title: Further studies on the dialkylation chemistry of [Pt₂(μ-S)₂(PPh₃)₄] with activated alkyl halides RC(O)CH₂X (X = Cl, Br)

authors: Ujam, Oguejiofo Theophilus

subjects: Dinuclear platinum complexes

abstract: Further studies have been carried out into the reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards a range of activated alkylating agents of the type RC(O)CH₂X (R = organic moiety e.g. phenyl, pyrenyl; X = Cl, Br). Alkylation of both sulfide centres is observed for PhC(O)CH₂Br, 3-(bromoacetyl)coumarin [CouC(O)CH₂Br], and 1-(bromoacetyl)pyrene [PyrC(O)CH2Br], giving dications [Pt₂{μ-SCH₂C(O)R}₂ (PPh₃)₄] ²⁺, isolated as their PF₆⁻ salts. The X-ray structure of [Pt₂{μ-SCH₂C(O)Ph}₂ (PPh₃)₄](PF₆) ₂ shows the presence of short Pt•••O contacts. In contrast, the corresponding chloro compounds [typified by PhC(O)CH₂Cl] and imino analogues [e.g. PhC(NOH)CH₂Br] do not dialkylate [Pt₂ (μ-S)₂(PPh₃)₄]. The ability of PhC(O)CH₂Br to dialkylate [Pt₂(μ-S)₂(PPh₃)₄] allows the synthesis of new mixed-alkyl dithiolate derivatives of the type [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₄]²⁺ (R = Et or n-Bu), through alkylation of in situ-generated monoalkylated compounds [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (from [Pt₂(μ-S)₂(PPh₃)₄] and excess RBr). In these heterodialkylated systems ligand replacement of PPh₃ occurs by the bromide ions in the reaction mixture forming monocations [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]⁺. This ligand substitution can be easily suppressed by addition of PPh₃ to the reaction mixture. The complex [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ was crystallographically characterised. X-ray crystal structures of the bromide-containing complexes [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]+ (R = Et, Bu) are also reported. In both structures the coordinated bromide is trans to the SCH₂C(O)Ph ligand, which adopts an axial position, while the ethyl and butyl substituents adopt equatorial positions, in contrast to the structures of the dialkylated complexes [Pt₂{μ-SCH₂C(O)Ph}₂(PPh₃)₄]²⁺ and [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ (and many other known analogues) where both alkyl groups adopt axial positions.

text: Further studies on the dialkylation chemistry of [Pt₂(μ-S)₂(PPh₃)₄] with activated alkyl halides RC(O)CH₂X (X = Cl, Br) Further studies have been carried out into the reactivity of [Pt₂(μ-S)₂(PPh₃)₄] towards a range of activated alkylating agents of the type RC(O)CH₂X (R = organic moiety e.g. phenyl, pyrenyl; X = Cl, Br). Alkylation of both sulfide centres is observed for PhC(O)CH₂Br, 3-(bromoacetyl)coumarin [CouC(O)CH₂Br], and 1-(bromoacetyl)pyrene [PyrC(O)CH2Br], giving dications [Pt₂{μ-SCH₂C(O)R}₂ (PPh₃)₄] ²⁺, isolated as their PF₆⁻ salts. The X-ray structure of [Pt₂{μ-SCH₂C(O)Ph}₂ (PPh₃)₄](PF₆) ₂ shows the presence of short Pt•••O contacts. In contrast, the corresponding chloro compounds [typified by PhC(O)CH₂Cl] and imino analogues [e.g. PhC(NOH)CH₂Br] do not dialkylate [Pt₂ (μ-S)₂(PPh₃)₄]. The ability of PhC(O)CH₂Br to dialkylate [Pt₂(μ-S)₂(PPh₃)₄] allows the synthesis of new mixed-alkyl dithiolate derivatives of the type [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₄]²⁺ (R = Et or n-Bu), through alkylation of in situ-generated monoalkylated compounds [Pt₂(μ-S)(μ-SR)(PPh₃)₄]⁺ (from [Pt₂(μ-S)₂(PPh₃)₄] and excess RBr). In these heterodialkylated systems ligand replacement of PPh₃ occurs by the bromide ions in the reaction mixture forming monocations [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]⁺. This ligand substitution can be easily suppressed by addition of PPh₃ to the reaction mixture. The complex [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ was crystallographically characterised. X-ray crystal structures of the bromide-containing complexes [Pt₂{μ-SCH₂C(O)Ph}(μ-SR)(PPh₃)₃Br]+ (R = Et, Bu) are also reported. In both structures the coordinated bromide is trans to the SCH₂C(O)Ph ligand, which adopts an axial position, while the ethyl and butyl substituents adopt equatorial positions, in contrast to the structures of the dialkylated complexes [Pt₂{μ-SCH₂C(O)Ph}₂(PPh₃)₄]²⁺ and [Pt₂{μ-SCH₂C(O)Ph}(μ-SBu)(PPh₃)₄]²⁺ (and many other known analogues) where both alkyl groups adopt axial positions.

year: 2011

title: A question of scale: How turbulence around aerial roots shapes the seabed morphology in mangrove forests of the Mekong Delta

authors: Mullarney, Julia C.

abstract: Mangrove forests are highly productive ecosystems that provide many physical, societal, and ecological services in tropical and subtropical regions. Accurate prediction of the morphological evolution for these areas, in the face of global sea level rise and changes in sediment supply, requires understanding of interactions between vegetation growth, water flows, and sediment transport. Data presented from a wave-exposed mangrove forest in the Mekong Delta, Vietnam, include unique measurements that resolved water flows in and around the aerial mangrove roots (known as pneumatophores) over scales from a few millimeters to hundreds of meters. Flows were highly turbulent, with turbulence values sometimes as large as those measured in surf zones. These energetic processes appear to stir up sediments, with small scour troughs observed around individual pneumatophores, and larger-scale scour around clusters of pneumatophores. The vegetation fringe (the boundary between forest and mudflat) was a particularly dynamic area, with elevated turbulence levels, greater vegetation densities, coarser sediments, and occasional wave breaking. Intense turbulent dissipation at the fringe then reduces the energy of shoreward-propagating waves, sheltering the forest interior. The small-scale processes appear to be linked with forest-wide patterns of sediment transport and deposition. We discuss these links in the context of the biophysical interactions that control the changing shapes of deltas worldwide.

text: A question of scale: How turbulence around aerial roots shapes the seabed morphology in mangrove forests of the Mekong Delta Mangrove forests are highly productive ecosystems that provide many physical, societal, and ecological services in tropical and subtropical regions. Accurate prediction of the morphological evolution for these areas, in the face of global sea level rise and changes in sediment supply, requires understanding of interactions between vegetation growth, water flows, and sediment transport. Data presented from a wave-exposed mangrove forest in the Mekong Delta, Vietnam, include unique measurements that resolved water flows in and around the aerial mangrove roots (known as pneumatophores) over scales from a few millimeters to hundreds of meters. Flows were highly turbulent, with turbulence values sometimes as large as those measured in surf zones. These energetic processes appear to stir up sediments, with small scour troughs observed around individual pneumatophores, and larger-scale scour around clusters of pneumatophores. The vegetation fringe (the boundary between forest and mudflat) was a particularly dynamic area, with elevated turbulence levels, greater vegetation densities, coarser sediments, and occasional wave breaking. Intense turbulent dissipation at the fringe then reduces the energy of shoreward-propagating waves, sheltering the forest interior. The small-scale processes appear to be linked with forest-wide patterns of sediment transport and deposition. We discuss these links in the context of the biophysical interactions that control the changing shapes of deltas worldwide.

year: 2017

title: Māori social identities in New Zealand and Hawai'i

authors: Nikora, Linda Waimarie

subjects: Maori

abstract: This research is comprised of two narrative interview studies of Māori in two different settings, New Zealand (n=20) and Hawai'i (n=30).  The data was gathered over the 1994-1996 period.  The two settings have some commonalities and differences.  In both settings Māori are required to make decisions about the continuity of their ethnic Māori identities and hereditary cultural identities of iwi, hapu and whanau, and the part that they wish these identities to play in their daily lives.  The focus of this research was about how Māori create meaning in their lives and maintain their social identities across and within those contexts they move through. 

The findings of this research suggest that Māori in New Zealand continue to value and gain meaning and satisfaction from their cultural collectivities and the social identities derived from them.  However, the results tend to suggest that there are changes in the ways that individuals conceptualise these identities and concomitantly, how they see of themselves.
For New Zealand participants, conceptions of hapu and iwi appear to be converging with an increasing focus on the physicality of marae, its environment and symbolism, and the social events and relationships negotiated in that space.  New Zealand participants saw some hapu and iwi maintenance activities as more legitimate than others.  More value was placed on returning to hapu and iwi homelands however irregular these returns were.  In contrast, conceptions of hapu and iwi held by participants in Hawai'i seemed less intense.  There were few opportunities to engage with other hapu or iwi members.  Being Māori had greater meaning and was understood, probed and valued by others in the culturally plural context of Hawai'i.  For New Zealand participants, being Māori was enacted in the context of being a discriminated, negatively constructed minority.  All were aware of the defining effect that the presence of a dominant majority could have and countered these effects by engaging in social justice and in-group solidarity activities.

The changing identity conceptions held by members of Māori social groups will have implications for a sense of community and social cohesion, for tribal asset management, service delivery and crown settlement processes.  If Māori are redefining and renegotiating their social identities to achieve greater meaning and satisfaction then these changes are important to respond to and recognise.

text: Māori social identities in New Zealand and Hawai'i This research is comprised of two narrative interview studies of Māori in two different settings, New Zealand (n=20) and Hawai'i (n=30).  The data was gathered over the 1994-1996 period.  The two settings have some commonalities and differences.  In both settings Māori are required to make decisions about the continuity of their ethnic Māori identities and hereditary cultural identities of iwi, hapu and whanau, and the part that they wish these identities to play in their daily lives.  The focus of this research was about how Māori create meaning in their lives and maintain their social identities across and within those contexts they move through. 

The findings of this research suggest that Māori in New Zealand continue to value and gain meaning and satisfaction from their cultural collectivities and the social identities derived from them.  However, the results tend to suggest that there are changes in the ways that individuals conceptualise these identities and concomitantly, how they see of themselves.
For New Zealand participants, conceptions of hapu and iwi appear to be converging with an increasing focus on the physicality of marae, its environment and symbolism, and the social events and relationships negotiated in that space.  New Zealand participants saw some hapu and iwi maintenance activities as more legitimate than others.  More value was placed on returning to hapu and iwi homelands however irregular these returns were.  In contrast, conceptions of hapu and iwi held by participants in Hawai'i seemed less intense.  There were few opportunities to engage with other hapu or iwi members.  Being Māori had greater meaning and was understood, probed and valued by others in the culturally plural context of Hawai'i.  For New Zealand participants, being Māori was enacted in the context of being a discriminated, negatively constructed minority.  All were aware of the defining effect that the presence of a dominant majority could have and countered these effects by engaging in social justice and in-group solidarity activities.

The changing identity conceptions held by members of Māori social groups will have implications for a sense of community and social cohesion, for tribal asset management, service delivery and crown settlement processes.  If Māori are redefining and renegotiating their social identities to achieve greater meaning and satisfaction then these changes are important to respond to and recognise.

year: 2007