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.     

Thermal Dehydration and Infrared Studies of Mg 2 P 2 O 7 · 6H 2 O Diphosphate

The thermal dehydration of Mg 2 P 2 O 7 ·; 6H 2 O were studied, in the range 25-800°;C, by thermogravimetric analysis (TG-DSC), x-ray diffraction, and infrared spectroscopy. According to the TG-DSC curves, the dehydration of this salt takes place in two stages. The results of thermal analysis, x-ray patterns, and infrared spectra of this compound heated at different temperatures showed that, after dehydration, Mg 2 P 2 O 7 ·; 6H 2 O decomposes into dihydrate Mg 2 P 2 O 7 ·; 2H 2 O diphosphate then to an amorphous Mg 2 P 2 O 7 product which crystallises at 665°;C to give anhydrous diphosphate f Mg 2 P 2 O 7 . The j H enthalpy of the dehydration of Mg 2 P 2 O 7 ·; 6H 2 O and of the formation of f Mg 2 P 2 O 7 have been calculated from thermogravimetric data. The infrared spectroscopic study of Mg 2 P 2 O 7 ·; 6H 2 O and of its heated products, reveals the existence of the characteristic bands of the P 2 O 7 group ( x as POP and x s POP) and showed that the POP angle is bent in these salts. In these compounds, the POP angle values are estimated using the Lazarev's relationship.     

Infrared spectra and electronic structure calculations for the group 2 metal M(OH)2 dihydroxide molecules

Reactions of laser-ablated Mg, Ca, Sr, and Ba atoms with O2 and H2 in excess argon give new absorptions in the O-H and O-M-O stretching regions, which increase together upon UV photolysis and are due to the M(OH)2 molecules (M = Mg, Ca, Sr, and Ba). The same product absorptions are observed in the metal atom reactions with H2O2. The M(OH)2 identifications are supported by isotopic substitution and theoretical calculations (B3LYP and MP2). The O-H stretching frequencies of the alkaline earth metal dihydroxide molecules decrease from 3829.8 to 3784.6 to 3760.6 to 3724.2 cm(-1) in the family series in solid argon, while the base strength of the solid compounds increases. Calculations show that Sr(OH)2 and Ba(OH)2 are bent at the metal center, owing to d orbital involvement in the bonding. Although these molecules are predominantly ionic, the O-H stretching frequencies do not reach the ionic limit of gaseous OH- going down the family group because of cation-anion polarization and p(pi) --> d(pi) interactions.     

N4 ring as a square planar ligand in novel MN4 species

Ab initio (MP2) and density functional theory (DFT) methods are used to examine a series of MN4 compounds, where M is an alkaline-earth cation (Mg2+, Ca2+, Sr2+, Ba2+), and N4(2-) is a six--electron ring. All pyramidal structures except MgN4 are the most energetically favored for all singlet MN4 systems considered here. For MgN4, the CS structure with dicoordinated Mg out of the N4 ring plane is the most stable of all. Among these systems, the pyramidal CaN4, SrN4, BaN4 and the planar C(S) structure containing dicoordinated Ba are stable as singlet molecules due to their significant isomerization or dissociation barriers (21.3-94.1 kcal/mol). Structural, natural bond orbital (NBO), and molecular orbital (MO) analyses indicate that the bonding in the BaN4 system has a larger covalent character as compared with other MN4 systems. In addition, substantial d character is found in the bonding of the MN4 (M = Ca2+, Sr2+, Ba2+) species.     

Metal complexes of tetrapodal ligands: synthesis, spectroscopic and thermal studies, and X-ray crystal structure studies of Na(I), Ca(II), Sr(II), and Ba(II) complexes of tetrapodal ligands N,N,N',N'-tetrakis(2-hydroxypropyl)ethylenediamine and N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine

Twelve complexes 1-12 of general category [M(ligand)(anion)(x)(water)(y)], where ligand = N,N,N',N'-tetrakis(2-hydroxypropyl/ethyl)ethylenediamine (HPEN/HEEN), anion = anions of picric acid (PIC), 3,5-dinitrobenzoic acid (DNB), 2,4-dinitrophenol (DNP), and o-nitrobenzoic acid (ONB), M = Ca(2+), Sr(2+), Ba(2+), or Na(+), x = 1 and 2, and y = 0-4, were synthesized. All of these complexes were characterized by elemental analysis, IR, (1)H and (13)C NMR, and thermal studies. X-ray crystal studies of these complexes 1-12, [Ca(HPEN)(H(2)O)(2)](PIC)(2).H(2)O (1), [Ca(HEEN)(PIC)](PIC) (2), Ba(HPEN)(PIC)(2) (3), [Na(HPEN)(PIC)](2) (4), Ca(HPEN)(H(2)O)(2)](DNB)(2).H(2)O (5),Ca(HEEN)(H(2)O)](DNB)(2).H(2)O (6), [Sr(HPEN)(H(2)O)(3)](DNB)(2) (7), [Ba(HPEN)(H(2)O)(2)](DNB)(2).H(2)O](2) (8), [[Ba(HEEN)(H(2)O)(2)](ONB)(2)](2) (9), [[Sr(HPEN)(H(2)O)(2)](DNP)(2)](2) (10), [[Ba(HPEN)(H(2)O)(2)](DNP)(2)](2) (11), and [Ca(HEEN)(DNP)](DNP) (H(2)O) (12), have been carried out at room temperature. Factors which influence the stability and the type of complex formed have been recognized as H-bonding interactions, presence/absence of solvent, nature of the anion, and nature of the cation. Both the ligands coordinate the metal ion through all the six available donor atoms. The complexes 1 and 5-11 have water molecules in the coordination sphere, and their crystal structures show that water is playing a dual character. It coordinates to the metal ion on one hand and strongly hydrogen bonds to the anion on the other. These strong hydrogen bonds stabilize the anion and decrease the cation-anion interactions by many times to an extent that the anions are completely excluded out of the coordination sphere and produce totally charge-separated complexes. In the absence of water molecules as in 2 and 3 the number of hydrogen bonds is reduced considerably. In both the complexes the anions case interact more strongly with the metal ion to give rise to a partially charge-separated 2 or tightly ion-paired 3 complex. High charge density Ca(2+) forms only monomeric complexes. It has more affinity toward stronger nucleophiles such as DNP and PIC with which it gives partially charge-separated eight-coordinated complexes. But with relatively weaker nucleophile like DNB, water replaces the anion and produces a seven coordinated totally charge-separated complex. Sr(2+) with lesser charge/radius ratio forms only charge-separated monomeric as well as dimeric complexes. Higher coordination number of Sr(2+) is achieved with coordinated water molecules which may be bridging or nonbridging in nature. All charge-separated complexes of the largest Ba(2+) are dimeric with bridging water molecules. Only one monomeric ion-paired complex was obtained with Ba(PIC)(2). Na(+) forms a unique dinuclear cryptand-like complex with HPEN behaving as a heptadentate chelating-cum-bridging ligand.     

Hybrid organic-inorganic framework structures: influence of cation size on metal-oxygen-metal connectivity in the alkaline earth thiazolothiazoledicarboxylates

We report the synthesis of four organic-inorganic frameworks of alkaline earth cations with the organic ligand 2,5-thiazolo[5,4-d]thiazoledicarboxylate (C6N2S2O4(2-), Thz(2-)). Structures with remarkably different connectivities result when Mg(2+), Ca(2+), Sr(2+), and Ba(2+) react with Thz(2-). Mg(Thz)(H2O)4 (I) forms a 1-D coordination polymer in which one carboxylate oxygen on each terminus of the ligand connects individual MgO6 octahedra from their axial positions, while the remaining equatorial sites are coordinated by water molecules. Ca2(Thz)2(H2O)8 (II) forms a 1-D coordination polymer in which dimeric clusters with 7-fold Ca coordination are connected via the ligand in a linear fashion, with a second, uncoordinated Thz(2-) providing charge balance. Sr(Thz)(H2O)3 (III) has 1-D infinite inorganic connectivity built from edge-sharing SrO7N polyhedra having one carboxylate oxygen and one water molecule acting as M-O-M bridges. Ba2(Thz)2(H2O)7 (IV) has 2-D inorganic connectivity based upon face- and edge-sharing BaO9N polyhedra. One carboxylate oxygen and all water molecules act as bridges between each Ba(2+) and its three neighbors. We shall discuss the manner in which the increasing coordination requirements of the cations (MgO6 < CaO7 < SrO7N < BaO9N) lead to an increase in inorganic connectivity through the series.     

Tetrakis(imidazolyl)borate-based coordination polymers: group II network solids,M[B(Im)4]2(H2O)2 (M = Mg,Ca, Sr)

We are using the coordinating anion tetrakis(imidazolyl)borate to construct new metal-organic framework structures. In this report, we present three alkaline earth metal network solids incorporating this anion. All three compounds have the same formula, M[B(Im)(4)](2)(H(2)O)(2) (M = Mg, Ca, Sr), and the same coordination environment about the metal. However, the three compounds have different network structures with different degrees of hydrogen bonding; the Mg material forms a two-dimensional network and the Ca and Sr compounds form one-dimensional chains. In addition, we present the structure of the protonated anion B(HIm)(Im)(3) as a model for the default structure of this anion and discuss how the conformation of tetrakis(imidazolyl)borate can affect the structure of network solids.     

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.     

Crystal structures of calcium and barium oxalato(ethylenediamine-N,N′-diacetato)× chromates(III) M[Cr(Edda)(C2O4)]2·5H2O (M = Ca, Ba)

The crystal structure of Ca[Cr(Edda)(C₂O₄)]₂·5H₂O and Ba[Cr(Edda)(C₂O₄)]₂·5H₂O (H₂Edda — ethylenediamine-N,N′-diacetic acid) was determined by X-ray diffraction analysis. The nearest environment of alkaline earth ions consists of the oxygen atoms of the neighboring [Cr(Edda)(C₂O₄)]^? complex ions (five for Ca and four for Ba) and the water molecules that complete the coordination number to eight. Two atoms and two complex ions are linked into a ring; each Ca atom in the ring is bonded by the oxalate ion bridge to another anion. This results in a centrosymmetric hexanuclear supramolecular assembly. The atoms and the complex anions alternate to form an infinite chain, in which each Ba atom is additionally linked via the oxalate ion bridge with one anion.     

Synthesis and characterization of protonated zirconium trisilicate and its exchange phases with strontium

A partially protonated form of the mineral umbite has been prepared by ion exchange of K2ZrSi3O9 x H2O with acetic acid. The protonated phase, compound 1, is assigned the formula H1.45K0.55ZrSi3O9 x 2 H2O and crystallizes in the space group P2(1)/c with unit cell dimensions of a = 7.1002(2), b = 10.1163(3), c = 13.1742(5), and beta = 91.181(1) degrees. The characteristic building blocks of the acid phase are almost identical to those of the parent compound. The framework is composed of polymeric chains of trisilicate groups linked by zirconium atoms, resulting in zeolite-type channels. When viewed down the a axis, two unique ion-exchange channels can be seen. Site 1 is marked by a 12-membered ring and contains 2 cations. Site 2, a 16-membered ring, contains 4 water molecules. Compound 2, consists of a mixed Sr2+ and K+ phase synthesized from 1 by ion exchange with Sr(NO3)2. Compound 2 has the formula K0.34Sr0.83ZrSi3O9 x 1.8 H2O and crystallizes in the same space group P2(1)/c. It has cell dimensions of a = 7.1386(3), b = 10.2304(4), c = 13.1522(4), and beta = 90.222(1) degrees. The Sr2+ cations are distributed evenly among the two exchange sites, showing no preference for either cavity. Compound 3 is the fully substituted Sr phase, SrZrSi3O9 x 2 H2O, and retains the same space group as that of the previous two compounds having unit cell dimensions of a = 7.1425(5), b = 10.2108(8), c = 13.0693(6), and beta = 90.283(1) degrees. The strontium cations show a slight affinity for ion-exchange site 2, having a higher occupancy of 0.535, while site 1 is occupied by the remainder of the Sr2+ cations with an occupancy of 0.465. Batch uptake studies demonstrate a selectivity series among alkaline earth cations of Ba2+ > Sr2+ > Ca2+ > Mg2+.     

Synthesis and structures of monomeric magnesium, calcium, strontium, and barium amides involving the N,N-(2,4,6-trimethylphenyl)(trimethylsilyl)amido ligand

An extended family of aryl-substituted alkaline earth metal silylamides M{N(2,4,6-Me3C6H2)(SiMe3)}donor(n) was prepared using alkane elimination (Mg), salt elimination (Ca, Sr, Ba), and direct metalation (Sr, Ba). Three different donors, THF, TMEDA (TMEDA = N,N,N',N'-tetramethylethylenediamine), and PMDTA (PMDTA = N,N,N',N',N'-pentamethyldiethylenetriamine) were employed to study their influence on the coordination chemistry of the target compounds, producing monomeric species with the composition M{N(2,4,6-Me3C6H2)(SiMe3)}2(THF)2 (M = Mg, Ca, Sr, Ba), M{N(2,4,6-Me3C6H2)(SiMe3)}2TMEDA (M = Ca, Ba), and M{N(2,4,6-Me3C6H2)(SiMe3)}2PMDTA (M = Sr, Ba). For the heavier metal analogues, varying degrees of agostic interactions are completing the coordination sphere of the metals. Compounds were characterized using IR and NMR spectroscopy in addition to X-ray crystallography.     

Nano-SIMS analysis of Mg, Sr, Ba and U in natural calcium carbonate.

Concentrations of minor (Mg and Sr) and trace (Ba and U) elements in four natural calcium carbonate samples were first analyzed by inductively coupled plasma mass spectrometry (ICP-MS) after chemical dissolution and calibrated against a standard dolomite. Their homogeneities were checked by in situ laser ablation (LA) ICP-MS with 10-20 spots. The carbonate samples were measured by using a high lateral resolution secondary ion mass spectrometer (Nano-SIMS NS50). A approximately 4 nA O- primary beam was used to sputter a 5-6-microm diameter crater on the sample surface, and secondary positive ions were extracted for mass analysis using an accelerating voltage of 8 kV and a Mattauch-Herzog geometry. A multi-collector system was adjusted to detect 26Mg+, 43Ca+, 88Sr+, 138Ba+, 238U16O+ and 238U16O2+ ions at the same time. A resolving power of 2500-5000 at 10% peak height was attained by an entrance slit set at 40 microm, and each exit slit at 50 microm with adequate flat-topped peaks. The observed 26Mg/43Ca, 88Sr/43Ca, 138Ba/43Ca and 238U16O2/43Ca ratios agreed well with those measured by LA-ICP-MS. Foraminifera shells were analyzed at 5-6 microm scale by Nano-SIMS. There was a large variation of the Mg/Ca ratios, up to +/- 38%, even in a single fragment of the shell, suggesting that although the ratios provide a useful paleoceanographic proxy at bulk scale, they may reflect a more complex pattern at < 10 microm scale.     

V2O5/MO-Al2O3（M = Mg，Ca，Sr，Ba）催化剂用于正丁烷催化氧化脱氢反应

采用浸渍法制备了不同V2O5担载量的V2O5/MO-Al2O3(M = Mg, Ca, Sr, Ba)催化剂,钒物种的前驱体为偏钒酸铵.对制备的催化剂进行了一系列表征,并对催化剂上正丁烷选择性氧化脱氢制取丁烯进行了反应研究.表征结果(包括比表面积、X射线衍射、傅里叶红外光谱、氢气程序升温还原和拉曼光谱)显示,不同碱土金属元素掺杂的催化剂显示不同的钒价态信息和催化性能.其中掺杂Ca, Sr, Ba的催化剂,正钒酸盐相很难被还原,因此催化剂的氧化还原循环难以建立,导致以上三种催化剂在正丁烷氧化脱氢反应中活性较低.然而, Mg掺杂的催化剂却显示出较高的催化活性和选择性.实验结果表明：在Mg掺杂的载体上担载5% V2O5的催化剂上600°C时可获得高达30.3%的正丁烷转化率和64.3%的烯烃总选择性.这与V2O5担载量为5%时,在获得高度分散的钒氧化合物物种时可使MgO晶相稳定存在密切相关.     

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.     

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.     

FT-IR and FT-Raman study of Nasicon type phosphates, ASnFe(PO4)3 [A=Na2, Ca, Cd

FT-Raman and FT-IR spectra of ASnFe(PO4)3 [A=Na2, Ca, Cd] were recorded and analyzed. The bands were assigned in terms of the vibrational group frequencies of SnO6 octahedral and PO4 tetrahedral. The spectral analysis shows that the symmetry of corner shared octahedral (SnO6) and the tetrahedral (PO4) are lowered from their free ion symmetry state. The presence of Fe3+ ions disrupts the S-N-O-S-N chain in the structure. This causes distortion of SnO6 and PO4 in the structure of all the compounds. Also it is seen that there are two distinct PO4 tetrahedra of different P-O bond lengths. One of these tetrahedra is linearly distorted in all the title compounds. The PO4 frequencies and bond lengths are calculated theoretically and are in agreement with the experimental values. The presence of PO4 polyanion in the structure can reduce the redox energy and hence reduce the metal oxygen covalency strength in the structure.     

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.     

Synthesis and spectral characterization of alkaline earth metal complexes: Crystal structure of a Ca(II) hippuric acid complex

Alkaline earth metal (Mg, Ca, Sr and Ba) complexes of hippuric acid (hipH) have been synthesized and characterized by elemental analyses and IR spectroscopy. One of the complexes, [Ca(hip)₂(H₂O)₂]·H₂O, was characterized by single crystal X-ray diffraction studies. The polymeric structure is based on a dimeric unit and each calcium is coordinated to four hippurate anions and two coordinated water molecules. The hippurate anion functions as a bidentate ligand through the oxygen atoms of the carboxylate groups, one of which is bridging, forming a two dimensional coordination polymer. The water coordination is further confirmed by thermal analysis. The non-linear optical activity of the complexes was also measured.     

Lithol Red: a systematic structural study on salts of a sulfonated azo pigment

The first systematic series of single-crystal diffraction structures of azo lake pigments is presented (Lithol Red with cations=Mg(II), Ca(II), Sr(II), Ba(II), Na(I) and Cd(II)) and includes the only known structures of non-Ca examples of these pigments. It is shown that these commercially and culturally important species show structural behaviour that can be predicted from a database of structures of related sulfonated azo dyes, a database that was specifically constructed for this purpose. Examples of the successful structural predictions from the prior understanding of the model compounds are that 1) the Mg salt is a solvent-separated ion pair, whereas the heavier alkaline-earth elements Ca, Sr and Ba form contact ion pairs, namely, low-dimensional coordination complexes; 2) all of the Lithol Red anions exist as the hydrazone tautomer and have planar geometries; and 3) the commonly observed packing mode of alternating inorganic layers and organic bilayers is as expected for an ortho-sulfonated azo species with a planar anion geometry. However, the literature database of dye structures has no predictive use for organic solvate structures, such as that of the observed Na Lithol Red DMF solvate. Interestingly, the Cd salt is isostructural with the Mg salt and not with the Ca salt. It is also observed that linked eight-membered [MOSO](2) rings are the basic coordination motif for all of the known structures of Ca, Sr and Ba salts of sulfonated azo pigments in which competing carboxylate groups are absent.     

Ultrafine Na-4-mica: uptake of alkali and alkaline earth metal cations by ion exchange

The cation exchange properties of alkali and alkaline earth metal cations at room temperature were investigated on an ultrafine, highly charged Na-4-mica (with the ideal mica composition Na4Mg6Al4Si4O20F4.xH2O). Ultrafine mica crystallites of 200 nm in size led to faster Sr2+ uptake kinetics in comparison to larger mica crystallites. The alkali metal ion (K+, Cs+, and Li+) exchange uptake was rapid, and complete exchange occurred within 30 min. For the alkaline earth metal ions Ba2+, Ca2+, and Mg2+, however, the exchange uptake required lengthy periods from 3 days to 4 weeks to be completed, similar to its Sr uptake, as previously reported. Kinetic models of the modified Freundlich and parabolic diffusion were examined for the experimental data on the Ba2+, Ca2+, and Mg2+ uptakes. The modified Freundlich model described well the Ba2+ ion uptake kinetics as well as that for the Sr2+ ion, while for the Ca2+ and Mg2+ ions the parabolic diffusion model showed better fitting. The alkali and alkaline earth ion exchange isotherms were also determined in comparison to the Sr2+ exchange isotherm. The thermodynamic equilibria for these cations were compared by using Kielland plots evaluated from the isotherms.