Bohdan Korybut-Daszkiewicz

Macrocyclic ligands and their metal ion complexes. Part VI. Preparation, stereochemistry and conformational analysis of polyalkyl1,4,8,11-tetra-azacyclotetradeca-4,11-dienenickel(II) diperchlorates

Abstract α,β-Unsaturated ketones react with ethylenediamine monohydrogenperchlorate to form dihydrogenperchlorates of polyalkyl-1,4,8,11-tetra-azacyclotetradeca-4,11-dienes (L). These Schiffs base amines react with nickel(II) acetate to form square-planar complexes NiL(ClO4)2. The C- and N-diastereoisomeric complexes were separated and ligand configuration and conformation were assigned on the basis of chemical and spectroscopical, mainly p.m.r. evidence. Partial resolution of some complexes was achieved by chromatography on starch.

Crystal structure and magnetic properties of two heteronuclear thiocyanate bridged compounds: (CuL)[Co(NCS)4] (L=N-meso-(5,12-Me2-7,14-Et2-[14]-4,11-dieneN4) and N-rac-(5,12-Me2-7,14-Et2-[14]-4,11-dieneN4))

Abstract Complexes of general formula [CuL][Co(NCS)4] (where L=N-meso-(5,12-Me2-7,14-Et2-[14]-4,11-dieneN4) (1); N-rac-(5,12-Me2-7,14-Et2-[14]-4,11-dieneN4) (2)) were obtained and characterised by X-ray diffraction, magnetic measurements and by infrared spectroscopy. For both compounds the crystal and molecular structures have been determined. We observed two different environments of copper(II) ions in the cell for both complexes. Complex 1 formed 1-D polymeric chains where copper(II) is square bipyramidal, while complex 2 has a binuclear structure with square pyramidal environments of copper(II) ions. The magnetic susceptibility of both complexes was measured over a temperature range 1.9–300 K by the SQUID method. The magnetic behaviour of complexes 1 and 2 is characteristic for compounds with ferromagnetic interactions.

Voltammetric behaviour of Ni(II) and Co(III) tetraazamacrocyclic complexes containing a pendant amino group

Abstract The electrochemical behaviour of tetraazamacrocyclic Ni(II) and Co(III) complexes containing a pendant amino group has been studied by cyclic voltammetry at glassy carbon and Hg electrodes in aqueous and acetonitrile solutions. The behaviour of these complexes has been compared with the behaviour of Ni(II) and Co(III) cyclams and dimethylated cyclams. The internal pH-dependent equilibrium between the open and chelated forms of the pendant arm has been studied and discussed.

Heteronuclear thiocyanate-bridged compounds of the type (NiL)3[M(NCS)6]2 (M = Fe(III), Cr(III); L = 5,6,12,13-Me4-[14]-4,11-dieneN4)

The complexes of the general formula (NiL) 3 [M(NCS) 6 ] 2 (where L = 5,6,12,13-Me 4 -[14]-4,11-dieneN 4 , M = Fe(III) (1), Cr(III) (2)) were obtained and their magnetic and spectroscopic properties characterized. For the compound (NiL) 3 [Fe(NCS) 6 ] 2 , the crystal structure was determined and X-ray analysis showed that it forms a linear pentanuclear compound NiFeNiFeNi in which the peripheral nickel(II) ions are five-co-ordinate. Magnetic studies for both compounds showed the existence of structural differences between them.

An electrochemically switchable foldamer - a surprising feature of a rotaxane with equivalent stations

A novel, mechanically interlocked molecular device was obtained from unique supramolecular tectons – π-deficient tetraazamacrocyclic complexes of copper(II) and nickel(II). We present the synthesis of the first rotaxanes based on donor–acceptor interactions involving transition metal complexes. While spontaneous shuttling manifests itself in the variability of the NMR spectra, voltammetric experiments reveal a surprising mode of potential-controlled molecular switching, which does not employ common co-conformational changes. Significantly, it relies on reversible folding/unfolding of the rotaxane. The process is driven by the interplay between electrostatic repulsion and cohesive π–π interaction – a tug of war with a critical point at 1.31 V. Although rotaxanes with equivalent stations are considered degenerate molecular shuttles, we show that this is not the case when an unusual mechanism of switching is involved.

Tetra-aza macrocyclic complexes containing a pendant amino group. Copper(II), nickel(II), and cobalt(III) complexes of 5-aminomethyl-2,5,10,12-tetramethyl-1,4,8,1 1-tetra-azacyclotetradecane (L) and X-ray structural characterisation of the cobalt(III) complex [Co(L)Cl][ClO4]Cl·EtOH

The macrocycle 5-aminomethyl-2,5,10,12-tetramethyl-1,4,8,11-tetra-azacyclotetradecane (L) containing a pendant amino group has been prepared. A variety of copper(II), nickel(II), and cobalt(III) complexes have been characterised. Octahedral [NiL(H2O)]2+ complexes are readily protonated to give yellow or orange planar [Ni(HL)]3+ species. Analogous copper(II) complexes have also been prepared. X-ray crystallographic investigation of the complex [Co(L)Cl][ClO4]Cl·EtOH confirms the ligand stereochemistry and establishes a trans III (2 N–H bonds up, 2 N–H bonds down) stereochemistry for the chiral NH centres. The pendant amino group acts as a donor in one of the axial sites and lies trans to the chloride ligand. Rapid base hydrolysis of the Cl– ligand occurs with kOH= 2.2 × 104 dm3 mol–1 s–1 and kaq= 3.5 × 10–5 s–1 at 25 °C and I= 0.1 mol dm–3.

Neutral Nickel(II) and Copper(II) Tetraazamacrocyclic Complexes as Molecular Rods Attached to Gold Electrodes

New dithiolated derivatives of neutral Cu(II) and Ni(II) tetraazamacrocyclic complexes have been synthesized and characterized by spectroscopic and diffractional methods. These rod-shaped molecules were assembled in monocomponent and mixed monolayers on gold electrodes. In the mixed monolayers, the active molecules were embedded in a hexanethiol matrix. The dithiolated complexes are oriented perpendicularly to the electrode, and reveal faster kinetics of electron transfer than those assembled in a single-component monolayer. They appear as protrusions, which are easily addressed by using the STM method. In the presence of a suitable electron acceptor in the solution, the donor properties of the anchored Cu complex were weakened, which revealed donor-acceptor interactions with the monolayer. The peak position in the voltammogram indicates a stronger interaction of the solution-based acceptor with the reduced Cu(II) form than with the Cu(III) complex. This suggests the possibility of switching the association on or off by applying an appropriate potential.

Determination of Experimental Charge Density in Model Nickel Macrocycle: [3,11-Bis(methoxycarbonyl)-1,5,9,13-tetraazacyclohexadeca-1,3,9,11-tetraenato-(2-)-κ4N]nickel(II)

Experimental and theoretical atomic charges and d-orbital populations were obtained for [3,11-bis(methoxycarbonyl)-1,5,9,13-tetraazacyclohexadeca-1,3,9,11-tetraenato(2-)-kappa(4)N]nickel(II) monocrystal (16Ni) using the Hansen and Coppens formalism. Several models of this structure were tested as a function of quality of the fit, convergence of the refinement, value of residual peaks and holes, and Hirshfelds rigid-bond test. The models with Ni-atomic scattering factors applied for the metal center are significantly better than those with the Ni-ionic scattering factors. The properties of the final electron density distributions are very consistent and similar for all of the models tested. The values of the d-orbital populations for Ni roughly agree with the occupation order of the d-electron levels for square-planar complexes derived from crystal field theory and are comparable with those obtained by the natural population analysis method. Experimental atoms-in-molecules charges calculated for four different models agree quite well for models with different symmetry restrictions and the same scattering factor for the Ni. Both experimental and theoretical methods predict relatively high negative values of charges for the nitrogen and oxygen atoms and also a quite high positive charge for the C(7) atom. The values of rho(r(BCP)) for the Ni-N bonds are in the range from 0.60 up to 0.75e A(-3), with positive laplacian values indicating noncovalent bonding. For the laplacian of the electron density evaluated in the plane of the macrocyclic ring, a typical map for a square-planar complex was obtained with four charge concentrations--3d(xy) orbitals--pointing toward the regions between the M-N bonds and charge depletions directed toward the (3,-1) critical points of the negative laplacian for the nitrogen atoms.

Self-assembly of a nickel(II) pseudorotaxane nanostructure on a gold surface

Tetraazamacrocyclic complexes of NiII and CuII can be used as components of catenanes or rotaxanes showing electrochemically switched intramolecular motion in solution. In our present studies, we modify these compounds with organothiol chains to attach them to the surface of the electrode using the self-assembly method and employ them next as molecular switches, which change conductivity upon applying appropriate potential. The electrochemical properties of these compounds are studied in the solution and, in the case of thiol derivative, immobilized on the electrode surface. The macrocyclic complex of NiII, immobilized on the Au surface, forms the axis of the rotaxane. This compound can be anchored to the surface by one or two thiol groups. The data obtained from scanning tunneling microscopy (STM) experiments using colloidal Au confirm that the orientation normal to the surface dominates. The electrochemical experiments reveal reversible one-electron oxidation of metal center from +2 to +3. The behavior of the electrode modified with the macrocyclic complex of NiII upon immersion in a solution containing bismacrocyclic complex of NiII points to the formation of a new rotaxane-like nanostructure on the surface of the electrode.

NICKEL(II) COMPLEXES OF NOVEL MACROCYCLIC LIGANDS CONTAINING PENDANT NITRO GROUPS

Abstract The addition of nitromethane anion to the C=N group of polyalkyl-1,4,8,11-tetraazacyclotetradeca-4, 11-dienenickel(II) diperchlorate gave Ni(II) complexes of new macrocyclic ligands containing a pendant 5-nitromethyl group. Variable temperature (80–290 K) magnetic susceptibilities were determined for the paramagnetic monoperchlorates and the diamagnetic square-planar diperchlorates. Conformations of the nitromethyl groups in the macrocyclic ligands were established on the basis of 1H NMR evidence.