An efficient synthesis of the novel {6-[1,1-di(pyridin-2-yl)ethyl]pyridine-2-yl}2-methyl-1,3-propanediamine (2) is reported, as well as a reliable large-scale synthesis (of the order of 100 g) of previously known 2,2'-[1-(6-chloropyridin-2-yl)ethane-1,1-diyl]dipyridine (4); the latter is the starting material for the preparation of the former, as well as a multitude of other polypodal polyamine/polyimine ligands. Both materials, as well as the intermediates in their multi-step syntheses, have been fully characterised. Ligand 2, in conjunction with ligands 2,2'-(pyridine-2,6-diyl)bis(2-methylpropane-1,3-diamine) (1) and 2,6-bis(1,1-di(pyridin-2-yl)ethyl)pyridine (3), establishes a series of tetrapodal pentadentate N5 ligands L of like scaffold, and thus coordination geometry, but graded primary amine/imine donor atom ratios. The iron(II) complexes [Fe(L)NCCH3](OTf)2 (L = 1: A; L = 2: B; L = 3: C; OTf = triflate) have been prepared and fully characterised, including X-ray single-crystal structure analyses. The metal-centred one-electron oxidation/reduction potential (FeII/FeIII) depends sensitively on the electron donor capacity of the capping ligand used, as demonstrated by cyclic voltammetry. Whereas the acetonitrile ligand in A and C is readily exchanged for a methanol ligand in methanol solution, the resulting complexes showing variable-temperature spin crossover (SCO) in solution, B has been found to be inert to this type of ligand exchange.

Abstract 4-(2,6-Di(2H-indazol-2-yl)pyridin-4-yl)benzoic acid (1) and 10-(2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)anthracene-9-carboxylic acid (2) were required for adsorption studies on Ag(111), with a view to subsequent iron(II) complexation and formation of well-ordered spin-responsive self-assembled monolayers. While the generation of these compounds has remained elusive, several intermediates and by-products were obtained, potentially useful as dipyrazolylpyridine-related derivatives and for metal ion coordination. 3,5-Dichloro-2,6-diindazolylpyridine-4-amine, which forms as a mixture of regioisomers, was synthesised, the mixture separated, and the components characterised (3,5-dichloro-2,6-di(2H-indazol-2-yl)pyridin-4-amine; 3,5-dichloro-2-(1H-indazol-1-yl)-6-(2H-indazol-2-yl)pyridin-4-amine; 3,5-dichloro-2,6-di(1H-indazol-1-yl)pyridin-4-amine). Their iron(II) complexes have been prepared and fully characterised, including single crystal X-ray structure determination. The complexes are instructive examples of the influence of ligand design (“steric jamming”) on the spin-crossover (SCO) activity of FeII centres. Bulky substitution, which entails twisted ligand conformation, increases intramolecular crowding. This prevents contraction of the metal coordination sphere, which would be a prerequisite for thermally inducible SCO. Mössbauer spectroscopy has revealed that the complexes remain predominantly high-spin (HS) between 20 and 200 K, and that a mixture of conformational HS isomers is present in the microcrystalline solid.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Abstract We report the chelation-assisted oxidative CH2 extrusion from a PtII-coordinated dipyridylmethane, resulting in the formation of a 2,2′-bipyridyl ligand. This unusual one-pot reaction (solvent: dimethylformamide, DMF), which is quantitative, proceeds in air at mildly elevated temperature, with CH2 → C=O conversion, decarbonylation, and ipso-ipso C–C coupling of the two pyridyl residues (“fragment coupling”). It constitutes, in effect, a chelate ring contraction by one member.

Reduced graphene oxide enhances photocatalytic hydrogen production in the system composed of Eosin Y and molecular catalyst Co(bpy)32+.

Typical electroless copper baths (ECBs), which are used to chemically deposit copper on printed circuit boards, consist of an aqueous alkali hydroxide solution, a copper(II) salt, formaldehyde as reducing agent, an l-(+)-tartrate as complexing agent, and a 2,2′-bi­pyridine derivative as stabilizer. Actual speciation and reactivity are, however, largely unknown. Herein, we report on the synthesis and crystal structure of aqua-1κO-bis­(4,4′-dimeth­oxy-2,2′-bi­pyri­dine)-1κ2N,N′;2κ2N,N′-[μ-(2R,3R)-2,3-dioxidosuccinato-1κ2O1,O2:2κ2O3,O4]dicopper(II) octa­hydrate, [Cu2(C12H12N2O2)2(C4H2O6)(H2O)]·8H2O, from an ECB mock-up. The title compound crystallizes in the Sohncke group P21 with one chiral dinuclear complex and eight mol­ecules of hydrate water in the asymmetric unit. The expected retention of the tartrato ligand’s absolute configuration was confirmed via determination of the absolute structure. The complex mol­ecules exhibit an ansa-like structure with two planar, nearly parallel bi­pyridine ligands, each bound to a copper atom that is connected to the other by a bridging tartrato ‘handle’. The complex and water mol­ecules give rise to a layered supra­molecular structure dominated by alternating π stacks and hydrogen bonds. The understanding of structures ex situ is a first step on the way to prolonged stability and improved coating behavior of ECBs.

Typical electroless copper baths (ECBs), which are used to chemically deposit copper on printed circuit boards, consist of an aqueous alkali hydroxide solution, a copper(II) salt, formaldehyde as reducing agent, an l-(+)-tartrate as complexing agent, and a 2,2'-bi-pyridine derivative as stabilizer. Actual speciation and reactivity are, however, largely unknown. Herein, we report on the synthesis and crystal structure of aqua-1κO-bis-(4,4'-dimeth-oxy-2,2'-bi-pyri-dine)-1κ2 N,N';2κ2 N,N'-[μ-(2R,3R)-2,3-dioxidosuccinato-1κ2 O 1,O 2:2κ2 O 3,O 4]dicopper(II) octa-hydrate, [Cu2(C12H12N2O2)2(C4H2O6)(H2O)]·8H2O, from an ECB mock-up. The title compound crystallizes in the Sohncke group P21 with one chiral dinuclear complex and eight mol-ecules of hydrate water in the asymmetric unit. The expected retention of the tartrato ligand's absolute configuration was confirmed via determination of the absolute structure. The complex mol-ecules exhibit an ansa-like structure with two planar, nearly parallel bi-pyridine ligands, each bound to a copper atom that is connected to the other by a bridging tartrato 'handle'. The complex and water mol-ecules give rise to a layered supra-molecular structure dominated by alternating π stacks and hydrogen bonds. The understanding of structures ex situ is a first step on the way to prolonged stability and improved coating behavior of ECBs.

Formation of the O-O bond is considered the critical step in oxidative water cleavage to produce dioxygen. High-valent metal complexes with terminal oxo (oxido) ligands are commonly regarded as instrumental for oxygen evolution, but direct experimental evidence is lacking. Herein, we describe the formation of the O-O bond in solution, from non-heme, N5 -coordinate oxoiron(IV) species. Oxygen evolution from oxoiron(IV) is instantaneous once meta-chloroperbenzoic acid is administered in excess. Oxygen-isotope labeling reveals two sources of dioxygen, pointing to mechanistic branching between HAT (hydrogen atom transfer)-initiated free-radical pathways of the peroxides, which are typical of catalase-like reactivity, and iron-borne O-O coupling, which is unprecedented for non-heme/peroxide systems. Interpretation in terms of [FeIV (O)] and [FeV (O)] being the resting and active principles of the O-O coupling, respectively, concurs with fundamental mechanistic ideas of (electro-) chemical O-O coupling in water oxidation catalysis (WOC), indicating that central mechanistic motifs of WOC can be mimicked in a catalase/peroxidase setting.

Typical electroless copper baths (ECBs), which are used to chemically deposit copper on printed circuit boards, consist of an aqueous alkali hydroxide solution, a copper(II) salt, formaldehyde as reducing agent, an l-(+)-tartrate as complexing agent, and a 2,2′-bipyridine derivative as stabilizer. Actual speciation and reactivity are, however, largely unknown. Herein, we report on the synthesis and crystal structure of aqua-1κO-bis(4,4′-dimethoxy-2,2′-bipyridine)-1κ2N,N′;2κ2N,N′-[μ-(2R,3R)-2,3-dioxidosuccinato-1κ2O1,O2:2κ2O3,O4]dicopper(II) octahydrate, [Cu2(C12H12N2O2)2(C4H2O6)(H2O)]·8H2O, from an ECB mock-up. The title compound crystallizes in the Sohncke group P21 with one chiral dinuclear complex and eight molecules of hydrate water in the asymmetric unit. The expected retention of the tartrato ligand's absolute configuration was confirmed via determination of the absolute structure. The complex molecules exhibit an ansa-like structure with two planar, nearly parallel bipyridine ligands, each bound to a copper atom that is connected to the other by a bridging tartrato `handle'. The complex and water molecules give rise to a layered supramolecular structure dominated by alternating π stacks and hydrogen bonds. The understanding of structures ex situ is a first step on the way to prolonged stability and improved coating behavior of ECBs.

The new titanium(IV) coordinative compound (dpp-bian)TiCl2 (2) was obtained by metathesis of the disodium salt (dpp-bian)Na-2 (1) (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) with TiCl4. It was shown that the chlorido ligands can be exchanged for chelating dpp-bian ligands, or tert-butoxy groups, with the formation of (dpp-bian)(2)Ti (3) and (dpp-bian)Ti((OBu)-Bu-t)(2) (4), respectively. Complexes 2-4 were isolated and fully characterized. It was demonstrated that dpp-bian is in the reduced dianionic form and acts as a sigma(2)pi-donor ligand.

Monolayers of 4-(2,6-di(1 H-pyrazol-1-yl)pyridine-4-yl)benzoic acid (DPP-BA) on Au substrates modified by an underpotential-deposited bilayer of Ag were studied by X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy, and scanning tunneling microscopy. Highly crystalline layers are formed with molecules coordinatively bonding to the surface through the carboxylate moiety in a bidentate configuration. The molecules assemble to rows characterized by densely packed upright-orientated DPP units occupying an area of 41 Å2. The DPP units adopt a trans-trans conformation as inferred from the N 1s XPS spectra taken at different photon energies. Their alignment alternates between adjacent rows, giving rise to a herringbone pattern. The pronouncedly different structure of the weakly commensurate self-assembled monolayer (SAM) of DPP-BA on Ag compared to the commensurate SAM of a DPP thiol on Au is a manifestation of the shift from substrate-directed assembly in the latter case to assembly dominated by intermolecular interactions in the former case.

Deprotonation of ligand-appended alkoxyl groups in mononuclear copper(II) complexes of N,O ligands L1 and L2 , gave dinuclear complexes sharing symmetrical Cu2 O2 cores. Molecular structures of these mono- and binuclear complexes have been characterized by XRD, and their electronic structures by UV/Vis, 1 H NMR, EPR and DFT; moreover, catalytic performance as models of catechol oxidase was studied. The binuclear complexes with anti-ferromagnetically coupled copper(II) centers are moderately active in quinone formation from 3,5-di-tert-butyl-catechol under the established conditions of oxygen saturation, but are strongly activated when additional dioxygen is administered during catalytic turnover. This unforeseen and unprecedented effect is attributed to increased maximum reaction rates vmax , whereas the substrate affinity KM remains unaffected. Oxygen administration is capable of (partially) removing limitations to turnover caused by product inhibition. Because product inhibition is generally accepted to be a major limitation of catechol oxidase models, we think that our observations will be applicable more widely.

Synthetic diiron compounds of the general formula Fe2(μ-S2R)(CO)n(L)6-n (R = alkyl or aromatic groups; L = CN- or phosphines) are versatile models for the active-site cofactor of hydrogen turnover in [FeFe]-hydrogenases. A series of 18 diiron compounds, containing mostly a dithiolate bridge and terminal ligands of increasing complexity, was characterized by X-ray absorption and emission spectroscopy in combination with density functional theory. Fe K-edge absorption and Kβ main-line emission spectra revealed the varying geometry and the low-spin state of the Fe(i) centers. Good agreement between experimental and calculated core-to-valence-excitation absorption and radiative valence-to-core-decay emission spectra revealed correlations between spectroscopic and structural features and provided access to the electronic configuration. Four main effects on the diiron core were identified, which were preferentially related to variation either of the dithiolate or of the terminal ligands. Alteration of the dithiolate bridge affected mainly the Fe-Fe bond strength, while more potent donor substitution and ligand field asymmetrization changed the metal charge and valence level localization. In contrast, cyanide ligation altered all relevant properties and, in particular, the frontier molecular orbital energies of the diiron core. Mutual benchmarking of experimental and theoretical parameters provides guidelines to verify the electronic properties of related diiron compounds.

The coordination chemistry of the tetrapodal-pentadentate ligand L, which has a mixed N3O2 donor set, has been studied in the presence of copper(I) sources. The metal-to-ligand stoichiometry of the mononuclear copper(I) complexes resulting from 1:1 metal/ligand mixtures is markedly dependent on the character of the counter ion, giving 1:1 ([Cu(L)Cl]) and 1:2 complexes ([Cu(L)2](PF6)), with coordinating chloride and non-coordinating hexafluorophosphate, respectively. 1H NMR and UV–Vis spectroscopy and single crystal X-ray structure analysis reveal tetrahedral coordination in both cases, with the “soft” copper centre engaging only two pyridine donors out of the N3O2 donor set. Upon chemical oxidation of [Cu(L)2](PF6) with dioxygen or 3,5–di-tert-butyl-quinone, the same binuclear copper(II) complex [Cu2(L–H)2](PF6)2 is selectively formed, indicating metal-oxidation induced deprotonation of one ligand, extrusion of the second ligand and subsequent fusion of the coordination spheres via alkoxide bridges. Elongation along a Jahn-Teller active molecular axis in [Cu2(L–H)2]2+ is affected by the nature of the counter ion, giving N2O3 and N3O2 coordination patterns in the hexafluorophosphate and in the chloride salt, respectively. In addition to the oxidised complex, isolated in close-to-quantitative yield, catechol is identified as the only reduction product, indicating a 2e−/2H+ reduction of the quinone. Electron transfer from copper(I) to the chemical oxidant is suggested to steer the formation of base equivalents from O2 and Q, which then drive ligand deprotonation and complex nucleation.

Three copper(II) complexes of a series of bidentate dipyridylmethane ligands, as well as their structurally related platinum(II) analogues, have been synthesised and fully characterised to evaluate their coordination chemistry and antiproliferative properties. New crystal structures of the complexes L3CuCl2, L2PtCl2 and L3PtCl2, where L2, L3 have one and two methyl substituents on the bridgehead carbon atom between the coordinated pyridine ligands, respectively, were obtained. The in vitro cytotoxicity of the free ligands and their corresponding platinum and copper complexes was evaluated in the cisplatin‐sensitive ovarian teratocarcinoma cell line CH1/PA1, as well as in rather cisplatin‐insensitive colon (SW480) and lung (A549) carcinoma cells, using the MTT assay. All six complexes showed higher cytotoxicity than the ligands L1–L3 alone, giving IC50 values in the low micromolar range.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.