Academic staff : Cameron J Kepert

Professor of Chemistry Federation Fellow Address: School of Chemistry, Building F11 The University of Sydney, NSW, 2006 Australia Email address: c.kepert@chem.usyd.edu.au Telephone: +61 (2) 9351-5741 Fax: +61 (2) 9351-3329 Home Page: http://www.chem.usyd.edu.au/~cjkgroup/

Career Profile:

Areas of interest:

• Materials chemistry
  

• Molecular framework materials
  

• X-ray diffraction
  

• Nanoporosity
  

• Electronic and magnetic properties of solids
  

• Phase transitions (structural, electronic and magnetic)
  
  

Research:

Coordination Framework Materials

Coordination frameworks are crystalline solids that contain extended networks constructed by the linkage of metal atoms by multiply-coordinating polydentate ligands. A rapid growth in the study of these materials has arisen from the realisation that metal-organic framework synthesis offers considerable flexibility and control over structure and properties, thereby offering rare pathways to rational materials design. This flexibility originates from the enormous structural and chemical diversities afforded by molecular systems, features that are less prevalent in many other branches of materials chemistry.

The recent emergence of nanoporosity in molecular frameworks has led to widespread speculation that such materials may be ideally suited for applications such as molecular separation, sensing and heterogeneous catalysis. Our primary research efforts are being directed towards exploring these issues, addressing, in particular, whether there are any limitations to this porosity and to what extent the frameworks may be thought of as rigid. Experimentation involves the synthesis of new materials by diffusion-controlled and solvothermal methods, and structural and physical characterisations using techniques that include single crystal and powder X-ray diffraction, vibrational spectroscopy (IR and Raman), TGA/DSC of guest desorption and sorption, NMR, SQUID magnetometry, EPR and theoretical modelling of guest molecule docking and packing.

Chiral Phases: The search for chiral nanoporous materials, widely regarded as a Holy Grail within solid state chemistry, is driven by the potential application of such materials for chiral separations and enantioselective syntheses. We have recently made significant in-roads into this area by developing a large and diverse array of porous, chiral molecular framework solids, including some that are the only such materials known that can be synthesised homochirally. Experiments show that these materials display a high degree of selectivity to molecular guest-exchange, as well as retaining structural framework integrity with guest removal. Investigations into the direct application of these phases for enantioseparation are underway, with an aim towards designing systems for the separation of small drug-precursor molecules.

In-situ Structural Investigations: We have recently performed unique in-situ single crystal X-ray diffraction experiments of guest desorption and sorption to demonstrate the nanoporosity of specific molecular framework materials. These studies are noteworthy in providing the first quantitative proof that desolvated phases of both co-ordination and hydrogen-bonded framework lattices may be robust enough to support large regions of complete void, thereby drawing a direct link with more conventional nanoporous materials such as zeolites. Such studies are being combined with in-situ techniques such as DSC/TGA, vibrational spectroscopy, NMR and molecular modelling to generate an overall picture that combines structural information with an understanding of the selectivity, dynamics and energetics of guest-exchange.

Electronic and Magnetic Properties: The incorporation of atomic or molecular constituents with electronic or magnetic function (e.g., localised electrons, delocalised pI-systems, redox-active species, etc.) into molecular frameworks is being investigated with an aim towards constructing materials with novel electronic and magnetic properties. The vast control over structure and chemical functionality that is afforded by this molecular approach allows the property-directed design and synthesis of new magnetic and electronic materials, including, importantly, the possible combination of these properties with nanoporosity.

Hydrogen Storage: The safe and efficient storage of hydrogen gas represents one of the central challenges on the road to the proposed Hydrogen Economy. Nanoporous coordination framework materials have recently been shown to sorb large volumes of hydrogen gas at low temperature and high pressure, a property that may be attributed to their very high surface areas. Two principal challenges exist to optimise the extent and conditions of loading: 1) maximisation of surface area per mass and volume, thereby maximising potential uptake, and 2) maximisation of the dihydrogen physisorption interaction energy, thereby favouring loading at higher temperatures and lower pressures. Our investigations in this area have uncovered very high hydrogen uptakes in Prussian Blue materials and a range of highly porous metal-organic frameworks.

Negative Thermal Expansion: We have recently discovered that a broad family of coordination frameworks undergo negative thermal expansion (NTE, ie. contraction upon warming) over broad temperature ranges. We attribute this highly unusual and potentially useful property to the existence of low energy transverse vibrations of molecular bridges within the open framework structures, the amplitude of which increase with increasing temperature. Through tuning the energy of these vibrational modes we have achieved both unprecedented NTE and approximate zero thermal expansion (ZTE) behaviour.

Selected publications:

• A. L. Goodwin, B. J. Kennedy, C. J. Kepert, “Thermal Expansion Matching via Framework Flexibility in Zinc Dicyanometallates”, J. Am. Chem. Soc., accepted (2009).
  
  

• M.B. Duriska, S.M. Neville, B. Moubaraki, J.D. Cashion, G.J. Halder, K.W. Chapman, C. Balde, J-F. Létard, K.S. Murray, C.J. Kepert, S.R. Batten, “A Supramolecular ‘Nanoball’ with Thermal, Light and Guest-Induced Switching”, Angew. Chem., Int. Ed., 48, 2549-2552 (2009).
  
  

• G.J. Halder, K.W. Chapman, S.M. Neville, B. Moubaraki, K.S. Murray, J. F. Létard, C.J. Kepert, “Elucidating the Mechanism of a Two-Step Spin Transition in a Nanoporous Metal-Organic Framework”, J. Am. Chem. Soc., 130, 17552-17562 (2008).
  
  

• S.S. Iremonger, P.D. Southon, C.J. Kepert, “A Nanoporous Chiral Metal-Organic Framework Material that Exhibits Reversible Guest Adsorption”, Dalton Trans., 6103 - 6105 (2008).
  
  

• Y. Wu, A. Kobayashi, G.J. Halder, V.K. Peterson, K.W. Chapman, N. Lock, P.D. Southon, C.J. Kepert, “Negative Thermal Expansion in the Metal-Organic Framework Material Cu₃(btc)₂ (btc = 1,3,5-benzenetricarboxylate)”, Angew. Chem. Int. Ed., 47, 8929-8932 (2008).
  
  

• S.M. Neville, B.A. Leita, G.J. Halder, C.J. Kepert, B. Moubaraki, J.-F. Létard, K.S. Murray, “Understanding the Two-Step Spin Transition Phenomenon in Iron(II) 1-D Chain Materials”, Chem. Eur. J., 14, 10123 (2008).
  
  

• P. Yuan, P.D. Southon, Z. Liu, M.E.R. Green, J.M. Hook, S.J. Antill, C.J. Kepert, “The Functionalization of Halloysite Clay Nanotubes by Grafting with Aminopropyltriethoxysilane (APTES)”, J. Phys. Chem. C, 112, 15742–15751 (2008).

• S.M. Neville, G.J. Halder, K.W. Chapman, M.B. Duriska, P.D. Southon, J.D. Cashion, J.F. Létard, B. Moubaraki, K.S. Murray, C.J. Kepert, “Single-Crystal to Single-Crystal Structural Transformation and Photomagnetic Properties of a Porous Iron(II) Spin Crossover Framework”, J. Am. Chem. Soc., 130, 2869-2876 (2008).
  
  

• A.E. Phillips, A.L. Goodwin, G.J. Halder, P.D. Southon, C.J. Kepert, “Nanoporosity and Exceptional Negative Thermal Expansion in Single-Network Cadmium Cyanide”, Angew. Chem. Int. Ed., 47, 1396-1399 (2008); Angew. Chem., 120, 1418-1421 (2008). Highlighted Communication.
  
  

• S.M. Neville, B. Moubaraki, K.S. Murray, C.J. Kepert, “A Thermal Spin Transition in a Nanoporous Iron(II) Coordination Framework Material”, Angew. Chem. Int. Ed., 46, 2059-2062 (2007); Angew. Chem., 119, 2105-2108 (2007).
  
  

• C.J. Kepert, "Advanced Functional Properties in Nanoporous Coordination Framework Materials", Chem. Commun., 40th Anniversary Focus Article, 695-700 (2006).

• V.K. Peterson, Y. Liu, C.M. Brown, C.J. Kepert, "Neutron Powder Diffraction Study of D2 Sorption in Cu3(1,3,5-benzenetricarboxylate)2", J. Am. Chem. Soc., 128, 15578-15579 (2006). Highlighted in Chemical and Engineering News: Hydrogen Storage Gets a Boost

• J.J.M. Amoore, C.J. Kepert, B. Moubaraki, K.S. Murray, S.M. Neville, "Structural and Magnetic Resolution of a Two-Step Spin-Crossover Transition in a Dinuclear Iron(II) Pyridyl-Bridged Compound", Chem. Eur. J., 12, 8220-8227 (2006). Very Important Paper with Cover Picture.

• G.J. Halder, C.J. Kepert, "Single-Crystal-to-Single-Crystal Structural Transformations in Molecular Framework Materials", Aust. J. Chem., 59, 597-604 (2006). Invited Review with Cover Picture.

• K.W. Chapman, P.J. Chupas, C.J. Kepert, "Compositional Dependence of Negative Thermal Expansion in the Prussian Blue Analogues MIIPtIV(CN)6 (M = Mn-Zn, Cd)", J. Am. Chem. Soc., 128, 7009-7014 (2006).

• T. Pretsch, K.W. Chapman, G.J. Halder, C.J. Kepert, "Dehydration of the Nanoporous Coordination Framework ErIII[CoIII(CN)6]4(H2O): Single Crystal to Single Crystal Transformation and Negative Thermal Expansion in ErIII[CoIII(CN)6]" Chem. Commun., 1857-1859 (2006).

• A.L. Goodwin, K.W. Chapman, C.J. Kepert, "Guest-Dependent Negative Thermal Expansion in Nanoporous Prussian Blue Analogues MIIPtIV(CN)6x{H2O} (0 ≤ x ≤ 2; M = Zn, Cd)", J. Am. Chem. Soc., 127, 17980-17981 (2005). download

• K.W. Chapman, P.J. Chupas, C.J. Kepert, "Direct Observation of a Transverse Vibrational Mechanism for Negative Thermal Expansion in Zn(CN)2: an Atomic Pair Distribution Function Analysis", J. Am. Chem. Soc., 127, 15630-15636 (2005). download
  

• K.W. Chapman, P.J. Chupas, C.J. Kepert, "Selective Recovery of Dynamic Guest Structure in a Nanoporous Prussian Blue Through In-Situ X-ray Diffraction: a Differential Pair Distribution Function Analysis", J. Am. Chem. Soc., 127, 11232 - 11233 (2005).

• G.J. Halder, C.J. Kepert, "In-situ Single Crystal X-ray Diffraction Studies of Desorption and Sorption in a Flexible Nanoporous Molecular Framework Material", J. Am. Chem. Soc., 127, 7891-7900 (2005). download

• K.W. Chapman, P.D. Southon, C.L. Weeks, C.J. Kepert, "Reversible Hydrogen Gas Uptake In Nanoporous Prussian Blue Analogues", Chem. Commun., 3322 - 3324 (2005).

• M. Kurmoo, H. Kumagai, K.W. Chapman, C.J. Kepert, "Reversible Antiferromagnetic-Ferromagnetic Transformation upon Dehydration-Hydration in the Porous Metal-Organic Framework, [Co3(OH)2(C4O4)2]·3H 2O", Chem. Commun., 3012 - 3014 (2005).

• A.L. Goodwin, C.J. Kepert, "Negative Thermal Expansion and Low-Frequency Modes in Cyanide-Bridged Framework Materials", Phys. Rev. B, 71, 140301 (2005).

• K.S. Murray, C.J. Kepert, "Cooperativity in Spin-Crossover Systems: Memory, Magnetism and Microporosity", in "Spin-Crossover in Transition Metal Compounds", Topics Curr. Chem., P. Gütlich, H.A. Goodwin (Ed.), Springer-Verlag, Heidelberg, 233, 195-228 (2004).

• P.V. Ganesan, C.J. Kepert, "Nanoporosity of an Interpenetrated NbO-type Molecular Framework Studied by Single Crystal X-ray Diffraction", Chem. Commun., 2168 (2004).

• M. Kurmoo, H. Kumagai, S.M. Hughes, C.J. Kepert, "Reversible Guest Exchange and Ferrimagnetism (TC = 60.5 K) in a Porous Cobalt(II)-Hydroxide Layer Structure Pillared with trans-1,4-Cyclohexanedicarboxylate", Inorg. Chem., 42, 6709-6722 (2003).

• G.J. Halder, C.J. Kepert, B. Moubaraki, K.S. Murray, J.D. Cashion, "Guest-Dependent Spin Crossover in a Nanoporous Molecular Framework Material", Science, 298, 1762-1765 (2002). abstract full text
  {Perspective: M.M. Turnbull, C.P. Landee, "Porous Materials with a Difference", Science 298 1723-1724 (2002)}. Chosen as a Chemistry Highlight of 2002 by Chemical and Engineering News .

• E.J. Cussen, J.B. Claridge, M.J. Rosseinsky, C.J. Kepert, "Flexible Sorption and Transformation Behavior in a Microporous Metal-Organic Framework", J. Am. Chem. Soc, 124, 9574-9581 (2002).

• A.J. Fletcher, E.J. Cussen, T.J. Prior, M.J. Rosseinsky, C.J. Kepert, K.M. Thomas, "Adsorption Dynamics of Gases and Vapours on Ni2(4,4'-bipyridine)3(NO3)4: a Nanoporous Metal Organic Framework Material", J. Am. Chem. Soc., 123, 10001-10011 (2001).

• A. Rujiwatra, C.J. Kepert, J.B. Claridge, M.J. Rosseinsky, H. Kumagai, M. Kurmoo, "Layered Cobalt Hydroxysulfates with both Rigid and Flexible Organic Pillars: Synthesis, Structure, Porosity, and Cooperative Magnetism", J. Am. Chem. Soc., 123, 10584-10594 (2001).

• C.J. Kepert, T.J. Prior, M.J. Rosseinsky, "A Versatile Family of Interconvertible Microporous Chiral Molecular Frameworks: The First Example of Ligand Control of Network Chirality", J. Am. Chem. Soc., 122, 5158-5168 (2000).

• C.J. Kepert, M.J. Rosseinsky, "Zeolite-like Crystal Structure of an Empty Microporous Molecular Framework", Chem. Commun., 375-376 (1999).

• A. Rujiwatra, C.J. Kepert, M.J. Rosseinsky, "The Novel Organo-Pillared Porous Magnetic Framework Co4(SO4)(OH)6(H2NC2H4NH2)0.5.3H2O", Chem. Commun., 2307-2308 (1999).

• C.J. Kepert, D. Hesek, P.D. Beer, M.J. Rosseinsky, "Desolvation of a Novel Microporous Hydrogen-Bonded Framework: Characterization by In Situ Single-Crystal and Powder X-ray Diffraction", Angew. Chem. Int. Ed. Engl., 37(22), 3158-3160 (1998); Angew. Chem., 110(22), 3335-3337 (1998).