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A totally unanticipated regio- and stereoisomerically pure C2h -symmetric trans-1-(bis-pyrrolidine)-tetra-malonate hexa-adduct of C60 was obtained via a topologically controlled method, followed by a 1,3-dipolar cycloaddition reaction. The structures of the products were elucidated by 1 H and 13 C NMR and by X-ray crystallography. The unexpected regio- and stereoselectivity observed, supported by theoretical calculations, was found to be a consequence of malonate-pyrrolidine interactions.

The crystal structure determination based on 90 K data of the title imine ligand, C18H10ClNO, revealed non-merohedral twinning with three twin domains. In our experience, this is an indication of an ordering phase transition. Consequently, the structure was redetermined with higher temperature data, and a reversible phase transition was discovered. The higher temperature phase is indeed an ordered structure. At the higher temperature, the 4-chlorophenyl group has rotated by ca 7° into a crystallographic mirror plane. Warming the crystal from 90 K to 250 K changes the space group from triclinic P-1, to monoclinic P21/m. Diverse non-classical interactions are present in the crystal packing, and these are described for the phase change reported in this work. The crystal structure of the title imine ligand, measured at 100 K, has been reported on previously [Kovach et al. (2011). J. Mol. Struct. 992, 33–38].

The structure of Ni(Hpydc)2·3H2O (H2pydc = pyridine-2,6-dicarboxylic acid, also known as dipicolinic acid) has been reinvestigated at variable temperatures. At room temperature, it matches the known structure in the space groupP21/c, but at 180 K it undergoes a phase transformation to a twinned structure inCc. By 120 K, the structure is ordered and twinned withZ′ = 4, and shows interesting short hydrogen-bonding interactions that include the formation of hydroxonium species.

Noncoordinating anions, which generally play a subordinate role in coordination chemistry, alter the structure, the luminescence, as well as the thermochromic and vapochromic behaviors of salts of the two-coordinate cation, [(C

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.

According to the well-accepted mechanism, methyl-coenzyme M reductase (MCR) involves Ni-mediated thiolate-to-disulfide conversion that sustains its catalytic cycle of methane formation in the energy saving pathways of methanotrophic microbes. Model complexes that illustrate Ni-ion mediated reversible thiolate/disulfide transformation are unknown. In this paper we report the synthesis, crystal structure, spectroscopic properties and redox interconversions of a set of NiII complexes comprising a tridentate N2 S donor thiol and its analogous N4 S2 donor disulfide ligands. These complexes demonstrate reversible NiII -thiolate/NiII -disulfide (both bound and unbound disulfide-S to NiII ) transformations via thiyl and disulfide monoradical anions that resemble a primary step of MCR's catalytic cycle.

The synthesis of pyreno[

Purified samples of Ho

Additions of adamantylidene (Ad) to M3 N@Ih -C80 (M=Sc, Lu) and Sc3 N@D5h -C80 have been accomplished by photochemical reactions with 2-adamantyl-2,3'-[3H]-diazirine (1). In M3 N@Ih -C80 , the addition led to rupture of the [6,6]- or [5,6]-bonds of the Ih -C80 cage, forming the [6,6]-open fulleroid as the major isomer and the [5,6]-open fulleroid as the minor isomer. In Sc3 N@D5h -C80 , the addition also proceeded regioselectively to yield three major isomeric Ad mono-adducts, despite the fact that there are nine types of C-C bonds in the D5h -C80 cage. The molecular structures of the seven Ad mono-adducts, including the positions of the encaged trimetallic nitride clusters, have been unambiguously determined through single-crystal XRD analyses. Furthermore, results have shown that stepwise addition of Ad to Lu3 N@Ih -C80 affords several Ad bis-adducts, two of which have been isolated and characterized. The X-ray structure of one bis-adduct clearly revealed that the second Ad addition took place at a [6,6]-bond close to an endohedral metal atom. Theoretical calculations have also been performed to rationalize the regioselectivity.

Conditions for the crystallization and interconversion of the green and brown polymorphs of bis(3-ethylamino-1-phenyl-but-2-en-1-ono)nickel(II) (Ni(B–Et)2), which contain planar and tetrahedral complexes in accord with previous magnetic and spectroscopic studies, have been determined. Additionally, the series of β-diketoamine-containing complexes, M(B–Et)2 and M(B–Bn)2, (M = CoII, NiII, CuII, ZnII) obtained from condensation of benzoylacetone (B) with either ethylamine (Et) or benzylamine (Bn) followed by treatment with [MCl4]2− under basic conditions has been prepared and their structures characterized crystallographically. In contrast to Ni(B–Et)2, Ni(B–Bn)2 has been crystallized only in the planar form. M(B–Et)2 and M(B–Bn)2 (M = Co or Zn) have similar, nearly tetrahedral structures, while Cu(B–Et)2 and Cu(B–Bn)2 have structures that are decidedly intermediate between tetrahedral and planar. Despite the abilities of these complexes to exist in tetrahedral, planar, or intermediate structures in solution, it has not been possible to induce much structural variation in crystalline forms. While two polymorphs of Zn(B–Bn)2 have been obtained, both have similar, tetrahedral structures. Only Ni(B–Et)2 crystallizes in both planar and tetrahedral forms. None of the complexes formed cocrystals with fullerenes or solvates in which structural variation as seen in Ni(B–Et)2 occurred.

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 photochemical reaction of piperazine with C70 produces a mono-adduct (N(CH2 CH2 )2 NC70 ) in high yield (67 %) along with three bis-adducts. These piperazine adducts can combine with various Lewis acids to form crystalline supramolecular aggregates suitable for X-ray diffraction. The structure of the mono-adduct was determined from examination of the adduct I2 N(CH2 CH2 )2 NI2 C70 that was formed by reaction of N(CH2 CH2 )2 NC70 with I2 . Crystals of polymeric {Rh2 (O2 CCF3 )4 N(CH2 CH2 )2 NC70 }n ⋅nC6 H6 that formed from reaction of the mono-adduct with Rh2 (O2 CCF3 )4 contain a sinusoidal strand of alternating molecules of N(CH2 CH2 )2 NC70 and Rh2 (O2 CCF3 )4 connected through Rh-N bonds. Silver nitrate reacts with N(CH2 CH2 )2 NC70 to form black crystals of {(Ag(NO3 ))4 (N(CH2 CH2 )2 NC70 )4 }n ⋅7nCH2 Cl2 that contain parallel, nearly linear chains of alternating (N(CH2 CH2 )2 NC70 molecules and silver ions. Four of these {Ag(NO3 )N(CH2 CH2 )2 NC70 }n chains adopt a structure that resembles a columnar micelle with the ionic silver nitrate portion in the center and the nearly non-polar C70 cages encircling that core. Of the three bis-adducts, one was definitively identified through crystallization in the presence of I2 as 12 {N(CH2 CH2 )2 N}2 C70 with addends on opposite poles of the C70 cage and a structure with C2v symmetry. In 12 {I2 N(CH2 CH2 )2 N}2 C70 , individual 12 {I2 N(CH2 CH2 )2 N}2 C70 units are further connected by secondary I2⋅⋅⋅N2 interactions to form chains that occur in layers within the crystal. Halogen bond formation between a Lewis base such as a tertiary amine and I2 is suggested as a method to produce ordered crystals with complex supramolecular structures from substances that are otherwise difficult to crystallize.

The crystal structures of the title compounds, C19H19NO and C31H34N2O, were determined as part of an experiment in an undergraduate teaching laboratory that demonstrates the relationship between molecular structure and function. 1′,3′,3′-Trimethylspiro[chromene-2,2′-indoline] is both a photoswitch and thermochromic molecule. Students synthesized it and a bis-indoline adduct and compared the crystallographically determined structures to computed gas-phase models.

We report that Ce@C2v(9)-C82 forms a centrosymmetric dimer when co-crystallized with Ni(OEP) (OEP = octaethylporphyrin dianion). The crystal structure of {Ce@C2v(9)-C82}2⋅2[Ni(OEP)]⋅4 C6H6 shows that a new C−C bond with a bond length of 1.605(5) A connects the two cages. The high spin density of the singly occupied molecular orbital (SOMO) on the cage and the pyramidalization of the cage are factors that favor dimerization. In contrast, the treatment of Ni(OEP) with M@C2v(9)-C82 (M = La, Sc, and Y) results in crystallization of monomeric endohedral fullerenes. A systematic comparison of the X-ray structures of M@C2v(9)-C82 (M = Sc, Y, La, Ce, Gd, Yb, and Sm) reveals that the major metal site in each case is located at an off-center position adjacent to a hexagonal ring along the C2 axis of the C2v(9)-C82 cage. DFT calculations at the M06-2X level revealed that the positions of the metal centers in these metallofullerenes M@C2v(9)-C82 (M = Sc, Y, and Ce), as determined by single-crystal X-ray structure studies, correspond to an energy minimum for each compound.

A non-isolated pentagon rule metallic carbide clusterfullerene containing a heptagonal ring, Sc2C2@Cs(hept)-C88, was isolated from the raw soot obtained by electric arc vaporization of graphite rods packed with Sc2O3 and graphite powder under a helium atmosphere. The Sc2C2@Cs(hept)-C88 was purified by multistage high-performance liquid chromatography (HPLC), cocrystallized with Ni–(octaethylporphyrin), and characterized by single-crystal X-ray diffraction. The diffraction data revealed a zigzag Sc2C2 unit inside an unprecedented Cs(hept)-C88 carbon cage containing 13 pentagons, 32 hexagons, and 1 heptagon. Calculations suggest that the observed nonclassical fullerene could be a kinetically trapped species derived from the recently reported Sc2C2@C2v(9)-C86 via a direct C2 insertion.

The formation of endohedral metallofullerenes (EMFs) in an electric arc is reported for the mixed-metal Sc-Ti system utilizing methane as a reactive gas. Comparison of these results with those from the Sc/CH4 and Ti/CH4 systems as well as syntheses without methane revealed a strong mutual influence of all key components on the product distribution. Whereas a methane atmosphere alone suppresses the formation of empty cage fullerenes, the Ti/CH4 system forms mainly empty cage fullerenes. In contrast, the main fullerene products in the Sc/CH4 system are Sc4 C2 @C80 (the most abundant EMF from this synthesis), Sc3 C2 @C80 , isomers of Sc2 C2 @C82 , and the family Sc2 C2 n (2 n=74, 76, 82, 86, 90, etc.), as well as Sc3 CH@C80 . The Sc-Ti/CH4 system produces the mixed-metal Sc2 TiC@C2 n (2 n=68, 78, 80) and Sc2 TiC2 @C2 n (2 n=80) clusterfullerene families. The molecular structures of the new, transition-metal-containing endohedral fullerenes, Sc2 TiC@Ih -C80 , Sc2 TiC@D5h -C80 , and Sc2 TiC2 @Ih -C80 , were characterized by NMR spectroscopy. The structure of Sc2 TiC@Ih -C80 was also determined by single-crystal X-ray diffraction, which demonstrated the presence of a short Ti=C double bond. Both Sc2 TiC- and Sc2 TiC2 -containing clusterfullerenes have Ti-localized LUMOs. Encapsulation of the redox-active Ti ion inside the fullerene cage enables analysis of the cluster-cage strain in the endohedral fullerenes through electrochemical measurements.

Research on plasmonic photoactive materials has resulted in some significant advancements in UV–Vis photo-active catalytic reactions. In this study, pristine ZnO and Ag-ZnO thin films were deposited onto fluorine doped tin oxide (FTO) coated glass substrate from a newly synthesized zinc molecular precursor, {Zn5(TFA)7(OH)2(H2O)4(OAc)}n.2(C4H6O2) [TFA = trifluoroacetate, OAc = acetate], and its homogenous solution with Ag(CH3COO), respectively, via the aerosol assisted chemical vapor deposition (AACVD) technique. The precursor was analyzed by microanalysis, melting point, proton nuclear magnetic resonance (1H NMR), Fourier transformed infra-red (FT-IR), thermogravimetry (TG) and single crystal analysis. Powder X-ray diffraction (PXRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray (EDX), UV–Vis spectroscopic and photoluminescence (PL) analyses were carried out to investigate the phase purity, structural morphology, composition and optical properties of the as-synthesized thin films. Linear scan voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) confirmed that the photo-electrochemical performance of Ag-ZnO for water splitting was much improved compared to ZnO. These results confirm that Ag is an efficient surface plasmon resonance photosensitizer which mediates the interfacial charge transfer process, thus extending the light response of pristine ZnO into the visible region.

The structure of Sc3N@D 3h -C78, which has been examined crystallographically and found to obey the isolated pentagon rule (IPR), will be discussed and compared to other related endohedral fullerenes. The effect of the composition of the interior M3N unit in this and other endohedral fullerenes will be shown to influence cage structure, sometimes in a predictable fashion. Structural studies of other fullerenes will also be presented.

The solid-state structures of seven solvates of C

Aliphatic thiolato-S-bridged tri- and binuclear nickel(II) complexes have been synthesized and characterized as models for the Ni

Two new molecular boxes, the mono-bromo box [Au

The mono- and di-chloroform solvates of [Au

A method has been developed for isolating a pure sample of Er

After more than 50 years, the synthesis and electronic structure of the first and only reported "U0 complex" [U(bipy)4 ] (1) has been reinvestigated. Additionally, its one-electron reduced product [Na(THF)6 ][U(bipy)4 ] (2) has been newly discovered. High resolution crystallographic analyses combined with magnetic and computational data show that 1 and its derivative 2 are best described as highly reduced species containing mid-to-high-valent uranium ligated by redox non-innocent ligands.

The reaction of bis-[2-amino-4-pheny1-5-thiazolyl] disulfide with 5-nitro-salicylaldehyde in absolute ethanol resulted in the formation of a new Schiff base ligand H2L (1). Characterization of the ligand was performed by FT-IR, 1H NMR, 13C NMR, UV-Vis, elemental analysis and single crystal X-ray diffraction. The ligand, (1), possesses a disulfide –S–S– bridge of 2.1121 (3) ? length, and the molecule adopts a cis-conformation around this bond. In the crystal structure of (1), an intramolecular O–H···N hydrogen bond with D… A distance of 2.69 (3) ? was present. The reaction of (1) with Co(NO3)2·6H2O and CuCl2·2H2O in methanol afforded the corresponding metal complexes. The obtained solids were further investigated by elemental analysis and UV-Vis titration that confirmed the formation of [CoL] and [ClCuHL] complexes. However, recrystallizaion of the Co(II) complex in dimethylsulfoxide caused the complete hydrolysis of the imine bond and afforded a Co(II) complex in which two 5-nitro-salicylaldehyde and two DMSO molecules were coordinated to the central metal in an octahedral fashion. This structure (2) was also confirmed by single crystal X-ray analysis.

Two related nickel(II) porphyrins, etioporphyrin-I (Etio-I) and octaethylporphyrin (OEP), were cocrystallized with C70 to produce the new cocrystal structures C70·Ni(Etio-I)·2C6H6 and C70·Ni(OEP)·2C6H6. Etio-I is a variant of OEP, where four alternating ethyl groups from OEP are replaced with methyl substituents. This isomer of etioporphyrin has the potential to act as an agent in chiral sorting of asymmetric fullerenes. However, the replacement of four ethyl groups has nontrivial structural consequences. Further host–guest investigation of M(Etio-I) (M = Co, Ni, Cu, Zn) with C60 or C70 was conducted, producing new X-ray structures of Co(Etio-I) and Zn(Etio-I), and a redetermination of Ni(Etio-I). Despite numerous and varied attempts, C60 cocrystallized with M(Etio-I) could not be obtained.

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.

Bis-silylated and bis-germylated derivatives of Lu3 N@Ih -C80 (3, 4, 5) were successfully synthesized by the photochemical addition of disiliranes 1 a, 1 b or digermirane 2, and fully characterized by spectroscopic, electrochemical, and theoretical studies. Interestingly, digermirane 2 reacts more efficiently than disiliranes 1 a and 1 b because of its good electron-donor properties and lower steric hindrance around the Ge-Ge bond. The 1,4-adduct structures of 3, 4, 5 were unequivocally established by single-crystal X-ray crystallographic analyses. The electrochemical and theoretical studies reveal that the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the 1,4-adducts are remarkably smaller than those of Lu3 N@Ih -C80 , because the electron-donating groups effectively raise the HOMO levels. It is also observed that germyl groups are slightly more electron-donating than the silyl groups on the basis of the redox properties and the HOMO-LUMO energies of 4 and 5. Bis-silylation and bis-germylation are effective and versatile methods for tuning the electronic characteristics of endohedral metallofullerenes.

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.

The synthesis, isolation, and characterization of a new endohedral fullerene, Sc2C88, is reported. Characterization by single crystal X-ray diffraction revealed that it is the carbide Sc2C2@C(2v)(9)-C86 with a planar, twisted Sc2C2 unit inside a previously unseen C(2v)(9)-C86 fullerene cage.

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.

The single crystal X-ray structures of three well-ordered cocrystals of C70 with brominated benzenes are examined. The crystals are those of C70·C6Br6·C7H8, C70·C6Br6·C6H6, and C70·2(1,2,4,5-tetrabromobenzene)·CS2. While all three structures exhibit extensive van der Waals interactions, the presence of a wavelike C–Br---Br structural motif is a distinctive part of the cocrystal assembly. In these three crystal structures, it is observed that the Br---Br interactions are a cross between type I and II halogen–halogen bonds. In our hands, this structural motif does not occur in structures with C60.

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).

A square-planar Ni(II) dibenzotetraaza[14]annulene complex substituted with two 3,3-dimethylindolenine groups in the meso positions has recently been synthesized and characterized experimentally. In the solid-state, the Ni(II) complex forms linear π-interacting stacks with Ni···Ni separations of 3.448(2) Å. Measurements of the temperature dependence of the magnetic susceptibility revealed a drastic change in the magnetic properties at a temperature of 13 K, indicating a transition from low-to-high spin states. The molecular structures of the free-base ligand, the lowest singlet, and triplet states of the monomer and the dimer of the Ni complex have been studied computationally using density functional theory (DFT) and ab initio correlation levels of theory. In calculations at the second-order Møller-Plesset (MP2) perturbation theory level, a large energy of 260 kcal mol(-1) was obtained for the singlet-triplet splitting, suggesting that an alternative explanation of the observed magnetic properties is needed. The large energy splitting between the singlet and triplet states suggests that the observed change in the magnetism at very low temperatures is due to spin-orbit coupling effects originating from weak interactions between the fine-structure states of the Ni cations in the complex. The lowest electronic excitation energies of the dibenzotetraaza[14]annulene Ni(II) complex calculated at the time-dependent density functional theory (TDDFT) levels are in good agreement with values deduced from the experimental UV-vis spectrum. Calculations at the second-order algebraic-diagrammatic construction (ADC(2)) level on the dimer of the meso-substituted 3,3-dimethylindolenine dibenzotetraaza[14] annulene Ni(II) complex yielded Stokes shifts of 85-100 nm for the lowest excited singlet states. Calculations of the strength of the magnetically induced ring current for the free-base 3,3-dimethylindolenine-substituted dibenzotetraaza[14]annulene show that the annulene ring is very weakly antiaromatic, sustaining a paratropic ring-current strength of only -1.7 nA/T.

The reaction of the tetrakis[di(ethoxycarbonyl)methano]-C60 (1) with Ru3(CO)12 afforded the first bis-parallel C60-metal cluster complex: parallel-[Ru3(CO)9]2{μ3-η(2),η(2),η(2)-C60[C(COOC2H5)2]4}. The two triruthenium groups are found in either a parallel or a tilted orientation relative to each other, as determined by NMR. Only the parallel form was characterized by X-ray crystallography.

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.

The compound [PtMe(bzpy)(DMSO)] (1; bzpy = 2-benzylpyridinate) was synthesized by reaction of cis-[PtMe2(DMSO)2] with 1 equiv. of bzpyH under reflux conditions in toluene through C–H activation of the carbon–hydrogen bond in 2-benzylpyridine. Then, the complex [PtMe(bzpy)(PPh3)], 2, was prepared by addition of PPh3 to complex 1. Complex 2 undergoes oxidative addition with methyl iodide to give [PtMe2I(bzpy)(PPh3)], 3. NMR spectroscopy (1H and 31P) and X-ray crystallography (supported by DFT calculations) clearly showed that the thermodynamic isomer product 3, with iodide trans to C of bzpy rather than the related kinetic isomer, 3, in which iodide is trans to methyl, is obtained. Mechanistic studies using UV-vis spectroscopy and DFT calculations indicate that the reaction occurs via a SN2 mechanism. The kinetic study of the oxidative addition of methyl iodide to the non-planar, six-membered cyclometalated complex with that of the five-membered cyclometalated [PtMe(ppy)(PPh3)], in which ppy = 2-phenylpyridinate, shows that the ring size of the chelating unit has a significant impact on the rate of the reaction.

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 crystal structure determination based on 90 K data of the title imine ligand revealed non-merohedral twinning with three twin domains. In our experience, this is an indication of an ordering phase transition. Consequently, the structure was redetermined with higher temperature data, and a reversible phase transition was discovered., The crystal structure determination based on 90 K data of the title imine ligand, C18H10ClNO, revealed non-merohedral twinning with three twin domains. In our experience, this is an indication of an ordering phase transition. Consequently, the structure was redetermined with higher temperature data, and a reversible phase transition was discovered. The higher temperature phase is indeed an ordered structure. At the higher temperature, the 4-chloro­phenyl group has rotated by ca 7° into a crystallographic mirror plane. Warming the crystal from 90 K to 250 K changes the space group from triclinic P-1, to monoclinic P21/m. Diverse non-classical inter­actions are present in the crystal packing, and these are described for the phase change reported in this work. The crystal structure of the title imine ligand, measured at 100 K, has been reported on previously [Kovach et al. (2011 ▸). J. Mol. Struct. 992, 33–38].

A totally unanticipated regio- and stereoisomerically pure C

Reactions of the Sn(II) hydrides [ArSn(μ-H)]2 (1) (Ar = AriPr4 (1a), AriPr6 (1b); AriP4 = C6H3-2,6-(C6H3-2,6-iPr2)2, AriPr6 = C6H3-2,6-(C6H2-2,4,6-iPr3)2) with norbornene (NB) or norbornadiene (NBD) readily generate the bicyclic alkyl-/alkenyl-substituted stannylenes, ArSn(norbornyl) (2a or 2b) and ArSn(norbornenyl) (3a or 3b), respectively. Heating a toluene solution of 3a or 3b at reflux afforded the rearranged species ArSn(3-tricyclo[2.2.1.02,6]heptane) (4a or 4b), in which the norbornenyl ligand is transformed into a nortricyclyl group. 1H NMR studies of the reactions of 4a or 4b with tert-butylethylene indicated the existence of an apparently unique reversible β-hydride elimination from the bicyclic substituted aryl/alkyl stannylenes 2a or 2b and 3a or 3b. Mechanistic studies indicated that the transformation of 3a or 3b into 4a or 4b occurs via a β-hydride elimination of 1a or 1b to regenerate NBD. Kinetic studies showed that the conversion of 3a or 3b to 4a or 4b is first order. The rate constant k...

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...

The thermal reaction of the endohedral metallofullerene La2 @D2 (10611)-C72 , which contains two pentalene units at opposite ends of the cage, with 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine proceeded selectively to afford only two bisfulleroid isomers. The molecular structure of one isomer was determined using single-crystal X-ray crystallography. The results suggest that the [4+2] cycloaddition was initiated in a highly regioselective manner at the C-C bond connecting two pentagon rings of C72 . Subsequent intramolecular electrocyclization followed by cycloreversion resulted in the formation of an open-cage derivative having three seven-membered ring orifices on the cage and a significantly elongated cage geometry. The reduction potentials of the open-cage derivatives were similar to those of La2 @D2 -C72 whereas the oxidation potentials were shifted more negative than those of La2 @D2 -C72 . These results point out that further oxidation could occur easily in the derivatives.