ABSTRACT The complex [CoL6(Cl)][CoCl4]·H2O, where L6 is the reinforced macrocycle 7-amino-7-methy... more ABSTRACT The complex [CoL6(Cl)][CoCl4]·H2O, where L6 is the reinforced macrocycle 7-amino-7-methyl-1,5,9,13-tetraazabicyclo[11.2.2]heptadecane, has been prepared and its crystal structure determined. The green-black crystals are monoclinic, space group P21/c, with a= 8.778(2), b= 13.344(4), c= 19.380(8)Å, β= 98.48(2)°, Z= 4, and a final conventional R= 0.0736. The cobalt is co-ordinated in a planar fashion in the cavity of the macrocycle, with one axial co-ordination site occupied by the pendant primary amine group, and the other by a chloride. The Co–N bond lengths to the tertiary nitrogens of the piperazine bridge of the macrocycle are 2.01(1) and 2.02(1)Å, distinctly longer than those [1.97(1)Å] to the secondary amines in the cavity of the macrocycle. The Co–N distance to the pendant primary amine is 2.01(1)Å, and Co–Cl to the axially co-ordinated chloride trans to the pendant amine group is 2.26(1)Å. Molecular mechanics calculations are used to analyse the highly distorted co-ordination sphere around the CoIII, where the N–Co–N angle involving the nitrogens of the piperazine bridge of the macrocycle is only 73.5(4)°. The calculations reproduce the co-ordination geometry around the CoIII well, including the variation in Co–N bond length and the highly distorted N–Co–N angles.
Abstract The coordinating properties of open-chain ligands containing alcoholic or ethereal oxyge... more Abstract The coordinating properties of open-chain ligands containing alcoholic or ethereal oxygen donors are examined. Addition of oxygen donors usually leads to complex stabilisation for large metal ions (Pb2+, Cd2+) and to less favourable effects on complex stability for small metal ions (Cu2+, Ni2+). The formation constants of these metal ions with the set of ligands RN(CH2CHOH·CH3)2 where R is H, CH2CHOH·CH3, CH2CH2OCH3, CH2CH2OCH2CH2OH, and CH2CHOCH2CH2CH2 are reported. The largest stabilisation for each case where R is an O-donor group relative to R = H occurs for Pb2+, the largest metal ion, while Cu2+, the smallest metal ion, shows the smallest stabilisation. The crystal structure of [Ni(HOCH2CH2NHCH2CH2NH2)2] (NO3)2 is reported. The space group is P 1 , with cell constants a = 13.098(3), b = 8.737(4), and c = 7.746(3) A, β = 112.66(3), β = 90.65(3), and γ = 85.03(2), and Z = 2. Disorder of the nitrate anions hindered refinement, with the result that a final conventional R factor of 0.0903 was achieved. The NiN bond lengths average 2.06(1) (secondary nitrogen) and 2.10(2) (primary nitrogen). The NiO bond lengths are rather long, averaging 2.15(1) A, which is used to support the idea that the steric effects are responsible for destabilising the complexes of small metal ions such as Ni(11) when neutral oxygen donors are present.
Journal of The Chemical Society-dalton Transactions, 1990
... Peter W. Wade and Robert D. Hancock" Department of Chemistry, University of the Witw... more ... Peter W. Wade and Robert D. Hancock" Department of Chemistry, University of the Witwatersrand, Johannesburg 2050, South Africa ... Experimental Synthesis oft he Complex [ CuL7( H20)] [C104] ,OH, 0.-This is analogous to that of the capped cryptands described by Comba et al ...
Observed mortalities of Daphnia pulexl/Ig exposed to a single concentration of zinc in different ... more Observed mortalities of Daphnia pulexl/Ig exposed to a single concentration of zinc in different test waters are explained in terms of the chemical behaviour of zinc in solution, as predicted by chemical speciation modelling. Multivariate correlation analysis indicates that the hydrated zinc species, Zn 2+ , was primarily responsible for the observed lIgDaphnial/Ig mortality. Although this method provides useful results in a well-defined laboratory setting, its application to field conditions proves to be less certain because of our incomplete understanding of processes affecting metal speciation in complex natural systems. These results indicate that metal bioavailability should be accounted for in the management of metal discharges into the natural environment.
... change in pesticide concentration and environmental variables. 2. Materials and methods. 2.1.... more ... change in pesticide concentration and environmental variables. 2. Materials and methods. 2.1. Study area. The Lourens River estuary is a typical temporarily openclosed estuary (Whitfield, 1995). It is located in the Western ...
Proceedings of the International Conference on Mine Closure, 2008
ABSTRACT Following the World Summit on Sustainable Development in 2002, the South African Departm... more ABSTRACT Following the World Summit on Sustainable Development in 2002, the South African Department of Minerals and Energy (DME) initiated the “Sustainable Development through Mining” (SDM) programme to assist in the development of a strategic framework for sustainable development in the minerals and mining sector. This initiative supported a variety of projects including a project specifically orientated towards integrated regional mine closure and its implications. This paper focuses on the increasingly challenging environment of changing community expectations, stricter regulatory controls and greater public scrutiny in areas of cumulative, interconnected, or multi-mine, and/or an integrated environmental and socio-economic impact at a regional level. The paper discusses the challenges in the development and implementation of the concept of regional mine closure strategies, as support to further policy and legislative interventions in South Africa, and outlines proposed strategies to address these challenges. Regional closure strategies aim to provide a framework within which mines can develop closure plans that address broader development priorities as well as possible cumulative impacts of a number of mines, taking into consideration socioeconomic and environmental issues on a regional basis. A strategic framework was developed for the Witwatersrand gold mining region within which individual mines will be able to plan for mine closure. In order for the strategy to be implemented there are a number of key success factors. These include issues around closure planning, buy-in from stakeholders, trade-offs, stakeholder engagement, setting-up of completion criteria (balanced scorecard for regional mine closure), targeted research and data management. This paper is a follow-up on work reported. This paper has been reproduced with the permission of Australian Centre for Geomechanics (ACG) as published in the 4th International Seminar on Mine Closure. www.acg.uwa.edu.au
Journal of the Chemical Society, Dalton Transactions, 1992
... Thembakazi N. Mali, Peter W. Wade and Robert D. Hancock" Centre for Molecular Design... more ... Thembakazi N. Mali, Peter W. Wade and Robert D. Hancock" Centre for Molecular Design, Department of Chemistry, University of the Witwatersrand, Wits 2050, Johannesburg, South Africa ... 13 P. Comba, NF Curtis, GA Lawrance, MA O'Leary, BW Skelton and AH White, J. Chem ...
Aurocyanide ion-pairs with alkali-metal ions are extracted efficiently into organic phases with t... more Aurocyanide ion-pairs with alkali-metal ions are extracted efficiently into organic phases with the aid of long-chain polyethers. The results of distribution experiments can be rationalized by molecular mechanics calculations. The polyether is shown to co-ordinate to the alkali-metal cation through the ether oxygen atoms, wrapping around the cation in a helical configuration. High extraction efficiencies are obtained with high dielectric-constant solvents, which tend to stabilize the helical polyether-cation complex. The preferential secondary solvation of the aurocyanide anion by the chosen solvents also has an important influence on the extraction efficiency.
ABSTRACT The complex [CoL6(Cl)][CoCl4]·H2O, where L6 is the reinforced macrocycle 7-amino-7-methy... more ABSTRACT The complex [CoL6(Cl)][CoCl4]·H2O, where L6 is the reinforced macrocycle 7-amino-7-methyl-1,5,9,13-tetraazabicyclo[11.2.2]heptadecane, has been prepared and its crystal structure determined. The green-black crystals are monoclinic, space group P21/c, with a= 8.778(2), b= 13.344(4), c= 19.380(8)Å, β= 98.48(2)°, Z= 4, and a final conventional R= 0.0736. The cobalt is co-ordinated in a planar fashion in the cavity of the macrocycle, with one axial co-ordination site occupied by the pendant primary amine group, and the other by a chloride. The Co–N bond lengths to the tertiary nitrogens of the piperazine bridge of the macrocycle are 2.01(1) and 2.02(1)Å, distinctly longer than those [1.97(1)Å] to the secondary amines in the cavity of the macrocycle. The Co–N distance to the pendant primary amine is 2.01(1)Å, and Co–Cl to the axially co-ordinated chloride trans to the pendant amine group is 2.26(1)Å. Molecular mechanics calculations are used to analyse the highly distorted co-ordination sphere around the CoIII, where the N–Co–N angle involving the nitrogens of the piperazine bridge of the macrocycle is only 73.5(4)°. The calculations reproduce the co-ordination geometry around the CoIII well, including the variation in Co–N bond length and the highly distorted N–Co–N angles.
Abstract The coordinating properties of open-chain ligands containing alcoholic or ethereal oxyge... more Abstract The coordinating properties of open-chain ligands containing alcoholic or ethereal oxygen donors are examined. Addition of oxygen donors usually leads to complex stabilisation for large metal ions (Pb2+, Cd2+) and to less favourable effects on complex stability for small metal ions (Cu2+, Ni2+). The formation constants of these metal ions with the set of ligands RN(CH2CHOH·CH3)2 where R is H, CH2CHOH·CH3, CH2CH2OCH3, CH2CH2OCH2CH2OH, and CH2CHOCH2CH2CH2 are reported. The largest stabilisation for each case where R is an O-donor group relative to R = H occurs for Pb2+, the largest metal ion, while Cu2+, the smallest metal ion, shows the smallest stabilisation. The crystal structure of [Ni(HOCH2CH2NHCH2CH2NH2)2] (NO3)2 is reported. The space group is P 1 , with cell constants a = 13.098(3), b = 8.737(4), and c = 7.746(3) A, β = 112.66(3), β = 90.65(3), and γ = 85.03(2), and Z = 2. Disorder of the nitrate anions hindered refinement, with the result that a final conventional R factor of 0.0903 was achieved. The NiN bond lengths average 2.06(1) (secondary nitrogen) and 2.10(2) (primary nitrogen). The NiO bond lengths are rather long, averaging 2.15(1) A, which is used to support the idea that the steric effects are responsible for destabilising the complexes of small metal ions such as Ni(11) when neutral oxygen donors are present.
Journal of The Chemical Society-dalton Transactions, 1990
... Peter W. Wade and Robert D. Hancock" Department of Chemistry, University of the Witw... more ... Peter W. Wade and Robert D. Hancock" Department of Chemistry, University of the Witwatersrand, Johannesburg 2050, South Africa ... Experimental Synthesis oft he Complex [ CuL7( H20)] [C104] ,OH, 0.-This is analogous to that of the capped cryptands described by Comba et al ...
Observed mortalities of Daphnia pulexl/Ig exposed to a single concentration of zinc in different ... more Observed mortalities of Daphnia pulexl/Ig exposed to a single concentration of zinc in different test waters are explained in terms of the chemical behaviour of zinc in solution, as predicted by chemical speciation modelling. Multivariate correlation analysis indicates that the hydrated zinc species, Zn 2+ , was primarily responsible for the observed lIgDaphnial/Ig mortality. Although this method provides useful results in a well-defined laboratory setting, its application to field conditions proves to be less certain because of our incomplete understanding of processes affecting metal speciation in complex natural systems. These results indicate that metal bioavailability should be accounted for in the management of metal discharges into the natural environment.
... change in pesticide concentration and environmental variables. 2. Materials and methods. 2.1.... more ... change in pesticide concentration and environmental variables. 2. Materials and methods. 2.1. Study area. The Lourens River estuary is a typical temporarily openclosed estuary (Whitfield, 1995). It is located in the Western ...
Proceedings of the International Conference on Mine Closure, 2008
ABSTRACT Following the World Summit on Sustainable Development in 2002, the South African Departm... more ABSTRACT Following the World Summit on Sustainable Development in 2002, the South African Department of Minerals and Energy (DME) initiated the “Sustainable Development through Mining” (SDM) programme to assist in the development of a strategic framework for sustainable development in the minerals and mining sector. This initiative supported a variety of projects including a project specifically orientated towards integrated regional mine closure and its implications. This paper focuses on the increasingly challenging environment of changing community expectations, stricter regulatory controls and greater public scrutiny in areas of cumulative, interconnected, or multi-mine, and/or an integrated environmental and socio-economic impact at a regional level. The paper discusses the challenges in the development and implementation of the concept of regional mine closure strategies, as support to further policy and legislative interventions in South Africa, and outlines proposed strategies to address these challenges. Regional closure strategies aim to provide a framework within which mines can develop closure plans that address broader development priorities as well as possible cumulative impacts of a number of mines, taking into consideration socioeconomic and environmental issues on a regional basis. A strategic framework was developed for the Witwatersrand gold mining region within which individual mines will be able to plan for mine closure. In order for the strategy to be implemented there are a number of key success factors. These include issues around closure planning, buy-in from stakeholders, trade-offs, stakeholder engagement, setting-up of completion criteria (balanced scorecard for regional mine closure), targeted research and data management. This paper is a follow-up on work reported. This paper has been reproduced with the permission of Australian Centre for Geomechanics (ACG) as published in the 4th International Seminar on Mine Closure. www.acg.uwa.edu.au
Journal of the Chemical Society, Dalton Transactions, 1992
... Thembakazi N. Mali, Peter W. Wade and Robert D. Hancock" Centre for Molecular Design... more ... Thembakazi N. Mali, Peter W. Wade and Robert D. Hancock" Centre for Molecular Design, Department of Chemistry, University of the Witwatersrand, Wits 2050, Johannesburg, South Africa ... 13 P. Comba, NF Curtis, GA Lawrance, MA O'Leary, BW Skelton and AH White, J. Chem ...
Aurocyanide ion-pairs with alkali-metal ions are extracted efficiently into organic phases with t... more Aurocyanide ion-pairs with alkali-metal ions are extracted efficiently into organic phases with the aid of long-chain polyethers. The results of distribution experiments can be rationalized by molecular mechanics calculations. The polyether is shown to co-ordinate to the alkali-metal cation through the ether oxygen atoms, wrapping around the cation in a helical configuration. High extraction efficiencies are obtained with high dielectric-constant solvents, which tend to stabilize the helical polyether-cation complex. The preferential secondary solvation of the aurocyanide anion by the chosen solvents also has an important influence on the extraction efficiency.
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