Generation of an equilibrating collection of crystalline solids from a dynamic combinational library

Article abstract of DOI:10.1021/ic034176o

Thermodynamically controlled crystallization of a copper-containing building block [CuL] (H₂L = 2-(2′- hydroxyphenyl)-Δ ²-thiazoline-4-carboxylic acid) from a methanol-ethanol mixture solvent leads to a combinatorial mixture of four crystalline solids, from which each of them is isolated and structurally characterized.

Full text of DOI:10.1021/ic034176o

Inorg. Chem. 2003, 42, 5453−5455
Generation of an Equilibrating Collection of Crystalline Solids from a
Dynamic Combinational Library
Ke-liang Pang, Dong Guo, Chun-ying Duan,* Hong Mo, and Qing-jin Meng*
Coordination Chemistry Institute, the State Key Laboratory of Coordination Chemistry,
Nanjing UniVersity, Nanjing, 210093, P. R. China
Received February 17, 2003
Scheme 1
Thermodynamically controlled crystallization of a copper-containing
building block [CuL] (H L ) 2-(2′-hydroxyphenyl)-∆2-thiazoline-4-
2
carboxylic acid) from a methanol−ethanol mixture solvent leads
to a combinatorial mixture of four crystalline solids, from which
each of them is isolated and structurally characterized.
The recent surge in research devoted to designing crystal-
line solids with molecules that encode well-defined nonco-
valent motifs is spawned by a fundamental interest in the
development of new approaches to the prediction of crystal
structures and has subsequently been fueled by the practical
opportunities that are offered by new classes of functional
materials.1-3 In order to design species of crystalline solids
presenting specific structural and functional features, it is
of great importance to establish rules by which control of
the molecular packing process can be achieved through
chemical programming. Crystallization of compounds from
mixed solvent, containing preferentially one out of a wide
range of possible crystalline solids, provides an opportunity
for studying how the solvent influences the product distribu-
tion and thus the molecular packing pathway.
combinatorial chemistry (DCC) of crystal engineering,
making potentially available a wide variety of combinations
representing the members of a virtual combinatorial library
(VCL).4,5 Of special interest is then the possibility to select
and express a given member of the VCL for specific
purposes, by means of changing the external factors such as
evaporating the solvent. We present here the crystallization
of a copper-containing building block [CuL] (H2L ) 2-(2′-
hydroxyphenyl)-∆2-thiazoline-4-carboxylic acid6) in methanol-
ethanol (1:1) solvent. From this solution were generated four
crystalline solids, and all of them were isolated in the solid
state by careful evaporation of the solution in air.
On the other hand, crystallization of compounds from
mixed solvent may yield a mixture of crystalline solids
resulting from the reversible combination of different
constituents. Such a situation represents a process of dynamic
Reaction of the ligand H2L with Cu(OAc)2‚4H2O in
methanol-ethanol (1:1) solvent gives a green solution
(Scheme 1). After careful evaporation of the solution in
air for a few days, green crystals with a strip shape were
formed, 1. After evaporation of the solution for another
few days, the crystalline solids of compound 1 disappeared.
* To whom correspondence should be addressed. E-mail: duancy@
nju.edu.cn.
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10.1021/ic034176o CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/01/2003
Inorganic Chemistry, Vol. 42, No. 18, 2003 5453

COMMUNICATION
Figure 1. Crystal structure of 1 showing the one-dimensional chain
cooperated by weak coordination bonds and hydrogen bonds.
As an alternative, rhomboid crystals were formed, 2.
Elemental7 and crystal structure analyses8 clearly indicate
that the two kinds of crystals correspond to two different
materials.
Figure 2. Crystal structure of 2 showing the two-dimensional channeled
structure.
Compound 1 crystallizes in centrosymmetric space group
Pbca, and the basic building block for crystal packing is a
dicopper [CuL(MeOH)]2 unit. Since the center of the dimeric
unit occupies the inversion center, consequently the mol-
ecules occur as nonchiral of ∆-Λ configuration for the two
copper centers and R-S configuration for the two chiral
carbon centers. The copper atom is coordinated in a
pyramidal manner with the NO2 tridentate donors of the
ligand and a phenyl oxygen atom from another ligand of
the dimer forming the equatorial plane, while the oxygen
atom of the methanol molecule occupies the apical position.
The uncoordinated carboxyl oxygen atom from another
dimeric unit contacts the copper atom with a weak coordina-
tion bond connecting the dimeric units into a one-dimensional
chain (Figure 1). Hydrogen bonds between the oxygen atoms
in methanol molecules and the oxygen atoms are also found
to stabilize the molecular aggregation.
Figure 3. Powder X-ray pattern of the residue formed fresh (a), after
standing for a few days (b), and after standing for a month (c).
Compound 2 is a two-dimensional channel structure
(Figure 2) based on the dimeric unit [CuL(CH3CH2OH)]2.
The copper atom is coordinated in a lengthened octahedral
geometry with the NO2 tridentate donors of the ligand and
a phenyl oxygen atom from another ligand of the dimer
forming the equatorial plane. The oxygen atom of the ethanol
molecule and the carboxyl oxygen atom from another
molecule occupy the axial positions, thus the dimeric units
are further connected into a two-dimensional network with
channels. Ethanol molecules are included in the channels.
Classic O-H‚‚‚O hydrogen bonds between the oxygen atoms
of ethanol molecules and the oxygen atoms in carboxyl
groups are also found to be important in stabilizing the two-
dimensional network.
Figure 4. Powder X-ray patterns of the four crystalline solids calculated
from the single-crystal structure.
To further evaluate the solvent-dependent crystallization
of this system, the solution, with crystals of compound 2 in
it, was evaporated until almost dry. The precipitate formed
was studied using powder X-ray diffraction analysis (Figure
3a). It is surprising to find that the residue does not exhibit
any peak corresponding to either compound 1 or 2 (Figure
4).
Crystal structure and elemental analyses9 clearly indicate
that the residue is a water-coordinated copper compound, 3.
After standing for another few days, powder X-ray diffraction
of the residue (Figure 3b) reveals that, in addition to
compound 3, another new compound 4 was formed. One
month later, powder X-ray diffraction (Figure 3c) of the last
residue clearly reveals that compound 3 disappeared, and
compound 410 was isolated. It is also interesting to note that
(7) For compound 1, calculated for (C10H7NO3S)Cu(CH3OH): C, 41.7;
H, 3.5; N, 4.4. Found: C, 41.1; H, 3.8; N, 4.1. For compound 2,
calculated for (C10H7NO3S)Cu(C2H5OH): C, 43.6; H, 4.0; N, 4.2.
Found: C, 43.3; H, 4.1; N, 3.9.
(8) Crystal structure of 1, C11H11NO4SCu: Mr ) 316.81 g‚mol-1
,
orthorhombic, space group Pbca, a ) 16.411(3) Å, b ) 7.482(1) Å,
c ) 19.545(3) Å, V ) 2399.7(7) Å3, Z ) 8, T ) 293K, µ ) 1.999
mm-1, 10969 unique reflections were collected on a Bruker CCD
SMART system,12 R1 ) 0.049, and wR2 ) 0.082 for 2118 reflections
with I > 2σ(I). Crystal structure of 2, C12H13NO4SCu: Mr ) 330.83
g‚mol-1, monoclinic, space group C2/c, a ) 23.175(7) Å, b ) 7.431-
(4) Å, c ) 14.542(16) Å, â ) 93.67(2)°, V ) 2499(3) Å3, Z ) 8, T
) 293K, µ ) 1.923 mm-1, 5133 unique reflections were collected on
a Siemens P4 system,13 R1 ) 0.069, and wR2 ) 0.191 for 2212
reflections with I > 2σ(I). The structures were solved by direct methods
and refined on F2 using full-matrix least-squares methods using
SHELXTL version 5.1.14 Anisotropic thermal parameters were refined
for non-hydrogen atoms. Hydrogen atoms were localized in their
calculation positions and refined using a riding model.
(9) For compound 3. Calculated for C10H13NO6SCu: C, 35.4; H, 3.9; N,
4.1. Found: C, 35.4; H, 4.1; N, 4.1. Crystal structure of 3, C10H13-
NO6SCu: Mr ) 338.81 g‚mol-1, monoclinic, space group P21/c, a )
13.876(2) Å, b ) 5.543(1) Å, c ) 16.389(2) Å, â ) 97.80(1)°, V )
1249.0(3) Å3, Z ) 4, T ) 293K, µ ) 1.938 mm-1, 5869 unique
reflections were collected on a Bruker CCD SMART system, R1 )
0.034, and wR2 ) 0.096 for 2203 reflections with I > 2σ(I).
5454 Inorganic Chemistry, Vol. 42, No. 18, 2003

COMMUNICATION
In compound 4, the apical water molecule serves as a
bridge to form a dimeric copper unit. Extensive hydrogen
bonds are found to link the molecules together, forming a
two-dimensional hydrogen-bonding sandwichlike sheet. The
inner layer is formed by the CuNO4 units and water
molecules linked through hydrogen bonds, and the two outer
layers are consist of sulfur atoms and phenyl rings.
Crystal engineeringsthe planning and construction of
crystalline supramolecular architectures from modular build-
ing blocksspermits the rational design of functional molec-
ular materials that exhibit technologically useful behavior11
such as conductivity, superconductivity, ferromagnetism, and
nonlinear optical properties. Crystallization of a copper-
containing compound in methanol-ethanol (1:1) solvents
generates in an equilibrating mixture of four crystalline
solids, from which each of them is isolated. These features
represent an alternative illustration of a dynamic combina-
torial chemistry process. Such a result is quite interesting
with respect to crystal engineering and the investigation of
the factors that dictate the solid-state selection process.
Figure 5. Crystal structure of compound 3 showing the two-dimensional
layered structure.
Acknowledgment. This work was supported by the
National Natural Science Foundation of China (No. 20131020).
We also thank Mr. Liu Yong-jiang for collecting the crystal
data.
Figure 6. Crystal structure of compound 4 showing the two-dimensional
layered structure.
after compound 3 or 4 is dissolved in a methanol-ethanol
(1:1) mixture solvent and the solution carefully evaporated
again, a new cycle of the crystallization takes place.
Both compounds 3 and 4 have two-dimensional hydrogen-
bonded layered structures (Figures 5 and 6). The copper
centers in the two compounds have tetragonal pyramidal
geometry with the N2O planar tridentate ligand and one water
molecule forming the basal plane and another water molecule
occupying the apical position.
Supporting Information Available: Complete synthetic
procedure and tables of crystal structure data in CIF format. This
material is available free of charge via the Internet at
http://pubs.acs.org.
IC034176O
(11) (a) Coronado, E.; Gala´n-Mascaro´s, J. R.; Go´mez-Garc´ıa, C. J.; Laukhin,
V. Nature 2000, 408, 447. (b) Miller, J. S.; Epstein, A. J. Angew.
Chem., Int. Ed. Engl. 1994, 33, 385. (c) Zyss, J. Molecular Nonlinear
Optics; Academic: New York, 1994.
(12) SMART and SAINT. Area Detector Control and Integration Software;
Siemens Analytical X-Ray Systems, Inc.: Madison, WI, 1996.
(13) XSCANS, version 2.1; Siemens Analytical X-ray Instruments, Inc.:
Madison, WI, 1994.
(10) For compound 4. Calculated for C20H24N2O11S2Cu2: C, 36.4; H, 3.7;
N, 4.2. Found: C, 36.5; H, 3.8; N, 4.2. Crystal structure of 4,
C20H24N2O11S2Cu2: Mr ) 659.61 g‚mol-1, orthorhombic, space group
Pbcn, a ) 5.635(1) Å, b ) 15.872(2) Å, c ) 26.691(3) Å, V ) 2387.0-
(4) Å3, Z ) 4, T ) 293K, µ ) 2.022 mm-1, 10185 unique reflections
were collected on a Bruker CCD SMART system, R1 ) 0.037, and
wR2 ) 0.084 for 2107 reflections with I > 2σ(I).
(14) Sheldrick, G. M. SHELXTL V5.1 Software Reference Manual; Bruker
AXS, Inc.: Madison, WI, 1997.
Inorganic Chemistry, Vol. 42, No. 18, 2003 5455