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.     

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 M(OH)(1,2,3) (M = Mn, Fe, Co, Ni) molecules in solid argon and the character of first row transition metal hydroxide bonding

Reactions of laser-ablated Mn, Fe, Co, and Ni atoms with H(2)O(2) and with H(2) + O(2) mixtures in excess argon give new absorptions in the O-H and M-O stretching regions, which are assigned to metal dihydroxide and trihydroxide molecules, M(OH)(2) and M(OH)(3). Isotopic substitutions (D(2)O(2), (18)O(2), (16,18)O(2), D(2)) confirmed the assignments and DFT calculations reproduced the experimental results. The O-H stretching frequencies decreased in the dihydroxides from Sc to Zn. Mulliken and natural charge distributions indicate significant electron transfer from metal d orbitals to OH ligands that decreases from Sc to Zn, suggesting that the early transition metal hydroxides are more ionic and that the later transition metal hydroxides are more covalent.     

Contrasting products in the reactions of Cr, Mo, and W atoms with H2O2: Argon matrix infrared spectra and theoretical calculations

Products in the reactions of H2O2 and H2, O2 mixtures have been observed by matrix infrared absorptions and identified through comparisons with vibrational frequencies calculated for these molecules. The chromium reactions are dominated by lower oxidation state products, whereas molybdenum and tungsten chemistry favors higher oxidation state products. For example chromium dihydroxide, Cr(OH)2, molybdenum hydride oxide, H2MoO2, and tungsten hydride oxide, H2WO2, were observed in laser-ablated metal atom reactions with H2O2, and calculations show that these are the most stable molecules for this stoichiometry. Chromium monohydroxide, CrOH, was identified through O-H and Cr-O stretching modes, while HWO was observed by W-H and W=O stretching modes. The metal oxyhydroxides, HMO(OH), were observed for all metals. However, reactions with two H2O2 molecules give OCr(OH)2, MoO2(OH)2, and WO2(OH)2. The relative stabilities of different structures for Cr, Mo, and W are due to different participations of occupied d orbitals. The reactivity of the cold metal atoms with H2O2 on annealing the solid argon matrix increases on going down the group.     

Infrared spectra of the OH+ and H2O+ cations solvated in solid argon

Infrared spectra of various OH+ and H2O+ isotopomers solvated in solid argon are presented. The OH+ and H2O+ cations were produced by co-deposition of H2O/Ar mixture with high-frequency discharged Ar at 4 K. Detailed isotopic substitution studies confirm the assignments of absorptions at 3054.9 and 3040.0 cm(-1) to the antisymmetric and symmetric H-O-H stretching vibrations of H2O+ and 2979.6 cm(-1) to the O-H stretching vibration of OH+. The frequencies of H2O+ solvated in solid argon are red-shifted, whereas the frequency of OH+ is blue-shifted with respect to the gas-phase fundamentals. On the basis of previous gas-phase studies and quantum chemical calculations, the OH+ and H2O+ cations solvated in solid argon may be regarded as the OH+-Ar5 and H2O+-Ar4 complexes isolated in the argon matrix.     

Infrared spectra and density functional calculations for M(OH)(2,3) and HOMO molecules and M(OH)2+ cations (M = Y, La)

Reactions of laser-ablated Y and La atoms with H2O2 gives the M(OH)2 and M(OH)3 molecules and the HOMO dehydration product, and the cation M(OH)2+ in solid argon. Density functional calculations show that the dihydroxide molecules and cations are bent at the metal center, and the symmetric and antisymmetric O-H stretching modes are both observed in the infrared spectra. The trihydroxide molecules have calculated C(3h) structures characterized by strong antisymmetric O-H and M-O stretching modes. Mulliken charges increase for all product molecules going down the Group 3 family and increase as one, two, and three OH ligands are bonded to the metal center. Evidence is also presented for the Y(OH)4- anion.     

Synthesis,spectral characterization,and structural studies of 2-aminobenzoate complexes of divalent alkaline earth metal ions: X-ray crystal structures of [Ca(2-aba)2(OH2)3]infinity, [[Sr(2-aba)2(OH2)2].H2O]infinity,and [Ba(2-aba)2(OH2)]infinity (2-abaH = 2-NH2C6H4COOH)

Reactions of alkaline earth metal chlorides with 2-aminobenzoic acid (2-abaH) have been investigated. The treatment of MCl2.nH2O (M = Mg, Ca, Sr or Ba) with 2-abaH in a 1:2 ratio in a MeOH/H2O/NH3 mixture leads to the formation of anthranilate complexes [Mg(2-aba)2] (1), [Ca(2-aba)2(OH2)3]infinity (2), [[Sr(2-aba)2(OH2)2].H2O)]infinity (3), and [Ba(2-aba)2(OH2)]infinity (4) respectively. Alternatively, these products can also be obtained starting from the corresponding metal acetates. Anthranilate complexes 1-4 have been characterized with the aid of elemental analysis, pH measurements, thermal analysis, and infrared, ultraviolet, and NMR (1H and 13C) spectroscopic studies. All the products are found to be thermally very stable and do not melt on heating to 250 degrees C. Thermal studies of complexes 2-4, however, indicate the loss of coordinated and lattice water molecules below 200 degrees C. In the case of the magnesium complex, the analytical and thermogravimetric studies indicate the absence of any coordinated or uncoordinated water molecules. Further, the solid-state structures of metal anthranilates 2-4 have been established by single-crystal X-ray diffraction studies. While the calcium ions in 2 are heptacoordinated, the strontium and barium ions in 3 and 4 reveal a coordination number of 9 apart from an additional weak metal-metal interaction along the polymeric chains. The carboxylate groups show different chelating and bridging modes of coordination behavior in the three complexes. Interestingly, apart from the carboxylate functionality, the amino group also binds to the metal centers in the case of strontium and barium complexes 3 and 4. However, the coordination sphere of 2 contains only O donors. All three compounds form polymeric networks in the solid state with the aid of different coordinating capabilities of the carboxylate anions and O-H...O and N-H...O hydrogen bonding interactions.     

Vibrational spectra of four alkaline earth cyclo-hexaphosphates

FT-IR and FT-Raman spectra of four alkaline earth (Mg, Ca, Sr and Ba) cyclo-hexaphosphates have been recorded and analysed. FT-Raman spectra of the deuterated analogues of these compounds are used to clear the ambiguity regarding the OH vibrations in the low frequency region. The spectra reveal that the P6O18(6) anion ring in all compounds have independent PO4 tetrahedra present in it. The P-O(P)and P-O(M')(M'-Mg, Ca, Sr and Ba) bonds become stronger as the cation size decreases. The P6O18(6-) anion ring is distorted in the Mg and Ca compounds. In the Sr and Ba compounds, free and hydrogen bonded water molecules of varying strength are present, whereas in Mg and Ca compounds no free water molecules exist. The POP bridge angle of the Mg, Ca and Sr compounds are estimated using the correlations between the POP bridge stretching frequencies and the bridge angle value.     

Infrared spectroscopic observation of the group 13 metal hydroxides, M(OH)1,2,3 (M =Al, Ga, In, and Tl) and HAl(OH)2

Reactions of laser-ablated Al, Ga, In, and Tl atoms with H2O2 and with H2 + O2 mixtures diluted in argon give new absorptions in the O-H and M-O stretching and O-H bending regions, which are assigned to the metal mono-, di-, and trihydroxide molecules. Isotopic substitutions (D2O2, 18O2, 16,18O2, HD, and D2) confirm the assignments, and DFT calculations reproduce the experimental results. Infrared spectra for the Al(OH)(OD) molecule verify the calculated C2v structure. The trihydroxide molecules increase on annealing from the spontaneous reaction with a second H2O2 molecule. Aluminum atom reactions with the H2 + O2 mixtures favor the HAl(OH)2 product, suggesting that AlH3 generated by UV irradiation combines with O2 to form HAl(OH)2.     

Infrared spectra and structures of the coinage metal dihydroxide molecules

Laser-ablated Cu, Ag, and Au atoms react with H2O2 and with H2 + O2 molecules during condensation in excess argon to give four new IR absorptions in each system (O-H stretch, M-O-H bend, O-M-O stretch, and M-O-H deformation modes) that are due to the coinage metal M(OH)2 dihydroxide molecules. Isotopic substitution (D2O2, 18O2, 16O18O, D2, and HD) and comparison with frequencies computed by DFT verify these assignments. The calculations converge to 2B(g) ground electronic state structures with C2h symmetry, 111-117 degrees M-O-H bond angles, and substantial covalent character for these new metal dihydroxide molecules, particularly for Au(OH)2. This is probably due to the high electron affinity of gold owing to the effect of relativity.     

Cooperative binding of phosphate anion and a neutral nitrogen donor to alkaline-Earth metal ions. Investigation of group 2 metal-organophosphate interaction in the absence and presence of 1,10-phenanthroline

Alkaline-earth metal phosphates containing nitrogen-donor ligands have been prepared by the reaction of alkaline-earth metal acetates M(OAc) 2. xH 2O (M = Mg, Ca, Sr, Ba) with 2,6-diisopropylphenyl phosphate (dippH 2) in the absence and presence of 1,10-phenanthroline (phen). Interaction of strontium or barium acetate with dippH 2 in methanol at room temperature leads to the isolation of ionic phosphates [{M 2(mu-H 2O) 4(H 2O) 10}{dipp} 2].4L [M = Sr, L = CH 3OH ( 1); M = Ba, L = H 2O ( 2)]. The addition of a bidentate nitrogen-donor phen to these reactions leads to the isolation of dinuclear metal phosphates [Mg(dipp)(phen)(CH 3OH) 2] 2 ( 3) and [M(dippH) 2(phen) 2(H 2O)] 2 [M = Ca ( 4), Sr ( 5), Ba ( 6)]. While ionic phosphates 1 and 2 are soluble in water, the predominately covalent dimeric compounds 3- 6 are insoluble in all common solvents including water. The new compounds have been characterized in the solid state by elemental analysis, IR, UV-vis, and emission spectroscopy, and single-crystal X-ray diffraction studies. The cationic part in 1 and 2 is a {M 2(mu-H 2O) 4(H 2O) 10} unit, where each metal ion is surrounded by four bridging and five terminal water molecules as ligands. The dipp anion does not directly bind to the metal ions but is extensively hydrogen-bonded to the cationic unit through the phosphate oxygen and water hydrogen atoms to result in an infinitely layered structure where the hydrophobic aryl group protrudes out of the hydrophilic layer formed by the cationic part and -PO 3 (2-) units. In contrast, compounds 3- 6 are discrete dimeric molecules built around a central M 2O 4P 2 eight-membered ring. While the dippH 2 ligand exists in a doubly deprotonated form in 3, two monodeprotonated dippH 2 ligands are present per metal ion in compounds 4- 6. While 3 prefers only one phen ligand in the metal coordination sphere, two phen ligands chelate each metal ion in 4- 6. The conformations of the eight-membered rings in 3- 6 vary significantly from each other depending on the size of the cation and the coordination number around the metal. Further, intermolecular hydrogen bonding involving the phenanthroline C-H linkages result, in a gridlike structure in 1, one-dimensional chains in isostructural 2 and 3, and a two-dimensional layer arrangement in 4. Compounds 3- 6 are the only examples of alkaline-earth metal phosphate complexes with neutral M-N donor bonds. The thermal behavior of compounds 1- 6 has been examined with the help of thermogravimetric analysis and differential scanning calorimetry and also by bulk thermolysis followed by powder X-ray diffraction measurements. While compounds 1 and 2 yield M 2P 2O 7, decomposition of 4- 6 results in the formation of M(PO 3) 2, consistent with the M-P ratio in the precursor complexes.     

Hydration energies and structures of alkaline earth metal ions, M2+(H2O)n, n = 5-7, M = Mg, Ca, Sr, and Ba

The evaporation of water from hydrated alkaline earth metal ions, produced by electrospray ionization, was studied in a Fourier transform mass spectrometer. Zero-pressure-limit dissociation rate constants for loss of a single water molecule from the hydrated divalent metal ions, M(2+)(H(2)O)(n) (M = Mg, Ca, and Sr for n = 5-7, and M = Ba for n = 4-7), are measured as a function of temperature using blackbody infrared radiative dissociation. From these values, zero-pressure-limit Arrhenius parameters are obtained. By modeling the dissociation kinetics using a master equation formalism, threshold dissociation energies (E(o)) are determined. These reactions should have a negligible reverse activation barrier; therefore, E(o) values should be approximately equal to the binding energy or hydration enthalpy at 0 K. For the hepta- and hexahydrated ions at low temperature, binding energies follow the trend expected on the basis of ionic radii: Mg > Ca > Sr > Ba. For the hexahydrated ions at high temperature, binding energies follow the order Ca > Mg > Sr > Ba. The same order is observed for the pentahydrated ions. Collisional dissociation experiments on the tetrahydrated species result in relative dissociation rates that directly correlate with the size of the metals. These results indicate the presence of two isomers for hexahydrated magnesium ions: a low-temperature isomer in which the six water molecules are located in the first solvation shell, and a high-temperature isomer with the most likely structure corresponding to four water molecules in the inner shell and two water molecules in the second shell. These results also indicate that the pentahydrated magnesium ions have a structure with four water molecules in the first solvation shell and one in the outer shell. The dissociation kinetics for the hexa- and pentahydrated clusters of Ca(2+), Sr(2+), and Ba(2+) are consistent with structures in which all the water molecules are located in the first solvation shell.     

Infrared spectroscopic and density functional theory study on the reactions of lanthanum atoms with carbon dioxide in rare-gas matrices

Reactions of laser-ablated La atoms with CO2 molecules in solid argon and neon have been investigated using matrix-isolation infrared spectroscopy. On the basis of isotopic shifts, mixed isotopic splitting patterns, and CCl4-doping experiments, absorptions at 1839.9 and 753.6 cm-1 in argon and 1855.9 and 771.3 cm-1 in neon are assigned to the C-O and La-O stretching vibrations of the OLaCO molecule, respectively. Ultraviolet-visible photoinduced isomerization of OLaCO to La-(eta2-OC)O and OLa-(eta2-CO) have been observed under different wavelength photolyses in the solid matrix. The neon matrix experiments give the C-O and La-O stretching vibrations of the OLaCO- anion at 1769.5 and 779.3 cm-1, respectively. Density functional theory calculations have been performed on these products, which support the experimental assignments of the infrared spectra. The present study reveals that the C-O stretching vibrational frequencies of OMCO decrease from Sc to La, which indicates an increase in metal d orbital --> CO pi* back-donation in this series.     

Experimental and theoretical studies of the products of laser-ablated thorium atom reactions with H2O in excess argon

Reactions of laser-ablated Th atoms with H2O during condensation in excess argon have formed a variety of intriguing new Th, H, O species. Infrared absorptions at 1406.0 and 842.6 cm-1 are assigned to the H-Th and Th=O stretching vibrations of HThO. Absorptions at 1397.2, 1352.4, and 822.8 cm-1 are assigned to symmetric H-Th-H, antisymmetric H-Th-H, and Th=O stretching vibrations of the major primary reaction product H2ThO. Thorium monoxide (ThO) produced in the reaction inserts into H2O to form HThO(OH), which absorbs at 1341.0, 804.0, and 542.6 cm-1. Both HThO(OH) and ThO2 add another H2O molecule to give HTh(OH)3 and OTh(OH)2, respectively. Weaker thorium hydride (ThH1(-4)) absorptions were also observed. Relativistic DFT and ab initio calculations were performed on all proposed molecules and other possible isomers. The good agreement between experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts provides support for these first identifications of Th, H, O molecular species.     

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.     

The Recently Synthesized Dimagnesiabutadiene and the Analogous Dimetalla‐Beryllium, ‐Calcium, ‐Strontium,and ‐Barium Compounds

The 2014 synthesis of the remarkable dimagnesium compound Mg₂[C₄(CH₃)₂(Si(CH₃)₃)₂](C₃H₇)₂(C₄H₈O)₂ may point the way to a new chapter in alkaline earth organometallic chemistry. Accordingly, we have studied the known Mg compound and the analogous Be, Ca, Sr, and Ba structures. Although most of our theoretical predictions come from density functional methods, the latter have been benchmarked using coupled cluster theory including single, double, and perturbative triplet excitations, CCSD(T) using cc‐pVTZ basis sets. Among our most important predictions are the energies for dissociation to the butadiene plus the RM?MR [R=(C₃H₇)₂(C₄H₈O)₂; M=Be, Mg, Ca, Si, and Ba] entities. The most reliable predictions for the dissociation energies are 99–104 (Be), 85–93 (Mg), 90–99 (Ca), 83–92 (Sr), and 83–94 (Ba) kcal mol^?1. Thus, there is reason to anticipate that the four unknown compounds should be achievable synthetically. The predicted metal–metal distances (not single bonds) are 2.89 Å (Mg???Mg), 3.46 Å (Ca???Ca), 3.75 Å (Sr???Sr), and 4.04 Å (Ba???Ba). The separated RM?MR compounds have longer M?M distances but genuine metal–metal single bonds. This perhaps counter intuitive result is due to the presence of the bridging carbons in the alkaline earth butadiene compounds. All five compounds incorporate metal–carbon ionic interactions.     

Infrared spectra and structures for group 4 dihydroxide and tetrahydroxide molecules

Hafnium and zirconium atoms react with H(2)O(2) molecules and with H(2) + O(2) mixtures to form M(OH)(2) and M(OH)(4) molecules, which are trapped in solid argon and identified from isotopic shifts in the infrared spectra. Electronic structure calculations at the MP2 level converge to almost linear M(OH)(2) and tetrahedral M(OH)(4) molecules and predict vibrational frequencies for mixed isotopic molecules of lower symmetry that are in excellent agreement with experimental measurements, thus substantiating the identification of hafnium and zirconium dihydroxide and tetrahydroxide molecules. Titanium atoms react to give the same product molecules, but Ti(OH)(4) has an S(4) structure with bent Ti-O-H bonds, Ti(OH)(2) appears to be nearly linear, and the more stable tetravalent HM(O)OH isomer is more prominent for Ti. The Group 4 tetrahydroxides reported here are the first examples of pure metal tetrahydroxide molecules.     

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.     

Infrared spectra of the M(NO)n (M = Sn, Pb; n = 1, 2) and PbNO- molecules

Reactions of laser-ablated tin and lead atoms with nitric oxide molecules in solid argon and neon have been investigated using matrix-isolation infrared spectroscopy. In the argon experiments, absorptions at 1560.1, 1625.8, and 1486.7 cm(-1) are assigned to the N-O stretching vibrations of the SnNO and Sn(NO)2 molecules, and absorptions at 1541.9, 1630.0, 1481.8, and 1457.5 cm(-1) are assigned to the N-O stretching vibrations of the PbNO, Pb(NO)2, and PbNO- molecules on the basis of isotopic shifts and splitting patterns. The present neon experiments only produce neutral tin and lead mononitrosyls. Density functional theory calculations have been performed on these tin and lead nitrosyls. The good agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts substantiates the identification of these nitrosyls from the matrix infrared spectra.     

Supramolecuar motifs in s-block metal-bound sulfonated monoazo dyes: The case of Orange G

Solid-state structures of Mg, Sr, Ba, Na2, Na0.8K1.2, NaRb, and Na1.5Cs0.5 complexes of the disulfonated dye 7-hydroxy-8-(phenylazo)-1,3-naphthalenedisulfonic acid, Orange G, are presented. It is shown that the s-block metal salts of the Orange G dianion (Og) can be categorized into three structural classes related to those previously proposed for simple monosulfonated azo dyes. All of the structures feature alternate organic/inorganic layering, but whereas the Mg, Ca, and Li complexes are solvent-separated ion-pair species, the Sr and Ba complexes form simple discrete molecules based on metal-sulfonate bonding, and the heavy alkali metal complexes utilize a variety of M-O interactions to form 2- and 3-dimensional coordination networks. These structural differences are rationalized in terms of simple properties of the metals (charge, size, and electronegativity) and the steric demands of the arylsulfonate groups. The Ag2 complex of Orange G is also structurally characterized, and in contrast to the s-block salts, it is found to exhibit strong Ag pi bonds. In confirmation of the above, the crystal structures of [Mg(H2O)6][Og] . 3.33H2O, [Sr(Og)(H2O)7].H2O, [Ba(Og)(H2O)7]2 . 2H2O, [Na2(Og)(H2O)6.67], [Na2(Og)(H2O)2(HOEt)], [Na0.8K1.2(Og)(H2O)6] . 1.75H2O, [NaRb(Og)(H2O)6.5] . 2.375H2O, [Na1.5Cs0.5(Og)(H2O)6] . 0.5H2O, and [Ag2(Og)(H2O)4].H2O are presented.