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Four Schiff base ligands of the general formulas [6-(

Examination of crystals of cis-Ir(CO)2X(p-toluidine) (X = Cl, Br, I), by single crystal X-ray diffraction shows that the individual monomers self-associate to form extended columns with Ir⋯Ir separations ranging from 3.33 A for the chloro complex to 3.68 A in the iodo complex. The columnar structure is reinforced by hydrogen bonding between the halide ligand in one molecule with an N-H group in an adjacent molecule. This hydrogen bonding causes adjacent molecules to adopt nearly eclipsed orientations. In contrast, the positions of the methyl groups in cis-Ir(CO)2Cl(o-toluidine) and cis-Ir(CO)2Cl(2,6-dimethylaniline) limit intermolecular interactions to the formation of dimers connected by Ir⋯Ir interactions, and hydrogen bonding again occurs between the halide ligand in one molecule and the N-H group in an adjacent molecule. The UV/vis spectrum of cis-Ir(CO)2Cl(p-toluidine) provides evidence that the self-association also occurs in solution. The positive ion mass spectrum of laser ablated crystals of cis-Ir(CO)2Br(p-toluidine) reveals the presence of monomeric, dimeric, and trimeric cations.

With aromatic and aliphatic thiol-S donor Schiff base ligands, the copper–sulfur clusters, [(L1)8CuI6CuII2](ClO4)2·DMF·0.5CH3OH (1) and [(L2)12CuI5CuII11(μ4-S)(μ4-O)6](ClO4)·4H2O, respectively, hav...

The unsymmetrical coordination of gold(I) by 2,2'-bipyridine (bipy) in some planar, three-coordinate cations has been examined by crystallographic and computational studies. The salts [(Ph3P)Au(bipy)]XF6 (X = P, As, Sb) form an isomorphic series in which the differences in Au-N distances range from 0.241(2) to 0.146(2) A. A second polymorph of [(Ph3P)Au(bipy)]AsF6 has also been found. Both polymorphs exhibit similar structures. The salts [(Et3P)Au(bipy)]XF6 (X = P, As, Sb) form a second isostructural series. In this series the unsymmetrical coordination of the bipy ligand is maintained, but the gold ions are disordered over two unequally populated positions that produce very similar overall structures for the cations. Although many planar, three-coordinate gold(I) complexes are strongly luminescent, the salts [(R3P)Au(bipy)]XF6 (R = Ph or Et; X = P, As, Sb) are not luminescent as solids or in solution. Computational studies revealed that a fully symmetrical structure for [(Et3P)Au(bipy)]+ is 7 kJ/mol higher in energy than the observed unsymmetrical structure and is best described as a transition state between the two limiting unsymmetrical geometries. The Au-N bonding has been examined by natural resonance theory (NRT) calculations using the "12 electron rule". The dominant Lewis structure is one with five lone pairs on Au and one bond to the P atom, which results in a saturated (12 electron) gold center and thereby inhibits the formation of any classical, 2 e- bonds between the gold and either of the bipy nitrogen atoms. The nitrogen atoms may instead donate a lone pair into an empty Au-P antibonding orbital, resulting in a three-center, four-electron (3c/4e) P-Au-N bond. The binuclear complex, [μ2-bipy(AuPPh3)2](PF6)2, has also been prepared and shown to have an aurophillic interaction between the two gold ions, which are separated by 3.0747(3) A. Despite the aurophillic interaction, this binuclear complex is not luminescent.

The averages (average deviations from the mean are given in square brackets) of uncorrected Cl—O bond distances in a perchlorate anion from an X-ray diffraction analysis of (N-{2-[bis(pyridin-2-ylmethyl)amino]ethyl}pyridine-2-carboxamidato)(nitric oxide)manganese perchlorate acetonitrile disolvate, [Mn(C20H20N5O)(NO)]ClO4·2CH3CN or [Mn(PaPy3)(NO)]ClO4·2CH3CN, decrease from 1.447 [4] Å at 10 K to 1.428 [4] Å at 170 K. The 10 K value is close to the neutron value (1.441 [1] Å) at 18 K. Comparisons are made with a second X-ray study at 30 K [1.444 (8) Å] and to libration-corrected, density functional theory (DFT), and Cambridge Structural Database (CSD) values.

The crystallization of two solvates of Au11(PPh3)7(SCN)3, 2Au11(PPh3)7(SCN)3·2C6H6·0.5EtOH (1) and Au11(PPh3)7(SCN)3·3EtOH (2), with (1) containing two independent molecules of the cluster, allows the positions of all of the ligands to finally be identified. Despite the bent nature of the thiocyanate ligands, they occupy similar sites to the ones that contain halogen ligands in Au11(PPh3)7Cl3, Au11(PPh3)7I3, and related molecules. However, the relative orientations of these thiocyanate ligands differ in the three cluster sites.

Aliphatic thiolato-S-bridged tri- and binuclear nickel(II) complexes have been synthesized and characterized as models for the Nip site of the A cluster of acetyl coenzyme A synthase (ACS)/carbon m...

Attempts to form covalent C S bonds between fullerenes and dithiolene complexes, Ni(S2C2R2)2, lead only to the formation of the cocrystals C60·Ni(S2C2Ph2)2·0.5C7H8 and 2C70·2Ni(S2C2Ph2)2·C7H8. Both cocrystals contained pairs of Ni(S2C2Ph2)2 molecules that make offset face-to-face contact with Ni⋯Ni distances of 3.8793(5) A in the C60 crystal and 3.7529(9) and 3.7983(9) A in the C70 crystal. The fullerenes are nestled near the NiS4 portion of the Ni(S2C2Ph2)2 molecules. In 2C70·2Ni(S2C2Ph2)2·C7H8 there are two distinctly different interactions between the fullerene and the nickel complex. In one C70·Ni(S2C2Ph2)2 pair, the long axis of the fullerene is nearly parallel to the long axis of the nickel complex, while in the other pair, the long axis of the C70 cage is oriented nearly perpendicular to the long axis of the nickel complex. Thus, the immediate intimate contact between molecules such as fullerenes and flat molecules like Ni(S2C2Ph2)2 is not fixed, but can be altered by other aspects of crystal packing. The structure of a new solvated form of Ni(S2C2Ph2)2, Ni(S2C2Ph2)2·2C6H6, is also reported.

A simple exchange reaction between [AriPr4Sn(μ-Cl)]2 (1) and sodium azide afforded the doubly bridged Sn(II) azide, [AriPr4Sn(μ-N3)]2 (2) (AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2) in 85% yield. Photolysis of a diethyl ether solution of 2 for ca. 16 h yielded an azepinyl-substituted insertion product, [C6H3-2-(C6H3-2,6-iPr2)-6-(C6H3N-3,7-iPr2)Sn]2 (3). The reaction of the Lewis acid, B(C6F5)3 (BCF), or the Lewis base, pyridine, with 2 dissociates the dimer to afford the corresponding complexed monomeric Sn(II) azide, AriPr4SnN3BCF (4) in which BCF coordinates the α-nitrogen, or AriPr4Sn(pyridine)N3 (6) in which pyridine coordinates to the tin atom. Photolysis of 4 in diethyl ether for 12 h results in the insertion of the α-nitrogen of the azide group into one of the B-C bonds of the BCF acceptor to yield the tin(II) amide, AriPr4SnN(C6F5)B(C6F5)2 (5). In contrast, photolysis of 6 for over 36 h afforded no apparent reaction. A highly reactive Sn nitride intermediate, AriPr4Sn≡N, is proposed as part of the mechanistic pathway for the formation of 3 and 5 as a result of trapping the tin-centered radical isomers. This was effected by immediate freezing the samples of 2 or 4 after ca. 30 min of UV photolysis and recording their electron paramagnetic resonance spectra. These exhibited a rhombic g tensor of [g1, g2, g3] = [2.029, 1.978, 1.933]. This radical intermediate could be related to the valence isomers of the nitride [-SnIV≡N] intermediate, in isomeric equilibrium with the nitrene [-SnII-N] and nitridyl [-SnIII═N·] forms, but with the spin density on the nitrogen being quenched, possibly by the H atom abstraction to form an S = 1/2 species of formula -Sn·═N(H).

The structures of Er3N@Ih-C80 and Ho3N@Ih-C80 have been determined by single crystal X-ray diffraction in the cocrystals Er3N@Ih-C80·Ni(OEP)·2benzene and Ho3N@Ih-C80·Ni(OEP)·2benzene where OEP is the dianion of octaethylporphyrin. Comparison of the structural data for M3N@Ih-C80.with M = Gd, Tb, Dy, Ho, Er, Tm, and Sc reveals that, as the ionic radii of the metal ions increase, the anisotropic thermal ellipsoid of the nitrogen becomes more and more elongated until it is better to refine it as split and isotropic as in the cases of Gd3N@Ih-C80 and Tb3N@Ih-C80. The data also indicate that the M3N unit becomes pyramidalized to some extent when the sum of the Shannon-Prewitt crystal radii for six-coordinate M3+ of the three metal ions involved exceeds 3.05 A. There is a gradual progression in the degree of distortion as the metal ion sizes increase. This statement holds true for both homometallic and heterometallic endohedrals of the type M3N@Ih-C80.

The reaction of the piperazine mono-adduct, N(CH2CH2)2NC60, with diiodine produced well ordered, black crystals of (I2N(CH2CH2)2NI2)C60·2.884(C6H6)·0.116I2, which contains two nearly linear N-I-I units. Reaction of N(CH2CH2)2NC60 with iodine monochloride produced two materials: the dihalogen adduct, (ClIN(CH2CH2)2NICl)C60·2.3(CS2)·0.7(CH2Cl2), when crystallization occurred rapidly from carbon disulfide/dichloromethane solution or the salt, [(N(CH2CH2)2NH)C60+][ICl2-]·CS2, when crystallization happened more slowly from toluene/dichloromethane solution where hydrolysis of the iodine monochloride by adventitious water presumably occurred.

Fully spin delocalized mixed valence copper–sulfur clusters, 1 and 2, supported by μ4-sulfido and NSthiol donor ligands are synthesized and characterized. Wheel shaped 1 consists of Cu2S2 units. The unprecedented nanoball 2 can be described as S@Cu4(tetrahedron)@O6(octahedron)@Cu12S12(cage) consisting of both Cu2S2 and (μ4-S)Cu4 units. The Cu2S2 and (μ4-S)Cu4 units resemble biological CuA and CuZ sites respectively.

The proton-coupled reduction of CuII-bound nitrite (NO2-) to nitric oxide (NO2- + 2H+ + e- → NO(g) + H2O), such as occurs in the enzyme copper nitrite reductase, is investigated in this work. Our studies focus on the copper(II/I) model complexes [(L2)Cu(H2O)Cl] (1), [(L2)Cu(ONO)] (2), [(L2)Cu(CH3CO2)] (3), and [Co(Cp)2][(L2)Cu(NO2)(CH3CN] (4), where HL2 = N-[2-(methylthio)ethyl]-2'-pyridinecarboxamide. Complex 1 readily reacts with a NO2- anion to form the nitrito-O-bound copper(II) complex 2. Electrochemical reduction of CuII → CuI indicates coordination isomerization from asymmetric nitrito-κ2-O,O to nitro-κ1-N. Isolation and spectroscopic characterization of 4 support this notion of nitrite coordination isomerization (νCu-N ∼ 460 cm-1). A reduction of 2, followed by reaction with acetic acid, causes evolution of stoichiometric NO via the transient copper(II) nitrosyl species and subsequent formation of the acetate-bound complex 3. The probable copper nitrosyl intermediate [(L2)Cu(NO)(CH3CN)]+ of the {CuNO}10 type is evident from low-temperature UV-vis absorption (λmax = 722 nm) and electron paramagnetic resonance spectroscopy. A density functional theory (DFT)-optimized model of [(L2)Cu(NO)(CH3CN)]+ shows end-on NO binding to Cu with Cu-N(NO) and N-O distances of 1.989 and 1.140 A, respectively, and a Cu-N-O angle of 119.25°, consistent with the formulation of CuII-NO•. A spin-state change that triggers NO release is observed. Considering singlet- and triplet-state electronic configurations of this model, DFT-calculated νNO values of 1802 and 1904 cm-1, respectively, are obtained. We present here important mechanistic aspects of the copper-mediated nitrite reduction pathway with the use of model complexes employing the ligand HL2 and an analogous phenyl-based ligand, N-[2-(methylthio)phenyl]-2'-pyridinecarboxamide (HL1).

One new 2D coordination polymer of Ni(II) namely [Ni2(ndc)2(DMSO)4(H2O)] n , where ndc = naphthalene-1,4-dicarboxylic acid and DMSO = dimethyl sulfoxide, has been synthesized and characterized by elemental analysis, spectral (IR, UV–Vis), thermal (TG/DTG) analysis and single-crystal X-ray diffraction. This coordination polymer possesses a 2D layer structure constructed from dinuclear nickel(II) building blocks in which two crystallographically independent Ni2+ ions are bridged by ndc2− ligands and water molecule. The ndc2− ligands adopt μ3 bridging modes, linking the metal centers into a two-dimensional coordination network. The two independent NiII cations are surrounded by dimethyl sulfoxide and naphthalene-1,4-dicarboxylate molecules in a distorted octahedron geometry. In the crystal structures of Ni(II) coordination polymer, there are non-classical hydrogen bonding arrangements and C–H∙∙∙π stacking interactions. Electrochemical behavior of [Ni2(ndc)2(DMSO)4(H2O)] n , (Ni-NDA) on the surface of carbon nanotubes (CNTs)/glassy carbon electrode (GCE) was described. The surface structure of the sensor was characterized by scanning electron microscopy (SEM). Oxidation of fructose on the surface of modified electrode was investigated with cyclic voltammetry and electrochemical impedance spectroscopy (EIS) and the results showed that the Ni-NDA/CNTs film displays excellent electrochemical catalytic activities toward fructose oxidation.

While several nonchromatographic methods are available for the isolation and purification of endohedral fullerenes of the type M3N@Ih-C80, little work has been done that would allow other members of the M3N@C2n family to be isolated with minimal chromatography. Here, we report that Gd3N@D2(35)-C88 can be isolated from the multitude of endohedral and empty cage fullerenes present in carbon soot obtained by electric-arc synthesis using Gd2O3-doped graphite rods. The procedure developed utilizes successive precipitation with the Lewis acids CaCl2 and ZnCl2 followed by treatment with amino-functionalized silica gel. The structure of the product was identified by single-crystal X-ray diffraction.

New insight into the complexity of the reaction of the prominent catalyst RuCl2(PPh3)3 with carbon disulfide has been obtained from a combination of X-ray diffraction and (31)P NMR studies. The red-violet compound originally formulated as a cationic π-CS2 complex, [RuCl(π-CS2)(PPh3)3]Cl, has been identified as a neutral molecule, RuCl2(S2CPPh3)(PPh3)2, which contains the unstable zwitterion S2CPPh3. In the absence of RuCl2(PPh3)3, there is no sign of a reaction between triphenylphosphine and carbon disulfide, although more basic trialkylphosphines form red adducts, S2CPR3. Despite the presence of an unstable ligand, RuCl2(S2CPPh3)(PPh3)2 is remarkably stable. It survives melting at 173-174 °C intact, is stable to air, and undergoes reversible electrochemical oxidation to form a monocation. When the reaction of RuCl2(PPh3)3 with carbon disulfide is conducted in the presence of methanol, crystals of orange [RuCl(S2CPPh3)(CS)(PPh3)2]Cl·2MeOH and yellow RuCl2(CS)(MeOH)(PPh3)2 also form. (31)P NMR studies indicate that the unsymmetrical dinuclear complex (SC)(Ph3P)2Ru(μ-Cl)3Ru(PPh3)2Cl is the initial product of the reaction of RuCl2(PPh3)3 with carbon disulfide. A path connecting the isolated products is presented.

In order to gain insight into the coordination site and oxidative activity of the CuM site of hydroxylases such as peptidylglycine α-hydroxylating monooxygenase (PHM), dopamine β-monooxygenase (DβM), and tyramine β-monooxygenase (TβM), we have synthesized, characterized and studied the oxidation chemistry of copper complexes chelated by tridentate N2Sthioether, N2Osulfoxide or N2Osulfone donor sets. The ligands are those of N-2-methylthiophenyl-2'-pyridinecarboxamide (HL1), and the oxidized variants, N-2-methylsulfenatophenyl-2'-pyridinecarboxamide (HL1(SO)), and N-2-methylsulfinatophenyl-2'-pyridinecarboxamide (HL1(SO2)). Our studies afforded the complexes [(L1)Cu(II)(H2O)](ClO4)·H2O (1·H2O), {[(L1(SO))Cu(II)(CH3CN)](ClO4)}n (2), [(L1)Cu(II)(ONO)] (3), [(L1(SO))Cu(II)(ONO)]n (4), [(L1)Cu(II)(NO3)]n (5), [(L1(SO))Cu(II)(NO3)]n (6) and [(L1(SO2))Cu(II)(NO3)] (7). Complexes 1 and 3 were described in a previous publication (Inorg. Chem., 2013, 52, 11084). The X-ray crystal structures revealed either distorted octahedral (in 2, 4-6) or square-pyramidal (in 1, 3) coordination geometry around Cu(II) ions of the complexes. In the presence of H2O2, conversion of 1→2, 3-5→6 and 6→7 occurs quantitatively via oxidation of thioether-S and/or Cu(ii) coordinated NO2(-) ions. Thioether-S oxidation of L1 also occurs when [L1](-) is reacted with [Cu(I)(CH3CN)4](ClO4) in DMF under O2, albeit low in yield (20%). Oxidations of thioether-S and NO2(-) were monitored by UV-Vis spectroscopy. Recovery of the sulfur oxidized ligands from their metal complexes allowed for their characterization by elemental analysis, (1)H NMR, FTIR and mass spectrometry.

Bio-inspired manganese [Mn(N5Py)(H2O)(CH3OH)](ClO4)2 (1) and iron [Fe(N5Py)(H2O)(ClO4)]ClO4 (2) complexes derived from a pentadentate ligand (N5Py = 2,6-bis((E)-1-phenyl-2-(pyridin-2-ylmethylene)hydrazinyl)pyridine) framework containing a N5 binding motif were synthesized and characterized using different spectroscopic methods. The molecular structures of complexes 1 and 2 were determined by X-ray crystallography. These complexes were found to be stable under physiological conditions and exhibited an excellent superoxide dismutase (SOD) activity. The SOD activity was determined by a xanthine-xanthine oxidase-nitro blue tetrazolium assay and the IC50 values were determined to be 1.53 and 2.09 μM, respectively.

The tin(II) hydride [AriPr6Sn(μ-H)]2(AriPr6 = C6H3-2,6(C6H2-2,4,6-iPr3)2) (1a) reacts with 2 equiv of ethylene or t-butylethylene at ca. 25 °C to yield Sn2(AriPr6)2R2(R = ethyl or t-butylethyl), which exist either as a symmetric distannene AriPr6(R)SnSn(R)AriPr6 (2a or 5a) or an unsymmetric stannylstannylene AriPr6SnSnR2AriPr6 (3a). In contrast, the less crowded Sn(II) hydride [AriPr4Sn(μ-H)]2 (AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2) (1b) reacts with excess ethylene to give AriPr4(CH2CH3)2Sn(CH2CH2)Sn(CH2CH3)(CHCH2)AriPr4 (4) featuring five ethylene equivalents, one of which is dehydrogenated to an vinyl, −CH═CH2, group. The AriPr4 isomers of 2a and 3a, i.e., [AriPr4Sn(C2H5)]2 (2b) and AriPr4SnSn(C2H5)2AriPr4 (3b) are obtained by reaction of [AriPr4Sn(μ-Cl)]2 with EtLi or EtMgBr. The isomeric pairs 2a and 3a are separated by crystallization at different temperatures. Variable-temperature 1H NMR spectroscopy indicates fast ethyl group exchange between Ar(C2H5)SnSn(C2H5)Ar (Ar = AriPr6 (2a) or AriPr4 (2b)) and A...

A functionalized β-dialdimine was prepared, bearing a 3,3-dimethylindoleninyl group at the meso-position and two N-phenolic groups. The structure contains three labile protons, which can be lost or migrate through tautomerism to provide an N2O2 coordination core. A number of divalent and trivalent metal ions (CuII, NiII, CoII/III, and MnIII) were accommodated inside the core, forming a series of intensely colored products consisting of a tricyclic MN2O2 chelate. In the resulting divalent metal complexes, the dialdimine ligand is deprotonated only at the two phenolic oxygen atoms and is thus dianionic, whereas in the trivalent metal complexes, the dialdiminato ligand is triply deprotonated. The copper and nickel complexes adopt square-planar geometries, whereas in the trivalent cobalt and manganese complexes, two neutral ancillary ligands complete an octahedral geometry around the metal center. In each case, the denticity of the diimino–diiminato ligand is four. The electrochemical oxidation of the copper and nickel complexes was studied by cyclic voltammetry.

Ag(I)–Ag(I) interactions in supramolecular structures have been achieved through the use of structural support from the ligand frames. In structures involving simple ligands like pyridine, strong π–π interaction leads to spatial ordering of the individual [Ag(L)2]+ units. In such structures anions also play a crucial role in dictating the final arrangement of the [Ag(L)2]+ synthons. In order to determine whether the anions can solely dictate the arrangement of the [Ag(L)2]+ synthons in the supramolecular structure, four Ag(I) complexes of 4-pyridylcarbinol (PyOH), namely, [Ag(PyOH)2]X (X = NO3– (1), BF4– (2), CF3SO3– (3), and ClO4– (4)) have been synthesized and structurally characterized. Gradual transformation of the extended structures observed in 1–3 eventually merges into a unique linear alignment of the [Ag(PyOH)2]+ units in 4 along the c axis, a feature that results in strong argentophilic interactions. Complex 4 is sensitive to light and is inherently less stable than the other three analogues. The structural variations in this set of extended assemblies are solely dictated by the anions, since π–π interaction between the substituted pyridine ligands is significantly diminished due to disposition of the −CH2OH substituent at the 4 position and H-bonding throughout the structure., Anions direct the topologies of the supramolecular structures derived from Ag(I) and 4-pyridylcarbinol.

A proton-transfer ion pair compound, (acrH)+(pydcH)−·H2O (1), was synthesized by the reaction of acridine (acr) and pyridine-2,6-dicarboxylic acid (pydcH2). The reaction of compound 1 with palladium (II) chloride led to palladium (II) complex formulated as [Pd(pydc)(acr)] (2). Compounds 1 and 2 were characterized by elemental analysis, 1H NMR, IR, UV–Vis spectroscopy as well as X-ray diffraction method. Intermolecular hydrogen-bonding interactions, as well as π–π stacking, play important roles in the structure of compound 1. The equilibrium constants of acid (pydc) and acridine (acr), as well as complex, were investigated by a potentiometric pH titration method.

The reactions of the air- and water-stable tris(aqua) complex [Cp*Rh(H2O)3](OTf)2 (1; OTf = trifluoromethanesulfonate) with nucleobases and nucleosides that included 9-methyladenine (9-MA), 9-ethylguanine (9-EG), 9-methylhypoxanthine (9-MH), 9-ethylhypoxanthine (9-EH), 1-methylcytosine (1-MC), 1-methylthymine (1-MT), adenosine (Ado), and guanosine (Guo) provided new bonding modes, all as a function of pH. The 9-MA nucleobase provided a novel cyclic trimer, at pH 6, characteristic for all Ado complexes: [Cp*Rh(μ2-η1(N1):η2(N6,N7)-9-MA/Ado)]3(OTf)3. The Cp*Rh(9-EG) and Cp*Rh(Guo) complexes showed N7 and 6-C═O binding modes in water, [Cp*Rh((η2(N7,O6)-9-EG/Guo)(OH)](OTf), and no cyclic trimer products, due to a pronounced steric effect of the 2-amino group. This was shown convincingly by the results with 9-MH and 9-EH, which did form cyclic trimers at pH 6.1, [Cp*Rh(μ2-η1(N1):η2(N7,O6)-9-MH/9-EH)]3(OTf)3, with a structure similar to that of 9-EG, but with no 2-amino group available. At pH 10.2, the pKa of th...

Gadolinium-containing endohedral fullerenes represent a new class of effective relaxation agents for magnetic resonance imaging (MRI). The range of different structures possible for this class of molecules and their properties as MRI agents are reviewed here.

We report high-frequency (up to 219 GHz) and correspondingly high-field electron paramagnetic resonance spectra and X-ray crystal structure of [Co4O4(pyridine)(4)(acetate)(4)](+) ([Co4O4(py)(4)(OAc ...

Three new supramolecular compounds, (aacrH)2[Zn(hypydc)2]� 4H2O 1, (aacrH)2[UO2(hypydc)2]� 2DMSO 2, and (aacrH)2[Ni(hypydc)2]� 4H2O 3, [where hypydcH2 = 4-hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid), aacr = 9-aminoacridine and DMSO = dimethyl sulfoxide] have been synthesized and characterized by elemental analysis, spectral (IR, UV–Vis, fluorescence), 1 H NMR spectroscopy, thermal (TG/ DTG/DTA) analysis and single crystal X-ray diffraction. All three compounds are proton transfer salts of the aminoacridinium cation and transition metal complex anions that crystallized from a solution of the dicarboxylic acid, aminoacridine, and metal nitrates as starting materials. The coordinating dicarboxylic acid is deprotonated at the carboxyl rather than the hydroxyl group, and the aminoacridine is selectively protonated at the pyridyl nitrogen but not at the amino group. In the crystal structures of 1–3 complex hydrogen bonding arrangements and p–p stacking play important roles. Water clusters (H2O)n [n = 2–4] are formed in compounds 1 and 3. The complexes are strongly luminescent at room temperature, exhibiting a sharp emission at 400 nm. The equilibrium constants of chelidamic acid (hypydc), 9-aminoacridine (aacr), proton transfer system as well as those of the complexes, were investigated by a potentiometric pH titration method.

Black crystals of Sc 3 N@ D 3h (5)–C 78 ·Ni II (OEP)·2(benzene) contain a fully ordered endohedral fullerene cage and fully ordered contents. Thus, the X-ray crystallographic study allows detailed examination of its structural properties. The planar Sc 3 N group lies perpendicular to the threefold axis of the fullerene cage with the scandium ions bound to the three 6:6 ring junctions that lie in the horizontal mirror plane of the molecule. The Sc–N distances are 2.0111(10), 2.0106(10), and 1.9998(10) A and the shortest Sc–C distances fall in the range 2.2371(13)–2.2591(13) A. Those six carbon atoms nearest the scandium ions are the most pyramidalized carbon atoms in the molecule with an average θ p = 13.9° compared to θ p = 11.6° for C 60 and to average θ p = 11.3° for the 12 carbon atoms along the C 3 axis at the poles of the molecule. The C–C bond distances at the 6:6 and 5:6 ring junctions do not show the distinct variations that are found in C 60 . The shortest average C–C bond length, 1.391(2) A, and the longest average bond length, 1.466(1) A, occur at 6:6 ring junctions.

The complexes, Pb(ChAr(Pri4))2 (Ch = O (1), S (2); Ar(Pri4) = C6H3-2,6-(C6H3-2,6-Pr(i)2)2) were synthesized by alcoholysis and salt metathesis routes and represent the first fully characterized monomeric, two-coordinate, lead dichalcogenolates in the solid state. Structural studies showed that the S-Pb-S angle (77.21(4)°) is about 22° narrower than the corresponding O-Pb-O angle. (207)Pb NMR and electronic spectroscopy show that the separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) decreases from the bisaryloxo plumbylene to the bisthiolato derivative. Reaction of LiSAr(Me6) with PbBr2 in a 2:1 ratio led not to Pb(SAr(Me6))2, but to a mixture of the monothiolato lead(II) complex, {Pb(Br)(μ-SAr(Me6))}2 (3) and the lithium tristhiolato plumbate, LiPb(SAr(Me6))3 (4). 3 and 4 were isolated and purified by fractional recrystallization, and both were characterized by X-ray crystallography and spectroscopic studies.

A new dibenzotetraaza[14]annulene bearing two 3,3-dimethylindolenine fragments at the meso positions (LH(2)), has been synthesized through a nontemplate method. X-ray crystallography shows that the whole molecule is planar. The basicity of the indolenine ring permits the macrocycle to be protonated external to the core and form LH(4)(2+)·2Cl(-). Yet another structural modification having strong C-H···π interactions was found in the chloroform solvate of LH(2). The latter two modifications are accompanied by a degree of nonplanar distortion. The antiaromatic core of the macrocycle can accommodate a number of metal ions, Mn(III), Fe(III), Co(II), Ni(II) and Cu(II), to form complexes of [Mn(L)Br], [Mn(L)Cl], [Fe(LH(2))Cl(2)](+)·Cl(-), [Co(L)], [Ni(L)], and [Cu(L)]. In addition, the reaction of LH(2) with the larger Pd(II) ion leads to the formation of [Pd(2)(LH(2))(2)(OAc)(4)] wherein the macrocycle acts as a semiflexible ditopic ligand to coordinate pairs of metal ions via its indolenine N atoms into dinuclear metallocycles. The compounds LH(2), [Co(L)], and [Ni(L)] are isostructural and feature close π-stacking as well as linear chain arrangements in the case of the metal complexes. Variable temperature magnetic susceptibility measurements showed thermally induced paramagnetism in [Ni(L)].

Direct reaction of potassium molybdate (with natural abundance Mo or enriched with (92)Mo or (100)Mo) with excess hydrolyzed homocitric acid-γ-lactone in acidic solution resulted in the isolation of a cis-dioxo bis-homocitrato molybdenum(VI) complex, K(2)[*MoO(2)(R,S-H(2)homocit)(2)]·2H(2)O (1) (*Mo=Mo, 1; (92)Mo, 2; (100)Mo, 3; H(4)homocit=homocitric acid-γ-lactone·H(2)O) and K(2)[MoO(2)((18)O-R,S-H(2)homocit)(2)]·2H(2)O (4). The complex has been characterized by elemental analysis, FT-IR, solid and solution (13)C NMR, and single crystal x-ray diffraction analysis. The molybdenum atom in (1) is quasi-octahedrally coordinated by two cis oxo groups and two bidentate homocitrate ligands. The latter coordinates via its α-alkoxy and α-carboxy groups, while the β- and γ-carboxylic acid groups remain uncomplexed, similar to the coordination mode of homocitrate in the Mo-cofactor of nitrogenase. In the IR spectra, the MoO stretching modes near 900 cm(-1) show 2-3 cm(-1) red- and blue-shifts for the (92)Mo-complex (2) and (100)Mo-complex (3) respectively compared with the natural abundance version (1). At lower frequencies, bands at 553 and 540 cm(-1) are assigned to ν(Mo-O) vibrations involving the alkoxide ligand. At higher frequencies, bands in the 1700-1730 cm(-1) region are assigned to stretching modes of protonated carboxylates. In addition, a band at 1675 cm(-1) was observed that may be analogous to a band seen at 1677 cm(-1) in nitrogenase photolysis studies. The solution behavior of (1) in D(2)O was probed with (1)H and (13)C NMR spectra. An obvious dissociation of homocitrate was found, even though bound to the high valent Mo(VI). This suggests the likely lability of coordinated homocitrate in the FeMo-cofactor with its lower valence Mo(IV).

Highly regioselective 1,3-dipolar cycloaddition of 3,5-dichloro-2,4,6-trimethoxybenzonitrile oxide (1) to Sc3N@Ih-C80 or C60 affords the corresponding isoxazoline-ring-fused derivatives Sc3N@Ih-C80(C10H9O4NCl2) (2a) and C60(C10H9O4NCl2) (2b). 2a represents the first example of an endohedral metallofullerene derivative with an isoxazoline ring. Crystallographic and NMR spectroscopic studies reveal a [5,6]-bond addition pattern in 2a but a [6,6]-bond addition manner in 2b.

Ditetryldiyl ethers (Ar′E)2(μ-O) (E = Ge, Sn; Ar′ = C6H3-2,6-(C6H3-2,6-iPr2)2) which contain a pair of two-coordinate Sn or Ge atoms were successfully prepared by the reaction of the corresponding ...

An adaptation of Kagan’s method for preparing 2-substituted ferrocenecarboxaldehydes has allowed us to directly prepare enantiopure (Sp)-2-chloromercurio-ferrocenecarboxaldehyde, (Sp)-3. Subsequent condensation of this aldehyde with (1R,2R)-(+)-1,2-diphenyl-1,2-ethanediamine ((R,R)-4) yielded a novel, enantiopure bis-cyclomercurated ferrocenylimine, (Sp,Sp,Rc,Rc)-N,N-bis(2-(chloromercurio)ferrocenylidene)-1,2-diphenylethane-1,2-diimine ((Sp,Sp,Rc,Rc)-5). In addition to the chiroptical data collected for both (Sp)-3 and (Sp,Sp,Rc,Rc)-5, the solid-state structure and absolute configuration of (Sp,Sp,Rc,Rc)-5 were confirmed by X-ray crystallography.

Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the catalytic sites, the rates of which are unknown. Here we report the exchange rates of water ligated to Co(II) atoms in two polyoxotungstate sandwich molecules using the (17)O-NMR-based Swift-Connick method. The compounds were the [Co(4)(H(2)O)(2)(B-α-PW(9)O(34))(2)](10-) and the larger αββα-[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-) ions, each with two water molecules bound trans to one another in a Co(II) sandwich between the tungstate ligands. The clusters, in both solid and solution state, were characterized by a range of methods, including NMR, EPR, FT-IR, UV-Vis, and EXAFS spectroscopy, ESI-MS, single-crystal X-ray crystallography, and potentiometry. For [Co(4)(H(2)O)(2)(B-α-PW(9)O(34))(2)](10-) at pH 5.4, we estimate: k(298)=1.5(5)±0.3×10(6) s(-1), ΔH(≠)=39.8±0.4 kJ mol(-1), ΔS(≠)=+7.1±1.2 J mol(-1) K(-1) and ΔV(≠)=5.6 ±1.6 cm(3) mol(-1). For the Wells-Dawson sandwich cluster (αββα-[Co(4)(H(2)O)(2)(P(2)W(15)O(56))(2)](16-)) at pH 5.54, we find: k(298)=1.6(2)±0.3×10(6) s(-1), ΔH(≠)=27.6±0.4 kJ mol(-1) ΔS(≠)=-33±1.3 J mol(-1) K(-1) and ΔV(≠)=2.2±1.4 cm(3) mol(-1) at pH 5.2. The molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions. This dissociation is detectable by EPR spectroscopy as S=3/2 Co(II) species (such as the [Co(H(2)O)(6)](2+) monomer ion) and by the significant reduction of the Co-Co vector in the XAS spectra.

Three indolyl-imine ligands have been synthesized through the condensation of S-benzyldithiocarbazate with indole-2-carbaldehyde, indole-3-carbaldehyde and indole-7-carbaldehyde. Treatment of these Schiff bases with acetate salts of Ni(II), Zn(II) and Cd(II) in ethanol yielded a series of complexes of 2:1 type (ligand/metal ratio) in which the ligands coordinated to the metal ions as monoanionic NS bidentate chelates. While the 2-imineindole and 3-imineindole formed the expected five-membered chelate rings, the X-ray crystal structure of [Cd(HL 3 )(py) 2 ], (HL 3 = the mono-deprotonated 7-imineindole), revealed an unusual mode of coordination, namely formation of four-membered rings with the metal atom. Reaction of the 7-imineindole with the metal ions in the presence of potassium hydroxide produced complexes of the type [M(L 3 )(H 2 O)] in which the Schiff base acts as a dianionic NNS tridentate ligand.

Several new ferrocenylimines containing both planar and central chirality were prepared from (Sp)-2-(diphenylphosphino)ferrocenecarboxaldehyde and chiral primary amines. One of these compounds, (Sp,Sc)-3, induced particularly high conversions (92−99%) and enantioselectivities (91−94% ee) when applied as a P−N ligand in the asymmetric allylic alkylation (AAA). In addition, a precatalyst complex was formed from (Sp,Sc)-3 and di-μ-chlorobis[(η3-C3H5)palladium(II)] and isolated after anion exchange with NaBF4 to give [Pd(η3-C3H5)((Sp,Sc)-3)]BF4 (4). High conversions (99%) and enantioselectivities (90−93% ee) were also observed when the isolated precatalyst (4) was used in the AAA reaction. Crystal structures were obtained for all three ligands prepared for this study ((Sp,Sc)-1−3) and for the isolated precatalyst (4). These compounds were also investigated by CD spectroscopy.

The ambidentate ligand nitrite (NO2) binds to transition metal centers through the N (nitro) or O (nitrito) atom. In metal porphyrin complexes, the energy difference between the two linkage isomers is small and hence slight differences in reaction conditions and/or ligand design give rise to formation of the isomers in different ratios. In the present work, similar behavior has been observed in case of the {Fe–NO}6 nitrosyl [(Me2bpb)Fe(NO)(NO2)] (2), derived from a non-heme planar dicarboxamide ligand N,N′-bispyridinecarboxamido-4,5-dimethylbenzenediamine (H2Me2bpb). Under anaerobic conditions, reaction of the Fe(III) complex [(Me2bpb)Fe(py)2]ClO4 (1) with NO(g) in MeCN affords 2, a product that contains both the N- and O-bound isomer in different ratios depending on the reaction conditions. In protic solvents, the same reaction affords the {Fe–NO}7 nitrosyl [(Me2bpb)Fe(NO)] (3). Both nitrosyls have been characterized by infrared spectroscopy and X-ray diffraction studies.

The solvent-free reaction of M{N(SiMe(3))(2)}(2) (M = Ge, Sn, or Pb) with the sterically encumbered primary amine 2,6-dimesitylaniline Ar(#)NH(2) [Ar(#) = C(6)H(3)-2,6(C(6)H(2)-2,4,6-Me(3))(2)] at ca. 165-175 degrees C afforded the highly colored imido dimers {M(mu-NAr(#))}(2), where M = Ge (1), Sn (2), or Pb (3), with disilylamine elimination. The compounds were characterized by single-crystal X-ray crystallography and heteronuclear NMR spectroscopy. The structures of 1-3 were very similar and had nonplanar four-membered M(2)N(2) ring cores that are folded along the M---M axis. The nitrogen atoms are planar-coordinated, and the M-N distances are consistent with single bonding. The reaction of M{N(SiMe(3))(2)}(2) with Ar(#)NH(2) in a 2:1 ratio in solution at lower temperature afforded the relatively stable monomeric primary amido species M{N(H)Ar(#)}(2), where M = Ge (4), Sn (5), or Pb (6). Complexes 4-6 displayed V-shaped MN(2) structures, and 5 and 6 revealed close approaches between the metal atom and ipso-carbon atoms of two flanking Mes groups of the terphenyl substituents [Sn(II)---C (2.957 A) and Pb(II)---C (2.965 A)]. The secondary metal-ligand interactions exerted large effects on their electronic and NMR spectra.

The relative energies of the carbene species in a variety of metathesis reactions catalyzed by Grubbs first-generation catalyst (Cy3P)2Cl2Ru═CHC6H5 have been determined. High-quality equilibrium data are obtainable by 1H NMR methods. In the case of para-substituted aromatic derivatives (Cy3P)2Cl2Ru═CH(p-C6H4X), the carbenes are stabilized by donor substituents, and energies may be determined indirectly by use of either NMR data or Hammett correlations, because only electronic effects are operative. Four systems have been characterized by X-ray crystallography. The energies of alkyl-substituted carbenes (Cy3P)2Cl2Ru═CHR are almost entirely dependent on steric interactions.

Complex cis-(PMe3)4RuCl(OAc) (1) acts as a catalyst for CO2 hydrogenation into formic acid in the presence of a base and an alcohol cocatalyst. NMR spectroscopy has revealed that 1 exists in solution in equilibrium with fac-(PMe3)3RuCl(η2-OAc) (2), [(PMe3)4Ru(η2-OAc)]Cl (3a), and free PMe3. Complex 2 was found to be a poor CO2 hydrogenation catalyst under the conditions of catalysis used for 1. Complex 3a can be prepared by adding certain alcohols, such as MeOH, EtOH, or C6H5OH, to a solution of 1 in CDCl3. The chloride ion of 3a was exchanged for the noncoordinating anion BPh4− or B(ArF)4− (B(ArF)4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate) to produce [(PMe3)4Ru(η2-OAc)]BPh4 (3b) and [(PMe3)4Ru(η2-OAc)]B(ArF)4 (3c). Complexes 3b and 3c were found to be as efficient as 1 in the catalytic hydrogenation of CO2 to formic acid in the presence of an alcohol cocatalyst. In contrast to 1, 3b and 3c continued to show high catalytic activity in the absence of the alcohol cocatalyst. High-pressure NMR spectr...

An isomerically pure sample of Gd(3)N@C(78) has been extracted from the carbon soot formed in the electric-arc generation of fullerenes using hollow graphite rods packed with Gd(2)O(3) and graphite powder under an atmosphere of helium and dinitrogen. Purification has been achieved by chromatographic methods and the product has been characterized by mass spectrometry, UV/vis absorption spectroscopy, and cyclic voltammetry. Although a number of endohedral fullerenes have been found to utilize the D(3h)(5)-C(78) cage, comparison of the spectroscopic and electrochemical properties of the previously characterized Sc(3)N@D(3h)(5)-C(78) with those of Gd(3)N@C(78) reveals significant differences that indicate that these two endohedrals do not possess the same cage structure. A single crystal X-ray diffraction study indicates that the fullerene cage does not follow the isolated pentagon rule (IPR) but has two equivalent sites where two pentagons abut. The endohedral has been identified as Gd(3)N@C(2)(22010)-C(78). Two of the gadolinium atoms of the planar Gd(3)N unit are located within the pentalene folds formed by the adjacent pentagons. The third gadolinium atom resides at the center of a hexagonal face of the fullerene.

Dimeric arylgallium/indium chalcogenides 7−10 of formula [Ar′ME]2 (Ar′ = C6H3-2,6-(C6H3-2,6-Pri2)2; M = Ga or In, E = O or S) were synthesized by the treatment of Ar′MMAr′ with N2O or elemental sulfur and characterized by NMR spectroscopy and X-ray crystallography. Their structures feature three-coordinate, +3 oxidation state metal centers with planar M2E2 cores. The cores were almost perfectly square for E = O, but for E = S, they were distorted parallelograms in 7−10. The M–E bond lengths were shorter than those in the higher aggregated species [RME]n (n ≥ 4) but comparable to those in M3+ aryloxides or thiolates featuring three-coordinate metals. Short M···M separations [2.553(1) A in 7, 2.8882(4) A in 8, 2.8276 A (avg.) in 9, and 3.1577(8) A in 10] are observed. Low oxidation heavier group 13/group 16 chalcogenolate isomers 16−19 of formula [Ar′EM]2 (M = In or Tl, E = O or S) were also synthesized and characterized. In the +1 compounds [Ar′EIn]2 (O, 16; S, 19) together, with the In +3 species [Ar′InE]...

The synthesis and characterization of arylzinc hydrides Ar*Zn(μ-H)2ZnAr* (Ar* = C6H3-2,6-(C6H2-2,4,6-Pri3)2, 5) and {(4-Me3Si-Ar*)Zn(μ-H)2Zn(Ar*-4-SiMe3)} (4-Me3Si-Ar* = C6H2-2,6-(C6H2-2,4,6-Pri3)2-4-SiMe3, 7) as well as the monomeric arylcadmium hydride Ar*CdH (9) are described. They were prepared by the transmetalation of the corresponding aryl metal iodides with NaH. The Ar*CdH monomer displayed significantly greater thermal stability than its recently reported dimeric congener Ar′Cd(μ-H)2CdAr′ (Ar′ = C6H3-2,6-(C6H3-2,6-Pri2)2), which decomposed at room temperature to afford Ar′CdCdAr′. This result supports the proposal that decomposition of the metal hydrides occurs by an associative mechanism. The reactions of these compounds with TEMPO (2,2,6,6-tetramethylpiperidinyl oxide) were also examined, but the only crystalline product obtained was 4-Me3Si-Ar*ZnTEMPO, in which the metal is bound to the TEMPO ligand in a quasi side-on fashion primarily through the oxygen but with a significant zinc−nitrogen in...