Showing papers in "Inorganic Chemistry in 1997"

Abstract: The hydrothermal reaction of Ni(II) and the rodlike 4,4‘-bipyridine ligand yields an extended 1-D noninterpenetrated open framework resembling a railroad with large pores of 11 × 11 A aperture. (4,4‘-Bipyridine is illustrated as lines, and Ni atoms are at the intersections.)

Abstract: Three compounds were obtained from the reactions of Co(NCS)2 with pyrazine and 4,4‘-bipyridine in different solvents: Co(NCS)2(pyz)2 (1) has a 2D sheet structure, monoclinic, C2/m, a = 10.039(2) A, b = 10.382(2) A, c = 7.190(1) A, β = 118.64(1)°, Z = 2; Co(NCS)2(H2O)2(4,4‘-bipy)·4,4‘-bipy (2) has linear Co−bipy−Co chains connected by hydrogen bonds between H2O and noncoordinated 4,4‘-bipy molecules to form stair type sheets, triclinic, P1, a = 7.450(1) A, b = 9.020(1) A, c = 10.122(1) A, α = 107.74(1)°, β = 104.02(1)°, γ = 97.16(1)°, Z = 1; Co(NCS)2(4,4‘-bipy)2·2(CH3CH2)2O (3) has ether molecules intercalated between layers formed by Co(NCS)2 and coordinated 4,4‘-bipyridine ligands, monoclinic, P2/c, a = 11.483(2) A, b = 11.397(3) A, c = 13.609(1) A, β = 107.55(1)°, Z = 2. Compounds 2 and 3 thermally decompose to form the same products. The identities of the decomposition products are discussed.

Abstract: The influence of the simplifications introduced by modeling a molecular structure on the exchange coupling constant is studied for hydroxo-bridged Cu(II) binuclear complexes. This study focuses on the role of the terminal ligands and the counterions. The terminal ligands are responsible for marked changes in the exchange coupling constant, depending on their donor properties, while the counterions have an effect only when directly coordinated to the copper atoms. The study of the magneto−structural correlations for the hydroxo-bridged Cu(II) binuclear complexes has been extended by analyzing the influence of the Cu−O distance, the effect of the asymmetry at the bridging backbone, and the hinge distortion of the bridge. The increase in the Cu−O distance and the absence of the hinge distortion of the Cu2O2 ring substantially enhance the antiferromagnetic interaction.

Abstract: U, Np, and Pu LII,III-edge X-ray absorption fine structure (XAFS) spectra were collected for the UO22+, NpO2+, Np4+, and Pu3+ ions as a function of chloride concentration in aqueous solution. At low chloride concentration, the hydration numbers and corresponding bond lengths for the different ions are as follows: UO22+, N = 5.3, R = 2.41 A; NpO2+, N = 5.0, R = 2.50 A; Np4+, N = 11.2, R = 2.40 A; Pu3+, N = 10.2, R = 2.51 A. As the Cl- concentration increases, inner-sphere Cl- complexation occurs, resulting in a decrease in the hydration numbers and an expansion of the actinide−oxygen (water) bond lengths. The Pu3+ ion shows only a decrease in hydration number (40%) and no inner-sphere Cl- complexation for [Cl-] < 14 M. For concentrations up to 10−14 M Cl-, the average Cl- coordination numbers and bond lengths are as follows: UO22+, N = 2.6, R = 2.73 A; NpO2+, N = 1.0, R = 2.84 A; Np4+, N = 2.0, R = 2.61 A. Structural changes are observed in the near-edge spectral region as shown by significant changes in...

Abstract: A variable-temperature, -pressure, and -ionic strength (1)H NMR study of the DOTA complexes of different trivalent cations (Sc, Y, La, Ce --> Lu) (DOTA = 1,4,7,10-tetraaza-1,4,7,10-tetrakis(carboxymethyl)cyclododecane) yielded data that are in contradiction with the hitherto used model of only two enantiomeric pairs of diastereoisomers that differ in the ligand conformations. A two-isomer equilibrium cannot explain the newly observed apparent reversal of the isomer ratio at the end of the series. As both conformers may lose their inner sphere water molecule, a coordination equilibrium may be superimposed on this conformational equilibrium, as shown by large positive reaction volumes for the isomerization of [Ln(DOTA)(H(2)O)(x)()](-) (Ln = Yb, Lu; x = 1, 0). The isomerization of [Nd(DOTA)(H(2)O)](-) and [Eu(DOTA)(H(2)O)](-) is purely conformational, as shown by near-zero reaction volumes. The measured isomerization enthalpies and entropies agree with this model. The shift of the isomerization equilibria by a variety of non-coordinative salts depends on the ligand conformation rather than the presence or absence of the inner sphere water molecule. This results from weak ion binding and water solvent stabilization of one ligand conformation, rather than the decrease of the activity of the bulk water in the solution, as shown by UV-vis measurements of the coordination number sensitive transition (5)F(0) --> (7)D(0) of Eu(III) as a function of ionic strength. Fluoride ions replace a water molecule in the inner coordination sphere, preferentially for one of the conformational isomers, as proven by (19)F-NMR shifts and the appearance of a third set of resonances corresponding to [Eu(DOTA)F](2)(-) in the (1)H-NMR spectrum of [Eu(DOTA)(H(2)O)](-).

Abstract: The structures of three linear-chain platinum(II) diimine complexes have been determined [Pt···Pt, A]: Pt(bpm)Cl_2·0.5(nmp) (3) [3.411(1), 3.371(1)], Pt(phen)(CN)_2 (6) [3.338(1), 3.332(1)], and Pt(bpy)(NCS)_2 (7) [3.299(2)] (bpm = 2,2‘-bipyrimidine, phen = 1,10-phenanthroline, bpy = 2,2‘-bipyridine, nmp = 1-methyl-2-pyrrolidinone). The Pt···Pt distances in these and in seven related compounds range from 3.24 to 3.49 A. While we find evidence of interligand interactions influencing these structures, the Pt···Pt bonds are the most important of the stacking forces. The metal−metal distances are generally consistent with an electronic structural model in which σ-donor/π-acceptor ligands strengthen Pt···Pt bonding interactions (for example, the Pt···Pt distances in 3 are 0.04 and 0.08 A shorter than in the bpy analogue). We have also found that the yellow form of Pt(dmbpy)(NCO)_2 (1b) (4,4‘-dimethyl-2,2‘-bipyridine) has a columnar structure; however, in contrast to the linear-chain form (1), which is orange, the Pt atoms are well separated (>4.9 A). Interestingly, the yellow form is 7% denser than the orange form; this result is consistent with the concept that directed intermolecular interactions give rise to lower density polymorphs. Crystal data: (3) monoclinic, C2/m (No. 12), a = 12.668(4) A, b = 15.618(6) A, c = 6.704(3) A, β = 93.43(3)°, Z = 4; (6) orthorhombic, Pbca (No. 61), a = 38.731(13) A, b = 18.569(3) A, c = 6.628(1) A, Z = 16; (7) orthorhombic, Pbcm (No. 57), a = 10.349(3) A, b = 19.927(5) A, c = 6.572(3) A, Z = 4; (1b) monoclinic, C2/c (No. 15), a = 17.313(4) A, b = 12.263(3) A, c = 14.291(4) A, β = 114.00(2)°, Z = 8.

Abstract: Three 1D coordination polymers were obtained from Ag(CF3SO3) and the conformationally flexible bidentate ligand 1,3-bis(4-pyridyl)propane (bpp), [Ag(bpp)](CF3SO3)·EtOH (1), [Ag(bpp)](CF3SO3) (2), and [Ag2(bpp)4](CF3SO3)2·bpp (3), the latter two exhibiting quite uncommon structural motifs. 2 contains an infinite double helical polymer, comprised of two chains of the type present in 1, and is the first example of a cationic infinite discrete double helix in coordination polymer chemistry. 3 contains a novel 1D polymer, comprised of interconnected macrocycles to give an infinite tubular shape. Uncoordinated bpp molecules are located inside the tubules, threading the rings in a pseudorotaxane-like manner.

Abstract: Coordination networks of 3,3‘-dicyanodiphenylacetylene (3,3‘-DCPA, 1) with silver(I) salts characterized by single-crystal X-ray analysis are described. Network topology is found to depend on both the counterion and solvent employed during crystallization. The conformation adopted by the ligand varies between planar cisoid and planar transoid. With silver(I) triflate (AgCF3SO3) in benzene, a sheet structure of composition [Ag(1)CF3SO3]C6H6 (2) forms in which silver(I) is five-coordinate and bonds to two nitrogen atoms of distinct 3,3‘-DCPA molecules, another silver(I) ion, and two oxygen atoms of the triflate ions. Changing the solvent to toluene produces an undulating sheet structure of composition [Ag2(1)(CF3SO3)2] (3) in which silver(I) is six-coordinate, bonding to a ligand nitrogen atom, to four oxygen atoms of bridging triflate ions, and to a neighboring silver(I) ion. In both triflate structures, 3,3‘-DCPA adopts a transoid conformation with respect to the positioning of the nitrile groups. With si...

Abstract: 1H and 31P NMR spectroscopies have been applied in the structural characterization of the enantioselective interactions between Λ- and Δ-[Ru(phen)2dppz]2+ (dppz = dipyridophenazine) and the hexamer oligonucleotide d(GTCGAC)2. Issues of intercalation, exchange rate, sequence specificity, enantioselectivity, and the distribution of binding geometries have been explored. Several forms of evidence support intercalation by both isomers: (i) upfield changes in 1H chemical shift for protons of the dppz ligand; (ii) characteristic downfield changes in 31P chemical shifts for the duplex bound by the metal complex; (iii) increases in duplex melting temperature in the presence of both isomers. Slow exchange is achieved near 0 °C, thus permitting the observation of individual binding events. While both isomers intercalate into the helix, enantioselective differences in intercalation are evident. Differences in intercalative geometries are clearly manifested through chiral shifts in racemic mixtures and distinct reso...

Abstract: Bimetallic, oxalate-bridged compounds with bi- and trivalent transition metals comprise a class of layered materials which express a large variety in their molecular-based magnetic behavior. Because of this, the availability of the corresponding single-crystal structural data is essential to the successful interpretation of the experimental magnetic results. We report in this paper the crystal structure and magnetic properties of the ferromagnetic compound {[N(n-C3H7)4][MnIICrIII(C2O4)3]}n (1), the crystal structure of the antiferromagnetic compound {[N(n-C4H9)4][MnIIFeIII(C2O4)3]}n (2), and the results of a neutron diffraction study of a polycrystalline sample of the ferromagnetic compound {[P(C6D5)4][MnIICrIII(C2O4)3]}n (3). Crystal data: 1, rhombohedral, R3c, a = 9.363(3) A, c = 49.207(27) A, Z = 6; 2, hexagonal, P63, a = 9.482(2) A, c = 17.827(8) A, Z = 2. The structures consist of anionic, two-dimensional, honeycomb networks formed by the oxalate-bridged metal ions, interleaved by the templating cations. Single-crystal field dependent magnetization measurements as well as elastic neutron scattering experiments on the manganese(II)−chromium(III) samples show the existence of long-range ferromagnetic ordering behavior below Tc = 6 K. The magnetic structure corresponds to an alignment of the spins perpendicular to the network layers. In contrast, the manganese(II)−iron(III) compound expresses a two-dimensional antiferromagnetic ordering.

Abstract: The structural, spectroscopic, and electrochemical properties of cobalt(III) derivatives of acacen (H2acacen = bis(acetylacetone) ethylenediimine) and related ligands have been investigated. Electronic structure calculations indicate that the absorption between 340 and 378 nm in CoIII(acacen) spectra is attributable to the lowest π−π* intraligand charge-transfer transition. Equatorial ligand substitutions affect reduction potentials less than axial ligand changes, consistent with an electronic structural model in which dz2 is populated in forming cobalt(II). The crystal structure of [Co(3-Cl-acacen)(NH3)2]BPh4 has been determined: The compound crystallizes in the monoclinic space group P21/m (No. 11) with a = 9.720(2) A, b = 18.142(4) A, c = 10.046(2) A, β = 100.11(3)°, Dc = 1.339 g cm-3, and Z = 2; the complex cation, [Co(3-Cl-acacen)(NH3)2]+, exhibits a slightly distorted octahedral coordination geometry. The distances between the cobalt atom and the two axial nitrogen donor atoms differ only slightly ...

Abstract: Starting from a single precursor, bis(3-methoxysalicylaldehydato)copper (II), which contains an O4Cu chromophore, three routes to discrete dinuclear Cu(II)/Ln(III) complexes (Ln = Pr, Eu, Gd, Yb) are described. The pairs of chromophores occurring in the resulting complexes are either O4Cu/O4Ln or O2N2Cu/O4Ln, the coordination sphere of the Ln ions being completed, in both cases, with six oxygen atoms afforded by three nitrato ions. Two Cu/Gd complexes involving either two tridentate ligands (2) or one hexadentate ligand (7) have been structurally characterized. They crystallize in the monoclinic space groups P21/n (No. 14) (2) and P21/c (No. 14) (7). The cell parameters are a = 9.7185(7) A, b = 16.7839(12) A, c = 14.8868(8) A, β = 97.445(5)°, and Z = 4 (2) and a = 9.7656(9) A, b = 19.889(2) A, c = 15.870(2) A, β = 95.512(9)°, and Z = 4 (7) respectively. The magnetic properties of six Cu/Ln complexes have been determined. A quantitative analysis of the magnetic properties of the Cu/Gd complexes shows that ...

Abstract: The crystal structures of three compounds have been determined at room temperature, namely [Gd(hfa)3Cu(salen)] (1), [Y(hfa)3Cu(salen)] (2), and [Gd(hfa)3Cu(salen)(Meim)] (3), and the crystal structure of a fourth compound, [La(hfa)3(H2O)Cu(salen)] (4), has been determined at −100 °C; hfa = hexafluoroacetylacetonato, salen = N,N‘-ethylenebis(salicylideneaminato), and Meim = 1-methylimidazole. [La(hfa)3Ni(salen)] (5), isomorphous with 1, has also been synthesized. 1 crystallizes in the monoclinic system, space group P21/n, with a = 17.292(5) A, b = 22.370(5) A, c = 19.658(6) A, β = 90.07(2)°, and Z = 8. 2 crystallizes in the triclinic system, space group P1, with a = 12.207(3) A, b = 13.019() A, c = 13.011(6) A, α = 82.87(4)°, β = 83.55(3)°, γ = 70.91(3)°, Z = 2. 3 crystallizes in the monoclinic system, space group P21/n, with a = 16.521(9) A, b = 20.381(5) A, c = 12.758(6)°, β = 93.22(6)°, and Z = 4. 4 crystallizes in the monoclinic system, space group P21/n, with a = 12.826(2) A, b = 23.067(8) A, c = 13....

Abstract: Layered birnessite-type manganese oxides have been synthesized by sol−gel reactions involving KMnO4 or NaMnO4 with glucose. These microporous manganese oxides are designated as octahedral layer materials, K-OL-1 and Na-OL-1, because their layered structure consists of edge-shared MnO6 octahedra. The interlayer regions are occupied by alkali metal cations and water molecules. K-OL-1 and Na-OL-1 have been characterized by elemental analysis, powder X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, and Auger electron spectroscopy. The empirical formula of K-OL-1 has been determined to be K0.28MnO1.96(H2O)0.19. An interlayer spacing of 7 A, typical of natural and synthetic birnessites, has been measured by X-ray diffraction. The sol−gel synthesis of K-OL-1 is carried out with concentrated aqueous solutions of glucose and KMnO4 in a 1.5:1 mole ratio. Diluted reaction mixtures produce flocculent gels or precipitates which yield other manganese oxide phases such as cryptomelane and Mn2O3. The ...

Abstract: An alternating di-(μ-(end-on)azido)−di-(μ-(end-to-end)azido) manganese(II) one-dimensional compound, with formula [Mn(bipy)(N3)2] (bipy = 2,2‘-bipyridine), has been synthesized and characterized. I...

Abstract: This investigation focuses on a series of pseudotetrahedral complexes of the form Cu(NN)2+, where NN denotes a 1,10-phenanthroline ligand with alkyl substituents in the 2 and 9 positions and the counterion is PF6-. In these copper(I) systems, steric effects are of considerable interest because the electronic configuration predisposes the reactive charge-transfer excited state to undergo a flattening distortion or to add a fifth ligand. Both effects lead to emission quenching and a shorter excited-state lifetime. Bulky substituents inhibit these processes, but the spatial distribution of the atoms involved is more important than the total molecular volume in determining the influence of a substituent. According to the results of this study, the effective size decreases in the following order: sec-butyl > neopentyl > n-octyl ≈ n-butyl > methyl. In conjunction with the electrochemical data, the absorption and the emission spectra reveal three kinds of steric effects: (1) Clashes between substituents on opp...

Abstract: The three isomers of diferrocenylbenzenes (ortho, 1o; meta, 1m; para, 1p) as well as 5-substituted derivatives of m-diferrocenylbenzene with R = NH2 (2), Cl (3), CH3 (4), CN (5), NO2 (6), and N(CH3)33+ (7) have been prepared. Crystal structures of 1o, 3, and 5 have been solved. In 3 and 5, the cyclopentadienyl rings are nearly parallel to the benzene mean planes with angles ranging from 9.99(5)° to 14.74(5)°. One ferrocene group is above and the other below the mean molecular plane. For 1o, there is an important twist between the benzene and cyclopentadiene rings (68.6(8)° and 32.5(8)°) for steric reasons. Controlled potential electrolysis yields the mixed-valence ferrocene/ferrocenium species in comproportionation equilibrium with homovalent species. Intervalence transitions have been observed and corrected from comproportionation. From the intervalence band parameters, metal−metal couplings (Vab) are calculated using Hush's equation. The values are much higher for 1o (0.025 eV) and 1p (0.043 eV) than fo...

Abstract: We report the results of an investigation on the preparation, spectral, and photoelectrochemical properties of Ru(II)−polypyridyl complexes containing a new phosphonated terpyridine (P-terpy) ligand: [Ru(H2P-terpy)2] and [Ru(HP-terpy)(Me2bpy)(NCS)]. Resonance Raman spectral and luminescence studies allow probing into the nature of the low-energy MLCT transitions observed in these complexes. The crystal and molecular structure of the mixed-ligand complex [Ru(HP-terpy)(Me2bpy)(NCS)] based on X-ray diffraction study is reported. This complex appears to be a promising candidate as a photosensitizer in dye-sensitized photoelectrochemical cells based on nanocrystalline films of TiO2.

Abstract: Luminescent multiporphyrin molecular square assemblies have been synthesized in high yield from Re(CO)5Cl and a highly soluble dipyridylporphyrin ligand. Both free-base and ZnII-metalated variants of squares have been synthesized. The ZnII-containing squares are capable of strongly binding selected polyimine ligands in CH2Cl2 solution. Advantage has been taken of the effect to construct pentaporphyrin host−guest assemblies.

Abstract: Two effective computational approaches for the study of magnetic exchange interactions in large molecules are discussed and tested on a number of model systems, namely, broken-symmetry (BS) and single-determinant (SD) models. Both methods are based on the density functional theory (DFT) but exploit different approximations to deal with multiconfigurational problems. Our results show that the BS model provides semiquantitative results for widely different situations, such as metal−radical interactions and metal−metal interactions mediated by inert organic bridges. Although more refined (and expensive) methods are needed for truely quantitative work, the BS/DFT approach provides a very useful tool for the rationalization of magneto−structural correlations and for the comparison of different bonding situations in large systems involving transition metal atoms.

Abstract: The compounds Cs12[VIV18O42(H2O)]·14H2O (1a), K12[VIV18O42(H2O)]·16H2O (1b), Rb12[VIV18O42(H2O)]·19H2O (1c), K9[H3VIV18O42(H2O)]·14H2O·4N2H4 (1d), K11[H2VIV18O42(Cl)]·13H2O·2N2H4 (2a), K9[H4VIV18O4...

Abstract: Several new complexes containing 1,10-phenanthroline-5,6-diolate (dipyridocatecholate, dpcat2-) ligand are reported. The complex (dpcat)Pt(dbbpy) (4; dbbpy = di-tert-butylbipyridine) was synthesized from Cl2Pt(dbbpy) and dpcat2-. The reaction of (dpcat)Pt(dbbpy) with Cl2Pt(PhCN)2 yielded Cl2Pt(dpcat)Pt(dbbpy) (5). The latter complex was reacted with 3,4-dimercaptotoluene (toluenedithiolate, tdt2-), 3,5-di-tert-butylcatecholate (dbcat2-), and dpcat2- to give (tdt)Pt(dpcat)Pt(dbbpy) (6), (dbcat)Pt(dpcat)Pt(dbbpy) (7), and (dpcat)Pt(dpcat)Pt(dbbpy) (8), respectively. All of these complexes containing Pt(diimine)(diolate) centers display intense absorption bands in the 500−600 nm range. However, excitation at these wavelengths does not result in photoemission similar to that seen for closely related Pt(diimine)(dithiolate) complexes. The absorption bands of the dinuclear species are unsymmetrical, possibly indicating isolated but overlapping transitions for the two chromophores in each complex. The complex (d...

Abstract: The new Schiff base ligand 2-chlorobenzaldehyde thiosemicarbazone (L, 1) has been synthesized and characterized by spectral techniques and single-crystal X-ray analysis. Crystals of 1 are monoclinic, space group P2(1)/n with a = 12.964(4) A, b = 5.131(5) A, c = 4.970(1) A, beta = 94.32(2) degrees, and Z = 4. The thiosemicarbazone moiety adopts a configuration with N(1) cis to N(3) and places the E configuration about both the bonds C(1)-N(2) and C(2)-N(3). The monodentate behavior of the neutral ligand (L) has been investigated in two cadmium halides CdL(2) Br(2) (2) and CdL(2)I(2) (3). Compound 2 crystallizes in space group Cc witha = 8.175(1) A, b = 14.176(1) A, c = 21.073(1) A, beta = 94.02(1) degrees, and Z = 4. Compound 3 crystallizes in space group Po with a = 10.9577(1) A, b = 16.174(1) A, c = 7.878(1) A, alpha = 100.50(1) degrees, beta = 109.39(1) degrees, gamma = 83.67(1) degrees, and Z = 2. The coordination geometry about the cadmium(II) atom in compound 2 conforms to a tetrahedral configuration with two sulfur atoms from two unequivalent neutral ligands and two bromide atoms. Whereas the coordination geometry about the cadmium(II) atom in compound 3 is (4 + 1) distorted trigonal bipyramidal with two iodide atoms and one sulfur atom in the equatorial plane, the other thiosemicarbazone sulfur and the iodide atom I(1a) of an adjacent moiety occupy the axial positions. Compound 2 exhibits powder SHG efficiencies ca. 20 times that of urea, whereas compound 3 does not exhibit any SHG efficiency. Theory and experiment suggested that intermolecular contact is the main factor controlling the SHG efficiencies of compounds.

Abstract: The spectroelectrochemical properties of a novel light switch for DNA, Ru(phen)2(PHEHAT)2+ (phen = 1,10-phenanthroline; PHEHAT = 1,10-phenanthrolino[5,6-b]1,4,5,8,9,12-hexaazatriphenylene), are exa...

Abstract: Electrides are ionic compounds in which the cations are complexed by cryptands or crown ethers and the “anions” are trapped electrons. The crystal structures of five electrides are known and are similar to the corresponding alkalides (in which the anions are alkali metal anions) except that the anionic sites are “empty”. Theory and experiment strongly support a model in which the “excess” electrons are trapped in these anionic cavities and interact with each other through connecting channels, whose geometries vary significantly from one electride to another. Measurements of optical, alkali metal NMR, and EPR spectra, magnetic susceptibilities, and conductivities provide many data that can be correlated with the structures. Three electrides have essentially 1D chains of cavities connected by channels through which the electrons communicate, as indicated by magnetic susceptibilities that are well described by a 1D Heisenberg model. The electride, K+(cryptand[2.2.2])e- has a 2D array of cavities and channels...

Abstract: Oxidations of arylalkanes by nBu4NMnO4 have been studied in toluene solvent: toluene, ethylbenzene, diphenylmethane, triphenylmethane, 9,10-dihydroanthracene, xanthene, and fluorene. Toluene is oxidized to benzoic acid and a small amount of benzaldehyde; other substrates give oxygenated and/or dehydrogenated products. The manganese product of all of the reactions is colloidal MnO2. The kinetics of the reactions, monitored by UV/vis spectrometry, show that the initial reactions are first order in the concentrations of both nBu4NMnO4 and substrate. No induction periods are observed. The same rate constants for toluene oxidation are observed in neat toluene and in o-dichlorobenzene solvent, within experimental errors. The presence of O2 increases the rate of nBu4NMnO4 disappearance. The reactions of toluene and dihydroanthracene exhibit primary isotope effects: kC7H8/kC7D8 = 6 (±1) at 45 °C and kC14H12/kC14D12 = 3.0 (±0.6) at 25 °C. The rates of oxidation of substituted toluenes show only small substituent...

Abstract: The synthesis and structural and magnetic properties of the pentanuclear complex [(Ni(bpm)2)3(Fe(CN)6)2]·7H2O (1) are reported. Complex 1 crystallizes in the tetragonal space group P43212 (No. 96) with the following cell parameters at 23(1) °C: a = b = 12.888(2) A, c = 42.927(2) A, V = 7130(3) A3, and Z = 4. The structure was refined using 3197 unique reflections with I > 3σ(I) to give R = 0.047 and Rw = 0.038. The neutral [(Ni(bpm)2)3(Fe(CN)6)2] clusters contain two unconnected FeIII(CN)63- groups each bridged, via three facial CN groups, to three cis-Ni(bpm)2 moieties, thus making the cis-(CN)2NiII(bpm)2 centers six-coordinate. Metal···metal distances within the cluster are Fe···Ni = 5.042(3) and 5.058(2) A, Fe···Fe = 6.438(4) A, and Ni···Ni = 6.654(3) and 7.028(5) A. The seven water molecules form an intriguing hydrogen-bonded “cluster” which connects, via hydrogen-bonding, to the other facial CN ligands on each Fe. A wide array of magnetic susceptibility and magnetization measurements has been used t...

Abstract: The discrete trinuclear complex [(NEt4){Mn(H2O)(5-Cl-salen)}2{Fe(CN)6}]·H2O, 3, and a two-dimensional heterometal assembly [(NEt4){Mn(5-Cl-salen)}2{Fe(CN)6}]n, 4, have been prepared (NEt4 = tetraethylammonium, 5-Cl-salen = N,N‘-ethylenebis(5-chlorosalicylidene)aminato) dianion). Compound 4 crystallizes in the monoclinic space group P21/c with cell dimensions of a = 13.104(3) A, b = 12.861(3) A, c = 15.526(2) A, β = 105.98(1)°, Z = 2 and is isostructural to the previously synthesized metamagnetic compound, [K{Mn(3-MeOsalen}2{Fe(CN)6}·2DMF]n, 5. The structure assumes a two-dimensional network consisting of the cyclic tetramer (−Mn−NC−Fe−CN−)4 as a net unit [with dimensions of Fe−C1 = 1.947(8) A, Fe−C2 = 1.951(8) A, Mn−N1 = 2.286(7) A, Mn−N2 = 2.266(7) A, Mn−N−C = 154.4(7)°, Mn−N−C = 146.1(7)°]. The magnetic study (magnetic susceptibility vs T, field-cooled magnetization and zero-field cooled magnetization vs T, hysteresis loop and saturation magnetization vs H up to 55 kOe) shows that the compound is a meta...

Abstract: Structures and stabilization due to stacking of ternary copper(II) complexes containing an aromatic amino acid (AA) and an aromatic diamine (DA), Cu(AA)(DA), have been investigated by potentiometric, spectroscopic, and X-ray diffraction methods. For the systems with AA = para-X-substituted l-phenylalanine (l-XPhe; X = H, NO2, OH, NH2) and DA = 2,2‘-bipyridine (bpy) or 1,10-phenanthroline (phen), the difference absorption spectra in the region 320−400 nm exhibited a peak assignable to the charge transfer interaction between the aromatic rings of DA and l-XPhe, the intensity being in the order NH2 > OH > H ≫ NO2 with respect to X. The stability constants of Cu(AA)(DA) determined for AA = dl-XPhe (X = F, Cl, Br) and l-XPhe (X = NH2, NO2, I) at 25 °C and I = 0.1 M (KNO3) indicated that stabilization of Cu(l-XPhe)(DA) relative to Cu(l-Ala)(en) (Ala = alanine; en = ethylenediamine) is in the order Br > OH > Cl ≈ NH2 > NO2 ≥ H ≥ F. The structures of [Cu(l-NH2Phe)(bpy)]NO3·H2O (1), [Cu(l-Tyr)(phen)]ClO4·2.5H2O (2...

Abstract: The tripodal bis(thioimidazolyl)(pyrazolyl)hydroborato [NSS] donor ligand, [HB(timMe)2pz]-, has been synthesized by the sequential reaction of LiBH4 with methimazole and pyrazole. Importantly, the ...