Towards High Throughput Single Crystal Neutron Diffraction of Hydrogen Bonded Molecular Complexes

Andrew Jones

Research output: ThesisDoctoral Thesis

Abstract

This work presents findings from experiments carried out using the neutron Laue method in tandem with laboratory source X-ray diffraction to characterise a series of organic molecular complexes which exhibit interesting, and potentially “tunable”, temperature dependent charge transfer effects, such as proton migration and proton disorder within hydrogen bonded networks. These subtle processes are studied by variable temperature neutron diffraction studies, allowing the positional and anisotropic displacement parameters of the hydrogen atoms to be refined accurately and their evolution with temperature followed. The hydrogen atom behaviour is found to be influenced by the local environment, including weak intermolecular interactions in the vicinity of the hydrogen bond under study.
Complexes of urea and methyl substituted ureas with small organic acids are presented, which show robust and reproducible structural motifs. In favourable circumstances, these contain short, strong hydrogen bonds (SSHBs) within which the proton may undergo temperature dependent migration. By synthesising a number of complexes containing SSHBs, potential routes to the design of proton migration complexes are found, which utilise crystal engineering principles and pKa matching. Variable temperature studies conducted on these complexes also show unusual thermal expansion properties and phase transitions in urea-acid complexes which do not display proton migration.
Systems containing hydrogen bonded dimers of 3,5-dinitrobenzoic acid are also studied, and shown to contain temperature proton disorder within moderate strength hydrogen bonds linking the dimers. The presence and potential onset temperature of any disorder is found to be influenced by interactions around the acid dimers and potential routes to controlling proton disorder are discussed.
Complexes of the proton sponge, 1,8-bis(dimethylamino)napthalene (DMAN), with organic acids are also presented, in which the structures have been determined using neutron diffraction. DMAN readily accepts a proton from the acid co-molecules used in forming the complexes, forming a strong intramolecular SSHB within the protonated DMAN. Strong intermolecular hydrogen bonds are also induced between the acid molecules in many cases. The neutron studies presented here investigate the effect of weak interactions on the behaviour of hydrogen atoms located within these SSHBs, and also indicate over what distance such interactions significantly affect the hydrogen atom behaviour.
LanguageEnglish
QualificationPh.D.
Awarding Institution
  • University of Bath
Supervisors/Advisors
  • Wilson, Charles, Supervisor
Award date30 Sep 2012
StatusUnpublished - Sep 2012

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Neutron diffraction
Protons
Hydrogen
Throughput
Single crystals
Hydrogen bonds
Dimers
Urea
Atoms
Acids
Organic acids
Temperature
Neutrons
Crystal engineering
Molecules
Thermal expansion
Charge transfer
Phase transitions
X ray diffraction

Keywords

  • hydrogen bond
  • diffraction
  • x-ray
  • neutron

Cite this

Towards High Throughput Single Crystal Neutron Diffraction of Hydrogen Bonded Molecular Complexes. / Jones, Andrew.

2012. 291 p.

Research output: ThesisDoctoral Thesis

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N2 - This work presents findings from experiments carried out using the neutron Laue method in tandem with laboratory source X-ray diffraction to characterise a series of organic molecular complexes which exhibit interesting, and potentially “tunable”, temperature dependent charge transfer effects, such as proton migration and proton disorder within hydrogen bonded networks. These subtle processes are studied by variable temperature neutron diffraction studies, allowing the positional and anisotropic displacement parameters of the hydrogen atoms to be refined accurately and their evolution with temperature followed. The hydrogen atom behaviour is found to be influenced by the local environment, including weak intermolecular interactions in the vicinity of the hydrogen bond under study.Complexes of urea and methyl substituted ureas with small organic acids are presented, which show robust and reproducible structural motifs. In favourable circumstances, these contain short, strong hydrogen bonds (SSHBs) within which the proton may undergo temperature dependent migration. By synthesising a number of complexes containing SSHBs, potential routes to the design of proton migration complexes are found, which utilise crystal engineering principles and pKa matching. Variable temperature studies conducted on these complexes also show unusual thermal expansion properties and phase transitions in urea-acid complexes which do not display proton migration.Systems containing hydrogen bonded dimers of 3,5-dinitrobenzoic acid are also studied, and shown to contain temperature proton disorder within moderate strength hydrogen bonds linking the dimers. The presence and potential onset temperature of any disorder is found to be influenced by interactions around the acid dimers and potential routes to controlling proton disorder are discussed.Complexes of the proton sponge, 1,8-bis(dimethylamino)napthalene (DMAN), with organic acids are also presented, in which the structures have been determined using neutron diffraction. DMAN readily accepts a proton from the acid co-molecules used in forming the complexes, forming a strong intramolecular SSHB within the protonated DMAN. Strong intermolecular hydrogen bonds are also induced between the acid molecules in many cases. The neutron studies presented here investigate the effect of weak interactions on the behaviour of hydrogen atoms located within these SSHBs, and also indicate over what distance such interactions significantly affect the hydrogen atom behaviour.

AB - This work presents findings from experiments carried out using the neutron Laue method in tandem with laboratory source X-ray diffraction to characterise a series of organic molecular complexes which exhibit interesting, and potentially “tunable”, temperature dependent charge transfer effects, such as proton migration and proton disorder within hydrogen bonded networks. These subtle processes are studied by variable temperature neutron diffraction studies, allowing the positional and anisotropic displacement parameters of the hydrogen atoms to be refined accurately and their evolution with temperature followed. The hydrogen atom behaviour is found to be influenced by the local environment, including weak intermolecular interactions in the vicinity of the hydrogen bond under study.Complexes of urea and methyl substituted ureas with small organic acids are presented, which show robust and reproducible structural motifs. In favourable circumstances, these contain short, strong hydrogen bonds (SSHBs) within which the proton may undergo temperature dependent migration. By synthesising a number of complexes containing SSHBs, potential routes to the design of proton migration complexes are found, which utilise crystal engineering principles and pKa matching. Variable temperature studies conducted on these complexes also show unusual thermal expansion properties and phase transitions in urea-acid complexes which do not display proton migration.Systems containing hydrogen bonded dimers of 3,5-dinitrobenzoic acid are also studied, and shown to contain temperature proton disorder within moderate strength hydrogen bonds linking the dimers. The presence and potential onset temperature of any disorder is found to be influenced by interactions around the acid dimers and potential routes to controlling proton disorder are discussed.Complexes of the proton sponge, 1,8-bis(dimethylamino)napthalene (DMAN), with organic acids are also presented, in which the structures have been determined using neutron diffraction. DMAN readily accepts a proton from the acid co-molecules used in forming the complexes, forming a strong intramolecular SSHB within the protonated DMAN. Strong intermolecular hydrogen bonds are also induced between the acid molecules in many cases. The neutron studies presented here investigate the effect of weak interactions on the behaviour of hydrogen atoms located within these SSHBs, and also indicate over what distance such interactions significantly affect the hydrogen atom behaviour.

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KW - x-ray

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M3 - Doctoral Thesis

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