[sdpd] New SDPD (or whatever) record ~702.000 A**3

[Armel Le Bail <alb...@cristal.org>]

Hi,

New giant structure (solved by "direct access" method from
powder data) by "combined targeted chemistry and computational
design."

Cubic with a ~ 89 A,
V ~702.000 A**3.

Férey et al., A Chromium Terephthalate-Based Solid with Unusually Large 
Pore Volumes and S..., Science 2005 309: 2040-2042
http://www.sciencemag.org/cgi/content/full/309/5743/2040

Method description :

"...the first step in our tailormade
approach is to control the nature of the
inorganic cluster and the chemical conditions
required for its formation and stability in
solution. In the second step, we use computational
strategies, typically our global optimization
AASBU (automated assembly of
secondary building units) method, as
recently adapted to hybrids, or other
closely related methods. The AASBU
method explores how an inorganic cluster and
an organic linker, or even predefined hybrid
building blocks, may connect in 3D space to
form periodic lattices. A virtual library of candidate
frameworks is produced, along with their
crystallographic features (space group, cell parameters,
atomic coordinates) and their simulated
x-ray diffraction (XRD) patterns. The
comparison of the simulated pattern of each
candidate structure with the experimental one
identifies the targeted experimental structure,
giving direct access to the structural solution
without any recourse to single crystals. The final
structure is refined with the Rietveld method
from powder data, the guest species being localized
from Fourier difference maps. While
tackling the underlying issue of polymorphism
of hybrid materials, our computational
approach provides a direct-space tool for solving
structures that may be highly complex.
To implement our combined method,we first
determined the adequate chemical conditions
leading to the existence of trimeric
inorganic building blocks, formed by the assembly
of three octahedra sharing a m3-O common
vertex. Simulations were then performed to
combine these inorganic trimers in 3D space
with 1,3,5-benzene tricarboxylate (BTC)
through the assembly of a computationally
designed hybrid building block. Among the
various predicted crystal structures, one candidate
exhibited the same powder XRD pattern as
the powdered chromium trimesate MIL-100
(MIL, Mat2rial Institut Lavoisier), revealing
a giant cell volume (380,000 A**3) and large
pore sizes consistent with the very high surface area
measurement . This hybrid crystal structure was
then refined from synchrotron powder data, allowing
the further localization of the guest
moities. MIL-100 showed the feasibility of
creating simulation-assisted chemical structures.
With that adressed, we investigated other
carboxylates, here terephthalic acid E1,4-benzene
dicarboxylate (1,4-BDC) combined with similar
trimers. Compared to other MOFs (metalorganic
frameworks), the resulting solid, MIL-101, has the
best characteristics in terms of
cell dimensions (702,000 A**3), pore sizes (29
to 34 A), and surface area (5900 m2 gj1)."

Some comments :

- Software availability ? Nothing said.

- I propose to name the method for solution :
"direct access method", as suggested by the authors,
telling that " The comparison of the simulated pattern of
each candidate structure with the experimental one
identifies the targeted experimental structure,
giving direct access to the structural solution
without any recourse to single crystals. "

- Availability of the database of candidate structures ?
Nothing said. Let me suggest the PCOD (Predicted
Crystallography Open Database) at :
http://www.crystallography.net/pcod/
Please send CIFs.

Armel



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