters Na(x)H(22-x)[(BiW(9)O(33))(4)(WO(3)){Bi(6)(μ(3)-O)(4)(μ(2)-OH)(3)}(Ln(3)(H(2)O)(6)CO(3))]·nH(2)O {Ln = Pr(3+) (1), Nd(3+) (2), La(3+) (3), x = 22 (1), 22 (2), 20 (3), n = 95 (1), 91 (2), 73 (3)}. These three complexes represent the first examples of lanthanide ions encapsulated in polyoxotungstobismuthates and the largest polytungstobismuthates so far. Furthermore, a [{Bi(6)(μ(3)-O)(4)(μ(2)-OH)(3)}](7+) polyoxo cation was incorporated into the structure of these compounds. All complexes are characterized by single-crystal X-ray diffraction, IR spectra, electronic spectroscopy, thermogravimetric and elemental analysis. Magnetic investigation revealed that the progressive depopulation of excited Stark sublevels of the lanthanide ions at low temperature and the weak antiferromagnetic interaction between the neighboring metal centres are responsible for the magnetic properties of 1 and 2. The original synthesis strategy in this work may open a gateway to assembly of large lanthanide-tungstobismuthates clusters and novel multifunctional solid materials in aqueous solution under mild conditions.     

Effect of cyanato, azido, carboxylato, and carbonato ligands on the formation of cobalt(II) polyoxometalates: characterization, magnetic, and electrochemical studies of multinuclear cobalt clusters

Five Co(II) silicotungstate complexes are reported. The centrosymmetric heptanuclear compound K(20)[{(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)}(2)Co(H(2)O)(2)]47 H(2)O (1) consists of two {(B-beta-SiW(9)O(33)(OH))(beta-SiW(8)O(29)(OH)(2))Co(3)(H(2)O)} units connected by a {CoO(4)(H(2)O)(2)} group. In the chiral species K(7)[Co(1.5)(H(2)O)(7))][(gamma-SiW(10)O(36))(beta-SiW(8)O(30)(OH))Co(4)(OH)(H(2)O)(7)]36 H(2)O (2), a {gamma-SiW(10)O(36)} and a {beta-SiW(8)O(30)(OH)} unit enclose a mononuclear {CoO(4)(H(2)O)(2)} group and a {Co(3)O(7)(OH)(H(2)O)(5)} fragment. The two trinuclear Co(II) clusters present in 1 enclose a mu(4)-O atom, while in 2 a mu(3)-OH bridging group connects the three paramagnetic centers of the trinuclear unit, inducing significantly larger Co-L-Co (L=mu(4)-O (1), mu(3)-OH (2)) bridging angles in 2 (theta(av(Co-L-Co))=99.1 degrees ) than in 1 (theta(av(Co-L-Co))=92.8 degrees ). Weaker ferromagnetic interactions were found in 2 than in 1, in agreement with larger Co-L-Co angles in 2. The electrochemistry of 1 was studied in detail. The two chemically reversible redox couples observed in the positive potential domain were attributed to the redox processes of Co(II) centers, and indicated that two types of Co(II) centers in the structure were oxidized in separate waves. Redox activity of the seventh Co(II) center was not detected. Preliminary experiments indicated that 1 catalyzes the reduction of nitrite and NO. Remarkably, a reversible interaction exists with NO or related species. The hybrid tetranuclear complexes K(5)Na(3)[(A-alpha-SiW(9)O(34))Co(4)(OH)(3)(CH(3)COO)(3)]18 H(2)O (3) and K(5)Na(3)[(A-alpha-SiW(9)O(34))Co(4)(OH)(N(3))(2)(CH(3)COO)(3)]18 H(2)O (4) were characterized: in both, a tetrahedral {Co(4)(L(1))(L(2))(2)(CH(3)COO)(3)} (3: L(1)=L(2)=OH; 4: L(1)=OH, L(2)=N(3)) unit capped the [A-alpha-SiW(9)O(34)](10-) trivacant polyanion. The octanuclear complex K(8)Na(8)[(A-alpha-SiW(9)O(34))(2)Co(8)(OH)(6)(H(2)O)(2)(CO(3))(3)]52 H(2)O (5), containing two {Co(4)O(9)(OH)(3)(H(2)O)} units, was also obtained. Compounds 2, 3, 4, and 5 were less stable than 1, but their partial electrochemical characterization was possible; the electronic effect expected for 3 and 4 was observed.     

Synthesis, structures, and magnetic properties of the copper(II), cobalt(II), and manganese(II) complexes with 9-acridinecarboxylate and 4-quinolinecarboxylate ligands

To explore the relationships between the structures of ligands and their complexes, we have synthesized and characterized a series of metal complexes with two structurally related ligands, 9-acridinecarboxylic acid (HL(1)) and 4-quinolinecarboxylate acid (HL(2)), [Cu(2)(mu(2)-OMe)(2)(L(1))(2)(H(2)O)(0.69)](n) 1, [Cu(2)(L(1))(4)(CH(3)OH)(2)] 2, [Cu(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 3, [Mn(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 4, [Co(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 5, [Cu(L(2))(2)](n) 6, [Mn(L(2))(2)(H(2)O)](n) 7, and [Co(L(2))(2)(H(2)O)](n) 8. 1 is a three-dimensional (3D) polymer with an interpenetrating NbO type network showing one-dimensional (1D) channels, whereas 2 and 3 take bi- and trinuclear structures, respectively, because of the differences in basicity of the reaction systems in preparing the three complexes. 4 and 5 have trinuclear structures similar to that of 3. In 1-5, ligand L(1) performs different coordination modes with N,O-bridging in 1 and O,O'-bridging in 2-5, and the metal ions also show different coordination geometries: square planar in 1, square pyramidal in 2, and octahedral in 3-5. 6 has a two-dimensional structure containing (4,4) grids in which L(2) adopts the N,O-bridging mode and the Cu(II) center takes square planar geometry. 7 and 8 are isostructural complexes showing 1D chain structures, with L(2) adopting the O,O-bridging mode. In addition, the intermolecular O-H...N hydrogen bonds and pi-pi stacking interactions further extend the complexes (except 1 and 6), forming 3D structures. The magnetic properties of 2-7 have been investigated and discussed in detail.     

Novel 3D, 2D, and 0D first-row coordination compounds with 4,4'-bipyridine-N,N'-dioxide incorporating sulfur-containing anions

The reaction of M(S2O6) (M = Cu(II), Ni(II), and Co(II)) with 4,4'-bipyridine-N,N'-dioxide (bpdo) results in the formation of novel 3D, 2D, and mononuclear complexes. Complex 1, {[Cu(H2O)(bpdo)2](S2O6)(H2O)}n, is a 2-D wavelike polymer with the Cu(II) ion located on a 2-fold axis and having a distorted square-pyramidal coordination sphere. With Co(II) and Ni(II), 3-D complexes, {[M(bpdo)3](S2O6)(C2H5OH)7}n [M = Co(II) (2), Ni(II) (3)], were obtained. The metal atoms are situated on centers of symmetry and have octahedral environments coordinated to six bpdo molecules. The same reaction in aqueous solution with a metal/ligand ratio of 1:1 results in the formation of mononuclear complexes, {[M(bpdo)(H2O)5](SO4)(H2O)2} [M = Co(II) (4), Ni(II) (5)], accompanied by the decomposition of the dithionate anions S2O6(2-) to sulfate anions SO4(2-).     

Novel acetate polyoxomolybdate "host" accommodating a zigzag-chainlike "guest" of five edge-shared sodium cations: Na(21)[[Na(5)(H(2)O)(14)]within[Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]].CH(3)COONa. approximately equal to 95H(2)O

A novel ESR-silent polyoxomolybdate Na(21)([Na(5)(H(2)O)(14)][Mo(46)O(134)(OH)(10)(mu-CH(3)COO)(4)]).CH(3)COONa.approximately equal to 90H(2)O (3) was simply synthesized in high yield by reducing an acidified aqueous solution of Na(2)MoO(4).2H(2)O and CH(3)COONa.3H(2)O. The structure of 3 is constructed by a 46-member crown-shaped anion, [Na(5)(H(2)O)(14)]within[Mo(V)(20)Mo(VI)(26)O(134)(OH)(10)(mu-CH(3)COO)(4)](21-), 3a, which is built up by three different but related building blocks in a new mode and further connected into layers via Na(+) and hydrogen bonds. Crystal data of compound 3: triclinic space group P(-1); a = 16.4065(3), b = 17.4236(2), c = 20.8247(3) A; alpha= 87.57, beta= 67.9810(10), gamma= 80.6970(10)o; V = 5445.08(14) A(3); Z = 1; D(calcd) = 2.902. Structure solution and refinement are based on 19014 reflections, R = 0.0750.     

2-Aminoisobutyric acid in Co(II) and Co(II)/Ln(III) chemistry: homometallic and heterometallic clusters

The synthesis and magnetic properties of 13 new homo- and heterometallic Co(II) complexes containing the artificial amino acid 2-amino-isobutyric acid, aibH, are reported: [Co(II)(4)(aib)(3)(aibH)(3)(NO(3))](NO(3))(4)·2.8CH(3)OH·0.2H(2)O (1·2.8CH(3)OH·0.2H(2)O), {Na(2)[Co(II)(2)(aib)(2)(N(3))(4)(CH(3)OH)(4)]}(n) (2), [Co(II)(6)La(III)(aib)(6)(OH)(3)(NO(3))(2)(H(2)O)(4)(CH(3)CN)(2)]·0.5[La(NO(3))(6)]·0.75(ClO(4))·1.75(NO(3))·3.2CH(3)CN·5.9H(2)O (3·3.2CH(3)CN·5.9H(2)O), [Co(II)(6)Pr(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·[Pr(NO(3))(5)]·0.41[Pr(NO(3))(3)(ClO(4))(0.5)(H(2)O)(1.5)]·0.59[Co(NO(3))(3)(H(2)O)]·0.2(ClO(4))·0.25H(2)O (4·0.25H(2)O), [Co(II)(6)Nd(III)(aib)(6)(OH)(3)(NO(3))(2.8)(CH(3)OH)(4.7)(H(2)O)(1.5)]·2.7(ClO(4))·0.5(NO(3))·2.26CH(3)OH·0.24H(2)O (5·2.26CH(3)OH·0.24H(2)O), [Co(II)(6)Sm(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·[Sm(NO(3))(5)]·0.44[Sm(NO(3))(3)(ClO(4))(0.5)(H(2)O)(1.5)]·0.56[Co(NO(3))(3)(H(2)O)]·0.22(ClO(4))·0.3H(2)O (6·0.3H(2)O), [Co(II)(6)Eu(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)OH)(4.87)(H(2)O)(1.13)](ClO(4))(2.5)(NO(3))(0.5)·2.43CH(3)OH·0.92H(2)O (7·2.43CH(3)OH·0.92H(2)O), [Co(II)(6)Gd(III)(aib)(6)(OH)(3)(NO(3))(2.9)(CH(3)OH)(4.9)(H(2)O)(1.2)]·2.6(ClO(4))·0.5(NO(3))·2.58CH(3)OH·0.47H(2)O (8·2.58CH(3)OH·0.47H(2)O), [Co(II)(6)Tb(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·[Tb(NO(3))(5)]·0.034[Tb(NO(3))(3)(ClO(4))(0.5)(H(2)O)(0.5)]·0.656[Co(NO(3))(3)(H(2)O)]·0.343(ClO(4))·0.3H(2)O (9·0.3H(2)O), [Co(II)(6)Dy(III)(aib)(6)(OH)(3)(NO(3))(2.9)(CH(3)OH)(4.92)(H(2)O)(1.18)](ClO(4))(2.6)(NO(3))(0.5)·2.5CH(3)OH·0.5H(2)O (10·2.5CH(3)OH·0.5H(2)O), [Co(II)(6)Ho(III)(aib)(6)(OH)(3)(NO(3))(3)(CH(3)CN)(6)]·0.27[Ho(NO(3))(3)(ClO(4))(0.35)(H(2)O)(0.15)]·0.656[Co(NO(3))(3)(H(2)O)]·0.171(ClO(4)) (11), [Co(II)(6)Er(III)(aib)(6)(OH)(4)(NO(3))(2)(CH(3)CN)(2.5)(H(2)O)(3.5)](ClO(4))(3)·CH(3)CN·0.75H(2)O (12·CH(3)CN·0.75H(2)O), and [Co(II)(6)Tm(III)(aib)(6)(OH)(3)(NO(3))(3)(H(2)O)(6)]·1.48(ClO(4))·1.52(NO(3))·3H(2)O (13·3H(2)O). Complex 1 describes a distorted tetrahedral metallic cluster, while complex 2 can be considered to be a 2-D coordination polymer. Complexes 3-13 can all be regarded as metallo-cryptand encapsulated lanthanides in which the central lanthanide ion is captivated within a [Co(II)(6)] trigonal prism. dc and ac magnetic susceptibility studies have been carried out in the 2-300 K range for complexes 1, 3, 5, 7, 8, 10, 12, and 13, revealing the possibility of single molecule magnetism behavior for complex 10.