title: Gold(I) complexes and co oxidation catalysts

authors: Mathieson, Trevor J.

abstract: Isonitrile gold(I) nitrates, (RNC)AuNO₃ (R = Buᵗ, Et or Xy) have been prepared and fully characterised. These join the rare set of gold(I) species exhibiting ligation to oxygen and are the first examples of gold(I) bonded to both carbon and oxygen. Molecular aggregations of the monomeric units were revealed by X-ray crystal structure determinations. The aggregations are the result of secondary Au--Au interactions. These interactions are also apparent in the structures of the analogous complexes (RNC)AuCl (R = Et or Xy), which were characterised for comparative purposes.

(EtNC)AuCl and (BuᵗNC)AuNO₃ formed zig-zag chain structures from which the other unprecedented structures can be derived. (EtNC)AuNO₃ formed a concertinaed chain, (XyNC)AuNO₃ (1) a compressed chain and (XyNC)AuCl a tetrameric chain. The formations of these supramolecular motifs are attributed to various steric and electronic ligand influences on the inherent Au--Au attraction. In addition, intermolecular π-π contacts were observed for the (XyNC)AuX (X = Cl or NO₃) structures.

In each instance, the Au--Au interactions for (RNC)AuNO₃ were significantly shorter than those of the analogous (RNC)AuCl structure. The results demonstrated that the non-polarisable nitrate anion enhances the Au--Au attraction. This is contrary to previous theoretical calculations, which predict that soft anions enhance the Au--Au attraction. The structure of the ionic [(XyNC)₂Au]⁺NO₃- complex was also characterised. This did not exhibit Au--Au contacts; the packing structure was instead based on infinite π-π stacking.

The potential of gold(I) complexes as precursors to supported gold catalysts was assessed. The complexes were adsorbed (from a solution phase) onto transition metal oxide supports which were subsequently vacuum dried and calcined. Scanning Electron Microscopy (SEM) revealed a range of gold particle sizes on the calcined materials. The extent of gold dispersion was dependent on the chemical properties of the complex employed.

The use of the stable (Ph₃P)AuCl, (Ph₃P)AuMe and (BuᵗNC)AuCl complexes resulted in relatively large gold particles (20-200 nm). In the case of (Ph₃P)AuMe, metallic gold crystals were observed. Under ambient conditions these materials were inactive for CO oxidation. Under the same testing conditions, efficient catalytic CO oxidation was observed over materials prepared by using the unstable (BuᵗNC)AuNO₃ complex as a precursor. The gold particles on the active catalyst were too small to be resolved by SEM.

The observed CO oxidation activity was proposed to be a two-component catalytic reaction involving gold nano-particles in intimate contact with a reducible oxide support. Reactant inhibition, which is commonly observed for catalysts with inert supports, is avoided in this system. This form of catalysis has received considerable recent attention for the CO oxidation reaction and provides guidance for attempts to enhance other heterogeneous catalytic processes.

text: Gold(I) complexes and co oxidation catalysts Isonitrile gold(I) nitrates, (RNC)AuNO₃ (R = Buᵗ, Et or Xy) have been prepared and fully characterised. These join the rare set of gold(I) species exhibiting ligation to oxygen and are the first examples of gold(I) bonded to both carbon and oxygen. Molecular aggregations of the monomeric units were revealed by X-ray crystal structure determinations. The aggregations are the result of secondary Au--Au interactions. These interactions are also apparent in the structures of the analogous complexes (RNC)AuCl (R = Et or Xy), which were characterised for comparative purposes.

(EtNC)AuCl and (BuᵗNC)AuNO₃ formed zig-zag chain structures from which the other unprecedented structures can be derived. (EtNC)AuNO₃ formed a concertinaed chain, (XyNC)AuNO₃ (1) a compressed chain and (XyNC)AuCl a tetrameric chain. The formations of these supramolecular motifs are attributed to various steric and electronic ligand influences on the inherent Au--Au attraction. In addition, intermolecular π-π contacts were observed for the (XyNC)AuX (X = Cl or NO₃) structures.

In each instance, the Au--Au interactions for (RNC)AuNO₃ were significantly shorter than those of the analogous (RNC)AuCl structure. The results demonstrated that the non-polarisable nitrate anion enhances the Au--Au attraction. This is contrary to previous theoretical calculations, which predict that soft anions enhance the Au--Au attraction. The structure of the ionic [(XyNC)₂Au]⁺NO₃- complex was also characterised. This did not exhibit Au--Au contacts; the packing structure was instead based on infinite π-π stacking.

The potential of gold(I) complexes as precursors to supported gold catalysts was assessed. The complexes were adsorbed (from a solution phase) onto transition metal oxide supports which were subsequently vacuum dried and calcined. Scanning Electron Microscopy (SEM) revealed a range of gold particle sizes on the calcined materials. The extent of gold dispersion was dependent on the chemical properties of the complex employed.

The use of the stable (Ph₃P)AuCl, (Ph₃P)AuMe and (BuᵗNC)AuCl complexes resulted in relatively large gold particles (20-200 nm). In the case of (Ph₃P)AuMe, metallic gold crystals were observed. Under ambient conditions these materials were inactive for CO oxidation. Under the same testing conditions, efficient catalytic CO oxidation was observed over materials prepared by using the unstable (BuᵗNC)AuNO₃ complex as a precursor. The gold particles on the active catalyst were too small to be resolved by SEM.

The observed CO oxidation activity was proposed to be a two-component catalytic reaction involving gold nano-particles in intimate contact with a reducible oxide support. Reactant inhibition, which is commonly observed for catalysts with inert supports, is avoided in this system. This form of catalysis has received considerable recent attention for the CO oxidation reaction and provides guidance for attempts to enhance other heterogeneous catalytic processes.

year: 1998

title: Watching for invasive species: public engagement

authors: Burton, Tracey

abstract: Invasive species continue to be one of the greatest threats to the Rotorua lakes and include not only water weeds and wallabies, but other organisms too. Invasive molluscs such as zebra and quagga mussels have the potential to cause wide spread devastation to our freshwater ecosystems and are just one example of other invasive aquatic species not yet found in our New Zealand lakes.
The management of invasive species is a shared problem that requires the cooperation and support of a diverse range of stakeholders, interest groups and members of the general public. The early detection of an invasive species is critical and may make the difference in being able to appropriately manage, control or eradiate a species before it has a chance to spread.
Anyone can help prevent the incursion and spread of invasive species into our lakes. In New Zealand, we can learn from the success of programmes in other countries where they are recruiting citizen scientists to look for anything new or unusual. Citizen science,
broadly defined as the involvement of volunteers in research, provides a means of combining research activities with environmental education and public engagement in science. Volunteers are able to increase their knowledge and understanding of the environment, learn more about local issues of importance, and contribute to science based recommendations. In addition, observations collected by citizen scientists can provide valuable records and knowledge that otherwise wouldn’t have been available.

text: Watching for invasive species: public engagement Invasive species continue to be one of the greatest threats to the Rotorua lakes and include not only water weeds and wallabies, but other organisms too. Invasive molluscs such as zebra and quagga mussels have the potential to cause wide spread devastation to our freshwater ecosystems and are just one example of other invasive aquatic species not yet found in our New Zealand lakes.
The management of invasive species is a shared problem that requires the cooperation and support of a diverse range of stakeholders, interest groups and members of the general public. The early detection of an invasive species is critical and may make the difference in being able to appropriately manage, control or eradiate a species before it has a chance to spread.
Anyone can help prevent the incursion and spread of invasive species into our lakes. In New Zealand, we can learn from the success of programmes in other countries where they are recruiting citizen scientists to look for anything new or unusual. Citizen science,
broadly defined as the involvement of volunteers in research, provides a means of combining research activities with environmental education and public engagement in science. Volunteers are able to increase their knowledge and understanding of the environment, learn more about local issues of importance, and contribute to science based recommendations. In addition, observations collected by citizen scientists can provide valuable records and knowledge that otherwise wouldn’t have been available.

year: 2015

title: Promoting social and environmental justice to support Indigenous partnerships in urban ecosystem restoration

authors: Hall, Monique

subjects: Science & Technology

abstract: Urban ecological restoration typically employs western science approaches to restore degraded ecosystems. As yet, few restoration groups acknowledge the history of these degraded urban sites, despite connections, past and present, that root Indigenous Peoples (and others) in these lands. Here, we promote partnership with Indigenous communities from project inception and present two successful case studies from Aotearoa New Zealand. We specifically note that partnering and building relationships with Indigenous communities in restoration efforts require recognition of power inequalities and injustices. We consider success to include both restoration of ecological function and biodiversity and reconnection of all communities to urban ecosystems.

text: Promoting social and environmental justice to support Indigenous partnerships in urban ecosystem restoration Urban ecological restoration typically employs western science approaches to restore degraded ecosystems. As yet, few restoration groups acknowledge the history of these degraded urban sites, despite connections, past and present, that root Indigenous Peoples (and others) in these lands. Here, we promote partnership with Indigenous communities from project inception and present two successful case studies from Aotearoa New Zealand. We specifically note that partnering and building relationships with Indigenous communities in restoration efforts require recognition of power inequalities and injustices. We consider success to include both restoration of ecological function and biodiversity and reconnection of all communities to urban ecosystems.

year: 2020-11-27