PdII, ZnII and AgI Complexes of Tetrakis(N-7-azaindolyl)benzene: Variation of Bonding Modes, Extended Structures and Luminescence

Article abstract of DOI:10.1002/ejic.200300249

Pd^II, Ag^I and Zn^II complexes of tetrakis(7-azaindolyl)benzene (ttab), [(PdCl₂)₂(ttab)] (1), [(ZnCl₂)₂(ttab)] (2), [Ag(NO₃)] ₂-(ttab) (3a) and [Ag(NO₃)(DMSO)]₂(ttab) (3b) were synthe-sized and fully characterized by NMR spectroscopy, single-crystal X-ray diffraction and elemental analyses. The ttab ligand in these complexes displays two different bonding modes. In the Pd^II and Zn ^II complexes, the ttab ligand chelates to the metal center via two ortho 7-azaindolyl groups (the ortho mode). In contrast, in the Ag^I complex, it chelates to the Ag^I ion via two meta 7-azaindolyl groups (the meta mode). In the solid state, molecules of 1 and 2 form grid-like extended structures that host solvent molecules such as DMSO and CH ₂Cl₂. Compound 3a appears to be a coordination polymer and can be converted into compound 3b when dissolved in DMSO. A hydrogen bonded complex [Zn(O₂CCF₃)₂(H₂O) ₂](ttab) (4), which displays an unusual hydrogen bonded helical chain structure in the solid state, was also characterized. Except for compound 1, these new compounds all emit blue light when irradiated by UV radiation. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejic.200300249

FULL PAPER
PdII, ZnII and AgI Complexes of Tetrakis(N-7-azaindolyl)benzene: Variation of
Bonding Modes, Extended Structures and Luminescence
Datong Song[a] and Suning Wang*[a]
Keywords: N ligands / Coordination modes / Palladium / Zinc / Silver / Luminescence
PdII, AgI and ZnII complexes of tetrakis(7-azaindolyl)benzene
(ttab), [(PdCl2)2(ttab)] (1), [(ZnCl2)2(ttab)] (2), [Ag(NO3)]2-
(ttab) (3a) and [Ag(NO3)(DMSO)]2(ttab) (3b) were synthe-
sized and fully characterized by NMR spectroscopy, single-
crystal X-ray diffraction and elemental analyses. The ttab li-
like extended structures that host solvent molecules such as
DMSO and CH2Cl2. Compound 3a appears to be a coordina-
tion polymer and can be converted into compound 3b when
dissolved in DMSO.
A
hydrogen bonded complex
[Zn(O2CCF3)2(H2O)2](ttab) (4), which displays an unusual
gand in these complexes displays two different bonding hydrogen bonded helical chain structure in the solid state,
modes. In the PdII and ZnII complexes, the ttab ligand che- was also characterized. Except for compound 1, these new
lates to the metal center via two ortho 7-azaindolyl groups
(the ortho mode). In contrast, in the AgI complex, it chelates
to the AgI ion via two meta 7-azaindolyl groups (the meta
mode). In the solid state, molecules of 1 and 2 form grid-
compounds all emit blue light when irradiated by UV radi-
ation.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
thesis of the new ligand 1,2,4,5-tetrakis(7-azaindolyl)ben-
zene (ttab),[4] which is a bright blue luminescent emitter.
The organoplatinum complexes of ttab have been found to
display unusual structural features and chemical reactiv-
ity.[4] In the previously reported organoplatinum complexes,
the ttab ligand chelates to the PtII center in the ortho bond-
ing mode (D) as shown in Scheme 1. Further investigation
revealed that the ttab ligand also displays a second bonding
mode (E), the meta mode. The third bonding mode (F), the
cyclometallation mode, was not observed for the ttab li-
gand.
Luminescent transition metal complexes are of great
interest because of their potential application in chemical
optical sensors, photosensitization and electroluminescent
devices.[1,2] We have previously demonstrated that PtII and
PdII complexes of 7-azaindole based organic ligands can
emit green and orange light, either in frozen solutions or in
the solid state, when irradiated by UV light.[2f,3a] In ad-
dition to luminescent properties, the coordination chemistry
displayed by transition metal complexes of the 7-azaindole-
based ligands is also interesting. As we reported previously,
the coordination mode displayed by ligands involving 7-
azaindolyl groups varies drastically according to the ge-
ometry of the ligand. For example, as shown in Scheme 1,
the 1,3-bis(7-azaindolyl)benzene ligand has been found to
bind to PdII or PtII centers as a tridentate NCN-type ligand
through cyclometallation[3] (bonding mode A). In contrast,
the 1,2-bis(7-azaindolyl)benzene ligand usually acts as a bi-
dentate chelate ligand through the two 7-azaindolyl groups
(bonding mode B in Scheme 1).[3b] The 1,3,5-tris(7-aza-
indolyl)benzene ligand, on the other hand, uses two of the
7-azaindolyl groups to chelate to the metal center with the
NCN type of binding similar to that in A, and uses the
remaining 7-azaindolyl group as a bridging ligand to form
a trinuclear complex (C).[2f] Recently we reported the syn-
The metal ion and the ligands surrounding the metal ion
appear to play a key role in the bonding mode of the ttab
ligand. We report herein the results of our investigation on
PdII, AgI and ZnII complexes of the ttab ligand.
Results and Discussion
Syntheses of Complexes
The ttab ligand reacts readily with K2PdCl4 and ZnCl2
in solution to afford complexes [(PdCl2)2(ttab)] (1) and
[(ZnCl2)2(ttab)] (2), respectively, in nearly quantitative
yields. When ttab was reacted with AgNO3, we obtained a
white solid of 3a, which displays blue luminescence at ambi-
ent temperature and is insoluble in most organic solvents.
Based on elemental analysis results, 3a has the formula [Ag-
(NO3)]2(ttab). Compound 3a can be dissolved in DMSO
under sonication to form a dinuclear complex [Ag-
(NO3)(DMSO)]2(ttab) (3b), in which the DMSO molecules
coordinate to the AgI center through the oxygen atom, as
[a]
Department of Chemistry, Queen’s University, Kingston,
Ontario, Canada, K7 L 3N6
E-mail: wangs@chem.queensu.ca
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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DOI: 10.1002/ejic.200300249
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PdII, ZnII and AgI Complexes of Tetrakis(N-7-azaindolyl)benzene
FULL PAPER
˚
Table 1. Selected bond lengths [A] and angles [°]
1
Pd(1)ϪN(2)
Pd(1)ϪN(4)
Pd(1)ϪCl(2)
Pd(1)ϪCl(1)
2.022(4)
2.032(4)
2.2852(15)
2.2900(14)
N(2)ϪPd(1)ϪN(4)
N(2)ϪPd(1)ϪCl(2)
N(4)ϪPd(1)ϪCl(2)
N(2)ϪPd(1)ϪCl(1)
N(4)ϪPd(1)ϪCl(1)
Cl(2)ϪPd(1)ϪCl(1)
C(7)ϪN(2)ϪPd(1)
C(14)ϪN(4)ϪPd(1)
2
87.25(15)
176.34(13)
90.46(11)
90.51(12)
177.76(11)
91.78(6)
123.7(4)
124.0(3)
Zn(1)ϪN(2)
Zn(1)ϪN(4)
Zn(1)ϪCl(1)
Zn(1)ϪCl(2)
2.053(10)
2.068(9)
2.196(3)
2.246(3)
N(2)ϪZn(1)ϪN(4)
N(2)ϪZn(1)ϪCl(1)
N(4)ϪZn(1)ϪCl(1)
N(2)ϪZn(1)ϪCl(2)
N(4)ϪZn(1)ϪCl(2)
Cl(1)ϪZn(1)ϪCl(2)
C(7)ϪN(2)ϪZn(1)
C(14)ϪN(4)ϪZn(1)
3b
97.2(3)
116.7(2)
123.9(3)
105.6(3)
104.6(3)
107.05(12)
131.1(8)
129.4(7)
Ag(1)ϪN(1)
Ag(1)ϪN(3)
Ag(1)ϪO(1)
Ag(1)ϪO(3A)
2.300(7)
2.335(9)
2.403(7)
2.53(3)
N(1)ϪAg(1)ϪN(3)
N(1)ϪAg(1)ϪO(1)
N(3)ϪAg(1)ϪO(1)
N(1)ϪAg(1)ϪO(3A)
N(3)ϪAg(1)ϪO(3A)
O(1)ϪAg(1)ϪO(3A)
4
136.3(2)
128.9(3)
88.3(3)
106.4(13)
80.9(8)
103.8(15)
Zn(1)ϪO(6)
Zn(1)ϪO(5)
Zn(1)ϪO(3)
Zn(1)ϪO(1)
Zn(1)ϪO(4)
Zn(1)ϪO(2)
1.930(12)
1.943(10)
2.04(2)
2.066(17)
2.467(16)
2.557(16)
O(6)ϪZn(1)ϪO(5)
O(6)ϪZn(1)ϪO(3)
O(5)ϪZn(1)ϪO(3)
O(6)ϪZn(1)ϪO(1)
O(5)ϪZn(1)ϪO(1)
O(3)ϪZn(1)ϪO(1)
103.0(4)
98.9(6)
135.7(7)
96.0(6)
101.1(6)
114.4(9)
Scheme 1
confirmed by X-ray diffraction analysis. Anhydrous ZnCl2
reacts with ttab in a THF solution, resulting in a blue lumi-
nescent white solid of 2. Attempts to synthesize the com-
plex [Zn(O2CCF3)2]2(ttab) by reacting Zn(O2CCF3)2 hy-
drate with ttab were unsuccessful. Every attempt led to the
isolation of crystals of [Zn(O2CCF3)2(H2O)2](ttab) (4),
where the Zn(O2CCF3)2(H2O)2 molecule is not coordinated
to the ttab ligand but hydrogen bonded with the ttab ligand
in the crystal lattice as confirmed by the X-ray diffraction
study. The structures of ttab, 1, 2, 3b and 4 were determined
by X-ray diffraction analyses. Selected bond lengths and
angles for 1, 2, 3b and 4 are provided in Table 1.
Structures of ttab and of the Complexes
There are 1.5 independent molecules in each asymmetric
unit of the crystal lattice of ttab, with one of the ttab mol-
ecules being located at the inversion center of symmetry.
The structure of one of the independent molecules in the
crystal lattice of ttab is shown in Figure 1. The ttab ligand
Figure 1. A diagram showing the structure of one of the indepen-
dent ttab molecules in the crystal lattice with labeling schemes
has a non-planar structure. The 7-azaindolyl groups do not ating to the metal center, ttab has four nitrogen donor
have significant conjugation with the central benzene ring atoms available, which can chelate to the metal center either
as indicated by the dihedral angle between the central ben- with two ortho 7-azaindole moieties (ortho fashion, D) or
zene plane and the 7-azaindolyl plane that ranges from with two meta 7-azaindole moieties (meta fashion, E). In
46.6° to 76.7°. Unlike 1,2-bis(7-azaindolyl)benzene or 1,3- addition, it is conceivable that the ttab ligand could also
bis(7-azaindolyl)benzene, which have only one way of chel- form cyclometallated complexes (F), especially with the PdII
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D. Song, S. Wang
FULL PAPER
and PtII centers, in the same manner as 1,3-bis(7-azaindol- benzene ring as indicated by the dihedral angles between
yl)benzene and 1,3,5-tris(7-azaindolyl)benzene, as shown in the 7-azaindolyl plane and the benzene ring (100.2° and
Scheme 1. However, despite our repeated attempts to react 102.6°, respectively). The central benzene ring of the ttab
PdII and PtII ions with ttab under various conditions, no ligand is ‘‘sandwiched’’ midway between the two PdCl2N2
cyclometallated products were obtained. For the PdII ion, planes. The PdCl2N2 plane is approximately parallel to the
the ortho chelated complex 1 was isolated, instead.
central benzene plane as indicated by the dihedral angle
The structure of 1, as shown in Figure 2, has a crystallo- of 25.5° between these two planes. The separation distance
graphically imposed inversion center of symmetry. Each between the two PdII centers in 1 is 6.660(2) A. As a result,
˚
PdII ion in 1 is chelated by two ortho 7-azaindolyl groups the distance between the center of the benzene ring and the
˚
via the nitrogen atoms, resulting in a dinuclear complex. Pd atom is 3.33(1) A. The shortest contact distances be-
Each PdII center adopts a typical square-planar geometry, tween the Pd atom and the carbon atoms of the benzene
˚
˚
with the two nitrogen donor atoms cis to each other and ring are 2.99(1)
A
[Pd(1)ϪC(16)] and 3.01(1)
A
two chloride ligands trans to each nitrogen atom. The [Pd(1)ϪC(15)]. These distances are considerably shorter
˚
PdϪN and PdϪCl bonds in 1 show typical bond lengths than the sum (ഠ3.22 A) of the van der Waals radii of Pd
˚
˚
with averages of 2.027(4) A and 2.2876(14) A, respectively, and C, indicating the presence of some interactions between
which are close to those reported previously.[2f,3a] The four the Pd atom and the benzene ring. The structure of 1 re-
7-azaindolyl planes are nearly perpendicular to the central sembles that of [(PtR2)2(ttab)], where R equals methyl or
Figure 2. Top: a diagram showing the structure of 1 with labeling schemes; bottom, right: the hydrogen bond-linked 1D column; left:
unit cell packing diagram viewed down the 1D column, the DMSO solvent molecules are shown using space-filling models
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PdII, ZnII and AgI Complexes of Tetrakis(N-7-azaindolyl)benzene
FULL PAPER
phenyl, reported previously, where substantial interactions central benzene plane being 82.7° and 82.4°, respectively.
between the Pt atom and the central benzene ring were However, the bond angles of C(7)ϪN(2)ϪZn(1) [131.1(8)°]
also observed.[4]
and C(14)ϪN(4)ϪZn(1) [129.4(7)°] are considerably larger
Molecules of 1 stack along the b axis as shown in Fig- than the corresponding ones in 1 [C(7)ϪN(2)ϪPd(1) ϭ
ure 2. There are weak intermolecular hydrogen bonding in- 123.7(4)°, C(14)ϪN(4)ϪPd(1) ϭ 124.0(3)°]. The geometry
teractions between the chloride ligands and the protons on distortion around the metal ions and the nitrogen donor
the 7-azaindole rings of the neighboring molecules atoms in 2 is clearly a consequence of steric interactions
˚
˚
[Cl(1)···C(13) ϭ 3.62 A, Cl(2)···C(6) ϭ 3.70 A], leading to between the chloride ligands and the central phenyl group.
the formation of a 1D column. The shortest intermolecular Nonetheless, the structure of 2 demonstrates that the ortho
˚
Pd···Pd distance along the 1D column is 4.800(2) A. The bonding mode is possible and favorable for a tetrahedrally
void space between the 1D columns forms extended chan- coordinated ZnII ion. In solution, only one set of chemical
nels in the crystal lattice. DMSO solvent molecules are lo- shifts for the ttab ligand was observed in the 1H NMR spec-
cated in these channels, as shown in Figure 2. There are trum of 2. Therefore, we believe that only one bonding
hydrogen bonding interactions between the oxygen atom of mode, most likely the ortho mode, exists in solution for
the DMSO molecule and a proton on the central phenyl complex 2. In coordinating solvents such as DMSO, the
ring of the ttab ligand as indicated by the O···C distance of ZnCl2 units appear to dissociate from the ttab ligand as
1
˚
3.10 A. Crystals of 1 are stable at ambient temperature and indicated by the H NMR spectrum of 2 in [D6]DMSO,
no loss of DMSO solvent molecules was observed, as evi- which is exactly identical to that of the free ttab ligand in
dent by the elemental analysis results.
[D6]DMSO. We believe that the DMSO solvent molecules
Earlier we postulated that a ‘‘sandwich’’ structure similar are coordinated to the ZnCl2 unit in solution, replacing the
to 1 is only possible for metal ions that have a square-planar nitrogen donor atoms of the ttab ligand and resulting in the
geometry,[4] based on the assumption that if the metal ion dissociation of the complex 2.
has a tetrahedral geometry, it would bring the ligands
In the crystal lattice, molecules of 2 (Figure 3) form one-
bound to the metal center into close contact with the cen- dimensional chains through intermolecular hydrogen bond-
tral benzene ring of the ttab ligand and as a result, the ortho ing interactions between the chloride ligands of one mol-
coordination mode would not be possible. To prove this ecule and the protons on the 7-azaindole rings of the
postulation, we examined the structure of 2. As shown in neighboring molecules in a similar manner as observed in
Figure 3, the molecule of 2 has a crystallographically im- 1. The intermolecular Cl(1)···C(2Ј) separation distance is
˚
posed inversion center. One surprising finding is that the 3.67 A. An interesting feature is that the 1D columns of 2
ttab ligand adopts the ortho coordination mode with the are arranged in such a way that rhombohedral-shaped
ZnII ion in the same manner as that observed in 1. The channels are formed. Disordered CH2Cl2 solvent molecules
common coordination geometry for a four-coordinate ZnII occupy these channels. The crystals of 2 lose the trapped
ion is tetrahedral. The ortho bonding mode displayed by the solvent molecules rapidly at ambient temperature, causing
ttab ligand in 2 is therefore totally unexpected. Each ZnII the collapse of the crystal lattice. The structure of the di-
center in 2 has a distorted tetrahedral geometry, with two nuclear silver complex 3b is shown in Figure 4. In contrast
nitrogen donor atoms from the ttab ligand occupying two to the structures of 1 and 2, the ttab ligand in 3b adopts
coordination sites and two chloride ligands occupying the the meta bonding mode. The molecule of 3b has a crystallo-
other two sites. The bond angles of N(2)ϪZn(1)ϪN(4), graphically imposed center of inversion symmetry. Each
N(2)ϪZn(1)ϪCl(1), and N(4)ϪZn(1)ϪCl(1), which are AgI ion is coordinated to two 7-azaindolyl groups at the 1,3
97.2(3)°, 116.7(2) °, and 123.9(3) °, respectively, deviate sig- positions of the ttab ligand. The AgI center is also coordi-
nificantly from a typical tetrahedral geometry. To minimize nated to two oxygen atoms, one from the DMSO molecule
steric interactions between the chloride ligand Cl(1) and the and the other from a disordered nitrate anion. Coordi-
central phenyl ring of the ttab ligand, the Zn(1)ϪCl(1) nation to a metal center via the oxygen atom of the DMSO
bond is almost parallel to the central phenyl ring of ttab. ligand has previously been observed.[6] The bond angles
˚
The Zn(1)ϪZn(1A) separation distance is 7.538(2) A, much around the Ag(1) atom range from 80.9(8) to 136.3(2)°. The
longer than the Pd(1)ϪPd(1A) distance in 1. The distance geometry of the Ag(1) center can therefore be best de-
between Cl(1) and the center of the central phenyl ring of scribed as a highly distorted tetrahedron. The dihedral
˚
ttab is 3.19 A. The distances between the Cl(1) atom and angles between the 7-azaindolyl plane and the central ben-
C(15), C(16), C(17) atoms of the phenyl ring are in the zene ring are 123.7° and 115.9°, respectively, much greater
˚
range of 3.42 to 3.50 A, much shorter than the correspond- than those of 1 and 2. The preference for the ‘‘meta’’ bond-
ing ClϪC separation distances in 1 [the shortest ClϪC dis- ing mode shown by the ttab ligand in 3b could be attributed
Ϫ
˚
tance in 1, 3.76 A, is between Cl(1) and C(16)]. The to the relative bulkiness of the DMSO and NO3 ligands
Zn(1)ϪCl(2) bond is considerably longer than the compared to the chloride ligands. The meta mode appears
˚
Zn(1)ϪCl(1) bond (by 0.05 A). The ZnϪN and ZnϪCl to minimize the interactions between the oxygen donor li-
˚
˚
bond lengths in 2 [av. 2.060(9) A and 2.221(3)A, respec- gands and the central phenyl ring as well as satisfy the geo-
tively] are typical.[5] The orientation of the 7-azaindolyl metric preference of the Ag(1) ion. The distance between
˚
groups in 2 is similar to their orientation in 1, with the the two Ag(1) centers in 3b is 6.594(2) A, similar to the
dihedral angles between the 7-azaindolyl planes and the PdϪPd distance observed in 1. The distances between the
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D. Song, S. Wang
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Figure 3. Top: a diagram showing the structure of 2 with labeling schemes; bottom, right: the hydrogen bond-linked 1D column; left: unit
cell packing diagram viewed down from the 1D column, the disordered CH2Cl2 solvent molecules are shown using space-filling models
Ag(1) center and the carbon atoms C(15), C(16) and C(17) Due to the poor solubility of 3a, NMR and X-ray diffrac-
˚
˚
of the central phenyl ring, which are 3.20 A, 2.72 A and tion experiments could not be carried out. Based on the
˚
3.17 A, respectively, are either close to or less than the van poor solubility, the elemental analysis and the structure of
der Waals contact distance of AgϪC (literature CϪAg 3b, we believe that 3a is likely to be a one-dimensional coor-
[7b]
˚
bond length: ഠ2.58 A).
Therefore, some weak bonding dination polymer, where the nitrate anions function as
interactions between the Ag centers and the central phenyl bridging ligands, linking the dinuclear silver units together
ring appear to be present. The Ag(1)ϪO(1) and (in a similar way as that observed in 3b) to form a coordi-
Ag(1)ϪO(3A) bond lengths are similar to those reported nation polymer chain.
previously.[7]
Because the meta structure displayed by complex 3b ap-
The extended structure of 3b is shown in Figure 4. Each pears to be the consequence of the relatively large ligands
molecule of 3b is bonded to four neighboring molecules DMSO and nitrate, we decided to examine the reaction of
through hydrogen bonding between the oxygen atom of the Zn(O2CCF3)2 with the ttab ligand, anticipating a meta
nitrate ion and a proton (H14Ј) on the 7-azaindole ring of structure similar to that of 3b. However, surprisingly, the
the neighboring molecule, as indicated by the O(4)···C(12Ј) product we isolated does not contain any coordination
distance of 3.33 A, to form a two-dimensional layered net- bonds between the ZnII ion and the ttab ligand. Instead,
˚
work. In the crystal lattice, these layers stack on top of one the ttab ligand and the Zn(O2CCF3)2(H2O)2 molecule lo-
another in an ABAB fashion, with toluene molecules filling cated in the crystal lattice are linked together via hydrogen
the gaps. Compound 3b slowly loses the DMSO ligands and bonds, as shown in Figure 5. The H2O ligands are from the
reverts back to 3a upon standing at ambient temperature. starting material. Repeated efforts to synthesize the water-
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PdII, ZnII and AgI Complexes of Tetrakis(N-7-azaindolyl)benzene
FULL PAPER
tion of a chiral lattice as shown in Figure 5. Interestingly,
the hydrogen-bonding interactions between the zinc()
complex and the ttab molecule are apparently retained in
non-coordinating solvents such as CH2Cl2, as confirmed by
the 1H NMR study, which shows that the chemical shifts of
the ttab molecule in 4 are drastically different from those
of the free ttab molecule. In coordinating solvents such as
DMSO, the NMR spectrum of 4 is identical to that of the
free ttab ligand, indicating the ZnII complex is no longer
interacting with the ttab ligand through hydrogen bonds. It
is very likely that the DMSO molecules coordinate to the
ZnII center and saturate the coordination sphere of the ZnII
ion, which may or may not lead to the replacement of the
H2O ligands at the zinc center. Due to the presence of an
excess of DMSO molecules, the H2O ligands are very likely
to form hydrogen bonds with the DMSO solvent molecules
instead of the ttab molecule, thus resulting in the free li-
gand-like behavior of the ttab molecule in DMSO. Toluene
solvent molecules were also found in the lattice of 4 (one
toluene per molecule of 4), which do not escape from the
crystal lattice at ambient temperature, as indicated by el-
emental analysis results.
Luminescent Properties
When irradiated by UV light, ttab emits a bright blue
light both in solution and in the solid state. The emission
maximum of ttab in a CH2Cl2 solution is at 377 nm when
the concentration of the solution is approximately 10Ϫ4 ,
while at high concentrations a significant red shift is ob-
served (e.g. 0.10  solution, emission maximum at approxi-
mately 463 nm), which can be attributed to intermolecular
interactions or excimer emission. Compound 1 shows no
detectable luminescence in solution or in the solid state, at-
tributable to the quenching by the PdII ion. Compound 2
is blue luminescent in solution and in the solid state (λmax ϭ
380 nm). Compound 3a is blue luminescent in the solid
Figure 4. Top: a diagram showing the structure of 3b with labeling
schemes; for clarity, the oxygen atoms on DMSO and the NO3Ϫ are
shown as ideal spheres; one of the disordered oxygen atoms [O(4A)]
is not shown; bottom: unit cell diagram showing two layers (red
and yellow) of hydrogen bond-linked 2D sheets
free complex [Zn(O2CCF3)2]2(ttab) were unsuccessful. De- state with the emission maximum at 432 nm. The substan-
spite the poor quality of the crystal of 4, the crystal data tial red shift of the emission band of 3a, compared to that
established unambiguously that the ZnII ion is coordinated of free ttab in solution, is clearly caused by intermolecular
to two trifluoroacetate ligands and two H2O ligands with interactions in the solid state. Due to the insolubility of 3a
an irregular geometry: four normal ZnϪO bonds and two in most solvents, no spectrum was recorded in solution.
˚
long ZnϪO bonds [Zn(1)ϪO(2)
ϭ
2.557(16) A, Compound 3b does not display any significant lumi-
˚
Zn(1)ϪO(4) ϭ 2.467(16) A]. The four non-coordinating ni- nescence in the solid state, weak blue luminescence from 3b
trogen atoms of the ttab ligands form hydrogen bonds with in solution was observed (λmax ϭ 375 nm). The emission
the coordinated H2O ligands. The N(8) and N(6) atoms are spectra of ttab, 2, 3a, 3b and 4 are shown in Figure 6. The
hydrogen-bonded to the O(6) atom while the N(2) and N(4) emission maximum of 2 (375 nm) in a CH2Cl2 solution (ap-
atoms are bonded to the O(5A) atom from a neighboring prox. 10Ϫ4 ) is essentially the same as that of the free li-
Zn(O2CCF3)2 (H2O)2 group, as indicated by the distances gand ttab. The emission bands of 2 and 3b in solution at
˚
˚
of O(5A)···N(2), 2.73(2) A; O(5A)···N(4), 2.74(2) A; the same concentration resemble that of the free ttab ligand
˚
˚
O(6)···N(6), 2.70(2) A; O(6)···N(8), 2.71(2) A. The in solution, indicating that they are all ttab-based emissions.
[Zn(O2CCF3)2 (H2O)2] unit therefore functions as a linker However, the intensity of the emission bands of 2 and 3b
for the ttab ligands through hydrogen bonds, leading to the is much weaker than that of the free ttab under the same
formation of an unusual hydrogen-bond linked 1D chain conditions, indicating that the ZnII ion and the AgI ion par-
(Figure 5). Extended structures involving metal complexes tially quench the emission from the ttab ligand. Compound
and organic molecules linked by hydrogen bonds have been 4 displays blue luminescence in solution. However, the emis-
reported previously.[8] One important feature of 4 is that the sion spectrum of 4 recorded in CH2Cl2 is blue-shifted by
hydrogen-bonded 1D chains are helical and rotate in the about 20 nm, compared to that of the free ttab ligand re-
same direction in the crystal lattice, resulting in the forma- corded under the same conditions. Furthermore, the emis-
Eur. J. Inorg. Chem. 2003, 3774Ϫ3782
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D. Song, S. Wang
FULL PAPER
Figure 5. Top: a diagram showing the structure of 4 with labeling schemes (a second [Zn(O2CCF3)2(H2O)2] unit from a neighboring
molecule is also shown to demonstrate the hydrogen bond pattern.); for clarity, the disordered fluorine atoms are omitted and all atoms
except zinc are shown as ideal spheres; bottom, right: the hydrogen bond linked 1D chain; left: the view projected down the 1D chain;
middle: the packing of the 1D chains in the lattice
sion intensity of 4 is about 1% of the intensity of the free
ttab ligand. These experimental observations provide
further support for the presence of hydrogen-bonding inter-
actions between the [Zn(O2CCF3)2(H2O)2] group and the
ttab ligand in solution. This appears to partially quench the
emission of the ttab ligand.
In summary, both the meta and ortho coordination
modes of the ttab ligand were established. The cyclometal-
lated bonding mode was not observed for the ttab ligand.
Both the coordination geometry of the metal ion and the
nature of the surrounding ligands appear to influence the
bonding mode of the ttab ligand. The unusual extended
structures displayed by the complexes of the ttab ligand and
its hydrogen-bonded compound were demonstrated. The
fact that these extended structures have the tendency to
host solvent molecules makes these compounds potentially
Figure 6. The emission spectra of ttab (1.0 ϫ 10Ϫ4 , CH2Cl2), 2
useful for applications in host-guest chemistry. The PdII ion
(1.0 ϫ 10Ϫ4 , CH2Cl2), 3a (solid), 3b (1.0 ϫ 10Ϫ4 , DMSO) and
appears to be capable of completely quenching the lumi- 4 (1.0 ϫ 10Ϫ4 , CH2Cl2)
3780  2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.eurjic.org
Eur. J. Inorg. Chem. 2003, 3774Ϫ3782

PdII, ZnII and AgI Complexes of Tetrakis(N-7-azaindolyl)benzene
FULL PAPER
nescence of the ttab ligand while the ZnII and AgI ions par-
tially quench the emission of the ttab ligand. Hydrogen-
bonding interactions also lead to the significant quenching
of the ttab luminescence. The sensitivity of the ttab lumi-
nescence toward various metal ions and hydrogen-bonding
interactions makes it potentially useful as a fluorescent
sensor for certain metal ions and molecules, which are being
investigated in our laboratory.
(1053.52): calcd. C 43.32, H 3.25, N 10.64; found C 42.85, H 3.20,
N 10.48.
Synthesis of [(ZnCl2)2(ttab)] (2): Anhydrous ZnCl2 (0.054 g,
0.4 mmol) and ttab (0.108 g, 0.2 mmol) were mixed in 20 mL of
THF and stirred overnight under nitrogen. The white precipitate
formed was collected by decanting the solution, it was washed with
THF and dried under vacuum to afford a white powder of 2
(0.148 g, 91%). 1H NMR (500 MHz, CD2Cl2, 25 °C): δ ϭ 9.14 (dd,
J ϭ 5.5, J ϭ 1.5 Hz, 4 H, 7-aza), 8.16 (dd, J ϭ 8.0, J ϭ 1.5 Hz, 4
H, 7-aza), 7.74 (d, J ϭ 4.0 Hz, 4 H, 7-aza), 7.55 (s, 2 H, phenyl),
7.30 (dd, J ϭ 8.0, J ϭ 5.5 Hz, 4 H, 7-aza), 6.72 (d, J ϭ 4.0 Hz, 4
H, 7-aza) ppm. 13C NMR (CD2Cl2, 25 °C): δ ϭ 147.9, 145.2, 139.3,
Experimental Section
136.1,
134.3,
131.7,
124.7,
117.5,
104.1 ppm.
All the starting materials were purchased from Aldrich Chemical
Co. THF was dried by refluxing over sodium and was freshly dis-
tilled prior to use. All the other reagent-grade solvents were used
without further purification. 1H and 13C NMR spectra were re-
corded on a Bruker Advance 300 or 500 MHz spectrometer. Exci-
tation and emission spectra were recorded on a Photon Technol-
ogies International QuantaMaster Model 2 spectrometer. Elemen-
tal analyses were performed by Canadian Microanalytical Service,
Ltd, Delta, British Columbia.
C34H22Cl4N8Zn2·0.5CH2Cl2 (857.66): calcd. C 48.32, H 2.70, N
13.07; found C 48.56, H 2.73, N 13.02.
Synthesis of [Ag2(NO3)2(ttab)]n (3a):
A solution of AgNO3
(0.50 mmol, 0.085 g) in 5 mL of H2O was layered on top of a solu-
tion of ttab (0.10 mmol, 0.0542 g) in 5 mL of CH2Cl2. After 12
days standing at ambient temperature, the white precipitate formed
was collected and washed with H2O, ethanol and then CH2Cl2, and
dried under vacuum to afford 3a (0.064 g, 73%). Compound 3a is
not soluble in non-coordinating solvents. As a result, NMR spectra
were not recorded. C34H22Ag2N10O6 (882.32): calcd. C 46.28, H
2.51, N 15.87; found C 46.91, H 2.65, N 15.75.
Synthesis of [(PdCl2)2(ttab)] (1): A solution of ttab (0.20 mmol,
0.108 g) in 20 mL of CH3CN was added to a solution of K2PdCl4
(0.40 mmol, 0.130 g) in a minimum amount of water. The mixture
was stirred at room temperature for 0.5 h, and the yellow precipi-
tate was collected by filtration and washed with CH3OH and di-
ethyl ether. Recrystallization of the crude product from DMSO
Synthesis of [Ag2(NO3)2(ttab)(DMSO)2] (3b): Upon dissolution in
DMSO under sonication, 3a was converted into 3b quantitatively.
1H NMR (300 MHz, DMSO, 25 °C): δ ϭ 8.50 (s, 2 H, phenyl),
yielded orange crystals of 1 (0.204 g 97%). 1H NMR (500 MHz, 8.24 (d, J ϭ 4.5 Hz, 4 H, 7-aza), 8.08 (d, J ϭ 7.5 Hz, 4 H, 7-aza),
[D6]DMSO, 25 °C): δ ϭ 8.93 (d, J ϭ 5.0 Hz, 4 H, 7-aza), 8.17 (s,
2 H, phenyl), 8.14 (d, J ϭ 7.0 Hz, 4 H, 7-aza), 7.70 (d, J ϭ 3.5 Hz,
7.24 (dd, J ϭ 7.8, J ϭ 4.8 Hz, 4 H, 7-aza), 7.10 (d, J ϭ 3.0 Hz, 4
H, 7-aza), 6.52 (d, J ϭ 3.6 Hz, 4 H, 7-aza) ppm. 13C NMR: δ ϭ
4 H, 7-aza), 7.29 (dd, J ϭ 7.0, J ϭ 5.0, 4 H, 7-aza), 6.76 (d, J ϭ 146.6, 143.6, 132.4, 129.7, 128.6, 128.1, 121.3, 117.0, 102.2 ppm.
3.5 Hz, 4 H, 7-aza) ppm. 13C NMR: δ ϭ 147.4, 145.6, 137.7, 136.7, The CHN analysis results for 3b are identical to those of 3a, due
132.3, 131.3, 122.3, 117.7, 103.4 ppm. C34H22Cl4N8Pd2·2DMSO
to the loss of DMSO ligands prior to the analysis.
Table 2. Crystallographic data
Compound
1
2
3b
4
Formula
FW
C34H22Cl4N8Pd2·2DMSO C38H34N8Zn2Cl4·4CH2Cl2 C38H34Ag2N10O8S2·2C7H8 C38H24N8O6F6Zn·C7H8
1053.45 1154.79 1222.88 962.13
˚
˚
˚
˚
Wavelength
Space group
0.71073 A
P21/n
12.072(3)
11.333(3)
15.538(4)
90
93.693(4)
90
2121.4(8)
2
0.71073 A
P1
0.71073 A
P21/c
10.032(4)
19.692(9)
13.866(6)
90
106.307(10)
90
2628.9(19)
2
0.71073 A
Pca21
18.853(11)
12.279(7)
19.603(11)
90
¯
˚
a, A
9.553(5)
9.753(5)
14.156(7)
85.300(13)
89.561(11)
63.010(9)
1170.8(11)
1
˚
b, A
˚
c, A
α, °
β, °
γ, °
90
90
3
˚
V, A
2628.9(19)
4
Z
Dcalc, g cmϪ3
T, K
1.649
297
1.638
296
1.545
298
1.408
298
µ, cmϪ1
12.42
17.48
8.88
6.22
2θ, max, °
Reflns measured
Reflns used
Parameters
Final R [I Ͼ 2θ(I)]
56.66
14855
5043
56.80
8374
5373
56.70
17597
6286
56.80
29882
8729
253
265
317
559
[a]
[a]
[a]
[a]
R1 ϭ 0.0459
R1 ϭ 0.0948
R1 ϭ 0.0625
R1 ϭ 0.0893
[b]
[b]
[b]
[b]
wR2 ϭ 0.0694
wR2 ϭ 0.1961
wR2 ϭ 0.1262
wR2 ϭ 0.1871
R (all data)
R1 ϭ 0.1362
wR2 ϭ 0.0823
R1 ϭ 0.2833
wR2 ϭ 0.2458
0.745
R1 ϭ 0.2822
wR2 ϭ 0.1682
0.685
R1 ϭ 0.3045
wR2 ϭ 0.2440
0.777
Goodness-of-fit on F2 0.769
[a]
[b]
2
2 2
2 2
2
2
2
R1 ϭΣ|F0| Ϫ |Fc|/Σ|F0|. wR2 ϭ [Σw [(F0 ϪFc ) ]/Σ[w(F0 ) ]]1/2, w ϭ 1/[σ2(F0 )ϩ(0.075P)2], where P ϭ [Max(F0 ,0)ϩ2Fc ]/3.
Eur. J. Inorg. Chem. 2003, 3774Ϫ3782
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3781

D. Song, S. Wang
Synthesis of [Zn(O2CCF3)2(H2O)2](ttab) (4): Zn(CF3COO)2·3H2O Supporting Information Available (see footnote on the first page of
FULL PAPER
(0.079 g, 0.23 mmol) and ttab (0.070 g, 0.13 mmol) were dissolved
in 20 mL of THF at ambient temperature. Slow diffusion of toluene
into the solution afforded colorless crystals of 4. (0.114 g, 91%). 1H
NMR (300 MHz, CD2Cl2, 25 °C): δ ϭ 8.49 (br. s, 4 H, H2O), 8.17
(s, 2 H, phenyl), 8.10 (d, J ϭ 4.2 Hz, 4 H, 7-aza), 7.25 (m, 8 H, 7-
aza), 7.11 (d, J ϭ 3.6 Hz, 4 H, 7-aza), 6.56 (d, J ϭ 3.6 Hz, 4 H, 7-
aza) ppm. For comparison purposes, the ttab free ligand 1H NMR
spectroscopic data are also included here (CD2Cl2, 25 °C): δ ϭ 8.25
this article): A complete drawing of compound 3b and the exci-
tation and emission spectra.
Acknowledgments
We thank the National Sciences and Engineering Research Council
of Canada for financial support.
3
4
(s, 2 H, phenyl), 8.16 (dd, J ϭ 5.0, J ϭ 1.5 Hz, 4 H, 7-aza), 7.85
3
4
3
3
(dd, J ϭ 7.5, J ϭ 1.5 Hz, 4 H, 7-aza), 7.05 (dd, J1 ϭ 7.5, J2 ϭ
5.0 Hz, 4 H, 7-aza), 6.98 (d, 3J ϭ 3.5 Hz, 4 H, 7-aza), 6.37 (d, 3J ϭ
3.5 Hz, 4 H, 7-aza) ppm. C38H26F6N8O6Zn·C7H8 (962.20): calcd.
C 56.17, H 3.56, N 11.65; found C 55.94, H 3.44, N 11.98.
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tained by slow diffusion of hexanes into a CH2Cl2 solution. Single
crystals of 1 were obtained from a saturated DMSO solution. Sin-
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¯
ttab and 2 belong to the triclinic space group P1. The crystals of 1
and 3b belong to the monoclinic space groups P21/n and P21/c,
respectively. The crystals of 4 belong to the orthorhombic space
group Pca21. All structures were solved by direct methods. DMSO
molecules were located in the lattice of 1 (2 DMSO per molecule
of 1). Disordered CH2Cl2 molecules were located in the lattice of
2 (4 CH2Cl2 per molecule of 2). Toluene molecules were located in
the lattice of 3b and 4 (2 toluene per molecule of 3b, 1 toluene per
molecule of 4). There are 1.5 independent molecules in the asym-
metric unit of ttab. The disordered nitrate ions of 3b and the
CH2Cl2 molecules that co-crystallized with 2 were modeled success-
fully. All non-hydrogen atoms in 1؊3b were refined anisotropically
except for the disordered nitrate ion, the co-crystallized toluene and
CH2Cl2 molecules. The quality of the crystals of 4 is poor and
partially twin. The CF3 groups in 4 are all disordered. As a result,
not all non-hydrogen atoms in 4 can be refined anisotropically. The
positions of the hydrogen atoms were calculated and their contri-
butions in structural factor calculations were included. The crystal
data are summarized in Table 2. (The crystal data for the free ttab
ligand are provided in the supporting information).
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[8]
[9]
CCDC-213370 (1), -213371 (3b), -213372 (4), and -213374 (2) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge at www.ccdc.cam.ac.uk/conts/
retrieving.html [or from the Cambridge Crystallographic Data
Centre, 12, Union Road, Cambridge CB2 1EZ, UK; Fax: (in-
ternat.) ϩ44-1223/336-033; E-mail: deposit@ccdc.cam.ac.uk].
[10]
Received April 29, 2003
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Eur. J. Inorg. Chem. 2003, 3774Ϫ3782