Effect of the environment on molecular properties: Synthesis, structure, and photoluminescence of Cu(I) bis(2,9-dimethyl-1,10-phenanthroline) nanoclusters in eight different supramolecular frameworks

Article abstract of DOI:10.1021/ic0609709

By selection of different charge-balancing anionic frameworks and different host-to-guest ratios, the photosensitizer-dye cation [Cu(dmp)₂] ⁺ (dmp = 2,9-dimethyl-1,10-phenanthroline) has been embedded in a series of three-dimensional host structures. It occurs with variable geometry in different states of aggregation, including weakly interacting monomers, isolated dimers, columns, and layers. A large variation in its emission lifetime is correlated with the relative energy level spacings of the guest- and host-framework components. In a fully saturated host framework, the lifetime exceeds values reported for a series of conventional Cu(dmp)₂ salts.

Full text of DOI:10.1021/ic0609709

Inorg. Chem. 2006, 45, 9281−9289
Effect of the Environment on Molecular Properties: Synthesis,
Structure, and Photoluminescence of Cu(I)
Bis(2,9-dimethyl-1,10-phenanthroline) Nanoclusters in Eight Different
Supramolecular Frameworks
Shao-Liang Zheng,* Milan Gembicky, Marc Messerschmidt, Paulina M. Dominiak, and Philip Coppens*
Department of Chemistry, State UniVersity of New York at Buffalo,
Buffalo, New York 14260-3000
Received June 1, 2006
By selection of different charge-balancing anionic frameworks and different host-to-guest ratios, the photosensitizer-
dye cation [Cu(dmp)2]+ (dmp
2,9-dimethyl-1,10-phenanthroline) has been embedded in a series of three-dimensional
)
host structures. It occurs with variable geometry in different states of aggregation, including weakly interacting
monomers, isolated dimers, columns, and layers. A large variation in its emission lifetime is correlated with the
relative energy level spacings of the guest- and host-framework components. In a fully saturated host framework,
the lifetime exceeds values reported for a series of conventional Cu(dmp)2 salts.
Introduction
such as benzophenone,7 benzil,3,8 and xanthone,4 which
exhibit pronounced variations of molecular conformation. A
joint structural, theoretical, and photophysical analysis veri-
fied that the relative energy level spacings of the guest and
the host components play a crucial role in intermolecular
energy transfer in the supramolecular solids and the resulting
luminescence quenching.9
Because of the first emission and emission quenching
studies of the [Cu(dmp)2]+ (dmp ) 2,9-dimethyl-1,10-
phenanthroline) cation at room temperature in solution by
McMillin et al. in 1980,10 the photochemistry and photo-
physics of this and related systems have received extensive
attention.11 Our previous work has shown that in a series of
neat crystals the emission lifetimes of the [Cu(diimine)2]+
Supramolecular solids are of considerable interest because
of their potential applications, including separation, catalysis,
storage of sensitive compounds, and opto-magnetic materi-
als.1 They provide a well-defined environment that can be
varied by crystal engineering and thus offer an attractive
possibility to dilute and isolate molecular species in different
but periodic matrixes.2-4 Yet, the photophysical and chemical
properties of molecules embedded in supramolecular cavities
have so far received scant attention. Differences in the guest
molecule’s aggregation and the geometry of its ground and
excited states occur, which can be studied by conventional
and time-resolved diffraction methods.5,6
In preceding papers, we described a series of supramo-
lecular solids encapsulating photoactive guest molecules,
(5) (a) Coppens, P.; Novozhilova, I. V. Faraday Discuss. 2003, 122, 1-11.
(b) Coppens, P. Chem. Commun. 2003, 1317-1320. (c) Coppens, P.;
Vorontsov, I. I.; Graber, T.; Gembicky, M.; Kovalevsky, A. Yu. Acta
Crystallogr., Sect. A 2005, 61, 162-172.
(6) (a) Coppens, P.; Vorontsov, I. I.; Graber, T.; Kovalevsky, A. Yu.;
Chen, Y.-S.; Wu, G.; Gembicky, M.; Novozhilova, I. V. J. Am. Chem.
Soc. 2004, 126, 5980-5981. (b) Coppens, P.; Gerlits, O.; Vorontsov,
I. I.; Kovalevsky, A. Yu.; Chen, Y.-S.; Graber, T.; Novozhilova, I. V.
Chem. Commun. 2004, 2144-2145. (c) Vorontsov, I. I.; Kovalevsky,
A. Yu.; Chen, Y.-S.; Graber, T.; Novozhilova, I. V.; Omary, M. A.;
Coppens, P. Phys. ReV. Lett. 2005, 94, 193003.
(7) Ma, B.-Q.; Coppens, P. Crys. Growth Des. 2004, 4, 1377-1385.
(8) Ma, B.-Q.; Zhang, Y.-G.; Coppens, P. J. Org. Chem. 2003, 68, 9467-
9472.
* To whom correspondence should be addressed. E-mail: coppens@
buffalo.edu (P.C.), szheng4@buffalo.edu (S.-L.Z.).
(1) See for example: (a) Host-Guest-Systems Based on Nanoporous
Crystals; Laeri, F., Schuth, F., Simon, U., Wark, M., Eds.; John Wiley
& Sons: New York, 2003. (b) Separations and Reactions in Organic
Supramolecular Chemistry; Toda, F., Bishop, R., Eds.; John Wiley &
Sons: New York, 2004. (c) Holman, K. T.; Pivovar, A. M.; Swift, J.
A.; Ward, M. D. Acc. Chem. Res. 2001, 34, 107-118. (d) Rowsell, J.
L. C.; Yaghi, O. M. Angew. Chem., Int. Ed. 2005, 44, 4670-4679.
(2) Coppens, P.; Ma, B.-Q.; Gerlits, O.; Zhang, Y.; Kulshrestha, P.
CrystEngComm. 2002, 302-309.
(3) (a) Ma, B.-Q.; Vieira Ferreira, L. F.; Coppens, P. Org. Lett. 2004, 6,
1087-1090. (b) Zheng, S.-L.; Coppens, P. CrystEngComm. 2005,
289-293.
(9) Zheng, S.-L. Coppens, P. Crys. Growth Des. 2005, 5, 2050-2059.
(10) Blaskie, M. W.; McMillin, D. R. Inorg. Chem. 1980, 19, 3519-3522.
(11) Scaltrito, D. V.; Thompson, D. W.; O’Callaghan, J. A.; Meyer, G. J.
Coord. Chem. ReV. 2000, 208, 243-266.
(4) Zheng, S.-L.; Coppens, P. Chem.sEur. J. 2005, 11, 3583-3590.
10.1021/ic0609709 CCC: $33.50
Published on Web 10/18/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 23, 2006 9281

Zheng et al.
Scheme 1. Structures of (a) CMCR, CECR, (b) THPM, THPE, (c) THPiPB, (d) THPB, and (e) CHTA
[Cu(dmp)2][(CECR)--2H2O]-Benzene (1). Reactants in-
cluded freshly prepared Cu(OH)2 (0.5 mmol), CECR (0.5 mmol),
NaOH (0.5 mmol), water (2 mL), and benzene (1 mL). The tube
was allowed to stay at 160 °C for 48 h, followed by cooling to
room temperature over 60 h. Red crystals appeared during the
cooling period.
Synthesis of [Cu(dmp)2][(CMCR)--2H2O]-Benzene (2). The
preparation was identical to that for 1, with CECR replaced by
CMCR.
Synthesis of [Cu(dmp)2][(THPM)-] (3). Reactants included
freshly prepared Cu(OH)2 (0.5 mmol), THPM (0.5 mmol), NaOH
(0.5 mmol), and water (3 mL). The tube was allowed to stay at
120 °C for 30 h, followed by cooling to room temperature over 48
h. Red crystals appeared during the cooling period.
Synthesis of [Cu(dmp)2][(THPE)-] (4). Reactants included
freshly prepared Cu(OH)2 (0.5 mmol), THPE (0.5 mmol), NaOH
(0.5 mmol), and water (3 mL). The tube was allowed to stay at
160 °C for 48 h, followed by cooling to room temperature over 60
h. Red crystals appeared during the cooling period. Anal. Calcd
for 4 (C48H41CuN4O3): C, 73.40; H, 5.26; N, 7.13. Found: C, 73.07;
H, 5.32; N, 7.06.
(diimine ) substituted 1,10-phenanthroline) cations vary with
the counterion.12,13 In the current work, we describe the
trapping and dilution of [Cu(dmp)2]+ in eight different
anionic frameworks formed by resorcinerenes, poly(hydrox-
yphenyl) compounds, and fully saturated cyclohexanetricar-
boxylic acid. They have the composition [Cu(dmp)2]-
[(CECR)--2H2O]-benzene (1), [Cu(dmp)2][(CMCR)--
2H2O]-benzene (2), [Cu(dmp)2][(THPM)-] (3), [Cu(dmp)2]-
[(THPE)-] (4), [Cu(dmp)2][(THPiPB)-] (5), [Cu(dmp)2]-
[(2THPE)-]-H2O (6), [Cu(dmp)2][(THPB)-] (7), and [Cu-
(dmp)2][(CHTA)-]-EtOH (8) (CECR ) C-ethylcalix[4]-
resorcinarene, CMCR ) C-methylcalix[4]resorcinarene, THPM
) tris(4-hydroxyphenyl)methane, THPE ) tris(4-hydrox-
yphenyl)ethane, THPiPB ) R,R,R′-tris(4-hydroxyphenyl)-
1-ethyl-4-isopropylbenzene, THPB ) 1,1,4,4-tetrakis(4-
hydroxyphenyl)buta-1,3-diene, and CHTA ) 1,3,5-cyclo-
hexanetricarboxylic acid, Scheme 1). The synthetic strategies
used and the structures and photophysical properties of the
new phases are discussed below.
Synthesis of [Cu(dmp)2][(THPiPB)-] (5). Reactants included
freshly prepared Cu(OH)2 (0.5 mmol), THPiPB (0.5 mmol), NaOH
(0.5 mmol), and water (3 mL). The tube was allowed to stay at
140 °C for 36 h, followed by cooling to room temperature over 48
h. Red crystals appeared during the cooling period. Anal. Calcd
for 5 (C57H51CuN4O3): C, 75.77; H, 5.69; N, 6.20. Found: C, 75.77;
H, 5.58; N, 5.82.
Experimental Section
Synthesis. All compounds were prepared by hydrothermal
synthesis by sealing the reactants in a 6 mL tube and heating in an
oven to the temperatures specified below. Only for complexes 4-7
was sufficient material produced by hydrothermal synthesis to allow
microanalysis.
Synthesis of [Cu(dmp)2][(2THPE)-]-2H2O (6). The prepara-
tion was identical to that for 4, with 1.0 mmol of THPE instead of
0.5 mmol. Anal. Calcd for 6 (C68H61CuN4O7): C, 73.59; H, 5.54;
N, 5.05. Found: C, 73.15; H, 5.79; N, 5.42.
(12) Kovalevsky, A. Yu.; Gembicky, M.; Novozhilova, I. V.; Coppens, P.
Inorg. Chem. 2003, 42, 8794-8802.
(13) Kovalevsky, A. Yu.; Gembicky, M.; Coppens, P. Inorg. Chem. 2004,
43, 8282-8289.
9282 Inorganic Chemistry, Vol. 45, No. 23, 2006

Cu(I) Bis(2,9-dimethyl-1,10-phenanthroline) Nanoclusters
Table 1. Crystal Data and Structure Refinement of 1-8
1
2
3
4
empirical formula
fw
crystal system
space group
C67H70CuN4O10
1154.82
monoclinic
C66H65CuN4O10
1137.76
triclinic
P1h(no. 2)
A1h
C47H39CuN4O3
771.36
monoclinic
C2/c (no. 15)
C48H41CuN4O3
785.39
monoclinic
P21/c (no. 14)
P21/c (No. 14)
a (Å)
b (Å)
c (Å)
R (Å)
â (Å)
ø (Å)
V (Å3)
Z
13.049(1)
21.570(1)
22.153(1)
90
12.866(1)
12.866
37.340(1)a
10.621(1)
25.553(1)
90
14.890(2)
17.595(2)
20.016(2)
90
14.490(1)
21.193
15.224(1)
20.840
89.038(2)
92.832
83.673(2)
97.702
85.586(2)
88.479
2812.3(3)
5624.6
108.581(3)
90
129.339(1)
90
131.779(6)
90
5910.1(5)
4
7837.7(4)
8
3910.5(8)
4
2
4
µ (Mo KR)/mm-1
reflections collected
independent reflections
Rint
0.433
67736
16576
0.0309
1.033
0.454
23443
10883
0.0281
0.604
0.607
41947
57867
9976
9368
0.0215
1.031
0.0317
1.028
GOF on F2
1.125
R1 [I > 2σ(I)]
0.0579
0.1764
1.156/-0.766
0.0624
0.1636
1.641/-0.643
0.0368
0.1066
0.541/-0.453
0.0363
0.1091
1.497/-0.526
wR2 (all data)
∆Fmax/∆Fmin (e Å-3
)
5
6
7
8
empirical formula
fw
crystal system
space group
a (Å)
C57H51CuN4O3
903.56
C68H61CuN4O7
1109.75
monoclinic
P21/c (no. 14)
11.918(1)
20.779(1)
23.921(1)
111.663(1)
5505.6(3)
4
C56H45CuN4O4
901.50
C39H41CuN4O7
741.30
monoclinic
P21/c (no. 14)
9.827(1)
33.132(1)
14.180(1)
103.593(1)
4487.5(3)
4
1.337
60016
13699
0.0298
monoclinic
P21/c (no. 14)
11.059(1)
18.842(1)
23.524(1)
113.631(1)
4490.9(2)
4
0.540
48606
12611
0.0360
monoclinic
Cc (no. 9)
17.893(1)
18.539(1)
12.455(1)
120.122(1)
3573.8(3)
4
0.667
22176
6995
0.0196
b (Å)
c (Å)
â (Å)
V (Å3)
Z
µ (Mo KR)/mm-1
1.339
86190
13674
0.0238
reflections collected
independent reflections
Rint
GOF on F2
1.089
1.037
1.024
1.038
R1 [I > 2σ(I)]
0.0538
0.1389
1.610/-0.888
0.0440
0.1265
0.700/-0.467
0.0487
0.1404
0.871/-0.819
0.0654
0.1623
1.343/-0.781
wR2 (all data)
∆Fmax/∆Fmin (e Å-3
)
a Represents an alternative nonprimitive cell to illustrate the similarity with 1 (transformation matrix: (1, 0, 0; 0, -1, 1; 0, -1, -1)).
Synthesis of [Cu(dmp)2][(THPB)-] (7). The preparation was
identical to that for 3, with THPM replaced by THPB. Anal. Calcd
for 7 (C56H45CuN4O4): C, 74.60; H, 5.03; N, 6.21. Found: C, 74.17;
H, 5.18; N, 6.10.
Synthesis of [Cu(dmp)2][(CHTA)-]-EtOH (8). Reactants
included freshly prepared Cu(OH)2 (0.5 mmol), CHTA (0.5 mmol),
NaOH (0.5 mmol), toluene (2 mL), and EtOH (1 mL). The tube
was allowed to stay at 100 °C for 24 h, followed by cooling to
room temperature over 30 h. Orange-red crystals appeared during
the cooling period.
X-ray Crystallography. Diffraction data for 1-8 were collected
at 90 K on a Bruker APEXII charge-coupled device (CCD)
diffractometer (Mo KR, λ ) 0.71073 Å). The data were integrated,
scaled, sorted, and averaged using the SMART software package.14
The structures were solved with direct methods and refined with
full-matrix least-squares using the SHELXTL program package.15
Anisotropic thermal parameters were applied to all non-hydrogen
atoms. Hydrogen atoms were generated at idealized positions. The
hydroxyl OH hydrogens were refined starting from their positions
in the difference maps. Crystal data as well as details of data
collection and refinement are summarized in Table 1, and hydrogen
bond parameters are listed in Table S1. Drawings were produced
with Weblab Viewer Pro. 4.0.16 Atomic displacement probability
ellipsoid drawings of all structures are shown in Figure S1. Full
details can be found in CCDC-292225-292231, 274074, which can
be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/
retrieving.html or deposit@ccdc.cam.uk (the Cambridge Crystal-
lographic Data Center, 12 Union Road, Cambridge CB2 1EZ, U.K.;
fax: (+44) 1223-336-033).
(15) Sheldrick, G. M. SHELXTL 6.10, Program for Crystal Structure
Determination. Madison, Wisconsin, 2000.
(14) SMART and SAINTPLUS: Area Detector Control and Integration
Software. Madison, WI, 2004.
(16) Weblab Viewer Pro. 4.0; Molecular Simulations Inc.: San Diego, CA,
1997.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9283

Zheng et al.
Theoretical Calculations. Time-dependent density functional
theory (TD-DFT) calculations were performed with the B3LYP
functional and the 6-31G** basis set employing the Gaussian03
suite of programs.17 Starting with the X-ray geometries, the
structures were optimized by energy minimization.
UV-Vis Reflectance and Photoluminescence Spectroscopy.
UV-vis absorption measurements were made on a Perkin-Elmer
Lambda 35 UV-vis spectrometer equipped with an integrating
sphere for diffuse reflectance spectroscopy. The spectra were
collected at room temperature in the 210-800 nm range. Powdered
crystals homogeneously diluted with nonabsorbing MgO and gently
tapped into a sample holder were used as samples.
Photoluminescence measurements were carried out on a home-
assembled emission detection system. Samples consisting of several
small single crystals were mounted on a copper pin attached to a
DISPLEX refrigerator. A metallic vacuum chamber with quartz
windows attached to the cryostat was evacuated to approximately
10-7 bar with a turbomolecular pump. The crystals were irradiated
at 90 K with 366 nm light from a pulsed N2-dye laser. The emitted
light was collected by an Oriel 77348 PMT device, positioned at
90° to the incident laser beam, and processed by a LeCroy Digital
Oscilloscope with a 1-4 GHz sampling rate.
Results and Discussion
Synthesis Strategy and Crystal Structure. The self-
assembly of supramolecular frameworks is influenced by a
number of factors, which include the solvent(s) used, the
template, the stoichiometric ratio, the pH of the solution,
and steric requirements of the framework structure.9,18
Although the resorcinarenes, such as CMCR and CECR, are
versatile building blocks that can generate a remarkable
variety of different frameworks with bipyridyl-type spac-
ers,7,8,19 only a few examples of two-component complexes
incorporating large guest molecules are known,4 and very
few anionic hydrogen-bonded frameworks have been de-
scribed. We find that under hydrothermal conditions (i.e.,
100-160 °C, 2-4 days, and pH 8-9), tris(hydroxyphenyl)
compounds, such as THPE (Scheme 1b), can form anionic
hydrogen-bonded frameworks when combined with a cation20
and that careful choice of reaction conditions allows incor-
poration of large metallorganic cations.
Figure 1. (a) Three-dimensional supramolecular array in 1 viewed along
the a-axis direction (c-axis horizontal) and (b) top view (along b) of the
two-dimensional hydrogen-bonded anionic layer (c-axis horizontal).
conformation with four intramolecular hydrogen bonds along
their upper rim [O‚‚‚O ) 2.531(2)-2.846(2) Å, Table S1].
Adjacent anions are oriented in an up-and-down fashion and
are connected by intermolecular hydrogen bonds [O‚‚‚O )
2.461(2) Å], resulting in a chain along the c axis, which
extends into wavelike layers parallel to the (010) plane via
hydrogen bonding with two water molecules [O‚‚‚O ) 2.628-
(3)-2.921(2) Å, Figure 1]. Adjacent hydrogen-bonded layers
are juxtaposed along the b axis. The bowl-shaped hollows
of adjacent layers combine into nanosized cavities with a
10.7 × 13.0 × 22.1 Å effective cross-section, occupying
53.6% of the crystal volume.21 A [Cu(dmp)2]+ [Cu-N )
2.001(2)-2.043(2) Å, N-Cu-N ) 116.50(7)-128.60(7)°]
cation and its center-of-symmetry related equivalent (sym-
metry code: -x, -y, 1 - z) form well-defined dimers
embedded in each cavity. Two adjacent phenanthroline rings
interact by off-set intermolecular π-π interactions with an
interplanar distance of 3.45 Å (Figure 2a,b). No strong
intermolecular interactions occur between adjacent dimeric
[Cu(dmp)2]+ clusters or between the dimer and the host
framework (Figures 1a and S2). Each cavity also contains a
benzene molecule that fills a void left by the cations.
Replacement of CECR by CMCR gives compound 2, with
very similar two-dimensional hydrogen-bonded layers of host
molecules parallel to the (011) plane (Figures 3 and S3).
Resorcinarene-Based Frameworks. The (CECR)- anions
(Scheme 1a) in 1 adopt the bowl-shaped (r-cis-cis-cis)
(17) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L. D.; Fox, J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. GAUSSIAN03, revision C.02; Gaussian,
Inc.: Pittsburgh, PA, 2003.
(18) See for example: (a) Moulton, B.; Zaworotko, M. J. Chem. ReV. 2001,
101, 1629-1658. (b) Zheng, S.-L.; Tong, M.-L.; Chen, X.-M. Coord.
Chem. Rev. 2003, 246, 185-202. (c) Zheng, S.-L.; Yang, J.-H.; Yu,
X.-L.; Chen, X.-M.; Wong, W.-T. Inorg. Chem. 2004, 43, 830-838.
(19) See for example: (a) MacGillivray, L. R.; Holman, K. T.; Atwood, J.
L. J. Supramol. Chem. 2001, 1, 125. (b) MacGillivray, L. R.; Reid, J.
L.; Ripmeester, J. A. Chem. Commun. 2001, 1034-1035.
(20) Zheng, S.-L.; Messerschmidt, M.; Coppens, P. Angew. Chem., Int.
Ed. 2005, 44, 4614-4617.
(21) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Untrecht
University: Utrecht, The Netherlands, 2003.
9284 Inorganic Chemistry, Vol. 45, No. 23, 2006

Cu(I) Bis(2,9-dimethyl-1,10-phenanthroline) Nanoclusters
Figure 2. (a) Side view and (b) top view of the nanosized dimeric [Cu(dmp)2]+ cations connected by π-π interactions in 1, (c) side view and (d) top view
of the nanosized [Cu(dmp)2]+ column in 2, (e) top view of the [Cu(dmp)2]+ layer in 3, (f) side view and (g) top view of the dimeric [Cu(dmp)2]+ cations
in 5, (h) side view and (i) top view of the dimeric [Cu(dmp)2]+ cations in 6, and (j) side view of the weakly interacting [Cu(dmp)2]+ monomers in 8.
The similarity between the two structures is illustrated by
the transformation of the triclinic unit cell of 2 to a cell
centered in the A face, which leads to cell dimensions almost
identical to those of 1 (column 2 of Table 1). Because of
the smaller methyl tail of CMCR compared with CECR, the
bowl-shaped cavities in each of the layers combine into
channels parallel to the a-axis, with a volume corresponding
to 57.5% of the crystal space. Thus, different from 1, [Cu-
(dmp)2]+ cations [Cu-N ) 2.018(3)-2.071(3) Å, N-Cu-N
) 117.6(1)-140.3(1)°] form columns via π-π (interplanar
distance: 3.43 Å) and C-H‚‚‚π interactions [(C-)H‚‚‚π
distance: 2.47 Å, Figure 2c,d] in each channel. The columns
have a rectangular 14.4 × 12.8 Å cross-section and are well
separated by the host framework. The channels contain one
benzene molecule per unit cell, which fills a gap left by the
cations.
Though the structures are very similar, the two-resor-
cinarene-based anionic framework contains the guest in
different states of aggregation. Isolated dimeric [Cu(dmp)2]+
cations, such as that found in 1, have not been observed
before, even though a series of salts of [Cu(dmp)2]+ have
been reported.12
Inorganic Chemistry, Vol. 45, No. 23, 2006 9285

Zheng et al.
Figure 3. Three-dimensional supramolecular array in 2 viewed along the
a-axis direction, which is the channel direction.
Figure 5. Three-dimensional supramolecular array in 4 viewed along the
b-axis direction.
Figure 4. Three-dimensional supramolecular array in 3 viewed along the
b-axis direction (c-axis horizontal).
Tris(hydroxyphenyl)-Based Frameworks. Similar to
other T-shaped host molecules, such as 4,4-bis(4′-hydroxy-
phenyl)cyclohexanone,22 the (THPM)- anion (Scheme 1b)
in 3 is linked by hydrogen bonding to its symmetry-related
equivalents [symmetry codes: -x + 1/2, y - 1/2, -z + 3/2
and x, y - 1, z; O‚‚‚O 2.568(2) and 2.476(2) Å] to form a
one-dimensional hydrogen-bonded anionic ladder parallel to
[010] (Figures 4 and S4). Adjacent ladders are connected
along [201] by van der Waals interactions, resulting in a two-
dimensional supramolecular sheet of host molecules parallel
to the (102h) plane. Parallel sheets are at a distance of 9.3 Å,
leaving a space accounting for 70.2% of the crystal volume,
which contains cationic [Cu(dmp)2]+ layers [Cu-N ) 2.023-
(1)-2.075(1) Å, N-Cu-N ) 118.81(6)-138.82(5)°, Figure
2e]. The cations in the layers are connected by weak off-set
π-π (interplanar distance: 3.60 Å) and very weak C-H‚‚‚π
interactions [(C-)H‚‚‚plane distance: 3.00 Å].
Figure 6. Three-dimensional supramolecular array in 5 viewed along the
a-axis direction.
leave a space that contains [Cu(dmp)2]+ cations [Cu-N )
2.027(1)-2.039(1) Å, N-Cu-N ) 118.78(5)-128.52(5)°]
arranged in columns via π-π (interplanar distance: 3.31
Å) and C-H‚‚‚π interactions [(C-)H‚‚‚plane distance: 2.55
Å] with a 9.6 × 20.0 Å effective cross-section.
Replacement of THPE by THPiPB (Scheme 1c) gives 5,
which contains a similar two-dimensional wavelike hydrogen-
bonded layer parallel to (102h) (Figures 6 and S6). Adjacent
layers are juxtaposed so as to leave large cavities with a 9.4
× 13.2 × 20.9 Å effective cross-section, accounting for
58.2% of the crystal volume. One of the branches of the
THPiPB molecule is much longer than in THPE, which
interferes with layer structure formation. As a result, a [Cu-
(dmp)2]+ cation [Cu-N ) 2.005(2)-2.064(2) Å, N-Cu-N
) 113.05(7)-139.40(7)°] and its center-of-symmetry related
equivalent (symmetry code: x, y, 1 - z) are embedded in
each channel as a dimer, as in 1, the dimers being separated
by the long branch of THPiPB. The face-to-face stacking
In 4, (THPM)- is replaced by the (THPE)- anion (Scheme
1b). The structure features two-dimensional hydrogen-bonded
layers of anions (Figures 5 and S5), linked by hydrogen
bonding to their symmetry-related equivalents [symmetry
codes: x - 1, -y - 1/2, z - 1/2 and -x, y - 1/2, -z +
1/2; O‚‚‚O 2.525(2) and 2.491(2) Å], leading to a two-
dimensional wavelike layer parallel to the (102h) plane. As
(THPE)- acts as a Y-shaped host molecule, the two-
dimensional layers have an unusual (4.82) topological motif
(Scheme S1).23,24 Adjacent layers are juxtaposed so as to
(23) (a) Delgado-Friedrichs, O.; O’Keeffe, M. J. Solid State Chem. 2005,
178, 2480-2485. (b) Dolomanov, O. V.; Blake, A. J.; Champness,
N. R.; Schro¨der, M. J. Appl. Crystallogr. 2003, 36, 1283-1284. (c)
Dolomanov, O. V. OLEX, version 2.55, 2004.
(24) See for example: (a) Long, D.-L.; Blake, A. J.; Champness, N. R.;
Schro¨der, M. Chem. Commun. 2000, 1369-1370. (b) Zheng, S.-L.;
Tong, M.-L.; Zhu, H.-L.; Fang, Y.; Chen, X.-M. J. Chem. Soc., Dalton
Trans. 2001, 2049-2053.
(22) Aitipamula, S.; Nangia, A. Chem.sEur. J. 2005, 11, 6727-6742.
9286 Inorganic Chemistry, Vol. 45, No. 23, 2006

Cu(I) Bis(2,9-dimethyl-1,10-phenanthroline) Nanoclusters
Figure 7. Three-dimensional network in 6 viewed along the b-axis
direction (a-axis horizontal).
Figure 9. Three-dimensional network of in 8 viewed along the c-axis
direction.
Table 2. Some Characteristics of [Cu(dmp)2]+ Inclusion Compounds
states of
host
guest
cavity/
concn/
framework aggregation one guesta mol L-1
RT
90 K
1
2-D layer
isolated
dimer
727.5
1.123
371(9)
532(3)
2
3
4
5
2-D layer
1-D ladder
2-D layer
2-D layer
column
layer
column
isolated
dimer
663.0
687.5
671.7
652.5
1.181
1.696
1.699
1.481
348(5)
286(9)
310(4)
236(9)
520(2)
436(4)
458(2)
357(4)
Figure 8. Three-dimensional supramolecular array in 7 viewed along the
b-axis direction (c-axis horizontal).
distance of the aromatic rings, which are offset from each
other, is 3.35 Å (Figure 2f,g).
6
3-D network isolated
dimer
666.9
1.207
670(3) 1072(12)
40(2) 60(2)
7
8
2-D layer
3-D network weakly
interacting
monomer
layer
692.2
620.5
1.480
Doubling the THPE-host-to-[Cu(dmp)2]+-guest ratio used
for 4 yields 6 with completely embedded dimeric [Cu-
(dmp)2]+ cations. Two crystallographically independent
THPE molecules share one hydrogen atom, with a short
O‚‚‚O distance [O(1)‚‚‚O(5) ) 2.485(2) Å], typical for acid
salts. Adjacent (2THPE)- units are connected by intermo-
lecular hydrogen bonds [O‚‚‚O ) 2.520(2)-2.772(2) Å],
which extend into a three-dimensional hydrogen-bonded
anionic framework [O‚‚‚O 2.525(5)-2.528(5) Å] with large
channels (effective dimension: 12.8 × 10.3 Å), constituting
50.3% of the crystal volume and running along the b-axis
(Figures 7 and S7). In each channel, a [Cu(dmp)2]+ cation
[Cu-N ) 1.996(1)-2.068(2) Å, N-Cu-N ) 106.01(6)-
133.49(6)°] is connected with its center-of-symmetry related
equivalent (symmetry code: -x, 1 - y, 1 - z) via π-π
interactions (interplanar distance: 3.63 Å, Figure 2h,i) to
form an isolated dimer. One lattice water molecule is
clathrated in each channel and hydrogen-bonded to the
hydroxyl oxygen atom [O(1W)-H‚‚‚O ) 3.182(3) Å] of the
host network.
1.859 1120(18) 2680(12)
a Solvent molecules excluded in calculation of cavity volume.
discussed so far are limited to ∼1 µs for 6 and 0.5 µs or
less for 1-5. To obtain more information on the relation
between the lifetime and the nature of the framework, two
new phases with a fully conjugate framework based on
THPB25 and a fully saturated framework based on CHTA26
(Scheme 1d,e), respectively, were synthesized.
In 7, the (THPB)- anion is linked by hydrogen bonding
to its related equivalents [symmetry codes: x, -y + 1/2, z
+ 1/2; -x, y + 1/2, -z - 1/2; and x, -y - 1/2, z - 1/2;
O‚‚‚O 2.454(2) and 2.684(2) Å] to form a two-dimensional
wavelike hydrogen-bonded layer parallel to the (100) plane
(Figures 8 and S8). Adjacent layers are related by an a-axis
translation so as to leave a layer-shaped space accounting
for 61.7% of the crystal volume. Similar to 3, the tris(4-
hydroxyphenyl)methane inclusion compound, [Cu(dmp)2]+
ions [Cu-N ) 2.018(2)-2.045(2) Å, N-Cu-N )
Comparison with 4 confirms that supramolecular host
matrixes can be manipulated by variation in the stoichio-
metric ratio, in this case leading to different states of guest
aggregation.
Comparison of a Fully Conjugated and a Fully Satu-
rated Framework. The 90 K lifetimes of the complexes
(25) Itami, K.; Ushiogi, Y.; Nokami, T.; Ohashi, Y.; Yoshida, J. Org. Lett.
2004, 6, 3695-3698.
(26) (a) Bhogala, B. R.; Vishweshwar, P.; Nangia, A. Crys. Growth Des.
2002, 2, 325-328. (b) Bhogala, B. R.; Nangia, A. Crys. Growth Des.
2003, 3, 547-554. (c) Bhogala, B. R.; Vishweshwar, P.; Nangia, A.
Crys. Growth Des. 2005, 5, 1271-1281.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9287

Zheng et al.
Table 3. Distortion of the Cu(I) Coordination for [Cu(dmp)2]+ Complexes
1
2
3
4
5
6
7
8
rocking θx (deg)
wagging θy (deg)
flattening θz (deg)
Cu displacement
from dmp plane/Å
86.98
92.63
97.94
0.2105
0.0250
100.88
98.21
97.05
0.2234
0.1089
99.04
97.80
96.90
0.2712
0.0588
89.08
95.90
92.65
0.0654
0.0405
84.88
79.49
101.55
0.1869
0.1931
74.46
97.59
98.72
0.4875
0.0661
87.8
97.26
87.17
92.67
0.0731
0.0381
90.01
103.47
0.1462
0.0012
Table 4. Calculated Excited State Energy Separation of Anion Component in Different Inclusion Compounda
energy
separation
CECR- E/eV
(f)
CMCR- E/eV
(f)
THPM- E/eV
(f)
THPE- E/eV
(f)
THPiPB- E/eV
(f)
THPEa E/eV
THPB- E/eV
(f)
CHTA- E/eV
(f)
(f)
S0-T1
S0-S1
S0-S2
2.884
(0.000)
2.984
(0.004)
3.340
2.574
(0.000)
2.593
(0.001)
2.994
1.802
(0.000)
1.840
(0.003)
2.239
1.847
(0.000)
1.906
(0.005)
2.293
1.405
(0.000)
1.412
(0.004)
1.837
3.666
(0.000)
4.716
(0.021)
4.905
1.162
(0.000)
2.154
(0.477)
2.453
3.778
(0.000)
4.008
(0.018)
4.019
(0.024)
(0.004)
(0.021)
(0.012)
(0.002)
(0.035)
(0.001)
(0.005)
a For 6, which contains (2THPE)-, the gap was approximated by that for neutral THPE.
116.28(8)-133.11(7)°] are interspersed between the parallel
layers, connected by off-set π-π interactions (interplanar
distance: 3.38 Å) and a weak C-H‚‚‚π interaction [(C-
)H‚‚‚π distance: 2.93 Å].
In 8, the (CHTA)- ions are linked by hydrogen bonding
to their symmetry equivalents [symmetry codes: x, -y, z -
1/2 and x - 1/2, -y + 1/2, z - 1/2; O‚‚‚O ) 2.502(4) and
2.536(4) Å]. The molecule is essentially a four-connected
node (Figures 9 and S9), which extends into a three-
dimensional hydrogen-bonded anionic framework with 103
topology [O‚‚‚O 2.497(5)-2.535(5) Å].23 Weakly interacting
monomers are located in channels (effective dimension: 12.8
× 10.3 Å) along the c-axis [Cu(dmp)2]+ [Cu-N ) 1.932-
(3)-2.027(4) Å, N-Cu-N ) 115.9(2)-128.5(2)°], which
have a volume corresponding to 77.5% of the crystal space
(Figure 2j). Unlike in 1-7, no π‚‚‚π interactions and only a
weak C(sp3)-H‚‚‚π interaction [(C-)H‚‚‚plane distance:
2.89 Å] are found between adjacent [Cu(dmp)2]+ cations.
One ethanol molecule is clathrated in each channel and
hydrogen-bonded to the hydroxyl oxygen atom [O(1S)-
H‚‚‚O ) 2.822(6) Å] of the host network.
Figure 10. Diagram of superimposed [Cu(dmp)2]+ cations in 1 (red), 2
(brown), 3 (olive), 4 (dark yellow), 5 (green), 6 (blue), 7 (pink), and 8
(purple).
as in the Cu(I) displacement from the phenanthroline plane,
occur. This is even the case among isolated dimeric [Cu-
(dmp)2]+ complexes: 1 (Figure 2a,b), 5 (Figure 2f,g), and 6
(Figure 2h,i). There is no clear correlation between the
distortion of Cu(I) coordination and the cavity size. Other
factors, such as the cavity shape, nature of the intermolecular
interactions, and the presence of solvent molecules in some
cases, are clearly more important than the volume of the
cavity the molecule is embedded in.
Nature of the [Cu(dmp)2]+ Cations. Most of the hosts
examined form hydrogen-bonded layers between which the
guest cations are interspersed. The exceptions are the 2:1
host/guest phase 6 with THPE, in which the excess host
molecules form a three-dimensional framework; the tricar-
boxylic acid CHTA in 8, which similarly is capable of
forming a 3-D framework; and 3, in which one-dimensional
hydrogen-bonded ladders form sheets through van der Waals
interactions. The guests are arranged in layers, channels, or
cavities. Long side chains, as in 1 and 5, lead to cavity
formation.
The [Cu(dmp)2]+ cations occur in four different states of
aggregation: isolated dimers, columns, layers of stacked
molecules, and weakly interacting monomers (Figure 2, Table
2). The molecular distortions of the cation differ considerably
in the series, as summarized in Table 3 and illustrated in
Figure 10. Significant variation in the flattening, rocking,
and wagging distortions (as defined in Scheme S2),27 as well
The concentration of the [Cu(dmp)2]+ guests in the
structures surveyed is listed in column 5 of Table 2. It varies
from 1.1 to almost 1.8 mol/L, which may be compared with
-
concentrations of 2.5-2.6 mol/L in the more common PF6
-
and BF4 salts of Cu(dmp)2.12 Such dilution of photoactive
molecules in periodic solids is of importance in time-resolved
crystallographic studies, as, upon illumination, fewer photons
are required to achieve a large excitation percentage of the
photochemicaly active molecules.2
Spectroscopic Properties. Absoprtion spectra are shown
in Figure S10. As in the neat [Cu(dmp)2]+ compounds,12 the
longest wavelength absorption band of 1-8 at ca. 450-550
nm can be assigned to the metal-to-ligand charge transfer
(MLCT) transition of the Cu(I) cation. All complexes show
(27) Dobson, J. F.; Green, B. E.; Healy, P. C.; Kennard, C. H. L.;
Pakawatchai, C.; While, A. H. Aust. J. Chem. 1984, 37, 649-659.
9288 Inorganic Chemistry, Vol. 45, No. 23, 2006

Cu(I) Bis(2,9-dimethyl-1,10-phenanthroline) Nanoclusters
the fully conjugated THPB salt (7) at 60 ns, the partially
anionic THPE complex (6) (1072 ns), and especially the
saturated cyclohexane-tricarboxylic acid-based solid (8)
(2680 ns), with a longer lifetime at 90 K than that of any of
the conventional [Cu(dmp)2]+ salts reported in ref 12 at 17
K. Not unexpectedly, the use of saturated frameworks leads
to optimization of excited-state lifetimes of the guest
molecules.
Concluding Remarks
In summary, [Cu(dmp)2]+ cations have been embedded
in eight different supramolecular frameworks in different
states of aggregation. As this is only a very small fraction
of the supramolecular solids that can be synthesized, the
versatility of the field is enormous. Different states of
aggregation can be designed by only small variations in the
framework components, such as the replacement of methyl
by ethyl in the resorcinarenes. The photophysical properties
of the new phases are strongly affected by the electronic
structure of the framework components. Not unexpectedly,
the use of saturated frameworks leads to optimization of
excited-state lifetimes of the guest molecules. The short
lifetime of [Cu(dmp)2]+ in the conjugated-host solid 7,
compared with the long lifetime in the fully saturated 8,
which exceeds that observed in a series of conventional Cu-
(dmp)2 salts, is a prime manifestation of this effect. It follows
that host-guest solids can be designed so as to optimize the
desired photophysical properties.
Figure 11. Relation between the excited-state lifetimes of 1-8 and the
theoretical 3ES-GS energy gaps of the anionic framework components.
3
The vertical line represents the ES-GS energy gap for the [Cu(dmp)2]+
ion (2.78 eV).29 The increase in the lifetime of the embedded complexes
beyond this value of the framework gap is evident. For 6, which contains
(2THPE)-, the gap was approximated by that for neutral THPE.
strong orange-red emission with a broad, featureless profile
in the 700-760 nm range. Lifetimes vary from (room
temperature (RT)/90 K) 40/60 ns for 7 to 1120/2800 ns for
8, with 1-5 being intermediate in the (RT/90 K) 236/357
ns (3) to 371/532 ns (1) range (Table 2).
As pointed out by Lower and El-Sayed in 1965,28
luminescence quenching due to intermolecular energy trans-
fer in the solid state will be much more pronounced for triplet
than for singlet states. Our earlier analysis of the lumines-
cence properties of supramolecular solids9 shows that the
energy transfer responsible for luminescence quenching in
neutral guest-host systems correlates with the relative energy
level spacings of the luminescing donor and quenching
acceptor molecules. Examination of the excited state-ground
state (3ES-GS) energy gaps of the host molecules as
calculated by TD-DFT (Table 4) confirms that a similar
correlation exists for metallorganic cations embedded in an
anionic host lattice, as illustrated in Figure 11.29 The 1:2
THPE complex 6 (RT/90 K: 670/1072 ns) shows a much
longer lifetime than the 1:1 complex with THPE (4) (RT/90
K: 310/458 ns). This difference is in the direction suggested
by the larger excited state-ground state (3ES-GS) energy
gap of neutral THPE compared with (THPE)- (Table 4).
The lifetimes of the solids based on CECR, CMCR, and
the fully anionic trihydroxyphenyl complexes are similar to
each other in the 400-500 ns range (90 K). The outliers are
The analysis described here and those reported else-
where4,9,30 serve as a guide for strategies to be adopted in
the synthesis of long-lifetime luminescent materials.
Acknowledgment. We thank Dr. Irina Novozhilova for
assistance with the TD-DFT calculations and Dr. Andrey Yu.
Kovalesky for helpful discussions at the beginning of this
work. The authors thank the U.S. Department of Energy for
support of the spectroscopic experiments and theoretical
calculations through grant DE-FG02-02ER15372. Support
of this work by the National Science Foundation (CHE-
0236317) and the Petroleum Research Fund of the American
Chemical Society (PRF43594-AC4) is gratefully acknowl-
edged.
Supporting Information Available: Additional plots and
hydrogen bond tables (PDF), and X-ray data files (CIF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
(28) Lower, S. K.; El-Sayed, M. A. Chem. ReV. 1966, 66, 199-241.
(29) For [Cu(dmp)2]+, the 3ES-GS energy gap is 2.78 eV; see: Chen, L.
X.; Shaw, G. B.; Novozhilova, I.; Liu, T.; Jennings, G.; Attenkofer,
K.; Meyer, G. J.; Coppens, P. J. Am. Chem. Soc. 2003, 125, 7022-
7034.
IC0609709
(30) (a) Sudhakar, M.; Djurovich, P. I.; Hogen-Esch, T. E.; Thompson,
M. E. J. Am. Chem. Soc. 2003, 125, 7796-7797. (b) Tanaka, I.; Tabata,
Y.; Tokito, S. Chem. Phys. Lett. 2004, 400, 86-89.
Inorganic Chemistry, Vol. 45, No. 23, 2006 9289