Hexacoordinate Structure Research Articles

Experimental and theoretical studies of trinuclear cadmium(II) complex containing pyridine ring: Synthesis, crystallographic, spectroscopic, TD/DFT calculations and Hirshfeld surface analysis

Two three-dimensional supramolecular structures of L and [Cd3L2(CH3OH)4Cl6] complex (L = 2-(6-bromopyridin-2-yl)-4-methyl-1,2-dihydroquinazoline-N3-oxide), were synthesized and characterized by X-ray crystallography and elemental analysis, as well as FT-IR, UV–Vis, and fluorescence spectroscopy. The photoluminescence behavior of the Cd(II) complex was also investigated in different solvents. X-ray diffraction analysis results revealed that the Cd(II) complex was a trinuclear hexa-coordinate structure and made up of two L, three Cd2+ metal central, four methanol and six chlorine ions. In the crystal structures, it was noteworthy that L formed an infinite 1-D chain-like, 2-D square structure, parallelogram 3-D supramolecular skeleton, whereas the Cd(II) complex formed an infinite 1-D chain-like, 2-D ladder-like configuration, and even expanding into 3-D grid-like supramolecular frameworks. Density functional theory (DFT) calculation was used to compute the optimization, molecular frontier orbital energies (HOMO and LUMO). Specifically, owing to the combination of metal orbitals and the ligand, the energy gap of the complex was less than L. Electrostatic potential (ESP) was used to analyze the reaction sites of two compounds. On the basis of optimized geometry, time-dependent DFT (TD-DFT) simulated the electronic transitions rationalized the UV–Vis spectra peaks of L and Cd(II) complex. In addition, some non-covalent interactions were quantified by Hirshfeld surface and analyzed by Interaction region indicator (IRI).

Preference of C2v Symmetry in Low-Spin Hexacarbonyls of Rare-Earth and f Elements

The structures and bonding of selected neutral M(CO)6 complexes (M = Sc, Y, La, Lu, Ac and U) have been studied by density functional theory calculations. The calculations revealed the preference for C2v symmetry and low-spin electronic state for most of these complexes. The relative stability of the low-symmetry species increases gradually with the size of the metal atom. While the characteristic Oh hexa-coordinated structure is favored in the high-spin electronic state of the smaller metals, for heavier metals, important advantages of the C2v vs. Oh structures include larger charge transfer interactions in terms of transferred electrons as well as better steric conditions. Our joint experimental–theoretical analysis detected and confirmed the Oh structure of the Sc(CO)6 complex in cryogenic CO/Ar matrices.

Hypercoordination by multiple dangling benzylmethoxy ligands in highly crowded triaryltin bromide [(2-MeOCH2C6H4)3]SnBr and diaryltin mixed halides [(2-MeOCH2C6H4)2]SnBrCl.

The reaction between the Grignard reagent formed between Mg and 2-bromobenzylmethyl ether and SnCl4 produced four products: [2-(MeOCH2)C6H4]3SnBr (1), [2-(MeOCH2)C6H4]2SnX2 (2, X2 = Br2 (a) and BrCl (b)), [{2-(MeOCH2)C6H4}3Sn]2 (3), and [{2-(MeOCH2)C6H4}2SnBr]2O (4). In the case of 1, two of the three dangling arm O atoms coordinate to the central tin atom with O-Sn internuclear distances of 2.53 (O1) and 2.91 (O2) Å, the shorter interaction being trans to the Br atom, the other trans to a phenyl carbon atom. In the case of 2 the resulting hexacoordinate structure exhibits two very short O---Sn interactions of 2.42 and 2.50 Å, well below the sum of the VdW radii of O and Sn, 3.69 Å. The sterically crowded ditin compound 3 was obtained in trace amounts and the structure demonstrates no dangling O---Sn interactions. General changes in structure compared to other distannane systems are reflective of the great steric crowding. Distannoxane 4, has a Sn-O-Sn bond angle of 148.1(2)o which is larger compared to other distannoxane structures. The intermolecular interactions between Sn---O 2.470(3) and 2.521(3)Å and 2.665(3) and 2.629(3)Å for Sn1 and Sn2 respectively are responsible for a distorted octahedral geometry around the two tin atoms.

An Ab Initio Investigation of the Hydration of Lead(II)

The structure of lead(II) is not well known in aqueous solution. The Hartree–Fock and second order Møller–Plesset levels of theory using the CEP, LANL2, and SDD effective core potentials in combination with their associated basis sets, or with the 6-31G* and 6-31+G* basis sets were used to calculate the energies, structures, and vibrational frequencies of Pb2+(H2O)n, n = 0–9, 18. The lead–oxygen distances and totally symmetric stretching frequency of the aqualead(II) ions from different levels of theory were compared with each other, and with solution measurements where available. The calculations support a hemidirected hexacoordinate structure.

CT-DNA/HSA binding interactions and cytotoxicity activity of a new copper(II) complex

We designed and synthesized a novel copper (II) complex, [Cu(ambt)2(cnbz)2], using 2-amino-6-methoxybenzothiazole (ambt) and 2-chloro-5-nitrobenzoic acid (cnbz) as ligands. Single-crystal X-ray diffraction (XRD), IR (infrared) spectra along with elemental analysis were employed to characterize its structure. Single-crystal XRD analysis illustrated the copper (II) complex belonged to the triclinic crystal system, space group P-1 and formed mononuclear hexa-coordinated structure. Electronic absorption, fluorescence spectrum and viscosity analysis were employed to assess the binding properties of the complex with CT-DNA (calf thymus DNA), as well as HSA (human serum albumin). The calculated binding constants Ka were 5.89 × 104 M−1 and 3.31 × 106 M−1 for CT-DNA and HSA, respectively, implying that complex [Cu(ambt)2(cnbz)2] displays intercalative bindings with CT-DNA and HSA. It also statically quenched CT-DNA/HSA fluorescence. CCK-8 assay revealed that compared to cisplatin, the complex exerts greater anti-proliferative influence against HepG2, HeLa and A549 cell lines. Flow cytometry revealed that [Cu(ambt)2(cnbz)2] arrested the cycle of HepG2 cells at G0/G1 phase, inducing apoptosis / necrosis. The degree of apoptosis / necrosis and inhibition of cell cycle is dose-, as well as time-dependent.

A Benzothiazole-Based Fluorescent Probe for Ratiometric Detection of Al3+ in Aqueous Medium and Living Cells

Aluminum is the third (after O and Si) most abundant metal in the earth’s crust and associates with neurological diseases when abnormal level of Al3+ occurs in nervous center. Developing highly sensitive and selective methods for Al3+ detection is of significant interest. In this work, we developed an excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) active fluorescent probe for ratiometric detection of Al3+ in aqueous medium and living cells. The BTZ-SF can detect Al3+ with high selectivity and a good linear relationship (R2 = 0.9911) between fluorescence intensity ratio (I476 nm/I568 nm) and Al3+ concentration (0–100 μM). In addition, the detection limit was calculated as low as 2.2 μM. The single crystal structure of BTZ-SF–Al clearly exhibited the interaction between BTZ-SF and Al3+ with a hexa-coordinated structure. Furthermore, confocal fluorescence images of HeLa cell indicated that BTZ-SF could be used for monitoring Al3+ in living cells. Finally, a test s...

Chelating properties of EDTA-type ligands containing six-membered backbone ring toward copper ion: Structure, EPR and TD-DFT evaluation

The P-APC ligands (EDTA-like aminopolycarboxylate ligands comprising 1,3-propanediamine backbone) H4pdta, H4pd3ap, H4pddadp and H4pdtp (H4pdta=1,3-propanediamine-N,N,N′,N′-tetraacetatic acid; H4pd3ap=1,3-propanediamine-N,N,N′-triacetic-N′-3-propionic acid; H4pddadp=1,3-propanediamine-N,N′-diacetatic-N,N′-di-3-propionic acid; H4pdtp=1,3-propanediaminetetra-3-propionic acid) were investigated. The chelating ligands coordinate to copper(II) via five or six donor atoms affording distorted trigonal-bipyramid and octahedral structures that were verified by X-ray analysis for Ba[Cu(pd3ap)]·6H2O (1) and trans(O6)-Ba[Cu(pddadp)]·8H2O (2) complexes respectively. The impact of counter-ions on the P-APC complexes is shown in detail together with the analysis of another strain parameters. EPR spectral results confirm the penta-coordination of 1 and hexa-coordination of 2 in aqueous solution, even if several Cu(II) species with different protonation degree exist as a function of pH, and indicate that a hexa-coordinated structure is favored when the two axial COO− donors close five-membered chelate rings. We also present here the results of molecular mechanics (LFMM) calculations based on our previously-developed force field along with results of DFT (Density Functional Theory). On the basis of extensive DFT and TD-DFT calculations the B1LYP/6-311++G(d,p) level has been seen as an accurate theory for calculating and predicting the UV–Vis spectra in case of copper–P-APC compounds.

Electronic and optical properties of beryllium carbide monolayer: First principles calculations

New quasi-planar hexacoordinate structure for Be2C monolayer is studied by the first principles calculations in the framework of the density functional theory. The obtained cohesive energy present a good structural stability for this compound. A direct band gap exist in Γ direction about 1.65 eV, so a semiconducting character is obtained. Optical interband transitions are investigated and described by joint density of states. The optical studies exhibit a transparent character for this compound by 2.5% reflectivity in the visible range of light. The obtained results suggest this material for nano-electronic devices and applications.

3‐(Pyridin‐2‐yl)imidazo[1,5‐a]pyridine (Pyridylindolizine) as Ligand in Complexes of Transition and Main‐Group Metals

AbstractThe coordination of the easily prepared 3‐(pyridin‐2‐yl)imidazo[1,5‐a]pyridine (pyridylindolizine, Py‐indz) ligand to several metal moieties was studied, and its electronic properties, similar to those of the classical ligands 2,2′‐bipyridine (bipy) and 1,10‐phenanthroline (phen), are reported. The new complexes were prepared and fully characterized by X‐ray crystallography and other typical spectroscopic methods if possible. Paramagnetic complexes [Ni(S2X)2(Py‐indz)] X = P(OEt)2 (1), COEt (2); [Ni(acac)2(Py‐indz)] (3, acac = acetylacetonate); [Ni(Py‐indz)3](PF6)2 (4); [Mn2Cl4(Py‐indz)2] (6); and [MnCl2(Py‐indz)2] (7) have the magnetic moment expected for a metallic cation with two or five unpaired electrons. Diamagnetic complexes show NMR spectra with similar patterns with small differences depending on the complex. [M{S2P(OEt)2}2 (Py‐indz)] M = Zn (8), Cd (9) have pentacoordinate and hexacoordinate structures, respectively. Octahedral tin complexes [SnL4(Py‐indz)] L4 = I4 (10), Cl3Ph (11), and Cl2nBu2 (12) have different behaviors in solution; whereas complex 10 is practically insoluble, complex 11 displays the expected pattern in its NMR spectrum, and complex 12 shows dynamic behavior. The Py‐indz ligand is also able to stabilize copper(I) and forms [Cu(PPh3)2(Py‐indz)]BF4 (13). The synthesis of the carbonyl complexes [MBr(CO)3(Py‐indz)] M = Mn (14), Re (15) and [Mo(CO)4(Py‐indz)] (16) was followed by IR spectroscopy in solution. [RuCl·p‐cym(Py‐indz)]PF6 (17, p‐cym = p‐cymene) has the familiar half‐sandwich “three‐legged piano‐stool” geometry.

Zinc and mercury complexes of benzil bis(4-methyl-3-thiosemicarbazone)

The ligand benzil bis(4-methyl-3-thiosemicarbazone), LMe2H4, reacts with zinc and mercury nitrates, both in the presence or in the absence of lithium hydroxide. Complexes containing a neutral or a doubly deprotonated ligand, depending on the reaction conditions, have been prepared. In all the complexes, the bis(thiosemicarbazone) acts as a N2S2 tetradentate ligand and in complex 4 probably also as a bridge through the sulfur atom leading to a dinuclear structure, while complex 3 is a monomer with a water molecule coordinated to the zinc atom in a penta-coordinated environment. Complexes 1 and 2 contain monodentate nitrato ligands in a hexa-coordinated structure, which is confirmed by the crystal structure of complex 2, [Hg(LMe2H4)(NO3)2]. The complexes have been thoroughly characterized by elemental analysis, mass spectrometry, FTIR and 1H, 13C and 199Hg NMR spectroscopy and in the case of complex 2, also by single crystal X-ray diffraction.

Chelation and Stereodynamic Equilibria in Neutral Hypercoordinate Organosilicon Complexes of 1-Hydroxy-2-pyridinone

A series of neutral organosilicon compounds, R3Si(OPO) (R = Me (1), Et (2), Ph (3)), cis-R2Si(OPO)2 (R = Me (4), Et (5), iPr (6), tBu (7), Ph (9)), (CH2)3Si(OPO)2 (8), and cis-R2Si(OPO)Cl (R = Me (10), Et (11)) (OPO = 1-oxo-2-pyridinone) have been prepared and fully characterized. X-ray crystallographic analyses show 1 to be tetracoordinate, 3, 7, and 10 to be pentacoordinate, and 4–6, 8, and 9 to be hexacoordinate. In the hexacoordinate structures, a mixture of diastereomers is observed in the form of C/N site disorder in each OPO ligand. Variable-temperature 13C and 29Si NMR studies indicate reversible Si←OC bond dissociation occurring in all pentacoordinate and hexacoordinate complexes to a varying degree with greater tendency toward dissociation in hydrogen-bonding donor solvents. Significant weakening of the dative Si←OC bond in 3 is observed in the cocrystallized adduct solvate 3·Ph3SiOH·1/2C5H12, providing structural evidence for the decrease in coordination number of the OPO ligand by hydrogen-bonding donors. In the hexacoordinate complexes, increasing steric bulk of ancillary ligands also was found to promote dissociation. 1H and 13C VT-NMR studies of 4, 6, 8, and 9 indicate stereoisomerization equilibria concurrent with Si←OC bond dissociation proposed to occur through trigonal-bipyramidal intermediates.

Monomeric and dimeric red/NIR-fluorescent dipyrrin–germanium complexes: facile monomer–dimer interconversion driven by acid/base additions

Highly coordinate germanium complexes of the N2O2-type tetradentate dipyrrin ligand have been synthesized. X-ray crystallographic analysis revealed the pentacoordinate structure of dimeric germanium complex 2 (=(Ge)2O) and the hexacoordinate structure of monomeric complex 3 (=Ge(OMe)(HOMe)). The dimer 2 was easily hydrolyzed in a solution to give monomer 4, though the corresponding siloxane (Si)2O did not react under the same conditions. The addition of DBU to a solution of 4 gave dimer 5, and neutralization by adding acetic acid regenerated the monomer 4, providing the facile and reversible interconversion between the monomer and dimer. The dipyrrin germanium complexes showed an intense absorption and fluorescence near the NIR region, which is more red-shifted than the silicon complexes.

Interaction Between Neuroglobin and Caffeine by Multispectroscopic Methods

ABSTRACT The interaction between neuroglobin (Ngb) and caffeine was studied by spectroscopy. UV-Vis spectra revealed that caffeine did not influence the native hexa-coordinated heme structure of neuroglobin. Fluorescence spectra indicated that caffeine could quench the intrinsic fluorescence of neuroglobin through static quenching mechanisms. The calculated thermodynamic parameters showed that the electrostatic force was the main intermolecular force in the reaction. Results also indicated that the microenvironmental changes of tryptophan and tyrosine residues within neuroglobin are inapparent. Furthermore, the circular dichroism (CD) spectra implied that caffeine could induce the formation of α-helix structure of neuroglobin.

Synthesis and characterization of a dipyridocatecholate silicon complex

The reaction of [Si(bpy) 2 I 2 ]I 2 with 1,10-phenanthroline-5,6-dione followed by metathesis provides various salts of [Si(bpy) 2 (dpcat)] + 2 ( 1 , bpy = 2,2′-bipyridine and dpcat = dipyridocatecholate). Recrystallization of [Si(bpy) 2 (dpcat)](ClO 4 ) 2 from an aqueous solution of NaClO 4 afforded orange crystals of Na[Si(bpy) 2 (dpcatH)](ClO 4 ) 4 ·3H 2 O ( 2 ), in which silicon possesses a distorted octahedral geometry. The dipyridocatecholate ligand is coordinated to the silicon through the oxygen atoms, and one of the nitrogen atoms is protonated. 29 Si NMR and ESI-mass spectroscopy indicate [Si(bpy) 2 (dpcat)] + 2 maintains its hexacoordinate structure in solution. The complex is stable with respect to hydrolysis, and degassed aqueous solutions luminesce at 410 nm. The reaction of [Si(bpy) 2 I 2 ]I 2 with 1,10-phenanthroline-5,6-dione followed by metathesis provides salts of [Si(bpy) 2 (dpcat)] +2 ( 1 , bpy = 2,2′-bipyridine and dpcat = dipyridocatecholate). Recrystallization of [Si(bpy) 2 (dpcat)](ClO 4 ) 2 from an aqueous solution of NaClO 4 afforded orange crystals of Na[Si(bpy) 2 (H-dpcat)](ClO 4 ) 4 ·3H 2 O ( 2 ), in which silicon possessed a distorted octahedral geometry. • The reaction of [Si(bpy) 2 I 2 ]I 2 with 1,10-phenanthroline-5,6-dione generates [Si(bpy) 2 (dpcat)]I 3 I. • The structure of Na[Si(bpy) 2 (H-dpcat)](ClO 4 ) 4 ·3H 2 O was obtained by X-ray crystallography. • Degassed aqueous solutions of [Si(bpy) 2 (dpcat)]Cl 2 luminesce around 410 nm. • Complex is designed to act as a metalloligand.

Preparation, Structure, and Properties of Tetranuclear Vanadium(III) and (IV) Complexes Bridged by Diphenyl Phosphate or Phosphate

Three novel tetranuclear vanadium(III) or (IV) complexes bridged by diphenyl phosphate or phosphate were prepared and their structures characterized by X-ray crystallography. The novel complexes are [{V(III)(2)(μ-hpnbpda)}(2){μ-(C(6)H(5)O)(2)PO(2)}(2)(μ-O)(2)]·6CH(3)OH (1), [{V(III)(2)(μ-tphpn)(μ-η(3)-HPO(4))}(2)(μ-η(4)-PO(4))](ClO(4))(3)·4.5H(2)O (2), and [{(V(IV)O)(2)(μ-tphpn)}(2)(μ-η(4)-PO(4))](ClO(4))(3)·H(2)O (3), where hpnbpda and tphpn are alkoxo-bridging dinucleating ligands. H(3)hpnbpda represents 2-hydroxypropane-1,3-diamino-N,N'-bis(2-pyridylmethyl)-N,N'-diacetic acid, and Htphpn represents N,N,N',N'-tetrakis(2-pyridylmethyl)-2-hydroxy-1,3-propanediamine. A dinuclear vanadium(IV) complex without a phosphate bridge, [(VO)(2)(μ-tphpn)(H(2)O)(2)](ClO(4))(3)·2H(2)O (4), was also prepared and structurally characterized for comparison. The vanadium(III) center in 1 adopts a hexacoordinate structure while that in 2 adopts a heptacoordinate structure. In 1, the two dinuclear vanadium(III) units bridged by the alkoxo group of hpnbpda are further linked by two diphenylphosphato and two oxo groups, resulting in a dimer-of-dimers. In 2, the two vanadium(III) units bridged by tphpn are further bridged by three phosphate ions with two different coordination modes. Complex 2 is oxidized in aerobic solution to yield complex 3, in which two of the three phosphate groups in 2 are substituted by oxo groups.

Antimicrobial, antifertility, and antiradiation studies of Ga(III) and Tl(I) complexes with N∩S and N∩O donor systems

New complexes of gallium(III) and thallium(I) derived from 5,6-dimethyl-1H-indol-2,3-dione hydrazinecarbothioamide (L1H) and 5,6-dimethyl-1H-indol-2,3-dione hydrazinecarboxamide (L2H) have been prepared and investigated using a combination of microanalytical analysis, melting point, molar conductance measurement, electronic, IR, 1H NMR, and 13C NMR spectral studies. Gallium isopropoxide interacts with the ligands in 1 : 1, 1 : 2, and 1 : 3 molar ratios resulting in the formation of colored products, whereas TlCl forms only unimolar products. The mono- and bis-alkoxy derivatives are dimeric, while the tris ligand metal complexes are monomeric. On the basis of conductance and spectral evidences, a pentacoordinate structure for gallium(III) 1 : 1 complexes, hexacoordinate structure for 1 : 2 and 1 : 3 complexes, and a bicoordinate geometry for thallium(I) complexes have been assigned. The ligands are coordinated to gallium(III) and thallium(I) via the azomethine nitrogen and the thiolic sulfur/enolic oxygen. The antimicrobial activities of the ligands and complexes have been screened in vitro against bacteria Pseudomonas cepacicola and Bacillus subtilis and fungi Collectatrichum capsici and Fusarium oxysporum. The complexes have higher activities than the free bases. In vivo studies of the ligands and their corresponding complexes have also been carried out to assess their antifertility and antiradiation activities. The results of these activities indicate the antiandrogenic and radiation protective nature of these complexes.

Differences in coordination states of substituted tyrosine residues and quaternary structures among hemoglobin M probed by resonance Raman spectroscopy

Among the four types of hemoglobin (Hb) M with a substitution of a tyrosine (Tyr) for either the proximal (F8) or distal (E7) histidine in the alpha or beta subunits, only Hb M Saskatoon (betaE7Tyr) assumes a hexacoordinate structure and its abnormal subunits can be reduced readily by methemoglobin (metHb) reductase. This is distinct from the other three M Hbs. To gain new insight into the cause of the difference, we examined the ionization states of E7 and F8 Tyrs by UV resonance Raman (RR) spectroscopy and Fe-O(Tyr) bonding by visible RR spectroscopy. Hb M Iwate (alphaF8Tyr), Hb M Boston (alphaE7Tyr), and Hb M Hyde Park (betaF8Tyr) exhibited two extra UV RR bands at 1,603 cm(-1) (Y8a') and 1,167 cm(-1) (Y9a') arising from deprotonated (ionized) Tyr, but Hb M Saskatoon displayed the UV RR bands of protonated (unionized) Tyr at 1,620 and 1,175 cm(-1) in addition to those of deprotonated Tyr. Evidence for the bonding of both ionization states of Tyr to the heme in Hb M Saskatoon was provided by visible RR spectroscopy. These results indicate that betaE7Tyr of Hb M Saskatoon is in equilibrium between protonated and deprotonated forms, which is responsible for facile reducibility. Comparison of the UV RR spectral features of metHb M with that of metHb A has revealed that metHb M Saskatoon and metHb M Hyde Park are in the R (relaxed) structure, similar to that of metHb A, whereas metHb M Iwate, metHb M Boston and metHb M Milwaukee are in the T (tense) quaternary structure.

Preparation and Characterization of some Divalent Metal Ion Complexes with Schiff Base Ligands Derived from Amino Acids

A new complexes of some transition metal ions (Co(II),Ni(II),Cu(II)) and some non transition metal ions (Zn(II),Cd(II)) with a number of Schiff bases obtained from the condensation of some amino acids (Methionine) and (3-acetyl pyridine, 4-acetyl pyridine, acetoacetaanilide) have been prepared. All the prepared complexes have been characterized by elemental analysis, molar conductance, magnetic susceptibility infrared and electronic spectral. The complexes were classified as: A-mononuclear complexes: Complexes with the formulas [ML(CH3COO) ] (H2O) ,[ML (H2O) ] and [ML(CH3COO) (H2O)2]. B-Di nuclear complexes: Complexes with the formulas [M2(L)2(CH3COO)2] .2H2O and [M2(L) (CH3COO)3] H2O and [M2(L) (CH3COO)2(H2O)] M= Co(II),Ni(II),Cu(II),Zn(II)Cd(II). L= 3-acetylpyridine Methionineimine, 4-acetylpyridine Methionineimine and acetoacetanilide Methionineimine. The physical measurements showed that the prepared complexes may have a tetra coordinated (tetrahedral or square planer) and hexa-coordinated (octahedral) structure and that all the prepared complexes were non electrolyte.

Preparations, Structures, and Properties of Sulfato-Bridged Dinuclear and Tetranuclear Vanadium(III) Complexes with a Dinucleating Ligand, 2-Oxo-N,N′-bis(2-pyridylmethyl)-1,3-propanediamine-N,N′-diacetate

Abstract New dinuclear and tetranuclear vanadium(III) complexes with sulfato bridge(s), [{VIII(H2O)}2(μ-hpnbpda)(μ-OH)(μ-SO4)]·5.25H2O (1) and [VIII4(μ-hpnbpda)2(μ-OH)2(μ-SO4)2]·12H2O (2), where hpnbpda is an alkoxo-bridging dinucleating ligand, 2-oxo-N,N′-bis(2-pyridylmethyl)-1,3-propanediamine-N,N′-diacetate, were prepared, and their structures were determined by X-ray crystallography. The vanadium(III) center in 1 adopts heptacoordinate structure while that in 2 has a hexacoordinate structure. In 2, the two dinuclear vanadium(III) units bridged by the alkoxo group of hpnbpda are further linked by two hydroxo and two sulfato bridging groups, resulting in a dimer-of-dimers structure. Measurement of the temperature dependence of the magnetic susceptibility of 1 revealed that the two vanadium(III) ions are antiferromagnetically coupled with J = −5.9 cm−1 and g = 1.90.

A QM/MM study on the aqueous solvation of the tetrahydroxouranylate [UO2(OH)4]2− complex ion

We report a QM augmented QM/MM study on the coordination of the tetrahydroxouranylate ion in aqueous solution. QM/MM geometry optimizations followed by full QM single-point calculations on the optimized structures show that a hexa-coordinated structure is more stable than the hepta-coordinated structure by 43 kJ/mol. Charge transfer of the tetrahydroxouranylate to the solvating water molecules is relatively modest, and can be modeled by including a solvation layer consisting of 12 explicit water molecules.