Light-induced metastable linkage isomers of ruthenium sulfur dioxide complexes

The irradiation of ruthenium-sulfur dioxide complexes of general formula trans-[Ru(II)(NH(3))(4)(SO(2))X]Y with laser light at low temperature results in linkage isomerization of SO(2), starting with eta(1)-planar S-bound to eta(2)-side S,O-bound SO(2). The solid-state photoreaction proceeds with retention of sample crystallinity. Following work on trans-[Ru(NH(3))(4)Cl(eta(1)-SO(2))]Cl and trans-[Ru(NH(3))(4)(H(2)O)(eta(1)-SO2)](C(6)H(5)SO(3))(2) (Kovalevsky, A. Y.; Bagley, K. A.; Coppens, P. J. Am. Chem. Soc. 2002, 124, 9241-9248), we describe photocrystallographic, IR, DSC, and theoretical studies of trans-[Ru(II)(NH(3))(4)(SO(2))X]Y complexes with (X = Cl(-), H(2)O, or CF(3)COO(-) (TFA(-))) and a number of different counterions (Y = Cl(-), C(6)H(5)SO(3)(-), Tos(-), or TFA(-)). Low temperature IR experiments indicate the frequency of the asymmetric and symmetric stretching vibrations of the Ru-coordinated SO(2) to be downshifted by about 100 and 165 cm(-1), respectively. Variation of the trans-to-SO(2) ligand and the counterion increases the MS2 decay temperature from 230 K (trans-[Ru(II)(NH(3))(4)(SO(2))Cl]Cl) to 276 K (trans-[Ru(II)(NH(3))(4)(SO(2))(H(2)O)](Tos)(2)). The stability of the MS2 state correlates with increasing sigma-donating ability of the trans ligand and the size of the counterion. Quantum chemical DFT calculations indicate the existence of a third eta(1)-O-bound (MS1) isomer, the two metastable states being 0.1-0.6 eV above the energy of the ground-state complex.     

A novel series of vanadium-sulfite polyoxometalates: synthesis, structural, and physical studies

Reaction of NH4VO3 with sulfur dioxide affords the hexanuclear cluster (NH4)2(Et4N)[(V(IV)O)6(mu4-O)2(mu3-OH)2(mu3-SO3)4(H2O)2]Cl x H2O (1), and the decapentanuclear host-guest compound (Et4N)5{Cl subset [(VO)15(mu3-O)18(mu-O)3]} x 3 H2O (2). Sequential addition of magnesium oxide to an acidic aqueous solution of NH4VO3 (pH approximately 0) followed by (NH4)2SO3 resulted in the formation of either the non-oxo polymeric vanadium(IV) compound trans-(NH4)2[V(IV)(OH)2(mu-SO3)2] (3) or the polymeric oxovanadium(IV) sulfite (NH4)[V(IV)O(SO3)1.5(H2O)] x 2.5 H2O (4) at pH values of 6 and 4, respectively. The decameric vanadium(V) compound {Na4(mu-H2O)8(H2O)6}[Mg(H2O)6][V(V)10(O)8(mu6-O)2(mu3-O)14] x 3 H2O (5) was synthesised by treating an acidic aqueous solution of NH4VO3 with MgO and addition of NaOH to pH approximately 6. All the compounds were characterised by single-crystal X-ray structure analysis. The crystal structure of compound 1 revealed an unprecedented structural motif of a cubane unit [M4(mu4-O)2(mu3-OH)2] connected to two other metal atoms. Compound 3 comprises a rare example of a non-oxo vanadium(IV) species isolated from aqueous solution and in the presence of the reducing agent SO3(2-), while compound 4 represents a rare example of an open-framework species isolated at room temperature (20 degrees C). In addition to the synthesis and crystallographic studies, we report the IR and magnetic properties (for 1, 2 and 3) of these vanadium clusters as well as theoretical studies on compound 3.     

3d-Metal derivatives of the [Cu(I)(SO3)4]7- ion: structure and magnetism

The Cu(SO(3))(4)(7-) anion, which consists of a tetrahedrally coordinated Cu(I) centre coordinated to four sulfur atoms, is able to act as a multidentate ligand in discrete and infinite supramolecular species. The slow oxidation of an aqueous solution of Na(7)Cu(SO(3))(4) yields a mixed oxidation state, 2D network of composition Na(5){[Cu(II)(H(2)O)][Cu(I)(SO(3))(4)]}·6H(2)O. The addition of Cu(II) and 2,2'-bipyridine to an aqueous Na(7)Cu(SO(3))(4) solution leads to the formation of a pentanuclear complex of composition {[Cu(II)(H(2)O)(bipy)](4)[Cu(I)(SO(3))(4)]}(+); a combination of hydrogen bonding and π-π stacking interactions leads to the generation of infinite parallel channels that are occupied by disordered nitrate anions and water molecules. A pair of Cu(SO(3))(4)(7-) anions each act as a tridentate ligand towards a single Mn(II) centre when Mn(II) ions are combined with an excess of Cu(SO(3))(4)(7-). An anionic pentanuclear complex of composition {[Cu(I)(SO(3))(4)](2)[Fe(III)(H(2)O)](3)(O)} is formed when Fe(II) is added to a Cu(+)/SO(3)(2-) solution. Hydrated ferrous [Fe(H(2)O)(6)(2+)] and sodium ions act as counterions for the complexes and are responsible for the formation of an extensive hydrogen bond network within the crystal. Magnetic susceptibility studies over the temperature range 2-300 K show that weak ferromagnetic coupling occurs within the Cu(II) containing chains of Na(5){[Cu(II)(H(2)O)][Cu(I)(SO(3))(4)]}·6H(2)O, while zero coupling exists in the pentanuclear cluster {[Cu(II)(H(2)O)(bipy)](4)[Cu(I)(SO(3))(4)]}(NO(3))·H(2)O. Weak Mn(II)-O-S-O-Mn(II) antiferromagnetic coupling occurs in Na(H(2)O)(6){[Cu(I)(SO(3))(4)][Mn(II)(H(2)O)(2)](3)}, the latter formed when Mn was in excess during synthesis. The compound, Na(3)(H(2)O)(6)[Fe(II)(H(2)O)(6)](2){[Cu(I)(SO(3))(4)](2)[Fe(III)(H(2)O)](3)(O)}·H(2)O, contained trace magnetic impurities that affected the expected magnetic behaviour.     

Push-pull nitrile ligands exhibit specific hydration patterns

The reaction between K[PtCl(3)(Me(2)SO)] or prepared in this work cis- and trans-[PtCl(2)(NCNR(2))(Me(2)SO)] (R(2) = Me(2), 1; C(4)H(8)O, 2; C(5)H(10) 3) with an excess of NCNR(2) in water gives the cationic bischelate [Pt{κ(2)-N,N'-NH=C(NMe(2))OC(NMe(2))=NH}(2)](2+) (4(2+)) and the monochelates [PtCl{κ(2)-N,O-NH=C(NR(2))NC(NR(2))=O}(Me(2)SO)] (R(2) = C(4)H(8)O, 5; C(5)H(10), 6). Complex 4(2+) was released from the reaction mixture as 4·[PtCl(3)(Me(2)SO)](2)·(H(2)O)(2) or it was precipitated as 4·[A](2) (A = pic, 4·[pic](2); PF(6), 4·[PF(6)](2); BPh(4), 4·[BPh(4)](2)·(NH(2)CONMe(2))) by addition of picric acid, NaPF(6), or NaBPh(4), respectively, to the filtrate obtained after separation of 4·[PtCl(3)(Me(2)SO)](2)·(H(2)O)(2). In 2, the dialkylcyanamide ligand undergoes bond cleavage giving the known trans-[PtCl(2){N(H)C(4)H(8)O}(Me(2)SO)] (trans-7). All complexes were characterized by elemental analyses (C, H, N), high resolution ESI-MS, IR, (1)H and (13)C{(1)H} NMR spectroscopic techniques, including 2D NMR correlation experiments ((1)H,(1)H-COSY, (1)H,(13)C-HMQC/(1)H,(13)C HSQC, (1)H,(13)C-HMBC, and (1)H,(1)H-NOESY). The structures of cis-1, cis-3, 4·[PtCl(3)(Me(2)SO)](2)·(H(2)O)(2), 4·[BPh(4)](2)·(NH(2)CONMe(2)) and 5 were determined by a single-crystal X-ray diffraction.     

Complexes of molecular and ionic character in the same matrix layer: infrared studies of the sulfuric acid/ammonia system

The atmospherically important interaction products of sulfuric acid and ammonia molecules have been firstly observed by matrix isolation Fourier transform infrared spectroscopy (MIS-FTIR). Infrared spectra of solid argon matrix layers, in which both H(2)SO(4) and NH(3) molecules were entrapped as impurities, were analyzed for bands not seen in matrix layers containing either of the parent molecules alone. Results were interpreted on the basis of spectral changes, experimental conditions, and semiempirically scaled frequencies from the B3LYP/aug-cc-pVTZ and B3LYP/aug-cc-pVQZ calculations. Bands were assigned to complexes of the H(2)SO(4)·NH(3) and H(2)SO(4)·[NH(3)](2) general formulas. They differ significantly: the 1:1 H(2)SO(4)·NH(3) complex is a strongly hydrogen bonded complex, an analogue of the H(2)SO(4)·H(2)O complex, studied previously. For the 1:2 H(2)SO(4)·[NH(3)](2) complex, spectral results indicate an almost complete proton transfer forming a complex of essentially the two ionic moieties HSO(4)(-) and [H(3)N···H···NH(3)](+), an analogue of the [H(2)O···H···OH(2)](+) "Zundel ion".     

Crystallization pathways of sulfate-nitrate-ammonium aerosol particles

Crystallization experiments are conducted for aerosol particles composed of aqueous mixtures of (NH(4))(2)SO(4)(aq) and NH(4)NO(3)(aq), (NH(4))(2)SO(4)(aq) and NH(4)HSO(4)(aq), and NH(4)NO(3)(aq) and NH(4)HSO(4)(aq). Depending on the aqueous composition, crystals of (NH(4))(2)SO(4)(s), (NH(4))(3)H(SO(4))(2)(s), NH(4)HSO(4)(s), NH(4)NO(3)(s), 2NH(4)NO(3) x (NH(4))(2)SO(4)(s), and 3NH(4)NO(3) x (NH(4))(2)SO(4)(s) are formed. Although particles of NH(4)NO(3)(aq) and NH(4)HSO(4)(aq) do not crystallize even at 1% relative humidity, additions of 0.05 mol fraction SO(4)(2-)(aq) or NO(3)(-)(aq) ions promote crystallization, respectively. 2NH(4)NO(3) x (NH(4))(2)SO(4)(s) and (NH(4))(3)H(SO(4))(2)(s) appear to serve as good heterogeneous nuclei for NH(4)NO(3)(s) and NH(4)HSO(4)(s), respectively. 2NH(4)NO(3) x (NH(4))(2)SO(4)(s) crystallizes over a greater range of aqueous compositions than 3NH(4)NO(3) x (NH(4))(2)SO(4)(s). An infrared aerosol spectrum is provided for each solid based upon a linear decomposition analysis of the recorded spectra. Small nonzero residuals occur in the analysis because aerosol spectra depend on particle morphology, which changes slightly across the range of compositions studied. In addition, several of the mixed compositions crystallize with residual aqueous water of up to 5% particle mass. We attribute this water content to enclosed water pockets. The results provide further insights into the nonlinear crystallization pathways of sulfate-nitrate-ammonium aerosol particles.     

Oxyhalogen-sulfur chemistry: kinetics and mechanism of oxidation of N-acetylthiourea by chlorite and chlorine dioxide

The oxidation reactions of N-acetylthiourea (ACTU) by chlorite and chlorine dioxide were studied in slightly acidic media. The ACTU-ClO(2)(-) reaction has a complex dependence on acid with acid catalysis in pH > 2 followed by acid retardation in higher acid conditions. In excess chlorite conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of chlorine dioxide and sulfate. In some ratios of oxidant to reductant mixtures, oligo-oscillatory formation of chlorine dioxide is observed. The stoichiometry of the reaction is 2:1, with a complete desulfurization of the ACTU thiocarbamide to produce the corresponding urea product: 2ClO(2)(-) + CH(3)CONH(NH(2))C=S + H(2)O --> CH(3)CONH(NH(2))C=O + SO(4)(2-) + 2Cl(-) + 2H(+) (A). The reaction of chlorine dioxide and ACTU is extremely rapid and autocatalytic. The stoichiometry of this reaction is 8ClO(2)(aq) + 5CH(3)CONH(NH(2))C=S + 9H(2)O --> 5CH(3)CONH(NH(2))C=O + 5SO(4)(2-) + 8Cl(-) + 18H(+) (B). The ACTU-ClO(2)(-) reaction shows a much stronger HOCl autocatalysis than that which has been observed with other oxychlorine-thiocarbamide reactions. The reaction of chlorine dioxide with ACTU involves the initial formation of an adduct which hydrolyses to eliminate an unstable oxychlorine intermediate HClO(2)(-) which then combines with another ClO(2) molecule to produce and accumulate ClO(2)(-). The oxidation of ACTU involves the successive oxidation of the sulfur center through the sulfenic and sulfinic acids. Oxidation of the sulfinic acid by chlorine dioxide proceeds directly to sulfate bypassing the sulfonic acid. Sulfonic acids are inert to further oxidation and are only oxidized to sulfate via an initial hydrolysis reaction to yield bisulfite, which is then rapidly oxidized. Chlorine dioxide production after the induction period is due to the reaction of the intermediate HOCl species with ClO(2)(-). Oligo-oscillatory behavior arises from the fact that reactions that form ClO(2) are comparable in magnitude to those that consume ClO(2), and hence the assertion of each set of reactions is based on availability of reagents that fuel them. A computer simulation study involving 30 elementary and composite reactions gave a good fit to the induction period observed in the formation of chlorine dioxide and in the autocatalytic consumption of ACTU in its oxidation by ClO(2).     

Theoretical studies on the coupling interactions in H2SO4···HOO˙···(H2O)n (n = 0-2) clusters: toward understanding the role of water molecules in the uptake of HOO˙ radical by sulfuric acid aerosols

A detailed knowledge of coupling interactions among sulfuric acid (H(2)SO(4)), the hydroperoxyl radical (HOO˙), and water molecules (H(2)O) is crucial for the better understanding of the uptake of HOO˙ radicals by sulfuric acid aerosols at different atmospheric humidities. In the present study, the equilibrium structures, binding energies, equilibrium distributions, and the nature of the coupling interactions in H(2)SO(4)···HOO˙···(H(2)O)(n) (n = 0-2) clusters have been systematically investigated at the B3LYP/6-311++G(3df,3pd) level of theory in combination with the atoms in molecules (AIM) theory, natural bond orbital (NBO) method, energy decomposition analyses, and ab initio molecular dynamics. Two binary, five ternary, and twelve tetramer clusters possessing multiple intermolecular H-bonds have been located on their potential energy surfaces. Two different modes for water molecules have been observed to influence the coupling interactions between H(2)SO(4) and HOO˙ through the formations of intermolecular H-bonds with or without breaking the original intermolecular H-bonds in the binary H(2)SO(4)···HOO˙ cluster. It was found that the introduction of one or two water molecules can efficiently enhance the interactions between H(2)SO(4) and HOO˙, implying the positive role of water molecules in the uptake of the HOO˙ radical by sulfuric acid aerosols. Additionally, the coupling interaction modes of the most stable clusters under study have been verified by the ab initio molecular dynamics.     

Polyoxomolybdodiphosphonates: examples incorporating ethylidenepyridines

We have synthesized and structurally characterized three pyridylethylidene-functionalized diphosphonate-containing polyoxomolybdates, [{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](6-) (1), [{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)](8-) (2), and [{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)](12-) (3). Polyanions 1-3 were prepared in a one-pot reaction of the dinuclear, dicationic {Mo(V)(2)O(4)(H(2)O)(6)}(2+) with 1-hydroxo-2-(3-pyridyl)ethylidenediphosphonate (Risedronic acid) in aqueous solution. Polyanions 1 and 2 are mixed-valent Mo(VI/V) species with open tetranuclear and hexanuclear structures, respectively, containing two diphosphonate groups. Polyanion 3 is a cyclic octanuclear structure based on four {Mo(V)(2)O(4)(H(2)O)} units and four diphosphonates. Polyanions 1 and 2 crystallized as guanidinium salts [C(NH(2))(3)](5)H[{Mo(VI)O(3)}(2){Mo(V)(2)O(4)}{HO(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·13H(2)O (1a) and [C(NH(2))(3)](6)H(2)[{Mo(VI)(2)O(6)}(2){Mo(V)(2)O(4)}{O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(2)]·10H(2)O (2a), whereas polyanion 3 crystallized as a mixed sodium-guanidinium salt, Na(8)[C(NH(2))(3)](4)[{Mo(V)(2)O(4)(H(2)O)}(4){O(3)PC(O)(CH(2)-3-C(5)NH(4))PO(3)}(4)]·8H(2)O (3a). The compounds were characterized in the solid state by single-crystal X-ray diffraction, IR spectroscopy, and thermogravimetric and elemental analyses. The formation of polyanions 1 and 3 is very sensitive to the pH value of the reaction solution, with exclusive formation of 1 above pH 7.4 and 3 below pH 6.6. Detailed solution studies by multinuclear NMR spectrometry were performed to study the equilibrium between these two compounds. Polyanion 2 was insoluble in all common solvents. Detailed computational studies on the solution phases of 1 and 3 indicated the stability of these polyanions in solution, in complete agreement with the experimental findings.     

Polyoxomolybdenum(V/VI)-sulfite compounds: synthesis, structural, and physical studies

Reaction of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) in the mixed-solvent system H(2)O/CH(3)CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH(4))(4)[Mo(4)(VI)SO(16)] x H(2)O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH(4))(4)[Mo(5)(VI)S(2)O(21)] x 3H(2)O (2). Compound {(H(2)bipy)(2)[Mo(5)(VI)S(2)O(21)] x H(2)O}(x) (3) was obtained from the reaction of aqueous acidic solution of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) (pH = 2.5) and 4,4'-bipyridine (4,4'-bipy). The mixed metal/sulfite species (NH(4))(7)[Co(III)(Mo(2)(V)O(4))(NH(3))(SO(3))(6)] x 4H(2)O (4) was synthesized by reacting Na(2)Mo(VI)O(4) x 2H(2)O with CoCl(2) x 6H(2)O and (NH(4))(2)SO(3) with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing Mo(VI)O(6) octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo(4) ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo(5)(VI)S(2)O(21)](4-), and these coordinatively saturated clusters are joined by diprotonated 4,4'-H(2)bipy(2+) through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [Co(III)Mo(2)(V)SO(3)(2-)] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d(6) octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported.     

Tetra- to dodecanuclear oxomolybdate complexes with functionalized bisphosphonate ligands: activity in killing tumor cells

We report the synthesis and characterization of five novel Mo-containing polyoxometalate (POM) bisphosphonate complexes with nuclearities ranging from 4 to 12 and with fully reduced, fully oxidized, or mixed-valent (Mo(V), Mo(VI)) molybdenum, in which the bisphosphonates bind to the POM cluster through their two phosphonate groups and a deprotonated 1-OH group. The compounds were synthesized in water by treating [Mo(V)(2)O(4)(H(2)O)(6)](2+) or [Mo(VI)O(4)](2-) with H(2)O(3)PC(C(3)H(6)NH(2))OPO(3)H(2) (alendronic acid) or its aminophenol derivative, and were characterized by single-crystal X-ray diffraction and (31)P NMR spectroscopy. (NH(4))(6)[(Mo(V)(2)O(4))(Mo(VI)(2)O(6))(2)(O(3)PC(C(3)H(6)NH(3))OPO(3))(2)]·12H(2)O (1) is an insoluble mixed-valent species. [(C(2)H(5))(2)NH(2)](4)[Mo(V)(4)O(8)(O(3)PC(C(3)H(6)NH(3))OPO(3))(2)]·6H(2)O (2) and [(C(2)H(5))(2)NH(2)](6)[Mo(V)(4)O(8)(O(3)PC(C(10)H(14)NO)OPO(3))(2)]·18H(2)O (4) contain similar tetranuclear reduced frameworks. Li(8)[(Mo(V)(2)O(4)(H(2)O))(4)(O(3)PC(C(3)H(6)NH(3))OPO(3))(4)]·45H(2)O (3) and Na(2)Rb(6)[(Mo(VI)(3)O(8))(4)(O(3)PC(C(3)H(6)NH(3))OPO(3))(4)]·26H(2)O (5) are alkali metal salts of fully reduced octanuclear and fully oxidized dodecanuclear POMs, respectively. The activities of 2-5 (which are water-soluble) against three human tumor cell lines were investigated in vitro. Although 2-4 have weak but measurable activity, 5 has IC(50) values of about 10 μM, which is about four times the activity of the parent alendronate molecule on a per-alendronate basis, which opens up the possibility of developing novel drug leads based on Mo bisphosphonate clusters.     

Aerosol chamber study of optical constants and N2O5 uptake on supercooled H2SO4/H2O/HNO3 solution droplets at polar stratospheric cloud temperatures

The mechanism of the formation of supercooled ternary H(2)SO(4)/H(2)O/HNO(3) solution (STS) droplets in the polar winter stratosphere, i.e., the uptake of nitric acid and water onto background sulfate aerosols at T < 195 K, was successfully mimicked during a simulation experiment at the large coolable aerosol chamber AIDA of Forschungszentrum Karlsruhe. Supercooled sulfuric acid droplets, acting as background aerosol, were added to the cooled AIDA vessel at T = 193.6 K, followed by the addition of ozone and nitrogen dioxide. N(2)O(5), the product of the gas phase reaction between O(3) and NO(2), was then hydrolyzed in the liquid phase with an uptake coefficient gamma(N(2)O(5)). From this experiment, a series of FTIR extinction spectra of STS droplets was obtained, covering a broad range of different STS compositions. This infrared spectra sequence was used for a quantitative test of the accuracy of published infrared optical constants for STS aerosols, needed, for example, as input in remote sensing applications. The present findings indicate that the implementation of a mixing rule approach, i.e., calculating the refractive indices of ternary H(2)SO(4)/H(2)O/HNO(3) solution droplets based on accurate reference data sets for the two binary H(2)SO(4)/H(2)O and HNO(3)/H(2)O systems, is justified. Additional model calculations revealed that the uptake coefficient gamma(N(2)O(5)) on STS aerosols strongly decreases with increasing nitrate concentration in the particles, demonstrating that this so-called nitrate effect, already well-established from uptake experiments conducted at room temperature, is also dominant at stratospheric temperatures.     

Sulfur dioxide in water: structure and dynamics studied by an ab initio quantum mechanical charge field molecular dynamics simulation

An ab initio Quantum Mechanical Charge Field Molecular Dynamics Simulation (QMCF MD) was performed to investigate structure and dynamics behavior of hydrated sulfur dioxide (SO(2)) at the Hartree-Fock level of theory employing Dunning DZP basis sets for solute and solvent molecules. The intramolecular structural characteristics of SO(2), such as S═O bond lengths and O═S═O bond angle, are in good agreement with the data available from a number of different experiments. The structural features of the hydrated SO(2) were primarily evaluated in the form of S-O(wat) and O(SO(2))-H(wat) radial distribution functions (RDFs) which gave mean distances of 2.9 and 2.2 ?, respectively. The dynamical behavior characterizes the solute molecule to have structure making properties in aqueous solution or water aerosols, where the hydrated SO(2) can easily get oxidized to form a number of sulfur(VI) species, which are believed to play an important role in the atmospheric processes.     

Adsorption of sulfur dioxide on hematite and goethite particle surfaces

The adsorption of sulfur dioxide (SO(2)) on iron oxide particle surfaces at 296 K has been investigated using X-ray photoelectron spectroscopy (XPS). A custom-designed XPS ultra-high vacuum chamber was coupled to an environmental reaction chamber so that the effects of adsorbed water and molecular oxygen on the reaction of SO(2) with iron oxide surfaces could be followed at atmospherically relevant pressures. In the absence of H(2)O and O(2), exposure of hematite (alpha-Fe(2)O(3)) and goethite (alpha-FeOOH) to SO(2) resulted predominantly in the formation of adsorbed sulfite (SO(3)(2-)), although evidence for adsorbed sulfate (SO(4)(2-)) was also found. At saturation, the coverage of adsorbed sulfur species was the same on both alpha-Fe(2)O(3) and alpha-FeOOH as determined from the S2p : Fe2p ratio. Equivalent saturation coverages and product ratios of sulfite to sulfate were observed on these oxide surfaces in the presence of water vapor at pressures between 6 and 18 Torr, corresponding to 28 to 85% relative humidity (RH), suggesting that water had no effect on the adsorption of SO(2). In contrast, molecular oxygen substantially influenced the interactions of SO(2) with iron oxide surfaces, albeit to a much larger extent on alpha-Fe(2)O(3) relative to alpha-FeOOH. For alpha-Fe(2)O(3), adsorption of SO(2) in the presence of molecular oxygen resulted in the quantitative formation of SO(4)(2-) with no detectable SO(3)(2-). Furthermore, molecular oxygen significantly enhanced the extent of SO(2) uptake on alpha-Fe(2)O(3), as indicated by the greater than two-fold increase in the S2p : Fe2p ratio. Although SO(2) uptake is still enhanced on alpha-Fe(2)O(3) in the presence of molecular oxygen and water, the enhancement factor decreases with increasing RH. In the case of alpha-FeOOH, there is an increase in the amount of SO(4)(2-) in the presence of molecular oxygen, however, the predominant surface species remained SO(3)(2-) and there is no enhancement in SO(2) uptake as measured by the S2p : Fe2p ratio. A mechanism involving molecular oxygen activation on oxygen vacancy sites is proposed as a possible explanation for the non-photochemical oxidation of sulfur dioxide on iron oxide surfaces. The concentration of these sites depends on the exact environmental conditions of RH.     

Complexes of copper(II) with 3-(ortho-substituted phenylhydrazo)pentane-2,4-diones: syntheses, properties and catalytic activity for cyclohexane oxidation

Reactions of copper(II) with 3-phenylhydrazopentane-2,4-diones X-2-C(6)H(4)-NHN=C{C(=O)CH(3)}(2) bearing a substituent in the ortho-position [X = OH (H(2)L(1)) 1, AsO(3)H(2) (H(3)L(2)) 2, Cl (HL(3)) 3, SO(3)H (H(2)L(4)) 4, COOCH(3) (HL(5)) 5, COOH (H(2)L(6)) 6, NO(2) (HL(7)) 7 or H (HL(8)) 8] lead to a variety of complexes including the monomeric [CuL(4)(H(2)O)(2)]·H(2)O 10, [CuL(4)(H(2)O)(2)] 11 and [Cu(HL(4))(2)(H(2)O)(4)] 12, the dimeric [Cu(2)(H(2)O)(2)(μ-HL(2))(2)] 9 and the polymeric [Cu(μ-L(6))](n)] 13 ones, often bearing two fused six-membered metallacycles. Complexes 10-12 can interconvert, depending on pH and temperature, whereas the Cu(II) reactions with 4 in the presence of cyanoguanidine or imidazole (im) afford the monomeric compound [Cu(H(2)O)(4){NCNC(NH(2))(2)}(2)](HL(4))(2)·6H(2)O 14 and the heteroligand polymer [Cu(μ-L(4))(im)](n)15, respectively. The compounds were characterized by single crystal X-ray diffraction (complexes), electrochemical and thermogravimetric studies, as well as elemental analysis, IR, (1)H and (13)C NMR spectroscopies (diones) and ESI-MS. The effects of the substituents in 1-8 on the HOMO-LUMO gap and the relative stability of the model compounds [Cu(OH)(L(8))(H(2)O)]·H(2)O, [Cu(L(1))(H(2)O)(2)]·H(2)O and [Cu(L(4))(H(2)O)(2)]·H(2)O are discussed on the basis of DFT calculations that show the stabilization follows the order: two fused 6-membered > two fused 6-membered/5-membered > one 6-membered metallacycles. Complexes 9, 10, 12 and 13 act as catalyst precursors for the peroxidative oxidation (with H(2)O(2)) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H(2)O (total yields of ca. 20% with TONs up to 566), under mild conditions.     

Porous anionic, cationic, and neutral metal-carboxylate frameworks constructed from flexible tetrapodal ligands: syntheses, structures, ion-exchanges, and magnetic properties

A series of coordination polymers with anionic, cationic, and neutral metal-carboxylate frameworks have been synthesized by using a flexible tetrapodal ligand tetrakis[4-(carboxyphenyl)oxamethyl] methane acid (H(4)X). The reactions between divalent transition-metal ions and H(4)X ligands gave [M(3)X(2)]·[NH(2)(CH(3))(2)](2)·8DMA (M = Co (1), Mn (2), Cd(3)) which have anionic metal-carboxylate frameworks with NH(2)(CH(3))(2)(+) cations filled in channels. The reactions of trivalent metal ions Y(III), Dy(III), and In(III) with H(4)X ligands afforded cationic metal-carboxylate frameworks [M(3)X(2)·(NO(3))·(DMA)(2)·(H(2)O)]·5DMA·2H(2)O (M = Y(4), Dy(5)) and [In(2)X·(OH)(2)]·3DMA·6H(2)O (6) with the NO(3)(-) and OH(-) serving as counterions, respectively. Moreover, a neutral metal-carboxylate framework [Pb(2)X·(DMA)(2)]·2DMA (7) can also be isolated from reaction of Pb(II) and H(4)X ligands. The charged metal-carboxylate frameworks 1-5 have selectivity for specific counterions in the reaction system, and compounds 1 and 2 display ion-exchange behavior. Moreover, magnetic property measurements on compounds 1, 2, and 5 indicate that there exists weak antiferromagnetic interactions between magnetic centers in the three compounds.     

Temperature dependent thermodynamic model of the system H(+)-NH₄(+)-Na(+)-SO₄²⁻-NO₃⁻-Cl⁻-H₂O

A thermodynamic model of the system H(+)-NH?(+)-Na(+)-SO?2?-NO??-Cl?-H?O is parametrized and used to represent activity coefficients, equilibrium partial pressures of H?O, HNO?, HCl, H?SO?, and NH?, and saturation with respect to 26 solid phases (NaCl(s), NaCl·2H?O(s), Na?SO?(s), Na?SO?·10H?O(s), NaNO?·Na?SO?·H?O(s), Na?H(SO?)?(s), NaHSO?(s), NaHSO?·H?O(s), NaNH?SO?·2H?O(s), NaNO?(s), NH?Cl(s), NH?NO?(s), (NH?)?SO?(s), (NH?)?H(SO?)?(s), NH?HSO?(s), (NH?)?SO?·2NH?NO?(s), (NH?)?SO?·3NH?NO?(s), H?SO?·H?O(s), H?SO?·2H?O(s), H?SO?·3H?O(s), H?SO?·4H?O(s), H?SO?·6.5H?O(s), HNO?·H?O(s), HNO?·2H?O(s), HNO?·3H?O(s), and HCl·3H?O(s)). The enthalpy of formation of the complex salts NaNH?SO?·2H?O(s) and Na?SO?·NaNO?·H?O(s) is calculated. The model is valid for temperatures < or approximately 263.15 up to 330 K and concentrations from infinite dilution to saturation with respect to the solid phases. For H?SO?-H?O solutions the degree of dissociation of the HSO?? ion is represented near the experimental uncertainty over wide temperature and concentration ranges. The parametrization of the model for the subsystems H(+)-NH?(+)-NO??-SO?2?-H?O and H(+)-NO??-SO?2?-Cl?-H?O relies on previous studies (Clegg, S. L. et al. J. Phys. Chem. A 1998, 102, 2137-2154; Carslaw, K. S. et al. J. Phys. Chem. 1995, 99, 11557-11574), which are only partly adjusted to new data. For these systems the model is applicable to temperatures below 200 K, dependent upon liquid-phase composition, and for the former system also to supersaturated solutions. Values for the model parameters are determined from literature data for the vapor pressure, osmotic coefficient, emf, degree of dissociation of HSO??, and the dissociation constant of NH? as well as measurements of calorimetric properties of aqueous solutions like enthalpy of dilution, enthalpy of solution, enthalpy of mixing, and heat capacity. The high accuracy of the model is demonstrated by comparisons with experimentally determined mean activity coefficients of HCl in HCl-Na?SO?-H?O solutions, solubility measurements for the quaternary systems H(+)-Na(+)-Cl?-SO?2?-H?O, Na(+)-NH?(+)-Cl?-SO?2?-H?O, and Na(+)-NH?(+)-NO??-SO?2?-H?O as well as vapor pressure measurements of HNO?, HCl, H?SO?, and NH?.     

Polynuclear complexes of main group and transition metals with polyaminopolycarboxylate and polyoxometalate

Six supramolecular compounds constructed by main group and transition metals, polyoxotungstates (SiW(12)O(40)(4-)) and trans-N,N,N',N'-1,2-cyclohexanediaminotetraacetic acid (H(4)CyDTA), (NH(4))(3)[Ni(4)Na(H(2)O)(10)(CyDTA)(2)][SiW(12)O(40)]·10H(2)O (1) (NH(4))(2)[Cu(3)Na(2)(HCyDTA)(2)(H(2)O)(13)][SiW(12)O(40)]·5H(2)O (2), (NH(4))(2)[Zn(5)(CyDTA)(2)(H(2)O)(16)][SiW(12)O(40)]·8H(2)O (3), (NH(4))(4)[Cd(4)(CyDTA)(2)(H(2)O)(8)][SiW(12)O(40)]·6H(2)O (4), (NH(4))(4)[Sr(3)(HCyDTA)(2)(H(2)O)(14)][SiW(12)O(40)]·2H(2)O (5) and [Ca(4)(H(2)CyDTA)(2)(H(2)O)(22)][SiW(12)O(40)]·8H(2)O (6), were synthesized in aqueous solution and characterized by IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction techniques. Single-crystal structure analyses indicate they are constructed by the complexes with different nuclearity and polyoxometalates. In the sequence of Ni, Cu, Zn the nuclearity of the homometallic complex units increases from 2 to 5. Cadmium ions gives a tetranuclear complex with a compact structure. In 5 and 6 the main group metal ions and CyDTA form polymeric chains. CyDTA exhibits rather different coordination patterns to main group metal ions and transition metal ions due to their ionic radii and electronic configuration. The complex units and polyoxometalates arrange in different patterns due to the different shapes of the complex units. The compounds exhibit different thermal decomposition processes and the formation of compounds 3 and 4 quenches ligand-centered emissions and gives a ligand-to-metal emission. The study on various temperature susceptibilities of 1 and 2 shows that there is an antiferromagnetic coupling in the two compounds but coupling patterns are different.     

Syntheses, structural characterization and properties of transition metal complexes of 5,5'-(1,4-phenylene)bis(1H-tetrazole) (H(2)bdt), 5',5'-(1,1'-biphenyl)-4,4'-diylbis(1H-tetrazole) (H(2)dbdt) and 5,5',5'-(1,3,5-phenylene)tris(1H-tetrazole) (H(3)btt)

The hydrothermal chemistry of a variety of M(II)SO(4) salts with the tetrazole (Ht) ligands 5,5'-(1,4-phenylene)bis(1H-tetrazole) (H(2)bdt), 5',5'-(1,1'-biphenyl)4,4'-diylbis(1H-tetrazole) (H(2)dbdt) and 5,5',5'-(1,3,5-phenylene)tris(1H-tetrazole) (H(3)btt) was investigated. In the case of Co(II), three phases were isolated, two of which incorporated sulfate: [Co(5)F(2)(dbdt)(4)(H(2)O)(6)]·2H(2)O (1·2H(2)O), [Co(4)(OH)(2)(SO(4))(bdt)(2)(H(2)O)(4)] (2) and [Co(3)(OH)(SO(4))(btt)(H(2)O)(4)]·3H(2)O (3·3H(2)O). The structures are three-dimensional and consist of cluster-based secondary building units: the pentanuclear {Co(5)F(2)(tetrazolate)(8)(H(2)O)(6)}, the tetranuclear {Co(4)(OH)(2)(SO(4))(2)(tetrazolate)(6)}(4-), and the trinuclear {Co(3)(μ(3)-OH)(SO(4))(2) (tetrazolate)(3)}(2-) for 1, 2, and 3, respectively. The Ni(II) analogue [Ni(2)(H(0.67)bdt)(3)]·10.5H(2)O (4·10.5H(2)O) is isomorphous with a fourth cobalt phase, the previously reported [Co(2)(H(0.67)bat)(3)]·20H(2)O and exhibits a {M(tetrazolate)(3/2)}(∞) chain as the fundamental building block. The dense three-dimensional structure of [Zn(bdt)] (5) consists of {ZnN(4)}tetrahedra linked through bdt ligands bonding through N1,N3 donors at either tetrazolate terminus. In contrast to the hydrothermal synthesis of 1-5, the Cd(II) material (Me(2)NH(2))(3)[Cd(12)Cl(3)(btt)(8)(DMF)(12)]·xDMF·yMeOH (DMF = dimethylformamide; x = ca. 12, y = ca. 5) was prepared in DMF/methanol. The structure is constructed from the linking of {Cd(4)Cl(tetrazolate)(8)(DMF)(4)}(1-) secondary building units to produce an open-framework material exhibiting 66.5% void volume. The magnetic properties of the Co(II) series are reflective of the structural building units.     

Series of mixed uranyl-lanthanide (ce, nd) organic coordination polymers with aromatic polycarboxylates linkers

Three series of mixed uranyl-lanthanide (Ce or Nd) carboxylate coordination polymers have been successfully synthesized by means of a hydrothermal route using either conventional or microwave heating methods. These compounds have been prepared from mixtures of uranyl nitrate, lanthanide nitrate together with phthalic acid (1,2), pyromellitic acid (3,4), or mellitic acid (5,6) in aqueous solution. The X-ray diffraction (XRD) single-crystal revealed that the phthalate complex (UO(2))(4)O(2)Ln(H(2)O)(7)(1,2-bdc)(4)·NH(4)·xH(2)O (Ln = Ce(1), Nd(2); x = 1 for 1, x = 0 for 2), is based on the connection of tetranuclear uranyl-centered building blocks linked to discrete monomeric units LnO(2)(H(2)O)(7) via the organic species to generate infinite chains, intercalated by free ammonium cations. The pyromellitate phase (UO(2))(3)Ln(2)(H(2)O)(12)(btec)(3)·5H(2)O (Ce(3), Nd(4)) contains layers of monomeric uranyl-centered hexagonal and pentagonal bipyramids linked via the carboxylate arms of the organic molecules. The three-dimensionality of the structure is ensured by the connection of remaining free carboxylate groups with isolated monomeric units LnO(2)(H(2)O)(7). The network of the third series (UO(2))(2)(OH)Ln(H(2)O)(7)(mel)·5H(2)O (Ce(5), Nd(6)) is built up from dinuclear uranyl units forming layers through connection with the mellitate ligands, which are further linked to each other through discrete monomers LnO(3)(H(2)O)(6). The thermal decomposition of the various coordination complexes led to the formation of mixed uranium-lanthanide oxide, with the fluorite-type structure at 1500 °C (for 1, 2) or 1400 °C for 3-6. Expected U/Ln ratio from the crystal structures were observed for compounds 1-6.