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Inorganic Materials and Supramolecular Chemistry

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Major Research Interests

(A) Synthesis and Characterization of Nanoscale Materials: The study of nanometer size compounds is an exciting area of research which offers opportunities for innovation and creativity. Nanoscale materials exhibit quantum behavior due to their size and are promising materials for new technologies. Our research focuses on the synthesis of nanoscale metal chalcogenide materials and the characterization of their properties. The properties of nano depend on the size and shape of the nanomaterials. However synthesis of stable monodispersed nanocrystals is a real challenge in nanoscience.  Further shape control of nanocrystals is also very important because of the strong correlation between the shape and the chemical, physical, electronic, optical, magnetic and catalytic properties of nanoparticles. These shape and size of nanocrystals are mainly controlled by crystal growth kinetics.  Experience in the synthetic chemistry and crystallography provides plethora of opportunities to investigate these interesting problems in nanoscience.  

Single-source precursor Chemistry: We have been interested in developing the chemistry of transition and main group metal compounds with chalcogen containing ligands, RC{O}E-, RE-, R2NCS2- (where E = S, Se and Te), dithioacetylacetonato and related ligands. We have shown that many of these compounds can be used as precursors to metal chalcogenides (as amorphous or crystalline powders, films and nanoparticles). These metal-chalcogenide materials have potential applications in the areas of optical coatings, solid-state solar cells, electro optic modulators, photoconductors, field effect transistors, sensors and transducers. The main objective is to find the relationship between the nature of the single-source precursors and the quality of the chalcogenide materials obtained. Currently we are interested in the Group 6, 11, 12, 13, 14, transition and lanthanide metals.  We have also developed sing precursor routes to synthesize highly monodispersed nanoparticles of ZnSe, CdS (water and toluene soluble), CdSe, Cu2-xSe, Ag2Se, AInE2 (A = Cu, Ag; E = S, Se), MoS2 and Bi2S3 and we are investigating various physical properties of these nanomaterials including luminescent and non-linear optical properties.

Oxide Materials: Recently we have developed single-source precursor route to LiMO2 battery materials. The compounds [Li(H2O)M(N2H3CO2)3].H2O (M = Ni, Co) on pyrolysis yield LiNiO2 and LiCoO2 at 700oC in oxygen atmosphere and at T > 700°C in air, respectively.

(B) Crystal Engineering: Current research in our group includes rational design of metal coordination polymers with multi-dimensional network structures using a number of linear and angular spacer ligands. In this exploratory research we systematically study the properties of supramolecular building blocks such as shape, size and directionality of the functional groups to determine how these parameters control and influence the crystal packing and supramolecular structures. We are planning to design supramolecule-based magnets and porous materials by crystal engineering design.

Solid-state Supramolecular Structural Transformations: Transformation from one type of structure to another is not common in supramolecular chemistry. Solid-state supramolecular reactions involving transformation of different structures are very rare since they involve breaking and forming of bonds in more than one direction compared to solid-state organic photochemical reactions which mainly involve two molecules.  In 1998 we synthesized and characterized the dimer [Zn2(sala)2(H2O)2].2H2O (H2sala = N-(2-hydroxybenzyl)-L-alanine, in collaboration with Dr. Ranford. In the solid-state the dimers were cross-linked through N-H∙∙O and O-H∙∙O hydrogen bonds to have a porous honeycomb-like 3D coordination polymeric network with helical channels containing water molecules. The removal of water molecules by heating the solid resulted in another helical polymer, this time held by coordination bonds. On the other hand, thermal dehydration of 1D helical coordination polymer [Cu2(sala)2(H2O)] results in the solid state supramolecular conversion  into the chiral 3D coordination network [Cu2(sala)2]. This is the second example of what represents a new and potentially broadly relevant strategy for the rational development of new classes of polymer conversion of non-covalent architecture into coordination polymers via solid state reactions.

We have shown that the two supramolecular structures of Zn(II) compounds can be interconverted by substituting the backbone of the ligand by non-reactive functional groups . Such reversible structural transformations may find potential applications as molecular switches.  This work, we believe, is a step forward in the rationalization the solid-state supramolecular transformations. The knowledge gained in this study will help us to predict the transformations and to fine-tune the structures of the existing supramolecular architectures.

Helix inside a helix: We are also investigating the formation water molecules with different degree of aggregation and structures in various crystal lattices.  Recently we synthesized a staircase-like helical coordination polymer hosting a 1D helical chain of hydrogen-bonded lattice water molecules in the channel. This novel display of the lattice water assembled into hydrogen-bonded helical chain inside the hollow helical cavity exemplifies, in the field of metalla-supramolecular chemistry, a non-biological model for the water chains in membrane aquaporin proteins for the transport of water.

(C) Catecholase-Mimetic Activity of Dicopper(II) complexes: A number of dicopper(II) complexes of reduced Schiff base ligands, N-(2-hydroxybenzyl)-amino acids have been found to show significant catalytic activity on the oxidation of 3,5-di-tert-butylcatechol. The catalytic activity is found to increase with increasing the length of methylene side chain of the amino acid in the reduced Schiff base ligands.

(D) Photochemistry of Metal Coordination Polymers: One dimensional metal coordination polymers with molecular ladder structures can easily be prepared by self-assembly. Hence these structures provide an interesting possibility to align photoreactive duble bonds in the solid-state since the distance between the rails can be manipulated by judicious choice of the bridging ligands or metallophilic interactions. Such metal coordination polymeric structures have not been exploited for this purpose before. Recently we have investigated a topochemical transformation of a 1D metal-coordination polymer, with molecular ladder structure through [2+2] photochemical cycloaddition across the rails quantitatively. This cycloaddition is accompanied by single-crystal to single-crystal structural transformation. A number of metal coordination network structures may also be designed and employed for this purpose. Further new interesting network structures can be synthesized from a number of metal coordination polymeric structures in the solid-state via single-crystal to single-crystal structural transformation.  Our research group is currently exploring these possibilities.

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Top 10 of Publications since 1997

1.   L. Tian, H.I. Lim, W. Ji,* J.J. Vittal*, ‘One pot synthesis and third-order nonlinear optical properties of AgInS2 nanocrystals’, Chem. Commun., (2006) xxx.

2.   M. Nagarathinam and J.J. Vittal,* ‘Anisotropic movements of coordination polymers upon desolvation: Solid-state transformation of linear 1D coordination polymer to ladder-like structure.’ Angew. Chem. Int. Ed., 45 (2006) 4337.

3.   M.T. Ng, C.B. Boothroyd and J.J. Vittal,* ‘One-pot synthesis of new phase AgInSe2 nanorods.’ J. Amer. Chem. Soc., 128 (2006) 1178.

4.   M.T. Ng, C. Boothroyd and J.J. Vittal,* ‘Shape and size control of Ag2Se nanocrystals from single precursor [(Ph3P)3Ag2 (SeC{O}Ph)2].’ Chem. Commun., (2005) 3820.

5.   N.L. Toh, M. Nagarathinam and J.J. Vittal,* ‘Topochemical photodimerization in the molecular ladder metal coordination polymer [{(CF3CO2)(µ-O2CCH3)Zn}2(µ-bpe)2]n (where bpe = 4,4’-bipyridylethelene) via single-crystal to single-crystal transformation.’ Angew. Chem. Int. Ed., 44 (2005) 2237.

6.   B. Sreenivasulu and J.J. Vittal,* ‘Helix inside a helix: Encapsulation of Hydrogen-bonded Water Molecules inside a Staircase Coordination Polymer.’ Angew. Chem. Int. Ed., 43 (2004) 5769.

7.   M.T. Ng, T.C. Deivaraj, W.T. Klooster,* G.J. McIntyre* and J.J. Vittal,* ‘Hydrogen-bonded Polyrotaxane-like structure containing cyclic (H2O)4 in [Zn(OAc)2(μ-bpe)]×2H2O: X-Ray and Neutron Diffraction Studies.’ Chem. Eur. J., 10 (2004) 5853.

8.   M. Lin, K.P. Loh,* T.C. Deivaraj and J.J. Vittal,* ‘Heterogeneous reaction route to   CuInS2 thin films.’ Chem. Commun., (2002) 1400.

9.   “Thermal Conversion of a Helical Coil to a 3-D Chiral Framework”. J.D. Ranford, J.J. Vittal, D. Wu and X. Yang, Angew. Chem. Int. Ed., 38 (1999) 3498.

10. “Topochemical Conversion of Hydrogen Bonding to Covalent Three Dimensional Networks”. J.D. Ranford, J.J. Vittal and D. Wu, Angew. Chem. Int. Ed., 37 (1998) 1114.

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Selected Highlights on the Research

1.   M.J. Zaworotko, "From dissymmetric molecules to chiral polymers: A new twist for supramolecular synthesis?" (Angew. Chem. Int. Ed., 37 (1998) 1211) highlighted our publication Angew. Chem. Int. Ed., 37 (1998) 1114.

2.   D. Bradley in the web journal Catalyst, (http://chemweb.com/alchem) July 3, 1998 issue entitled "Molecular architecture: designs on chemistry", highlighted our work in Angew. Chem. Int. Ed., 37 (1998) 1114.

3.   Commentary "Super supramolecular synthesis" by J.D. Ranford, J.J. Vittal and D. Wu, Research Newsletter, Faculty of Science, Volume 2, No. 3, July 1998, pp. 1.

4.   Commentary "From Sand to TV Screens" an article about J.J. Vittal's work for Innovation, The Magazine of Research & Technology, NUS, March 2001, pp.12.

5.   Commentary "Supramolecule-based magnets - A supramolecular copper(II) complex with a magnetic ordering temperature above 400K." J. Ding and J.J. Vittal, Research Newsletter, Faculty of Science, Vol. 5, No. 3, September 2001, pp. 11.

6.   A company in USA was interested to fund our research in the area of electronic grade metal chalcogenide materials (Dr. Douglas L. Schulz, CeraMem Corporation, 12 Clematis Avenue, Waltham, MA  02453) in 2001.

7.   Dalton Trans., 2004, (1), 113 (No. 5 in the above list) was amongst the top ten accessed on the web from the online version of Dalton Transactions for the month of December 2003.

8.   Unilever R&D is interested in testing our compounds for bleaching activity. A letter from coordination Chemist, Unilever R&D, Wirral, UK, June 15, 2004.

9.   Invited to chair a Scientific session, International Conference on Neutron Scattering, Sydney, Australia, November 27- December 2, 2005

10. Invitation to give an invited talk, 1st J&K State Science Congress, Jammu, India, February 7-9, 2005

11. The Chem. Comm. (2005) 3820 paper on Ag2Se was a hot article.

12. Highlights of the article on nano Ag2Se work in the September, 2005 issue of MRS Web Bulletin in the Research/Researchers section in http://www.mrs.org/connections/researchnews/200508_1.html

13. Highlights in Molecular Torch, an Internet webpage dedicated for nanotechnology on the nano Ag2Se work in http://www.moleculartorch.com/2005_08_01. Excerpts: “I have known Dr. Vittal, the primary author, since is early days as a crystallographer at the University of Western Ontario in London Ontario Canada. It is wonderf ul to see his research is moving towards applications of his skills in crystallography to nanocrystal growth.”

14. An invitation from the Assistant Editor to submit a full paper of Chem. Commun., (2005) 3820 article in the Journal of Materials Chemistry as an invited article

15. Invited to talk in IUPAC New Directions in Chemistry, Workshop on Advanced Materials (WAM III), focusing on Nanostructured Advanced Materials, Stellenbosch, South Africa, September 5 – 8 , 2005

16. Cover page highlight of the paper in Angew Chem. 44 (2005) 2237 in the issue no.15, 2005. All the referees should consider the paper as significant to be considered for the cover page entry.

17. An email appreciation from Prof. G.R. Desiraju who is considered to be the father of crystal engineering. Email congratulatory remarks from the peers outside Singapore on our research published in Angew. Chem. Int. Ed. Engl., 44 (2005) 2237

18. Royal Society of Chemistry linking my NUS webpage to Crystal Engineering Research Group in the journal CrystEngComm

19. Invited to talk at the 16th International Symposium on Fine Chemistry and Functional Polymer (FCFP-XVI) to be held in Lanzhou, China, July 24-27, 2006 and Post-Symposium, July 28-30, 2006

20. Invited to give a plenary lecture at the 8th International Symposium on Biotechnology, Metal Complexes and Catalysis (BMC-VII) to be held in Haikou, China, November 6-9, 2006

21. Received invitation to talk at the Fourteenth Annual International Conference on Composites/NANO Engineering, ICCE-14, July 2-8, 2006, in Colorado, USA

22. Received invitation to talk at the 9th Eurasia Conference on Chemical Sciences (EuAsC2S-9)"Innovations in Chemical Biology at the Bridge of Eurasia, September 9-13, 2006 in Antalya, Turkey.

23. Received invitation to speak at the Missouri Nanotechnology Alliance, The Third Annual Meeting, Oct. 6-7, 2006, Columbia, USA.

24. Received invitation to talk at the International Symposium on Materials Science, Dec. 4-8, 2006 in Babha Atomic Research Centre, Mumbai, India.

25. Accepted invitation to be in the International Advisory Committee of the International Conference on Nano-Materials for Electronics organized by Centre for Materials For Electronics Technology, Pune India, November 23-25, 2006.

26. An invitation from the Editor-in-Chief and Associate Editor of Macromolecular Rapid Communications to contribute a Feature Article. Submitted a paper, “A Rational Approach to Cross-linking of Coordination Polymers by Photochemical [2+2] Cycloaddition Reaction’ co-authored by M. Nagarathinam. Accepted for publication.

27. Invited by Prof. Joan S. Valentine, Editor-in-Chief of the highly prestigious American Chemical Society journal Accounts of Chemical Research to write a review on my research work. Recently I submitted an article, ‘Chemistry of Metal Thio- and Selenocarboxylates – Precursors for Metal Sulfide/Selenide Materials, Thin Films and Nanocrystals,’ with my graduate student Meng Tack Ng as a co-author (Submitted for publication)

28. Invited to write a review in the journal Coordination Chemistry Reviews (impact factor 9.76). Accepted.

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Research Grants at NUS

External

1.   Title: "Single Source Precursors for LiMS2 and AM2S4 (A = Mg(II), Ca(II); M = Ga(III) and  In(III)." Period: 01-2002 to 01-2004. Agency: Nippon Sheet Glass Foundation for Materials Science and Engineering, Japan. Amount: US$8,000. Completed.

NUS

2.   Title: “Single molecular precursors for metal chalcogenide materials: Syntheses, characterization and properties of metal-selenocarboxylate”. Period: 1-2006 to 1-2009. University Research Fund, NUS. Amount $250,000. On going.  

3.   Title: “Syntheses, characterization and properties of supramolecular compounds containing N-(2-pyridylmethyl)-aminoacids.” Period: 12-2004 to 1-2008. Academic Research Fund, NUS. Amount $88,700. On going.

4.   Title: "Strategies for the Design and Assembly of Inorganic Supramolecular complexes.” Period: 09-2001 to 05-2005. Academic Research Fund, NUS. Amount $137,175. Completed.

5.   Title: "Chemistry of metal chalcogenide precursor compounds." Period: 01-2000 to 01-2002.  Academic Research Fund. Amount $131, 325. Completed.

6.   Title: "Application for a new Apex CCD and upgrade of SMART CCD." A joint proposal by the staff members for the department (coordinated and written by JJV). Amount: $ 845,000.

7.   Title: “Design of the superdiamondoid networks - Building Block Approach.”  Period: 07-1997 to 11-2000. Academic Research Fund. Amount $ 179,600. Completed.

8.   Title: "Orally active amino-acid derivatives as iron chelating and antimalarial drugs." Period July 1997-Dec. 2000. Amount: $208,500. Transferred from Dr. John Ranford and managed the final stages of the project. Completed.

9.   Title: "Metal chalcogenide Nanoparticles from single source molecular precursors".  Period: 04-2002 to 04-2004. Agency: Academic Research Fund, NUS. Amount $65,900. (Co-investigator). Completed.

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List of PhD Students Supervised at NUS

1.   Mr. T.C. Deivaraj (Dec. 2001) - Group 11 and 13 metal thiocarboxylates: Syntheses, structures, properties and applications as single source precursors for metal sulfide materials

2.   Ms. K.S. Anjali (Sept. 2002) - Structural studies of the group 12 metal compounds containing functionalized thiolato ligands

3.   Mr. Yang Chang Tong (June 2003) – Binary and ternary copper(II) complexes containing reduced Schiff base ligands

4.   Ms. Yang Xiandong (Jan. 2004) – Influence of reduced Schiff base ligand substituents on the solid-state structures of their Cu(II) and Zn(II) complexes

5.   Ms. Wang Xiaobai (Oct. 2004) – Syntheses, Structural and Magnetic Properties, and Catecholase Activity of Copper(II) and related Metal(II) Complexes containing reduced Schiff Base Ligands

6.   Mr. Bellam Sreenivasulu – Copper(II) and Ni(II) Complexes of reduced Schiff Base Ligands: Syntheses, Structural and Magnetic Properties, and Catecholase Activity (submitted May 2006)

 

List of MSc Students Supervised at NUS

7.   Mr. Ni Zheng (April 2002) - Chemistry of coordination polymers with nonchelating angular spacer ligands

8.   Mr. Lu Zheng (April 2001) - Metal selenocarboxylates as single source precursors for metal selenides

9.   Ms. Zu Ning (Dec. 2000) - Supramolecular Assemblies as Organic Materials (Main supervisor: Dr. Suresh Valiyaveettil)

 

List of Current PhD Students and Thesis Titles

10. Mr. Ng Meng Tack – Syntheses, structures, properties and applications as single source precursors for metal sulfide materials of Group 11 and 13 metal selenocarboxylates

11. Ms. Tian Lu – Single Source Precursor Chemistry of binary and ternary sulfides

12. Ms. Leong Wei Lee – Supramolecular compounds containing N-(2-pyridylmethyl)-aminoacids

13. Mr. Puthan Peedikakkal Abdul Malik – Stacking of double bonds for photodimerization reactions.

 

List of BSc Honours Students Supervised at NUS

1.   Mr. Chng Kok Poh Andy (2005) – Synthesis and complexation of multidentate ligands to cadmium(II) and silver(I)

2.   Mr. Lim Bee Chin (2005) – Synthesis of [(2,2’-bipy)(Cd(SC{O}(CH2)12CH­3] and formation of 1D Cadmium sulphide nanocrystals

3.   Mr. Tan Han Yao (2004) – Single-source approach toward the syntheis of Bi2S3 nanocrystals of various shapes

4.   Ms. Tey Szu Lui (2004) - Single precursor routes to double oxide related battery materials

5.   Mr. Lek Gim Chye (2004) - Synthesis and characterisation of orthometallated complexes containing reduced Schiff base ligands (Co-supervisor: Prof. Leung Pak Hing).

6.   Ms. Toh Ni Lian (2004) - In search of water clusters in inorganic solid-state structures

7.   Mr. Ong Tien Teng (2003) - Design and synthesis of metal thiocarboxylates as single source precursors for binary and ternary metal sulfides

8.   Ms. Sng Seow Peng (2003), “Chemical Vapor Deposition of Molybdenum Disulfide Thin Film (Main supervisor: Dr. Loh Kian Ping)

9.   Ms. Soh Xiao Fen (2003) - Structural magnetic and biomimetic properties of binary and ternary reduced Schiff base complexes of Cu(II)

10. Ms. Kee Koh Kheng (2003) - Heterogenous reaction route to CuInE2 (E = S or Se) thin films by CVD techniques (Co-supervisor: Dr. Loh Kian Ping)

11. Ms. Lee Sie Huey (2003) - Synthesis of PbS nanoparticles using single-source precursor (Main supervisor: Dr. Chin Wee Shong)

12. Mr. Ng Meng Tack (2002) - Reactivity of Group 12 metal salts towards N-donor spacer ligands and other linkers

13. Ms. Tai Xiang (Applied Chemistry, 2002) - Synthesis of bimetallic thiocarboxylates of Group 11 and Group 13 metals - Precursors for the most efficient solar cells

14. Ms. Lim Chin Tee (1999) - Synthesis and cytotoxic properties of potential anti-cancer gold-phosphines complexes (Main supervisor: Prof. Leung Pak-Hing)

15. Ms. Rema Devy (1998) - Synthesis and characterisation of transition metal thiobenzoate complexes

 

Research Assistants in the past and present

1.   Dr. Jeyagowry T. Sampanthar (PhD Liverpool) – 1997-99. Left to work as a PI at the Institute of Chemical and Engineering Science, Singapore.

2.   Dr. C.V. Amburose (PhD IIT Delhi) - June-December, 2000. Left for the USA to do postdoctoral research.

3.   Dr. T.C. Deivaraj (PhD, NUS) – July 2001 – March 2002. Left my group to work as a postdoctoral fellow at the Singapore MIT-Alliance project, Department of Chemical and Bioengineering, NUS

4.   Dr. Sebastian Muthu (PhD, NUS) – December 2002 – April 2003. Left my group to work as a postdoctoral fellow at the Institute of Chemical Engineering Sciences, Singapore.

5.   Dr. M. Vetrichelvan (PhD, NUS) – May 2002 – April 2003. Left to work as a postdoctoral fellow at the Singapore MIT-Alliance project, Department of Chemical and Bioengineering, NUS.

6.   Dr. Suman Mukhopadhyay (Phd, IACS, Jadavpur, India) – November 2003 – March 2004. Back to work as a Pool Officer at the Indian Association for the Cultivation of Sciences, Jadavpur, Kolkata, India.

7.   Dr. Mangayarkarasi Nagarathinum (PhD University of Hyderabad, India) – June 2004 – April 2006.

 

Part Time Student Assistants

1.   Benedict Tan Kim Peng (2002). Left to work at Schering-Plough, Singapore.

2.   Ng Meng Tack (2002).  Continuing PhD under my supervision.

3.   Tey Szu Lui (2005). Continuing MSc in Industrial Engineering at NUS.

4.   Lim Bee Chin (2005). Continuing BSc(Hons) at NUS.
 

High School, Junior College and Undergraduate Students Trained

1.   Undergraduate Research Opportunities Programme in Science (UROPS) – 8 students, 1999-2006.

2.   Student Research Programme (SRP) – 7 Students from Junior Colleges, since 1998

3.   Science Mentorship Programme (SMP) – 4 students from Raffles Institution, 2001.

4.   Science Mentorship Programme (SMP) – 2 students from Nayang Girls’ High School, 2004.

5.   Special Programme in Science (SPS) – 3 students (with co-supervision of Chin Wee Chong), 2000.

6.   Mentornet Programme, Hwa Chong Junior College, Singapore – 13 students, 1997-1999.

 

 

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