Acta Crystallographica Section A Foundations of Crystallography, 2002
Since the discovery of Mn12-acetate in the early 80s and the subsequent determination of its sing... more Since the discovery of Mn12-acetate in the early 80s and the subsequent determination of its single molecule magnet (SMM) characteristics, interest in the area of large metal clusters, particularly Mn cluster chemistry, has continued to grow. To date, several SMMs have been identified including Fe8, V4, Mn4 and Mn12 clusters but it has been found that Mn clusters often possess large values of ground state spin -an important requirement for SMM behaviour. Our group is interested in the synthesis of new Mn clusters and the investigation of their structural and magnetic properties. The focus currently is on the incorporation of bridging ligands other than O-donor ligands such as benzamidinate (bza-), which is an N-donor, isoelectronic analogue of benzoate. A [Mn4O(bza)6] tetramer was formed by the reaction of a MnII salt with deprotonated ligand under an inert atmosphere. The core consists of four MnII atoms arranged tetrahedrally around an oxygen atom. Each metal atom has a pseudo-tetrahedral arrangement of nitrogen atoms around it with each of the six bza-groups forming a bridge between two metal centres. A [Mn3O(bza)6(pyr)3] trimer was formed from a comproportionation reaction between a MnII salt and MnO4in the presence of bza. The cluster is mixed valent (2MnIII, MnII) and possess an oxo-centred Mn3O unit with 6 bzagroups providing peripheral ligation and three pyridine groups in terminal positions. The magnetic properties are similar to those of the benzoate analogue. Work is in progress on larger clusters of benzamidinate and with other bridging ligands.
Efficient catalysis of water oxidation represents one of the major challenges en route to efficie... more Efficient catalysis of water oxidation represents one of the major challenges en route to efficient sunlight-driven water splitting. Cobalt oxides (CoOx ) have been widely investigated as water oxidation catalysts, although the incorporation of these materials into photoelectrochemical devices has been hindered by a lack of transparency. Herein, the electrosynthesis of transparent CoOx catalyst films is described by utilizing cobalt(II) aminopolycarboxylate complexes as precursors to the oxide. These complexes allow control over the deposition rate and morphology to enable the production of thin, catalytic CoOx films on a conductive substrate, which can be exploited in integrated photoelectrochemical devices. Notably, under a bias of 1.0 V (vs. Ag/AgCl), the film deposited from [Co(NTA)(OH2 )2 ](-) (NTA=nitrilotriacetate) decreased the transmission by only 10 % at λ=500 nm, but still generated >80 % of the water oxidation current produced by a [Co(OH2 )6 ](2+) -derived oxide film...
ABSTRACT Current energy resources largely rely on fossil fuels that are expected to be depleted i... more ABSTRACT Current energy resources largely rely on fossil fuels that are expected to be depleted in 50-200 years. On a global scale, the intensive use of this energy source has resulted in highly detrimental effects to the environment. Hydrogen production by water splitting, with sunlight as the main energy source, is a promising way to augment the production of renewable energy. However, the development of an efficient and stable wateroxidizing catalyst remains a key task before a technological breakthrough based on water splitting can be realized. A main issue hampering the development of commercially viable, non-precious metal-based catalysts is their susceptibility to degradation. To efficiently address this major drawback, self-healing catalysts, that can repair their structure without human intervention, will be necessary. In this review, we focus on water oxidation by natural and artificial Mn-, Co- and Ni-based catalysts and then discuss the self-healing properties that contribute to sustaining their catalytic activity.
Hydrolysis and polymerization of [Fe(OH(2))(6)](3+) in aqueous solution leads, in the early stage... more Hydrolysis and polymerization of [Fe(OH(2))(6)](3+) in aqueous solution leads, in the early stages, to the oxo-bridged binuclear aqua ion [(H(2)O)(5)Fe(µ-O)Fe(OH(2))(5)](4+), which could be obtained in crystalline form through the use of [18]crown-6. The complex exhibits an almost linear Fe-O-Fe moiety and antiferromagnetic coupling that is consistent with current descriptions of exchange coupling in mono oxo-bridged binuclear Fe(III) complexes.
Thiosulfate and ammonia mixtures may be more environmentally benign alternatives to cyanide for l... more Thiosulfate and ammonia mixtures may be more environmentally benign alternatives to cyanide for leaching Au from ores. In this method, the Cu(I)/Cu(II) couple acts as a redox mediator aiding in the oxidative dissolution of metallic Au. Information about the speciation of Cu(I) and Cu(II) in these lixiviant solutions is paramount to the optimization of gold ore processing conditions. With this in mind, we have carried out XANES, EXAFS and UV-Vis spectroscopic studies of the speciation of Cu(I) in mixed thiosulfate-chloride and ammonia-chloride solutions. In thiosulfate-chloride solutions, the EXAFS studies indicate that the geometry of the predominant Cu(I) complex is distorted trigonal (triangular planar), with an average of 2 sulfur atoms + 1 oxygen atom occupying the coordination sphere. This indicates that the stability of the [Cu(S 2 O 3 ) 3 ] 52 complex is lower than previously proposed. Formation constants for Cu(I) thiosulfate complexes have been derived on the basis of systematic UV-Vis measurements of solutions with varying [S 2 O 3 ]/[Cl] ratios. Only one mixed chloride-thiosulfate complex, [Cu(H 2 O)(S 2 O 3 )Cl] 22 , was found to predominate over the range of conditions investigated.
Journal of the Chemical Society, Dalton Transactions, 1997
Solution studies of a trinuclear rhodium() aqua ion, using a variety of solution techniques (N... more Solution studies of a trinuclear rhodium() aqua ion, using a variety of solution techniques (NMR, UV/VIS spectroscopy, charge per Rh determination and elution behaviour) have shown that this oligomer can exist in several structural forms. The form isolated, by ion-exchange chromatography following aging of Rh 3ϩ solutions in base, does not have a linear (1) or bent (2) arrangement of rhodium() centres but consists of a triangular arrangement of such centres linked to each other by one µ-OH bridge (4). The fact that 4 exhibits two 103 Rh NMR signals at δ 9964 and 10 000 in a 2 : 1 ratio is rationalized in terms of the stabilization of a conformation with two rhodium environments through strong hydrogen-bonding between a terminal H 2 O or OH ligand and a µ-OH bridging group. On heating this form is transformed into a new ion which has a different UV/VIS spectrum and two 103 Rh NMR signals at δ 9671 and 9841 in a 1 : 2 ratio. The structure of this form is proposed to consist of a triangular arrangement of metal atoms, two magnetically equivalent rhodium() centres linked together by two µ-OH bridges and each linked to the third Rh III via a single µ-OH bridge. The low pK a1 for this ion of 0.5 ± 0.1 is attributed to the formation of a strong hydrogen-bond between one of the µ-OH groups bridging the two equivalent rhodium() centres and the terminal OH group generated by deprotonation. The existence of a hydrogen-bond interaction in both 3 and 4 has literature precedent. At high pH, 3 is transformed into a new aqua ion, 5, which exhibits a single 103 Rh NMR signal at δ 10 049 and a different UV/VIS spectrum to that of 3 and 4. This is interpreted in terms of a symmetric structure in which the three rhodium() centres are linked by a single µ 3 -OH group and pairs of Rh atoms are further linked by a µ-OH bridge. A variable-pH and -temperature kinetic study revealed that 4 undergoes an irreversible intramolecular condensation process which produces 3 or 5, depending on the pH. The increase in rate with pH is consistent with the existence of two pathways, attributable to the reaction of singly and doubly deprotonated forms of 4. The rate increase of ca. 100 fold matches those observed for related chromium() systems.
5th IEEE Conference on Nanotechnology, 2005., 2005
TiO2 nanocrystals have been synthesized from Titanium(IV) butoxide without the use of an autoclav... more TiO2 nanocrystals have been synthesized from Titanium(IV) butoxide without the use of an autoclave. It was found that using heat treatment temperatures below 600°C pure anatase phase was retained in the nanocrystals. In addition, with increasing heat treatment temperature the nanocrystals became larger in size and the homogeneity was dramatically reduced.
Dendritic polyglycerol sulfate (dPGS) is a biocompatible, bioactive polymer which exhibits anti-i... more Dendritic polyglycerol sulfate (dPGS) is a biocompatible, bioactive polymer which exhibits anti-inflammatory activity in vivo and thus represents a promising candidate for therapeutic and diagnostic applications. To investigate the in vivo pharmacokinetics in detail, dPGS with a molecular weight of ca. 10 kDa was radiolabeled with 3H and 64Cu, and evaluated by performing biodistribution studies and small animal positron emission tomography (PET). 3H-labeling was accomplished by an oxidation-reduction process with sodium periodate and [3H]-borohydride. 64Cu-labeling was achieved by conjugation of isothiocyanate- or maleimide-functionalized copper(II)-chelating ligands based on 1,4-bis(2-pyridinylmethyl)-1,4,7-triazacyclononane (DMPTACN) to an amino functionalized dPGS scaffold, followed by reaction with an aqueous solution containing 64CuCl2. Independent biodistribution by radioimaging and PET imaging studies with healthy mice and rats showed that the neutral dPG was quantitatively r...
A series of new asymmetrically N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) ma... more A series of new asymmetrically N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle have been prepared from the common precursor 1,4,7-triazatricyclo[5.2.1.0 4,10 ]decane: 1-ethyl-4-isopropyl-1,4,7-triazacyclononane (L1), 1-isopropyl-4-propyl-1,4,7-triazacyclononane (L2), 1-(3-aminopropyl)-4-benzyl-7-isopropyl-1,4,7-triazacyclononane (L3), 1-benzyl-4-isopropyl-1,4,7-triazacyclononane (L4) and 1,4-bis(3-aminopropyl)-7-isopropyl-1,4,7-triazacyclononane (L5). The corresponding monomeric copper(II) complexes were synthesised and were found to be of composition:
The attempted coupling of (ferrocenylmethyl)trimethylammonium iodide (1) with 1,4,7-(triformyl)-1... more The attempted coupling of (ferrocenylmethyl)trimethylammonium iodide (1) with 1,4,7-(triformyl)-1,4,7,10-tetraazacyclododecane (2) in water led to the formation of the expected compound 1-(ferrocenemethyl)-4,7,10-(triformyl)-1,4,7,10-tetraazacyclododecane (3). In addition, hydrolysis of the ferrocenyl precursor 1 led to the formation of two other known compounds, hydroxymethylferrocene (4) and bis(ferrocenylmethyl) ether . An X-ray crystal structure determination of 4 revealed the presence of H-bonding between the hydroxyl groups of one molecule of 4 and the oxygen atom of an adjacent molecule resulting in a left-handed helical chain of molecules lying along the b-axis direction. The OÁ Á ÁO distances are significantly shorter than those found in previously reported structures of hydroxymethylferrocene derivatives indicative of moderate strength H-bonding interactions. In the structure of 5, the orientation of the ferrocenyl groups are staggered relative to a vector comprising the two carbons of the C-O-C linker. Crown
Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) ... more Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) polymers Cu(2-qic)Br (2-qic = quinoline-2-carboxylate) (1) and Cu(2-pic)Br (2-pic = pyridine-2-carboxylate) (2) are described. These compounds are isostructural with Cu(2-qic)Cl and Cu(2-pic)Cl, respectively, the X-ray crystal structures of which were reported recently. Both complexes are polynuclear copper(II) compounds (1D and 2D, respectively) based on syn-anti carboxylate bridges and additionally on linear monobromo-(in 1) and dibromo-bridging (in 2) motifs. The magnetic properties were investigated in the temperature range 1.8-300 K. They reveal the occurrence of strong antiferromagnetic coupling (J 1 = À102.5 cm À1 ) through the single bromo-bridge in 1, which is much stronger than that transmitted by the single chloro-bridge (J = À57.0 cm À1 ). Very weak ferromagnetic interaction through the syn-anti carboxylate bridge J 2 is expected as it was observed in isomorphous Cu(2-qic)Cl (J = 0.37 cm À1 ). For 2 a weak ferromagnetic couplings through the syn-anti carboxylate (zJ 0 = 1.35 cm À1 ) and dibromo-bridges (J = 8.31 cm À1 ) were found. The experimental results indicate that the observed ferromagnetic exchange through dibromo-bridge is weaker than that in the chloride analog (J = 15.0 cm À1 ). The magnitude of magnetic interactions is discussed on the basis of structural data of compounds 1 and 2 and their halide analogues.
... 3. Results and discussion. The precursor solutions used in this study were transparent. ... ... more ... 3. Results and discussion. The precursor solutions used in this study were transparent. ... Effect of coating thickness in nanostructured coreshell electrodes on the efficiency of dye-sensitised solar cells; Paper presented at ISES2003, 2003, Göteburg, Sweden. ...
ABSTRACT Five amidinium, salts have been prepared from triazatricyclo[5.2.1.0(4,10)]decane (tacno... more ABSTRACT Five amidinium, salts have been prepared from triazatricyclo[5.2.1.0(4,10)]decane (tacnoa) and characterised by mass spectrometry, NMR spectroscopy and X-ray crystallography. The X-ray structures revealed a long distance between the methine carbon and the ammonium nitrogen, viz., C-N distance 1.64-1.70 angstrom, cf. other C-N distances of 1.40-1.50 angstrom An NMR study of 1-ethyl-4,7-diaza-1-azoniatricyclo[5.2.1.0(4,10)]decane and 1-benzyl-4,7-diaza-1-azoniatricyclo[5.2.1.0(4,10)]decane, confirmed that these amidinium salts hydrolyse in aqueous solution, the latter 60 times faster than the former. Tacnoa, which has C-N distances typical of single bonds, showed no evidence of hydrolysis after several days at 80 degrees C. Molecular modeling calculations indicate that the preferred gas phase structure of the salts is one where the positive charge is delocalised over the two secondary amines and the methine carbon. The calculated distance between this carbon and the ammonium nitrogen is 0.15-0.4 angstrom longer than in the crystal structure. The energy difference between the preferred gas phase and solid state conformations is 2 kJ mol(-1) and presents little barrier to nucleophilic attack of the methine carbon. Further analysis of the methine carbon geometry (C(7)) reveals that the bond angles in the benzyl salt are closer to those expected for an sp(2) centre than in the ethyl salt and that this could be the origin of the faster hydrolysis rate. (c) 2005 Elsevier Ltd. All rights reserved.
ABSTRACT Nanostructured porous tin-doped indium oxide (ITO) films were prepared by screen printin... more ABSTRACT Nanostructured porous tin-doped indium oxide (ITO) films were prepared by screen printing of an ITO nanoparticle paste onto conducting fluorine-doped tin oxide (FTO) substrates. The ITO films were subsequently coated with thin layers of TiO2 by the hydrolysis of TiCl4 to form the collector–shell photoelectrodes. The morphology of films was analysed by scanning electron microscope (SEM). It was found that a uniform coating of TiO2 was achieved when three or more deposition cycles were applied. Dye-sensitized solar cells were constructed with the collector–shell photoelectrodes using an electrolyte containing the [Co(bpy)3]2+/3+ (bpy = 2,2′-bipyridine) redox couple and MK-2, an organic sensitizer and efficiencies of 3.3% achieved. Charge transport in cells utilizing the collector–shell electrodes was found to be 2–6 times faster than those utilizing P25-based TiO2 electrodes.
ABSTRACT A device fabrication method is reported to efficiently produce CH3NH3PbI3-based planar p... more ABSTRACT A device fabrication method is reported to efficiently produce CH3NH3PbI3-based planar perovskite solar cells on polymer substrates with the entire process conducted at 150 °C or below. The hole blocking layer employed is a solution processed 100 nm thick mesoporous TiO2 layer. A gas-assisted perovskite deposition method is used to produce excellent coverage of the hole blocking layer by a ∼350 nm thick CH3NH3PbI3 film, resulting in high device performance reproducibility. We show that an average efficiency of 10.6 ± 1.2%, and a maximum efficiency of 12.3% are obtained for flexible perovskite solar cells, offering great promise for further improvement of this low-temperature, low-cost processing solar technology.
ABSTRACT The mechanism and kinetics of the liquid phase selective oxidation of benzyl alcohol to ... more ABSTRACT The mechanism and kinetics of the liquid phase selective oxidation of benzyl alcohol to benzaldehyde with oxygen on bare and Ce or Fe promoted (Mnat/Meat, 3) MnOx catalysts [1] have been investigated. Irrespective of toluene as solvent, the bare and promoted catalysts drive the selective oxidation of the substrate via the Mars-van Krevelen redox mechanism due to a high reactivity of oxygen species present on the catalyst surface. The experimental 0th-order dependence on alcohol concentration signals the occurrence of a Langmuir–Hinshelwood (L–H) reaction pathway, kinetically controlled by adsorption–desorption steps (r.d.s.). Apparent 1st-order conversion trends reflect the occurrence of deactivation phenomena (i.e., parallel fouling) leading to a residual constant activity level during 50 h. DRIFT analyses of the fresh and used catalysts uncover the incipient formation of benzoic acid hindering the oxidation functionality by strong adsorption on active sites. Calcination at T ≥ 473 K restores the functionality of the used catalysts by the removal of strongly adsorbed benzoate species.
Acta Crystallographica Section A Foundations of Crystallography, 2002
Since the discovery of Mn12-acetate in the early 80s and the subsequent determination of its sing... more Since the discovery of Mn12-acetate in the early 80s and the subsequent determination of its single molecule magnet (SMM) characteristics, interest in the area of large metal clusters, particularly Mn cluster chemistry, has continued to grow. To date, several SMMs have been identified including Fe8, V4, Mn4 and Mn12 clusters but it has been found that Mn clusters often possess large values of ground state spin -an important requirement for SMM behaviour. Our group is interested in the synthesis of new Mn clusters and the investigation of their structural and magnetic properties. The focus currently is on the incorporation of bridging ligands other than O-donor ligands such as benzamidinate (bza-), which is an N-donor, isoelectronic analogue of benzoate. A [Mn4O(bza)6] tetramer was formed by the reaction of a MnII salt with deprotonated ligand under an inert atmosphere. The core consists of four MnII atoms arranged tetrahedrally around an oxygen atom. Each metal atom has a pseudo-tetrahedral arrangement of nitrogen atoms around it with each of the six bza-groups forming a bridge between two metal centres. A [Mn3O(bza)6(pyr)3] trimer was formed from a comproportionation reaction between a MnII salt and MnO4in the presence of bza. The cluster is mixed valent (2MnIII, MnII) and possess an oxo-centred Mn3O unit with 6 bzagroups providing peripheral ligation and three pyridine groups in terminal positions. The magnetic properties are similar to those of the benzoate analogue. Work is in progress on larger clusters of benzamidinate and with other bridging ligands.
Efficient catalysis of water oxidation represents one of the major challenges en route to efficie... more Efficient catalysis of water oxidation represents one of the major challenges en route to efficient sunlight-driven water splitting. Cobalt oxides (CoOx ) have been widely investigated as water oxidation catalysts, although the incorporation of these materials into photoelectrochemical devices has been hindered by a lack of transparency. Herein, the electrosynthesis of transparent CoOx catalyst films is described by utilizing cobalt(II) aminopolycarboxylate complexes as precursors to the oxide. These complexes allow control over the deposition rate and morphology to enable the production of thin, catalytic CoOx films on a conductive substrate, which can be exploited in integrated photoelectrochemical devices. Notably, under a bias of 1.0 V (vs. Ag/AgCl), the film deposited from [Co(NTA)(OH2 )2 ](-) (NTA=nitrilotriacetate) decreased the transmission by only 10 % at λ=500 nm, but still generated >80 % of the water oxidation current produced by a [Co(OH2 )6 ](2+) -derived oxide film...
ABSTRACT Current energy resources largely rely on fossil fuels that are expected to be depleted i... more ABSTRACT Current energy resources largely rely on fossil fuels that are expected to be depleted in 50-200 years. On a global scale, the intensive use of this energy source has resulted in highly detrimental effects to the environment. Hydrogen production by water splitting, with sunlight as the main energy source, is a promising way to augment the production of renewable energy. However, the development of an efficient and stable wateroxidizing catalyst remains a key task before a technological breakthrough based on water splitting can be realized. A main issue hampering the development of commercially viable, non-precious metal-based catalysts is their susceptibility to degradation. To efficiently address this major drawback, self-healing catalysts, that can repair their structure without human intervention, will be necessary. In this review, we focus on water oxidation by natural and artificial Mn-, Co- and Ni-based catalysts and then discuss the self-healing properties that contribute to sustaining their catalytic activity.
Hydrolysis and polymerization of [Fe(OH(2))(6)](3+) in aqueous solution leads, in the early stage... more Hydrolysis and polymerization of [Fe(OH(2))(6)](3+) in aqueous solution leads, in the early stages, to the oxo-bridged binuclear aqua ion [(H(2)O)(5)Fe(µ-O)Fe(OH(2))(5)](4+), which could be obtained in crystalline form through the use of [18]crown-6. The complex exhibits an almost linear Fe-O-Fe moiety and antiferromagnetic coupling that is consistent with current descriptions of exchange coupling in mono oxo-bridged binuclear Fe(III) complexes.
Thiosulfate and ammonia mixtures may be more environmentally benign alternatives to cyanide for l... more Thiosulfate and ammonia mixtures may be more environmentally benign alternatives to cyanide for leaching Au from ores. In this method, the Cu(I)/Cu(II) couple acts as a redox mediator aiding in the oxidative dissolution of metallic Au. Information about the speciation of Cu(I) and Cu(II) in these lixiviant solutions is paramount to the optimization of gold ore processing conditions. With this in mind, we have carried out XANES, EXAFS and UV-Vis spectroscopic studies of the speciation of Cu(I) in mixed thiosulfate-chloride and ammonia-chloride solutions. In thiosulfate-chloride solutions, the EXAFS studies indicate that the geometry of the predominant Cu(I) complex is distorted trigonal (triangular planar), with an average of 2 sulfur atoms + 1 oxygen atom occupying the coordination sphere. This indicates that the stability of the [Cu(S 2 O 3 ) 3 ] 52 complex is lower than previously proposed. Formation constants for Cu(I) thiosulfate complexes have been derived on the basis of systematic UV-Vis measurements of solutions with varying [S 2 O 3 ]/[Cl] ratios. Only one mixed chloride-thiosulfate complex, [Cu(H 2 O)(S 2 O 3 )Cl] 22 , was found to predominate over the range of conditions investigated.
Journal of the Chemical Society, Dalton Transactions, 1997
Solution studies of a trinuclear rhodium() aqua ion, using a variety of solution techniques (N... more Solution studies of a trinuclear rhodium() aqua ion, using a variety of solution techniques (NMR, UV/VIS spectroscopy, charge per Rh determination and elution behaviour) have shown that this oligomer can exist in several structural forms. The form isolated, by ion-exchange chromatography following aging of Rh 3ϩ solutions in base, does not have a linear (1) or bent (2) arrangement of rhodium() centres but consists of a triangular arrangement of such centres linked to each other by one µ-OH bridge (4). The fact that 4 exhibits two 103 Rh NMR signals at δ 9964 and 10 000 in a 2 : 1 ratio is rationalized in terms of the stabilization of a conformation with two rhodium environments through strong hydrogen-bonding between a terminal H 2 O or OH ligand and a µ-OH bridging group. On heating this form is transformed into a new ion which has a different UV/VIS spectrum and two 103 Rh NMR signals at δ 9671 and 9841 in a 1 : 2 ratio. The structure of this form is proposed to consist of a triangular arrangement of metal atoms, two magnetically equivalent rhodium() centres linked together by two µ-OH bridges and each linked to the third Rh III via a single µ-OH bridge. The low pK a1 for this ion of 0.5 ± 0.1 is attributed to the formation of a strong hydrogen-bond between one of the µ-OH groups bridging the two equivalent rhodium() centres and the terminal OH group generated by deprotonation. The existence of a hydrogen-bond interaction in both 3 and 4 has literature precedent. At high pH, 3 is transformed into a new aqua ion, 5, which exhibits a single 103 Rh NMR signal at δ 10 049 and a different UV/VIS spectrum to that of 3 and 4. This is interpreted in terms of a symmetric structure in which the three rhodium() centres are linked by a single µ 3 -OH group and pairs of Rh atoms are further linked by a µ-OH bridge. A variable-pH and -temperature kinetic study revealed that 4 undergoes an irreversible intramolecular condensation process which produces 3 or 5, depending on the pH. The increase in rate with pH is consistent with the existence of two pathways, attributable to the reaction of singly and doubly deprotonated forms of 4. The rate increase of ca. 100 fold matches those observed for related chromium() systems.
5th IEEE Conference on Nanotechnology, 2005., 2005
TiO2 nanocrystals have been synthesized from Titanium(IV) butoxide without the use of an autoclav... more TiO2 nanocrystals have been synthesized from Titanium(IV) butoxide without the use of an autoclave. It was found that using heat treatment temperatures below 600°C pure anatase phase was retained in the nanocrystals. In addition, with increasing heat treatment temperature the nanocrystals became larger in size and the homogeneity was dramatically reduced.
Dendritic polyglycerol sulfate (dPGS) is a biocompatible, bioactive polymer which exhibits anti-i... more Dendritic polyglycerol sulfate (dPGS) is a biocompatible, bioactive polymer which exhibits anti-inflammatory activity in vivo and thus represents a promising candidate for therapeutic and diagnostic applications. To investigate the in vivo pharmacokinetics in detail, dPGS with a molecular weight of ca. 10 kDa was radiolabeled with 3H and 64Cu, and evaluated by performing biodistribution studies and small animal positron emission tomography (PET). 3H-labeling was accomplished by an oxidation-reduction process with sodium periodate and [3H]-borohydride. 64Cu-labeling was achieved by conjugation of isothiocyanate- or maleimide-functionalized copper(II)-chelating ligands based on 1,4-bis(2-pyridinylmethyl)-1,4,7-triazacyclononane (DMPTACN) to an amino functionalized dPGS scaffold, followed by reaction with an aqueous solution containing 64CuCl2. Independent biodistribution by radioimaging and PET imaging studies with healthy mice and rats showed that the neutral dPG was quantitatively r...
A series of new asymmetrically N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) ma... more A series of new asymmetrically N-substituted derivatives of the 1,4,7-triazacyclononane (tacn) macrocycle have been prepared from the common precursor 1,4,7-triazatricyclo[5.2.1.0 4,10 ]decane: 1-ethyl-4-isopropyl-1,4,7-triazacyclononane (L1), 1-isopropyl-4-propyl-1,4,7-triazacyclononane (L2), 1-(3-aminopropyl)-4-benzyl-7-isopropyl-1,4,7-triazacyclononane (L3), 1-benzyl-4-isopropyl-1,4,7-triazacyclononane (L4) and 1,4-bis(3-aminopropyl)-7-isopropyl-1,4,7-triazacyclononane (L5). The corresponding monomeric copper(II) complexes were synthesised and were found to be of composition:
The attempted coupling of (ferrocenylmethyl)trimethylammonium iodide (1) with 1,4,7-(triformyl)-1... more The attempted coupling of (ferrocenylmethyl)trimethylammonium iodide (1) with 1,4,7-(triformyl)-1,4,7,10-tetraazacyclododecane (2) in water led to the formation of the expected compound 1-(ferrocenemethyl)-4,7,10-(triformyl)-1,4,7,10-tetraazacyclododecane (3). In addition, hydrolysis of the ferrocenyl precursor 1 led to the formation of two other known compounds, hydroxymethylferrocene (4) and bis(ferrocenylmethyl) ether . An X-ray crystal structure determination of 4 revealed the presence of H-bonding between the hydroxyl groups of one molecule of 4 and the oxygen atom of an adjacent molecule resulting in a left-handed helical chain of molecules lying along the b-axis direction. The OÁ Á ÁO distances are significantly shorter than those found in previously reported structures of hydroxymethylferrocene derivatives indicative of moderate strength H-bonding interactions. In the structure of 5, the orientation of the ferrocenyl groups are staggered relative to a vector comprising the two carbons of the C-O-C linker. Crown
Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) ... more Synthesis, spectroscopic and magnetic properties, and X-ray crystal structures of two copper(II) polymers Cu(2-qic)Br (2-qic = quinoline-2-carboxylate) (1) and Cu(2-pic)Br (2-pic = pyridine-2-carboxylate) (2) are described. These compounds are isostructural with Cu(2-qic)Cl and Cu(2-pic)Cl, respectively, the X-ray crystal structures of which were reported recently. Both complexes are polynuclear copper(II) compounds (1D and 2D, respectively) based on syn-anti carboxylate bridges and additionally on linear monobromo-(in 1) and dibromo-bridging (in 2) motifs. The magnetic properties were investigated in the temperature range 1.8-300 K. They reveal the occurrence of strong antiferromagnetic coupling (J 1 = À102.5 cm À1 ) through the single bromo-bridge in 1, which is much stronger than that transmitted by the single chloro-bridge (J = À57.0 cm À1 ). Very weak ferromagnetic interaction through the syn-anti carboxylate bridge J 2 is expected as it was observed in isomorphous Cu(2-qic)Cl (J = 0.37 cm À1 ). For 2 a weak ferromagnetic couplings through the syn-anti carboxylate (zJ 0 = 1.35 cm À1 ) and dibromo-bridges (J = 8.31 cm À1 ) were found. The experimental results indicate that the observed ferromagnetic exchange through dibromo-bridge is weaker than that in the chloride analog (J = 15.0 cm À1 ). The magnitude of magnetic interactions is discussed on the basis of structural data of compounds 1 and 2 and their halide analogues.
... 3. Results and discussion. The precursor solutions used in this study were transparent. ... ... more ... 3. Results and discussion. The precursor solutions used in this study were transparent. ... Effect of coating thickness in nanostructured coreshell electrodes on the efficiency of dye-sensitised solar cells; Paper presented at ISES2003, 2003, Göteburg, Sweden. ...
ABSTRACT Five amidinium, salts have been prepared from triazatricyclo[5.2.1.0(4,10)]decane (tacno... more ABSTRACT Five amidinium, salts have been prepared from triazatricyclo[5.2.1.0(4,10)]decane (tacnoa) and characterised by mass spectrometry, NMR spectroscopy and X-ray crystallography. The X-ray structures revealed a long distance between the methine carbon and the ammonium nitrogen, viz., C-N distance 1.64-1.70 angstrom, cf. other C-N distances of 1.40-1.50 angstrom An NMR study of 1-ethyl-4,7-diaza-1-azoniatricyclo[5.2.1.0(4,10)]decane and 1-benzyl-4,7-diaza-1-azoniatricyclo[5.2.1.0(4,10)]decane, confirmed that these amidinium salts hydrolyse in aqueous solution, the latter 60 times faster than the former. Tacnoa, which has C-N distances typical of single bonds, showed no evidence of hydrolysis after several days at 80 degrees C. Molecular modeling calculations indicate that the preferred gas phase structure of the salts is one where the positive charge is delocalised over the two secondary amines and the methine carbon. The calculated distance between this carbon and the ammonium nitrogen is 0.15-0.4 angstrom longer than in the crystal structure. The energy difference between the preferred gas phase and solid state conformations is 2 kJ mol(-1) and presents little barrier to nucleophilic attack of the methine carbon. Further analysis of the methine carbon geometry (C(7)) reveals that the bond angles in the benzyl salt are closer to those expected for an sp(2) centre than in the ethyl salt and that this could be the origin of the faster hydrolysis rate. (c) 2005 Elsevier Ltd. All rights reserved.
ABSTRACT Nanostructured porous tin-doped indium oxide (ITO) films were prepared by screen printin... more ABSTRACT Nanostructured porous tin-doped indium oxide (ITO) films were prepared by screen printing of an ITO nanoparticle paste onto conducting fluorine-doped tin oxide (FTO) substrates. The ITO films were subsequently coated with thin layers of TiO2 by the hydrolysis of TiCl4 to form the collector–shell photoelectrodes. The morphology of films was analysed by scanning electron microscope (SEM). It was found that a uniform coating of TiO2 was achieved when three or more deposition cycles were applied. Dye-sensitized solar cells were constructed with the collector–shell photoelectrodes using an electrolyte containing the [Co(bpy)3]2+/3+ (bpy = 2,2′-bipyridine) redox couple and MK-2, an organic sensitizer and efficiencies of 3.3% achieved. Charge transport in cells utilizing the collector–shell electrodes was found to be 2–6 times faster than those utilizing P25-based TiO2 electrodes.
ABSTRACT A device fabrication method is reported to efficiently produce CH3NH3PbI3-based planar p... more ABSTRACT A device fabrication method is reported to efficiently produce CH3NH3PbI3-based planar perovskite solar cells on polymer substrates with the entire process conducted at 150 °C or below. The hole blocking layer employed is a solution processed 100 nm thick mesoporous TiO2 layer. A gas-assisted perovskite deposition method is used to produce excellent coverage of the hole blocking layer by a ∼350 nm thick CH3NH3PbI3 film, resulting in high device performance reproducibility. We show that an average efficiency of 10.6 ± 1.2%, and a maximum efficiency of 12.3% are obtained for flexible perovskite solar cells, offering great promise for further improvement of this low-temperature, low-cost processing solar technology.
ABSTRACT The mechanism and kinetics of the liquid phase selective oxidation of benzyl alcohol to ... more ABSTRACT The mechanism and kinetics of the liquid phase selective oxidation of benzyl alcohol to benzaldehyde with oxygen on bare and Ce or Fe promoted (Mnat/Meat, 3) MnOx catalysts [1] have been investigated. Irrespective of toluene as solvent, the bare and promoted catalysts drive the selective oxidation of the substrate via the Mars-van Krevelen redox mechanism due to a high reactivity of oxygen species present on the catalyst surface. The experimental 0th-order dependence on alcohol concentration signals the occurrence of a Langmuir–Hinshelwood (L–H) reaction pathway, kinetically controlled by adsorption–desorption steps (r.d.s.). Apparent 1st-order conversion trends reflect the occurrence of deactivation phenomena (i.e., parallel fouling) leading to a residual constant activity level during 50 h. DRIFT analyses of the fresh and used catalysts uncover the incipient formation of benzoic acid hindering the oxidation functionality by strong adsorption on active sites. Calcination at T ≥ 473 K restores the functionality of the used catalysts by the removal of strongly adsorbed benzoate species.
Uploads
Papers by Leone Spiccia