Structural chemistry of transition metal dicyanometallates
<p>Transition metal dicyanometallates are a family of coordination polymers characterised by their structural diversity and nanoscale separation between transition metal centres. This thesis addresses the relationships between molecular extra-framework cations and their host dicyanometallate f...
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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2016
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| _version_ | 1797104207657959424 |
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| author | Hill, J |
| author2 | Goodwin, A |
| author_facet | Goodwin, A Hill, J |
| author_sort | Hill, J |
| collection | OXFORD |
| description | <p>Transition metal dicyanometallates are a family of coordination polymers characterised by their structural diversity and nanoscale separation between transition metal centres. This thesis addresses the relationships between molecular extra-framework cations and their host dicyanometallate frameworks as determinants of structure type and phase transitions. It also addresses the new tilt degrees of freedom accessible to perovskite-structured dicyanometallates and molecular perovskites more generally. A number of new dicyanometallate frameworks are reported which contain the extra-framework cations tetraethylammonium, [NEt<sub>4</sub>]<sup>+</sup>, tetra-<em>n</em>-butylammonium, [NBu<sub>4</sub>]<sup>+</sup>, and bis(triphenylphosphine)iminium, [PPN]<sup>+</sup> = {[(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>P]<sub>2</sub>N}<sup>+</sup>. These new compounds are placed within the context of all known dicyanometallate frameworks of general formula A<sub>m</sub>B(L)X<sub>n</sub>·G where A is an extra- framework cation; B is a metal cation; X is [Au(CN)<sub>2</sub>]<sup>−</sup>, [Ag(CN)<sub>2</sub>]<sup>−</sup>, or [Cu(CN)<sub>2</sub>]<sup>−</sup>; L is a neutral ligand bound to the node metal centre (i.e., not to the linker metal); and G is a non-coordinating guest molecule. They are organised according to their stoichiometry, A<sub>m</sub>BX<sub>n</sub>, showing the dual importance of size/shape of extra- framework cations and the coordinational preferences of the framework cation. The interdependence of degrees of freedom associated with extra-framework cations and with their host frameworks are explored in a diamondoid system and in a number of perovskite-like systems. In the diamondoid system [NEt<sub>4</sub>]Ag[Ag(CN)<sub>2</sub>]<sub>2</sub>, coupling between [NEt<sub>4</sub>]+ conformation and lattice modes results in a second-order phase transition to an incommensurately modulated phase at low temperatures. There are few reports of incommensurability in coordination polymers; coupling of ‘molecular’ degrees of freedom with phonons is of fundamental interest and has been implicated in the performance of lead halide perovskites in solar cells. Dicyanometallates with perovskite(-related) structures are here shown to undergo a variety of displacive and reconstructive phase transitions as a function of temperature. In each case, the extra-framework species play a key role in determining the nature of the transitions. In molecular perovskite analogues, tilt degrees of freedom can couple at arbitrary periodicities not accessible to oxides/halides. The ‘tilt tensor’ is developed here as a tool for describing these tilts. This understanding of unconventional tilts is finally applied to the Prussian Blue analogue (NH<sub>4</sub>)<sub>2</sub>SrFe(CN)<sub>6</sub> in which such tilts can be switched on and off depending on hydration state.</p> |
| first_indexed | 2024-03-07T06:30:37Z |
| format | Thesis |
| id | oxford-uuid:f5ddf8b1-2115-4eac-a321-52600ea2a2d9 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T06:30:37Z |
| publishDate | 2016 |
| record_format | dspace |
| spelling | oxford-uuid:f5ddf8b1-2115-4eac-a321-52600ea2a2d92022-03-27T12:30:36ZStructural chemistry of transition metal dicyanometallatesThesishttp://purl.org/coar/resource_type/c_db06uuid:f5ddf8b1-2115-4eac-a321-52600ea2a2d9ChemistryX-ray CrystallographyCrystallographyStructural ChemistryChemistry, InorganicEnglishORA Deposit2016Hill, JGoodwin, A<p>Transition metal dicyanometallates are a family of coordination polymers characterised by their structural diversity and nanoscale separation between transition metal centres. This thesis addresses the relationships between molecular extra-framework cations and their host dicyanometallate frameworks as determinants of structure type and phase transitions. It also addresses the new tilt degrees of freedom accessible to perovskite-structured dicyanometallates and molecular perovskites more generally. A number of new dicyanometallate frameworks are reported which contain the extra-framework cations tetraethylammonium, [NEt<sub>4</sub>]<sup>+</sup>, tetra-<em>n</em>-butylammonium, [NBu<sub>4</sub>]<sup>+</sup>, and bis(triphenylphosphine)iminium, [PPN]<sup>+</sup> = {[(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>P]<sub>2</sub>N}<sup>+</sup>. These new compounds are placed within the context of all known dicyanometallate frameworks of general formula A<sub>m</sub>B(L)X<sub>n</sub>·G where A is an extra- framework cation; B is a metal cation; X is [Au(CN)<sub>2</sub>]<sup>−</sup>, [Ag(CN)<sub>2</sub>]<sup>−</sup>, or [Cu(CN)<sub>2</sub>]<sup>−</sup>; L is a neutral ligand bound to the node metal centre (i.e., not to the linker metal); and G is a non-coordinating guest molecule. They are organised according to their stoichiometry, A<sub>m</sub>BX<sub>n</sub>, showing the dual importance of size/shape of extra- framework cations and the coordinational preferences of the framework cation. The interdependence of degrees of freedom associated with extra-framework cations and with their host frameworks are explored in a diamondoid system and in a number of perovskite-like systems. In the diamondoid system [NEt<sub>4</sub>]Ag[Ag(CN)<sub>2</sub>]<sub>2</sub>, coupling between [NEt<sub>4</sub>]+ conformation and lattice modes results in a second-order phase transition to an incommensurately modulated phase at low temperatures. There are few reports of incommensurability in coordination polymers; coupling of ‘molecular’ degrees of freedom with phonons is of fundamental interest and has been implicated in the performance of lead halide perovskites in solar cells. Dicyanometallates with perovskite(-related) structures are here shown to undergo a variety of displacive and reconstructive phase transitions as a function of temperature. In each case, the extra-framework species play a key role in determining the nature of the transitions. In molecular perovskite analogues, tilt degrees of freedom can couple at arbitrary periodicities not accessible to oxides/halides. The ‘tilt tensor’ is developed here as a tool for describing these tilts. This understanding of unconventional tilts is finally applied to the Prussian Blue analogue (NH<sub>4</sub>)<sub>2</sub>SrFe(CN)<sub>6</sub> in which such tilts can be switched on and off depending on hydration state.</p> |
| spellingShingle | Chemistry X-ray Crystallography Crystallography Structural Chemistry Chemistry, Inorganic Hill, J Structural chemistry of transition metal dicyanometallates |
| title | Structural chemistry of transition metal dicyanometallates |
| title_full | Structural chemistry of transition metal dicyanometallates |
| title_fullStr | Structural chemistry of transition metal dicyanometallates |
| title_full_unstemmed | Structural chemistry of transition metal dicyanometallates |
| title_short | Structural chemistry of transition metal dicyanometallates |
| title_sort | structural chemistry of transition metal dicyanometallates |
| topic | Chemistry X-ray Crystallography Crystallography Structural Chemistry Chemistry, Inorganic |
| work_keys_str_mv | AT hillj structuralchemistryoftransitionmetaldicyanometallates |