Equatorial Water Molecules Research Articles

Water in the crystal structure of NaBiO3-based phase: A spectroscopical insight

Water embedded in the crystal structure of a solid hydrate may affect the functional properties of the material. A decisive step towards understanding the role of water in the restricted geometry is to unravel the arrangement and dynamics of water molecules. The paper attacks this issue using the example of NaBiO3–based material containing at ambient conditions a mixture of dehydrated NaBiO3 and hydrated NaBiO3⋅nH2O phase, with the latter being predominant. Inelastic neutron scattering and infrared spectroscopy are applied to explore the vibrations of water molecules for the hydrated phase in the initial state and during the release of water upon heating that eventually leads to a complete transformation to the dehydrated phase. The major peaks in the infrared spectra were assigned, particularly with the help of deuteration. Dynamic interaction of structurally equivalent water molecules was revealed from the analysis of water bending modes in infrared and Raman spectra. The change in the conformation of water molecules is discussed, as well as the deformation of matrix bonds during sample dehydration.

Spectroscopic/Computational Characterization and the X-ray Structure of the Adduct of the VIVO-Picolinato Complex with RNase A.

The structure, stability, and enzymatic activity of the adduct formed upon the reaction of the V–picolinato (pic) complex [VIVO(pic)2(H2O)], with an octahedral geometry and the water ligand in cis to the V=O group, with the bovine pancreatic ribonuclease (RNase A) were studied. While electrospray ionization-mass spectrometry, circular dichroism, and ultraviolet–visible absorption spectroscopy substantiate the interaction between the metal moiety and RNase A, electron paramagnetic resonance (EPR) allows us to determine that a carboxylate group, stemming from Asp or Glu residues, and imidazole nitrogen from His residues are involved in the V binding at acidic and physiological pH, respectively. Crystallographic data demonstrate that the VIVO(pic)2 moiety coordinates the side chain of Glu111 of RNase A, by substituting the equatorial water molecule at acidic pH. Computational methods confirm that Glu111 is the most affine residue and interacts favorably with the OC-6-23-Δ enantiomer establishing an extended network of hydrogen bonds and van der Waals stabilizations. By increasing the pH around neutrality, with the deprotonation of histidine side chains, the binding of the V complex to His105 and His119 could occur, with that to His105 which should be preferred when compared to that to the catalytically important His119. The binding of the V compound affects the enzymatic activity of RNase A, but it does not alter its overall structure and stability.

Interaction of V(V) complexes formed by picolinic and pyrazinecarboxylic acid derivatives with red blood cells

The interaction with red blood cells (RBC) of vanadium(V) complexes formed by 3,5-difluoropicolinic acid (HpicFF), 3-hydroxypicolinic acid (H2hypic) and pyrazinecarboxylic acid (Hprz) has been examined. Electron Paramagnetic Resonance (EPR) spectroscopy results suggest that V(V) is reduced in all cases to V(IV) inside the erythrocytes. The thermodynamic stability of V(V) and corresponding V(IV) complexes has been related with the species detected in the cellular environment; when the ligands form unstable complexes with both VVO2+ and VIVO2+ ions (picFF and prz), the species formed inside RBC are similar to those observed when starting with vanadate(V) alone, that is VIVO2+ – formed upon V(V) reduction – which distributes among the cellular bioligands forming different types of complexes. When in the ligand molecule other groups able to form chelated complexes are present (H2hypic), more stable species are formed inside the RBC. The amount of complex able to enter the RBC depends on the ligand structure which could influence the metal uptake. The interaction of different VIVO2+ complexes formed by picolinate (picFF, pic = picolinate, picCN = 5-cyanopicolinate) and pyrazinecarboxylate (prz and przNH2 = 3-aminopyrazine-2-carboxylate) derivatives with hemoglobin (Hb), which is the main candidate to bind the VIVO2+ ion in the cytosol, was also investigated to rationalize the results. The ligands which form at physiological pH relatively stable complexes with VIVO2+ (przNH2 and pic) can give inside the erythrocytes mixed species after the replacement of an equatorial water molecule by an imidazole nitrogen of a histidine residue of the protein, while the ligands which form with VIVO2+ unstable complexes (picCN, picFF, prz) yield the same species observed in the binary system VIVO2+–Hb.

Magnetization Dynamics on Isotope‐Isomorphic Holmium Single‐Molecule Magnets

AbstractHere we reported the deuteration of the metal‐binding equatorial water molecules in a reported HoIII single‐molecule magnet (SMM) with pentagonal‐bipyramidal geometry, from [Ho(CyPh2PO)2(H2O)5]3+ to [Ho(CyPh2PO)2(D2O)5]3+. The hyperfine structures originating from the nuclear spin of 165HoIII can be clearly observed. Moreover, the resulting magnetization dynamics revealed the switch of the relative relaxation rates for the two isotope‐isomorphic complexes—respectively faster/slower at low/high temperature. The noticeable isotope effect arises from not only the paramagnetic metal center but also the diamagnetic ligands, which can be explained by the ab initio calculated tunnel splitting and the involvement of the super‐hyperfine interaction related to the difference in the nuclear spin number of protium (1H, I=1/2) and deuterium (2H, I=1).

Magnetization Dynamics on Isotope-Isomorphic Holmium Single-Molecule Magnets.

Here we reported the deuteration of the metal-binding equatorial water molecules in a reported HoIII single-molecule magnet (SMM) with pentagonal-bipyramidal geometry, from [Ho(CyPh2 PO)2 (H2 O)5 ]3+ to [Ho(CyPh2 PO)2 (D2 O)5 ]3+ . The hyperfine structures originating from the nuclear spin of 165 HoIII can be clearly observed. Moreover, the resulting magnetization dynamics revealed the switch of the relative relaxation rates for the two isotope-isomorphic complexes-respectively faster/slower at low/high temperature. The noticeable isotope effect arises from not only the paramagnetic metal center but also the diamagnetic ligands, which can be explained by the ab initio calculated tunnel splitting and the involvement of the super-hyperfine interaction related to the difference in the nuclear spin number of protium (1 H, I=1 /2 ) and deuterium (2 H, I=1).

The crystal structure of synthetic kenyaite, Na2Si20O40(OH)2·8H2O

A synthetic kenyaite sample possessing the chemical composition Na16[Si160O320(OH)16]·64H2O per unit cell was structurally analysed using X-ray powder data. The powder pattern was indexed based on space group symmetry Fdd2 (No. 43) with lattice parameters a0 ​= ​10.080(1) Å, b0 ​= ​79.383(8) Å, c0 ​= ​10.604(1) Å. The crystal structure was solved by model building based on the unit cell parameters, the results of a general characterisation of the material and the comparison with the closely related structures of RUB-6, Na-RUB-18 and magadiite. A Rietveld refinement of this structure model converged to residual values of χ2 ​= ​3.1, RF ​= ​0.020 and RBragg ​= ​0.025, confirming the structure model. Physico-chemical characterisation using solid-state NMR spectroscopy, SEM, TG-DTA, and DRIFT spectroscopy further confirmed the structure. The structure of kenyaite contains thick silicate layers with a thickness of 15.9 ​Å (ignoring the van der Waals radii of the terminal oxygen atoms). The dense layers possess the same topology as the layers of RUB-6, exhibit no porosity and have a silicon Q4 to Q3 ratio of 4.0. 16 out of 32 terminal silanol groups are protonated while 16 siloxy groups (≡Si–O–) compensate the charge of the sodium cations. RUB-6 and kenyaite differ, however, with respect to the cation intercalated and to the stacking arrangement of layers. Bands of edge-sharing [Na(H2O)6/1.5] octahedra are intercalated between the silicate layers extending along [110] and [1¯10]. The equatorial water molecules of the octahedra are hydrogen bonded to terminal silanol groups with O⋯O distances of 2.5 ​Å to 2.6 ​Å. The structure of kenyaite is slightly disordered typical for hydrous layer silicates which possess only weak interactions between neighbouring silicate layers. In this respect, the result of the structure refinement represents a somewhat idealised structure. The structure analysis also revealed the presence of strong intra-layer hydrogen bonds (d(O⋯O) ≈ 2.5 ​Å) between the terminal O atoms (silanol/siloxy groups) confirmed by 1H MAS NMR spectroscopy. The surface zone of the silicate layers as well as the inter-layer region containing the edge-sharing [Na(H2O)6/1.5] octahedra are closely related to the structures of Na-RUB-18 and magadiite.

Crystal structure, Hirshfeld surface analysis, DFT and TD-DFT studies of nickel(II) monohydrate complex coordinated by bis (5-bromo-1- formyl phenolate) moiety and two water molecules

In the title compound [Ni(C 7 H 5 O 2 Br) 2 (H 2 O) 2 ]H 2 O, the Ni atom adopts distorted octahedral geometry in which the bidentate ligand acts as O,O’ donor defining an equatorial plane and water molecules occupy the axial positions. It is a mononuclear compound. This compound was crystallized on the monoclinic system, space group P2 1 /c with the unit cell parameters a = 18.4561(8) Å, b = 7.3442(4) Å,c = 14.5786(8)Å, a = 90°, b = 109.057°, γ = 90° and Z = 4. The two hydroxyl groups are deprotonated and oxygen anions get coordinated with nickel. The supramolecular self assembly of the complex is also stabilized by weak non-covalent interactions in the crystal packing, which is further quantified by using Hirshfeld surface analysis. The molecular architecture of the complex is examined by quantum chemical calculations using DFT and is compared with crystalline structure of the same. The electronic excitation energies of the complex has been simulated at TD-DFT level and are evaluated with experimental electronic spectrum.

Coordination Dynamics of Zinc Triggers the Rate Determining Proton Transfer in Human Carbonic Anhydrase II.

We present, for the first time, how transient changes in the coordination number of zinc ion affects the rate determining step in the enzyme human carbonic anhydrase (HCA) II. The latter involves an intramolecular proton transfer between a zinc-bound water and a distant histidine residue (His-64). In the absence of time-resolved experiments, results from classical and QM-MM molecular dynamics and transition path sampling simulations are presented. The catalytic zinc ion is found to be present in two possible coordination states; viz. a stable tetra-coordinated state, T and a less stable penta-coordinated state, P with tetrahedral and trigonal bipyramidal coordination geometries, respectively. A fast dynamical inter-conversion occurs between T and P due to reorganization of active site water molecules making the zinc ion more positively charged in state P. When initiated from different coordination environments, the most probable mechanism of proton transfer is found to be deprotonation of the equatorial water molecule from state P and transfer of the excess proton via a short path formed by hydrogen bonded network of active site water molecules. We estimate the rate constant of proton transfer as from P and from T. A quantitative match of estimated kP with the experimental value, ( ) suggests that dynamics of Zn coordination triggers the rate determining proton transfer step in HCA II.

Synthesis, crystal structure, phosphate hydrolysis activity and antibacterial activity of macrocyclic dinuclear Zn(II) complex with benzyl pendant-arms

A new macrocyclic dinuclear Zn(II) complex is synthesized by the cyclocondensation between 3,3’-(ethane-1,2-diylbis (benzylazanediyl))bis(methylene) bis (2-hydroxy-5-methyl-benzaldehyde) and 1,3-diaminopropane and the subsequent with zinc salts. The as-prepared complex is characterized by elemental analysis, FT-IR, ES-MS and single crystal X-ray diffraction. The complex consists of one independent molecular unit of [Zn2(μ-OAC)L]+ ClO4− and two water molecules with one on a symmetry element. Four of these units collectively form two pairs of dinuclear complex units of [Zn2(μ-OAc)L]+ with one unit sharing two perchlorate ions and one water molecule and the other unit sharing two perchlorate ions and one symmetry equivalent water molecule. Each zinc(II) ion exhibits a slightly distorted square pyramidal geometry. Two Zn atoms are bridged by two oxygen atoms of an acetate anion and two phenolic O atoms. The Zn–Zn distance is 2.951 Å. An ordered two-dimensional network is formed by weak intermolecular interactions in the crystal structure of the complex. The phosphate ester hydrolysis activity and the antibacterial activity of the complex are studied. The results showed that the synthesized complex has an efficient catalytic activity of phosphoester bond cleavage and the potential to inhibit the growth of E. coli. The optimum catalytic rate constant (kcat) at pH 7.8 for the hydrolysis of 4-nitrophenyl phosphate disodium salt hexahydrate (pNPP) by the synthesized complex is 2.98 × 10−4 s−1, and 105 times faster than that the spontaneous hydrolysis of the phosphate monoester.

High-Pressure Crystallographic and Magnetic Studies of Pseudo-D5h Symmetric Dy(III) and Ho(III) Single-Molecule Magnets.

Single-ion magnets based on lanthanide ions in pseudo-D5h symmetry have gained much attention in recent years as they are reported to possess a large blocking temperature and a large barrier for magnetization reversal. Magneto-structural correlations reveal that the axial O-Ln-O angle is an important parameter to control the barrier, and while it can be fine-tuned by chemical modification, an alternative would be to utilize hydrostatic pressure. Herein, we report the crystal structures and static magnetic properties of two air-stable isostructural lanthanide SIMs under applied pressures. The complexes exhibit pseudo-D5h symmetry around the Ln(III)-ion (Ln = Dy or Ho), which coordinates to five equatorial water molecules and two large neutral phosphonic diamide ligands along the axial direction. High-pressure single-crystal X-ray diffraction experiments revealed two phase-transitions and an increasing deviation from D5h-symmetry between ambient pressure and 3.6 GPa. High-pressure direct-current magnetic measurements of the Dy(III) compound showed large steps in the hysteresis loops near zero field, indicative of quantum tunneling of magnetization (QTM). These steps grow in size with increasing pressure, suggesting that QTM becomes progressively more active, which correlates well with the pressure-induced increased overall deviation from pseudo-D5h symmetry and decreasing axial O-Dy-O angle. A strong temperature dependence of the step size is seen at 0.3 GPa, which shows that the SMM character persists even at this pressure. To understand the origin of significant variation in the tunneling probability upon pressure, we performed a range of ab initio calculations based on the CASSCF/RASSI-SO/SINGLE_ANISO method on both Dy and Ho complexes. From the energies and magnetic anisotropy of the mJ sublevels, we find a complex variation of the energy barrier with pressure, and using a constructed geometrical parameter, R, taking into account changes in both bond angles and distances, we link the magnetic properties to the first coordination sphere of the molecules.

Electronic Structure and Chemical Bonding of [AmO2(H2O) n ]2+/1.

Systematic americyl-hydration cations were investigated theoretically to understand the electronic structures and bonding in [(AmO2)(H2O)n]2+/1+ (n = 1–6). We obtained the binding energy using density functional theory methods with scalar relativistic and spin–orbit coupling effects. The geometric structures of these species have been investigated in aqueous solution via an implicit solvation model. Computational results reveal that the complexes of five equatorial water molecules coordinated to americyl ions are the most stable due to the enhanced ionic interactions between the AmO22+/1+ cation and multiple oxygen atoms as electron donors. As expected, Am–Owater bonds in such series are electrostatic in nature and contain a generally decreasing covalent character when hydration number increases.

Unexpected Binding Mode of a Potent Indeno[1,2-b]indole-Type Inhibitor of Protein Kinase CK2 Revealed by Complex Structures with the Catalytic Subunit CK2α and Its Paralog CK2α′

Protein kinase CK2, a member of the eukaryotic protein kinase superfamily, is associated with cancer and other human pathologies and thus an attractive drug target. The indeno[1,2-b]indole scaffold is a novel lead structure to develop ATP-competitive CK2 inhibitors. Some indeno[1,2-b]indole-based CK2 inhibitors additionally obstruct ABCG2, an ABC half transporter overexpressed in breast cancer and co-responsible for drug efflux and resistance. Comprehensive derivatization studies revealed substitutions of the indeno[1,2-b]indole framework that boost either the CK2 or the ABCG2 selectivity or even support the dual inhibition potential. The best indeno[1,2-b]indole-based CK2 inhibitor described yet (IC50 = 25 nM) is 5-isopropyl-4-(3-methylbut-2-enyl-oxy)-5,6,7,8-tetrahydroindeno[1,2-b]indole-9,10-dione (4p). Herein, we demonstrate the membrane permeability of 4p and describe co-crystal structures of 4p with CK2α and CK2α′, the paralogs of human CK2 catalytic subunit. As expected, 4p occupies the narrow, hydrophobic ATP site of CK2α/CK2α′, but surprisingly with a unique orientation: its hydrophobic substituents point towards the solvent while its two oxo groups are hydrogen-bonded to a hidden water molecule. An equivalent water molecule was found in many CK2α structures, but never as a critical mediator of ligand binding. This unexpected binding mode is independent of the interdomain hinge/helix αD region conformation and of the salt content in the crystallization medium.

Kinetics and mechanism of the formation of CoIII(salen-type) complexes containing a nonstabilized pyridinium ylide as axial ligand: Computational and experimental studies

The reaction of [CoIII(4,4′dmsalen)(CH2Cl)(L)], where 4,4′dmsalen = 4,4′-dimethylsalen and L = solvent, with pyridine led to the isolation of [CoIII(4,4′dmsalen)(CH2py)(Cl)], in a two-step process involving a metallacyclized intermediate, cis β [CoIII(4,4′dmsalenCH2)(py)(L)]+, whereas a parallel direct conversion through the displacement of a Cl atom from the axial CH2Cl group of [CoIII(4,4′dmsalen)(CH2Cl)(L)] may be ruled out. Natural bond orbital analysis of the structures show that the ylide carbon atom has lower orbital occupancies in the cyclized complex, thus making it more susceptible to a nucleophilic attack of pyridine. The calculated potential energy surfaces indicate that the most energy feasible reaction path would be for the complex [CoIII(4,4′dmsalenCH2)(py)ax(H2O)]+, with an entering pyridine molecule and a leaving equatorial water molecule. Experimental kinetic studies of the formation of the ylide complex starting from [CoIII(4,4′dmsalenCH2)(py)eq(H2O)]+ strongly suggest that it is possible to obtain the ylide complex through an alternative, less energetically favourable path.

The new one-dimensional coordination polymer catena-poly[[diaquasodium(I)]-μ-oxalato-[diaquairon(III)]-μ-oxalato

The oxalate dianion is one of the most studied ligands and is capable of bridging two or more metal centres and creating inorganic polymers based on the assembly of metal polyhedra with a wide variety of one-, two- or three-dimensional extended structures. Yellow single crystals of a new mixed-metal oxalate, namely catena-poly[[diaquasodium(I)]-μ-oxalato-κ(4)O(1),O(2):O(1'),O(2')-[diaquairon(III)]-μ-oxalato-κ(4)O(1),O(2):O(1'),O(2')], [NaFe(C2O4)2(H2O)4]n, have been synthesized and the crystal structure elucidated by X-ray diffraction analysis. The compound crystallizes in the noncentrosymmetric space group I41 (Z = 4). The asymmetric unit contains one Na(I) and one Fe(III) atom lying on a fourfold symmetry axis, one μ2-bridging oxalate ligand and two aqua ligands. Each metal atom is surrounded by two chelating oxalate ligands and two equivalent water molecules. The structure consists of infinite one-dimensional chains of alternating FeO4(H2OW1)2 and NaO4(H2OW2)2 octahedra, bridged by oxalate ligands, parallel to the [100] and [010] directions, respectively. Because of the cis configuration and the μ2-coordination mode of the oxalate ligands, the chains run in a zigzag manner. This arrangement facilitates the formation of hydrogen bonds between neighbouring chains involving the H2O and oxalate ligands, leading to a two-dimensional framework. The structure of this new one-dimensional coordination polymer is shown to be unique among the A(I)M(III)(C2O4)2(H2O)n series. In addition, the absorption bands in the IR and UV-Visible regions and their assignments are in good agreement with the local symmetry of the oxalate ligand and the irregular environment of iron(III). The final product of the thermal decomposition of this precursor is the well-known ternary oxide NaFeO2.

Vibrational spectra of Cs2Cu(SO4)2·6H2O and Cs2Cu(SeO4)2·nH2O (n = 4, 6) with a crystal structure determination of the Tutton salt Cs2Cu(SeO4)2·6H2O

The solubility in the three-component systems Cs2SO4–CuSO4–H2O and Cs2SeO4–CuSeO4–H2O have been studied at 25 °C. The experimental results show that double salts, Cs2Cu(SO4)2·6H2O and Cs2Cu(SeO4)2·4H2O, crystallize from the ternary solutions within large concentration ranges. Crystals of Cs2Cu(SeO4)2·6H2O were synthesized at somewhat lower temperatures (7–8 °C). The thermal dehydration of the title compounds was studied by TG, DTA and DSC methods and the respective dehydration schemes are proposed. The calculated enthalpies of dehydration (ΔHdeh) have values of: 434.2 kJ mol−1 (Cs2Cu(SeO4)2·6H2O), 280.9 kJ mol−1 (Cs2Cu(SeO4)2·4H2O), and 420.2 kJ mol−1 (the phase transition of Cs2Cu(SO4)2·6H2O into Cs2Cu(SO4)2·H2O).The crystal structure of Cs2Cu(SeO4)2⋅6H2O was determined from single crystal X-ray diffraction data. It belongs to the group of Tutton salts, crystallizing isotypic to the respective sulfate in a monoclinic structure which is characterized by isolated Cu(H2O)6 octahedra and SeO4 tetrahedra, interlinked by hydrogen bonds and [9]-coordinated Cs+ cations.Infrared spectra of the cesium copper compounds are presented and discussed with respect to both the normal modes of the tetrahedral ions and the water molecules. The analysis of the infrared spectra of the double compounds reveals that the distortion of the selenate tetrahedra in Cs2Cu(SeO4)2·4H2O is stronger than those in Cs2Cu(SeO4)2·6H2O in agreement with the structural data. Matrix-infrared spectroscopy was applied to confirm this claim − Δν3 for SO42− ions matrix-isolated in Cs2Cu(SeO4)2·6H2O has a value of 35 cm−1 and that of the same ions included in Cs2Cu(SeO4)2·4H2O – 84 cm−1. This spectroscopic finding is due to the formation of strong covalent bands Cu–OSO3 on one hand, and on the other to the stronger deformation of the host SeO42− tetrahedra in Cs2Cu(SeO4)2·4H2O as compared to those in Cs2Cu(SeO4)2·6H2O.The strength of the hydrogen bonds as deduced from the frequencies of νOD of matrix-isolated HDO molecules (spectral range of 2500−2200 cm−1) is discussed. An interesting feature of the spectra is the appearance of two groups of infrared bands corresponding to νOD, which are separated with 71 cm−1 (sulfate compound) and about 120 cm−1 (selenate compounds) due to the existence of two types of water molecules − those coordinated to the copper ions via shorter Cu–OH2 bonds and those coordinated to the copper ions via longer Cu–OH2 bonds. The spectroscopic experiments reveal that the equatorial water molecules in the hexahydrates exhibit a local molecular symmetry close to C2v (at least at ambient temperature), while those forming long Cu–OH2 bonds are strongly asymmetrically hydrogen bonded. The differences in the wavenumbers of the bands corresponding to the wagging modes have values larger than 100 cm−1, thus indicating strong distortions of the coordination sphere of the copper ions due to the Jahn–Teller effect.

X-ray diffraction refinement of the structure of diaquadinitratouranyl tetrahydrate [UO2(NO3)2(H2O)2] • 4H2O

Single crystals of diaquadinitratouranyl tetrahydrate [UO2(NO3)2(H2O)2] • 4H2O (I) have been synthesized by evaporating an aqueous [UO2(NO3)2(H2O)2] • 2H2O solution containing nitric acid under air at room temperature. An experimental X-ray diffraction intensity set has been obtained from a single crystal of I. Crystals are ortorhombic, a = 13.113(2) A, b = 7.9847(12) A, c = 11.3323(17) A, space group Cmc21, Z = 4, V = 1186.5(3) A3. The structural units of a crystal of complex I are neutral molecular complexes [UO2(NO3)2(H2O)2] and crystal water molecules linked by a network of hydrogen bonds. The uranium atom is in a hexagonal bipyramidal surrounding. Axial positions are occupied by uranyl oxygen atoms, and two nonequivalent bidentate cyclic nitrato groups and two equivalent water molecules are coordinated in the equatorial plane in trans-positions to each other. Coordinated and outer-sphere water molecules in the molecular structure of complex I are linked by hydrogen bonds as O-H(H2Ocoord)⋯O(H2Oout). Outer-sphere water molecules are linked to each other and the terminal oxygen atoms of nitrato groups by hydrogen bonds as O-H(H2Oout)⋯O(H2Oout) and O-H(H2Oout)⋯O(ONO2-). Hydrogen bonds of the first type are stronger than those of the second and third types.

Molecular structure, bonding analysis and redox properties of transition metal–Hapca [bis(3-aminopyrazine-2-carboxylic acid)] complexes: A theoretical study

Density functional theory (DFT) calculations were carried out on M(Hapca)2(H2O)2 (M=Mn, Fe, Co, Ni and Hapca=bis(3-aminopyrazine-2-carboxylic acid) by means of the BP86 and B3LYP functional using the TZP basis set. The optimized structures were obtained by imposing C2 or Ci symmetries. The Ci structural arrangement consists of a slightly distorted octahedron centered by a transition-metal with bidentate Hapca ligands situated in equatorial positions and water molecules in axial ones. However, the C2 structure consists of a distorted arrangement with n con-planar Hapca ligands. The influence induced by including double polarized functions in the (TZ2P) basis set is small on the geometrical parameters. A bonding analysis of these species showed the weakness of M–O(H2O) bonds compared to M–O(Hapca) ones. The obtained MO diagrams showed substantial HOMO–LUMO gaps for the 18-MVE closed-shell configuration. Reduction of M(Hapca)2(H2O)2 led to the loss of the two water molecules, inducing four electrons downwards for [Co]− and [Ni] species. The calculated ionization potentials (IPs) and electronic affinities (EAs) showed the oxidation and reduction ease of the manganese species contrarily to the cobalt ones. A diffuse function in the basis set (QZ3P-ndiffuse, n=1 or 2) reduces remarkably the adiabatic electron affinities (AEAs).

Anion binding to a tetracopper resorcinarene-based complex

UV–vis and electron paramagnetic resonance (EPR) spectroscopic studies have been carried out on the multinuclear copper(II) complex Cu4BpaRes. The copper atoms are in a tetragonal distorted geometry with nitrogens from bispicolylamine (Bpa) coordinating in the equatorial plane and water molecules or anions completing four coordination sites. The interaction of anions with this polynuclear copper complex in aqueous solution supports the formation of different complex species, which depend on the type and the concentration of the anions. In the presence of excess anions, frozen solution EPR parameters show the formation of species in which the in-plane coordination is characterised by the presence of three nitrogen atoms coming from the ligand and a donor atom from the specific anion. For the bidentate anion ligands and especially for malonate, UV–vis titrations indicate the formation of a 1:4 (Cu4BpaRes:anion) species. EPR experiments support the formation of such a species and indicate that the four copper centres are equivalent and reach penta-coordination via the coordination of both oxygens from the bidentate ligand.

Magnetic properties of isostructural M(H2O)4[Au(CN)4]2-based coordination polymers (M = Mn, Co, Ni, Cu, Zn) by SQUID and μSR studies

A series of isomorphous M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Mn, Co, Ni, Zn; Cu is similar) coordination polymers was synthesized from the reaction of M(II) with KAu(CN)(4); they consist of octahedrally coordinated metal centres with four equatorial water molecules and trans-axial N-cyano ligands from [Au(CN)(4)](-) moieties, generating a linear 1-D chain of M(H(2)O)(4)[Au(CN)(4)]-units. An additional interstitial [Au(CN)(4)](-) unit forms AuN and hydrogen bonds with adjacent chains. The Cu(II) system readily loses water to yield Cu[Au(CN)(4)](2)(H(2)O)(4), which was not structurally characterized. The magnetic properties of these polymers were investigated by a combination of SQUID magnetometry and zero-field muon spin relaxation (ZF-μSR). Only weak antiferromagnetic interactions along the chains are mediated by the [Au(CN)(4)]-units, but the ZF-μSR data indicates that interchain interactions yield a phase transition to a magnetically ordered state for Cu[Au(CN)(4)](2)(H(2)O)(4) below 0.6 K, while for M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Co), depopulation of zero-field split Kramer's doublets to an effective "S = 1/2" ground state yields a transition to a spin-frozen magnetic state below 0.26 K. On the other hand, only a simple slowing-down of spins above 0.02 K is observed for the more weakly zero-field split M(H(2)O)(4)[Au(CN)(4)](2)·4H(2)O (M = Mn, Ni) complexes.

Tris(1,10-phenanthroline-κ2N,N′)cadmium(II) bis(perchlorate) 3.5-hydrate: a water chain stabilized by perchlorate anions

The title compound, [Cd(C(12)H(8)N(2))(3)](ClO(4))(2).3.5H(2)O, contains a cross-shaped one-dimensional channel along the c axis which encapsulates an ordered water chain. This water chain features a centrosymmetric cyclic water hexamer unit with a chair-like conformation. Neighbouring hexamers are linked by bridging water molecules. The host perchlorate anions recognize and stabilize the guest water chain via three kinds of hydrogen-bond patterns, leading to the formation of a complex one-dimensional {[(H(2)O)(7)(ClO(4))(4)](4-)}(n) anionic chain. One perchlorate acts as a single hydrogen-bond acceptor dangling on the chain, the second perchlorate on the chain serves as a double hydrogen-bond acceptor for only one water molecule to form an R(2)(2)(6) ring, where both entities lie on a twofold axis, while the third perchlorate, which also lies on a twofold axis, accepts two hydrogen bonds from two equivalent water molecules and is involved in the construction of an R(6)(5)(14) ring.