Octahedral Trans Research Articles

BiCuI4(Pyridine)5 a neutral ligand-supported compound of BiI3 and CuI

Reaction of equimolar pyridine (Py) solutions BiI3 and CuI produces the Py-supported 1:1 bimetallic complex BiCuI4(Py)5 in quantitative yield. The title complex is only the second neutral complex to feature Cu−I−Bi bridging and shows an octahedral trans-[BiI4(Py)2] unit joined to a distorted tetrahedral CuI(Py)3 unit by an iodide bridge. The complex shows low thermal stability, decomposing under modest heating or vacuum to produce a mixture of BiI3 and CuI. Thus, it is a potential entry/precursor to BiI3/CuI chemistry. Natural Localized Molecular Orbital (NLMO) calculations were performed to analyze the nature of the Cu−I−Bi bonds, revealing that the title compound lies on the cusp of being [Cu(Py)3]+[BiI4(Py)2]−. Diffuse reflectance spectroscopy measurements show a strong absorption band with an optical bandgap energy of 1.94 eV. Theoretical density of states (DOS) and time-dependent density functional theory (TD-DFT) experiments to map the electronic structure assign the primary electronic transition as a mixed halide/metal-to-ligand charge transfer between Cu−I−Bi donor orbitals and Py π* acceptor orbitals.

Mono- and Bis(iminoxolene)iridium Complexes: Synthesis and Covalency in π Bonding.

N-(2,6-Diisopropylphenyl)-4,6-di-tert-butyl-o-iminobenzoquinone (Diso) reacts with the (cyclooctadiene)iridium chloride dimer to form a monoiminoxolene complex, (Diso)Ir(cod)Cl. Reaction of 2 equiv of the iminoquinone with chlorobis(cyclooctene)iridium dimer affords the bis-iminoxolene (Diso)2IrCl. This five-coordinate complex adopts a distorted square pyramidal structure with an apical chloride ligand and undergoes halide exchange to form an air-stable iodide complex. (Diso)2IrCl can be reduced by one electron to form neutral, square planar (Diso)2Ir, while oxidation with PhICl2 gives octahedral trans-(Diso)2IrCl2. The cis isomer can be prepared by air oxidation of (Diso)2IrCl; cis/trans isomerization is not observed even on prolonged heating. Structural and spectroscopic features of the complexes are consistent with the presence of strong, covalent π bonding between the metal and the iminoxolene ligands, with structural data suggesting between 45 and 60% iridium character in the π bonding orbitals, depending on the ancillary ligands. The spectroscopic similarity of (Diso)2Ir and (Diso)2IrCl to their cobalt congeners suggests that the first-row metal complexes likewise have appreciably covalent metal-iminoxolene π bonds.

Syntheses, characterization, and antimicrobial studies of Ni(II), Cu(II), and Co(III) complexes with an N-pendant azamacrocyclic chelator

Condensation of 1,2-diamino propane with acetone in the presence of perchloric acid furnished a 14-membered octamethyl tetraazamacrocycle, Me8[14]diene⋅2HClO4, which further produced a mixture of isomeric ligands, Me8[14]anes (LA, LB, and LC), on reduction with NaBH4 and subsequent extraction with CHCl3 (pH > 12). The isomers were separated by fractional crystallization from xylene. Interaction of LC with excess acrylonitrile afforded an N-pendant derivative, LCX, in which two cyanoethyl groups were attached to less crowded nitrogen atoms (N4 and N11). Upon the interaction of LCX with Ni(CH3COO)2⋅4H2O, Cu(ClO4)₂⋅6H2O, and Co(CH3COO)₂⋅4H₂O, square planar [Ni(LCX)](ClO4)2 and [Cu(LCX)](ClO4)2 and octahedral trans-[Co(LCX)Cl2](ClO4), respectively, were produced. Axial substitution reactions of trans-[Co(LCX)Cl2](ClO4) with KCNS, KM (M = NO3, Br, or I), and NaNO2 afforded substituted trans-[Co(LCX)(NCS)2](SCN), trans-[CoLCX(X)2](ClO4), and trans-[Co(LCX)(NO2)2](ClO4), respectively. The ligand and corresponding metal complexes were characterized based on the analytical, spectroscopic, magnetic moment, and molar conductivity data. Gram-positive and gram-negative bacteria and different fungi were used to evaluate the antibacterial and antifungal activities of the ligand and its metal complexes.

Calculations on the non-classical β-hydride elimination observed in trans-(H)(OMe)-Ir(Ph)(PMe3)3: possible production and reaction of methyl formate

The octahedral trans hydrido-alkoxide complex trans-(H)(OMe)-Ir(Ph)(PMe3)3 (2-OCH3) was prepared by Milstein and coworkers by addition of methanol to Ir(Ph)(PMe3)3 (1). 2-OCH3 was discovered to undergo a methanol catalyzed outer-sphere carbonyl de-insertion in which a vacant coordination site is not required. The reaction yields the octahedral trans dihydride complex trans-(H)2-Ir(Ph)(PMe3)3 (2-H) as a kinetic product along with formaldehyde derivatives reported as [CH2=O]x. We investigate the mechanism and products of this reaction using density functional theory. The de-insertion transition state has an ion-pair character leading to a high barrier in benzene continuum: ΔG ‡ = 27.9 kcal/mol. Adding one methanol molecule by H-bonding to the alkoxide of 2-OCH3 lowers the barrier to 22.7 kcal/mol. When the calculations are conducted in a methanol continuum, the barrier drops to 8.8 kcal/mol. However, the thermodynamics of de-insertion are endergonic by near 5 kcal/mol in both benzene and methanol. The calculations identify a low energy outer-sphere H/OMe metathesis pathway that transforms the formaldehyde and another 2-OCH3 molecule directly into a second 2-H complex and methyl formate. Likewise, a second H/OCH3 metathesis reaction interconverting methyl formate and 2-OCH3 into 2-H and dimethyl carbonate is computed to be exergonic and kinetically facile. These results imply that the production of methyl formate and dimethyl carbonate from 2-OCH3 is plausible in this system. The net transformation from the square planar 1 and methanol to 2-H and either methyl formate or dimethyl carbonate would represent a unique stoichiometric dehydrogenative coupling reaction taking place at room temperature by an outer-sphere mechanism.

New hybrid nanostructures based on keggin-type 12-tungstophosphate and some metal-semicarbazone complexes: Synthesis, x-ray crystal structures and spectroscopic studies

Three novel inorganic-organic hybrid nanomaterials [Mn(HL)4Cl2](PW12O40)2.4CH3OH.8H2O (1), [Ni(L)2]2(PW12O40).2HCl.4CH3OH.8H2O (2) and [Cd(HL)6](PW12O40)2.3CH3OH.8H2O (3) have been synthesized by a simple one-pot reaction of phosphotungestic acid (H3PW12O40 abbreviated as PW12) and 2-pyridinecarbaldehyde semicarbazone ligand (HL). The synthesized hybrid nanomaterials were characterized by FT˗IR, UV˗Vis, powder and single crystal X˗ray diffraction (XRD), SEM, EDX and TGA. The FT-IR, UV–Vis, PXRD and TG results of nanomaterials 1–3 confirm their successful synthesis. Compound 1 with a monoclinic P21/c space group exhibits a three-dimensional (3D) framework composed Keggin-type PW12 clusters and discrete octahedral trans-[Mn(HL)4Cl2]. In compound 2, a 3D network constructed from octahedral [Ni(L)2] and individual PW12 clusters in the triclinic P-1 space group. Compound 3 crystallizes in the triclinic P-1 space group and displays a complicated 3D network built by the Keggin PW12 POM clusters and discrete tetrahedral [Cd(HL)4]2+complex subunits. In counds 1 and 3, the HL semicarbazone act as a O(CO)-donor monodentate ligand, while in the compound 2 the deprotonated L semicarbazone functions as a Npy,N,O(CO)-donor tridentate ligand. The crystal components in 1–3 are connected through numerous weak N/C–H⋯O(POM) and N/C–H⋯Cl hydrogen bonds to construct the three-dimensional networks. In 1–3, the 3D supramolecular networks are maintained through electrostatic and/or hydrogen bonding interactions. For compounds 1–3, both the simulated and experimental X-ray powder diffraction patterns match each other, indicating good phase purity of our samples. Furthermore, the performance of 1–3 in the removal of cationic methylene blue (MB) dye and anionic methyl orang (MO) dye from aqueous solutions was investigated.

Field-induced slow relaxation of magnetization in the S = 3/2 octahedral complexes trans-[Co{(OPPh2)(EPPh2)N}2(dmf)2], E = S, Se: effects of Co–Se vs. Co–S coordination

Magnetometry studies on octahedral trans-[Co{(OPPh2)(EPPh2)N}2(dmf)2], E = S, Se, complexes.

A one-dimensional iodido-bridged PtII/PtIV mixed-valence complex cation with a hydrogen sulfate counter-anion.

The title compound, catena-poly[[[bis-(ethyl-enedi-amine-κ2 N,N')platinum(II)]-μ-iodido-[bis-(ethyl-enedi-amine-κ2 N,N')platinum(IV)]-μ-iodido] tetra-(hydrogen sulfate) dihydrate], {[PtII(C2H8N2)2][PtIVI2(C2H8N2)2](HSO4)4·2H2O} n , has a linear chain structure comprising alternating platinum cations with mixed-valent oxidation states of +II/IV. Square-planar [Pt(en)2]2+ cations and elongated octa-hedral trans-[PtI2(en)2]2+ cations (en is ethyl-enedi-amine) are stacked alternately parallel to the b axis, and are bridged by the I ligands. The Pt site of the [PtII/IV(en)2] units is located on a twofold rotation axis. The I site, which is located on the same twofold rotation axis, is equally disordered over two positions. The Pt and I sites form a straight ⋯I-PtIV-I⋯PtII⋯ chain, with PtIV-I bond lengths of 2.7202 (6) and 2.6917 (6) Å, and PtII⋯I contacts of 3.2249 (6) and 3.2534 (6) Å. The mixed-valence state of the Pt site is expressed by the structural parameter δ = (PtIV-I)/(PtII⋯I), with values of 0.843 and 0.827 for the two independent I atoms. In the crystal structure, the cationic columnar structure is stabilized by hydrogen bonds of the type N-H⋯O between the amine groups of the Pt complex chains and the disordered hydrogen sulfate counter anions, and between the amine groups and water mol-ecules of crystallization. In addition, O-H⋯O hydrogen bonds between the hydrogen sulfate anions and water mol-ecules of crystallization and between the hydrogen sulfate anions themselves consolidate the crystal packing.

Cobalt(II) complexes with pyridine and 5-[(E)-2-(aryl)-1-diazenyl]-quinolin-8-olates: synthesis, electrochemistry and X-ray structural characterization

Nine new cobalt(II) compounds, trans-[Co(LPAQ)2(Py)2] (1), trans-[Co(LPAQ)2(3-MePy)2] (2), tran s-[Co(LMeAQ)2(Py)2] (3), trans-[Co(LOMeAQ)2(Py)2] (4), trans-[Co(LOEtAQ)2(Py)2]·2(H2O) (5), tran s-[Co(LCAQ)2(Py)2] (6), trans-[Co(LBAQ)2(Py)2] (7), ci s-[Co(LBAQ)2(3-MePy)2] (8a) and tran s-[Co(LBAQ)2(3-MePy)2]·2(3-MePy) (8b) (primary ligand: LXAQ = substituted 5-[(E)-2-(aryl)-1-diazenyl]quinolin-8-olate; secondary ligands: Py = pyridine, 3-MePy = 3-methylpyridine), have been synthesized and characterized by elemental analysis, IR and UV-vis spectroscopy. Magnetic measurements of the cobalt compounds were performed in solution by 1H NMR spectroscopy using the Evans’ method while their redox properties were studied by cyclic voltammetry. Single-crystal X-ray diffraction analysis of the compounds revealed their octahedral geometries and trans configuration, except for 8a, which has a cis configuration. Intermolecular noncovalent interactions were detected, π···π interactions in 5, C – H···π interactions in 2 and C – H···π edge-to-face (T-shaped) arrangements in 3, 4, 6, and 7.

Synthesis of some Cd(II) and Zn(II) complexes of a tetraazamacrocyclic ligand and their antimicrobial activities

Synthetic macrocycles specially the tetraazamacrocycles and their complexes have attracted considerable interests owing to their wide variety of applications. The ligand, 3, 10-C-meso- 3,5,7,7,10,12,14,14-octamethy1-1,4,8,11- tetraazacyclotetradeca-4,11-diene(L1), upon reaction with CdI2, Zn(ClO4)2, and Zn(CH3COO)2 produces corresponding square pyramidal cadmium (II) and zinc (II) complexes of formula [ML1X]Yn, (M = Cd or Zn; X = I, CH3COO or H2O; Y= I, ClO4 or CH3COO; n = 1 or 2). Among them, [CdL1I]I and [ZnL1(H2O)](ClO4)2 undergo substitution reactions with KSCN and NaNO2, respectively to produce octahedral trans- diisothiocyanatocadmium(II) complex, trans-[CdL1(NCS)2] and square pyramidal mononitratozinc(II) nitrate complex, [ZnL1(NO2)](NO2). Antifimgal and antibacterial activities of these complexes against some of phytopathogenic fungi and bacteria have been investigated in this study.
 Asian Australas. J. Biosci. Biotechnol. 2017, 2 (2), 136-144

A one-dimensional bromide-bridged PtII/PtIV mixed-valence complex with a 2-bromo-ethane-sulfonate counter-ion.

The title salt, catena-poly[[[bis-(ethyl-enedi-amine)-platinum(II)]-μ-bromido-[bis(ethyl-enedi-amine)-platinum(IV)]-μ-bromido] tetra-kis-(2-bromo-ethane-sulfon-ate) dihydrate], {[PtIIPtIVBr2(C2H8N2)4](C2H4BrSO3)4·2H2O} n , crystallizes in the space group P21212. It has a linear chain structure extending parallel to the c axis, composed of square-planar [Pt(en)2]2+ and elongated octa-hedral trans-[PtBr2(en)2]2+ cations (en is ethyl-enedi-amine) stacked alternately and bridged by the Br atoms. The Pt site of the [PtII/IV(en)2] unit is located on a general position. The Br site, which is also located on a general position, is equally disordered over two positions. The Pt and Br atoms form a slight zigzag ⋯Br-PtIV-Br⋯PtII⋯ chain, with PtIV-Br bond lengths of 2.453 (2) and 2.491 (3) Å, PtII⋯Br contacts of 3.069 (2) and 3.032 (3) Å, and PtIV-Br⋯PtII angles of 178.06 (13) and 177.70 (13)°. The mixed-valence state of the Pt site is expressed by the parameter δ = (PtIV-Br)/(PtII⋯Br), with values of 0.799 and 0.822 for the two independent Br atoms. In the crystal, N-H⋯O and O-H⋯O hydrogen bonds between the amine groups of the Pt complex chains, the sulfonate groups and water mol-ecules of crystallization, stabilize the cationic columnar structure.

Mechanistic investigation of cis and trans oxidative addition to acetylacetonato-1,5-cyclooctadieneiridium(I)

Density functional theory (DFT) calculations of the oxidative addition of CH3I, as well as Hg(CN)2, to [Ir(acac)(cod)] are described (acac=acetylacetone). Both cis and trans oxidative addition mechanisms are considered and compared to experimental data. The DFT calculated thermodynamically most stable oxidative addition products are trans-[Ir(acac)(cod)(CH3)(I)] and cis-[Ir(acac)(cod)(HgCN)(CN)]. The steric demand of the cod ligand leads to a distorted octahedral trans-[Ir(acac)(cod)(CH3)(I)] complex, with the CCH3-Ir-I angle deviating by more than 20° from 180°, as expected for real octahedral geometry. However, the steric demand of the cod ligand does not lead to any cis transition state for the [Ir(acac)(cod)]+CH3I reaction, rather the trans transition state is energetically favoured, as is generally found for oxidative addition of CH3I to square planar complexes. On the other hand, oxidative addition of Hg(CN)2 to [Ir(acac)(cod)], occurs via a concerted three-centre cis transition state structure. The concerted three-centre cis transition state structure is confirmed by the existence of a ring critical point, as obtained by the Bader’s quantum theory of atoms in molecules analysis of the cis transition state structure. Both trans addition of CH3I to [Ir(acac)(cod)] as well as cis addition of Hg(CN)2 to [Ir(acac)(cod)], are in agreement with experimental observation.

Structural comparison of copper(II) thiocyanate pyridine complexes

Copper(II) thiocyanate forms a series of closely related complexes when reacted with substituted pyridines (XPy) in methanol. Although these compounds are nominally square planar trans-[Cu(NCS)2(XPy)2], most show N,S-thiocyanate bridging via long Cu–S bonds of ⩾2.7Å. The resulting Jahn-Teller (J-T) distorted octahedra form edge-sharing chains. However, these units can also form sheets or small oligomers. For some 2- or 3-substituted pyridines, isolated square planar trans-[Cu(NCS)2(XPy)2], J-T distorted octahedral trans-[Cu(NCS)2(XPy)2(MeOH)2], or square pyramid trans-[Cu(NCS)2(XPy)2(MeOH)] were isolated. Polymorphism and/or solvento isomers appear to be common, being identified for five of 21 ligands studied. Use of 2-NH2Py produces methoxy-bridged dimers [Cu2(NCS)2(2-NH2Py)2(μ-OMe)2] that are further linked via bridging thiocyanate to form a sheet structure. Unusual aryl bromide metal chelation is noted in the mixed ligand complex trans-[Cu(NCS)2(2-BrPy)(3-BrPy)]. When LL=4,4′-bipyridyl (Bpy) or pyrazine (Pyz) is used, bridging by both the organic and thiocyanate ligands produces sheet networks, trans-[Cu(NCS)2(LL)].

Trioctahedral Fe-rich micas: Relationships between magnetic behavior and crystal chemistry

Six Fe-bearing mica samples with different Fe ordering, Fe 2+ /(Fe 2+ +Fe 3+ ) ratio, octahedral, and tetrahedral composition were studied. Four micas belong to the phlogopite-annite join (space group C 2/ m ), two are Mg-rich annite and two are Fe-rich phlogopite, one is a tetra-ferriphlogopite (space group C 2/ m ) and one is Li-rich siderophyllite (space group C 2). Thus these samples had a different environment around the Fe cations and layer symmetry. These micas were characterized by chemical analyses, single-crystal X-ray diffraction, X-ray absorption spectroscopy, and magnetic measurements. In samples with Fe mostly in octahedral coordination, dominant magnetic interactions among Fe atoms are ferromagnetic, which reach a maximum at higher Fe 2+ /(Fe 2+ +Fe 3+ ) ratios. Samples with higher Fe 2+ /(Fe 2+ +Fe 3+ ) ratio are also characterized by higher values of the Curie-Weiss θ constant. Where Fe 2+ /(Fe 2+ +Fe 3+ ) ratios decrease, θ values also decrease. The Fe 3+ -rich phlogopite shows predominant Fe 3+ in tetrahedral coordination and shows anti-ferromagnetic interactions with a negative value of the Curie-Weiss θ constant (i.e., θ = −25 K). Fe ordering in octahedral trans - and in one of the two cis -sites accounts for a greater θ value in Li-rich siderophyllite when compared to other samples showing similar octahedral Fe content. Our data suggest that Fe 3+ cations and other non-ferromagnetic cations hinder long range magnetic ordering. This observation may produce for the different role of octahedral Fe magnetic interactions that can in principle develop along long Fe-rich octahedral chains, when compared to tetrahedral-octahedral interactions that are confined within the layer by the non-ferromagnetic cations of the interlayer. Spin glass behavior is indicated by the dependency of the temperature to produce maxima in the susceptibility curve. These maxima are related to the frequency of the applied AC magnetic field.

Syntheses, structures and biological evaluation of some transition metal complexes with a tetradentate benzamidine/thiosemicarbazone ligand

The potentially tetradentate benzamidine/thiosemicarbazone ligand, Et2N–(CS)–NH-C(Ph)=N–(o-C4H6)–C(Me)=N–NH–(CS)–NH–Me (H2L) readily reacts with Ni(CH3COO)2, [PdCl2(CH3CN)2], [PtCl2(PPh3)2] and (NBu4)[ReOCl4] under formation of complexes of the compositions [M(L)] (M=Ni (1), Pd (2), Pt (3)) and [ReO(L)(OMe)] (4). In all complexes, H2L is doubly deprotonated and bonded to the central metal ion via its N2S2 donor set. Complexes 1, 2 and 3 have distorted square-planar coordination spheres, while the rhenium compound 4 is an octahedral trans oxido/methoxido complex. The H2L proligand shows a medium cytotoxicity with an IC50 value of 21.1μM. While the rhenium complex 4 exhibits a stronger antiproliferative effect (IC50=5.52μM), the nickel, palladium and platinum complexes are almost inactive.

Substitutional Lability of Diphosphine Ligands in Tetrahedral Iron(II) Chloro Complexes

A series of iron(II) dihalogenide complexes with two different bisphosphinoethane ligands is reported. In the case of 1,2-bis(diphenylphosphanyl)ethane (dppe), depending on the stoichiometry, the tetrahedral [(μ-dppe)FeCl2]n and octahedral trans-[(dppe)2FeCl2] complexes are formed. The polymeric complex [(μ-dppe)FeCl2]n, with iron in a tetrahedral environment, preferentially reacts with chelating amines to give the octahedral diphosphine complex, trans-[(dppe)2FeCl2], and different octahedral amine complexes. With the sterically more demanding 1,2-bis(diisopropylphosphanyl)ethane (dippe), the monomeric and tetrahedral halogen complexes [(dippe)FeX2] are exclusively obtained (X = Cl, Br). These complexes react with chelating amines in a similar manner, to give free ligand and the corresponding octahedral amine complex. The present results suggest that the diphosphines in the investigated iron(II) complexes are bound too weakly to form productive catalyst precursors.

Active Nature of Primary Amines during Thermal Decomposition of Nickel Dithiocarbamates to Nickel Sulfide Nanoparticles

Although [Ni(S2CNBui 2)2] is stable at high temperatures in a range of solvents, solvothermal decomposition occurs at 145 °C in oleylamine to give pure NiS nanoparticles, while in n-hexylamine at 120 °C a mixture of Ni3S4 (polydymite) and NiS results. A combined experimental and theoretical study gives mechanistic insight into the decomposition process and can be used to account for the observed differences. Upon dissolution in the primary amine, octahedral trans- [Ni(S2CNBui 2)2(RNH2)2] result as shown by in situ XANES and EXAFS and confirmed by DFT calculations. Heating to 90−100 °C leads to changes consistent with the formation of amide-exchange products, [Ni(S2CNBui 2){S2CN(H)R}] and/or [Ni{S2CN(H)R}2]. DFT modeling shows that exchange occurs via nucleophilic attack of the primary amine at the backbone carbon of the dithiocarbamate ligand(s). With hexylamine, amide-exchange is facile and significant amounts of [Ni{S2CN(H)Hex}2] are formed prior to decomposition, but with oleylamine, exchange is slower and [Ni(S2CNBui 2){S2CN- (H)Oleyl}] is the active reaction component. The primary amine dithiocarbamate complexes decompose rapidly at ca. 100 °C to afford nickel sulfides, even in the absence of primary amine, as shown from thermal decomposition studies of [Ni{S2CN(H)Hex}2]. DFT modeling of [Ni{S2CN(H)R}2] shows that proton migration from nitrogen to sulfur leads to formation of a dithiocarbimate (S2CNR) which loses isothiocyanate (RNCS) to give dimeric nickel thiolate complexes [Ni{S2CN(H)R}(μ-SH)]2. These intermediates can either lose dithiocarbamate(s) or extrude further isothiocyanate to afford (probably amine-stabilized) nickel thiolate building blocks, which aggregate to give the observed nickel sulfide nanoparticles. Decomposition of the single or double amide-exchange products can be differentiated, and thus it is the different rates of amideexchange that account primarily for the formation of the observed nanoparticulate nickel sulfides.

A new trans-dioxorhenium(V) complex with 4-aminopyridine: synthesis, structure, electrochemical aspects, DFT, and TD-DFT calculations

The reaction of 1 : 4.4 M proportion of cis-[ReO2I(PPh3)2] and 4-aminopyridine (ampy) in acetone–water gives trans-[ReO2(ampy)4]I·2H2O (1a) in 85% yield. 1a has been characterized by C, H, and N microanalyses, FT-IR, UV–vis, 1H NMR spectroscopy, and molar conductivity. The X-ray crystal structure of 1a reveals an octahedral trans dioxorhenium(V) complex with a “N4O2” coordination for rhenium. 1a has an orthorhombic space group C2221 with a = 17.576(4), b = 19.370(4), c = 15.730(4) Å, V = 5355(2) Å3, and Z = 8. Geometry optimization of the trans-O,O complex, 1a and its cis-O,O analog, 1b performed at the level of density functional theory reveal that 1a is more stable than 1b by 25 kcal M–1 in the gas phase. The electronic spectrum of 1a was also analyzed at the level of time-dependent density functional theory. Excitation of 1a in methanol at 450 nm leads to a fluorescent emission at 505 nm with a quantum yield (Ф) of 0.04. Electrochemical studies of 1a in acetonitrile show a quasi-reversible Re(V) to Re(VI) oxidation at 0.618 V versus Ag/AgCl. This redox potential matches with the calculated redox potential of 0.621 V versus Ag/AgCl.

Synthetic, Crystallographic, and Computational Study of Copper(II) Complexes of Ethylenediaminetetracarboxylate Ligands

Copper(II) complexes of hexadentate ethylenediaminetetracarboxylic acid type ligands H(4)eda3p and H(4)eddadp (H(4)eda3p = ethylenediamine-N-acetic-N,N',N'-tri-3-propionic acid; H(4)eddadp = ethylenediamine-N,N'-diacetic-N,N'-di-3-propionic acid) have been prepared. An octahedral trans(O(6)) geometry (two propionate ligands coordinated in axial positions) has been established crystallographically for the Ba[Cu(eda3p)]·8H(2)O compound, while Ba[Cu(eddadp)]·8H(2)O is proposed to adopt a trans(O(5)) geometry (two axial acetates) on the basis of density functional theory calculations and comparisons of IR and UV-vis spectral data. Experimental and computed structural data correlating similar copper(II) chelate complexes have been used to better understand the isomerism and departure from regular octahedral geometry within the series. The in-plane O-Cu-N chelate angles show the smallest deviation from the ideal octahedral value of 90°, and hence the lowest strain, for the eddadp complex with two equatorial β-propionate rings. A linear dependence between tetragonality and the number of five-membered rings has been established. A natural bonding orbital analysis of the series of complexes is also presented.

Structural preferences and isomerism in nickel(II) and copper(II) complexes with 3-hydroxypicolinic acid

Recrystallization of [Ni(3-OHpic)2(H2O)2] (1) from pyridine (py) affords trans-[Ni(3-OHpic)2(py)2] (2), while cis-[Ni(3-OHpic)2(4-pic)2] (3) is obtained from 4-picoline (4-pic). The nickel(II) ion is octahedrally coordinated by two N,O-bidentate 3-hydroxypicolinate ligands in both 2 and 3, and by two pyridine molecules in trans positions (2) or two 4-picoline molecules in cis positions (3). [Cu(3-OHpic)2] reacted with 4-picoline to yield the pentacoordinated species [Cu(3-OHpic)2(4-pic)] (4), but in the presence of 3-picoline (3-pic) the octahedral trans-[Cu(3-OHpic)2(3-pic)2] (5), similar to 2, was isolated. The crystal structures of 2–5 exhibit strong intramolecular O–H···O hydrogen bonds, but the intermolecular interactions are weak (C–H···O hydrogen bonds, π–π and C–H···π interactions). DFT calculations showed a preference for octahedral coordination for both the nickel(II) and copper(II) complexes, and a very small preference for a cis arrangement of the monodentate ligands, as observed in 2 and 5. The cooperative effect of weak intermolecular interactions should be responsible for reversing the preferences, but no major driving force could be identified. Calculated (DFT) and experimental IR spectra for 2–5 were compared and characteristic bands assigned. Thermogravimetric studies showed the initial loss of two coordinated pyridine, 4-picoline or 3-picoline molecules in 2, 3 and 5, respectively.

Bucky-blocks: templating a coordination network with C60

The reaction of NiCl2·6H2O with 4′-tert-butyl-4,2′:6′,4′′-terpyridine (1) in MeOH/1,2-Cl2C6H4 leads to the formation of the 2-dimensional coordination polymer 4[Ni2Cl4(1)4]·13(1,2-Cl2C6H4)·30H2O. Each sheet comprises [4 + 4] macrocycles interconnected by octahedral trans-{NiCl2N4} nodes. In the presence of C60, NiCl2·6H2O and ligand 1 combine in MeOH/1,2-Cl2C6H4 to give crystalline solvated 3[NiCl2(1)2]·C60 which has a lamellar structure intercalated with C60 molecules. The fullerene templates the formation of [3 + 3] bowl-shaped macrocycles which are connected through octahedral trans-{NiCl2N4} nodes to [6 + 6] macrocycles generating 2-dimensional sheets.