Charles Lochenie

Structural Complexity in Metal–Organic Frameworks: Simultaneous Modification of Open Metal Sites and Hierarchical Porosity by Systematic Doping with Defective Linkers

A series of defect-engineered metal-organic frameworks (DEMOFs) derived from parent microporous MOFs was obtained by systematic doping with defective linkers during synthesis, leading to the simultaneous and controllable modification of coordinatively unsaturated metal sites (CUS) and introduction of functionalized mesopores. These materials were investigated via temperature-dependent adsorption/desorption of CO monitored by FTIR spectroscopy under ultra-high-vacuum conditions. Accurate structural models for the generated point defects at CUS were deduced by matching experimental data with theoretical simulation. The results reveal multivariate diversity of electronic and steric properties at CUS, demonstrating the MOF defect structure modulation at two length scales in a single step to overcome restricted active site specificity and confined coordination space at CUS. Moreover, the DEMOFs exhibit promising modified physical properties, including band gap, magnetism, and porosity, with hierarchical micro/mesopore structures correlated with the nature and the degree of defective linker incorporation into the framework.

Modulation of the ligand-based fluorescence of 3d metal complexes upon spin state change

Two new Schiff base-like ligands bearing a heteroaromatic fluorophore were synthesised and converted into the corresponding Ni(II), Cu(II) and Zn(II) square planar complexes. The Ni(II) complexes were studied with regard to a coordination change-induced spin state change upon addition of pyridine in solution. An inverse correlation between the fluorescence properties and the spin state of the metal centre was observed, and investigated with steady state fluorescence and time-resolved spectroscopy.

1D iron(II) spin crossover coordination polymers with 3,3′-azopyridine – kinetic trapping effects and spin transition above room temperature

Two new iron(II) 1D coordination polymers with spin crossover behaviour were synthesised using 3,3′-azopyridine as bridging axial ligand and N2O2 coordinating Schiff base-like equatorial ligands. The X-ray structures of both complexes were solved revealing very different packing patterns for the two complexes. Magnetic measurements reveal a spin transition with hysteresis and kinetic trapping effects at lower temperatures for one complex and a spin transition above room temperature for the second complex.

Water channels and zipper structures in Schiff base-like Cu(II) and Ni(II) mononuclear complexes

The crystal structures of four Cu(ii) complexes and one Ni(ii) complex bearing a square planar N2O2 coordination sphere are discussed. In all cases a distorted square planar coordination sphere is observed that is independent of the metal centre and the ligand and is only influenced by the packing of the molecules in the crystal. For the less distorted copper complexes metal-aromatic interactions are observed, while no significant intermolecular interactions are found for the nickel complexes. This can be explained by the different electronic character of Cu(ii) and Ni(ii) and is also reflected in the differences in the solvatochromism of these complexes.

Iron(II) spin crossover complexes with diaminonaphthalene-based Schiff base-like ligands: 1D coordination polymers

The synthesis of iron(II) coordination polymers of new Schiff base-like ligands with an extended π-system is described. In total sixteen new compounds were synthesised. The complexes were characterised by X-ray powder diffraction and magnetic measurements. Four of these complexes remain in the low-spin state and six remain in the high-spin state in the entire temperature range investigated. The remaining six complexes show a spin crossover behaviour with a cooperative spin transition (28 and 40 K wide hysteresis loops) in two cases. The influence of the extended aromatic system on cooperative interactions is discussed.

N-Donor Competition in Iron Bis(chelate) Bis(pyrazolyl)pyridinylmethane Complexes

Abstract We report on the synthesis and structural characterisation of the bis(chelate) bis(pyrazolyl) pyridinylmethane iron(II) complexes [Fe{HC(Pz)2(Py)}2][CF3CO2]2, [Fe{HC(3-iPrPz)(5- iPrPz)(Py)}2][CF3SO3]2 and [Fe{HC(3-iPrPz)(5-iPrPz)(Py)}2][FeBr4]Br·2C4H8O. During the synthesis of the latter ones, an isomerisation of the ligand is observed: the pyrazolyl substituent formally moves from the 3 to the 5 position. Since the donor competition between pyrazolyl and pyridinyl moieties is important for the coordination properties, we also studied the donor properties by density functional theory and natural bond orbital analysis (NBO). As a result, the pyridinyl donor is generally weaker than the pyrazolyl donor, but the pyrazolyl donor is heavily influenced by the alkyl substitution pattern. To confirm the low-spin state of the complexes, magnetic susceptibility measurements have been performed