Quaterphenylterpyridine: Synthesis and metal-ion complexation

Article abstract of DOI:10.1002/ejic.201300816

A quaterphenylterpyridine ligand (qptpy) with the rodlike quaterphenyl unit attached in the 4′-position has been synthesised by a Pd-catalysed Suzuki cross-coupling reaction. A crystal structure determination on the complex [Zn(qptpy)Cl₂]·dmf (

Full text of DOI:10.1002/ejic.201300816

FULL PAPER
DOI:10.1002/ejic.201300816
Quaterphenylterpyridine: Synthesis and Metal-Ion
Complexation
[
a]
[b]
[c]
Young Hoon Lee, Akira Fuyuhiro, Jack M. Harrowfield,
[
a]
[d]
[e]
Yang Kim,* Alexandre N. Sobolev, and Shinya Hayami
Keywords: N ligands / X-ray diffraction / Aromatic interactions / Fluorescence spectroscopy / Zinc
A quaterphenylterpyridine ligand (qptpy) with the rodlike
quaterphenyl unit attached in the 4Ј-position has been syn-
thesised by a Pd-catalysed Suzuki cross-coupling reaction. A
crystal structure determination on the complex [Zn(qptpy)-
matic groups involving just the polar terpyridine head groups
to give an infinite, offset face-to-face (OFF) π-stacking array.
A comparison is made with the structures of the bis(ligand)
4 2 4 2
complexes of Zn(ClO ) and Cd(ClO ) with the bromobi-
Cl
2
]·dmf (dmf = dimethylformamide) has shown the ligand to
-tridentate manner to the essen-
phenylterpyridine ligand (Brbptpy) synthesised as an inter-
mediate for the formation of qptpy. A study of the absorption
and emission spectra of qptpy and a range of its metal-ion
complexes has shown that the ligand provides a ratiometric
be bound in the expected N
3
tially trigonal-bipyramidal dichloro metal ion, with the quat-
erphenyl substituents involving a twisted array of the sepa-
rate phenyl groups and the shortest contacts between aro-
II
II
fluorescence response for both Zn and Cd .
Introduction
that generally only just reaches the visible region. The ter-
pyridine platform, nonetheless, is one for which numerous
methods of functionalisation are well established and thus
A “push–pull” fluorophore in which electron-donating
and electron-withdrawing substituents are linked by a con-
jugated system can display efficient intramolecular charge
transfer (ICT) between the donor and the acceptor upon
excitation by light, which effectively leads to a redshift of
the emission from the initial excited state.[1] Metal-ion bind-
ing can result in significant enhancement of the acceptor
characteristics of a ligand, and this effect has been exploited
in the use of ICT fluorescence to detect and quantify vari-
ous metal ions. As a metal-ion binding site, the terpyrid-
ine core has received considerable attention owing to the
stability of its complexes with a wide range of metal ions.
It has not, however, been considered a useful fluorophore
in its unsubstituted form because of the need for short
wavelengths for its excitation and consequently an emission
[4]
it has been possible to produce a variety of derivatives of
[5]
real applicability.
Various well-known fluorophores such as difluorobora-
[6]
[7,8]
[9]
azaindacene (BODIPY), pyrene
and anthracene have
indeed been grafted to terpyridine to provide ICT-sensitive
fluorophores, which, as metal-ion complexes, have found
different applications. A BODIPY-functionalised terpyrid-
ine, for example, provides an extremely sensitive sensor for
[
2]
II [6]
II
Zn , whereas the Zn complex of a pyrene-appended ter-
pyridine shows a ratiometric fluorescence change in re-
[
3]
[7]
sponse to phosphate anions. Many other transition-metal
ions have been studied for their influence upon the emissive
[5,10]
properties of functionalised terpyridines,
and a particu-
larly significant aspect of this work has been the demonstra-
tion that the emission characteristics might depend not only
on the nature of the substituent but also upon aggregation
of the complex ions induced by their substituents. These
aggregation effects have been thoroughly studied for polycy-
[
a] Department of Chemistry & Advanced Materials, Kosin
University,
1
94, Wachi-Ro, Yeongdo-gu, Busan 606-701, South Korea
E-mail: ykim@kosin.ac.kr
http://ykim.tistory.com/
clic aromatic substituents, some as large as tetraphenyle-
[
[
[
[
b] Department of Chemistry, Graduate School of Science, Osaka
University,
[11]
thene.
A useful feature of such “push” components is
Toyonaka, Osaka 560-0043, Japan
that they are neither acidic nor basic, and thus, unlike
c] Laboratoire de Chimie Supramoléculaire, Institut de Science et
d’Ingénierie Supramoléculaires, Université de Strasbourg,
[12]
otherwise very effective amino substituents,
ted by changes in solution acidity.
are unaffec-
8, allée Gaspard Monge, 67083 Strasbourg, France
d] School of Chemistry and Biochemistry, M313, University of
Western Australia,
Recognising these facts and given our demonstration of
II
remarkable magnetic behaviour of Co complexes of
Crawley, WA 6009, Australia
e] Department of Chemistry, Graduate School of Science and terpyridines with very long alkyl-chain substituents,[ our
13]
Technology, Kumamoto University,
objective in the present work was to characterise a terpyrid-
ine functionalised in the 4Ј-position with a long quater-
phenyl substituent, thereby amplifying our previous
2
-39-1 Kurokami, Kumamoto 860-8555, Japan
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300816.
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work[14] on the introduction of linear polyphenyl units. As netics,[16] but the use of the metal(II) perchlorates and tri-
a preliminary investigation of 4Ј-[1,1Ј:4Ј,1ЈЈ:4ЈЈ,1ЈЈЈ]-quater- flates as reactants led with qptpy to the ready isolation of
phenyl-4-yl-[2,2Ј:6Ј,2ЈЈ]-terpyridine (qptpy), with its ex- [M(qptpy) ](ClO ) and [M(qptpy) ](CF SO ) for M = Zn,
2
4 2
2
3
3 2
tended, “rigid rod” aromatic substituent, the absorption Cd. The ESI mass spectra (see the Supporting Information)
and emission spectra of the free ligand and a variety of its of these materials in acetonitrile showed major peaks for
complexes formed with labile metal ions have been studied just [ML2]2 species.
to establish where luminescence may be observed and
+
The cations [M(Brdptpy)2]2 (M = Zn, Cd) were readily
+
whether there are appreciable metal-ion-induced redshifts crystallised as their (acetonitrile-solvated) perchlorate salts
in the emission. The nature of possible substituent-induced following essentially identical procedures to those used for
aggregation effects in the solid state has also been examined the qptpy complexes.
by a crystal structure determination on the complex
[
Zn(qptpy)Cl ]·dmf (dmf = dimethylformamide). Useful
2
Absorption and Emission Spectroscopy of the Ligand and
its Metal-Ion Complexes
comparisons can be drawn with the structures of the bis-
ligand) complexes of Cd(ClO ) and Zn(ClO ) with the
(
4
2
4 2
bromobiphenylterpyridine ligand Brbptpy formed as an in-
termediate for the synthesis of qptpy.
The very low solubility of qptpy even in solvents of but
moderate polarity rendered the study of metal-ion complex-
ation reactions difficult, but a 1:1 mixture of CHCl and
3
CH CN proved adequate for preliminary measurements on
3
Results and Discussion
both the ligand and its complexes. For qptpy, a strong peak
4
–1
–1
at 319 nm (ε = 6.1ϫ10 m cm ) was taken to be a π–π*
Syntheses
[
17]
transition, as in the case of the parent ligand.
A broad
As the first step, 4Ј-(4Ј-bromobiphenyl-4-yl)-[2,2Ј:6Ј,2ЈЈ]- emission centred about 410 nm was observed on excitation
terpyridine (Brbptpy) was synthesised by the reaction of 4Ј- at 319 nm (Figure S1 in the Supporting Information). Con-
bromobiphenyl-4-carbaldehyde,[
15]
[1,2]
2-acetylpyridine, KOH sistent with an ICT origin of the fluorescence,
the emis-
and ammonia in ethanol under reflux to give a white solid. sion maximum underwent a slight redshift (ca. 15 nm) with
The ligand qptpy was then obtained, also as a white solid, increasing solvent polarity (Figure S2 in the Supporting In-
by means of a Pd-catalysed Suzuki cross-coupling reaction formation). The absorption spectrum of
a dilute
was sensi-
3
of Brbptpy with biphenyl-4-boronic acid (Scheme 1). The (2ϫ10–5 m) solution of qptpy in CH
CN/CHCl
3
crude product had poor solubility in common organic sol- tive to the addition of an excess amount of several of the
vents and was purified by Soxhlet extraction into chloro- perchlorate salts of a variety of labile transition-metal ions
II
II
II
II
II
III
II
II
form.
(Cd , Co , Cu , Ni , Fe , Fe , Hg , Zn ) with, as ex-
II
pected, addition of Fe resulting in a dramatic colour
change to violet, which was indicative of the formation of
[
4,5,10]
the low-spin complex.
Thus, the presence of a pol-
yphenyl appendage appears to have no major detrimental
influence upon the coordinating ability of the terpyridine
unit.
For the same series of metal ions in a large (tenfold) ex-
II
II
cess amount over the ligand, only Zn and Cd caused sig-
nificant modification (redshift) of the emission spectrum
other than a simple diminution (quenching) of the free li-
Scheme 1. Ligand synthesis: (i) n-butyllithium, THF, –78 °C; (ii)
dmf, 40%; (iii) 2-acetylpyridine, NH
biphenyl-4-boronic acid, degassed 2 m aqueous Na
PPh ], 1,2-dimethoxyethane, 71%.
3
(aq.), KOH, EtOH, 51%; (iv)
2
CO , [Pd-
3
(
3 4
)
Complex [Zn(qptpy)Cl ]·dmf was obtained as a white
2
powder after reaction of L with ZnCl in dmf. This 1:1 com-
2
plex was obtained even when using a 1:2 (M/L) ratio in
the reaction mixture, presumably owing to its low solubility,
although since the stability constants for the binding of
[
3]
these metals to terpyridine are not extremely high, it is
2
+
2+
possible that both [Zn(qptpy)] and [Zn(qptpy)2] species
were present in the reaction mixture. It is known as well for
complexes of unsubstituted terpy that the species distri-
Figure 1. Fluorescence spectra of qptpy (L = 5 μm; λex = 319 nm)
3 3
in CHCl /CH CN (50:50 v/v) upon addition of 10 molar equiva-
lents of various metal perchlorates. Inset: visual emission of qptpy,
II
II
bution in solution is sensitive to the counter anion and ki- Zn /qptpy and Cd /qptpy solutions.
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Figure 2. Fluorescence changes for qptpy (5 μm) upon addition of (a) 0, 0.2, 0.4, 0.8, 1.0 equiv. of Zn(ClO
4
)
2
and (b) 0, 0.2, 0.4, 0.6, 0.8,
4 2 3 3
1.0 equiv. of Cd(ClO ) in CH CN/CHCl (1:1 v/v; λex = 319 nm).
gand emission (Figure 1). As closed-shell species it is of
II
II
course expected that Zn and Cd should not cause redox
quenching, and their weaker spin–orbit coupling might ex-
plain why they do not quench ICT state luminescence to
II [1,2,4,5,18]
the same extent as their congener Hg .
(Given the
high M/qptpy ratio, it is assumed that any complex present
was a 1:1 species).
More precise fluorescence titrations (Figure 2) were con-
II
II
ducted for Zn and Cd under conditions (L = 5 μm in
CH CN/CHCl ; λ = 319 nm) in which the ligand was ini-
3
3
ex
tially in large excess amount over the metal ions so that
presumably both ML and ML species were present in vary-
2
II
ing amounts throughout the titrations. For Zn (Figure 3,
a) and Cd (Figure 3, b), the diminution in the ligand emis-
II
sion near 400 nm was accompanied by the rise of a red-
shifted band with two components centred near 500 and
540 nm. The appearance of emission at a lower energy than
in the ligand is consistent with metal-ion binding enhancing
the “pull” character of the terpyridine terminus of the
ligand in an ICT transition, and it would appear that this
2
+
2+
is so in both [M(qptpy)] and [M(qptpy) ] .
2
When fluorescence spectra were recorded on solutions
(
5 μm) of the isolated [M(qptpy) ](ClO ) complexes in
2 4 2
acetonitrile, the observations were essentially identical, with
some dissociation being evident from the presence of a
weak band that corresponded to free ligand emission.
In the solid state (Figure 3, a), emission from the ligand
was remarkably broad but, in the absence of a crystal struc-
ture determination, it is unclear why this should have been
so. Emission from [Zn(qptpy)Cl ] (Figure 3, a) showed a Figure 3. (a) Solid-state emission, λex = 319 nm, from qptpy (black
2
trace; λem = 420, 439 nm) and [Zn(qptpy)Cl
09 nm), and (b) [Zn(qptpy) ](BPh (black trace; λem = 520 nm)
and [Cd(qptpy) ](CF SO (red trace; λem = 505 nm).
2
] (red trace; λem =
maximum at 509 nm, a slightly shorter wavelength than that
for the bis(ligand) complex [Zn(qptpy) ](BPh ) (Figure 3,
b), thus indicating that the bicomponent emission observed
in solution might be attributed to the presence of both bis-
5
2
4 2
)
2
4 2
2
3
3 2
)
and mono-ligand species. The emission from [Cd(qptpy)2]- by a similar amount to that seen for the qptpy complex.
CF SO ) (λ = 505 nm) indicated that in the solid state {The band shift for [Cd(Brdptpy) ](ClO ) was again rather
(
3
3 2
em
2
4 2
II
at least, Cd has a significantly weaker polarising effect on smaller than that of the Zn complex.} Whereas the crystal
qptpy than does Zn .
II
structures (see below) indicate that both the bromobiphenyl
The solid-state emission from the free ligand precursor and quaterphenyl tails are twisted relative to the terpyridine
to qptpy, Brbptpy, was considerably sharper than that of head, so that delocalisation is inhibited, the (counter)po-
qptpy, but the emission from [Zn(Brdptpy) ](ClO ) (Fig- larity due to the bromo substituent appears to have a sig-
2
4 2
ure 4) was shifted to lower energies from that of the ligand nificant effect on the ICT transition energy.
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are all rather remote, with the shortest being of the CH···π
type, though none are shorter than 3 Å. No C···C contact
is shorter than 3.5 Å. Despite the presence of the quater-
phenyl tail and solvent of crystallisation, the stacking in
[21]
[
Zn(L)Cl ]·dmf is very similar to that in [Zn(terpy)Cl ],
2
2
although in that lattice there are two slightly different stacks
to form parts of infinite columns.
Figure 4. Solid-state fluorescence of Brbptpy (black), [Zn-
Brdptpy) ](ClO (red) and [Cd(Brdptpy) ](ClO (green); λex
30 nm.
(
2
4
)
2
2
4 2
)
3
X-ray Structure Determinations
Although 1:2 metal-ion complexes of substituted terpyr-
Figure 5. Molecular structure of [Zn(qptpy)Cl ]·dmf with prob-
2
ability displacement ellipsoids plotted at the 50% level. The dmf
molecule is omitted.
[4,5,10,14]
idines are well known,
in the present work, with
II
Zn , the 1:1 species [Zn(qptpy)Cl ]·dmf was readily isolated
2
in a form suitable for an X-ray structure determination, and
its structure is therefore of interest in defining the metal–
ligand interaction in the presence of simple anionic co-
ligands. The complex ion present in this crystalline solid is
a five-coordinate species with, as expected, the ligand qptpy
bound in a tridentate manner through the terpyridine site
and two chlorido ligands occupying equatorial sites of the
essentially trigonal–bipyramidal coordination sphere (Fig-
ure 5). The structural characteristics of the ZnN unit are
3
unexceptional, with the central Zn–N2 bond [2.095(3) Å]
significantly shorter than either bond to the flanking N do-
nors [2.218(3); 2.208(3) Å], although all seem slightly long
2
Figure 6. Packing diagram for [Zn(qptpy)Cl ]·dmf showing the for-
relative to the corresponding bond lengths in closely related mation of supramolecular chains by π–π interactions (dotted lines;
[
10a,14]
ZnL species.
Whereas the first phenyl unit is nearly centroid···centroid distance of 3.260 Å). Hydrogen atoms and dmf
2
molecules are omitted for clarity.
coplanar with the central pyridine ring to which it is bound
dihedral angle ca. 3°), the other phenyl rings are all signifi-
cantly tilted (dihedral angles between 30 and 45°) with re-
spect to one another, presumably due to repulsions between structures of complexes of terpyridine and its derivatives is
(
The subtlety of factors that influence the solid-state
[
19]
hydrogen atoms. Thus, at least in the solid state, conjuga- nicely illustrated by comparison of the structure discussed
tion is limited to that of the first phenyl ring with the above with those of [Zn(Brbptpy) ](ClO ) ·2CH CN and
2
4 2
3
terpyridine unit. In relation to forms of aggregation that [Cd(Brbptpy) ](ClO ) ·CH CN. Although these two com-
2
4 2
3
might be a consequence of the introduction of a polyphenyl plexes have lattices that belong to the same space group,
tail, it is interesting that the dichlorozinc–terpyridine head they are not isostructural, and differ very clearly in the ex-
groups form stacked arrangements that are as prominent as tent to which the “terpyridine embrace” is retained. The
the “terpyridine embrace” commonly observed in bis- cationic complexes within the two crystals have a very sim-
terpyridine) complexes.[
10a,20]
This stacking results in co- ilar form (Figure 7), with the expected MN coordination
(
6
lumnar arrays (along c, Figure 6), which appear to be iso- sphere (Table 1) being slightly inflated for Cd relative to Zn
lated from one another by the interposition of quaterphenyl and very similar, for both metals, to those in complexes of
[
10a,14]
tails. This is probably an oversimplified view, since there do the bi- and terphenyl derivatives of terpyridine.
Disor-
appear to be at least some edge-to-face (EF) contacts be- der within one of the terminal bromophenyl rings of the Zn
tween tails and the terpyridine units, but it does raise the complex (accompanying disorder of the perchlorate anions
possibility that in aqueous solutions the complexes could and one acetonitrile molecule) renders its description a little
form micelles through tail association and that this could complicated, but the overall length of the cations, expressed
influence their luminescence behaviour. A significant fea- as the terminal Br substituent separations, is 30.357(2) Å
ture of the tail-to-tail contacts within the crystal is that they for the Zn complex (taking just the major component of
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the disorder) and 30.53(1) Å for the Cd. As expected, the bending in both cases being, presumably, a consequence of
bromobiphenyl substituents are twisted, both internally and lattice interactions. As for the analogous complexes with
[
10a]
[14]
with respect to the terpyridine units, with dihedral angles simple biphenyl
and terphenyl substituents on the 4Ј-
ranging from 18 to 35° for the Zn complex (major compo- position of terpyridine, the lattices of both complexes can
nent) and 11 to 31° for the Cd (the two substituents in each be considered to contain sheets of cations in which the sub-
cation being inequivalent). The Br···M···Br angles are 167° stituents lie within these sheets. Here, however, some
(Zn; major component) and 158° (Cd), which means that marked differences are apparent between the two Brdptpy
the latter complex can be considered slightly more bent, the complexes.
Figure 7. Molecular structure of (a) [Zn(Brbptpy)]2+ and [Cd(Brbptpy)]2+ cations with probability displacement ellipsoids plotted at the
50% level. Only the major component of the disordered bromophenyl ring (involving Br2) in the Zn complex is shown.
Table 1. Selected bond lengths [Å] and angles [°] for [Zn(qptpy)Cl
CH CN.
2
]·dmf, [Zn(Brbptpy)
2
](ClO
4
)
2
·2CH
3
CN and [Cd(Brbptpy)
2
4 2
](ClO ) ·
3
[Zn(qptpy)Cl
2
]·dmf
[Zn(Brbptpy)
2
](ClO
4
)
2
·2CH CN
3
2 4 2 3
[Cd(Brbptpy) ](ClO ) ·CH
CN
Zn–N1
Zn–N2
Zn–N3
Zn–Cl1
Zn–Cl2
2.218(3)
2.095(3)
2.208(3)
2.2698(10)
2.2444(11)
Zn–N1
Zn–N2
Zn–N3
Zn–N4
Zn–N5
Zn–N6
2.175(4)
2.067(4)
2.212(4)
2.175(4)
2.064(4)
2.182(4)
Cd–N1
Cd–N2
Cd–N3
Cd–N4
Cd–N5
Cd–N6
2.336(4)
2.287(4)
2.357(4)
2.359(4)
2.313(4)
2.305(4)
N1–Zn–N2
N1–Zn–N3
N2–Zn–N3
Cl1–Zn–N1
Cl1–Zn–N2
Cl1–Zn–N3
Cl2–Zn–N1
Cl2–Zn–N2
Cl2–Zn–N3
Cl1–Zn–Cl2
74.63(12)
149.17(11)
74.59(12)
101.91(9)
122.72(9)
93.26(8)
98.39(8)
121.48(9)
98.95(9)
N1–Zn–N5
N2–Zn–N5
N1–Zn–N2
N5–Zn–N6
N1–Zn–N6
N2–Zn–N6
N4–Zn–N5
N1–Zn–N4
N2–Zn–N4
N4–Zn–N6
N3–Zn–N5
N1–Zn–N3
N2–Zn–N3
N3–Zn–N6
N3–Zn–N4
105.06(15)
179.19(17)
75.74(16)
75.96(15)
89.86(15)
104.00(15)
76.21(14)
98.60(15)
103.81(15)
152.14(14)
103.38(15)
151.51(14)
75.81(15)
95.49(15)
89.61(15)
N2–Cd–N6
N2–Cd–N5
N6–Cd–N5
N2–Cd–N1
N6–Cd–N1
N5–Cd–N1
N2–Cd–N3
N6–Cd–N3
N5–Cd–N3
N1–Cd–N3
N2–Cd–N4
N6–Cd–N4
N5–Cd–N4
N1–Cd–N4
N3–Cd–N4
124.41(15)
160.44(14)
70.54(14)
70.72(14)
88.86(15)
125.63(14)
69.53(14)
102.39(15)
96.17(13)
137.92(14)
95.46(14)
139.79(14)
69.44(14)
111.48(15)
85.63(14)
115.63(4)
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In the lattice of [Zn(Brbptpy) ](ClO ) ·2CH CN, sheets but the sheets considered here are of a very simple form
2
4 2
3
II
that lie parallel to the bc plane contain the cations with and provide a convenient means of distinguishing the Zn
their bromobiphenyl substituents lying essentially in those complex from its Cd analogue (see below). Thus, in one
sheets. The distribution of the cations within these sheets sheet in which all the Zn atoms are coplanar, the cations
II
resembles those found in other bis(ligand) complexes of form a rectangular gridlike array (Figure 8, a), with the
polyphenylterpyridines,[
12a,14]
though with some particular Zn···Zn distances that define the sides of the rectangles be-
characteristics (as in the other cases). Dissection of the ing 9.1277(8) and 33.701(1) Å. The long edges are essen-
sheets in terms of weak interactions that involve the cations tially defined by confronting bromobiphenyl units and in-
can be performed in various ways, but if perchlorate O···C volve Br···Br contacts of 3.421(1) (major component of dis-
contacts Յ3.20 Å (for just the major component of the dis- order) and 3.738(3) Å (minor), which might be indicative of
[
22]
ordered anions) are taken as being indicative of significant some contribution of halogen bonding to the array. The
links, then they define zigzag chains of cations, with a mean short edges, which involve the shortest Zn···Zn separation
axis parallel to b, in which the Zn···Zn separation is of the lattice, define a vestigial “terpyridine embrace”[
20]
11.543(1) Å, with no clear direct contacts between the that involves two opposed pairs of peripheral pyridine rings
ligands. To form the sheet, these zigzag chains lie side by on each cation with, in what appear to be close to true OFF
side, thereby leading to interdigitation of the bromobi- contacts, a centroid···centroid separation of 3.8079(3) Å,
phenyl tails and the formation of cation pairs in which the three C···C separations Յ3.5 Å [3.408(8), 3.431(8) and
Zn···Zn separations are either 10.954(1) or 17.1279(8) Å. 3.445(8) Å] and two CH···π contacts just Ͻ3 Å [2.964(5),
(These are the only cation pairs in which part or all of an- 2.997(6) Å]. Each pair within the effectively infinite chain
other cation is not interposed.) The confrontations within of cations that involves these contacts is also bridged by
these pairs lead to a number of C···C contacts Յ3.50 Å, but contacts to perchlorate anions (C···OՅ3.20 Å), although
these cannot be described as reflecting true offset face-to- disorder renders the interactions difficult to describe (O···π
face (OFF) arrays in that the associated aromatic rings are and/or O···HC?) and ambiguous with respect to their ex-
far from lying parallel. In the more remote pair, one Br···π tent.
contact [Br2···C42Ј 3.537(6) Å; symmetry operation x, 0.5 –
y, 0.5 + z] bridges the two cations, but it might be that other the Zn and Cd complex cations, the lattice of
Despite the fairly minor dimensional differences between
II
II
interactions of the bromo units are more important. Thus, [Cd(Brbptpy) ](ClO ) ·CH CN differs markedly from that
2
4 2
3
an alternative dissection of the lattice is to consider that the of its Zn analogue, with all vestiges of a terpyridine em-
cations and their tails lie within sheets parallel to the ac brace, for example, being lost and all Br···Br contacts being
plane. This is a more complicated dissection in that the sep- Ͼ4.0 Å. The cations can be considered to lie in sheets, here
arations between the sheets alternate between 3.55 and parallel to the (1 0 –1) plane (Figure 8, b), defined by their
5.22 Å and it might be more appropriate to consider that inclusion of the substituent groups, with the metal centres
the closer sheets actually constitute one undulating sheet, alternating in a slight displacement about this plane. In pro-
Figure 8. (a) View of a portion of one sheet of complex cations lying parallel to the ac plane in the lattice of [Zn(Brbptpy)
CH CN. Only the major component of the disordered bromophenyl unit is shown. (Vertical) chains involving OFF interactions and
horizontal) chains involving Br···Br approaches are evident. (b) View of a portion of one sheet of complex cations lying parallel to the
1 0 –1) plane in the lattice of [Cd(Brbptpy) ](ClO ·CH CN. Here, the shortest Br···Br contacts are 4.083(2) Å. Hydrogen atoms, solvent
2 4 2
](ClO ) ·
2
3
(
(
2
4
)
2
3
molecules and anions are omitted from both views; the cations are shown as stick representations.
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jection onto the plane, this sheet resembles that which lies in the complexes [Zn(tptpy) ](ClO ) and [Cd(tptpy)2]-
2
4 2
II
[14]
parallel to the bc plane in the Zn complex lattice, and it is (ClO4)2
again possible to discern two types of cation pairs [Cd···Cd appear to involve the terminal and next-to-terminal rings.
5.494(6) and 19.46(1) Å] in which no other cation, in As noted above, these comparisons involve different anions,
the closest contacts to the terphenyl tail units
1
whole or in part, is interposed. The closer pair involves and although it can be said that in both [Zn(bptpy)2]-
OFF contacts between the terminal (bromo)phenyl ring (BF ) and [Zn(tptpy) ](ClO ) , for example, there is anion
4
2
2
4 2
and two rings of the terpyridine head [centroid separation bridging of the closest cation pairs, the exact nature of the
of 3.754(1) Å; one C···N contact of 3.426(6) Å plus C···C cation···anion contacts is quite different in the two cases.
contacts of 3.379(6), 3.446(7) and 3.480(6) Å], whereas the
more remote pair has two Br···HCaromatic links and two
C···C contacts between phenyl rings that do not lie parallel Conclusion
to one another. As in the Zn complex sheet, zigzag chains
of cations that run parallel to b and bridged by interactions
with the perchlorate anions (defined by O···C contacts
Յ3.20 Å) can be identified, but the Cd···Cd separation
Introduction of a quaterphenyl chain in the 4Ј-position
II
of terpyridine produces a ligand (qptpy) to give Zn and
II
Cd complexes with emissive properties consistent with an
ICT excited state being significantly modified in energy by
[
14.4844(8) Å] is relatively long and is not associated with
the metal-ion coordination. In the solid state for the molec-
any clear aromatic···aromatic contacts, again as for the Zn
complex. The shortest Cd···Cd distance [9.987(2) Å] in the
sheet is associated with a pair of complex cations in which
once more there is no indication of significant
aromatic···aromatic contacts, perhaps because of the
intrusion of two tails of other cation units between them,
and the approach of the cations might be a consequence
II
ular dichloro–(qptpy)Zn complex, π stacking of the terpy-
ridine head groups does not appear to be perturbed by in-
teractions with the polyphenyl tails and results in columnar
arrays of the complex units very similar to those seen in the
lattice of the unsubstituted ligand complex. There is segre-
gation of the quaterphenyl tails into particular regions of
the lattice, but this does not appear to be associated with π
stacking and might at most involve some rather remote
CH···π (edge-to-face) interactions. In contrast, in the cat-
of bridging by
O···HCCN···HCaromatic). In contrast, any two adjacent
chains of cations in which the Cd···Cd separation is
9.46(1) Å can be considered to define a zigzag chain with
a
perchlorate–acetonitrile chain
(
II
II
ionic bis(ligand) Zn and Cd complexes of the precursor
ligand Brbptpy found in the lattices of their perchlorate
salts, significant stacking interactions that involve the sub-
stituent tails as well as the terpyridine head groups do seem
to be evident. As in known structures of complexes of ter-
pyridine with 4Ј bi- and terphenyl substituents, the shortest
of these OFF interactions are always associated with anion
bridging (through CH···X and/or X···π interactions), so if
stacking interactions that involve single ring contacts can
be attributed no more significance than that of dispersion
1
a Cd···Cd pair separation of 11.522(4) Å, and here, despite
partial intrusion of tails of other cations between the pairs,
closely parallel bromophenyl and peripheral pyridine rings
can be discerned, with a centroid separation of 3.7705(6) Å
and four short C···C contacts [3.381(8), 3.428(7), 3.438(7),
3.476(8) Å], plus what might be an EF interaction that in-
volves a bromophenyl ring and a phenyl ring bridging ter-
pyridine and bromophenyl units. This reinforces the indica-
tion given by the consideration above of the 15.494(6) Å
pair that any aromatic···aromatic interactions are favoured
for the more polar entities (in accord with a well-known
model of porphyrin stacking[ ).
[
24]
forces, the dramatic changes in aromatic···aromatic inter-
action patterns with seemingly minor changes in the cation
seen in the present and related studies might be due to the
very minor contribution of stacking energies to the total
lattice energy and the adaptation of stacking to structures
determined by more powerful forces.
23]
The importance of ring polarisation in enhancing
aromatic···aromatic interactions is further indicated in com-
paring the above two structures with those known for their
analogues in which the bromo substituent is absent,
[10a]
[
Zn(bptpy) ](BF ) and [Cd(bptpy) ](PF ) .
Whilst the
2
4 2
2
6 2
Experimental Section
difference in anion components must have some influence,
and the vestigial terpyridine embraces (i.e., peripheral
pyridine···peripheral pyridine contacts) in these two crystals
are associated with anion bridging (assuming a C···F
contact distance of 3.20 Å to be significant), other
General: All chemicals were purchased from Wako Co. and used
without further purification. Elemental analyses (C,H,N) were car-
ried out at the Instrumental Analysis Centre of Kumamoto Univer-
1
sity. H NMR spectra were recorded with a JEOL (500-ECX) in-
strument (500 MHz) and Bruker 300 AM spectrometer
300.13 MHz) in deuterated solvents using TMS as internal refer-
ence. Electronic absorption and fluorescence spectra were recorded
with a SCINCO S-2100 spectrophotometer and a Perkin–Elmer
aromatic···aromatic
contacts,
characterised
by
(
centroid···centroid distances Ͻ4.3 Å but not necessarily by
closely parallel ring planes[
10a]
nor by anion bridging, ap-
pear to involve predominantly the inner phenyl ring of the LS55 spectrofluorimeter, respectively. Infrared spectra were mea-
tail. Its proximity to the polar terpryidine head must render sured with a Shimadzu FTIR 8700 instrument using KBr discs.
it the more polar of the two substituent rings. That
4
Ј-(4Ј-Bromobiphenyl-4-yl)[2,2Ј:6Ј,2ЈЈ]terpyridine (Brbptpy): A mix-
aromatic···aromatic interactions are relatively unimportant
ture of 4Ј-bromobiphenyl-4-carbaldehyde (2.80 g, 10.7 mmol), 2-
and thus subject to marked influence by seemingly minor acetylpyridine (3.0 g, 21 mmol), KOH (1.7 g, 30 mmol) and aque-
changes in a system, however, is indicated by the fact that ous ammonia (30%, 60 mL) in EtOH (100 mL) was heated at reflux
Eur. J. Inorg. Chem. 2013, 5862–5870
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for 3 d to afford a dark brown solution. The mixture was evapo-
rated to dryness under reduced pressure and the residue washed
with MeOH before being purified by column chromatography on
allowed to evaporate slowly at room temperature to give colourless
rodlike crystals suitable for X-ray diffraction studies.
C H34Cl N OZn (747.04): calcd. C 67.52, H 4.59, N 7.50; found
42 2 4
silica using ethyl acetate/hexane (1:3) to give a pale yellow powder,
C 67.65, H 4.48, N 7.61.
1
yield 2.54 g (51%). H NMR (500 MHz, CDCl
3
): δ = 8.77 (s, 2 H,
Crystallography: X-ray diffraction data for the single crystals were
collected at 100, 153 or 200 K with a Rigaku R-AXIS RAPID
PyH3 ), 8.73 (d, J = 4.0 Hz, 2 H, PyH ), 8.68 (d, J = 7.5 Hz,
Ј,5Ј
6,6ЈЈ
H, PyH3 ), 7.99 (d, J = 8.0 Hz, 2 H, ArH ), 7.89 (t, J = 7.0 Hz,
,3ЈЈ
2,6
2
2
8
1
91R diffractometer. Crystal evaluation and data collection were
performed using Cu-K λ = 1.54187 Å radiation with a detector-
to-crystal distance of 1.91 cm. The structures were solved by heavy-
4,4ЈЈ
3,5
H, PyH ), 7.70 (d, J = 8.0 Hz, 2 H, ArH ), 7.59 (d, J =
α
.0 Hz, 2 H, ArH3 ), 7.53 (d, J = 8.0 Hz, 2 H, ArH ), 7.36 (t,
Ј,5Ј
2Ј,6Ј
5
,5ЈЈ
J = 6.0 Hz, 2 H, PyH ) ppm.
Ј-[1,1Ј;4Ј,1ЈЈ;4ЈЈ,1ЈЈЈ]Quaterphenyl-4-yl-[2,2Ј:6Ј,2ЈЈ]terpyridine
qptpy): Brbptpy (0.50 g, 1.1 mmol), biphenyl-4-boronic acid
0.40 g, 1.8 mmol) and [Pd(PPh ] (0.30 g, 0.26 mmol) were added
[25]
atom Patterson methods
niques. The non-hydrogen atoms were refined anisotropically. Hy-
drogen atoms were refined using the riding model. The full-matrix
and expanded using Fourier tech-
4
(
2
(
3
)
4
least-squares refinements were based on F . The absolute structures
[26]
to a three-necked round-bottomed flask under an argon atmo-
sphere. Dimethoxyethane (50 mL) and degassed 2 m Na CO
25 mL, aqueous) were added, and this final mixture was heated at
were deduced based on the Flack parameter.
All calculations
were performed using the CrystalStructure[ crystallographic soft-
ware package except for the refinements, which were performed
using SHELXL-97.[
27]
2
3
(
28]
reflux for 48 h under argon. The solution was evaporated to dry-
ness under reduced pressure and the black residue was extracted
with ethyl acetate to remove unreacted precursors. The remaining
Crystal Data for [Zn(qptpy)Cl
2
]·dmf: C42
2 4 r
H34Cl N OZn, M =
747.04; colourless crystal, size: 0.250ϫ0.050ϫ0.040 mm; ortho-
solid was subjected to Soxhlet extraction using CHCl
give a pale yellow powder, yield 0.45 g (76%). H NMR (500 MHz,
3
for 2 d to
1
rhombic, space group: Pca2 ; a = 26.339(2) Å, b = 12.4920(2) Å, c
1
3
–3
=
10.7250(1) Å; V = 3528.8(3) Å ; Z = 4; Dcalcd. = 1.406 gcm ;
): δ = 8.75 (s, 2 H, PyH3 ), 8.69 (d, J = 4.5 Hz, 2 H,
Ј,5Ј
–1
CDCl
3
,6ЈЈ
α
F(000) = 1544.00; μ(Cu-K ) = 26.709 cm ; T = 200 K; 41795 re-
PyH6 ), 8.64 (d, J = 8.0 Hz, 2 H, PyH ), 7.98 (d, J = 8.5 Hz,
3,3ЈЈ
flections collected. Refinement of 6041 reflections (451 parameters)
with IϾ2σ(I) converged at final R = 0.0422, wR = 0.1065; GOF
1.061.
H, ArH2,6), 7.85 (t, J = 7.5 Hz, 2 H, PyH ), 7.76–7.68 (m, 8
4,4ЈЈ
2
1
2
3ЈЈ,5ЈЈ
H, ArH), 7.66 (d, J = 8.5 Hz, 2 H, ArH
), 7.43 (t, J = 7.0 Hz, 2 H, ArH
H, PyH 5ЈЈ and 1 H, ArH ) ppm.
), 7.61 (d, J = 7.0 Hz,
=
2ЈЈЈ,6ЈЈЈ
3ЈЈЈ,5ЈЈЈ
2
H, ArH
), 7.32 (m, 2
5,
4ЈЈЈ
Crystal
Data
for
Zn, M
.50ϫ0.30ϫ0.20 mm; monoclinic, space group: P2
.1277(3) Å, b = 17.5802(5) Å, c = 33.7013(9) Å; β = 90.177(1)°; V
[Zn(Brbptpy)
= 1275.09; colourless crystal, size:
/c;
2 4 2 3
](ClO ) ·2CH CN:
C
58
H42Br
2
Cl
2
N
8
O
8
r
[
Zn(Brbptpy)
2
](ClO
4
)
2
·2CH
3
CN:
Zn(ClO ) ·6H O (0.040 g,
4 2 2
0
9
1
a =
0.11 mmol) in dmf (5 mL) was added to a solution of Brbptpy
(0.10 g, 0.22 mmol) in hot dmf (30 mL). After stirring for 6 h at
3
–3
=
K
5407.9(3) Å ; Z = 4; Dcalcd. = 1.566 gcm ; F(000) = 2576; μ(Cu-
100 °C, the solvent was removed by evaporation under reduced
–1
α
) = 20.95 cm ; T = 153 K; 86922 reflections collected. Refine-
pressure, and the white residue was washed with methanol and
dried at room temperature (yield: 0.080 g). The product was dis-
solved in acetonitrile and diethyl ether was diffused in slowly to
give colourless rodlike crystals suitable for X-ray diffraction studies.
ment of 8789 reflections (800 parameters) with IϾ2σ(I) converged
at final R = 0.0608, wR = 0.1408; GOF = 1.003. The crystal used
1
2
was a twin, with twin-law –1 0 0 0 –1 0 0 0 1. The highest residual
density peak corresponded to approximately half a water molecule
but this was not included in the refinement. Partial disorder was
apparent in one bromophenyl group, the perchlorate anions and
one of the acetonitrile molecules.
C
58
H
42Br
2
Cl
2 8 8
N O Zn (1275.11): calcd. C 54.63, H 3.32, N 8.79;
1
found C 54.58, H 3.35, N 8.84. H NMR (300 MHz, CD
3
6,6ЈЈ
CN): δ
=
(
9.05 (s, 2 H, PyH3Ј,5Ј), 8.78 (d, J = 8.2 Hz, 2 H, PyH ), 8.34
d, J = 8.2 Hz, 2 H, PyH3 ), 8.23 (t, J = 7.8 Hz, 2 H, PyH ),
,3ЈЈ
4,4ЈЈ
Crystal
Data
CdCl
.40ϫ0.10ϫ0.05 mm; monoclinic, space group: P2
0.4947(4) Å, b = 27.9850(9) Å, c = 18.5146(5) Å; β = 101.002(1)°;
for
[Cd(Brbptpy)
= 1281.06; colourless crystal, size:
/n;
2 4 2 3
](ClO ) ·CH CN:
2,6
8.07 (d, J = 8.3 Hz, 2 H, ArH ), 7.88 (d, J = 4.6 Hz, 2 H,
C
56
H39Br
2
2
N
7
O
8
, M
r
3
Ј,5Ј
3,5
2Ј,6Ј
ArH ), 7.81–7.75 (m, 4 H, ArH and ArH ), 7.46 (t, J =
0
1
1
a =
7
.5 Hz, 2 H, PyH5 ) ppm.
Cd(Brbptpy) ](ClO ·CH CN:
.11 mmol) in dmf (5 mL) was added to a solution of Brbptpy
,5ЈЈ
3
3
[
2
4
)
2
3
Cd(ClO
4
)
2
·H
2
O
(0.040 g,
V = 5337.7(3) Å ; Z = 4; D
K ) = 20.68 cm ; T = 100 K; 51240 reflections collected. Refine-
α
calcd.
= 1.594 gcm ; F(000) = 2560; μ(Cu-
–
1
0
(0.10 g, 0.22 mmol) in hot dmf (30 mL). After stirring for 6 h at ment of 10008 reflections (685 parameters) with IϾ2σ(I) converged
100 °C, the solvent was removed by evaporation under reduced
at final R = 0.0497, wR = 0.1113; GOF = 1.044.
1
2
pressure and the white residue was washed with methanol and dried
at room temperature (yield: 0.07 g). The product was dissolved in
acetonitrile and diethyl ether was diffused in slowly to give colour-
less rodlike crystals suitable for X-ray diffraction studies.
CCDC-883280(for[Zn(qptpy)Cl
ClO ·2CH CN) and -936354 (for [Cd(Brbptpy)
CH CN) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
2
]·dmf),-936353(for[Zn(Brbptpy)
2
]-
(
4
)
2
3
2
](ClO ) ·
4 2
3
C
56
H
39Br
2
CdCl
2 7 8
N O (1281.08): calcd. C 52.50, H 3.07, N 7.65;
1
found C 52.55, H 3.03, N 7.61. H NMR (300 MHz, CD
3
6,6ЈЈ
CN): δ
3Ј,5Ј
=
(
9.01 (s, 2 H, PyH ), 8.82 (d, J = 8.2 Hz, 2 H, PyH ), 8.31
m, 4 H, PyH3,3ЈЈand PyH4,4ЈЈ), 8.14 (d, J = 4.8 Hz, 2 H, ArH ),
3Ј,5Ј
Supporting Information (see footnote on the first page of this arti-
2,6
3,5
cle): Absorption and emission spectra for qptpy in various solvents;
8.04 (d, J = 8.7 Hz, 2 H, ArH ), 7.77 (m, 4 H, ArH and
II
II
ArH ), 7.55 (m, 2 H, PyH5,5ЈЈ) ppm.
2Ј,6Ј
ESI mass spectra of qptpy and its Zn and Cd complexes.
[
Zn(qptpy)Cl
added to a solution of qptpy (0.10 g, 0.19 mmol) in hot dmf Acknowledgments
30 mL). After stirring for 6 h at 100 °C, the solvent was removed
2 2
]·dmf: ZnCl (0.030 g, 0.22 mmol) in dmf (5 mL) was
(
by evaporation under reduced pressure, and the white residue was
washed with methanol and dried at room temperature (yield:
This research was supported by the Basic Science Research Pro-
gram of the National Research Foundation of Korea (NRF)
funded by Korean Ministry of Education (2011-0011187), as well
0.090 g). The product was dissolved in dmf and the solution was
Eur. J. Inorg. Chem. 2013, 5862–5870
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