Iron(II) Spin Crossover Complexes Based on a Redox Active Equatorial Schiff-Base-Like Ligand.

In this work, two iron(II) coordination compounds with a N2O2 coordinating Schiff base-like ligand bearing a redox active tetrathiafulvalene (TTF) unit and pyridine or trans-1,2-bis(4-pyridylethylene) as an axial ligand are synthesized. Crystals suitable for single X-ray structure analysis were obtained for the new ligand. The complexes were characterized by magnetic susceptibility measurements, T-dependent UV-vis spectroscopy, and cyclic voltammetry. Both complexes display spin transition behavior below room temperature with T1/2 values of 146 and 156 K. The mononuclear iron(II) complex [FeTTFL(py)2] is relatively stable up to 400 K compared to similar complexes, showing no loss of axial ligands upon heating. Temperature dependent Mössbauer spectroscopy was conducted for the coordination polymer {[FeTTFL(bpee)]}n to get more information regarding the origin of the stepwise spin crossover (SCO) behavior observed in the magnetic measurements. The change of the spin state is accompanied by a change of the optical properties, which can be monitored by VT-UV-vis spectroscopy for the mononuclear complex and has been analyzed in theoretical studies. The redox behavior of the iron(II) complexes reveals three reversible redox steps which are located at the iron center and at the TTF unit of the ligand. Oxidation of the TTF unit induces characteristic changes in the UV-vis spectrum that can be followed by spectroelectrochemical UV-vis spectroscopy. Addressing the potential of the iron-centered redox process results in similar changes in the UV-vis spectrum, which indicates an electronic coupling of the redox active unit with the metal center under certain circumstances.

Iron(II) Spin Crossover Complexes with 4,4'-Dipyridylethyne-Crystal Structures and Spin Crossover with Hysteresis.

Three new iron(II) 1D coordination polymers with cooperative spin crossover behavior showing thermal hysteresis loops were synthesized using N2O2 Schiff base-like equatorial ligands and 4,4'-dipyridylethyne as a bridging, rigid axial linker. One of those iron(II) 1D coordination polymers showed a 73 K wide hysteresis below room temperature, which, upon solvent loss, decreased to a still remarkable 30 K wide hysteresis. Single crystal X-ray structures of two iron(II) coordination polymers and T-dependent powder XRD patterns are discussed to obtain insight into the structure property relationship of those materials.

Copper(ii) complexes with tridentate Schiff base-like ligands: solid state and solution structures and anticancer activity.

We report 15 new Cu(ii) complexes with tridentate NNO ß-acylenamino ligands derived from 2-picolylamine and bearing up to three alkyl, alkoxy, alkoxycarbonyl, or (pseudo)halide substituents. The structures of nine complexes were elucidated by single crystal X-ray diffraction analysis. Complexes with an unsubstituted pyridine ring crystallised with a square pyramidal coordination sphere, whereas substitution of the pyridine ring led to a square planar coordination sphere around the metal centre. The solution structures and properties of the complexes were characterised by UV-Vis spectroscopy and cyclic voltammetry. They were also tested for their cytotoxic effect on four human cancer cell lines. Two complexes were identified that were highly active with single-digit IC50 values, exceeding those of cisplatin by far. A tentative structure-activity relationship was proposed as well as topoisomerase I inhibition as a possible mode of action, while any significant interference with DNA and the level of reactive oxygen species could be excluded.

Towards New Robust Zn(II) Complexes for the Ring-Opening Polymerization of Lactide Under Industrially Relevant Conditions.

The synthesis of bio-based and biodegradable plastics is a hot topic in research due to growing environmental problems caused by omnipresent plastics. As a result, polylactide, which has been known for years, has seen a tremendous increase in industrial production. Nevertheless, the manufacturing process using the toxic catalyst Sn(Oct)2 is very critical. As an alternative, five zinc acetate complexes have been synthesized with Schiff base-like ligands that exhibit high activity in the ring-opening polymerization of non-purified lactide. The systems bear different side arms in the ligand scaffold. The influence of these substituents has been analyzed. For a detailed description of the catalytic activities, the rate constants k app and k p were determined using in-situ Raman spectroscopy at a temperature of 150 °C. The polymers produced have molar masses of up to 71 000 g mol-1 and are therefore suitable for a variety of applications. Toxicity measurements carried out for these complexes proved the nontoxicity of the systems.

Isostructural iron(iii) spin crossover complexes with a tridentate Schiff base-like ligand: X-ray structures and magnetic properties.

Here we present two isostructural iron(iii) spin crossover complexes with the same tridentate ligand and perchlorate or tetrafluoroborate as counter ion. Single crystal X-ray structures in the high spin and low spin state were obtained for both complexes. An abrupt spin transition above 100 K is observed with the transition temperature depending on the size of the anion.

Anticancer properties of a new non-oxido vanadium(IV) complex with a catechol-modified 3,3'-diindolylmethane ligand.

In order to identify new active drug candidates against cancer diseases we investigated the tumor cell growth inhibition, formation of reactive oxygen species, mitochondrial membrane damage, cell cycle arrest and DNA binding activity of a new bis(triethylammonium) tris[1,1-bis(indol-3-yl)-1-(3,4-catecholate)methane]vanadate(IV) complex. It exhibited significant antiproliferative activity against various cancer cell lines, showed a stronger DNA binding than cisplatin and led to mitochondrial damage, a formation of reactive oxygen species, and a cell cycle arrest in the G2/M phase of cancer cells.

Towards Dual-Functionality Spin-Crossover Complexes.

The multistep synthesis of a versatile new 4-substituted 3,5-bis(2-pyridyl)-1,2,4-triazole (Rdpt) ligand, 4-[4-(2-aminomethyl)phenyl]-3,5-bis(2-pyridyl)-4 H-1,2,4-triazole (apdpt), is reported, which features a reactive aminomethyl para-substituent on the phenyl group that points "out of the back" of the triazole. This enables further functionalisation under mild conditions by using a range of esters to form an amide link. Specifically, this proof of principle study demonstrates the synthesis of apdpt successfully appended with gold-binding thioctic acid (tpdpt), graphene-binding/emissive pyrene/propylpyrene (prdpt/pbdpt), and a Langmuir-Blodgett film-forming polyethylene glycol (PEG) tail (pgdpt). These ligands are subsequently reacted with [Fe(pyridine)4 (NCBH3 )2 ] to give the mononuclear iron(II) complexes [Fe(Rdpt)2 (NCBH3 )2 ]⋅solvent, in which Rdpt/solvent is tpdpt/2.5 H2 O (1), prdpt/0.5 CHCl3 ⋅H2 O (2), and pbdpt/0.5 CHCl3 ⋅2 H2 O (3), as red powders. Magnetic studies on these powders indicate that the complexes undergo only very gradual and incomplete spin crossover, from completely or mostly high spin at 300 K, to half or three-quarters high spin at 50 K. Gold nanoparticles are successfully functionalised with the thioctic acid tpdpt ligand to give tpdpt@Au with an average diameter (as determined by TEM) of (3.1±0.7) nm. Preliminary studies on the two pyrene systems in dimethylformamide show that upon excitation at λ=345 nm the blue fluorescence observed for the free ligands is retained, essentially unaffected, in the respective complexes.