三苯基氧膦钕盐配合物的振动光谱

本文测定了Ph_3PO、Nd(NCS)_3·4Ph_3PO、[Nd(ClO_4)_2·4Ph_3PO]~+ClO_4~-·2CH_3COCH_3以及Nd(NO_3)_3·2Ph_3PO·C_2H_5OH在4000～100 cm~(-1)区域内的FT-IR和激光Raman光谱,分析和讨论了各主要谱带的性质和配位结构.     

Inner- and outer-sphere complexation of ions at the goethite-solution interface

Formation of inner- and outer-sphere complexes of environmentally important divalent ions on the goethite surface was examined by applying the charge distribution CD model for inner- and outer-sphere complexation. The model assumes spatial charge distribution between the surface (0-plane) and the next electrostatic plane (1-plane) for innersphere complexation and between the 1-plane and the head end of the diffuse double layer (2-plane) for the outersphere complexation. The latter approach has been used because the distance of closest approach to a charged surface may differ for different ions. The surface structural approach implies the use of a Three-Plane model for the compact part (Stern layer) of solid-solution interface, which is divided into two layers. The thickness of each layer depends on the capacitance and the local dielectric constant. The new approach has been applied to describe the adsorption of magnesium, calcium, strontium, and sulfate ions. It is shown that the concept can successfully describe the development of surface charge in the presence of Ca(+2), Mg(+2), Sr(+2), and SO4(-2) as a function of loading, pH, and salt level, and also the shift in the isoelectric point (IEP) of goethite. The CD modeling revealed that, for the conditions studied, magnesium is mainly adsorbed as a bidentate innersphere complex, calcium can be a combination of bidentate innersphere and a monodentate inner- or outer-sphere complexes, and strontium is probably adsorbed as an outersphere complex. Sulfate is present as a mixture of inner- and outer-sphere monodentate complexes. Outersphere complexation is less pH dependent than innersphere complexation. The CD model predicts that the outersphere complexation of divalent cations and anions is relatively favorable at respectively low and high pH. Increase of ion loading favors the formation of innersphere complexes.     

Volatile magnesium octahydrotriborate complexes as potential CVD precursors to MgB2. Synthesis and characterization of Mg(B3H8)2 and its etherates

The solid-state reaction of MgBr2 and NaB3H8 at 20 degrees C, followed by sublimation at 80 degrees C and 0.05 Torr, affords Mg(B3H8)2 as a white solid. Similar reactions with MgBr2(Et2O) and MgBr2(Me2O)1.5 afford the crystalline ether adducts Mg(B3H8)2(Et2O)2 and Mg(B3H8)2(Me2O)2, respectively. In contrast, reactions of MgBr2 with NaB3H8, the presence of excess solvent result in the formation of nonvolatile, probably ionic, magnesium compounds of the type [MgLx][B3H8]2. The adducts Mg(B3H8)2(Et2O)2 and Mg(B3H8)2(Me2O)2 are the first crystallographically characterized magnesium complexes of the B3H8- ligand; in both structures, the magnesium center adopts a distorted cis-octahedral geometry with two bidentate B3H8 groups and two Et2O ligands. Owing to their volatility, Mg(B3H8)2(Et2O)2 and Mg(B3H8)2(Me2O)2 are potential precursors for the deposition of MgB2 thin films, although preliminary efforts to employ them as chemical vapor deposition sources produce boron-rich MgBx films instead, with x approximately 7. Finally, the synthesis and structure of Cp2Mg(thf) are described: this mono-thf adduct of Cp2Mg bears two eta5-Cp groups, unlike other Lewis base adducts of Cp2Mg, which contain one eta5-Cp group and one eta1- or eta2-Cp group.     

Direct measurement of a pK(a) near neutrality for the catalytic cytosine in the genomic HDV ribozyme using Raman crystallography

The hepatitis delta virus (HDV) ribozyme uses a cytosine to facilitate general acid-base catalysis. Biochemical studies suggest that C75 has a pKa perturbed to near neutrality. To measure this pKa directly, Raman spectra were recorded on single ribozyme crystals using a Raman microscope. A spectral feature arising from a single neutral cytosine was identified at 1528 cm(-1). At low pH, this mode was replaced with a new spectral feature. Monitoring these features as a function of pH revealed pKa values for the cytosine that couple anticooperatively with Mg2+ binding, with values of 6.15 and 6.40 in the presence of 20 and 2 mM Mg2+, respectively. These pKa values agree well with those obtained from ribozyme activity experiments in solution. To correlate the observed pKa with a specific nucleotide, crystals of C75U, which is catalytically inactive, were examined. The Raman difference spectra show that this mutation does not affect the conformation of the ribozyme. However, crystals of C75U did not produce a signal from a protonatable cytosine, providing strong evidence that protonation of C75 is being monitored in the wild-type ribozyme. These studies provide the first direct physical measurement of a pKa near neutrality for a catalytic residue in a ribozyme and show that ribozymes, like their protein enzyme counterparts, can optimize the pKa of their side chains for proton transfer.     

An H/D isotopic substitution study of the H5O2+.Ar vibrational predissociation spectra: exploring the putative role of Fermi resonances in the bridging proton fundamentals

To clarify the nature of the motions contributing to the observed multiplet structures in the low-energy (900-1800 cm-1) vibrational spectrum of the H5O2+ "Zundel" ion, we report the evolution of its vibrational fingerprint with sequential H/D isotopic substitution in a predissociation study of the Ar complexes. Of particular interest is the D4HO2+ complex, which displays a single intense band in the vicinity of the asymmetric OHO stretch of the bridging proton, in contrast to the more complex multiplet observed for both H5O2+ and D5O2+ isotopologues. These intensity patterns are consistent with the recent assignment of the bridging proton band's doublet in the H5O2+.Ne spectrum to a 2 x 2 Fermi resonance interaction between the shared proton stretch and a complex background level primarily derived from the O-O stretch together with two quanta of the wagging vibration involving the pyramidal deformations of the flanking H2O groups (Vendrell, O.; Gatti, F.; Meyer, H.-D. Angew. Chem., Int. Ed. 2007, 46, 6918). In addition, the observed trends rule out assignment of the approximately 1800 cm-1 feature in H5O2+ to a combination band of the bridging proton vibration with the O-O stretch, providing a secure foundation for the previously reported scheme that attributes this band to the out-of-phase intramolecular bending fundamental. The observed feature occurs at an unusually high energy for typical HOH bends, however, and we explore the participation of the bridging proton in these eigenstates by following how the calculated harmonic spectrum evolves when artificially large masses are assigned to the proton. The empirical assignments are supported by anharmonic estimates of the isotope shifts evaluated by the diffusion Monte Carlo method.     

Theoretical study of the complexes of horminone with Mg2+ and Ca2+ ions and their relation with the bacteriostatic activity

The coordination of the horminone molecule with hydrated magnesium and calcium divalent ions was studied by means of the density functional theory. All-electron calculations were performed with the B3LYP/6-31G method. The first layer of the water molecules surrounding the metallic cations was included. It was found that the octahedral [horminone(O(a)-O(d))-Mg-(H(2)O)(4)](2+) complex is more stable than [Mg(H(2)O)(6)](2+). That is, horminone is able to displace two water units from the hexahydrated complex. This behavior does not occur for Ca(2+). Consistently, [horminone(O(a)-O(d))-Mg-(H(2)O)(4)](2+) has a greater metal-ligand binding energy than [horminone(O(a)-O(d))-Ca-(H(2)O)(4)](2+). The preference of horminone by Mg(2+) is enlightened by these results. Moreover, its electronic structure, as shown by huge changes in the atomic populations, is strongly perturbed by Mg(2+). Indeed, horminone, bonded to [Mg(H(2)O)(4)](2+), is able to cross the bacterial membrane cell. Once inside, [horminone(O(a)-O(d))-Mg-(H(2)O)(4)](2+) binds to rRNA phosphate groups yielding [horminone(O(a)-O(d))-Mg-(H(2)O)(PO(4)H(2))(PO(4)H(3))(2)](+). These results give insights into how horminone may inhibit the initial steps of protein synthesis. The stability of the studied systems is accounted for in terms of the calculated structural and electronic properties: Mg-O and Ca-O bond lengths, charge transfers, and binding energies.     

共聚焦拉曼光谱研究过饱和硝酸铵液滴中NH4+, NO3- 和H2O之间的相互作用

将硝酸铵液滴沉积在石英基底上,通过降低该液滴周围环境的相对湿度,测定了该液滴由低浓度直至过饱和状态下高信噪比的拉曼光谱.其中,相对湿度的变化可以精确控制液滴浓度的改变.在相对湿度(RH)由72.1%降低至37.9%的过程中,硝酸铵液滴v1-NO-3峰位保持在1048cm-1,半峰宽为10cm-1.该现象表明NO-3周围的水分子被NH4+取代后不会对v1-NO-3造成影响,说明水分子和NH4+所形成的氢键具有相同的强度.对2500-4000cm-1范围内的拉曼光谱进行成分分析,2890、3090、3140、3220、3402及3507cm-1分别被指认为NH+4伞状弯曲振动的泛频、NH+4伞状弯曲振动与摇摆振动的组合谱带、NH+4的对称伸缩振动、NH+4的反对称伸缩振动、水峰中强氢键成分和弱氢键成分.从拟合结果得出:强氢键在氢键结构中所占百分含量随液滴相对湿度的降低而减少,弱氢键所占百分含量随液滴相对湿度的降低而增加.该变化趋势是NO-3和NH+4之间复杂相互作用的结果.     

碱式氯化镁5Mg(OH)2·MgCl2·3H2O的制备与表征

以氨水和盐湖盛产的水氯镁石为原料经过两步反应制备碱式氯化镁.第一步,水氯镁石和氨水反应制备氢氧化镁;第二步,利用氢氧化镁和水氯镁石,通过水热反应得到了具有纤维形貌、结晶较好的碱式氯化镁.应用化学分析、XRD、SEM和FIIR等手段对产物进行测试与表征.化学分析结果表明产物组成为5Mg(OH)2·MgCl2·3H2O.将得到的5Mg(OH)2·MgCl2·3H2O和碱式氯化镁系列标准XRD图对照,未有较好的匹配,且结合化学分析和已报道碱式硫酸镁具有5Mg(OH)2·MgSO4·3H2O物相,因而推测其为新物相;SEM图中5Mg(OH)2·MgCl2·3H2O纤维直径约为0.4μm,平均长度大于24 μm,长径比大于60;FTIR图谱中3419 cm-1附近出现了氢键的O-H伸缩振动吸收峰,1635 cm-1附近出现了游离水中H-O-H的弯曲振动吸收峰.水热合成的5Mg(OH)2·MgCl2·3H2O和常压下的产物相比直径较小,晶形更完整,强度更高.     

Mechanistic studies on the nitrite-catalyzed reductive nitrosylation of highly charged anionic and cationic Fe(III) porphyrin complexes

The nitrosyl complexes formed during the binding of NO to the (Pn)FeIII(H2O)2 (n = 8+ and 8-) complexes, viz., (P8-)FeII(H2O)(NO+) and (P8+)FeII(H2O)(NO+), undergo subsequent reductive nitrosylation reactions that were found to be catalyzed by nitrite, which was also produced during the reaction. The effect of the nitrite concentration, pH, temperature, and pressure on the nitrite-catalyzed reductive nitrosylation process was studied in detail for (P8-)FeIII(H2O)2, (P8+)FeIII(H2O)2, and (P8+)FeIII(OH)(H2O), from which rate and activation parameters were obtained. On the basis of these data, we propose mechanistic pathways for the studied reactions. The available results favor the operation of an innersphere electron-transfer process between nitrite and coordinated NO(+). By way of comparison, the cationic porphyrin complex (P8+)FeIII(L)2 (L = H2O or OH-) was found to react with NO2(-) to yield the nitrite adduct (P8+)FeIII(L)(NO2)(-)). A detailed kinetic studied revealed that nitrite binds to (P8+)FeIII(H2O)2 according to a dissociative mechanism, whereas nitrite binding to (P8+)FeIII(OH)(H2O) at higher pH follows an associative mechanism, similar to that reported for the binding of NO to these complexes.     

A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals, including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm-1 region and in the 950-1000 cm-1 region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example, soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm-1 (UO2)2+ (nu1), 909.6 and 898.0 cm-1 (UO2)2+ (nu3), 268.2, 257.8 and 246.9 cm-1 are assigned to the nu2 (delta) (UO2)2+. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm-1 are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm-1 region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm-1 and in the 390-420 cm-1 region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 cm-1 and 3600-3700 cm-1.     

镁合金化学转化膜的制备及其性能研究

在磷酸钠-磷酸二氢铵-高锰酸钾体系中对镁合金进行化学转化处理.研究了磷酸钠、磷酸二氢铵、高锰酸钾、温度、时间和添加剂对转化膜性能的影响.通过对转化膜结构、成分及性能的测试评价,得到了性能较好的化学转化溶液配方:Na3PO4为5g·L-1,NH4H2PO4为15 g· L-1,KMnO4为1g· L-1,添加剂(NH4)6 Mo7O24为0.5g·L-1.由SEM可观察到转化膜的表面成“干枯河床”状.XRD和EDS检测表明,膜层的主要成分是Mg,Al12 Mg17和无定形相,膜层表面主要有Mn,Mg,K,O和Al等元素组成.腐蚀实验和电化学测试表明,添加剂能够降低转化膜的腐蚀率,转化膜较基体的腐蚀电位正移了0.73 V,提高了镁合金的耐蚀性.     

Removal of aqueous ammonium with magnesium phosphates obtained from the ammonium-elimination of magnesium ammonium phosphate

In order to recycle magnesium ammonium phosphate (MgNH4PO4.6H2O: MAP) obtained from MAP process, which is one of the attractive processes for removal of aqueous ammonium and phosphate from wastewater, ammonium elimination from MAP to magnesium phosphates and ammonium incorporation into the magnesium phosphates have been investigated in the present study. It is confirmed that magnesium hydrogen phosphate (MgHPO4) is favorably obtained from the ammonium elimination from MAP at temperatures greater than 353 K, although magnesium phosphate (Mg3(PO4)2) and magnesium pyrophosphate (Mg2P2O7) have been suggested as possible candidates. Based on the dissolution-precipitation mechanism for the removal of aqueous ammonium with magnesium phosphates, three magnesium phosphates were employed for the removal of aqueous ammonium. The order of the removal rate of the aqueous ammonium was MgHPO4>Mg3(PO4)2>Mg2P2O7, as expected from the solubility of those magnesium phosphates. The removability of the solid obtained from ammonium elimination of MAP is also confirmed. The present results show that MAP can be employed as an advanced material for the removal/recovery of ammonium, although it is generally accepted that an excess of MAP obtained from the wastewater treatment can be only used as a slow-acting fertilizer.     

Multiporphyrin coordination arrays based on complexation of magnesium(II) porphyrins with porphyrinylphosphine oxides

Di- and triporphyrin arrays consisting of 5,15-diphenylporphyrinatomagnesium(II) (MgDPP) coordinated to free-base and Ni(II) porphyrinyl mono- and bis-phosphine oxides, as well as the self-coordinating diphenyl[10,20-diphenylporphyrinatomagnesium(II)-5-yl]phosphine oxide [MgDPP(Ph(2)PO)], were synthesised in excellent yields and characterised by various spectroscopic techniques. Phosphine oxides stabilise Mg(II) coordination to porphyrins and the resulting complexes have convenient solubilities, while the Ni(II) complexes exhibit interesting intramolecular fluorescence quenching behaviour. The binding constant of MgDPP to triphenylphosphine oxide (5.3 +/- 0.1 x 10(5) M(-1)) and the very high self-association constant of [MgDPP(Ph(2)PO)] (5.5 +/- 0.5 x 10(8) M(-1)) demonstrate the strong affinity of phosphine oxides towards Mg(II) porphyrins. These complexes are the first strongly bound synthetic Mg(II) multiporphyrin complexes and could potentially mimic the "special pair" in the photosynthetic reaction centre.     

Magnesium aminoethyl phosphonate (Mg(AEP)(H2O)): an inorganic-organic hybrid nanomaterial with high CO2:N2 sorption selectivity

The inorganic-organic hybrid magnesium aminoethyl phosphonate (Mg(AEP)(H(2)O), particle diameter: 20 nm; specific surface area: 322(10) m(2) g(-1); pore volume: 0.9(1) cm(3) g(-1)) shows reversible CO(2) sorption (152(5) mg g(-1)) at high pressure (≤110 bar). In contrast, N(2) uptake remains below 1.0(1) mg g(-1). Based on this selectivity (～100%) Mg(AEP)(H(2)O) expands the range of materials available for CO(2) capture.     

Intermolecular potential and second virial coefficient of the water-nitrogen complex

The authors construct a rigid-body (five-dimensional) potential energy surface for the water-nitrogen complex using the systematic intermolecular potential extrapolation routine. The intermolecular potential is then extrapolated to the limit of a complete basis set. An analytic fit of this surface is obtained, and, using this, the global minimum energy is found. The minimum is located in an arrangement in which N2 is near the H atom of H2O, almost collinear with the OH bond. The best estimate of the binding energy is 441 cm-1 (1 cm-1 approximately 1.986 43x10(-23) J). The extrapolated potential is then used to calculate the second cross virial coefficient over a wide temperature range (100-3000 K). These calculated second virial coefficients are generally consistent with experimental data, but for the most part the former have smaller uncertainties.     

丙烯选择氧化反应中钼基催化剂动态结构的研究

 用原位共焦显微拉曼光谱技术考察了丙烷选择氧化反应中Ag－M\r\no－P－O催化剂的结构，讨论了催化剂动态结构的成因及其对催化剂性\r\n能的影响．实验结果表明，在773K和n（C3H8）∶n（O2）∶n（N2）＝\r\n3∶1∶4的反应条件下，Ag－Mo－P－O催化剂中的Mo－O物种可转化为A\r\ngMoO2PO4中的Mo－O物种（多钼酸根），此时催化剂对丙烷选择氧化具\r\n有较高的催化活性．催化剂中Mo－O物种的转化是由MoO3中Mo－O物种和\r\nAgMoO2PO4中Mo－O物种的结构特性决定的．AgMoO2PO4中的Mo－O物种具\r\n有较强的参与MarsvanKrevelen氧化－还原循环的能力，可能是丙烷选\r\n择氧化反应的活性物种．     

Raman microscopy of autunite minerals at liquid nitrogen temperature

Uranyl micas are based upon (UO(2)PO(4))(-) units in layered structures with hydrated counter cations between the interlayers. Uranyl micas also known as the autunite minerals are of general formula M(UO2)2(XO4)2 x 8-12H2O where M may be Ba, Ca, Cu, Fe(2+), Mg, Mn(2+) or 1/2(HA1) and X is As or P. The structures of these minerals have been studied using Raman microscopy at 298 and 77K. Six hydroxyl stretching bands are observed of which three are highly polarised. The hydroxyl stretching vibrations are related to the strength of hydrogen bonding of the water OH units. Bands in the Raman spectrum of autunite at 998, 842 and 820 cm(-1) are highly polarised. Low intensity band at 915 cm(-1) is attributed to the nu(3) antisymmetric stretching vibration of (UO(2))(2+) units. The band at 820 cm(-1) is attributed to the nu(1) symmetric stretching mode of the (UO(2))(2+) units. The (UO(2))(2+) bending modes are found at 295 and 222 m(-1). The presence of phosphate and arsenate anions and their isomorphic substitution are readily determined by Raman spectroscopy. The collection of Raman spectra at 77K enables excellent band separation.     

Raman spectroscopy of newberyite Mg(PO3OH)·3H2O: a cave mineral

Newberyite Mg(PO3OH)·3H2O is a mineral found in caves such as from Moorba Cave, Jurien Bay, Western Australia, the Skipton Lava Tubes (SW of Ballarat, Victoria, Australia) and in the Petrogale Cave (Madura, Eucla, Western Australia). Because these minerals contain oxyanions, hydroxyl units and water, the minerals lend themselves to spectroscopic analysis. Raman spectroscopy can investigate the complex paragenetic relationships existing between a number of 'cave' minerals. The intense sharp band at 982 cm(-1) is assigned to the PO4(3-)ν1 symmetric stretching mode. Low intensity Raman bands at 1152, 1263 and 1277 cm(-1) are assigned to the PO4(3-)ν3 antisymmetric stretching vibrations. Raman bands at 497 and 552 cm(-1) are attributed to the PO4(3-)ν4 bending modes. An intense Raman band for newberyite at 398 cm(-1) with a shoulder band at 413 cm(-1) is assigned to the PO4(3-)ν2 bending modes. The values for the OH stretching vibrations provide hydrogen bond distances of 2.728 ? (3267 cm(-1)), 2.781 ? (3374 cm(-1)), 2.868 ? (3479 cm(-1)), and 2.918 ? (3515 cm(-1)). Such hydrogen bond distances are typical of secondary minerals. Estimates of the hydrogen-bond distances have been made from the position of the OH stretching vibrations and show a wide range in both strong and weak bonds.     

Raman spectroscopy of synthetic and natural iowaite

The chemistry of a magnesium based hydrotalcite known as iowaite Mg6Fe2Cl2(OH)16.4H2O has been studied using Raman spectroscopy. Iowaite has chloride as the counter anion in the interlayer. The formula of synthetic iowaite was found to be Mg5.78Fe2.09(Cl,(CO3)0.5)(OH)16.4H2O. Oxidation of natural iowaite results in the formation of Mg4FeO(Cl,CO3) (OH)8.4H2O. X-ray diffraction (XRD) shows that the iowaite is a layered structure with a d(001) spacing of 8.0 angtsroms. For synthetic iowaite three Raman bands at 1376, 1194 and 1084 cm(-1) are attributed to CO3 stretching vibrations. These bands are not observed for the natural iowaite but are observed when the natural iowaite is exposed to air. The Raman spectrum of natural iowaite shows three bands at 708, 690 and 620 cm(-1) and upon exposure to air, two broad bands are found at 710 and 648 cm(-1). The Raman spectrum of synthetic iowaite has a very broad band at 712 cm(-1). The Raman spectrum of natural iowaite shows an intense band at 527 cm(-1). The air oxidized iowaite shows two bands at 547 and 484 cm(-1) attributed to the (CO3)(2-)nu2 bending mode. Raman spectroscopy has proven most useful for the study of the chemistry of iowaite and chemical changes induced in natural iowaite upon exposure to air.     

Experimental investigation of the complete inner shell hydration energies of Ca2+: threshold collision-induced dissociation of Ca(2+)(H2O)x Complexes (x = 2-8)

The sequential bond energies of Ca(2+)(H(2)O)(x) complexes, where x = 1-8, are measured by threshold collision-induced dissociation (TCID) in a guided ion beam tandem mass spectrometer. From an electrospray ionization source that produces an initial distribution of Ca(2+)(H(2)O)(x) complexes where x = 6-8, complexes down to x = 2 are formed using an in-source fragmentation technique. Ca(2+)(H(2)O) cannot be formed in this source because charge separation into CaOH(+) and H(3)O(+) is a lower energy pathway than simple water loss from Ca(2+)(H(2)O)(2). The kinetic energy dependent cross sections for dissociation of Ca(2+)(H(2)O)(x) complexes, where x = 2-9, are examined over a wide energy range to monitor all dissociation products and are modeled to obtain 0 and 298 K binding energies. Analysis of both primary and secondary water molecule losses from each sized complex provides thermochemistry for the sequential hydration energies of Ca(2+) for x = 1-8 and the first experimental values for x = 1-4. Additionally, the thermodynamic onsets leading to the charge separation products from Ca(2+)(H(2)O)(2) and Ca(2+)(H(2)O)(3) are determined for the first time. Our experimental results for x = 1-6 agree well with previously calculated binding enthalpies as well as quantum chemical calculations performed here. Agreement for x = 1 is improved when the basis set on calcium includes core correlation.