Infrared spectrum and structure of the Hf(OH)4 molecule

Laser-ablated Hf atoms react with H2O2 and with H2 + O2 mixtures in solid argon to form the Hf(OH)2 and Hf(OH)4 molecules, which are identified from the effect of isotopic substitution on the matrix infrared spectra. Electronic structure calculations at the MP2 level varying all bond lengths and angles converge to nearly linear and tetrahedral molecules, respectively, and predict frequencies for these new product molecules and mixed isotopic substituted molecules of lower symmetry that are in excellent agreement with observed values, which confirms the identification of these hafnium hydroxide molecules. This work provides the first evidence for a metal tetrahydroxide molecule and shows that the metal atom reaction with H2O2 in excess argon can be used to form pure metal tetrahydroxide molecules, which are not stable in the solid state.     

Reactions of early lanthanide metal atoms (Nd, Sm, Eu) with water molecules. A matrix isolation infrared spectroscopic and theoretical study

The reactions of early lanthanide metal atoms Nd, Sm, and Eu with water molecules have been investigated using matrix isolation infrared spectroscopy and density functional calculations. The reaction intermediates and products were identified on the basis of isotopic labeled experiments and density functional frequency calculations. The ground state metal atoms react with water to form the M(H2O) and M(H2O)(2) complexes spontaneously on annealing (M = Nd, Sm, Eu). The M(H2O) complexes isomerize to the inserted HMOH molecules under red light irradiation, which further decompose to give the metal monoxides upon UV light irradiation. The Nd(H2O)(2) complex decomposes to form the trivalent HNd(OH)(2) molecule, while the Sm(H2O)(2) and Eu(H2O)(2) complexes rearrange to the divalent Sm(OH)(2) and Eu(OH)(2) molecules under red light irradiation.     

Infrared spectra and structures of the Th(OH)2 and Th(OH)4 molecules

Thorium atoms react with H2O2, H2 + O2 mixtures, and H2O in excess argon to form the Th(OH)2 and Th(OH)4 molecules as minor and major products, respectively. The vibrational frequencies observed in the matrix infrared spectra are in excellent agreement with MP2 computed values, which confirms the identification of these highly ionic thorium hydroxide molecules. Our MP2 calculations converge to slightly bent and tetrahedral structures, respectively. This investigation reports the first evidence for pure actinide dihydroxide and tetrahydroxide molecules.     

Zinc and cadmium dihydroxide molecules: matrix infrared spectra and theoretical calculations

Laser-ablated zinc and cadmium atoms were mixed uniformly with H2 and O2 in excess argon or neon and with O2 in pure hydrogen or deuterium during deposition at 8 or 4 K. UV irradiation excites metal atoms to insert into O2 producing OMO molecules (M = Zn, Cd), which react further with H2 to give the metal hydroxides M(OH)2 and HMOH. The M(OH)2 molecules were identified through O-H and M-O stretching modes with appropriate HD, D2, (16,18)O2, and (18)O2 isotopic shifts. The HMOH molecules were characterized by O-H, M-H, and M-O stretching modes and an M-O-H bending mode, which were particularly strong in pure H2/D2. Analogous Zn and Cd atom reactions with H2O2 in excess argon produced the same M(OH)2 absorptions. Density functional theory and MP2 calculations reproduce the IR spectra of these molecules. The bonding of Group 12 metal dihydroxides and comparison to Group 2 dihydroxides are discussed. Although the Group 12 dihydroxide O-H stretching frequencies are lower, calculated charges show that the Group 2 dihydroxide molecules are more ionic.     

Infrared spectra of the group 2 metal dihydroxide molecules

Group 2 metal atoms (Mg, Ca, Sr, and Ba) react on ultraviolet photoexcitation with O(2), H(2) mixtures in solid argon at 10 K to produce new absorptions in the O-H and O-M-O stretching regions. The effect of detailed isotopic substitution on these two absorptions identifies the M(OH)(2) molecules. The stepwise decrease in the O-H stretching modes in this chemical family demonstrates an increase in ionic character, which parallels the increase in base strength for the analogous solid compounds.     

Metal alkoxides as versatile precursors for group 4 phosphonates: synthesis and X-ray structure of a novel organosoluble zirconium phosphonate

Reactions of Ph2P(O)(OH) and t-BuP(O)(OSiMe3)(OH) with Ti(O-i-Pr)4 in equimolar ratios gave titanium phosphonates of the type [(O-i-Pr)3Ti(mu-O)2PR1R2]2 (1, R1 = R2 = Ph; 2, R1 = t-Bu, R2 = OSiMe3) as colorless crystalline solids in moderate yields. Reactions of Ph2P(O)(OH) and the isopropoxides of zirconium and hafnium resulted in products of the composition [(O-i-Pr)3M(mu-O-i-Pr)2(mu-OPOPh2)M(O-i-Pr)2]Ph2P(O)(OH) (M = Zr (3), Hf (4)) in high yields. The compounds were characterized by 1H, 31P, and 29Si NMR, infrared (IR), and mass spectroscopic (MS) techniques. The molecular structures of 2 and 3 were confirmed by X-ray crystallography.     

Reactions of late lanthanide metal atoms with water molecules: a matrix isolation infrared spectroscopic and theoretical study

The reactions of late lanthanide metal atoms (Gd-Lu) with water molecules have been investigated using matrix isolation infrared spectroscopy. The reaction intermediates and products were identified on the basis of isotopic substitution experiments and density functional theory calculations. All of the metal atoms except Lu react with water to form the M(H2O) complexes spontaneously upon annealing (M = Gd, Tb, Dy, Ho, Er, Tm, and Yb). The Dy(H2O) and Ho(H2O) complexes are able to coordinate a second water molecule to form the Dy(H2O)2 and Ho(H2O)2 complexes. The M(H2O) complexes isomerize to the inserted HMOH isomers under visible light irradiation, which further decompose to give the MO and/or HMO molecules upon UV light irradiation. The M(OH)2 molecules (M = Gd-Lu) were also produced. The results have been compared with our earlier work covering the early lanthanide metal atoms (Nd, Sm, Eu) to observe the existent trends for the lanthanide metal atom reactions.     

Infrared spectra of M(OH)(1,2,4) (M = Pb, Sn) in solid argon

Infrared absorptions for the matrix-isolated lead and tin hydroxides M(OH), M(OH)2 and M(OH)4 (M = Pb, Sn) were observed in laser-ablated metal atom reactions with H2O2 during condensation in excess argon. The major M(OH)2 product was also observed with H2 and O2 mixtures, which allowed the substitution of 18O2. The band assignments were confirmed by appropriate D2O2, D2, 16O18O, and 18O2 isotopic shifts. MP2 and B3LYP calculations were performed to obtain molecular structures and to reproduce the infrared spectra. The minimum energy structure found for M(OH)2 has C(s) symmetry and a weak intramolecular hydrogen bond. In experiments with Sn, HD, and O2, the internal D bond is favored over the H bond for Sn(OH)(OD). The Pb(OH)4 and Sn(OH)4 molecules are calculated to have S4 symmetry and substantial covalent character.     

Mechanisms of water oxidation catalyzed by the cis,cis-[(bpy)2Ru(OH2)]2O4+ ion

The cis,cis-[(bpy)(2)Ru(III)(OH(2))](2)O(4+) micro-oxo dimeric coordination complex is an efficient catalyst for water oxidation by strong oxidants that proceeds via intermediary formation of cis,cis-[(bpy)(2)Ru(V)(O)](2)O(4+) (hereafter, [5,5]). Repetitive mass spectrometric measurement of the isotopic distribution of O(2) formed in reactions catalyzed by (18)O-labeled catalyst established the existence of two reaction pathways characterized by products containing either one atom each from a ruthenyl O and solvent H(2)O or both O atoms from solvent molecules. The apparent activation parameters for micro-oxo ion-catalyzed water oxidation by Ce(4+) and for [5,5] decay were nearly identical, with DeltaH(++) = 7.6 (+/-1.2) kcal/mol, DeltaS() = -43 (+/-4) cal/deg mol (23 degrees C) and DeltaH(++) = 7.9 (+/-1.1) kcal/mol, DeltaS(++) = -44 (+/-4) cal/deg mol, respectively, in 0.5 M CF(3)SO(3)H. An apparent solvent deuterium kinetic isotope effect (KIE) of 1.7 was measured for O(2) evolution at 23 degrees C; the corresponding KIE for [5,5] decay was 1.6. The (32)O(2)/(34)O(2) isotope distribution was also insensitive to solvent deuteration. On the basis of these results and previously established chemical properties of this class of compounds, mechanisms are proposed that feature as critical reaction steps H(2)O addition to the complex to form covalent hydrates. For the first pathway, the elements of H(2)O are added as OH and H to the adjacent terminal ruthenyl O atoms, and for the second pathway, OH is added to a bipyridine ring and H is added to one of the ruthenyl O atoms.     

Structure of the hydrated, hydrolysed and solvated zirconium(IV) and hafnium(IV) ions in water and aprotic oxygen donor solvents. A crystallographic, EXAFS spectroscopic and large angle X-ray scattering study

The tetrameric hydrolysis products of zirconium(IV) and hafnium(IV), the zirconyl(IV) and hafnyl(IV) ions, [M(4)(OH)(8)(OH(2))(16)(8+)], often labelled MO(2+).5H(2)O, are in principle the only zirconium(IV) and hafnium(IV) species present in aqueous solution without stabilising ligands and pH larger than zero. These complexes are furthermore kinetically very stable and do not become protonated even after refluxing in concentrated acid for at least a week. The structures of these complexes have been determined in both solid state and aqueous solution by means of crystallography, EXAFS and large angle X-ray scattering (LAXS). Each metal ion in the [M(4)(OH)(8)(OH(2))(16)](8+) complex binds four hydroxide ions in double hydroxo bridges, and four water molecules terminally. The M-O bond distance to the hydroxide ions are markedly shorter, ca. 0.12 A, than to the water molecules. The hydrated zirconium(IV) and hafnium(IV) ions only exist in extremely acidic aqueous solution due to their very strong tendency to hydrolyse. The structure of the hydrated zirconium(IV) and hafnium(IV) ions has been determined in concentrated aqueous perchloric acid by means of EXAFS, with both ions being eight-coordinated, most probably in square antiprismatic fashion, with mean Zr-O and Hf-O bond distances of 2.187(3) and 2.160(12) A, respectively. The dimethyl sulfoxide solvated zirconium(IV) and hafnium(IV) ions are square antiprismatic in both solid state and solution, with mean Zr-O and Hf-O bond distances of 2.193(1) and 2.181(6) A, respectively, in the solid state. Hafnium(IV) chloride does not dissociate in N,N'-dimethylpropyleneurea, dmpu, a solvent with good solvating properties but with a somewhat lower permittivity (epsilon= 36.1) than dimethyl sulfoxide (epsilon= 46.4), and an octahedral HfCl(4)(dmpu)(2) complex is formed.     

Infrared spectrum of Hg(OH)2 in solid neon and argon

Mercury(II) hydroxide molecules have been prepared upon mercury arc lamp irradiation of Hg, H(2), and O(2) mixtures in solid neon and argon. The strongest three infrared absorptions are identified through isotopic substitution (D(2), HD, (18)O(2), (16)O(18)O) and comparison to frequencies from DFT calculations. The isolated Hg(OH)(2) molecule is stable and has a linear O-Hg-O linkage in a C(2) structure with an 86 degrees dihedral angle. However, in aqueous solution Hg(2+) and 2OH(-) may form an Hg(OH)(2) intermediate, which eliminates water and precipitates solid HgO: The solid Hg(OH)(2) compound is not known.     

Tetrahydrometalate species VH(2)(H(2)), NbH(4), and TaH(4): matrix infrared spectra and quantum chemical calculations

Laser ablated V, Nb, and Ta atoms react with molecular hydrogen in excess neon at 4 K to give vanadium, niobium, and tantalum dihydrides that further react with H(2) to form VH(2)(H(2)), NbH(4), and TaH(4). The reaction products are identified by deuterium and deuterium hydride isotopic substitution. DFT and CCSD theoretical calculations are used to predict energies, geometries, and vibrational frequencies for these novel metal hydrides complex and molecules. The vanadium dihydride hydrogen complex, VH(2)(H(2)), is identified, while the niobium and tantalum tetrahydrides, NbH(4) and TaH(4,) with D(2d) symmetry structures are confirmed. Reactions of group 5 metal atoms with H(2) condensing in solid hydrogen gave VH(2)(H(2)) and the higher tetrahydride-hydrogen complexes NbH(4)(H(2))(4) and TaH(4)(H(2))(4).     

Nanospheric [M20(OH)12(maleate)12(Me2NH)12]4+ clusters (M = Co, Ni) with O(h) symmetry

Nanospheric hydroxo-bridged clusters of [M(20)(OH)(12)(maleate)(12)(Me(2)NH)(12)](BF(4))(3)(OH)·nH(2)O (M = Co (1), Ni (2)) with O(h) symmetry were afforded under hydrothermal condition with Co(BF(4))(2)·6H(2)O/Ni(BF(4))(2)·6H(2)O and fumaric acid in a DMF/EtOH mixed solvent. They are characterized by elemental analysis, IR, and X-ray diffraction. X-ray single crystal diffraction analyses show that these two complexes are isostructural containing an ideally cubic M(8) core in that each two M atoms are doubly bridged at the edges by one OH(-) and one maleate, while these OH(-) and maleate groups are coordinated further by exterior identical 12 M atoms which construct a perfect M(12) icosahedron to encapsulate the cubic core. To our knowledge, such large clusters with O(h) symmetry are seldom. The variable-temperature magnetic susceptibility studies reveal that these two isostructures exhibit antiferromagnetic interactions.     

MRCI investigation of different isomers of Ni2O2H2(+)

The geometrical and electronic structures of different isomers of Ni(2)O(2)H(2)(+) are investigated by multireference configuration interaction (MRCI) calculations using natural atomic orbital basis sets. The lowest-lying isomer, Ni(2)(OH)(2)(+), has a rhombic shape with two OH groups bridging the Ni atoms. The next isomer in energetic order with a relative energy of 0.29 eV consists of a linear NiONi(OH(2))(+) chain. Other structures with a rhombic shape, (NiH)(2)O(2)(+), with H bound to the Ni atoms have considerably higher energies, above 4 eV. Especially the low-lying isomers are characterised by a large number of low-lying electronic terms. The product Ni(2)O(2)H(2)(+) of the reaction of Ni(2)O(2)(+) with small alkanes is likely to have the rhombic Ni(2)(OH)(2)(+) structure. The reaction energy of the reaction Ni(2)O(2)(+) + H(2)→ Ni(2)(OH)(2)(+) is estimated to be about -3.5 eV.     

Structure and vibrational spectra of Ti(IV) hydroxides and their clusters with expanded titanium coordination. DFT study

Equilibrium structures of H(4-n)Ti(OH)n (n = 2-4) molecules and the Ti(OH)4 dimer and trimers were optimized at the B3LYP level of theory. Theoretical vibrational frequencies of TiO stretching modes obtained with several basis sets were compared with the existing experimental frequencies of these vibrations, and the 6-31+G(d) set was chosen for cluster calculations. Only one energy minimum was found for the [Ti(OH)4](2) dimer, but two isomers without symmetry elements stabilized by internal hydrogen bonds and two isomers, belonging to C(s) and C(i) point groups, with free OH groups were found as minima at the [Ti(OH)4](3) potential energy surface. The structure with the linear arrangement of hexacoordinated titanium atoms in the Ti3O12 skeleton may be proposed for trimeric species observed in liquid titanium alkoxides as the only structure satisfying experimental spectroscopic evidence about the presence of center of inversion in these species. Frequency changes of TiO4 modes which accompany the oligomer formation are predicted and discussed.     

p-Xylene-selective metal-organic frameworks: a case of topology-directed selectivity

Para-disubstituted alkylaromatics such as p-xylene are preferentially adsorbed from an isomer mixture on three isostructural metal-organic frameworks: MIL-125(Ti) ([Ti(8)O(8)(OH)(4)(BDC)(6)]), MIL-125(Ti)-NH(2) ([Ti(8)O(8)(OH)(4)(BDC-NH(2))(6)]), and CAU-1(Al)-NH(2) ([Al(8)(OH)(4)(OCH(3))(8)(BDC-NH(2))(6)]) (BDC = 1,4-benzenedicarboxylate). Their unique structure contains octahedral cages, which can separate molecules on the basis of differences in packing and interaction with the pore walls, as well as smaller tetrahedral cages, which are capable of separating molecules by molecular sieving. These experimental data are in line with predictions by molecular simulations. Additional adsorption and microcalorimetric experiments provide insight in the complementary role of the two cage types in providing the para selectivity.     

Matrix isolation spectroscopic and theoretical study of water adsorption and hydrolysis on molecular tantalum and niobium oxides

The reactions of molecular tantalum and niobium monoxides and dioxides with water were investigated by matrix isolation infrared spectroscopy. In solid neon, the metal monoxide and dioxide molecules reacted with water to form the MO(H(2)O) and MO(2)(H(2)O) (M = Ta, Nb) complexes spontaneously on annealing. The MO(H(2)O) complexes photochemically rearranged to the more stable HMO(OH) isomers via one hydrogen atom transfer from water to the metal center under visible light excitation. In contrast, the MO(2)(H(2)O) complexes isomerized to the more stable MO(OH)(2) molecules via a hydrogen atom transfer from water to one of the oxygen atoms of metal dioxide upon visible light irradiation. The aforementioned species were identified by isotopic-substituted experiments as well as density functional calculations.     

Pentanuclear Ba(II) complex of a macrocyclic ligand

We report here the first pentanuclear Ba(II) complex of a new tri-aza, tri-oxa macrocycle with two carboxymethyl "arms" pending from two N atoms, H2L2. The crystal structure corresponds to the formula [Ba5(H0.375L2)4(ClO4)(CH3CH2OH)(H2O)2](ClO4)2.5 x 9.5H2O and reveals the presence of four molecules of the ligand surrounding five Ba(II) ions, giving rise to an unusual structure with the metal ions inside a spherical organic cavity.     

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-).     

Infrared spectroscopy of Cu+(H2O)(n) and Ag+(H2O)(n): coordination and solvation of noble-metal ions

M(+)(H(2)O)(n) and M(+)(H(2)O)(n)Ar ions (M=Cu and Ag) are studied for exploring coordination and solvation structures of noble-metal ions. These species are produced in a laser-vaporization cluster source and probed with infrared (IR) photodissociation spectroscopy in the OH-stretch region using a triple quadrupole mass spectrometer. Density functional theory calculations are also carried out for analyzing the experimental IR spectra. Partially resolved rotational structure observed in the spectrum of Ag(+)(H(2)O)(1) x Ar indicates that the complex is quasilinear in an Ar-Ag(+)-O configuration with the H atoms symmetrically displaced off axis. The spectra of the Ar-tagged M(+)(H(2)O)(2) are consistent with twofold coordination with a linear O-M(+)-O arrangement for these ions, which is stabilized by the s-d hybridization in M(+). Hydrogen bonding between H(2)O molecules is absent in Ag(+)(H(2)O)(3) x Ar but detected in Cu(+)(H(2)O)(3) x Ar through characteristic changes in the position and intensity of the OH-stretch transitions. The third H(2)O attaches directly to Ag(+) in a tricoordinated form, while it occupies a hydrogen-bonding site in the second shell of the dicoordinated Cu(+). The preference of the tricoordination is attributable to the inefficient 5s-4d hybridization in Ag(+), in contrast to the extensive 4s-3d hybridization in Cu(+) which retains the dicoordination. This is most likely because the s-d energy gap of Ag(+) is much larger than that of Cu(+). The fourth H(2)O occupies the second shells of the tricoordinated Ag(+) and the dicoordinated Cu(+), as extensive hydrogen bonding is observed in M(+)(H(2)O)(4) x Ar. Interestingly, the Ag(+)(H(2)O)(4) x Ar ions adopt not only the tricoordinated form but also the dicoordinated forms, which are absent in Ag(+)(H(2)O)(3) x Ar but revived at n=4. Size dependent variations in the spectra of Cu(+)(H(2)O)(n) for n=5-7 provide evidence for the completion of the second shell at n=6, where the dicoordinated Cu(+)(H(2)O)(2) subunit is surrounded by four H(2)O molecules. The gas-phase coordination number of Cu(+) is 2 and the resulting linearly coordinated structure acts as the core of further solvation processes.