Synthesis, characterization, and complexation of tetraarylborates with aromatic cations and their use in chemical sensors

Article abstract of DOI:10.1002/chem.200400992

Five aromatic borate anions, namely tetrakis(4-phenoxyphenyl)borate (1), tetrakis(biphenyl)borate (2), tetrakis(2-naphthyl)borate (3), tetrakis(4-phenylphenol)borate (4), and tetrakis(4-phenoxy)borate (5), have been prepared and tested as ion-recognition

Full text of DOI:10.1002/chem.200400992

FULL PAPER
Synthesis, Characterization, and Complexation of Tetraarylborates with
Aromatic Cations and Their Use in Chemical Sensors
Terhi Alaviuhkola,*[a] Johan Bobacka,[b] Maija Nissinen,[c] Kari Rissanen,[c]
Ari Ivaska,[b] and Jouni Pursiainen[a]
Abstract: Five aromatic borate anions,
namely tetrakis(4-phenoxyphenyl)bo-
rate (1), tetrakis(biphenyl)borate (2),
tetrakis(2-naphthyl)borate (3), tetra-
kis(4-phenylphenol)borate (4), and tet-
rakis(4-phenoxy)borate (5), have been
prepared and tested as ion-recognition
sites in chemical sensors for certain ar-
omatic cations and metal ions. To gain
further insight into the complexation of
the cations, some complexes have been
prepared and structurally character-
ized. The complexation behavior of 1
and 2 towards N-methylpyridinium (6),
1-ethyl-4-(methoxycarbonyl)pyridinium
(7), tropylium (8), imidazolium (9), and
1-methylimidazolium (10) cations has
been studied, and the stability con-
stants of the complexes of 1 with cat-
ions 6 and 8 have been measured to
compare them with the values for the
previously studied complexes of tetra-
phenylborate. The structures of the
borate anions and their complexes
have been characterized by NMR and
mass spectrometric methods. X-ray
crystal structures have been deter-
mined for potassium tetrakis(4-
phenoxyphenyl)borate (K+·1), N-meth-
ylpyridinium tetrakis(4-phenoxyphen-
yl)borate (6·1), 1-ethyl-4-(methoxycar-
bonyl)pyridinium tetrakis(4-phenoxy-
phenyl)borate (7·1), tropylium tetra-
kis(4-phenoxyphenyl)borate (8·1), and
imidazolium tetrakis(biphenyl)borate
(9·2). The results show that borate de-
rivatives are potential candidates for a
completely new family of charged car-
riers for use in cation-selective electro-
des.
Keywords:
aromatic cations
·
borates · charged carrier · ion-selec-
tive electrode · molecular recogni-
tion · noncovalent interactions
Introduction
cules has not attracted a great deal of interest, although a
variety of substituted borates bearing aryl groups have been
synthesized.[3,4] Electrochemical sensors constitute an impor-
tant group of chemical sensors that are attractive for practi-
cal applications allowing the use of small-size, portable, and
low-cost instrumentation.[5,6] Potentiometric ion sensors
(ion-selective electrodes, ISEs) based on neutral or charged
carriers (receptors, ionophores) are one of the oldest and
most successful types of chemical sensors in routine use
today, especially in clinical analysis.[7] These ion sensors are
normally based on plasticized polymer membranes contain-
ing specific ionophores and ionic additives.[8]
Tetraphenylborate was introduced in analytical chemistry in
the 1940s, when it was used for the precipitation of mono-
cations such as those of potassium, rubidium, cesium, and
quaternary ammonium compounds.[1] Tetraphenylborate is
an example of a simple organic precipitating reagent, but
there have also been numerous studies of other substituted
borates that form saltlike precipitates.[2] The investigation of
borate complexes containing organic cations as guest mole-
Tetraphenylborate derivatives have been used as ionic ad-
ditives in ISEs, initially just to reduce the anionic interfer-
ence observed in the presence of lipophilic anions (Donnan
exclusion).[8] They cannot form specific, strong ion pairs due
to their shielded negative charge, but they nevertheless
seem to play an active role as complexing agents, in addition
to bringing negative charge to the sensor surface. For exam-
ple, it has recently been shown that the Hg2+ interference
on Ag+-ISEs can be reduced by six orders of magnitude
when replacing tetrakis(4-chlorophenyl)borate by a weakly
[a] T. Alaviuhkola, Prof. Dr. J. Pursiainen
University of Oulu, Department of Chemistry
P.O. Box 3000, 90014 Oulu (Finland)
Fax : (+358)8-553-1603
E-mail: Terhi.Alaviuhkola@oulu.fi
[b] Dr. J. Bobacka, Prof. Dr. A. Ivaska
ꢀbo Akademi University, Process Chemistry Centre
c/o Laboratory of Analytical Chemistry, 20500 ꢀbo-Turku (Finland)
[c] Dr. M. Nissinen, Prof. Dr. K. Rissanen
University of Jyvꢁskylꢁ, Department of Chemistry
P.O. Box 35, 40351 Jyvꢁskylꢁ (Finland)
Chem. Eur. J. 2005, 11, 2071 – 2080
DOI: 10.1002/chem.200400992
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2071

coordinating carborane as the anionic additive in the ion-se-
lective membrane.[9] In the complexes of borates, hydrogen-
bonding, p-p, and cation-p interactions are the principal at-
tractive forces.[4,10,11] Complexation of the organic cations is
an important field in supramolecular chemistry, having ap-
plications in synthetic, analytical, as well as in industrial
fields.
Of these, tetrakis(4-phenylphenol)borate (4) has not been
characterized previously, whereas tetrakis(4-phenoxyphe-
nyl)borate[12,13] (1), tetrakis(biphenyl)borate[14] (2), tetra-
kis(2-naphthyl)borate[15] (3), and tetrakis(4-phenoxy)bo-
rate[16] (5) were prepared by modification of the literature
procedures. Additionally, we have studied the complexation
of the N-methylpyridinium (6), 1-ethyl-4-(methoxycarbo-
nyl)pyridinium (7), tropylium (8), imidazolium (9), and 1-
We have previously reported the complexation of tetra-
phenylborate with organic N-heterocyclic cations.[11] Weak,
methylimidazolium (10) cations with borates
1 and 2
À
À
noncovalent interactions such as C H···p and N H···p hy-
drogen bonds or p-stacking were identified as the principal
intermolecular forces between the aromatic p-systems of tet-
raphenylborate and the organic cations in the crystalline
(Scheme 1) by means of NMR and mass spectrometry and
in some cases also by X-ray crystallography. Stability con-
stants of complexes of N-methylpyridinium (6) and 1-ethyl-
4-(methoxycarbonyl)pyridinium (7) with 1 have been mea-
1
1
state. Stability constants measured by H NMR titrations of
sured by H NMR titration in a mixture of [D3]acetonitrile
the tetraphenylborate complexes were relatively low.
In this work, we have prepared five different borates (1–
5; Scheme 1) to study their properties in chemical sensors.
and [D4]methanol (1:1, v/v).
Scheme 1. Structural formulae and crystallographic numbering of tetrakis(4-phenoxyphenyl)borate (1), tetrakis(biphenyl)borate (2), tetrakis(2-naphthyl)-
borate (3), tetrakis(4-phenylphenol)borate (4), tetrakis(4-phenoxy)borate (5), N-methylpyridinium (iodide) (6), 1-ethyl-4-(methoxycarbonyl)pyridinium
(iodide) (7), tropylium (tetrafluoroborate) (8), imidazolium (perchlorate) (9), and 1-methylimidazolium (perchlorate) (10).
2072
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 2071 – 2080

Complexes of Tetraarylborates with Aromatic Cations
FULL PAPER
Results and Discussion
Synthesis of borates: Lithium tetrakis(2-naphthyl)borate
was originally prepared by Williams et al.[15] in 1968 accord-
ing to the general method described by Wittig and Raff.[17]
A modification of this procedure was used in the prepara-
tion of sodium tetrakis(2-naphthyl)borate (3) and sodium
tetrakis(biphenyl)borate[14] (2). Sodium tetrakis(4-phenoxy)-
borate (5) was synthesized by a modification of the proce-
dure reported by Cole et al.,[16] in which sodium borohydride
in THF was reported to react with three equivalents of
phenol to give NaBH(OPh)3. In our studies, this method
produced NaB(OPh)4, and we used an analogous procedure
to prepare the new compound sodium tetrakis(4-phenylphen-
ol)borate (4). The synthesis of tetrakis(4-phenoxyphenyl)-
borate (1) from bromodiphenyl ether and potassium tetra-
fluoroborate in THF has been described previously.[12]
*
Figure 1. Calibration plots for ISEs based on tetraarylborates 1 ( ), 2
(
), 3 ( ), and 4 ( ) in 10À6–10À2 m N-methylpyridinium iodide.
~
!
&
Table 1. Potentiometric selectivity coefficients for ISEs based on the
tetraarylborates 1–4 using N-methylpyridinium as primary ion.
logKN-MePy,j
3
À[b]
Ion-selective electrodes: We find it of particular interest to
vary the aryl substituents on boron in tetraarylborates to de-
termine their influence on the sensitivity and selectivity of
ion-selective electrodes (ISEs). The tetraarylborates 1–4
were incorporated as ion receptors (charged carriers) in
plasticized poly(vinyl chloride) (PVC) membranes by using
2-nitrophenyl octyl ether (o-NPOE) as plasticizer. The ion-
selective membranes contained around 30 mmolgÀ1 of the re-
spective tetraarylborate. Borate 5 could not be evaluated
due to its limited solubility in THF, the solvent used to dis-
solve the membrane components. The distinguishing struc-
tural features of the borate anions used here in comparison
j
1
2
4
BPh4
Li+
Na+
K+
À3.0
À3.1
À2.6
À2.6
À4.2
À4.1
À0.6
À0.4
À3.4
À3.3
À2.4
À3.0
À4.9
À4.7
À1.1
À0.7
À3.1
À3.1
À2.7
À3.0
À4.5
À4.6
À0.6
À0.1
À0.7
À0.7
À0.7
À0.5
À1.7
À1.6
0.8
À2.8
À2.7
À2.9
À2.9
À4.0
À4.0
À1.5
À0.4
+
NH4
Ca2+
Mg2+
Py+
TMA+ [a]
À0.4
[a] TMA+ = tetramethylammonium. [b] Data from reference [12].
more selective towards N-methylpyridinium than towards
alkali metal ions. The selectivity obtained by using tetraaryl-
borate 4 clearly deviates from that seen with borates 1–3.
À
with BPh4 are the nature of the aromatic units (1–3) and
the oxygen bridge between boron and the aromatic moiety
(4, 5). In borates 1 and 4, the oxygen bridges impart flexibil-
ity to the structure, which could have an effect on the com-
plex formation.
The ISEs were constructed by using poly(3,4-ethylene-
dioxythiophene) (PEDOT) as the solid contact material, fol-
lowing the same procedure as described earlier.[9] The ISEs
were investigated as potentiometric sensors for the N-meth-
ylpyridinium cation, which was used as a model aromatic
cation.
À
Results obtained previously with BPh4 are included in
Table 1 for comparison.[12]
In compounds 1–3, the boron center is bound to four aryl
groups, while in compound 4, the boron center is bound to
four oxygen atoms, which obviously has a large effect on the
ion sensitivity. When the oxygen centers are located further
away from the boron center, as in compound 1, they have
only a small effect on the ion-recognition process. These re-
sults indicate that the substituents closest to boron play a
determining role in ion recognition of N-methylpyridinium
by tetraarylborates. A detailed comparison of borates 1–3,
Typical potentiometric responses of the ISEs in N-methyl-
pyridinium iodide solutions (10À2–10À6 m) are shown in
Figure 1. ISEs based on the tetraarylborates 1, 2, and 3
show Nernstian responses in the concentration range 10À5–
10À2 m, with a detection limit of about 10À5.4 m. The responses
of these ISEs based on borates 1–3 are similar to that previ-
À
and BPh4 (Table 1) clearly shows that the nature of the ar-
omatic unit bound to the boron center also has some effect
on the selectivity.
The ISE based on tetraarylborate 4 was further studied by
using the local anaesthetic bupivacaine as the primary ion,
yielding a linear response in the concentration range 10À2–
10À4 (slope = 53 mV/dec) and a detection limit of about
10À4.4 m. Here again, the selectivity coefficients for the ISE
based on 4 differ from those obtained with ISEs based on 1
and 2, as shown in Table 2.
It is noteworthy that the ISE based on 4 shows a signifi-
cantly higher selectivity towards pyridinium than towards N-
methylpyridinium (Table 1 and Table 2), despite the greater
lipophilicity of the latter. This indicates some specific inter-
À
[12]
ously observed for BPh4
.
On the contrary, the ISE based
on tetraarylborate 4 shows only a slight response to N-meth-
ylpyridinium. The potentiometric selectivity coefficients esti-
mated by using the separate solution method are summar-
ized in Table 1. It can be seen that all the ISEs are more se-
lective towards N-methylpyridinium than to the other cat-
ions tested (logKN-MePy,j <0), except for the ISE based on
borate 4, which is more selective towards pyridinium than
towards N-methylpyridinium (logKN-MePy,Py >0). For exam-
ple, ISEs based on borates 1–3 are 2–3 orders of magnitude
Chem. Eur. J. 2005, 11, 2071 – 2080
www.chemeurj.org
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2073

T. Alaviuhkola et al.
Table 2. Potentiometric selectivity coefficients for ISEs based on the
tetraarylborates 1, 2, and 4 using bupivacaine as primary ion.
Table 3. Stability constants (Ka) of the complexes of borate 1 with two
six-membered aromatic cations in [D3]acetonitrile/[D4]methanol solution
at 308C determined by 1H NMR titration. Tetraphenylborate complexes
are included for comparison.
logKBupivacaine,j
j
1
2
4
Complex
Ka [dm3 molÀ1
]
DdC [ppm]
r2[a]
Li+
Na+
K+
À3.1
À3.1
À3.0
À2.6
À4.0
À4.1
À1.8
À1.6
À1.1
À1.2
À2.0
À3.0
À2.9
À2.9
À2.3
À3.8
À3.9
À1.7
À1.6
À1.1
À1.2
À2.0
À2.2
À2.2
À2.2
À1.9
À3.2
À3.2
À0.6
À1.8
À0.8
À0.9
À1.9
6·1
7·1
6·BPh4
12Æ2
13Æ1
17Æ2
10Æ1
À0.35Æ0.03
À0.37Æ0.03
À0.43Æ0.05
À1.4Æ0.1
0.997
0.999
0.998
0.997
+
[b]
NH4
[b]
Ca2+
7·BPh4
Mg2+
[a] Regression correlation for Benesi–Hildebrand plot. [b] Data from ref-
erence [11].
Py+
N-MePy+
lidocaine
procaine
TMA+[a]
When borate was added to a solution of the respective
cation in [D3]acetonitrile/[D4]methanol, an upfield shift was
observed in the proton resonance. The stability constants for
the complexation were calculated directly from the chemical
shift differences of the cation protons in the borate com-
plexes and in the free form using the Benesi–Hildebrand
equation. The errors in Ka and DdC were evaluated numeri-
cally based on the standard deviations of single Ka and DdC
values, usually obtained from measurements. In each case,
the differences in the chemical shifts of the free and com-
plexed cations proved to be a linear function of the inverse
of the borate concentration ([borate]À1), indicating 1:1 stoi-
chiometry. The regression values for the least-squares fitting
were generally better than 0.99, reflecting also the goodness
of the fitting. The measurements would not have been relia-
ble had there been prominent deviations from linearity. De-
viations from linearity would also have indicated the forma-
tion of higher aggregates than 1:1 complexes. The stability
constant determined for N-methylpyridinium tetrakis(4-phen-
oxyphenyl)borate (6·1) was 12 Æ 2 dm3 molÀ1, while that for
[a] TMA+ = tetramethylammonium.
actions between 4 and pyridinium cations. Furthermore, a
“dummy” membrane containing only PVC and o-NPOE
without any borate showed a significantly lower selectivity
towards pyridinium (logKBupivacaine,Py = À3.0) compared to
the membrane containing borate 4 (logKBupivacaine,Py = À0.6).
These results show that substituted borates offer interesting
possibilities for the design of new charged carriers for use in
cation-selective electrodes.
Complexation studies: The complexation of borates 1 and 2
with selected aromatic cations was studied to gain further
information about the nature of the complexes. Delocalized
p systems were chosen on the basis of our previous stud-
ies,[11] in which these five selected cations were found to
form complexes with tetraphenylborate.
The complexes of cations 6–8 with borate 1 and of cation
9 with borate 2 could be prepared in a straightforward
manner. In a suitable solvent (methanol, ethanol, or aceto-
nitrile), the formation of a 1:1 complex was observed in
each case by NMR spectroscopy and later verified by X-ray
crystallography. The complexes precipitated immediately
upon mixing of the warm solutions, and X-ray quality single
crystals could be grown direct from the reaction solutions by
slow evaporation of the solvent. The complex formation of
cations 9 and 10 with borate 1 and of cations 7, 8, and 10
with borate 2 was detected by mass spectrometry and NMR
spectroscopy, but the crystal structures of these five com-
plexes could not be determined due to the poor quality of
the crystals.
The stability constants of the complexes of N-methylpyri-
dinium (6) and 1-ethyl-4-(methoxycarbonyl)pyridinium (7)
with borate 1 were measured by 1H NMR titration in
[D3]acetonitrile/[D4]methanol solution (Table 3). This mix-
ture of solvents was chosen because methanol increases the
solubility of the tetrakis(4-phenoxyphenyl)borate (1), there-
by allowing comparison with the previously studied tetra-
phenylborate systems.[11] No precipitation occurred during
the stability constant measurements. Tropylium, however,
decomposes in the presence of alcohols,[18] so the stability
constant of the tropylium complex could not be measured in
[D3]acetonitrile/[D4]methanol solution.
1-ethyl-4-(methoxycarbonyl)pyridinium
tetrakis(4-phen-
oxyphenyl)borate (7·1) was 13Æ1 dm3 molÀ1. These values
are similar to the stability constants determined for the pre-
viously studied tetraphenylborate complexes (17Æ2 and
10Æ1 dm3 molÀ1, respectively[11]). In our previous studies,
corresponding measurements were also made for imidazoli-
um and 1-methylimidazolium tetraphenylborates (19Æ4 and
46Æ2 dm3 molÀ1, respectively[11]), and the stability constants
of these complexes were also of similar magnitude. As a
polar solvent, methanol was also studied, which has a
marked effect on the complexation environment. It increas-
es the solubility of the charged species, decreasing the
degree of association of the complexes and thereby lowering
the stability constants.
As a complexing agent, tetrakis(4-phenoxyphenyl)borate
(1) differs from tetraphenylborate in that the additional
phenyl rings may also take part in the binding and even en-
capsulate the cation. The anion also contains electronegative
oxygens, which make the structure flexible and provide hy-
drogen-bonding sites for suitably predisposed guests. How-
ever, the stability constants do not indicate any significant
positive impact of these two structural features on the com-
plexation. In addition, the crystal structures show that the
cations are situated between the inner aromatic rings, closer
to the boron, while the outer phenyl rings have no interac-
2074
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 2071 – 2080

Complexes of Tetraarylborates with Aromatic Cations
FULL PAPER
tions with the cations, as might be expected in view of the
similarity of the stability constants to those of the tetraphe-
nylborate complexes.
In the crystal structures of planar aromatic cations with
tetrakis(4-phenoxyphenyl)borate (1) and tetrakis(biphenyl)-
borate (2), the significance of p-interactions in the complex
formation is obvious. They all show relatively short face-to-
À
X-ray crystallographic studies: The crystal structures of po-
tassium tetrakis(4-phenoxyphenyl)borate (K+·1), N-methyl-
pyridinium tetrakis(4-phenoxyphenyl)borate (6·1), 1-ethyl-4-
(methoxycarbonyl)pyridinium tetrakis(4-phenoxyphenyl)bo-
rate (7·1), tropylium tetrakis(4-phenoxyphenyl)borate (8·1),
and imidazolium tetrakis(biphenyl)borate (9·2) were deter-
mined.
The starting compound, potassium tetrakis(4-phenoxyphe-
nyl)borate (K+·1), was crystallized from a mixture of ben-
zene and ethanol. Potassium cations and the borate anions
form a beautiful complex, in which each potassium cation is
packed between two hosts with strong cation–p interactions
(Figure 2) (potassium–centroid distances are K···Ct1
face p···p contacts and also edge-to-face-type C H···p inter-
actions. In all of the complexes, most of the interactions be-
tween the anion and cation involve the inner, more electro-
negative aromatic rings.
The crystal structure of N-methylpyridinium tetrakis(4-
phenoxyphenyl)borate (6·1) was somewhat problematic to
determine because the crystals decomposed at low tempera-
tures and to some extent also at room temperature. The
data collection was performed at two temperatures (173 K
and 263 K), giving the same result in both cases, with almost
equal R values (R = 0.127 at 173 K and 0.115 at 263 K).
Due to the instability of the crystals, the resulting structure
is not excellent but still good enough to give information
about the solid-state structure of the complex.
N-Methylpyridinium
tetrakis(4-phenoxyphenyl)borate
(6·1) also forms continuous chains, in which each cation is
located between two hosts (Figure 3). The complexation
Figure 3. Crystal structure of N-methylpyridinium tetrakis(4-phenoxyphen-
yl)borate (6·1). The cation and anion are in face-to-face p···p contact
forming infinite chains.
stems from the sandwich-type of face-to-face packing of the
cation and the aromatic rings of the adjacent anions (cent-
roid-to-centroid distances between the cation and the anion
are 3.63(1) ꢀ) and, on the other hand, from the edge-to-face
interactions between the cation and other aromatic rings of
the anion (edge-to-face distances between C29 of the cation
and the centroid of the aromatic ring are 3.82(1) ꢀ). As in
the potassium structure, the cation is located between the
inner rings while the outer rings do not interact with the
cation. Instead, the outer aromatic units are edge-to-face
connected to nearby anions, thereby connecting the adjacent
chains together.
The 1-ethyl-4-(methoxycarbonyl)pyridinium tetrakis(4-
phenoxyphenyl)borate complex (7·1) shows the greatest de-
viation from the structures of the other complexes since the
cation interacts with more than two anions and even slightly
with the outer aromatic units of the anion owing to the in-
teractions of the extended side chains of the larger cation.
However, the most important and the strongest intermolecu-
lar interactions are still the slightly offset face-to-face-type
Figure 2. Top: Crystal structure of potassium tetrakis(4-phenoxyphenyl)-
borate (K+·1) showing potassium with VDW radius. Potassium fits per-
fectly into the cavity formed by the inner aromatic rings of two adjacent
borate anions. Bottom: Crystal packing reveals continuous chains of
anions connected by strong cation···p interactions.
2.917(1), K···Ct2 3.020(1), K···Ct3* 2.932(1), and K···Ct4* =
2.997(1) ꢀ), forming continuous chains of potassium tetra-
kis(4-phenoxyphenyl)borate. An interesting feature is that,
as noted above, the potassium is situated between the inner
aromatic rings, that is, between the rings closer to boron,
while the outer phenyl rings have no interactions with the
cation. This can be attributed to the more electronegative
nature of the closer rings, and also to the packing efficiency:
potassium fits perfectly into the cavity formed by the inner
aromatic rings. The outer aromatic rings point outwards, al-
lowing ethanol solvent molecules to occupy interstitial sites
in the crystal lattice.
Chem. Eur. J. 2005, 11, 2071 – 2080
www.chemeurj.org
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2075

T. Alaviuhkola et al.
p···p interactions between the cation and two adjacent
anions (centroid-to-centroid distances are 3.647(2) ꢀ and
4.122(2) ꢀ) and edge-to-face interactions (C58···Ct1
3.434(2) ꢀ) (Figure 4). No clear chain or column type of
packing pattern can readily be discerned in this case.
Figure 4. 1-Ethyl-4-(methoxycarbonyl)pyridinium tetrakis(4-phenoxyphen-
yl)borate complex (7·1) with offset face-to-face-type p···p interaction.
The crystal data for tropylium tetrakis(4-phenoxyphenyl)-
borate (8·1) were obtained from a weakly diffracting crystal
crystallized from acetonitrile. The tropylium cation is disor-
dered so that it can only be described as an eight-membered
ring. Even though the formation of continuous chains of
anions mediated by the cations is again observed in this
case, the anions also interact with each other forming a sub-
structure which could be described as two facing “tweezers”.
The cation–anion interactions are very similar to those ob-
served in N-methylpyridinium tetrakis(4-phenoxyphenyl)bo-
rate (6·1). Thus, tropylium is “sandwiched” between two ar-
omatic rings of the adjacent hosts, and there are additional
edge-to-face p···p interactions with two other rings
(Figure 5). The centroid-to-centroid distances between the
cation and the anions are 3.653(3) ꢀ and the closest edge-
to-face distance, C54···Ct2, is 3.431(3) ꢀ.
Figure 5. Top: Infinite chains of anions and cations of tropylium tetra-
kis(4-phenoxyphenyl)borate complex (8·1) with face-to-face p···p inter-
action. Bottom: Adjacent chains of tweezer-like borate anions depicted
in red and blue. Cations have been omitted for clarity.
The only tetrakis(biphenyl)borate (2) structure that we
succeeded in crystallizing was imidazolium tetrakis(biphen-
yl)borate (9·2), which was obtained from ethanol solution.
Imidazolium is a somewhat smaller cation than the other
cations used in this study and tetrakis(biphenyl)borate is a
more rigid anion than tetrakis(4-phenoxyphenyl)borate (1),
hence the properties and interactions of this structure are
slightly different. Imidazolium is also complexed by p-inter-
actions, but instead of the sandwich-type of face-to-face
p···p interactions, the cation here is offset face-to-face
stacked with one of the inner phenyl rings (C50 of imidazo-
lium is directly above the center of the inner phenyl ring
Figure 6. Top: Imidazolium tetrakis(biphenyl)borate complex (9·2). The
complexation involves both offset face-to-face p···p interactions and
À
edge-to-face C H···p interactions. Bottom: The packing of the anion–
À
C37–C42; C50···Ct4 3.296(7) ꢀ) and edge-to-face (C H···p)
cation complexes is similar to that of tetrakis(4-phenoxyphenyl)borate
complexes, that is, chainlike.
connected to three other aromatic units (C50···Ct3
3.277(6) ꢀ,
C52···Ct1*
3.397(6) ꢀ,
and
C53···Ct2*
3.602(7) ꢀ; Figure 6). There are also some p-interactions
with the outer aromatic rings of the anion owing to the
shorter distance and rigid bridge between the two aromatic
moieties. Owing to the rigid nature of the anion and the
small size of the cation, the packing of the anion–cation ad-
2076
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 2071 – 2080

Complexes of Tetraarylborates with Aromatic Cations
FULL PAPER
ray quality crystals of this compound were grown by slow evaporation of
the solvents from a solution in a benzene/ethanol mixture.
ducts is not as efficient as with tetrakis(4-phenoxyphenyl)-
borate. Consequently, there is space in the crystal lattice for
ethanol solvent molecules, which occupy interstitial sites be-
tween the anions and cations and are hydrogen-bonded to
Sodium tetrakis(biphenyl)borate (2): One-fifth of a solution of 4-bromo-
biphenyl (3.78 g, 16.2 mmol) in THF (20 mL) was slowly added to Mg
turnings (0.39 g, 16.0 mmol) containing an I2 crystal. The mixture was stir-
red under nitrogen and warmed until the reaction started. The rest of the
solution was then slowly added, and the mixture was stirred for 1.5 h
with occasional warming. A solution of boron trifluoride diethyl etherate
(0.45 g, 3.2 mmol) in THF (10 mL) was added to the aryl Grignard re-
agent thus produced over a period of about 30 min. The reaction mixture
was stirred for an additional 45 min, warming occasionally. It was then
poured into a solution of Na2CO3 (1.7 g) in distilled water (40 mL), and
the resulting mixture was stirred vigorously for 20 min, during which the
inorganic material separated, which could be filtered off. The aqueous fil-
trate was extracted with THF (3ꢃ25 mL) and the combined THF frac-
tions were dried over Na2CO3 overnight. The solution was then filtered
and the solvent was removed under reduced pressure, whereupon a pre-
cipitate formed. The crude product was redissolved in acetone (20 mL),
and benzene (60 mL) was added. The mixture was concentrated to a
quarter of its original volume and the precipitated product was collected
À
the N H groups of the imidazolium, thus preventing the
latter from participating in NH–p interactions. The packing,
however, is still similar to that of the other complexes, being
also a chain-like assembly of anions and cations.
Conclusion
The present results indicate that the synthesized borate
structures can form complexes with aromatic cations and
metal ions. This has been shown by the stability constant
measurements, as well as by spectroscopic and crystallo-
graphic methods. The complexation involves weak, noncova-
lent interactions between the aromatic cation and the aro-
matic rings closest to the boron atom. We directed our stud-
ies with a view to highlighting the influence of borate struc-
ture modification on the sensitivity and selectivity of ion-se-
lective electrodes. Borates were used as ion receptors for
certain selected organic cations and metal ions. The research
described in this paper has shown that borate structure mod-
ification influences the selectivity of potentiometric ion sen-
sors. The borates gave different results when incorporated
into chemical sensors, indicating that they play an active
role. Thus, they show potential for the future development
of anionic receptor molecules in chemical sensors. The re-
sults strongly indicate that borate derivatives may give rise
to a new family of charged carriers for cation-selective elec-
trodes.
by filtration and dried in vacuo. 11B NMR (200 MHz, CD3CN): d
=
À6.30 ppm; 1H NMR (200 MHz, CD3CN): d = 7.2–7.6 ppm (m, arom.);
13C NMR (500 MHz, CD3CN): d = 125.62 and 125.63 (arom., 3C), 127.3
(arom., 1C), 127.6 (arom., 2C), 129.8 (arom., 2C), 135.7 (arom., 1C),
137.3 (arom., 2C), 143.6 ppm (arom., 1C); ESI-MS: m/z: 622 [ÀB(-Ph-
Ph)4], 669 [ÀB(-Ph-Ph)4+2Na+]; exact mass: 669.2715 [M+2Na]+ (calcd.
for C48H36BNa2, 669.2705).
Sodium tetrakis(2-naphthyl)borate (3): The procedure used for the prep-
aration of sodium tetrakis(2-naphthyl)borate was similar to that de-
scribed for the synthesis of sodium tetrakis(biphenyl)borate (2). The re-
action set-up was identical. One-fifth of a solution of 2-bromonaphtha-
lene (3.40 g, 16.4 mmol) in THF (20 mL) was slowly added to Mg turn-
ings (0.39 g, 16.0 mmol). The mixture was stirred under nitrogen and
warmed until the reaction started. The rest of the solution was added and
the reaction mixture was stirred. A solution of boron trifluoride diethyl
etherate (1.89 g, 13.3 mmol) in THF (10 mL) was slowly added to the
Grignard reagent. The reaction mixture was stirred for 45 min and then
poured into a solution of Na2CO3 (1.7 g) in distilled water (40 mL), and
the resulting mixture was stirred, filtered, and extracted. The combined
organic layers were dried and purified. The product was dried in vacuo.
11B NMR (200 MHz, CD3CN
+
THF): d
=
À5.68 ppm; 1H NMR
(200 MHz, CDCl3): d = 5.8–6.6 ppm (m, arom.); 13C NMR (500 MHz,
CDCl3): d = 125.9 (arom., 1C), 126.2 (arom., 1C), 126.3 (arom., 1C),
126.6 (arom., 1C), 127.9 (arom., 1C), 128.4 (arom., 1C), 128.7 (arom.,
1C), 132.7 (arom., 1C), 133.8 (arom., 1C), 138.5 ppm (arom., 1C); ESI-
MS: m/z: 565.5 [ÀB(-2-naphthalene)4+2Na+]; exact mass: 519.2286 [M]À
(calcd. for C40H28B, 519.2284).
Experimental Section
1
General procedures: The basic H and 11B NMR measurements were car-
ried out at room temperature on a 200 MHz Bruker Avance DPX200
spectrometer and the 13C NMR measurements on a Bruker DRX500
spectrometer. Complex formation was also studied by MS analysis. Elec-
trospray ionization mass spectra (ESI-MS) were recorded on an LCT
(Micromass, Ltd.) time-of-flight mass spectrometer equipped with an
OpenLynx 3 data system. Exact mass peaks of the borates were deter-
mined on a Micromass LCT using ESIÀ or ESI+ methods. ESI mass spec-
tra showed 2:1 complexation in the gas phase, where two cation mole-
cules formed a complex with one borate molecule. No 1:1 complexes
were observed in ESI-MS.
Sodium tetrakis(4-phenylphenol)borate (4): A solution of 4-hydroxybi-
phenyl (1.37 g, 8.0 mmol) in THF (25 mL) was slowly added to a solution
of sodium tetrahydroborate (0.08 g, 2.1 mmol) in THF (10 mL). The reac-
tion mixture was warmed and then stirred for 24 h at room temperature.
The solvent was evaporated and the product was dried under vacuum
with heating by means of a water bath for 6 h. The crude product was
dissolved in acetone and three times the volume of benzene was added.
The mixture was concentrated to a quarter of its original volume under
reduced pressure and the precipitate formed was collected by filtration.
The product was washed with cyclohexane and dried in vacuo. 11B NMR
All operations were carried out under a nitrogen atmosphere using stan-
dard Schlenk techniques. 2-Bromonaphthalene, 4-bromobiphenyl,
phenol, boron trifluoride diethyl etherate, sodium tetrahydroborate, po-
tassium tetrafluoroborate, 1-ethyl-4-(methoxycarbonyl)pyridinium iodide
(7), and tropylium tetrafluoroborate (8) were obtained from commercial
sources and were used without further purification or drying. The compo-
sitions of the products were verified crystallographically and by NMR
and MS analyses. Chemical shifts in the 11B NMR spectra are reported in
ppm with respect to external BF3·Et2O (with CD3CN as solvent).
(200 MHz, CD3CN
+ THF): d =
3.21 ppm; 1H NMR (200 MHz,
CD3CN): d = 6.9 (d, arom., 8H), 7.3–7.6 ppm (m, arom., 28H); 13C
NMR (500 MHz, CD3CN): d = 116.7 (arom., 2C), 127.5 (arom., 2C),
127.7 (arom., 1C), 129.2 (arom., 2C), 130.0 (arom., 2C), 133.5 (arom.,
1C), 141.8 (arom., 1C), 157.9 ppm (arom., 1C); ESI-MS: m/z: 687 [ÀB-
(-O-Ph-Ph)4]; exact mass: 687.2723 [M]À (calcd for C48H36O4B, 687.2707).
Sodium tetrakis(4-phenoxy)borate (5):
A solution of phenol (0.75 g,
8.0 mmol) in THF (15 mL) was slowly added to a solution of sodium tet-
rahydroborate (0.0767 g, 2.1 mmol) in THF (10 mL). The reaction mix-
ture was stirred for 24 h at room temperature. The solvent was removed
and the product was dried under vacuum with heating by means of a
Synthesis
Potassium tetrakis(4-phenoxyphenyl)borate (1): The synthesis of potassi-
um tetrakis(4-phenoxyphenyl)borate has been described previously.[12] X-
Chem. Eur. J. 2005, 11, 2071 – 2080
www.chemeurj.org
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2077

T. Alaviuhkola et al.
water bath for 6 h. 11B NMR (200 MHz, CD3CN): d = À3.06 ppm; 1H
borate), 9.2 ppm (s, 7H; tropylium); ESI-MS: m/z: 806 [2·(8)+ÀB(-Ph-
Ph)4]; exact mass: 805.3981 [M+2·8]+ (calcd for C62H50B, 805.4006).
NMR (200 MHz, CD3CN): d
=
6.6–7.3 ppm (m, arom.); 13C NMR
(500 MHz, CD3CN): d = 116.7 (arom., 2C), 119.6 (arom., 1C), 130.6
(arom., 2C), 159.6 ppm (arom., 1C); ESI-MS: m/z: 429 [ÀB(-O-
Ph)4+2Na+]; exact mass: 429.1245 [M+2Na]+ (calcd for C24H20O4BNa2,
429.1250).
Imidazolium tetrakis(biphenyl)borate (9·2): The complex was prepared
by mixing equimolar amounts of solutions of imidazolium perchlorate (9)
and borate 2 in ethanol (no precipitate). X-ray quality crystals were
grown from ethanol by slow evaporation. 1H NMR (200 MHz, CD3CN):
d = 7.2–7.7 (m, 36H; borate + 2H; imidazolium), 8.5 ppm (s, 1H; imi-
dazolium); ESI-MS: m/z: 761 [2·(9)+ÀB(-Ph-Ph)4]; exact mass: 761.3792
[M+2·9]+ (calcd for C54H46N4B, 761.3816).
Synthesis of the complexes
N-Methylpyridinium tetrakis(4-phenoxyphenyl)borate (6·1): The cation
was prepared according to the literature procedure.[16] The complex was
prepared by mixing equimolar amounts of solutions of N-methylpyridini-
um iodide (6) and borate 1 in acetonitrile (no precipitate). X-ray quality
crystals were grown from acetonitrile by slow evaporation. 1H NMR
(200 MHz, CD3CN + TMS): d = 4.3 (s, 3H; N-CH3), 6.7–7.2 (m, 36H;
borate), 8.0 (m, 2H; Me-pyridinium), 8.5 (t, 1H; Me-pyridinium),
8.6 ppm (d, 2H; Me-pyridinium); ESI-MS: m/z: 876 [2·(6)+ÀB(-Ph-O-
Ph)4]; exact mass: 875.4012 [M+2·6]+ (calcd. for C60H52O4N2B, 875.4020).
1-Methylimidazolium tetrakis(biphenyl)borate (10·2): The complex was
prepared by mixing equimolar amounts of solutions of 1-methylimidazoli-
um perchlorate (10) and borate 2 in acetonitrile (no precipitate). 1H
NMR (200 MHz, CD3CN): d = 3.6 (s, 3H; N-CH3), 7.2–7.6 (m, 36H;
borate + 2H; 1-Me-imidazolium), 8.2 (s, 1H; 1-Me-imidazolium); ESI-
MS: m/z: 790 [2·(10)+ÀB(-Ph-Ph)4]; exact mass: 789.4108 [M+2·10]+
(calcd for C56H50N4B, 789.4129).
1-Ethyl-4-(methoxycarbonyl)pyridinium tetrakis(4-phenoxyphenyl)borate
(7·1): The complex was prepared by mixing equimolar amounts of solu-
tions of 7 and borate 1 in methanol. The solid complex formed immedi-
ately upon mixing of the solutions. X-ray quality crystals were grown
from a solution in acetonitrile by slow evaporation. 1H NMR (200 MHz,
CD3CN): d = 1.6 (t, 3H; N-CH2CH3), 4.0 (s, 3H; OCH3), 4.6 (q, 2H; N-
CH2CH3), 6.8–7.4 (m, 36H; borate), 8.4 (m, 2H; arom. cation), 8.8 ppm
(d, 2H; arom. cation); ESI-MS: m/z: 1020 [2·(7)+ÀB(-Ph-O-Ph)4]; exact
mass: 1019.4431 [M+2·7]+ (calcd for C66H60O8N2B, 1019.4443).
Ion-selective electrodes: Plasticized polymer membrane-based ion-selec-
tive electrodes (ISEs) were prepared by using poly(3,4-ethylenedioxy-
thiophene) (PEDOT) as a solid contact material.[12] PEDOT was deposit-
ed on a glassy carbon (GC) disk electrode (area = 0.07 cm2) by galvano-
static electrochemical polymerization (current
= 0.014 mA, time =
714 s) from a deaerated aqueous solution containing 0.01m 3,4-ethylene-
dioxythiophene and 0.1m sodium poly(sodium 4-styrenesulfonate). The
electropolymerization was performed by using an Autolab General Pur-
pose Electrochemical System (Eco Chemie B.V., The Netherlands) con-
nected to a conventional one-compartment, three-electrode electrochem-
ical cell. The GC disk electrode was used as the working electrode, a GC
rod as an auxiliary electrode, and an Ag/AgCl (3m KCl) electrode as the
reference electrode. Prior to electropolymerization, the GC disk elec-
trode was polished with 0.3 mm alumina, rinsed with deionized water, and
cleaned ultrasonically. After electropolymerization, the GC/PEDOT elec-
trodes were rinsed with deionized water and conditioned for at least 24 h
in 0.01m N-methylpyridinium iodide solution. The GC/PEDOT electro-
des were then coated with ion-selective membranes of the following com-
position (w/w): tetraarylborate (1.6–2.2%), PVC (32–33%), and o-NPOE
(65–66%). The components of the membrane were dissolved in THF and
applied by means of a micropipette onto the GC/PEDOT electrode.
After evaporation of the THF, the resulting ion-selective membrane cov-
ered the underlying PEDOT film completely. The resulting ISEs were
conditioned in 0.01m N-methylpyridinium iodide for at least 24 h. Poten-
tiometric measurements were performed with a home-made multichannel
mV meter, using an Ag/AgCl (3m KCl) electrode as the reference elec-
trode. Activity coefficients were calculated by using the extended
Debye–Hꢄckel equation.[21] Selectivity coefficients were estimated by the
separate-solution method (SSM) employing 0.01m concentrations of dif-
ferent cations (chloride or iodide salts).[22] The measurements were con-
ducted at room temperature (23Æ28C). Selected ISEs were also studied
by using bupivacaine as the primary ion. Bupivacaine (1-butyl-N-[2,6-di-
methylphenyl]-2-piperidinecarboxamide) is an aromatic cation that is
used as a local anaesthetic and is commercially available (Sigma Chemi-
cal Co.) in the form of a hydrochloride salt. Two other local anaesthetics,
namely lidocaine (2-diethylamino-N-[2,6-dimethylphenyl]acetamide) and
procaine (p-aminobenzoic acid diethylaminoethyl ester), in the form of
their hydrochloride salts (Sigma Chemical Co.), were used for compari-
son purposes.
Tropylium tetrakis(4-phenoxyphenyl)borate (8·1): The complex was pre-
pared by mixing equimolar amounts of solutions of 8 and borate 1 in ace-
tonitrile. The crystalline complex formed immediately. 1H NMR
(200 MHz, CD3CN): d = 6.7–7.4 (m, 36H; borate), 9.2 ppm (s, 7H; tro-
pylium); ESI-MS: m/z: 869 [2·(8)+ÀB(-Ph-O-Ph)4]; exact mass: 869.3832
[M+2·8]+ (calcd for C62H50O4B, 869.3802).
Imidazolium tetrakis(4-phenoxyphenyl)borate (9·1): The cation was pre-
pared according to the literature procedure.[20] The complex was prepared
by mixing equimolar amounts of solutions of imidazolium perchlorate (9)
and borate
1
in acetonitrile (no precipitate). 1H NMR (200 MHz,
CD3CN): d = 6.7–7.4 (m, 36H; borate + 2H; imidazolium), 8.4 ppm (s,
1H; imidazolium); ESI-MS: m/z: 826 [2·(9)+ÀB(-Ph-O-Ph)4]; exact
mass: 825.3588 [M+2·9]+ (calcd. for C54H46O4N4B, 825.3612).
1-Methylimidazolium tetrakis(4-phenoxyphenyl)borate (10·1): The cation
was prepared according to the literature procedure.[20] The complex was
prepared by mixing equimolar amounts of solutions of 1-methylimidazoli-
um perchlorate (10) and borate 1 in acetonitrile (no precipitate). 1H
NMR (200 MHz, CD3CN): d = 3.8 (s, 3H; N-CH3), 6.7–7.3 (m, 36H;
borate), 8.3 ppm (s, 1H; 1-Me-imidazolium); ESI-MS: m/z: 854
[2·(10)+ÀB(-Ph-O-Ph)4]; exact mass: 853.3959 [M+2·10]+ (calcd for
C56H50O4N4B, 853.3925).
N-Methylpyridinium tetrakis(biphenyl)borate (6·2): The complex was
prepared by mixing equimolar amounts of solutions of N-methylpyridini-
um iodide (6) and borate 2 in acetonitrile. The solid complex formed im-
mediately upon mixing of the solutions. Crystals were grown from aceto-
1
nitrile by slow evaporation. H NMR (200 MHz, CD3CN + CD3OD): d
= 4.3 (s, 3H; N-CH3), 7.3–7.6 (m, 36H; borate), 8.0 (m, 2H; Me-pyridi-
nium), 8.5 (t, 1H; Me-pyridinium), 8.6 ppm (d, 2H; Me-pyridinium);
ESI-MS: m/z: 812 [2·(6)+ÀB(-Ph-Ph)4]; exact mass: 811.4194 [M+2·6]+
(calcd for C60H52N2B, 811.4224).
Stability constant determination by 1H NMR titration: A standard so-
lution of the guest in [D3]acetonitrile/[D4]methanol (1:1, v/v) was pre-
pared at a concentration of 2ꢃ10À3 m, just sufficient to give an observable
NMR signal. A series of donor solutions (0.01–1.0m) were prepared by
weighing out appropriate amounts of the donor. A 2-mL portion of the
standard solution was then added and the flask was re-weighed. The solu-
tions were thoroughly mixed and the spectrum was measured immediate-
ly; 5 mm NMR tubes sealed with Parafilm to avoid evaporation were
used. The temperature (303 K) was held constant during the measure-
ments. The stability constant Ka for the complexation was calculated
from NMR chemical shifts using the Benesi–Hildebrand least-squares
line-fitting procedure.[23]
1-Ethyl-4-(methoxycarbonyl)pyridinium tetrakis(biphenyl)borate (7·2):
The complex was prepared by mixing equimolar amounts of solutions of
7 and borate 2 in acetonitrile. The yellow solid complex formed immedi-
ately upon mixing of the solutions. 1H NMR (200 MHz, CD3CN): d =
1.6 (t, 3H; N-CH2CH3), 4.0 (s, 3H; OCH3), 4.6 (q, 2H; N-CH2CH3), 7.2–
7.7 (m, 36H; borate), 8.4 (m, 2H; arom. cation), 8.9 ppm (d, 2H; arom.
cation); ESI-MS: m/z: 956 [2·(7)+ÀB(-Ph-Ph)4]; exact mass: 955.4621
[M+2·7]+ (calcd for C66H60O4N2B, 955.4646).
Tropylium tetrakis(biphenyl)borate (8·2): The complex was prepared by
mixing equimolar amounts of solutions of tropylium tetrafluoroborate (8)
and borate 2 in acetonitrile (no precipitate). Black crystals formed within
a few hours. 1H NMR (200 MHz, CD3CN): d
= 6.9–7.9 (m, 38H;
2078
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 2071 – 2080

Complexes of Tetraarylborates with Aromatic Cations
Table 4. Crystal data for the complexes.
FULL PAPER
Compound
formula
K+·1
6·1 at 263.0 K
6·1 at 173.0 K
7·1
8·1
9·2
+
+
+
C48H36O4BÀ·K+· C48H36O4BÀ·C6H8N+ C48H36O4BÀ·C6H8N+ C48H36O4BÀ·C9H12NO2 C48H36O4BÀ·C7H7 C48H36BÀ·C3H4N2
·
0.5CH3CH2OH
749.71
2CH3CH2OH
784.80
formula weight
crystal system
space group
a [ꢀ]
b [ꢀ]
c [ꢀ]
781.71
781.71
853.77
778.70
monoclinic
P21/n (no. 14)
15.9719(4)
15.4125(5)
16.7234(5)
106.976(2)
3937.3(2)
4
orthorhombic
Pcnb (no. 60)
8.4500(4)
20.666(1)
24.704(2)
90
4314.0(5)
4
1.204
orthorhombic
Pcnb (no. 60)
8.000(2)
19.957(6)
25.614(6)
90
4089(2)
4
1.270
monoclinic
P21/c (no. 14)
16.3291(3)
13.5383(3)
20.6400(3)
99.946(1)
4494.3(1)
4
monoclinic
C2/c (no. 15)
27.7530(9)
8.2586(3)
21.4186(5)
120.598(2)
4225.6(2)
4
monoclinic
P21/c (no. 14)
16.2123(7)
13.5315(7)
22.2775(8)
101.248(3)
4793.3(4)
4
b [8]
volume [ꢀ3]
Z
1calcd [MgmÀ3
]
1.265
1.262
1.224
1.088
absorption coefficient 0.182
0.075
0.079
0.081
0.075
0.065
[mmÀ1
]
F(000)
1572
1648
1648
1800
1640
1672
refl. collected/unique
data/restraints/param- 6893/0/499
eters
17898/6893
15132/3768
3768/0/256
9199/1788
3092/0/276
22303/7943
7943/0/588
11372/3707
3707/0/276
21436/5476
8247/0/581
GooF
1.030
1.123
1.134
1.052
1.088
1.067
final R indices
[I>2s(I)]
0.044/0.104
0.115/0.224
0.127/0.213
0.044/0.093
0.053/0.122
0.110/0.294
R indices (all data)
largest diff. peak and
0.057/0.1094
0.571/À0.257
0.172/0.249
0.594/À0.417
0.210/0.245
0.377/À0.280
0.072/0.104
0.129/À0.193
0.067/0.129
0.319/À0.385
0.152/0.326
0.788/À0.362
hole [eꢀÀ3
]
Crystal structures: X-ray crystallographic data for the complexes were re-
corded with a Nonius Kappa CCD diffractometer using graphite-mono-
chromated MoKa radiation (l = 0.71073 ꢀ) at a temperature of 173.0Æ
0.1 K, except for the structure of 6·1, which was measured both at 173Æ
0.1 and 263.0Æ0.1 K due to the decay of the crystals at low temperatures.
The CCD data were processed with the Denzo-SMN v.0.93.0 program[24]
and all reflections were corrected for Lorentz and polarization effects.
An absorption correction was not applied. The structures were solved by
direct methods (SHELXS-97[25]) and refined against F2 (SHELXL-97[26]).
The hydrogen atoms were calculated to their idealized positions with iso-
tropic temperature factors (1.2 or 1.5 times the carbon temperature
factor) and refined as riding atoms. The solvent ethanol in K+·1 was
found to be disordered over two positions with site occupancies of 0.5.
The hydrogen of the hydroxy group could not be determined for disor-
dered ethanol. N27, C30, and C33 of the N-methylpyridinium molecule
of 6·1 were found to be disordered over two positions with occupancies
of 0.50. The tropylium cation of 8·1 proved to be disordered as an eight-
membered ring, with C56 having a site occupancy of 0.50. The -CH2- unit
of one of the ethanol molecules in 9·2 was found to be disordered over
two positions (0.702:0.298), and two other ethanols have occupancies of
0.5. The hydroxy hydrogen of one of the ethanol molecules could not be
reliably determined. Detailed crystal data for the complexes are present-
ed in Table 4. CCDC-250232–250237 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.cam.a-
c.uk/data_request/cif.
[2] S. Chao, C. E. Moore, Anal. Chim. Acta 1978, 100, 457–467, and ref-
erences therein.
[3] S. V. Lindeman, D. Kosynkin, J. K. Kochi, J. Am. Chem. Soc. 1998,
120, 13268–13269.
[4] P. K. Bakshi, A. Linden, B. R. Vincent, S. P. Roe, D. Adhikesavalu,
T. S. Cameron, O. Knop, Can. J. Chem. 1994, 72, 1273–1293.
[5] E. Bakker, Anal. Chem. 2004, 76, 3285–3298.
´
[6] J. Janata, M. Josowicz, P. Vanysek, D. M. DeVaney, Anal. Chem.
1998, 70, 179R–208R.
[7] E. Bakker, D. Diamond, A. Lewenstam, E. Pretsch, Anal. Chim.
Acta 1999, 393, 11–18.
[8] E. Bakker, P. Bꢄhlmann, E. Pretsch, Chem. Rev. 1997, 97, 3083–
3132.
[9] J. Bobacka, V. Vꢁꢁnꢁnen, A. Lewenstam, A. Ivaska, Talanta 2004,
63, 135–138.
[10] G. J. Kruger, A. L. du Preez, R. J. Haines, J. Chem. Soc. Dalton
Trans. 1974, 1302–1305.
[11] S. Kiviniemi, M. Nissinen, T. Alaviuhkola, K. Rissanen, J. Pursiai-
nen, J. Chem. Soc. Perkin Trans. 2 2001, 2364–2369.
[12] J. Bobacka, T. Alaviuhkola, V. Hietapelto, H. Koskinen, A. Lewen-
stam, M. Lꢁmsꢁ, J. Pursiainen, A. Ivaska, Talanta 2002, 58, 341–349.
[13] M. Brookhart, B. Grant, A. F. Volpe Jr., Organometallics 1992, 11,
3920–3922.
[14] H. Holzapfel, C. Richter, J. Prakt. Chem. 1964, 4, 15–23.
[15] J. L. R. Williams, P. J. Grisdale, J. C. Doty, M. E. Glogowski, B. E.
Babb, D. P. Maier, J. Organomet. Chem. 1968, 14, 53–62.
[16] T. E. Cole, R. K. Bakshi, M. Srebnik, B. Singaram, H. C. Brown, Or-
ganometallics 1986, 5, 2303–2307.
[17] G. Wittig, P. Raff, Justus Liebigs Ann. Chem. 1951, 573, 195–209.
[18] K. M. Harmon, F. E. Cummings, D. A. Davis, D. J. Diestler, J. Am.
Chem. Soc. 1962, 84, 3349–3355, and references therein.
[19] N. Whittaker, J. Chem. Soc. 1953, 1646.
[20] a) D. H. Bonsor, B. Borah, R. L. Dean, J. L. Wood, Can. J. Chem.
1976, 54, 2458–2464; b) A. R. Katritzky, Y.-K. Yang, B. Gabrielsen,
J. Marquet, J. Chem. Soc. Perkin Trans. 2 1984, 857–866.
[21] J. Koryta, J. Dvorak, L. Kavan, Principles of Electrochemistry, 2nd
ed., Wiley, Chichester, UK, 1993, p. 38.
Acknowledgements
Financial support from the National Technology Agency (TEKES) is
gratefully acknowledged. M.N. and J.B. thank the Academy of Finland
for financial support. We also thank Dr. Vesa Hietapelto for his contribu-
tions in the initial part of the project, and Ms. Anna Saloranta, Ms. Heli
Koskinen, and Mr. Sçren Sundblom for experimental assistance.
[22] Y. Umezawa, K. Umezawa, H. Sato, Pure Appl. Chem. 1995, 67,
507–518.
[1] F. P. Cassaretto, J. J. McLafferty, C. E. Moore, Anal. Chim. Acta
1965, 32, 376–380.
[23] H. A. Benesi, J. H. Hildebrand, J. Am. Chem. Soc. 1949, 71, 2703–
2707.
Chem. Eur. J. 2005, 11, 2071 – 2080
www.chemeurj.org
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2079

T. Alaviuhkola et al.
[24] Z. Otwinowski, W. Minor, Methods in Enzymology, 276: Macromo-
lecular Crystallography, part A, (Eds.: C. W. Carter Jr., R. M.
Sweet), Academic Press, 1997, pp. 307–326.
[26] G. M. Sheldrick, SHELXL-97, A Program for Crystal Structure Re-
finement, University of Gçttingen, Gçttingen (Germany), 1997.
[25] G. M. Sheldrick, SHELXS-97, A Program for Automatic Solution of
Crystal Structures, University of Gçttingen, Gçttingen (Germany),
1997.
Received: September 29, 2004
Published online: January 26, 2004
2080
ꢂ 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2005, 11, 2071 – 2080