Single-crystal to single-crystal phase transitions of bis(N- phenylisonicotinamide)silver(I) nitrate reveal cooperativity properties in porous molecular materials

Article abstract of DOI:10.1039/b616502h

Two single-crystal to single-crystal phase transitions in trans-[Ag(NPI)₂](NO₃)·2CH₃OH (1a), (NPI = N-phenylisonicotinamide) were characterized with X-ray crystallography; the first transition is reversible and arises from a desolvation transition induced by vacuum and generated 1b; the second transition was induced by heat at 140°C and generated 1c. The Royal Society of Chemistry.

Full text of DOI:10.1039/b616502h

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Single-crystal to single-crystal phase transitions of
bis(N-phenylisonicotinamide)silver(I) nitrate reveal cooperativity
properties in porous molecular materials{
Partha S. Mukherjee,a Nazario Lopez,b Atta M. Arif,c Francisco Cervantes-Leeb and Juan C. Noveron*b
Received (in Austin, TX, USA) 13th November 2006, Accepted 9th January 2007
First published as an Advance Article on the web 30th January 2007
DOI: 10.1039/b616502h
The NPI ligand was made by the stoichiometric reaction of
isonicotinic acid chloride, aniline and triethylamine in chloroform.
The Ag-complex was prepared by slow evaporation of a mixture
of the nitrate salt of Ag(I) and NPI in methanol over two days to
yield a crystalline batch (93%) of product. Single-crystal X-ray
crystallographic studies and elemental analysis revealed structure
1a, Scheme 1, with the molecular formulation of trans-
[Ag(NPI)2](NO3)?2CH3OH.17a
Two single-crystal to single-crystal phase transitions in trans-
[Ag(NPI)2](NO3)?2CH3OH (1a), (NPI = N-phenylisonicotin-
amide) were characterized with X-ray crystallography; the first
transition is reversible and arises from a desolvation transition
induced by vacuum and generated 1b; the second transition was
induced by heat at 140 uC and generated 1c.
Recent progress in crystal engineering has expanded into under-
standing the relationship between single-crystal structure and
structural dynamism with respect to non-covalent interactions.1–12
Of particular interest are phase transitions of porous materials
because of their implications to numerous applications such as
separation science, catalysis, sensing, and gas storage.6–12 Recently,
it was demonstrated that open channels in solids are not
necessarily a requirement for the solid to behave as a porous
material. Dynamic cooperativity in the ensemble may transport
guest molecules into the crystal matrix, even in the absence of
traditional open channels.13–15 This new paradigm for what is a
porous material is intriguing and represents a new facet in crystal
engineering that could play a role in functional materials design.
Here we report two single-crystal to single-crystal phase transfor-
mations of a porous crystalline material derived from [AgL2]NO3,
where L = N-phenylisonicotinamide (NPI), studied with single-
crystal X-ray crystallography and differential scanning calorimetry
(DSC). The first transition was induced by vacuum and involves a
desolvation/solvation process in which the pores of the crystalline
framework close and open reversibly, and the second transition
was induced by heat and generated an irreversible thermodyna-
mically stable crystal phase, Scheme 1.
˚
The supramolecular structure of 1a exhibits channels (8 A in
diameter) filled with methanol molecules along the a-axis, Fig. 1.
There are four types of hydrogen bonds in the unit cell of
which two are between the ligand and solvent in the form of
…
…
N–H(amide) O(methanol) and OLC(amide) HO(methanol)
˚
with average distances of 2.88 and 2.86 A, respectively, and
˚
between adjacent methanol molecules (2.73 A), and NPI with
…
nitrate ions via N–H(amide) O(nitrate), 2.99 A. The average
˚
˚
distance between the nearest Ag centers is 3.31 A, which is
significantly longer than other crystals with suspected Ag–Ag
interactions such as silver acetate (2.79 A).18 The average distance
˚
˚
between Ag(I) and the nearest nitrate ion is 2.64 A. The bond angle
of N(1)–Ag–N(3) is 158u, which is smaller than those present in
analogous Ag-complexes (169u).19 Despite the expected planar
structure of NPI, 1a reveals that the ligand twist half way forming
a torsion angle at C(2)–C(3)–C(6)–N(2) of 45u and its homologous
in the same complex of 31u, presumably induced by the hydrogen
bonds and the crystal packing forces.
When single crystals of 1a are placed under vacuum (0.1 Torr)
for 2 h a new metastable crystal phase (1b) was observed via single-
crystal X-ray crystallography, Fig. 2.17b The formulation of this
crystal phase is trans-[Ag(NPI)2](NO3), which lacks solvent and the
channels that once held the methanol molecules are closed,
apparently, via an orchestrated rearrangement of alternate layers
of the Ag-complex that rotate counter-clockwise by 63u towards
the a-direction. Unlike 1a, pairs of Ag-complexes in 1b interact via
…
two complementary N–H(amide) OLC(amide) hydrogen bonds
˚
that have an average distance of 2.91 A. Additionally, the nitrate
Scheme 1
ions bridge adjacent pairs of Ag-complexes via hydrogen bonds
…
˚
with N–H(amide) O(nitrate) average distance 2.94 A, and their
aDepartment of Inorganic and Physical Chemistry, Indian Institute of
Science, Bangalore, 560012, India
˚
average distances to Ag centers are 2.80 and 2.68 A. Interestingly,
there are no significant changes in the torsion angles of the NPI
moieties (,2u), but the bond angle of N(1)–Ag–N(3) changed to
173u. In addition, face-edge interactions between phenyl moieties
of NPI are observed. The crystal phase 1b may be described as a
metastable pseudo-polymorph of 1a.20
bDepartment of Chemistry, University of Texas at El Paso, El Paso, TX,
79968-0513, USA. E-mail: jcnoveron@utep.edu; Fax: (915)747-5748;
Tel: (915) 747-7572
cDepartment of Chemistry, University of Utah, Salt Lake City, UT,
87764, USA
{ Electronic supplementary information (ESI) available: Crystallographic
data of 1a–c and detailed experimental preparations. See DOI: 10.1039/
b616502h
The phase transition of 1a A 1b was examined with DSC and
an endothermic DH value of 7.3 ¡ 0.2 kJ mol21 was obtained at
This journal is ß The Royal Society of Chemistry 2007
Chem. Commun., 2007, 1433–1435 | 1433

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Fig. 1 (a) Thermal ellipsoid plot (probability level 50%) of [Ag(NPI)2]2. (b) Expanded unit cell of 1a as viewed from the a-direction. Methanol and Ag
shown as CPK.
305 K. When crystals of 1b are exposed to methanol, they revert
back to phase 1a, as indicated by X-ray powder diffraction and
elemental analysis. Similar solvent-driven reversible transforma-
tions have been observed in other systems. Although the crystalline
phase of 1b lacks any imminent porosity, the fact that it can take
up methanol to reconstitute 1a suggests a well-orchestrated
mechanism reminiscent of cooperativity dynamics. This behavior
is consistent with other recent crystals that lack porosity, but yet
they are able to incorporate guest molecules into their lattice via
cooperativity effects.14–16
When crystals of either 1a or 1b are heated slowly (5 uC min21
)
to higher temperatures, there is a second phase change around
453 K with an endothermic DH value of 16.5 ¡ 0.3 kJ mol21. This
new phase change also occurs with the preservation of the single-
crystal quality of the material forming a new crystal phase, 1c,17c
with molecular formula trans-[Ag(NPI)2](NO3), Fig. 3. Single-
crystal X-ray crystallography studies on 1c revealed that the Ag-
complexes interact primarily via p–p stacking interactions and
pack in columns along the c-axis. The nitrate ions hydrogen bond
Fig. 2 Expanded unit cell of 1b as viewed from the a-direction.
1434 | Chem. Commun., 2007, 1433–1435
Fig. 3 Expanded unit cell of 1c as viewed from the a-direction.
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…
9 S. Noro, R. Kitaura, M. Kondo, S. Kitagawa, T. Ishii, H. Matsuzaka
and M. Yamashita, J. Am. Chem. Soc., 2002, 124, 2568–2583.
10 S. S.-Y. Chui, S. M.-F. Lo, J. P. H. Charmant, A. G. Orpen and
I. D. Williams, Science, 1999, 283, 1148–1150.
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8319–8320.
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to the columnar Ag-complexes via N–H(amide) O(nitrate),
˚
(2.92 A). The NPI ligand moieties become more planar on one
side of the complex, which exhibits a torsion angle C(16)–C(15)–
C(18)–N(4) of 4u (vs. 45u in 1a), while the other side undergoes
little change (33u). On the other hand, no significant changes occur
in the bond angle of N(1)–Ag–N(3) (,2u). In contrast to 1b,
crystalline samples of 1c do not uptake methanol and with further
heating decompose above 270 uC.
In summary, we reported the single-crystal to single-crystal
phase transformations of the Ag-complex 1a to the pseudopoly-
morphic phases 1b and 1c, which were induced by vacuum and by
heat, respectively. The results indicated that each phase transition
was accompanied by changes in intermolecular hydrogen bonding
and p–p stacking interactions, which may have played a role in
orchestrating the structural changes in the crystal lattice and
maintaining single-crystal quality. The study of phase transforma-
tions in designed crystals will eventually lead to practical materials
with flexible and dynamic frameworks that can switch their
structure upon external stimuli with well-defined molecular
motions in the solid state.
15 J. C. Noveron, A. M. Arif and P. J. Stang, Chem. Mater., 2003, 15,
372–374.
16 C. J. Kepert, T. J. Prior and M. J. Rosseinsky, J. Am. Chem. Soc., 2000,
122, 5158–5168.
17 (a) Crystal data for 1a: C26 H28N5O7Ag, Mr = 630.40, colorless plates of
¯
dimensions 0.30 6 0.25 6 0.05 mm, triclinic, space group P1, a =
˚
8.72340(10), b = 9.6897(3), c = 16.9513(5) A, a = 74.6602(12),
3
˚
b = 76.7586(16), c = 76.8878(16)u, V = 1323.80(6) A , Z = 2, Dc =
1.582 Mg m23. A total of 9546 reflections were measured, of which 5982
were unique. Final residuals were R1 = 0.0283 and wR2 = 0.0614; (b)
Crystal data for 1b: C24H20N5O5Ag, Mr = 566.32, colorless plates of
dimensions 0.25 6 0.25 6 0.08, monoclinic, space group P21/c, a =
˚
12.7187(6), b = 8.4330(2), c = 21.2767(9) A, b = 98.2743(17)u, V =
2258.32(15) A , Z = 4, Dc = 1.666 Mg m23. A total of 9388 reflections
3
˚
were measured, of which 5111 were unique. Final residuals were R1 =
0.0371 and wR2 = 0.0703; (c) Crystal data for 1c: C24H20N5O5Ag, Mr =
566.32, colorless plates of dimensions 0.25 6 0.10 6 0.10, monoclinic,
We gratefully acknowledge Prof. Peter J. Stang for helpful
discussions and Prof. Charles A. Wight for assistance with the
DSC. Financial support for N. L. by the Border Health Research
Fund from the University of Texas at El Paso is gratefully
acknowledged.
˚
space group P21/c, a = 8.8731(10), b = 36.1311(5), c = 13.9696(2) A, b =
93.3705(5)u, V = 4470.83(10) A , Z = 8, Dc = 1.683 Mg m23. A total of
3
˚
19602 reflections were measured, of which 10777 were unique. Final
residuals were R1 = 0.0414 and wR2 = 0.0747. The data for all
structures were collected at 150(1) K on a Nonius Kappa CCD
˚
diffractometer equipped with Mo-Ka radiation (l = 0.71073 A).
References
Structure refinements by full-matrix least-squares on F2 and Fourier
Transform techniques and location of hydrogen atoms and their
isotropically refinement was done using SHELXTL-97 (Bruker-AXS,
Inc. Madison, WI). Further crystallographic data can be obtained from
the ESI.{ CCDC 627373–627375. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/b616502h.
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