Hexaaqua Complex Research Articles

Synergy of {Co(H2O)6}2+ with a Polyoxometalate Leads to Aqueous Homogeneous Hydrogen Evolution: Experiments and Computations.

In this work, we have described a polyoxometalate (POM)-based inexpensive and easily synthesizable compound [Co(H2O)6]2[{K(H2O)}2V10O28]·2H2O (1), which exhibits electrocatalytic hydrogen evolution in its aqueous solution without its decomposition (or electrodeposition), acting as a rare homogeneous electrocatalyst. Even though the compound [Co(H2O)6]2[{K(H2O)}2V10O28]·2H2O (1) (soluble in water) shows electrocatalytic hydrogen evolution reaction (HER) activity because of the Coulombic attraction, including H-bonding interactions, between the [Co(H2O)6]2+ cationic species and [{K(H2O)}2V10O28]4-anionic species, the individual homogeneous solutions of [V10O28]6- (source: Na6[V10O28]·18H2O) and [Co(H2O)6]2+ (source: CoCl2·6H2O) do not show any electrocatalytic HER activity. We have thus established that the synergy of [V10O28]6- with [Co(H2O)6]2+ in crystal matrix as well as in the aqueous solution of 1 makes the compound 1 a stable and highly active electrocatalyst for homogeneous HER in an aqueous solution. In order to corroborate these homogeneous HER studies, we performed density functional theory (DFT) calculations to show that decavanadate cluster anion [V10O28]6- interacts with hexa-aqua complex cation [Co(H2O)6]2+ via strong H-bonding interactions, leading to a synergy effect that enables the cobalt center of [Co(H2O)6]2+ to be an active site of HER in the present work.

Solvation and speciation of cobalt(II). A theoretical X-ray absorption and RIXS study

The X-ray spectroscopic signatures of solvated Co2+ ions mimicking the aqueous solution of CoCl2 are investigated accounting for multiconfigurational as well as spin–orbit coupling effects. To this end the RASSCF/RASSI methodology with second order corrections due to dynamical correlation (RASPT2) is employed. Emphasis is put on the identification of spectral signatures of different species in octahedral, [Co(H2O)6−xClx](2−x)+, and tetrahedral, [Co(H2O)4−xClx](2−x)+, coordination. X-ray absorption spectra show distinct differences in the L3 band only. Here, the best agreement between theory and experiment is obtained for the hexaaqua complex [Co(H2O)6]2+. For better identification of particular species it is proposed to use RIXS spectroscopy, which shows pronounced species-dependent inelastic features.

Comprehensive understanding of multiple binding of D-penicillamine with Cu2+-hexa aqua complex: a DFT approach

The multiple-ligand-binding of D-penicillamine with [Cu(H2O)6]2+ has been explored computationally using density functional theory (DFT). Because of the implementation of bulk aqueous medium and considering the pH at physiological level, both neutral as well as de-protonated analogues of D-penicillamine are taken into account to study the binding phenomena with Cu2+. In doing so, at first, we have studied the binding of both neutral and de-protonated analogues of two D-penicillamine with Cu2+ in bi-dentate mode by replacing four molecules of H2O (di-amino complex) and afterward, the binding of three D-penicillamine with Cu2+ has been investigated by substituting all six molecules of H2O (tri-amino complex). Apart from bi-dentate binding, the de-protonated form of D-penicillamine can also bind in tri-dentate mode and in that case, all six H2O molecules are substituted during di-amino complex formation. Based on the coordinating modes of the artificial amino acids, for each di- and tri-amino complex, more than one isomer has been detected and the isomers are designated accordingly. By analyzing the optimized geometries, it is noticed that most of the di- and tri-amino complexes are distorted hexa-coordinated in nature and in few cases, they adopt penta-coordinated geometry. To analyze the stability of the complexes, we have determined the binding energy (BE) in both DCM and CDCM mechanisms for each di- and tri-amino complex. Overall, the present study is arranged in such a way so that it can provide a complete understanding about the binding process of the aforementioned artificial amino acid with Cu2+-aqua complex.

Synthesis and crystal structure of solvent-free dodecahydro closo-dodecaborate of nickel, NiB12H12.

Nickel closo-dodecaborate NiB12H12 was prepared by mechanosynthesis (ball milling) of mixtures of Na2B12H12 + NiCl2 followed by hydration and drying under dynamic vacuum. The crystal structures of hydrated and anhydrous closo-dodecaborates were characterized by temperature dependent synchrotron radiation X-ray powder diffraction, ab initio calculations, thermal analysis and infrared spectroscopy. Three different water containing complexes were found: a homoleptic octahedral complex in Ni(H2O)6B12H12 crystallizing in two different deformation variants of a complex centred closo-dodecaborate cube, and a heteroleptic octahedral complex in Ni(H2O)4B12H12 containing four water molecules and two hydrogens and centring also a deformed closo-dodecaborate cube. Anhydrous nickel closo-dodecaborate was obtained by drying the hydrated sample under dynamic vacuum. It crystallizes with bcc packing of B12H122- anions and Ni2+ is disordered close to the triangular face of the tetrahedral interstice coordinated by a H5 square pyramid.

The Isotope Geochemistry of Zinc and Copper

Copper, a native metal found in ores, is the principal metal in bronze and brass. It is a reddish metal with a density of 8920 kg m−3. All of copper’s compounds tend to be brightly colored: for example, copper in hemocyanin imparts a blue color to blood of mollusks and crustaceans. Copper has three oxidation states, with electronic configurations of Cu([Ar]3 d 104 s 1), Cu+([Ar]3 d 10), and Cu2+([Ar]3 d 9). Cu does not react with aqueous hydrochloric or sulfuric acids, but is soluble in concentrated nitric acid due to its lesser tendency to be oxidized. Cu(I) exists as the colorless cuprous ion, Cu+. Cu(II) is found as the sky-blue cupric ion, Cu2+. The Cu+ ion is unstable, and tends to disproportionate to Cu and Cu2+. Nevertheless, Cu(I) forms compounds such as Cu2O. Cu(I) bonds more readily to carbon than Cu(II), hence Cu(I) has an extensive chemistry with organic compounds. In aqueous solutions, Cu2+ ion occurs as an aquacomplex. There is no clearly predominant structure among the four-, five-, and six-fold coordinated Cu(II) species (Chaboy et al. 2006). Hydrated Cu(II) ion has been represented as the hexaaqua complex Cu(H2O)62+, which shows the Jahn–Teller distortion effect (Sherman 2001; Bersuker 2006), whereby the two Cu–O distances of the vertical axial bond (Cu–Oax) are longer than four Cu–O distances in the equatorial plane (Cu–Oeq). The Jahn–Teller effect lowers the symmetry of Cu(H2O)62+ from octahedral Th to D2h. The sixfold coordination of hydrated Cu(II) species is questioned by a finding of fivefold coordination (Pasquarello et al. 2001; Chaboy et al. 2006; Little et al. 2014b …

Revisiting the iron pools in cucumber roots: identification and localization.

Fe deficiency responses in Strategy I causes a shift from the formation of partially removable hydrous ferric oxide on the root surface to the accumulation of Fe-citrate in the xylem. Iron may accumulate in various chemical forms during its uptake and assimilation in roots. The permanent and transient Fe microenvironments formed during these processes in cucumber which takes up Fe in a reduction based process (Strategy I) have been investigated. The identification of Fe microenvironments was carried out with (57)Fe Mössbauer spectroscopy and immunoblotting, whereas reductive washing and high-resolution microscopy was applied for the localization. In plants supplied with (57)Fe(III)-citrate, a transient presence of Fe-carboxylates in removable forms and the accumulation of partly removable, amorphous hydrous ferric oxide/hydroxyde have been identified in the apoplast and on the root surface, respectively. The latter may at least partly be the consequence of bacterial activity at the root surface. Ferritin accumulation did not occur at optimal Fe supply. Under Fe deficiency, highly soluble ferrous hexaaqua complex is transiently formed along with the accumulation of Fe-carboxylates, likely Fe-citrate. As (57)Fe-citrate is non-removable from the root samples of Fe deficient plants, the major site of accumulation is suggested to be the root xylem. Reductive washing results in another ferrous microenvironment remaining in the root apoplast, the Fe(II)-bipyridyl complex, which accounts for ~30% of the total Fe content of the root samples treated for 10min and rinsed with CaSO4 solution. When (57)Fe(III)-EDTA or (57)Fe(III)-EDDHA was applied as Fe-source higher soluble ferrous Fe accumulation was accompanied by a lower total Fe content, confirming that chelates are more efficient in maintaining soluble Fe in the medium while less stable natural complexes as Fe-citrate may perform better in Fe accumulation.

Ln12 -Containing 60-Tungstogermanates: Synthesis, Structure, Luminescence, and Magnetic Studies.

A new class of hexameric Ln12 -containing 60-tungstogermanates, [Na(H2 O)6 ⊂Eu12 (OH)12 (H2 O)18 Ge2 (GeW10 O38 )6 ](39-) (Eu12 ), [Na(H2 O)6 ⊂Gd12 (OH)6 (H2 O)24 Ge(GeW10 O38 )6 ](37-) (Gd12 ), and [(H2 O)6 ⊂Dy12 (H2 O)24 (GeW10 O38 )6 ](36-) (Dy12 ), comprising six di-Ln-embedded {β(4,11)-GeW10 } subunits was prepared by reaction of [α-GeW9 O34 ](10-) with Ln(III) ions in weakly acidic (pH 5) aqueous medium. Depending on the size of the Ln(III) ion, the assemblies feature selective capture of two (for Eu12 ), one (for Gd12 ), or zero (for Dy12 ) extra Ge(IV) ions. The selective encapsulation of a cationic sodium hexaaqua complex [Na(H2 O)6 ](+) was observed for Eu12 and Gd12 , whereas Dy12 incorporates a neutral, distorted-octahedral (H2 O)6 cluster. The three compounds were characterized by single-crystal XRD, ESI-MS, photoluminescence, and magnetic studies. Dy12 was shown to be a single-molecule magnet.

Multireference Ab Initio Study of Ligand Field d–d Transitions in Octahedral Transition-Metal Oxide Clusters

We have used multiconfigurational (MC) and multireference (MR) methods (CASSCF, CASPT2, and MRCI) to study d–d transitions and other optical excitations for octahedral [M(H2O)6]n+ clusters (M = Ti, V, Mn, Cr, Fe, Co, Ni, Cu) as models of hematite and other transition-metal oxides of interest in solar fuels. For [Fe(H2O)6]3+, all calculations substantially overestimate the d–d transition energies (∼3.0 versus ∼1.5 eV) compared to what has been experimentally assigned. This problem occurs even though theory accurately describes (1) the lowest d–d transition energy in the atomic ion Fe3+ (∼4.4 eV), (2) the t2g–eg splitting (∼1.4 eV) in [Fe(H2O)6]3+, and (3) the ligand-to-metal charge transfer (LMCT) energy in [Fe(H2O)6]3+. Indeed, the results for Fe3+ and the t2g–eg splitting suggest that the lowest d–d excitation energy in the hexa-aqua complex should be ∼3 eV (or slightly below because of Jahn–Teller stabilization), as we find. Possible origins for the d–d discrepancy are examined, including Fe2+ and low-s...

Mechanism of Cobalt Self-Exchange Electron Transfer

A heptanuclear cobalt cluster was synthesized in two different oxidation states, Co(II)7 and a mixed valence Co(III)Co(II)6, as a soluble model of a cobalt-phosphate/borate (Co-OEC) water splitting catalyst. Crystallographic characterization indicates similar cluster cores, distinguished primarily at the central Co atom. An anion associates to the cluster cores via hydrogen bonding. Using an isotope exchange method, an anomalously slow self-exchange electron transfer rate constant (k(obs) = 1.53 × 10(-3) M(-1) s(-1) at 40 °C and 38 mM [OTf] in MeCN), as compared to that predicted from semiclassical Marcus theory, supports a charge transfer process that is accelerated by dissociation of the anion from the oxidized cluster. This mechanism sheds light on the inverse dependence of anions in the self-repair mechanism of Co-OECs. Moreover, because H2O cannot directly bridge cobalt centers, owing to the encapsulation of the central Co within the cluster core, the observed results address a long-standing controversy surrounding the Co(2+/3+) self-exchange electron transfer reaction of the hexaaqua complex.

Bis(2-amino-4-methylpyrimidin-1-ium) hexaaquacobalt(II) disulfate dihydrate

In the title hydrated mixed-cation salt, (C5H8N3)2[Co(H2O)6](SO4)2·2H2O, the complete octa­hedral hexa­aqua complex cation is generated by crystallographic inversion symmetry. In the crystal, the components are linked by O—H⋯O and N—H⋯O hydrogen bonds, the latter, involving pyrimidinium cations and sulfate anions, generating R 2 2(8) loops. These, together with π–π inter­actions between centrosymmetrically related pyrimidinium cations [centroid–centroid separation = 3.5460 (8) Å], lead to the formation of a three-dimensional network.

H-bonds superstructures built by aquacomplexes and an azapurine derivative: a case of molecular recognition

The crystal structures of six compounds involving the divalent cations of Mn, Zn and Cd, the anionic form of the heterocycle 4,6-dimethyl-1,2,3-triazolo[4,5-d]pyrimidin-5,7-dione (Hdmax) and bipyridyl based spacer ligands are reported. The most important feature of these structures is the presence, in all cases, of a topologically identical 1-D polymeric superstructure (tape), involving tetra- or hexaaqua complex cations and triazolopyrimidine anions, built through hydrogen bonds. Adding these results to others previously published, we may consider these tapes as robust supramolecular synthons where a defined/clear case of molecular recognition between these two moieties takes place.

Hexaaquanickel(II) disulfato(1,4,8,11-tetraazacyclotetradecane)nickelate(II) dihydrate

The title compound, [Ni(H(2)O)(6)][Ni(SO(4))(2)(C(10)H(24)N(4))].2H(2)O, is an unusual compound in that it is composed of a hexaaqua complex, formally a dication, and a mixed-donor complex (four N and two O atoms), formally a dianion, with substantial charge separation between the two nickel centres (6.536 A). The homoleptic dication complex consists of the weaker-field ligands, whilst the dianion retains the coordination of all the higher-field donors. Both nickel ions are located at centres of symmetry. This rare compound is placed in the context of previously reported structures which emphasizes its peculiarity.

ChemInform Abstract: Raman Spectroscopic Measurements of Scandium(III) Hydration in Aqueous Perchlorate Solution and ab initio Molecular Orbital Studies of Scandium(III) Water Clusters: Does Sc(III) Occur as a Hexaaqua Complex?

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Coordination behaviour and two-dimensional-network formation in poly[[μ-aqua-diaqua(μ5-propane-1,3-diyldinitrilotetraacetato)dilithium(I)cobalt(II)] dihydrate]: the first example of anMII–1,3-pdta complex with a monovalent metal counter-ion

The title compound, {[CoLi2(C11H14N2O8)(H2O)3].2H2O}n, constitutes the first example of a salt of the [M(II)(1,3-pdta)](2-) complex (1,3-pdta is propane-1,3-diyldinitrilotetraacetate) with a monopositive cation as counter-ion. Insertion of the Li+ cation could only be achieved through application of the ion-exchange column technique which, however, appeared unsuccessful with other alkali metals and the ammonium cation. The structure contains two tetrahedrally coordinated Li+ cations, an octahedral [Co(1,3-pdta)](2-) anion and five water molecules, two of which are uncoordinated, and is built of two-dimensional layers extending parallel to the (010) lattice plane, the constituents of which are connected by the coordinate bonds. O-H(water)...O hydrogen bonds operate both within and between these layers. The crystal investigated belongs to the enantiomeric space group P2(1) with only one (Lambda) of two possible optical isomers of the [Co(1,3-pdta)](2-) complex. A possible cause of enantiomer separation during crystallization might be the rigidification and polarization of the [M(1,3-pdta)](2-) core, resulting from direct coordination of Li+ cations to three out of four carboxylate groups constituting the 1,3-pdta ligand. The structure of (I) differs considerably from those of the other [M(II)(1,3-pdta)](2-) complexes, in which the charge compensation is realized by means of divalent hexaaqua complex cations. This finding demonstrates a significant structure-determining role of the counter-ions.

Searching for Stable, Five-Coordinate Aquated Al(III) Species. Water Exchange Mechanism and Effect of pH

Density functional theory calculations have been performed for the water exchange mechanism of aquated Al(III). The effect of pH was considered by studying the exchange processes for [Al(H2O)6]3+ and its conjugated base, [Al(H2O)5OH]2+. Both complexes were found to exchange water in a dissociative way with activation energies (EA) of 15.9 and 10.2 kcal/mol, respectively. The influence of solvent molecules on the gas-phase cluster model was considered by the addition of up to four water molecules to the model system. The stabilizing effect of the solvent on the transition state decreases EA to 8.6 (hexa-aqua complex) and 7.6 (monohydroxo complex) kcal/mol, whereas EA for all hydroxo species is consistently significantly lower than those for the related aqua systems, which indicates a much faster water exchange rate. For the hydroxo complex, all calculated five-coordinate intermediates, nH2O.[Al(H2O)4(OH)]2+ (n = 1, 2, 3, 4, 5), are more stable than the corresponding six-coordinate reactants. Our results therefore suggest the presence of a stable five-coordinate species of aquated Al(III), namely, the [Al(H2O)4(OH)]2+ complex.

Mössbauer study of iron uptake in cucumber root

57Fe Mossbauer spectroscopy was used to study the uptake and distribution of iron in the root of cucumber plants grown in iron-deficient modified Hoagland nutrient solution and put into iron-containing solution with 10 μM Fe citrate enriched with 57Fe (90%) only before harvesting. The Mossbauer spectra of the frozen roots exhibited two Fe3+ components with typical average Mossbauer parameters of δ = 0.5 mm s−1, Δ = 0.46 mm s−1 and δ = 0.5 mm s−1, Δ = 1.2 mm s−1 at 78 K and the presence of an Fe2+ doublet, assigned to the ferrous hexaaqua complex. This finding gives a direct evidence for the existence of Fe2+ ions produced via root-associated reduction according to the mechanism proposed for iron uptake for dicotyledonous plants. Monotonous changes in the relative content of the components were found with the time period of iron supply. The Mossbauer results are interpreted in terms of iron uptake and transport through the cell wall and membranes.

Kinetic studies on the first dihydrogen aquacomplex, [Ru(H 2)(H 2O) 5] 2+: Formation under H 2 pressure and catalytic H/D isotope exchange in water

The ruthenium(II) hexaaqua complex [Ru(H 2O) 6] 2+ reacts with dihydrogen under pressure to give the η 2-dihydrogen ruthenium(II) pentaaqua complex [Ru(H 2)(H 2O) 5] 2+.The complex was characterized by 1H, 2H and 17O NMR: δ H = −7.65 ppm, J HD = 31.2 Hz, δ O = −80.4 ppm ( trans to H 2) and δ O = −177.4 ppm ( cis to H 2).The H–H distance in coordinated dihydrogen was estimated to 0.889 Å from J HD, which is close to the value obtained from DFT calculations (0.940 Å).Kinetic studies were performed by 1H and 2H NMR as well as by UV–Vis spectroscopy, yielding the complex formation rate and equilibrium constants: k f = (1.7 ± 0.2) × 10 −3 kg mol −1 s −1 and K eq = 4.0 ± 0.5 mol kg −1.The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn ( I d).In deuterated water, one can observe that [Ru(H 2)(H 2O) 5] 2+ catalyses the hydrogen exchange between the solvent and the dissolved dihydrogen.A hydride is proposed as the intermediate for this exchange.Using isotope labeling, the rate constant for the hydrogen exchange on the η 2-dihydrogen ligand was determined as k 1 = (0.24 ± 0.04) × 10 −3 s −1.The upper and lower limits of the p K a of the coordinated dihydrogen ligand have been estimated:3 < p K a < 14.

Synthese, Kristallstruktur und thermischer Abbau von Mg(H2O)6[B12H12] · 6 H2O

AbstractBei der Umsetzung einer wäßrigen Lösung der Säure (H3O)2[B12H12] mit MgCO3 und anschließendem isothermen Eindampfen der erhaltenen Lösung entstehen farblose, polyederförmige Einkristalle von Magnesium‐Dodekahydro‐closo‐Dodekaborat‐Dodekahydrat Mg(H2O)6[B12H12] · 6 H2O (kubisch, F4132; a = 1643, 21(9) pm, Z = 8). Die Kristallstruktur läßt sich auf den NaTl‐Strukturtyp zurückführen, wobei die Schwerpunkte der quasi‐ikosaedrischen [B12H12]2—‐Anionen (d(B—B) = 178—180 pm, d(B—H) = 109 pm) die Tl—‐ und die Mg2+‐Kationen die Na+‐Positionen besetzen. Ein direkter koordinativer Einfluß der [B12H12]2—‐Einheiten auf die Mg2+‐Kationen ist nicht festzustellen. Letztere werden lediglich von sechs Sauerstoffatomen der umgebenden Wassermoleküle oktaedrisch koordiniert und bilden isolierte Hexaaqua‐Komplexkationen [Mg(H2O)6]2+ (d(Mg—O) = 206 pm, 6×). Zusätzlich dazu sind in der Kristallstruktur sechs „zeolithische”︁ Wassermoleküle lokalisiert, die für die Bildung eines starken O—Hδ+···δ—O‐Wasserstoffbrückenbindungssystems sorgen. Die Ausbildung schwacher B—Hδ—···δ+H—O‐Wasserstoffbrücken wird ebenfalls diskutiert. Differenzthermoanalytische und thermogravimetrische Studien zum thermischen Verhalten des Dodekahydrats Mg[B12H12] · 12 H2O (≡ Mg(H2O)6[B12H12] · 6 H2O) belegen erwartungsgemäß einen zweistufigen Abbau im Temperaturbereich zwischen 71 und 76 °C sowie bei 202 °C, der schließlich zum wasserfreien Magnesium‐Dodekahydro‐closo‐Dodekaborat Mg[B12H12] führt.

Aqua Ions. 2. Structural manifestations of the Jahn-Teller effect in the beta-alums.

Variable-temperature single-crystal neutron diffraction structures of the alums CsM(III)(SO(4))(2).12D(2)O, where M(III) = Ti, V, Mn, and Ga, are reported. Structural differences are highlighted by the titanium and manganese alums, which undergo cubic (Pathremacr;) to orthorhombic (Pbca) phase transitions at approximately 13 and approximately 156 K, respectively. The structural instability exhibited by these salts is interpreted as arising from cooperative Jahn-Teller interactions, and these measurements characterize the structural changes that result from the coupling between the electronic and vibrational states. Although the symmetry changes associated with the phase transformations are analogous for the Ti and Mn alums, the low-temperature geometries of the tervalent hexaaqua cations are markedly different. Whereas the MnO(6) framework is subject to a pronounced tetragonal elongation, changes in the Ti-O bond lengths are very modest; but significant changes in the O-Ti-O bond angles and in the disposition of the coordinated water molecules are identified. The large differences in the transition temperatures and in the low-temperature stereochemistries of the [Ti(OD(2))(6)](3+) and [Mn(OD(2))(6)](3+) cations are related to the sensitivity of the energies of the t(2g) (O(h)) and e(g) (O(h)) orbitals to the various asymmetric vibrations of the hexaaqua complex.

Raman Spectroscopic Measurements of Scandium(III) Hydration in Aqueous Perchlorate Solution and ab Initio Molecular Orbital Studies of Scandium(III) Water Clusters: Does Sc(III) Occur as a Hexaaqua Complex?

We have shown that Sc(III) in aqueous perchlorate solution occurs as a hexaaqua cation. The weak, polarized Raman band assigned to the ν1(a1g)(ScO6) mode of the hexaaqua Sc(III) ion has been studied as a function of concentration. Besides the isotropic component at 442 cm-1, two weak depolarized modes at 295 and 410 cm-1 were measured in the Raman effect. These two modes of the ScO6 unit were assigned to ν5(f2g) and ν2(eg), respectively. The infrared active mode,ν3(f1u), was found at 460 cm-1. The Raman spectroscopic data suggest that the hexaaqua Sc(III) ion is stable in perchlorate solution within the concentration range measured. Furthermore, the frequency data confirm the centrosymmetry of the Sc(III) aqua complex, contrary to earlier Raman results. The ScO6 unit possesses Oh symmetry (water seen as point mass). These findings are in contrast to ScCl3 solutions, where chloride replaces water in the first hydration sphere and forms one or more chloro complexes. Gas-phase structures, binding energies, and enthalpies are reported for small [Sc(OH2)n]3+ clusters, with one to nine water molecules in the first sphere. Ab initio molecular orbital calculations were performed at the HF and MP2 levels of theory using different basis sets up to 6-31+G*. The water molecules in these clusters coordinate the Sc3+ in highly symmetric arrangements that tend to enhance electrostatic charge−dipole interactions while minimizing ligand−ligand repulsion. The Sc−O bond length for the [Sc(OH2)6]3+ cluster reproduces the experimentally determined bond length (EXAFS) of 2.18 Å. The theoretical binding energy for the [Sc(OH2)6]3+ ion was calculated and accounts for ca. 54−59% of the experimental single ion hydration enthalpy of Sc(III). The stability of the hexaaquascandium(III) cluster could be demonstrated by comparing the stability of the [Sc(OH2)6(OH2)]3+ cluster with the [Sc(OH2)7]3+ cluster, resulting in the stability of the former. The frequencies of ν1(ScO6) of the [Sc(OH2)6]3+ cluster are ca. 11% lower than the experimental frequency. The reason for this discrepancy was discussed and found to lie in the lack of the second hydration sphere which was subsequently modeled as the [Sc(OH2)18]3+ cluster, denoted Sc[6+12]. Frequencies of the ScO6 unit for the Sc[6+12] cluster were calculated and agree with the experimental values. The binding enthalpy resembles that of the single ion hydration enthalpy.