H2O Ligands Research Articles

PH-Dependent Transfer Hydrogenation, Reductive Amination, and Dehalogenation of Water-Soluble Carbonyl Compounds and Alkyl Halides Promoted by Cp*Ir Complexes

This paper reports pH-dependent transfer hydrogenation, reductive amination, and dehalogenation of water-soluble substrates with the organometallic aqua complexes [Cp*IrIII(H2O)3]2+ (1, Cp* = η5-pentamethylcyclopentadienyl), [(Cp∧py)IrIII(H2O)2]2+ (2, Cp∧py = η5-(tetramethylcyclopentadienyl)methylpyridine), and [Cp*IrIII(bpy)(H2O)]2+ (3, bpy = 2,2‘-bipyridine) as catalyst precursors and the formate ions HCOONa and HCOONH4 as hydrogen donors. Because of the difference in the electron-donating ability of the Cp*, Cp∧py, and bpy ligands, the Lewis acidity of the iridium ions of 1−3 are ordered in strength as follows: 1 > 2 > 3. Complexes 1−3 are reversibly deprotonated to form the catalytically inactive hydroxo complexes [(Cp*IrIII)2(μ-OH)3]+ (5), [{(Cp∧py)IrIII}2(μ-OH)2]2+ (6), and [Cp*IrIII(bpy)(OH)]+ (7) around pH 2.8, 4.5, and 6.6, respectively. The deprotonation behavior of 1−3 indicates that the more Lewis acidic iridium ions would lower the pKa values of the coordinated H2O ligands. As a function of ...

Electronic properties of hard and soft ions in solution: Aqueous Na+ and Ag+ compared

The electronic structure of model aqueous solutions of Na+ and Ag+ is investigated using ab initio molecular-dynamics methods. We compute a number of electronic response coefficients in solution, such as global hardness and nuclear Fukui functions. The nuclear Fukui functions are found to be particularly sensitive to the chemical nature of the component species giving for Ag+ a susceptibility 3.5 times the value for a H2O molecule while the result for Na+ is more than a factor of 4 smaller compared to a solvent molecule. The electronic structure of the solution is further characterized by construction of effective molecular orbitals and energies. This analysis reveals that the effective highest occupied molecular orbital (HOMO) of the hard cation, Na+, remains buried in the valence bands of the solvent, whereas the HOMO of Ag+ is found to mix with the lone pair electrons of its four ligand H2O molecules to form the (global) HOMO of the solution. This observation, highlighting the importance of the electronic structure of the solvent, is used to rationalize the results for the electronic response.

Water penetration and binding to ferric myoglobin.

Flash photolysis investigations of horse heart metmyoglobin bound with NO (Mb(3+)NO) reveal the kinetics of water entry and binding to the heme iron. Photodissociation of NO leaves the sample in the dehydrated Mb(3+) (5-coordinate) state. After NO photolysis and escape, a water molecule enters the heme pocket and binds to the heme iron, forming the 6-coordinate aquometMb state (Mb(3+)H2O). At longer times, NO displaces the H2O ligand to reestablish equilibrium. At 293 K, we determine a value k(w) approximately 5.7 x 10(6) s(-1) for the rate of H2O binding and estimate the H2O dissociation constant as 60 mM. The Arrhenius barrier height H(w) = 42 +/- 3 kJ/mol determined for H2O binding is identical to the barrier for CO escape after photolysis of Mb(2+)CO, within experimental uncertainty, consistent with a common mechanism for entry and exit of small molecules from the heme pocket. We propose that both processes are gated by displacement of His-64 from the heme pocket. We also observe that the bimolecular NO rebinding rate is enhanced by 3 orders of magnitude both for the H64L mutant, which does not bind water, and for the H64G mutant, where the bound water is no longer stabilized by hydrogen bonding with His-64. These results emphasize the importance of the hydrogen bond in stabilizing H2O binding and thus preventing NO scavenging by ferric heme proteins at physiological NO concentrations.

Phase Transitions and Water Dynamics of [Co(H2O)6](ClO4)2 and [Mn(H2O)6](BF4)2 Studied by Neutron Scattering Methods

Abstract Inelastic incoherent neutron scattering (IINS) spectra and neutron powder diffraction (NPD) patterns, registered for [Co(H2O)6](ClO4)2 at 18 -270 K and for [Mn(H2O)6](BF4)2 at 18 -230 K, provided evidence that these crystals possess three solid phases in these ranges of temperatures. In both compounds the phase transition occurring at TC3 is connected with a change of the crystal structure, and that occurring at TC2 with a change in the rate of the reorientational motions of H2O ligands.

Single-molecule magnets: Jahn-Teller isomerism and the origin of two magnetization relaxation processes in Mn12 complexes.

Several single-molecule magnets with the composition [Mn12O12(O2CR)16(H2O)x] (x = 3 or 4) exhibit two out-of-phase ac magnetic susceptibility signals, one in the 4-7 K region and the other in the 2-3 K region. New Mn12 complexes were prepared and structurally characterized, and the origin of the two magnetization relaxation processes was systematically examined. Different crystallographic forms of a Mn12 complex with a given R substituent exist where the two forms have different compositions of solvent molecules of crystallization and this results in two different arrangements of bound H2O and carboxylate ligands for the two crystallographically different forms with the same R substituent. The X-ray structure of cubic crystals of [Mn12O12(O2CEt)16(H2O)3]. 4H2O (space group P1) (complex 2a) has been reported previously. The more prevalent needle-form of [Mn12O12(O2CEt)16(H2O)3] (complex 2b) crystallizes in the monoclinic space group P2(1)/c, which at -170 degrees C has a = 16.462(7) A, b = 22.401(9) A, c = 20.766(9) A, beta = 103.85(2) degrees, and Z = 4. The arrangements of H2O and carboxylate ligands on the Mn12 molecule are different in the two crystal forms. The complex [Mn12O12-(O2)CC6H4-p-Cl)16(H2O)4].8CH2Cl2 (5) crystallizes in the monoclinic space group C2/c, which at -172 degrees C has a = 29.697(9) A, b = 17.708(4) A, c = 30.204(8) A, beta = 102.12(2) degrees, and Z = 4. The ac susceptibility data for complex 5 show that it has out-of-phase signals in both the 2-3 K and the 4-7 K ranges. X-ray structures are also reported for two isomeric forms of the p-methylbenzoate complex. [Mn12O12(O2CC6H4-p-Me)16(H2O)4]. (HO2CC6H4-p-Me) (6) crystallizes in the monoclinic space group C2/c, which at 193 K has a = 40.4589(5) A, b = 18.2288(2) A, c = 26.5882(4) A, beta = 125.8359(2) degrees, and Z = 4. [Mn12O12(O2CC6H4-p-Me)16(H2O)4].3(H2O) (7) crystallizes in the monoclinic space group I2/a, which at 223 K has a = 29.2794(4) A, b = 32.2371(4) A, c = 29.8738(6) A, beta = 99.2650(10) degrees, and Z = 8. The Mn12 molecules in complexes 6 and 7 differ in their arrangements of the four bound H2O ligands. Complex 6 exhibits an out-of-phase ac peak (chi(M)' ') in the 2-3 K region, whereas the hydrate complex 7 has a chi(M)' ' signal in the 4-7 K region. In addition, however, in complex 6, one Mn(III) ion has an abnormal Jahn-Teller distortion axis oriented at an oxide ion, and thus 6 and 7 are Jahn-Teller isomers. This reduces the symmetry of the core of complex 6 compared with complex 7. Thus, complex 6 likely has a larger tunneling matrix element and this explains why this complex shows a chi(M)' ' signal in the 2-3 K region, whereas complex 7 has its chi(M)' ' peak in the 4-7 K region, i.e., the rate of tunneling of magnetization is greater in complex 6 than complex 7. Detailed 1H NMR experiments (2-D COSY and TOCSY) lead to the assignment of all proton resonances for the benzoate and p-methyl-benzoate Mn12 complexes and confirm the structural integrity of the (Mn12O12) complexes upon dissolution. In solution there is rapid ligand exchange and no evidence for the different isomeric forms of Mn12 complexes seen in the solid state.

The crystal structure of nesquehonite, MgCO 3 · 3H 2 O, from Lavrion, Greece

Nesquehonite, MgCO3 · 3H2O, has been observed from Sounion, Lavrion mining district, Greece as a late alteration product in crystals up to 4 mm in size. The structure was refined in P21/n, Z = 4, to R = 0.032 using CCD X-ray single-crystal data of a twinned specimen showing orthorhombic pseudosymmetry. The precise cell parameters a = 7.701(1) A, b = 5.365(1) A, c = 12.126(2) A, β = 90.41(1)°, and V = 501.0(1) A3 were obtained from a Rietveld refinement of high resolution X-ray powder data with a calculated density of 1.835 gcm−3. The atomic coordinates of the Mg, C and O atoms are in accordance to published data, the hydrogen bond system, however, could now be established on the basis of experimentally determined H positions. The structure of nesquehonite is characterized by infinite chains along [010], formed by cornersharing MgO6 octahedra. Within the chains, CO3 groups link three MgO6 octahedra by two common corners and one edge, which causes strong distortions of the involved polyhedra. These chains are interconnected via hydrogen bonds only: each Mg atom is coordinated by two H2O ligands, and one free water molecule is situated between the chains. Mean bond lengths are 2.076 A for Mg-O and 1.283 A for C–O, the aplanarity of the carboate group is 0.025(3) A Of the six hydrogen bonds, five are usual ones with O–H⋯O from 2.738(2) A to 2.820(2) A the sixth one is found to be bifurcated.

Synthesis and reaction of the novel complex [AsPh4][OsCl5(H2O). X-ray structure analysis of [AsPh4][OsCl5(H2O)].2EtOH and [AsPh4][OsCl5(EtOH)].EtOH.

The synthesis and characterization of the anionic mononuclear and homobinuclear osmium complexes [AsPh4][OsCl5L].xEtOH [L = H2O, x = 2 (9); L = EtOH, x = 1 (10a); L = py, x = 0 (10b)] and [AsPh4]2[Cl5Os(pyz)OsCl5] (12) (pyz = pyrazine) are described. Upon reduction in a chloride-containing medium, OsO4 (1) affords the osmium(IV) species [OsCl5(H2O)]- (2), which could be isolated by extraction with n-tributyl phosphate (TBP). Complex 9 is the first fully characterized chloroaquo complex of Os(IV). This complex is an effective starting material for the preparation of novel species, such as 10a, 10b, and 12. The X-ray structures of 9 and 10a were determined. Both compounds crystallize in the monoclinic space group P2(1)/n. 9: C28H34AsCl5O3Os, a = 10.910(4) A, b = 17.127(5) A, c = 17.555(7) A, beta = 103.77(2) degrees, V = 3186(2) A3, and Z = 4. 10a: C28H32AsCl5O2Os, a = 10.7762(2) A, b = 17.3939(1) A, c = 17.1477(3) A, beta = 103.645(1) degrees, V = 3123.45(8) A, and Z = 4. Complexes 9 and 10a crystallize with two and one molecule of EtOH and are bonded via hydrogen bridges to the H2O and EtOH ligand in 9 and 10a, respectively.

Ruthenium(II) ammine and hydrazine complexes with [N(Ph2PQ)2]- (Q = S, Se) ligands.

Reactions of coordinatively unsaturated Ru[N(Ph2PQ)2]2(PPh3) (Q = S (1), Se (2)) with pyridine (py), SO2, and NH3 afford the corresponding 18e adducts Ru[N(Ph2PQ)2]2(PPh3)(L) (Q = S, L = NH3 (5); Q = Se, L = py (3), SO2 (4), NH3 (6)). The molecular structures of complexes 2 and 6 are determined. The geometry around Ru in 2 is pseudo square pyramidal with PPh3 occupying the apical position, while that in 6 is pseudooctahedral with PPh3 and NH3 mutually cis. The Ru-P distances in 2 and 6 are 2.2025(11) and 2.2778(11) A, respectively. The Ru-N bond length in 6 is 2.185(3) A. Treatment of 1 or 2 with substituted hydrazines L or NH2OH yields the respective adducts Ru[N(Ph2PQ)2]2(PPh3)(L) (Q = S, L = NH2NH2 (12), t-BuNHNH2 (14), l-aminopiperidine (C5H10NNH2) (15); Q = Se, L = PhCONHNH2 (7), PhNHNH2 (8), NH2OH (9), t-BuNHNH2 (10), C5H10NNH2 (11), NH2NH2 (13)), which are isolated as mixtures of their trans and cis isomers. The structures of cis-14 and cis-15 are characterized by X-ray crystallography. In both molecular structures, the ruthenium adopts a pseudooctahedral arrangement with PPh3 and hydrazine mutually cis. The Ru-N bond lengths in cis-14.CH2Cl2 and cis-15 are 2.152(3) and 2.101(3) A, respectively. The Ru-N-N bond angles in cis-14.CH2Cl2 and cis-15 are 120.5(4) and 129.0(2) degrees, respectively. Treatment of 1 with hydrazine monohydrate leads to the isolation of yellow 5 and red trans-Ru[N(Ph2PS)2]2(NH3)(H2O) (16), which are characterized by mass spectrometry, 1H NMR spectroscopy, and elemental analyses. The geometry around ruthenium in 16 is pseudooctahedral with the NH3 and H2O ligands mutually trans. The Ru-O and Ru-N bond distances are 2.118(4) and 2.142(6) A, respectively. Oxidation reactions of the above ruthenium hydrazine complexes are also studied.

Direct Evidence for O−H···NC Hydrogen Bonding in a Cyanide-Bridged Lanthanide−Transition-Metal Complex (H2O)6(DMF)6Ho2[Ni(CN)4]3: An Eight-Coordinated Holmium Center with a Bicapped (Square Face) Trigonal Prismatic Geometry

The lanthanide−transition-metal complex (H2O)6(DMF)6Ho2[Ni(CN)4]3, 1, was prepared from the reaction of Ho(NO3)3·6.5H2O with K2[Ni(CN)4] at a 2:3 molar ratio in DMF (DMF = N,N-dimethylformamide). This compound is a model compound for studying the effects of H2O ligands on the coordination geometry of lanthanide centers and the tendency to form oligomers rather than extended arrays with cyanide bridges. The presence of multiple hydrate water molecules appears to inhibit the formation of an extended array complex containing cyanide bridges but favors intermolecular hydrogen bonds between oligomers. The Ho centers are trans-bridged through a [Ni(CN)4]2- unit. Each Ho center also forms an isocyanide linkage with a terminal [Ni(CN)4]2- unit. Holmium is eight-coordinated. It is bound to three DMF molecules and three H2O molecules in addition to two [Ni(CN)4]2- units. The coordination geometry of Ho is a distorted bicapped (square face) trigonal prism. The X-ray crystal structure and IR spectra support the prese...

Laser Photolysis of Chromium(III) Porphyrins with Axial Pyridines in Dichloromethane and Toluene Solutions. Novel Effects of a Hydrogen Bond in the Ligand Exchange Reaction

Laser photolysis studies were carried out for (chloro)(pyridine)(5,10,15,20-tetraphenylporphyrinato)chromium(III), [Cr(TPP)(Cl)(Py)], in both dichloromethane and toluene containing water. The five-coordinate [Cr(TPP)(Cl)] produced by the photoinduced dissociation of pyridine from [Cr(TPP)(Cl)(Py)] initially reacts with H2O to give [Cr(TPP)(Cl)(H2O)], which eventually exchanges the axial H2O with Py to regenerate [Cr(TPP)(Cl)(Py)]. The rate for the ligand exchange of [Cr(TPP)(Cl)(H2O)] with exogenous Py is found to exhibit a bell-shaped pyridine-concentration dependence. Kinetic studies revealed that at a high Py concentration, the exogenous Py probably makes a hydrogen bond with the axial H2O of [Cr(TPP)(Cl)(H2O)] to yield [Cr(TPP)(Cl)(HO−H···Py)] as a dead-end complex. A similar structure of the Cr−TPP complex having 2-methylpyridine molecules bound to the coordinated H2O ligand by a hydrogen bond was determined by X-ray structure analysis. The exchange reaction of the axial HO−H···Py in [Cr(TPP)(Cl)(HO−...

Direct Detection of the Proton-Containing Group Coordinated to Mo(V) in the High pH Form of Chicken Liver Sulfite Oxidase by Refocused Primary ESEEM Spectroscopy: Structural and Mechanistic Implications

A refocused primary electron spin−echo envelope modulation (RP ESEEM) technique and an adjustable frequency S/C-band pulsed EPR spectrometer have been used to produce ESEEM spectra with the lines due to nearby protons being greatly enhanced relative to those due to distant matrix protons. Application of this technique to the high pH (hpH) form of the Mo(V) center of sulfite oxidase has enabled nearby protons to be directly detected for the first time. Simulation of the RP ESEEM spectrum of the hpH form suggests the presence of two nearby protons that have distributed hyperfine interactions (hfi); these protons are ascribed to a MoV−OH group with strong H-bonding interactions to other nearby proton donors or to the presence of a coordinated H2O ligand. The RP ESEEM technique promises to be widely applicable to the investigation of mutant forms of SO with altered Mo centers and paramagnetic centers in other metalloproteins where a nearby proton of interest is often masked by much more numerous distant protons and where high spectral resolution is not required. The distinctive differences in the CW and pulsed EPR spectra of the lpH and hpH forms are proposed to result from differences of the MoV−OH torsional angle and variations in the H-bonding interactions, which control the orientation of the MoV−OH proton(s) relative to the half-filled 4dxy orbital. The large isotropic hfi for the lpH form is suggested to result from an intramolecular MoV−OH···Scys hydrogen bonding interaction that places the proton of the MoV−OH group in the equatorial plane of the square pyramidal oxo-Mo(V) center of SO.

Aqua(n-hexyl)[3,3'-(propane-1,3-diyldinitrilo)bis(butan+ ++-2-one) dioximato-kappa 4N]cobalt(III) perchlorate.

The title compound, [Co(C6H13)(C11H19N4O2)(H2O)]ClO4, is in the general class of coenzyme B12 models which contain a ClO4 anion and a [Co(C6H13)(C11H19N4O2)(H2O)]+ cation. In the cation, the Co atom has a distorted octahedral coordination, with the n-hexyl and H2O ligands in axial positions. The crystal data reveal some degree of flexibility in the Costa-type system, which is similar to the coenzyme B12.

Metalloion−Ligand Binding Energies and Biological Function of Metalloenzymes Such as Carbonic Anhydrase. A Study Based on ab Initio Calculations and Experimental Ion−Ligand Equilibria in the Gas Phase

The known structure of carbonic anhydrase includes the structure of the active site, which consists of Zn2+, coordinated to three histidine (His) residues and a water molecule. The ligand involved in the catalysis is the water molecule. Using imidazole (Im) to model histidine, it is found that histidine is the strongest bonding residue to Zn2+ of all neutral amino acid residues. On the basis of high-level ab initio calculations, the sequential bond energies for one to three imidazoles attached to Zn2+ were evaluated. The bond energy Zn(Im)32+−(H2O) was also determined by ab initio calculations and (gas phase) ion equilibria measurements. From a comparison of the free energy of stabilization of Zn2+ in the enzyme and that in aqueous solution, we conclude that very strongly bonding residues such as histidine are essential to make the Zn2+ ion in the enzyme stable, relative to the aqueous environment. The strongly bonding histidine also has another more important role. Due to the very large charge transfer and polarizability energy component with such a ligand and ligand−ligand repulsion, the bonding to the fourth, i.e., the H2O ligand, is very much weakened. It is shown that weakening of the Zn(L)32+−(H2O) bond energy is unfavorable, i.e., increases the energy required for the first step of the accepted mechanism, Zn(His)3OH22+ → Zn(His)3OH+ + H+, while the second step, Zn(His)3OH+ + CO2 Zn(His)3(H2O)2+ + HCO3-, is favorably affected, i.e., requires less energy. The choice of the ligands L therefore must be such so as to lead to a compromise between the two opposing effects. By making a semiquantitative inclusion of the solvent effect of the protein and aqueous environment on the reaction free energies for the above two ionic reactions, it was possible to show that the “choice” of the three histidine ligands is “just right” to provide this compromise. These ligands lead to reaction free energies that are close to zero for both reactions.

Precipitation Reactions in Water Clusters

The reactions of hydrated metal cations Ag+(H2O)n, n = 11−26, and Na+(H2O)n, n = 12−28, with HCl were studied by FT-ICR mass spectrometry. One observes an efficient fragmentation due both to collisions and to blackbody radiation, as well as ligand exchange reactions. The number of HCl molecules which can be stabilized in a cluster depends on the number of H2O ligands. In the case of Na+(H2O)n clusters, 12 and 15 H2O ligands are needed to “dissolve” 1 and 2 HCl molecules, respectively, results very similar to H+(H2O)n. On the other hand, in the case of hydrated silver cations, only 4 and 7 H2O molecules are necessary to stabilize 1 and 2 HCl molecules. The difference is due to the fact that many water ligands are needed to stabilize the HCl and NaCl species which are ionically dissolved, while much less water is needed in the case of hydrated Ag+ cations, which form within the cluster a covalently bound AgCl. The observed behavior reflects the large difference in the solubility products of NaCl and AgCl and shows that an analogue to bulk precipitation reaction occurs on a molecular level in clusters.

Dinuclear and hexanuclear iron(III) carboxylate clusters with a bis(bipyridine) ligand: supramolecular aggregation of [Fe2O2] units to give a [Fe6O6] ladder structure †

The use of the bis-bipyridine ligand L (1,2-bis(2,2′-bipyridyl-6-yl)ethane) in iron(III) chemistry has yielded a variety of new dinuclear and hexanuclear iron complexes, the latter containing a ladder-like supramolecular architecture. Treatment of L with two equivalents of HBF4 yields [H2L][BF4]21, the doubly protonated ligand. The FeX3/NaO2CR/L (2∶4∶1) reaction system in MeCN gives [Fe2OX2(O2CR)2L] (X = Cl, R = Ph 2; X = Br, R = Ph 3; X = Cl, R = Me 4). The same FeCl3/NaO2CPh/L (2∶4∶1) reaction system but in a 1∶1 MeCN–water solution gives green [Fe2OCl2(O2CPh)L(H2O)2]Cl 5, and in a water solution gives brown [Fe6O6(O2CPh)3L3(H2O)2]Cl36. Treatment of a 1∶2 MeOH–acetone solution of the nitrate salt of 6 with an excess of NaNO3 gives brown-red [Fe2O(NO3)4L] 7. Reaction of [NEt4]2[Fe2OCl6] with L and NaNO3 (2∶2∶1) in MeCN gives orange-brown Na2[Fe2OCl6L] 8, whereas reaction with L and NaO2CPh (1∶1∶1) in MeCN gives red-green [Fe2OCl2L2]Cl29. Complexes 1, 2 and 5–7 were characterized by X-ray crystallography. The cation of 1 exists in a single-step conformation, with planar bpy units stabilized by the presence of intra-bpy hydrogen bonding and intermolecular hydrogen bonding with the anion. All the dinuclear complexes contain a [Fe2O]4+ unit bridged by one L and either zero, one or two carboxylate groups. Complexes 2–4 are bridged by two carboxylate groups, with the two terminal halide ligands in a cis conformation. Complex 5 contains only one bridging benzoate group, and octahedral geometry at each FeIII is completed with terminal Cl− and H2O ligands, with the Cl− ligands in a trans conformation. Complex 6 can be described as three [Fe2O2(O2CPh)L]+ units joined together to give a near-planar [Fe6O6]6+ ladder-like core. This chain of Fe2 units is terminated by water molecules. The cation can be prepared as a Cl−, Br−, NO3−, ClO4−, PF6−, or BF4− salt. Complex 7 contains four chelating NO3− ligands and no bridging carboxylate group. Variable-temperature magnetic susceptibility studies of 4 and 6 in the 5.00 to 300 K range reveal both complexes to have S = 0 ground states. The data for 4 were fitted by the appropriate theoretical expression for a FeIII2 complex and a molar fraction (p) of S = 5/2 paramagnetic impurity, giving J = −119 (1.5) cm−1, g = 1.96(2) and p = 0.0102(2), with temperature-independent paramagnetism held constant at 500 × 10−6 cm3 mol−1. The obtained J value is consistent with that predicted by a previously published magnetostructural relationship.

Two Pillared Three-Dimensional Inorganic/Organic Hybrid Structures Composed of Bimetallic Layers Bridged by Exo-bidentate Ligands

ABSTRACTThe hydrothermal reactions of Cu(NO3)2.3H2O, K2CrO4 and exo-bidentate ligand bpy/bpe, (bpy = 4,4'-bipyridine, bpe = trans-1,2-bis(4-pyridyl)ethylene) result in two pillared 3D organic-inorganic hybrid compounds. Both contain bimetallic layers of copper(II) cations and chromate anions, which are directly connected by different organic ligands, leading to pillared structures with varying pillar length and thickness of layers. Crystal data for [Cu3(CrO4)2(OH)2(bpy)2] (1): triclinic, P1, a = 5.358(1), b = 5.603(1), c = 13.515(3) Å, α = 81.78(3), γ = 86.56(3), Å3 = 79.75(3)°, V = 394.91(13) Å3, Z = 1; [CuCrO4(bpe)] (2): monoclinic, C2/c, a = 23.282(5), b = 11.917(2), c = 9.726(2) Å, β = 112.99(3)°, V = 2484.2(8) Å3, Z = 8.

Isomeric Forms of [Mn12O12(O2CR)16 H2O)4] Complexes Showing Different Magnetization Relaxation Processes

The characterization of two new single-molecule magnets,[Mn12O12(O2CCH2C6H5H5)16(H2O)4] (7) and [Mn12O12(O2CCH2But)16(H2O)4] (8) is reported here. Even though the two complexes have the same isomeric arrangement of H2O ligands the ac magnetic susceptibility responses are different for the two complexes. Complex 7 shows an out-of-phase (XM′) peak in the 4–7 K region, whereas complex 8 shows a XM′ peak in the 2–4 K region. The influence of solvate molecules upon the magnetization relaxation rates of these Mn12 complexes is studied.

Synthesis and characterization of [PtMe3L(H2O)]BF4·H2O (L=3-O-acetyl-1,2-O-isopropylidene-α-D-glucofuranose)

Reaction of [PtMe3(Me2CO)3]BF4 (1) with 3-O-acetyl-1,2;5,6-di-O-isopropylidene-α-D-glucofuranose in acetone affords [PtMe3L]BF4 (2) (L=3-O-acetyl-1,2-O-isopropylidene-α-D-glucofuranose). In wet methylene chloride, complex2 transforms to [PtMe3L(H2O)]BF4·H2O (3). Complex3 was characterized by microanalysis and NMR spectroscopy (1H,13C,195Pt). The X-ray structure analysis (monoclinic, P21, a=10.529(3) A, b=7.322(2) A, c=14.668(4) A, Z=2) reveals that 3-O-acetyl-1,2-O-isopropylidene-α-D-glucofuranose acts as a neutral bidentate ligand which is coordinated via two hydroxyl groups (κ2O5,6 coordination). The five-membered 1,3,2-dioxaplatina rings exhibit an envelope conformation. The coordination sphere of platinum is completed by H2O ligand.

Synthesis and structural characteristics of metal–acyclovir (ACV) complexes: [Ni(or Co)(ACV)2(H2O)4]Cl2·2ACV, [Zn(ACV)Cl2(H2O)], [Cd(ACV)Cl2]·H2O and [{Hg(ACV)Cl2}x]. Recognition of acyclovir by Ni–ACV

The monomeric [M(ACV)2(H2O)4]Cl2·2ACV (M = NiII 1 or CoII 2), [Zn(ACV)Cl2(H2O)] 3 and the polymeric [Cd(ACV)Cl2]·H2O 4 [ACV = acyclovir = 9-(2-hydroxymethoxymethyl)guanine] complex have been prepared and characterised by X-ray diffraction and IR data; 1H and 13C NMR have been used to interpret the structural characteristics of the complexes in solution. Compounds 1 and 2 exist as octahedral complexes with four H2O ligands in the basal plane [Ni–OW 2.053(2) and 2.057(7) A] and two axial ACV molecules linked to Ni through N(7) [Ni–N(7) 2.160(2) A]. Two additional ACV molecules are included in the outer sphere of the complex, interacting by means of hydrogen bonds with the co-ordinated ACVs. This reveals the unprecedented recognition of free acyclovir molecules by Ni(or Co)-ACV (1 and 2). The monomeric zinc(II) complex 3 exhibits a distorted-tetrahedral geometry, involving two chlorides, the N(7) of the ACV ligand [Zn–N(7) 2.009(2) A] and a water molecule. The hydrogen bonding of two guanine bases via NH2 and N(3) (unit 1) with N(3) and NH2 (unit 2) represents a novel type of interaction between nucleobases. In the case of the cadmium(II) complex 4 the structure is built by polymeric (CdCl2)n chains which are held together by ACV ligands. The cadmium cation is octahedrically coordinated by four chlorides, the N(7) from an ACV molecule and the hydroxylic oxygen from another ACV molecule, the latter two atoms being placed in cis disposition. On the other hand, the complex [{Hg(ACV)Cl2}x] 5 can be tentatively assigned as a polymer by comparison with analogous guanosine systems and spectroscopic and conductometric data.

Crystal structures of nitridotechnetium(V) complexes of amine oximes differing in carbon chain lengths

Structures of nitridotechnetium(V) amine oxime complexes, [TcN(pnao)(H2O)][BPh4] 1, [TcN(bnao)(H2O)][BPh4] 2 and [TcN(pentao)(H2O)][BPh4] 3 [Hpnao = HONCMeCMe2NH(CH2)3NHCMe2CMeNOH; Hbnao = HONCMeCMe2NH(CH2)4NHCMe2CMeNOH; Hpentao = HONCMeCMe2NH(CH2)5NHCMe2CMeNOH], differing in carbon chain length of the amine oxime ligands, were characterized by X-ray crystallography. These complexes are six-co-ordinated and distorted octahedral. Four nitrogen atoms of the amine oxime ligands are in the equatorial plane and both the nitrido and H2O ligands in the apical positions. These complexes have an asymmetrical intramolecular hydrogen bond between the two oxime oxygen atoms. Their intramolecular O· · ·O distances are 2.720 A in 1, 2.512 A in 2 and 2.531 A in 3. The longest O· · ·O distance in 1 is ascribed to a steric effect of the carbon chain length between the amine nitrogens. Namely, the shorter carbon chain of the pnao ligand causes strain on the co-ordinated pnao moiety, and the O· · ·O distance in 1 is longer than that in 2 and 3 with longer carbon chains.