Influence of the metal size in the structure of the complexes derived from a pentadentate [N3O2] hydrazone

Modulating the Structures and Magnetic Properties of Dy(III) Single-Molecule Magnets through Acid-Base Regulation

Chemical modulation on the structures and physical properties of the coordination complexes is of great interest for the preparation of new functional materials. By changing the acidity or basicity of the reaction medium, the deprotonation degree of a multidentate ligand with multiple active protons, H₄daps (H₄daps = N',N'″-((1E,1'E)-pyridine-2,6-diylbis(ethan-1-yl-1-ylidene))bis(2-hydroxybenzohydrazide)), can be regulated on purpose. With this ligand of different deprotonation and charges, three new Dy^III complexes ([Dy(H₃daps)(CH₃COO)₂(EtOH)]·CH₃COOH (1Dy), [Dy₂(H₂daps)₂(EtOH)₂(H₂O)₂(MeOH)₂](CF₃SO₃)₂·(H₂O)₂ (2Dy), and [Dy₃(H₁daps)₂(H₂daps)(μ₃-OH)(EtOH)(H₂O)] (3Dy)) of different nuclearities (mono-, di-, and trinuclear for 1Dy to 3Dy, respectively) have been synthesized and characterized structurally and magnetically. Analyses on the related bond lengths and resulting hydrogen bond modes in the complexes provide the details of the deprotonation position and the charge of the ligands, which can be in the form of H₃daps^-, H₂daps^2-, and H₁daps^3-. Interestingly, the more deprotonated ligand can act as a bridging ligand between the Dy^III centers using the phenol and/or carbonyl oxygen atoms, which leads to the multinuclear structures. Magnetic studies on these complexes revealed that complex 1Dy is a field-induced single-molecule magnet (SMM), while complexes 2Dy and 3Dy show SMM behavior under a zero dc field.

Neutral and anionic zinc compounds supported by a bis(imino)phenyl NCN ligand

The new zinc complexes 2,6-(ArNCH)₂C₆H₃ZnBu (6) and 2,6-(ArNCH)₂C₆H₃ZnCl₂Li(THF)₃ (7), supported by a bis(imino)phenyl NCN pincer ligand, were prepared (Ar = 2,6-ⁱPr₂C₆H₃).

An unusual assembled Pb(ii) meso-helicate that shows the inert pair effect

We report on a meso-helicate exhibiting the inert pair effect for the first time, demonstrating that this effect must be considered for the controlled assembly of Pb(ii) supramolecular helicates/mesocates.

Mimicking Peroxidase Activity by a Manganese(II) Complex Involving a New Asymmetric Tetradentate Ligand Containing Both Amino and Imino Groups

The asymmetric ligand (E)-4-bromo-2-(((2-((5-bromo-2-hydroxybenzyl)(methyl)amino)ethyl)imino)methyl)phenol has been prepared by a novel seven-step route. All organic compounds isolated in each step have been characterised by elemental analysis, infrared and1H NMR spectroscopy, and mass spectrometry. Interaction of this ligand with manganese has been investigated employing an electrochemical method. This method leads to the formation of a neutral manganese(II) complex7in high yield and purity. The complex has been thoroughly characterised by elemental analysis, infrared spectroscopy, mass spectrometry, magnetic susceptibility measurements, and cyclic voltammetry. Complex7behaves as peroxidase mimic in the presence of the water-soluble trap ABTS, probably due to its ease to coordinate the substrate molecule.

Lateral cis-1,3,5,7-tetraazadecalin podands and their complexes: synthesis, structure, and strong binding with Pb(II) and other heavy metal ions

The chemistry and complexation behavior of diaminal podands based on cis-1,3,5,7-tetraazadecalin (cis-TAD) were elaborated, reassessed, and extended. The synthesis of 2,6-bis(hydroxymethylene)-cis-TAD (9) and 2,6-bis(α,α'-dimethyl-β- hydroxyethyl)-cis-TAD (10) as well as of suitably substituted 2,6-diaryl-cis-TAD podands is laid out. For the latter, the effect of electron donating or withdrawing substituents on the benzaldehyde reagents was examined while 9 and 10 were probed and showed considerable propensity for heavy metal-ion chelation. The [Cd(II)·(9)] and [Pb(II)·(9)] complexes stood out indeed, and their structure and properties show a particularly interesting 5-amino-1,3-diazane chelation type and strong ligand-ion binding mode, with intramolecular donor exchange in solution, all strongly influenced by the anomeric effect in the ligand.

Metal induced folding: synthesis and conformational analysis of the lanthanide complexes of two 44-membered hydrazone macrocycles

Six new lanthanide complexes of two 44-membered macrocycles have been prepared and characterised in solution. An analysis of the conformations of the free macrocycles and their lanthanide complexes both in solution (2D NMR) and in solid state (X-ray crystallography) demonstrate that the complexation induces changes in folding of the macrocycles.

Dynamic combinatorial libraries for the recognition of heavy metal ions

We present the use of hydrazone dynamic combinatorial libraries (DCLs) to identify macrocyclic receptors that are selective for alkaline earth metal ions over alkali metal ions. In particular, the toxic heavy metal ions Sr(2+) and Ba(2+) induce characteristic changes in the DCLs. Four macrocycles were isolated and characterised by LCMS, HRMS, NMR and X-ray crystallography; binding studies by UV-Vis spectroscopy confirm the selectivity observed in the DCLs.

Remarkably stable chalcogen(II) dications

Air-stable, chalcogen-centered dications have been synthesized and comprehensively characterized. These represent the first diiminopyridine (DIMPY) complexes of the chalcogens as well as the single nonmetallic (sulfur) complex of this ubiquitous ligand. Their stability under ambient conditions is a distinct contrast to other highly charged main-group cations.

Pentadentate thiosemicarbazones as versatile chelating systems. A comparative structural study of their metallic complexes

We have prepared some transition and post-transition metal complexes derived from the pentadentate thiosemicarbazone ligand bis(4-N-ethylthiosemicarbazone)-2,6-diacetylpyridine H(2)L(Et), by both chemical and electrochemical procedures. The complexes have been synthesised and fully characterised, including the crystal structures for the ligand H(2)L(Et) and its manganese, cadmium and lead complexes. We have also performed multinuclear (109)Ag, (113)Cd, (119)Sn and (207)Pb studies for silver, cadmium, tin and lead compounds, respectively. Moreover we present here a comparative study on the different structures found for pentadentate thiosemicarbazonate complexes, trying to check the influence of different factors, such as experimental procedure, size of metal, structure of the ligand, and metal oxidation state, on the final structure of the complex formed. Our aim is gaining a better insight into the coordination trends of pentadentate thiosemicarbazone ligands.

Metal-catalysed oxidation processes in thiosemicarbazones: new complexes with the ligand N-{2-([4-N-ethylthiosemicarbazone]methyl)phenyl}-p-toluenesulfonamide

The coordination behaviour of a new thiosemicarbazone Schiff-base building block, N-{2-([4-N-ethylthiosemicarbazone]methyl)phenyl}-p-toluenesulfonamide, H2L1 (1), incorporating a bulky tosyl group, towards Mn II, Fe II, Co II, Ni II, Cu II, Zn II, Cd II, Ag I, Sn II, and Pb II has been investigated by means of an electrochemical preparative procedure. Most metal complexes of L1 have the general formula [M(L1)]2.nX (M=Mn, Fe, Co, Ni, Cu, Cd, Pb; n=0-4, X=H2O or CH3CN), as confirmed by the structure of [Pb(L1)]2 (15), in which the lone pair on lead is stereochemically active. This lead(II) complex shows an intense fluorescence emission with a quantum yield of 0.13. In the case of silver, the complex formed was found to possess a stoichiometry of [Ag2(L1)]2.3H2O. During reactions with manganese and copper metals, interesting catalysed processes have been found to take place, with remarkable consequences regarding the ligand skeleton structure. In synthesising the manganese complex, we obtained an unexpected dithiolate thiosemicarbazone tosyl ligand, H2L2, as a side-product, which has been fully characterised, including by X-ray diffraction analysis. In the case of copper, the solid complex has the formula [CuL1]2, but the crystallised product shows the copper atoms coordinated to a new cyclised thiosemicarbazone ligand, H2L3, as in the structures of the complexes [Cu(L3)]2.CH3CN (8) and [Cu(L3)(H2O)]2.CH3CN.H2O (9). The zinc complex [Zn(L1)]4 (12) displays a particular tetranuclear zeolite-type structure capable of hosting small molecules or ions, presumably through hydrogen bonding.