Identification and in vitro anti-esophageal cancer activity of a series of halogenated monoterpenes isolated from the South African seaweeds Plocamium suhrii and Plocamium cornutum

Five known (1, 2, 4, 6 and 7) halogenated monoterpenes together with 1Z,3R^∗,4S^∗,5E,7Z)-1-bromo-3,4,8-trichloro-7-(dichloromethyl)-3-methylocta-1,5,7-triene (3) and (3R^∗,4S^∗)-3,4,6,7-tetrachloro-3,7-dimethyl-octen-1-ene (5) were isolated from the red macroalga Plocamium suhrii and their structures deduced from their spectroscopic data. The seven compounds from P. suhrii together with five related compounds from Plocamium cornutum have been evaluated for their cytotoxic effects on an esophageal cancer cell line (WHCO1). Compounds 1-6 showed greater cytotoxicity in this assay as compared to the known anticancer drug cisplatin.     

Unexpected reactivity resulting from modifications of the ligand periphery: Synthesis, structure, and spectroscopic properties of iron complexes of new tripodal N-heterocyclic carbene (NHC) ligands

The chelating ligand tris-[2-(3-aryl-imidazol-2-ylidene)ethyl]amine (TIMEN^R, R = aryl = 2,6-xylyl (xyl), mesityl (mes)) has provided access to reactive transition metal complexes. Here, two new tripodal N-heterocyclic carbene ligands of the TIMEN^R system (R = aryl = tolyl (tol), 3,5-xylyl (3,5xyl)), featuring sterically less demanding aryl substituents were synthesized. With these ligands, Fe(II) precursor complexes could be obtained, namely [(TIMEN^tol)Fe](BF₄)₂ (3) and [(TIMEN^3,5xyl)Fe(CH₃CN)](PF₆)₂ (7), which showed unexpected reactivity upon reduction. Treatment of the compounds with sodium amalgam yield the tris- and bis-metallated products, [(TIMEN^tol∗∗∗)Fe] (4) and [(TIMEN^3,5xyl∗∗)Fe] (8), respectively. While the Fe(III) complex 4 is relatively inert towards oxygen, the Fe(II) complex 8 is prone to oxidation. This oxidation of 8 can readily be observed in chlorinated solvents, producing the Fe(III) complex [(TIMEN^3,5xyl∗∗)Fe](PF₆) (9). All new ligand imidazolium precursors and metal complexes were characterized by single crystal X-ray structure determination.     

Molecular interactions of zinc(II) cyclams with polycarboxylato ligands

Four new zinc(II) cyclams of the composition {Zn(L)(tp²⁻) · H₂O}_n (1), {Zn(L)(H₂bta²⁻) · 2H₂O}_n (2), [Zn₂(L)₂(ox²⁻)] 2ClO₄ · 2DMF (3), and Zn(L)(H₂btc⁻)₂ · 2DMF (4), where L = cyclam, tp²⁻ = 1,4-benzenedicarboxylate ion, H₂bta²⁻ = 1,2,4,5-benzenetetracarboxylate ion, ox²⁻ = oxalate ion, DMF = N,N-dimethylformamide, and H₂btc⁻ = 1,3,5-benzenetricarboxylate ion, have been synthesized and structurally characterized by a combination of analytical, spectroscopic and crystallographic methods. The carboxylato ligands in the complexes 1-4 show strong coordination tendencies toward zinc(II) cyclams with hydrogen bonding interactions between the pre-organized N-H groups of the macrocycle and oxygen atoms of the carboxylato ligands. The macrocycles in 1, 2, and 4 adopt trans-III configurations with the appropriate R,R,S,S arrangement of the four chiral nitrogen centers, respectively. However, the complex 3 shows an unusual cis V conformation with the R,R,R,R nitrogen configuration. The finding of strong interactions between the carboxylato ligands and the zinc(II) ions may provide additional knowledge for the improved design of receptor-targeted zinc(II) cyclams in anti-HIV agents.     

Uranium complexes of cyclic O,O-bidentate ligands with the P-N-P backbone

The formation of uranium complexes of novel ligands belonging to phosphorylated 2-oxo-1,2-azaphospholane series, namely 2-ethoxy-1-diethoxyphosphoryl-2-oxo-1,2λ⁵-azaphospholane (1a) and both individual R^∗,R^∗- and R^∗,S^∗-diastereomers of the related 2-oxo-2-phenyl-1,2λ⁵-azaphospholanes 1b,c with different surrounding at the exocyclic phosphorus atom, has been studied. The structures of the complexes of ML composition obtained in the reaction with uranyl nitrate in 1:1 ratio were found to depend on the difference in donor properties of the oxygen atom of endo- and exocyclic phosphoryl groups. The ligand 1a possessing the greater difference, serves as O-monodentate one with metal-oxygen bonding via the endocyclic PO function while both isomers of 1b,c coordinate to uranyl cation in a O,O-bidentate fashion. In solutions the ML complexes reacted with air oxygen to afford (μ₂-peroxo)-bridged uranium complexes [{UO₂(L)NO₃}₂(μ₂-O₂)] which structures were confirmed by X-ray crystallography data.     

The effects of point of substitution on the electrochemical behavior of new manganese phthalocyanines, tetra-substituted with diethylaminoethanethiol

The syntheses and comparative studies of the spectral, voltammetry and spectroelectrochemical properties of new manganese phthalocyanine complexes, tetra-substituted with diethylaminoethanethio at the peripheral (complex 3a) and non-peripheral positions (complex 3b) are reported. Solution electrochemistry of complex 3a showed quasi-reversible metal-based (Mn^IIIPc⁻²/Mn^IIPc⁻², E_1/2 = −0.07 V vs. Ag|AgCl) and ring-based (Mn^IIPc⁻²/Mn^IIPc⁻³, E_1/2 = −0.78 V vs. Ag|AgCl) reductions, but no ring-based oxidation. However, complex 3b showed weak irreversible ring-oxidation signal (E_p = +0.86 vs. Ag|AgCl). Reversible metal-based (Mn^IIIPc⁻²/Mn^IIPc⁻², E_1/2 = −0.04 V vs. Ag|AgCl) and ring-based (Mn^IIPc⁻²/Mn^IIPc⁻³, E_1/2 = −0.68 V vs. Ag|AgCl) reductions were also observed for complex 3b. Spectroelectrochemistry was used to confirm these processes. Reduction process involving the metal (Mn^IIIPc⁻²/Mn^IIPc⁻²) was associated with the formation of manganese μ-oxo complex in complex 3a.     

A series of oxo-vanadium(IV) complexes containing mixed ligands of poly(pyrazolyl)borate and organic carboxylic acid: Synthesis, structural characterization and primary study of bromination reaction activities

A series of oxo-vanadium(IV) complexes: Tp^∗VO(pzH^∗)(CH₃COO) (1), Tp^∗VO(pzH^∗)(CCl₃COO) (2), Tp^∗VO(pzH^∗)(C₆H₅COO) (3), Tp^∗VO(pzH^∗)(m-NO₂-C₆H₄COO)·CH₃CN (4) and [Tp^∗VO(pzH^∗)(H₂O)]⁺[m-NO₂-C₆H₄-SO₃]⁻·CH₃OH (5) (Tp^∗ = hydrotris(3,5-dimethylpyrazolyl)borate; pzH^∗ = 3,5-dimethylpyrazole) are synthesized in methanol solution under physiological conditions. They are characterized by elemental analysis, IR, UV-Vis and X-ray crystallography. Structural analyses show that the vanadium atoms in complexes 1-5 are all in a distorted-octahedral environment with the N₄O₂ donor set, and intra- or inter-hydrogen bonding linkages have been also observed in each complex. Bromination reaction activity of the complexes has been evaluated by the method with phenol red as organic substrate in the presence of H₂O₂, Br⁻ and phosphate buffer, indicating that they can be considered as potential functional model vanadium-dependent haloperoxidases. In addition, thermal analysis and quantum chemistry calculations were also performed and discussed in detail.     

Electronic circular dichroism of monomethyl [O, O, O]-phosphate and [O, O, O]-thiophosphate revisited

Phosphoryl-transfer reactions have long been of interest due to their importance in maintaining numerous cellular functions. A phosphoryl-transfer reaction results in two possible stereochemical outcomes: either retention or inversion of configuration at the transferred phosphorus atom. When the product is phosphate, isotopically-labeled [¹⁶O, ¹⁷O, ¹⁸O]-phosphate derivatives can be used to distinguish these outcomes; one oxygen must be replaced by sulfur or esterified to achieve isotopic chirality. Conventionally, stereochemical analysis of isotopically chiral phosphate has been based on ³¹P NMR spectroscopy and involves complex chemical or enzymatic transformations. An attractive alternative would be direct determination of the enantiomeric excess using chiroptical spectroscopy. (S)-Methyl-[¹⁶O, ¹⁷O, ¹⁸O]-phosphate (MePi^∗), 7 and enantiomeric [¹⁶O, ¹⁷O, ¹⁸O]-thiophosphate (TPi^∗), 10, were previously reported to exhibit weak electronic circular dichroism (ECD), although with 10 the result was considered to be uncertain. We have now re-examined the possibility that excesses of 7 and 10 enantiomers can be detected by ECD spectrometry, using both experimental and theoretical approaches. 7 and both the (R) and (S) enantiomers of 10 (10a, 10b) were synthesized by the ‘Oxford route’ and characterized by ¹H, ³¹P and ¹⁷O NMR, and by MS analysis. Weak ECD could be found for 7, with suboptimal S/N. No significant ECD could be detected for the 10 enantiomers.Time-dependent DFT (TDDFT) calculations of the electronic excitation energies and rotational strengths of the same three enantiomers were carried out using the functional B3LYP and the basis set 6-311G^∗∗. The isotopically-perturbed geometries were predicted using the anharmonic vibrational frequency calculational code in GAUSSIAN 03. In the case of 10, calculations were also carried out for the hexahydrated complex to investigate the influence of the aqueous solvent. The predicted excitation wavelengths are greater than the observed wavelengths, a not unusual result of TDDFT calculations. The predicted anisotropy ratios are 2.9 × 10⁻⁵ for 7, −5.3 × 10⁻⁶ for 10a/b, and 1.7 × 10⁻⁶ for 10a/b⋅(H₂O)₆. For 7 the predicted anisotropy ratio approximates that observed in this work, 4.5 × 10⁻⁵ at 208 nm. For 10a/b, the upper limits of the experimental anisotropy ratios (<5 × 10⁻⁶ at 225 nm, pH 9; <5 × 10⁻⁶ at 236 nm, pH 12) are comparable to the predicted magnitude of the value for 10a/b. The lower predicted value for 10a/b · (H₂O)₆ suggests that the aqueous environment affects the ECD significantly. Altogether, the TDDFT calculations together with a stereochemical analysis based on NMR and the MS data support the conclusion that the experimental ECD results for MePi^∗ and TPi^∗ may be reliable in order of magnitude.     

Syntheses and characterization of titanium malonato and amino acid complexes: [Ti(cp)2(OOCCH2NMe2)] - The first structurally characterized α-amino acid titanium(III) complex

The reaction of [Ti(cp^∗)₂(BTMSA)] (1) (cp^∗ = η⁵-C₅Me₅, BTMSA = bis(trimethylsilyl)acetylene) with malonic acids ((HOOC)₂CR₂, R = H, Me) and N,N-dimethylglycine resulted in the formation of titanium(IV) dicarboxylato complexes [Ti(cp^∗)₂{(OOC)₂CR₂}] (R = H, 2; R = Me, 3) and an α-amino acid titanium(III) complex [Ti(cp^∗)₂(OOCCH₂NMe₂)] (4). The identities of complexes 2-4 were confirmed by microanalysis, ¹H and ¹³C NMR spectroscopy (2, 3), ESI-MS and CID experiments (2, 3) as well as by ESR and magnetic measurements (μ_eff = 1.81, 298 K) for 4. Single X-ray diffraction analyses of 2 and 4 exhibited monomolecular complexes in which the titanium atom is distorted tetrahedrally coordinated by two η⁵-C₅Me₅ rings and by the chelating bound malonato-κ²O,O′ (2) and N,N-dimethylglycinato-κ²O,O′ ligand (4).     

Synthesis, photoluminescence and electrochemiluminescence of ruthenium(II) polypyridyl complexes based on bipyridine derivatives with carbazole moieties

Six complexes (1-6) with the type of [Ru(bpy)₂L]X₂ (1-3: L = L1-L3, X = Cl⁻; 4-6: L = L1-L3, X = PF₆⁻) were synthesized based on 2,2′-bipyridine and three 2,2′-bipyridine derivatives L1, L2 and L3 (L1 = 5,5′-dibromo-2,2′-bipyridine, L2 = 5-bromo-5′-carbazolyl-2,2′-bipyridine, L3 = 5,5′-dicarbazolyl-2,2′-bipyridine). The complexes 1-6 were characterized by ¹H NMR, MS(ESI) and IR spectra, along with the X-ray crystal structure analysis for 1, 5 and 6. Their photophysical properties and electrochemiluminescence (ECL) properties were investigated in detail. In the UV-Vis absorption spectra, all complexes 1-6 show strong intraligand (π → π^∗) transitions and metal-ligand charge transfer (MLCT, dπ (Ru) → π^∗) bands. Upon the excitation wavelengths at ∼508 nm, all complexes 1-6 exhibit typical MLCT emission of ruthenium(II) polypyridyl complexes. The introduction of carbazole moieties improves the MLCT absorption and emission intensity. The ruthenium(II) complexes 1-6 exhibit good electrochemiluminescence (ECL) properties in [Ru(bpy)₂L]²⁺/tri-n-propylamine (TPrA) acetonitrile solution and the complexes with PF₆⁻ showed higher ECL emission intensity than that of the complexes with Cl⁻ based on the same ligands.     

Zinc(II) complexes based on sterically hindered hydrotris(pyrazolyl)borate ligands: Synthesis, reactivity and solid-state structures

The coordination chemistry and reactivity of zinc(II) complexes supported by monoanionic hydrotris(pyrazolyl)borate ligands substituted by 3,3,3-mesityl groups (Tp^Ms) and 3,3,5-mesityl groups (Tp^Ms∗) have been investigated. Salt metathesis of ZnCl₂, ZnEt₂, and Zn(OAc)₂ with Tl[Tp^Ms] or Tl[Tp^Ms∗] cleanly afforded the corresponding compounds Tp^MsZnCl (1), Tp^MsZnEt (2), Tp^Ms∗ZnEt (3), and Tp^MsZnOAc (5). Compound 3 slowly disproportionates in benzene solution to afford the bis(ligand) complex (κ²-Tp^Ms∗)₂Zn (4). Acetate complex 5 as well as Tp^MsZnOCOPh (6) and [Tp^Ms∗ZnOAc]₂ (7) were alternatively prepared by acidolysis of the parent ethyl complexes (2, 3) with the corresponding carboxylic acid. No reaction was observed between 2 and 3 and alcohols (ROH; R = Et, iPr, Bn), while salt metathesis reactions of ZnEt(OR) with Tl[Tp^Ms] led to 2 instead of the desired zinc-alkoxide complex. Compounds 1-7 were characterized by elemental analysis, ¹H and ¹³C NMR spectroscopy, as well as by X-ray diffraction studies for 1, 2, 4, 5 and 7. The former compounds adopt a monomeric structure in the solid state while [Tp^Ms∗ZnOAc]₂ (7) exists as an anti-syn bridged acetate dimer. Complex 4 is four-coordinated, featuring a rare bidentate coordination mode of the Tp^Ms∗ ligands. The results are rationalized in terms of the variable steric constraint around the zinc atom provided by the Tp^Ms and Tp^Ms∗ ligands.     

Design, Syntheses, and Characterization of a Sterically Encumbered Dioxo Molybdenum (VI) Core

Dioxo-Mo^VI complexes of general formula Tp^∗MoO₂(p-SC₆H₄Dn) (6a-6c) (where Tp^∗ = hydrotris(3,5-dimethyl-pyrazol-1-yl)borate and Dn = dendritic unit) have been synthesized and characterized by spectroscopy and mass spectrometry. ¹H NMR spectra of the metal complexes indicate that the C_s local symmetry about the metal core does not change by the incorporation of dendritic functionality at the thiophenolato ring. Electrochemical data show a ∼20 mV change in the redox potential in the complexes with dendritic ligands suggesting a very small perturbation in the redox orbital, which is also supported by small changes in the electronic spectra. The peak-to peak separation (ΔE_p) increases from 125 mV in 6(a) to 240 mV in 6(c), suggesting sluggish electron transfer in molecules with larger dendritic ligands.     

New pyridyl modified phosphines: Synthesis and late transition-metal coordination studies

Using a phosphorus based Mannich condensation reaction the new pyridylphosphines {5-Ph₂PCH₂N(H)}C₅H₃(2-Cl)N (1-Cl) and {2-Ph₂PCH₂N(H)}C₅H₃(5-Br)N (1-Br) have been synthesised in good yields (60% and 88%, respectively) from Ph₂PCH₂OH and the appropriate aminopyridine. The ligands 1-Cl and 1-Br display variable coordination modes depending on the choice of late transition-metal complex used. Hence P-monodentate coordination has been observed for the mononuclear complexes AuCl(1-Cl) (2), AuCl(1-Br) (3), RuCl₂(p-cymene)(1-Cl) (4), RuCl₂(p-cymene)(1-Br) (5), RhCl₂(Cp^∗)(1-Cl) (6), RhCl₂(Cp^∗)(1-Br) (7), IrCl₂(Cp^∗)(1-Cl) (8), IrCl₂(Cp^∗)(1′-Cl) (8′), IrCl₂(Cp^∗)(1-Br) (9), cis-/trans-PdCl₂(1-Cl)₂ (10), cis-/trans-PdCl₂(1-Br)₂ (11), cis-PtCl₂(1-Cl)₂ (12) and cis-PtCl₂(1-Br)₂ (13). Reaction of Pd(Me)Cl(cod) (cod = cycloocta-1,5-diene) with either 1 equiv. of 1-Br or the known pyridylphosphines 1′-Cl, 1-OH or 1-H gave the P/N-chelate complexes Pd(Me)Cl(1-Br-1-H) (14)-(17). All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 4, 5, 10 and 16 · (CH₃)₂SO have been elucidated by single crystal X-ray crystallography. A crystal structure of the dinuclear metallocycle trans,trans-[PdCl₂{μ-P/N-{Ph₂PCH₂N(H)}C₅H₄N}]₂ · CHCl₃, 18 · CHCl₃, has also been determined. Here 1-H bridges, using both P and pyridyl N donors, two dichloropalladium centres affording a 12-membered ring with the PdCl₂ units adopting a head-to-tail arrangement.     

Synthesis and electrochemical aspects of group 14 iron complexes of the type (η-C5H5)Fe(L)2ER3, L2 = (CO)2, (Ph2P)2CH2; E = C, Si, Ge, Sn

The dicarbonyl and diphosphine complexes of the type (η⁵-C₅H₅)Fe(L)₂ER₃ (L₂ = (CO)₂ (a), (Ph₂P)₂CH₂ (b); ER₃ = CH₃ (1a/b); SiMe₃ (2a/b), GeMe₃ (3a/b), SnMe₃ (4a/b)) were synthesized and studied electrochemically. Cyclic voltammetric studies on the dicarbonyl complexes 1a-4a revealed one electron irreversible oxidation processes whereas the same processes for the chelating phosphine series 1b-4b were reversible. The E_ox values found for the series 1a-4a were in the narrow range 1.3-1.5 V and in the order Si > Sn ≈ Ge > C; those for 1b-4b (involving replacement of the excellent retrodative π-accepting CO ligands by the superior σ-donor and poorer π-accepting phosphines) have much lower oxidation potentials in the sequence Sn > Si ≈ Ge > C. This latter oxidation potential pattern relates directly to the solution ³¹P NMR chemical shift data illustrating that stronger donation lowers the E_ox for the complexes; however, simple understanding of the trend must await the results of a current DFT analysis of the systems.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

Synthesis and structure of dichloropalladium(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif, and Mizoroki-Heck catalysis mediated by complexes of N,S-donor ligands

Ligands containing the 2-organochalcogenomethylpyridine motif with substituents in the 4- or 6-position of the pyridyl ring, R⁴,R⁶-pyCH₂ER¹ [R⁴ = R⁶ = H, ER¹ = SMe (1), SeMe (2), SPh (6), SePh (7); R⁴ = Me, R⁶ = H, ER¹ = SMe (3), SPh (8), SePh (9); R⁴ = H, R⁶ = Me, ER¹ = SMe (4), SPh (10), SePh (11); R⁴ = H, R⁶ = Ph, ER¹ = SMe (5), SPh (12), SePh (13)] are obtained on the reaction of R⁴,R⁶-pyMe with LiBuⁿ followed by R¹EER¹. On reaction with PdCl₂(NCMe)₂, the ligands with a 6-phenyl substituent form cyclopalladated species PdCl{6-(o-C₆H₄)pyCH₂ER¹-C,N,E} (5a, 12a, 13a) with the structure of 13a (ER¹ = SePh) confirmed by X-ray crystallography; other ligands form complexes of stoichiometry PdCl₂(R⁴,R⁶-pyCH₂ER¹). Complexes with R⁶ = H are monomeric with N,E-bidentate configurations, confirmed by structural analysis for 3a (R⁴ = Me, ER¹ = SMe), 7a (R⁴ = H, ER¹ = SePh) and 9a (R⁴ = Me, ER¹ = SePh). Two of the 6-methyl substituted complexes examined by X-ray crystallography are oligomeric with trans-PdCl₂(N,E) motifs and bridging ligands, trimeric [PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃ (10a) and dimeric [PdCl₂(μ-6-MepyCH₂SePh-N,Se)]₂ (11a). This behaviour is attributed to avoidance of the Me···Cl interaction that would occur in the cis-bidentate configuration if the pyridyl plane had the same orientation with respect to the coordination plane as observed for 3a, 7a and 9a [dihedral angles 8.0(2)-16.8(2)°]. When examined as precatalysts for the Mizoroki-Heck reaction of n-butyl acrylate with aryl halides in N,N-dimethylacetamide at 120 °C, the complexes exhibit the anticipated trends in yield (ArI > ArBr > ArCl, higher yield for electron withdrawing substituents in 4-RC₆H₄Br and 4-RC₆H₄Cl). The most active precatalysts are PdCl₂(R⁴-pyCH₂SMe-N,S) (R = H (1a), Me (3a)); complexes of the selenium containing ligands exhibit very low activity. For closely related ligands, the changes SMe to SPh, 6-H to 6-Me, and 6-H to 6-Ph lead to lower activity, consistent with involvement of both the pyridyl and chalcogen donors in reactions involving aryl bromides. The precatalyst PdCl₂(pyCH₂SMe-N,S) (1a) exhibits higher activity for the reaction of aryl chlorides in Buⁿ₄NCl at 120 °C as a solvent under non-aqueous ionic liquid (NAIL) conditions.     

Monodentate, didentate chelating, and bridging 1,8-naphthyridine complexes of pentamethylcyclopentadienyliridium(III): Syntheses and structures in the solid states and in solution

A series of new iridium(III) complexes containing pentamethylcyclopentadienyl (Cp^∗ = η⁵-C₅Me₅) and 1,8-naphthyridine (napy) have been prepared. X-ray crystallography revealed that napy acted as a monodentate, a didentate chelating, and a bridging ligand in complexes of [Cp^∗IrCl₂(napy)] (1), [Cp^∗IrCl(napy)]PF₆ (2), and [(Cp^∗IrCl)₂(H)(napy)]PF₆ (4), respectively. The crystal structure of [Cp^∗Ir(napy)₂](PF₆)₂ (3) has also been determined; the dicationic complex bore both monodentate and chelating napy ligands. Dinuclear Cp^∗Ir^III complex bridged by napy was only isolable if two Ir^III centers were supported by a hydride (H⁻) bridge. In complexes 2 and 3, the four-membered chelate rings formed by napy exhibited a large steric strain; in the rings the NIrN bond angles were only 60.5(2)-61.0(4)° and the IrNC angles were 94.7(8)-96.7(8)°. The bridging coordination of napy in complex 4 also afforded a large strain, i.e., the Ir^III centers were displaced by 0.84(3) Å from the napy plane, due to the steric interaction between two Cp^∗IrCl moieties. The monodentate napy complex 1 in CDCl₃ or CD₂Cl₂ at ambient temperature showed a rapid coordination-site exchange reaction, which gave two N sites of napy equivalent; at temperatures below −40 °C, the ¹H NMR spectra corresponded to the molecular structure of [Cp^∗IrCl₂(napy-κN)]. The analogous diazido complex of [Cp^∗Ir(N₃)₂(napy)] (5) has also been prepared, and the crystal structure has been determined. In contrast to the dichloro complex 1, the diazido complex 5 exhibited a dissociation equilibrium of coordinated napy in solution.     

Structural comparison of (pentamethylcyclopentadienyl)iridium(III) azido complexes containing potentially N,S-bidentate N-heterocyclic thiolates: 2- or 8-quinolinethiolate and benzimidazole-2-thiolate

The crystal structures of mononuclear (azido)(pentamethylcyclopentadienyl)iridium(III) complexes bearing 2- or 8-quinolinethiolate (n-Sqn⁻), [Cp^∗Ir(N₃)(n-Sqn)] {n = 2 (1) or 8 (2); Cp^∗ = η⁵-C₅Me₅} have been determined by X-ray analysis. The 2-Sqn complex, 1, acquires severe steric strains in the four-membered κ²N,S chelate ring, while the 8-Sqn isomer, 2, forms a strain-free five-membered planar κ²N,S chelate ring. It has also been revealed that the corresponding benzimidazole-2-thiolate (Hbimt⁻) complex, which was obtained similarly to the above n-Sqn complexes from [Cp^∗Ir(N₃)₂]₂ and Na(Hbimt), takes an unsymmetrical dinuclear structure bridged by two Hbimt⁻ ligands with different bonding modes, [Cp^∗Ir(N₃){μ(S:N¹)-Hbimt}{μ(S:S)-Hbimt}Ir(N₃)Cp^∗] · MeOH (3).     

Potential tridentate salicylaldehyde hydrazone of arylalkanoic acid coordinate to copper(II) acting as dinegative tetradentate ligands

A chiral Schiff base N-(S)-2-(6-methoxylnaphthyl)-propanoyl-N′-(2-hydroxylbenzylidene)hydrazine (H₂L) has been synthesized. Reaction of H₂L with Cu(OAc)₂ · H₂O led to the formation of a metal complex {[CuL] · H₂O · 2DMF}_∞ (1). In complex 1, the potential dinegative tridentate L²⁻ ligand acting as tetradentate bridging ligand coordinate to two metal ions so as to form a novel infinite metal-organic coordination chain structure. The enantiomerically pure ligand H₂L presents two different sets of signals in the ¹H NMR spectrum either in chloroform solution or in dimethylsulfoxide solution, showing the presence of both (E) and (Z) isomers. The X-ray structural investigations of H₂L revealed that it is the fully extended E-configuration in the solid state.     

Molecular structures of nickel(II) monochelates of a racemic tridentate ligand and co-ligand induced structural variations

Using a racemic mixture of the tridentate ligand, (((2-pyridyl)ethylamine)methyl)phenolate ion (L⁻) and , NCS⁻, (NC)₂N⁻, OAc⁻ as coligands, complexes having the formula [Ni(L)(N₃)] (1), [Ni(L)(NCS)]₂ (2), [Ni₂(L)₂(OAc)(N(CN)₂)]_n (3) were prepared and structurally characterized. In 1, Ni(II) has a square planar geometry and phenolate oxygen is involved in dipolar ?N^δ+ interaction with electrophilic central nitrogen atom of coordinated azide ion. Complex 2 is dimeric in nature and nickel(II) is penta-coordinated. Compounds 1 and 2 exist as centrosymmetric dimers made up of a pair of R and S enantiomers of L. In 3, an acetate and phenoxo bridged dinickel complex is present which is further linked to a zig-zag coordination polymer by the dicyanamide ion. In a given chain of 3, both L have same enantiomeric form and either RR or SS dimers are repeated along the chain. The magnetic properties are described.     

Carboxy-derived (tpy)2Ru complexes as sub-units in supramolecular architectures: The solubilized ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy and its homoleptic Ru(II) complex

We herein describe the synthesis and characterization of a series of homoleptic, Ru(II) complexes bearing peripheral carboxylic acid functionality based upon the novel ligand 4′-(4-carboxyphenyl)-4,4″-di-(tert-butyl)tpy (L₁), as well as 4′-(4-carboxyphenyl)tpy (L₂) and 4′-(carboxy)tpy (L₃) (where tpy = 2,2′: 6′,2″-terpyridine). Inspection of the metal-based oxidations (E_1/2 = 1.22-1.42 V) indicates an anodic shift (∼0.2 V) for (L₃)₂Ru²⁺ (3b) (E_1/2 = 1.40 V) relative to (L₂)₂Ru²⁺ (2b) (E_1/2 = 1.22 V). The metal-based oxidation (E_1/2 = 1.22 V) and ligand-based reductions (E_1/2 = −1.25 to −1.52 V) of (L₁)₂Ru²⁺ (1) are essentially invariant relative to those of the structural analogue 2b (PF₆)₂, which suggests no significant electronic effect caused by the tert-butyl groups. This is supported by invariance in the metal-to-ligand charge transfer bands in both the electronic absorption (494-489 nm) and emission spectra (654-652 nm). However, contrary to 2b, complex 1 is both very soluble and exhibits a highly porous solid-state structure with internal cavity dimensions of 15 Å × 14 Å due to the preclusion of inter-annular interactions by the bulky tert-butyl substituents.