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| T. N.
Guru Row |
| Ph. D (IISc) |
| Professor |
| Chairman |
| e-mail : ssctng@sscu.iisc.ernet.in |
| phone : +91-80-2293 2796 |
| fax : +91-80-2360 1310 |
| Internet : http://144.16.75.32 |
or
| or |
| Internet : http://10.96.13.12 |
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| Chemical Crystallography and Materials
Design: |
| Since
the inception of this group in 1989, the emphasis has been on two
broad areas of structural chemistry viz. High resolution Powder Diffraction
and Crystal Engineering. |
| Rietveld
refinements, Phase transitions and ab-initio structures |
| Studies
on the structure-function correlation in complex inorganic oxides,
sulfates and phosphates have been carried out using high-resolution
data collected on a STOE/STADI-P powder diffractometer with a variable
temperature gadget along with a cryo-stream facility. Most of these
data sets have been subjected to Rietveld refinement based on existing
starting models from data bases or from deriving starting models using
a variety of approaches including ab
initio structure solution using direct methods. These studies
have clearly demonstrated that the Rietveld approach is best suited
in case the models are as complete as possible and very close to the
final structure. Some initial attempts have been made to obtain starting
models from MD simulations. |
| Some
of the results obtained in these analyses are (i) An approach akin
to isomorphous replacement to locate quantitatively the position and
occupancy of heavy elements in complex oxides (ii) structure determination
and refinement of La4BaCu5O12 using
space group symmetry principles, (iii) Analysis of phase transitions
in CsHSO4 and (NH4)3H(SO4)2
and complete structure elucidation at elevated temperatures using
appropriate models in Rietveld strategy, (v) A novel approach for
the study of stabilization via doping using Rietveld and Micro-structural
analysis in complex oxides and (iv) ab initio structure of polymorphs
of a new class of oxide ion conductors in solid solution of Na2O-Bi2O3-V2O5
ternary system and n=4 family of Aurivillius oxides. |
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| Weak interactions involving organic
fluorine: |
| Fluorine as a steering Agent: |
| The
correlation between the reactive molecular arrangement in crystals
and the configuration of the photoproduct which results upon irradiation
lead to the classification of dimers as α, β and γ
based on the geometrical disposition of the individual monomers. The
α - modification leads to centrosymmetric dimerization across
the double bond, the β leads to mirror symmetric dimers across
the double bond and the γ, which has a double bond separation
distance of greater than 4.2 Å, remains unreactive. Generally,
centrosymmetric dimerisation is observed. Substitution by halogens
other than fluorine has shown that the molecules are steered to mirror
symmetric orientations and is the preferred mode. Systematic X-ray
structural investigations followed by photo dimerization studies on
fluoro substituted coumarins, styryl coumarins and butadienes have
revealed that the steering effect of fluorine to orient molecules
in the packing mode is dominant in the absence of other weak intermolecular
interactions. The possible role of C-H...F interaction, if any, is
very weak and is less dominant that even C=O...interactions. |
| A
large number of structures depicting interactions like C-H...F, C-F...[Trial
mode] and F...F have been studied and it is established that interactions
involving organic fluorine indeed prefer not to have hydrogen bonding. |
| Charge density analysis towards
crystal engineering: |
 The
understanding of molecular structure and bonding via high-resolution
X-ray diffraction studies is of fundamental importance in chemistry.
The study of interactions involving organic fluorine is of particular
interest and three systems 7-fluoro styryl coumarin, 5-fluorouracil
and 1,3, dimethyle-5-fluorouracil have been studied to evaluate interactions
of the type F...F, C-H...F and C-F... π respectively. Data sets
from SRS, Daresbury, UK and from conventional X-ray CCD facility at
Enraf-Nonius have been analyzed and topological properties have been
derived. The inputs are correlated to engineer motifs for specific
interactions involving fluorine. |
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| Towards the generation of novel
organic SHG materials: |
| The
construction of multi-molecular hydrogen bonded template forms the
basic design element in the generation of new, novel organic SHG materials.
A large number of networks built on hydrogen bonded tartrates and
polarizable cations (mainly amines) have been examined based on the
crystal structures determined by single crystal x-ray diffraction
and other cognate techniques in this context. These acid-base salts
show SHG (Second Harmonic Generation) activities comparable to that
of urea. The tartrate frameworks provide conformationally rigid blocks
and the SHG depends on the nature of the framework, which decides
the orientation of the anilinium cations. These salts can be classified
into three categories: Type I which occurs more frequently has its
SHG restricted to the value corresponding to the spacer units that
build up the network. The most significant result is that the incorporation
of cations with reasonably large molecular hyper-polarizabilities
would not lead to the formation of materials with a large SHG. However,
the value of SHG could become large in Type II cases, which are only
a few in numbers so far, where the frameworks are generally flexible.
Type III is a category in which the framework is completely absent
and the SHG has no bearing on the building units. |
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| Polymorphism in drugs and pharmaceuticals: |
| The
control of nucleation and growth of molecular crystals by using tailor
made auxiliaries lead to the possible generation of polymorphs. At
present, several experiments like monitoring the growth of faces using
a polarizing microscope, evaluation from X-ray diffraction experiments
and other related techniques of the potential usage of this method
for the generation of new polymorphic modifications in drugs and pharmaceuticals
is being explored. |
| A
large number of drugs and pharmaceuticals contain fluorine and a systematic
evaluation of the potential of weak interactions is being utilized
to generate new polymorphs. A series of anti-fertility compounds designed
to produce specific, pre-defined interactions involving fluorine have
been solved. |
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| Representative
publications |
| 1. |
|
G.Nalini, R. Somashekar, T.
N. Guru Row, X-ray structure refinements and strain analysis
of substituted cubic lead pyrochlores Pb2M(2-y)Pb2O
(0.0<Y<0.8; M = Nb or Ta),
J. Solid State Chem. 156
(2001) 207. |
| 2. |
|
K. Vishnu Murthy, T.
N. Guru Row and K. Venkatesan “Observations on
the Photochemical Behavior of Coumarins and Related Systems
in the Crystalline Stat" Understanding and Manipulating
Excited oState Processes, edited by V. Ramamurthy
and K.S.Schanze, Molecular and Supramolecular
Photochemistry , Marcel Dekker, Inc., 8
(2001) 427. |
| 3. |
|
D. G. Porob and T.
N. Guru Row, A novel oxide ion conductor in doped Bi2O3-V2O5
system: Ab initio structure of NaBi3V2O10
via powder X-ray diffraction, Chem.
Mater. 12 (2001)
3658. |
| 4. |
|
P. R. Mallinson, G. Barr,
S. J. Coles, T. N. Guru Row,
D. D. MacNicol, S. J. Teat and K. Wozniak, Charge densities
from high-resolution synchrotron X-ray diffraction experiments,
J. Synchrotron Rad. 7
(2000) 160. |
| 5. |
|
M. D. Prasanna and T.
N. Guru Row, C-halogen[Trial mode] interactions and their
influence on molecular conformation and crystal packing: A database
analysis, Cryst. Engg. 3
(2000) 135. |
| 6. |
|
M. D. Prasanna and T.
N. Guru Row, Analysis of weak interactions involving
fluorine: a comparative study of crystal packing of some benzodiazepinone
drug intermediates and their non-fluorinated analogues, CrystEngComm
(2000) 25. |
| 7. |
|
T.N.
Guru Row, Hydrogen and Fluorine in crystal engineering:
Systematics from crystallographic studies of hydrogen bonded
tartrate-amine complexes and fluoro- substituted coumarins,
styryl coumarins and butadienes, Coordination
Chemistry reviews 183 (1999)
81. |
| 8. |
|
R. Kadirvelraj, S. Bhattacharya,
T. N. Guru Row; Materials
with conserved hydrogen bonded anionic motifs: Implications
on SHG; J. Incl. Phenom. and Molecular
Recognition 4 (1998)
321. |
| 9. |
|
K.Sooryanarayana, R Somashekar
and T N Guru Row; Mechanistics
of Stabilization via Doping in Bismuthsesquioxide (Bi2-2xHo2xO3
; x = 0.2): A Combined Approach of Rietveld and Micro Structural
Analysis ; Solid State Ionics 104
(1997) 319. |
| 10. |
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K.Sooryanarayana and T.N.Guru
Row; Phase transitions in Tri ammonium hydrogen disulfate:
Crystal structures at -110oC and +140oC., Phase
Transitions 58 (1996)
263. |
| 11. |
|
R. Kadirvelraj, A.M. Umarji,
W.T. Robinson, S. Bhattacharya, T.N.
Guru Row; A systematic crystallographic investigation
of hydrogen bonded networks involving monohydrogen tartrate-amine
complexes: Potential materials for nonlinear optics; Chem.
Mater. 8 (1998) 2313.
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| 12. |
|
N. Rangavittal, G.N. Subbanna,
T.N. Guru Row, and C.N.R.
Rao.; An Investigation of insulating La4BaCu5O12
obtained by reduction of metallic La4BaCu5O13.1;
J .Solid.State Chem. 114
(1995) 95. |
| 13. |
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S. Bhattacharya, P. Dastidar
and T.N. Guru Row.; Hydrogen
bond directed self-assembly of D(+)-Dibenzoyl Tartaric acid
and 4-amino-pyridine: Optical non linearities and stoichiometry
dependent novel structural features; Chem.
Mater. 4 (1994) 531.
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| 14. |
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N. Rangavittal, T.N.
Guru Row and C.N.R. Rao.; Location of rare earths in
isomorphous series of complex oxides: (a)La3LnBaCu5O13
(Ln=Nd, Gd, Y) and (b)LnBa2Cu3O7(Ln=Y,
Nd, Pr, Gd, Dy) by employing difference fourier synthesis based
on Powder profile analysis. J. Appl.Cryst.
28 (1993) 363. |
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