Cationic borabenzene complexes as electron accepting groups for molecular material with nonlinear optical properties

Article abstract of DOI:10.1002/zaac.200300101

The dinuclear dipolar borabenzene complexes [(η⁵-C ₅H₅)Fe{μ-(η⁵-C₅H ₄)C₂(η⁶-BC₅H₅)}ML]X [ML = Ru(η⁶-C₆H₆), X = Cl (4aCl), PF ₆ (4aPF₆), B(C₆H₅)₄ (4aBPh₄); ML = Rh(η⁵-C₅Me₅), X = Cl (4bCl), PF₆ (4bPF₆); ML = Ir(η⁵-C ₅Me₅), X = Cl (4cC1), PF₆ (4cPF₆)] were synthesized by a nucleophilic substitution reaction of the trimethylphosphane adduct of borabenzene (1) with lithium ferrocenylacetylide, subsequent lithium-thallium exchange and coordination of the appropriate ML unit obtained from [Ru(η⁶-C₆H₆)Cl(μ -Cl)]₂, [M(η⁵-C₅Me₅)Cl(μ -Cl)]₂ (M = Rh, Ir); the formed chloride salts, which are soluble in water, were transformed to the PF₆ salts by adding [NH ₄][PF₆] to the corresponding water solution. BPh ₄ salts can be produced, when a methanolic solution of Na[BPh ₄] were added to CH₂Cl₂-solutions of the appropriate PF₆ salt. X-ray structure analyses of single crystals of 4aBPh₄ and 4bPF₆ were successful, illustrating the cation 4a⁺ in an ideal cis-conformation, whereas 4b⁺ displays a cis- and trans-conformation. Spectroscopic and cyclic voltammetry studies reveal a small but distinct donor-acceptor interaction between the ferrocenyl donor and the cationic borabenzene complex acceptor which increases in the order 4aPF₆ < 4cPF₆ < 4bPF₆. The nonlinear optical properties of these donor-acceptor complexes were studied by means of hyper-Rayleigh scattering (HRS), resulting in the determination of small values for the first hyperpolarisability β, which increase in the same order as the donor-acceptor interaction.

Full text of DOI:10.1002/zaac.200300101

Cationic Borabenzene Complexes as Electron Accepting Groups for Molecular
Material with Nonlinear Optical Properties
U. Behrens, T. Meyer-Friedrichsen, and J. Heck*
Hamburg, Institut für Anorganische und Angewandte Chemie der Universität
Received March 18th, 2003.
Dedicated to Professor Heinrich Nöth on the Occasion of his 75th Birthday
Abstract. The dinuclear dipolar borabenzene complexes [(η5-
C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)}ML]X [ML ϭ Ru(η6-C6H6),
X ϭ Cl (4aCl), PF6 (4aPF6), B(C6H5)4 (4aBPh4); ML ϭ Rh(η5-
C5Me5), X ϭ Cl (4bCl), PF6 (4bPF6); ML ϭ Ir(η5-C5Me5), X ϭ Cl
(4cCl), PF6 (4cPF6)] were synthesized by a nucleophilic substitution
reaction of the trimethylphosphane adduct of borabenzene (1) with
lithium ferrocenylacetylide, subsequent lithium-thallium exchange
and coordination of the appropriate ML unit obtained from
[Ru(η6-C6H6)Cl(µ-Cl)]2, [M(η5-C5Me5)Cl(µ-Cl)]2 (M ϭ Rh, Ir); the
formed chloride salts, which are soluble in water, were transformed
to the PF6 salts by adding [NH4][PF6] to the corresponding water
solution. BPh4 salts can be produced, when a methanolic solution
of Na[BPh4] were added to CH2Cl2-solutions of the appropriate
PF6 salt. X-ray structure analyses of single crystals of 4aBPh4 and
4bPF6 were successful, illustrating the cation 4a؉ in an ideal cis-
conformation, whereas 4b؉ displays a cis- and trans-conformation.
Spectroscopic and cyclic voltammetry studies reveal a small but
distinct donor-acceptor interaction between the ferrocenyl donor
and the cationic borabenzene complex acceptor which increases in
the order 4aPF6 < 4cPF6 < 4bPF6. The nonlinear optical properties
of these donor-acceptor complexes were studied by means of hyper-
Rayleigh scattering (HRS), resulting in the determination of small
values for the first hyperpolarisability β, which increase in the same
order as the donor-acceptor interaction.
Keywords: Dipolar dinuclear complexes; Nonlinear optical proper-
ties; Borabenzene complexes; Ferrocene; Hyper-Rayleigh scattering
Kationische Borabenzol-Komplexe als Elektronenakzeptor-Gruppen für molekulare
Materialien mit nichtlinearoptischen Eigenschaften
Inhaltsübersicht. Der Weg zur Darstellung der zweikernigen, dipo-
laren Borabenzolkomplexe
[(η5-C5H5)Fe{µ-(η5-C5H4)C2(η6-
stellt werden, indem methanolische Lösungen von Na[BPh4] zu
CH2Cl2-Lösungen der entsprechenden PF6-Salze gegeben werden.
Einkristallstrukturanalysen von 4aBPh4 und 4bPF6 waren erfolg-
reich. Sie ergeben für das Kation 4a؉ eine ideale cis-Konformation,
während für 4b؉ eine cis- und trans-Konformation gefunden wird.
Spektroskopische und cyclovoltammetrische Studien zeigen eine
geringe aber merkliche Donor-Akzeptor-Wechselwirkung zwischen
dem Ferrocenyldonor und dem kationischen Borabenzolkomplex-
Akzeptor, die in der Reihenfolge 4aPF6 < 4cPF6< 4bPF6 ansteigt.
Die nichtlinear optischen Eigenschaften dieser Donor-Akzeptor-
komplexe wurden mit Hilfe der hyper-Rayleigh-Streuungsmethode
(HRS) untersucht. Danach konnten für die erste Hyperpolarisier-
barkeit β relativ kleine Werte bestimmt werden, die in der gleichen
Reihenfolge wie die Donor-Akzeptor-Wechselwirkung ansteigen.
BC5H5)}ML]X [ML ϭ Ru(η6-C6H6), X ϭ Cl (4aCl), PF6 (4aPF6),
B(C6H5)4 (4aBPh4); ML ϭ Rh(η5-C5Me5), X ϭ Cl (4bCl), PF6
(4bPF6); ML ϭ Ir(η5-C5Me5), X ϭ Cl (4cCl), PF6 (4cPF6)] führte
über die nucleophile Substitutionsreaktion am Trimethylphosphan-
addukt von Borabenzol (1) mit Lithiumferrocenylacetylid; das ent-
standene Lithiumsalz des ferrocenylethinylsubstituierten Borata-
benzols (2) wurde zunächst einer Li/Tl-Austauschreaktion unter-
worfen und zur Koordination an ML-Einheiten anschließend mit
[Ru(η6-C6H6)Cl(µ-Cl)]2, [M(η5-C5Me5)Cl(µ-Cl)]2 (M ϭ Rh, Ir) um-
gesetzt. Die entstandenen Cl-Salze sind wasserlöslich und lassen
sich durch Zugabe von [NH4][PF6] zu wässrigen Lösungen der
Chloride in die PF6-Salze überführen. BPh4-Salze können herge-
Introduction
ability β, has been shown to be very powerful [2]. These
complexes consist of the combination of an organometallic
electron donating and accepting group connected with a
bridge, which enables electronic π-interaction between
them. By far the most used donating units are sandwich
type complexes, like ferrocene and ruthenocene, due to their
inertness and facile synthetic manipulations [2c-t]. Another
type of frequently used organometallic donating groups are
half-sandwich complexes wherein the π-bridge is directly
linked to the metal atom [2a, 2b].
The concept of dipolar cationic heterobimetallic organome-
tallic complexes for compounds with non-linear optical
(NLO) properties [1] e.g. with high first order hyperpolaris-
* Prof. Dr. J. Heck
Institut für Anorgan. u. Angew. Chemie der Universität
Martin-Luther-King-Platz 6
D-20146 Hamburg
Tel.: ϩ49 40 42838 6375
fax ϩ49 40 42838 6945
For organometallic electron accepting groups carbonyl
complexes were employed [2a, 2b, 2g, 2i, 2k, 2m, 2o,] as
well as Fischer carbenes [2l] and cationic complexes of or-
email: juergen.heck@chemie.uni-hamburg.de
Z. Anorg. Allg. Chem. 2003, 629, 1421Ϫ1430
DOI: 10.1002/zaac.200300101
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U. Behrens, T. Meyer-Friedrichsen, J. Heck
Solid state structure
The PF6-salts of 4a, 4b and 4c crystallize in very thin plates,
which were not very proper for X-ray structure analyses.
Therefore, 4aPF6 was transformed to the BPh4-salt and
suitable crystals were obtained by gasphase diffusion of
Et2O into a concentrated solution of 4aBPh4 in acetonitrile.
Figure 1 Mesomeric forms of cationic borabenzene complexes il-
lustrating the electron accepting properties of the borabenzene ent-
ity.
¯
4aBPh4 crystallizes in the triclinic space group P1 with two
independent molecules in the asymmetric unit. The cationic
bis(sandwich)complex 4aϩ adopts an almost perfect cis-
conformation (Figure 2); the substituted Cp ligand of the
ferrocenyl unit is twisted only about 1.9(2)° with respect to
the borabenzene ligand. The two Cp ligands of the ferro-
cenyl moiety are in an eclipsed conformation, whereas a
gauche conformation is found for the two six-membered
rings of the borabenzene complex. The iron atom is placed
equidistant with respect to the planes of the two Cp ligands
(165.2(2) pm and 165.1(2) pm, respectively), and the FeϪC
bond lengths are quite normal for monosubstituted ferro-
cene derivatives with weak electronic interaction with the
substituent.
The borabenzene complex moiety reveals the typical
structural features found for similar-sandwich complexes:
the Ru-C(benzene) distances are as expected (216.9(4) Ϫ
220.9(4) pm), however, a strong variation of the C,C bond
distances is found, indicating some disorder of the benzene
ligand. The Ru-C(borabenzene) bond lengths fall in the
range of 218.8(4) Ϫ 224.2(4) pm (Table 2), with the shortest
Ru-C bond lengths in p-position with respect to the boron
atom, which is in agreement with other borabenzene com-
plexes [8] .The Ru-B bond length of 237.8(5) pm corre-
sponds to published metal-boron distances found for other
borabenzene complexes [9].
The four atoms C1, C11, C12, and B1, forming the
bridge between the donor and the acceptor, are arranged in
an almost linear fashion (C1-C11-C12: 178.6 (4)°, C11-C12-
B1: 175.2(4)°). Of particular interest for donor-acceptor
molecules is the bond length variation in the π-linker, since
it manifests the extent of electronic communication between
the donor and the acceptor, and gives some hints on NLO-
properties [10,11]. However, complex cation 4a contains a -
CϵC- length about 120.3(5) pm, which is slightly elongated
compared to 118.3 pm in RϪCϵCϪR with isolated car-
bon-carbon triple bonds or in the donor-acceptor com-
pound 4-nitro-4Ј-amino tolane [11]. Whether this small
elongation is caused by a delocalisation of the π-bonding
electrons, as depicted in Figure 3, is not quite clear, since
the carbon-carbon and carbon-boron single bonds (143.3(5)
and 155.0(6) pm, respectively) of the acetylenic linker in
4a؉ are as long as the corresponding bond lengths for the
donor-acceptor tolane compound [11] and diborylacetyl-
enes [12], respectively. Therefore, a pronounced donor-ac-
ceptor interaction in 4a؉, which may be deduced from
structural features of the π-bridge between the donor and
the acceptor, cannot be concluded. This is in good harmony
with results obtained from theoretical calculation about
ethynylboranes which prove a very small tendency to form
delocalized heteroallenes (Figure 4) [13].
ganic π-ligands [2d, 2e, 2j, 2n, 2p, 2r, 2t]. Recently, we have
been able to demonstrate that the cationic η6-borabenzene
complex of a cyclopentadienylcobalt unit can also be used
as an electron accepting group for NLO chromophores [3].
Its electron accepting capability is reinforced by two effects:
first by the cationic nature of the metal complex, and se-
cond, by the π-acidity of the boron atom (Figure 1). Ad-
ditionally, the cationic borabenzene complexes are very
stable in air [4], which would be an essential prerequisite for
further applications.
In this paper we describe the synthesis, structure and
spectroscopic properties of dipolar dinuclear borabenzene
complexes wherein the electron donating group (ferrocenyl)
and the accepting unit are separated by an ethyndiyl bridge.
Results and Discussion
Synthesis
Just recently, it was shown by Fu et al. [5] that boron-linked
alkyne derivatives of boratabenzene can be obtained by nu-
cleophilic substitution of the trimethylphosphane adduct of
borabenzene (1) with lithium acetylides [6]. In order to
combine a ferrocenyl donor with cationic borabenzene
complexes the lithium salt of ferrocenylacetylide was suc-
cessfully employed (Scheme 1,a). Since lithium salts of bor-
atabenzene compounds as 2 display strong nucleophilicity,
which hampers a good yield in the formation of boraben-
zene complexes of Ru, Rh and Ir, the lithium salt 2 was
transformed to the thallium salt 3 by stirring 2 in acetonitril
in the presence of excess of thallium chloride (Scheme
1,b) [7].
The thallium salt 3 was isolated once as a pyridine adduct
and fully characterized. However, since the isolated yield of
3 is rather low (10 Ϫ 12 %), the product of the metathesis
reaction (Scheme 1, b) was allowed to react directly with
the halfsandwich complexes [Ru(η6-C6H6)Cl2]2, [Rh(η5-
C5Me5)Cl2]2 and [Ir(η5-C5Me5)Cl2]2 without further iso-
lation of the thallium salt 3 (Scheme 2). The intermediate
generated chloride salts 4aCl, 4bCl and 4cCl are water sol-
Ϫ
uble and can be precipitated as PF6 salts by adding
[NH4][PF6]. The tetraphenyl borate salt 4aBPh4 was ob-
tained by adding a methanol solution of Na[BPh4] to a
solution of 4aPF6 in CH2Cl2. Crystals of 4a BPh4 are stable
in air for years and corresponding solutions for weeks at
least.
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Cationic Borabenzene Complexes as Electron Accepting Groups
Scheme
1
Synthesis
of the thallium salt of
ferrocenylethynyl
boratabenzene (3)
Scheme
2
Synthesis
of [(η5-C5H5)Fe{µ-(η5-
C5H4)C2(η6-
BC5H5)}ML]X, X ϭ
Cl, PF6
Crystals of 4bPF6 were obtained by diffusion of an Et2O
layer into a concentrated solution of 4bPF6 in CH2Cl2. A
red, plate-shaped crystal was subjected to X-ray crystal
structure determination. For compound 4bPF6 a large B-
centred cell with an orthorhombic metric was found (see
table 1, cell parameters). However, there is no mmm sym-
metry in the intensity data set, but only monoclinic sym-
metry with the b axis (1057.48 pm) as the monoclinic axis.
In a monoclinic setting (half volume of the orthorhombic
cell; half ac diagonal as c axis) the space group is P21/c. For
convenience the orthorhombic cell setting was maintained
(non standard space group B21/d). In the structure of 4bPF6
Z. Anorg. Allg. Chem. 2003, 629, 1421Ϫ1430
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U. Behrens, T. Meyer-Friedrichsen, J. Heck
Table
1
Crystallographic
data
of
[(η5-C5H5)Fe{µ-(η5-
Table 2 Selected interatomic distances /pm and angles /° of [(η5-
C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)}Ru(η6-C6H6)][(B(C6H5)4]
(4aBPh4) and [(η5-C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)}Rh(η5-
C5Me5)]PF6 (4bPF6)
C5H4)C2(η6-BC5H5)}Ru(η6-C6H6)][B(C6H5)4] (4aBPh4) and [(η5-
C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)}Rh(η5-C5Me5)]PF6 (4bPF6)
4aBPh4
4bPF6
4aBPh4
4bPF6
Empirical formula
Formula mass
T /K
C47H40B2FeRu
783.33
293
C27H29BF6FePRh
668.04
153
C1 Ϫ C2
C2 Ϫ C3
C3 Ϫ C4
C4 Ϫ C5
C5ϪC1
C6 Ϫ C7
C7 Ϫ C8
C8 Ϫ C9
C9 Ϫ C10
C10 Ϫ C6
C1 Ϫ C11
C11ϪC12
C12 Ϫ B1
C13 Ϫ B1
C13 Ϫ C14
C14 Ϫ C15
C15 Ϫ C16
C16 Ϫ C17
C17 Ϫ B1
Fe Ϫ C1
143.3(5)
141.4(5)
141.4(5)
141.2(5)
144.2(5)
142.8(6)
141.0(6)
141.8(6)
142.2(6)
140.5(6)
143.3(5)
120.3(5)
155.0(6)
153.1(7)
140.9(6)
140.9(7)
140.8(7)
141.1(6)
150.7(8)
204.3(4)
204.5(3)
205.0(3)
205.5(4)
204.4(4)
165.1(2)
165.2(2)
237.7(4)
140.9(9)
137.2(10)
140.5(11)
143.9(10)
145.0(9)
140.2(10)
148.0(11)
139.9(12)
137.4(10)
141.4(10)
143.2(8)
122.0(8)
151.6(9)
153.6(10)
137.9(8)
141.2(8)
140.4(9)
141.7(9)
152.5(9)
203.5(8)
203.1(9)
204.5(9)
202.0(9)
206.4(9)
164.6(5)
165.8(5)
229.7(9)
228.7(8)
227.3(7)
228.2(7)
219.9(7)
222.2(7)
205.6(8)
211.9(8)
205.5(8)
208.6(9)
213.7(8)
211.0(8)
161.2(5)
163.3(5)
λ /pm)
71.073
71.073
Crystal size /mm3
Crystal system
Space group
a /pm
0.4 x 0.4 x 0.2
triclinic
0.2 x 0.2 x 0.05
monoclinic
B21/d
692.27(5)
1057.48(8)
7083.4(5)
90
90.00
90
5185.5(7)
8
1.711
1.32
54
Ϫ8 Յ h Յ 8
Ϫ13 Յ k Յ 13
Ϫ89 Յ l Յ 89
30541/5803
3734
¯
P1
1057.0(2)
1092.2(2)
1835.3(4)
86.73(3)
75.18(3)
61.34(3)
1791.9(6)
2
1.452
0.860
50
Ϫ11 Յ h Յ 0
Ϫ12 Յ k Յ 11
Ϫ21 Յ l Յ 21
b /pm
c /pm
Ͱ /°
β /°
γ/°
V /106 pm3
Z
ρcalc /Mg/m3
µ /mmϪ1
2 °max /°
Index range
Reflections total/indep. 6802/6218
Fe Ϫ C2
Fe Ϫ C3
Fe Ϫ C4
Reflections [I>4σ(I)]
Parameters
5392
460
1.023
0.038
0.100
350
GoFa)
Fe Ϫ C5
R1 factor (I>4σ(I))b)
wR2 (all data)b)
0.069
0.157
Fe Ϫ [C1-C5] a)
Fe Ϫ [C6-C10] b)
M Ϫ B1
M ϭ Rh1
Rh2
Rh1
Rh2
Rh1
Rh2
Rh1
Rh2
Rh1
Rh2
Rh1
Rh2
Rh1
Rh2
Ϫ3
˚
Resd. min/max (e/A
)
Ϫ0.98/1.25
Ϫ2.08/1.11
M Ϫ C13
223.9(4)
220.3(4)
218.8(4)
220.1(4)
224.2(4)
171.3(2)
169.7(2)
w(F02 Ϫ Fc
)
2 2
͚
a)
GoF (goodness of fit) ϭ
M Ϫ C14
Ί
nϪp
(n ϭ numbers of reflections, p ϭ numbers of parameters).
M Ϫ C15
2 2
ʈF0͉Ϫ͉Fcʈ
w(F02 Ϫ Fc
)
͚
͚
b)
R1 ϭ
; wR2 ϭ
M Ϫ C16
2 2
Ί
͉F0͉
w(F0 )
͚
͚
M Ϫ C17
M Ϫ [B1-C17] c)
Ru Ϫ [C18-C23] d)
the Rh atom is disordered over two sites (s.o.f. 0.5/0.5). Re-
finement as a twin (twin components 0.8 and 0.2) lowered
the conventional R value from about 0.11 to 0.069.
Remarkably, the molecular structure of 4bϩ is rep-
resented by an ideal cis- and trans-conformation in the crys-
talline state (Figure 5). Usually, sandwich-type donor-ac-
ceptor pairs seem to prefer a cis-conformation, when they
are separated at least by a C2-linker like ethendiyl or ethyn-
diyl [2d, 2j, 2n, 2t]. One exception is known for a dinuclear
monohydro sesquifulvalene which bears a pentamethylated
cyclopentadienyl (Cp*) ligand as well [2t]. Apparently, the
steric interaction between the Cp* ligand of one sandwich
unit and the Cp ligand of the other one does not prefer the
cis-arrangement of both sandwich moieties as the only con-
former.
Rh1
182.7(5)
Rh Ϫ [C18-C23] e)
Rh2
185.1(5)
177.9(8)
177.5(8)
4.3(5)°
C1 Ϫ C11 Ϫ C12
178.6(4)
175.2(4)
1.9(2)°
C11 Ϫ C12 Ϫ B1
[C1 Ϫ C5][B1 Ϫ C17] f)
a) [C1-C5]: best plane of C1, C2, C3, C4 and C5; b) [C6-C10]: best plane of
C6, C7, C8, C9 and C10; c) [B1-C17]: best plane of B1, C13, C14, C15, C16
and C17; d) [C18-C23]: best plane of C18, C19, C20, C21, C22 and C23;
e) [C18-C22]: best plane of C18, C19, C20, C21 and C22; f) inter planar angle
between [C1-C5] and [B1-C17].
The coordination of the Rh atom to the borabenzene li-
gand demonstrates the typical bonding mode with a long
rhodium-boron distance (229.7(9) and 228.7(8) pm) similar
to other Rh-B distances in comparable borabenzene com-
plexes, and a general Rh-C(borabenzene) bond shortening
in the opposite position. This bonding situation very much
resembles the common coordination feature of borabenzene
complexes (vide supra) [9,14], however, in this case a more
precise statement suffers from the disorder of 4bPF6. The
As already observed for the Ru derivative 4a؉ the Cp
,
ligand and the joined borabenzene ligand deviate only
about 4.4° from coplanarity and the linking unit C1, C11,
C12, and B(1) is linear arranged (C1-C11-C12: 177.9°;C11-
C12-B1: 177.5°). The bond lengths within the π-linker are
very similar to the corresponding bond lengths of 4a؉, only
the C12-B1 distance (151.6(9) pm) seems to be slightly
shortened with respect to C12-B1 of 4aϩ (155.0(6) pm).
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Cationic Borabenzene Complexes as Electron Accepting Groups
Table 3 Selected spectroscopic data of the bimetallic borabenzene complexes [(η5-C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)}ML]PF6 [ML ϭ
Ru(η6-C6H6) (4aPF6), Rh(η5-C5Me5) (4bPF6), Ir(η5-C5Me5) (4cPF6)]
a)
c)
ML
1H NMR
δ/ppm
C5H4
IR
Electrochemistry
UV-VIS
HRS
∆ν˜h)/cmϪ1 βi)
ν˜CϭC
λmaxf)(ε)g)
λmaxf)(ε)g)
MeCN
C5H5 H-4 b) H-3,5 b) H-2,6 b)
L
cmϪ1
E1/2(ox) d) Epc(red) e) CH2Cl2
Ru(η6-C6H6)
(4a)
4.32, 4.50 4.25
5.39
5.62
5.64
6.39
6.68
6.65
6.39
6.52
6.65
6.60
2166 (m)
2156 (m)
2160 (m)
288(11120) 288(8080)
Ϫ
n.d.
0.10
0.18
Ϫ1.84
Ϫ1.6
ഠ370(sh)
446 (970)
ഠ355(sh)
440 (600)
Ϫ
Ϫ305
Rh(η5-C5Me5) 4.33, 4.55 4.28
(4b)
2.26
2.36
293(12200) 290(12480) Ϫ306
59
335 (7070)
456 (1330)
331 (5810)
450 (sh)
Ϫ361
Ϫ
Ir(η5-C5Me5)
(4c)
4.31, 4.52 4.26
0.13
Ϫ2.05
292(18860) 288(12780) Ϫ476
46
ഠ360 (sh)
442(985)
ഠ350 (sh)
442(480)
Ϫ
Ϫ
a) 200 MHz, [D6]acetone, room temperature; δ (FcH) ϭ 4.15 ppm; b) borabenzene ligand; c) KBr pellets; d) half-wave potential for oxidation in V vs. [FcH]/
e)
[FcH]ϩ;
E
ϭ peak potential in V vs [FcH]/[FcH]ϩ, v ϭ 50 mV/s; f) nm; g) MϪ1cmϪ1 h) ∆ν˜ ϭ ν˜(CH2Cl2) Ϫ ν˜(MeCN)‚ i) given as units of 10Ϫ30 esu; as
;
pc
reference p-nitroaniline was used: β(MeNO2) ϭ 34.6 mol 10Ϫ30 esu [28].
ferent values for comparable bonds e.g. within the Cp li-
gands.
Spectroscopic Properties
1
The assignment of the H and 13C NMR signals was per-
1
formed by using the splitting pattern in the H NMR spec-
1
tra and by means of H13C correlation spectroscopy. From
1
the H NMR spectroscopic data (Table 3) it becomes evi-
dent that the shifts of the resonance signals can be sepa-
rated into two domains: one for the borabenzene ligand
(5.39 Ϫ 6.68 ppm) and the other for the ferrocenyl donor
(4.25 Ϫ 4.55 ppm). The general low field shifts of the ferro-
cenyl signals compared to the unsubstituted ferrocene (δ ϭ
4.15) indicate the electron accepting capability of the cat-
ionic borabenzene complex moiety. From the relative low-
field shift of the Cp signals of the ferrocene donor an elec-
tron withdrawing strength can be deduced in the order
Ru(η6-C6H6) < Ir(η5-C5Me5) < Rh(η5-C5Me5), although
the differences are not very pronounced.
Figure 2 Molecular structure of [(η5- C5H5)Fe{µ-(η5-C5H4)C2(η6-
BC5H5)}Ru(η6-C6H6)][B(C6H5)4] (4aBPh4) in the crystalline state
(50 % ellipsoids, the counterion [BPh4]Ϫ is omitted for clarity)
This order would be in agreement with the position of
the stretching mode of the carbon-carbon triple bond in the
IR spectra of 4aPF6, 4bPF6 and 4cPF6, if only electronic
changes in the acetylenic bridge are important (Table 3):
with increasing contribution of the cummulenic resonance
form a decrease in the bond order of the central carbon-
carbon bond is expected (Figure 3), which causes a decrease
in the energy of the corresponding carbon-carbon stretch-
ing vibration. However, the differences in the CϵC-stretch-
ing energies are very small and have to be regarded with
care, since they may additionally be influenced by mecha-
nical coupling effects, which, in particular, are important
for linear arranged atoms.
Figure 3 Limiting mesomeric forms of the cationic borabenzene
complex [(η5-C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)]ML]ϩ [ML ϭ
Ru(η6-C6H6), Rh(η5-C5Me5), Ir(η5-C5Me5)]
Figure 4 Limiting mesomeric forms for ethynyl boranes
The cyclic voltammetry (CV) study of the complexes
4aPF6, 4bPF6 and 4cPF6 reveal an electrochemically rever-
sible oxidation step, the potential and characteristic of
which are indicative for the ferrocenyl entity. Therefore, this
mean values of other bond lengths are as expected as well
taking into account the disorder which results in quite dif-
Z. Anorg. Allg. Chem. 2003, 629, 1421Ϫ1430
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U. Behrens, T. Meyer-Friedrichsen, J. Heck
Figure
6
Representative cyclic voltammogram for [(η5-
C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)}ML]PF6 [ML
ϭ
Ru(η6-
C6H6); Rh(η5-C5Me5); Ir(η5-C5Me5)]; here ML ϭ Rh(η5-C5Me5)
(4bPF6). Upper CV: scan direction is cathodic first, then anodic;
lower CV: scan direction is first anodic, then cathodic (the voltage
is measured against Ag/AgCl).
Figure 5 Molecular structure of [(η5-C5H5)Fe{µ-(η5-C5H4)C2(η6-
BC5H5)}Rh(η5-C5Me5)]PF6 (4bPF6) in the crystalline state (50 %
ellipsoids, the counterion [PF6]Ϫ is omitted for clarity). This figure
includes both conformers which gives raise for a disorder (top:
trans-conformer, bottom: cis-conformer) (For more details see text)
zene substituent. However, the extent of the anodic shift of
E
1/2(ox) for 4aPF6 - 4cPF6 is distinctly lower than for the
oxidation step is combined with a one-electron transfer
(Table 3). In addition, an irreversible reduction wave can be
recorded at very low potential(< Ϫ1.60 V vs [FcH]/[FcH]ϩ)
which is attributed to the borabenzene complex unit (Figure
6). A comparison of the peak currents of the two redox
steps proves a one-electron transfer for the reduction as
well. Whereas for 4aPF6 and 4cPF6 this reduction step is
completely irreversible, for 4bPF6 a partial electrochemical
reversibility is observed (Figure 6). In addition a small re-
oxidation wave appears at about 1 V anodically shifted with
respect to the reduction step. This wave is only observed,
when the reduction step was first recorded; in contrast to
it, starting at Ϫ1.0 V vs. [FcH]/[FcH]ϩ and recording the
CV first anodically, no corresponding wave is observed.
This result indicates that the oxidation wave at about
Ϫ0.6 V is a consequence of a chemical reaction upon the
reduction at Ϫ1.6 V vs. FcH/FcHϩ [15].
sesquifulvalene congener [(η5-C5H5)Fe{µ-(η5-C5H4)C2(η7-
C7H6)}Cr(CO)3]ϩ [2d] with E1/2(ox) ϭ 220 mV vs. [FcH]/
[FcH]ϩ. It is worthwhile to note that the increasing electron
withdrawing capability of the metal-ligand unit ML on the
oxidation potential E1/2 reflects the same order as found
from the NMR and IR studies.
UV-vis spectroscopic studies were performed with solu-
tions of different polarity such as dichloromethane and ace-
tonitril, to elucidate solvatochromism which gives an indi-
cation of the dipole change ∆µ between the ground and the
excited state [16], and is thus relevant for the first hyperpol-
arisability β. The UV-vis spectra of 4aPF6 Ϫ 4cPF6 ob-
tained from CH2Cl2 and MeCN, illustrate three absorption
maxima of quite different intensities (Figure 7, Table 3).
The strongest absorption maximum is observed at λ <
300 nm, which undergoes no (for 4aPF6) or moderate hyp-
sochromic shift, when the solvent has changed from
CH2Cl2 to MeCN (Figure 8). The absorption maximum be-
tween 300 and 400 nm, which is much lower in intensity, is
only resolved for the rhodium complex 4bPF6, whereas for
The clear anodic shift of the reversible oxidation poten-
tial E1/2(ox) in relation to unsubstituted ferrocene is due to
the electron accepting capability of the cationic boraben-
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Cationic Borabenzene Complexes as Electron Accepting Groups
sorption [18]. Amongst different methods [18], we chose for
the “low-cost” check for the two photon-absorption in-
duced fluorescence (TFP), which was recently described [2s,
19], and used bandpass filters with peak transmittance at
different wavelengths, which are introduced in front of the
photomultiplier of the HRS set-up. The broad fluorescence
signal, which yields the emission maximum at λ/2 of the
fundamental wavelength only by chance, is easily discerned
from the narrow second harmonic signal at λ/2. In course
of this study no fluorescence intensity was observed.
The NLO studies on 4aPF6 Ϫ 4cPF6 have been per-
formed in nitromethane solutions with concentrations at
about 10Ϫ4 Ϫ 10Ϫ6 M. For complex 4aPF6 no second har-
monic generation (SHG) could be observed in contrast to
4bPF6 and 4cPF6 (Table 3) [20]. The experimentally ob-
tained first hyperpolarisabilities β for 4bPF6 and 4cPF6 are
still rather low and considerably smaller than β values ob-
tained from similar ferrocene containing NLO chromoph-
ores. The corresponding static first hyperpolarisability was
not calculated, since all of the charge-transfer transitions
may contribute to the SHG effect. Nevertheless, the charac-
teristic of the electronic excitation spectra of all compounds
under investigation is quite similar, hence the contribution
to the resonance enhancement of β will be similar for
4aPF6, 4bPF6 and 4cPF6. Therefore, a conservative com-
parison of the SHG effect of the borabenzene cations may
be allowed, which demonstrates a slight increase of the β
values in the order 4aPF6 < 4cPF6 < 4bPF6. This order
matches the extent of the donor-acceptor interaction dem-
onstrated by 1H NMR, IR and cyclic voltammetry data
(vide supra).
Figure
7
UV-vis spectra of [(η5-C5H5)Fe{µ-(η5-C5H4)C2(η6-
BC5H5)]ML]PF6 [ML ϭ Ru(η6-C6H6) (4aPF6), Rh(η5-C5Me5)
(4bPF6), Ir(η5-C5Me5) (4cPF6)] obtained from CH2Cl2 solutions.
Figure
8
UV-vis spectra of [(η5-C5H5)Fe{µ-(η5-C5H4)C2(η5-
BC5H5)Ir(η6-C5Me5)]PF6 (4cPF6) obtained from CH2Cl2 and
MeCN solutions illustrating the solvatochromic effect.
Conclusions
4aPF6 and 4cPF6 only a shoulder is observed, which ham-
pers the determination of the solvatochromic effect.
A weak absorption maximum (ε < 1000 MϪ1cmϪ1) is re-
corded beyond 400 nm. Since this absorption band is only
poorly resolved, no solvatochromism is estimated for this
energetically low lying weak absorption band.
In general a negative solvatochromism of the absorption
bands in the electronic excitation spectra for 4aPF6, 4bPF6,
and 4cPF6 is observed, which is characteristic for other cat-
ionic donor-acceptor complexes, and indicate a donor-ac-
ceptor charge-transfer transition upon electronic excitation.
However, the extent of the hypsochromic shift is only mod-
erate compared to corresponding cationic sesquifulvalene
type complexes giving raise for a poor polarisability, and
thus also poor hyperpolarisability.
Three different dinuclear, cationic borabenzene complexes
[(η5-C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)ML]ϩ [(ML
ϭ
Ru(η6-C6H6) (4a؉), Rh(η5-C5Me5) (4b؉), Ir(η5-C5Me5)
(4c؉)] displaying donor-acceptor interactions, have been su-
cessfully synthesized and fully characterised: X-ray struc-
ture determinations of complex 4aBPh4 and 4bPF6 reveal
an almost unchanged acetylenic linker between the ferro-
cene donor and the cationic borabenzene complex moiety
compared to more or less symmetrically substituted
alkynes. However, a weak donor-acceptor interaction,
which may be considered as a subtle contribution of the
cummulenic resonance form to the ground state (Figure 3),
1
can be concluded from H NMR, IR and cyclic voltamme-
try data. NLO studies on 4aPF6, 4bPF6 and 4cPF6 by me-
ans of HRS experiments point to a slight increasing first
hyperpolarisability β with increasing electron accepting
capability of the cationic borabenzene moiety. Unfortu-
nately, the β values of the present cationic borabenzene
complexes are rather small compared to other ferrocene
containing donor-acceptor compounds. However, regarding
the inertness of the complexes under study and the possibil-
ity to increase the SHG effect more than a factor of two
when changing the pentamethylated cyclopentadienyl li-
NLO Measurements
The cationic nature of the borabenzene complexes
4a؉Ϫ4c؉ requires the hyper-Rayleigh scattering (HRS) [17]
as the only method to determine the first hyperpolaris-
ability β which presents the molecular capability to double
the frequency of incoming light. However, a pit-fall of the
HRS method may be fluorescence due to two-photon ab-
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U. Behrens, T. Meyer-Friedrichsen, J. Heck
gand with a simple cyclopentadienyl ligand on the acceptor
site [2s], and “vice versa” on the donor site [21] it would be
worthwhile to synthesize and study corresponding dinuclear
borabenzene complexes.
General Procedure of the Synthesis of [(η5-
C5H5)Fe{µ-(η5-C5H4)C2(η6-BC5H5)ML]PF6 (ML ؍
Ru(η6-C6H6) (4aPF6), Rh(η5-C5Me5) (4bPF6), Ir(η5-
C5Me5) (4cPF6)
For the synthesis of 4aPF6 Ϫ 4cPF6 the thallium salt 3 was not
isolated. The reaction mixture obtained from the synthesis of 3
(vide supra) was directly treated with an appropriate amount of the
corresponding ruthenium, rhodium and iridium halide (vide infra).
After stirring for 2 h at room temperature, 5 h at 40 Ϫ 50 °C and
finally overnight at room temperature again, the reaction mixture
was filtered and the filtrate evaporated to dryness. The residue was
redissolved in water and filtered. Solid NH4PF6 was added to the
water solution whereupon an orange coloured solid material was
formed. The product was several times recrystallised from dichloro-
methane/diethyl ether.
Experimental Section
Manipulations were carried out under a dry nitrogen atmophere
using standard Schlenk technique. Solvents were saturated with ni-
trogen, diethyl ether (Et2O), tetrahydrofuran (THF), n-hexane and
toluene were freshly distilled from the appropriate alkali metal or
metal alloy. Dichloromethane (CH2Cl2), acetonitril (MeCN) and
nitromethane (MeNO2) were dried over calcium hydride. NMR:
Varian Gemini 200 BB; Bruker AM 360; measured at 295 K rel.
TMS. UV-vis: Perkin-Elmer Model 554. IR: KBr pills, FT-IR, Per-
kin-Elmer Model 325. MS: Finnigan MAT 311 A. Elemental
analyses: CHN-O-Rapid, Fa. Heraeus (Zentrale Elementanalytik,
Fachbereich Chemie, Universität Hamburg). Trimethylphosphane
borabenzene [6a], ethynylferrocene [2d], di[chloro-µ-chloro(η6-ben-
zene)ruthenium(II)] [22], di[chloro-µ-chloro(η5-pentamethylcyclo-
pentadienyl)rhodium(III)] [23], and di[chloro-µ-chloro(η5-penta-
methylcyclopentadienyl)iridium(III)] [24] were synthesized accord-
ing the literature.
4aPF6: Used quantities: 2 (279 mg, 0.96 mmol), TlCl (345 mg,
1.44 mmol), MeCN (40 mL) and [Ru(η6-C6H6)Cl(µ-Cl)]2 (226 mg,
0.45 mmol). Yield: 315 mg (54 %) orange-coloured solid material.
Anal. calc. for C23H20BFeRuPF6 (609.1): C 45.35, H 3.31; found:
C 44.83, H 3.37 %.
1H NMR ([D6]acetone, rel. TMS): δ ϭ 4.25 (s, 5 H, C5H5), 4.32 (br s, 2 H,
C5H4), 4.50 (br s, 2 H, C5H4), 5.39 (m, 2 H, BC5H5), 6.39 (m, 3 H, BC5H5),
6.60 (s, 6 H, C6H6); 13C NMR ([D6]acetone, rel. TMS): δ ϭ 69.9 (C5H4Ј),
70.9 (C5H5), 72.6 (C5H4), 86.4 (C-4), 90.5 (C6H6), 99.0 (C-3,5); IR (KBr):
ν˜ ϭ 3097, 2166 (νCϵC), 1485, 1444, 1406, 1106, 838 (νP-F), 558 cmϪ1; UV-vis
(CH2Cl2): λmax (ε) ϭ 288 (11120), 370 (sh), 446 (970) nm (MϪ1cmϪ1);
(MeCN): λmax (ε) ϭ 288 (8080), 355 (sh), 440 (sh) nm (MϪ1cmϪ1); MS
(FAB): m/z (%) ϭ 465 (100) Mϩ ϩ 1-PF6);
Lithium [1-ferrocenyl-2-(boratabenzene)ethyne] (2)
A
solution of trimethylphosphane borabenzene (1) (455 mg,
4bPF6: Used quantities: 2 (700 mg, 2.4 mmol), TlCl (863 mg,
3.6 mmol), MeCN (60 mL), [RhCl(µ-Cl)(η5-C5Me5)]2 (750 mg,
1.2 mmol). Yield: 1.06 g (67 %) red needles.
Anal. calc. for: C27H29BFeRhPF6 (668.1): C 48.54, H 4.38; found
C 47.99, H 4.33 %.
1H NMR ([D6]acetone, rel. TMS): δ ϭ 2.26 (s, 15 H, C5Me5), 4.28 (s, 5 H,
C5H5), 4.33 (t, J ϭ 1.8 Hz, 2 H, C5H4), 4.55 (t. J ϭ 1.8 Hz, 2 H, C5H4), 5.62
(d, J ϭ 8.6 Hz, 2 H, H-2,6), 6.52 (t, J ϭ 6.0 Hz, 1 H, H-4), 6.68 (dd, J ϭ
8.6, 6.0 Hz, 2 H, H-3,5); (CD2Cl2, rel. TMS): δ ϭ 2.12 (s, 15 H, C5Me5), 4.26
(s, 5 H, C5H5), 4.30 (t, J 1.8 Hz, 2 H, C5H4), 4.52 (t, J ϭ 1.8 Hz, 2 H, C5H4),
5.44 (d, J ϭ 8.5 Hz, 2 H, H-2,6 ), 6.26 (t, J ϭ 6.0 Hz, 1 H, H-4), 6.39 (dd,
J ϭ 8.5, 6.0 Hz, 2 H, H-3,5); IR (KBr): ν˜ ϭ 3092, 2156 (νCϵC), 1490, 1403,
1105, 1026, 837 (νP-F), 558 cmϪ1; UV-vis (CH2Cl2): λmax (ε) ϭ 293 (12200),
335 (7070), 456 (1330) nm (MϪ1cmϪ1), (MeCN): λmax (ε) ϭ 290 (12480),
331 (5810), 450 (sh) nm (MϪ1cmϪ1);
2.86 mmol) and lithium ferrocenylacetylide (658 mg, 3.05 mmol) in
THF (30 mL) was stirred for 30 min at room temperature and an
additional 1 h under reflux. The reaction mixture was allowed to
cool to room temperature and was evaporated to dryness. The
sticky oily residue was stirred with a portion of benzene (20 mL)
to dissolve residual PMe3 and the obtained suspension was again
evaporated to dryness. This procedure was repeated until the resi-
due became an ochre coloured solid material, which was filtered
and washed with n-hexane and dried in vacuo. Yield: 695 mg (83 %)
of 2.
1H NMR ([D8]THF rel. TMS): δ ϭ 4.02 (t, J ϭ 1.8 Hz, 2 H, C5H4), 4.12 (s,
5 H, C5H5), 4.24 (t, J ϭ 1.8 Hz, 2 H, C5H4), 6.09 (t, J ϭ 7.3 Hz, 1 H, H-4),
6.51 (d, J ϭ 9.9 Hz, 2 H, H-2,6), 7.07 (dd, J ϭ 9.9, 7.3 Hz, H-3,5).
4cPF6: Used quantities: 2 (510 mg, 1.8 mmol), TlCl (648 mg,
2.7 mmol), MeCN (30 mL), [IrCl(µ-Cl)(η5-C5Me5)]2 (710 mg,
0.89 mmol). Yield: 909 mg (67 %).
Thallium [1-ferrocenyl-2-(boratabenzene)ethyne] (3)
The lithium salt 2 (1.08 g, 3.7 mmol) and thallium chloride (1.34 g,
5.6 mmol) were stirred in MeCN (40 mL) for 1 h at room tempera-
ture and over night at 50 °C. The reaction mixture was evaporated
to dryness, the red solid material was dissolved in a small amount
of pyridine and filtered. The filtrate was evaporated to dryness. The
dry residue was suspended in MeCN whereupon an ochre coloured
precipitate was formed. The precipitate was filtered off, washed
with Et2O and dried in vacuo. Yield: 190 mg (10.5 %) of 3.
Anal. calc. for: C27H29BFeIrPF6 (757.4): C 42.82, H 3.86; found C
42.37, H 4.16.
1H NMR ([D6]acetone, rel. TMS): δ ϭ 2.36 (s, 15 H, C5Me5), 4.26 (s, 5 H,
C5H5), 4.31 (t, J ϭ 1.9 Hz, 2 H, C5H4), 4.52 ( t, J ϭ 1.9 Hz, 2 H, C5H4),
5.64 ( m, 2 H, H-2,6), 6.65 (m, 3 H, H-3,5, H-4); (CD2Cl2, rel. TMS): δ ϭ
2.23 (s, 15 H, C5Me5), 4.25 (s, 5 H, C5H5), 4.29 (t, J ϭ 1.8 Hz, 2 H, C5H4),
4.49 (t, J ϭ 1.8 Hz, 2 H, C5H4), 5.44 (d, J ϭ 8.8 Hz, 2 H, H-2,6), 6.32 (m,
1 H, H-4), 6.36 (m, 2 H, H-3,5); 13C NMR ([D6]acetone, rel. TMS): δ ϭ 9.9
(C5Me5), 69.8 (C5H4), 70.7 (C5H5), 72.4 (C5H4), 87.6 (C-4), 99.3 (C5Me5),
100.8 (C-3,5); (CD2Cl2, rel. TMS): δ ϭ 10.2 (C5Me5), 69.6 (C5H4), 70.4
(C5H5), 72.3 (C5H4), 86.4 (C-4), 92 (br, C-2,6), 98.7 (C5Me5), 99.9 (C-3,5);
IR (KBr): ν˜ ϭ 3094, 2160 (νCϵC), 1470, 1400, 1107, 1034, 837(νP-F),
558 cmϪ1; UV-vis (CH2Cl2): λmax (ε) ϭ 292 (18860), 360 (sh), 442 (980) nm
(MϪ1cmϪ1); (MeCN): λmax (ε) ϭ 288 (12780), 350 (sh), 442 (480), nm
(MϪ1cmϪ1);
Anal. calc. for (C17H14BFeTl)1/2(C5H5N), 528.9: C 44.28, H 3.14,
N 1.32; found C 44.0, H 3.43, N 0.91 %.
1H NMR ([D6]DMSO, rel. TMS): δ ϭ 4.12 (t, J ϭ 1.8 Hz, 2 H, C5H4), 4.16
(s, 5 H, C5H5), 4.32 (t, J ϭ 1.8 Hz, 2 H, C5H4), 6.02 (t, J ϭ7.1 Hz, 1 H, H-
4), 6.30 (d, J ϭ 9.8 Hz, 2 H, H-2,6), 6.89 (dd, J ϭ 9.8, 7.1 Hz, 2 H, H-3,5);
7.39 (m, 1 H, C5H5N), 7.78 (m, 0.5 H, C5H5N), 8.56 (d, J ϭ 4.1 Hz, 1 H,
C5H5N); 13C NMR ([D6] DMSO, rel. TMS): δ ϭ 67.3 (C5H4), 69.4 (C5H5),
69.9 (C5H4), 111.2, 123.9 (C5H5N); 128.3, 130 (br, C-2,6), 131.7 (C-3,5),
136.2 (C5H5N), 149.6 (C5H5N); IR (KBr): ν˜ ϭ 3119, 3016, 2159 (νCϵC),
4aBPh4: 4aPF6 (110 mg, 0.18 mmol) was dissolved in a minimum
amount of CH2Cl2. An equimolar solution of Na[BPh4] (62 mg,
0.18 mmol) in MeOH was added. The precipitation was filtered
and recrystallised from MeCN/EtOH.
1521, 1412, 1102, 1091, 744 cmϪ1
.
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 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Z. Anorg. Allg. Chem. 2003, 629, 1421Ϫ1430

Cationic Borabenzene Complexes as Electron Accepting Groups
`
Anal. calcd. for (C47H40B2FeRu) (783.4): C 72.06, H 5.15; found C
71.86, H 5.20 %.
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Cyclic Voltammetry
Measurements were performed in CH2Cl2 with 0.4 M [N(nBu)4]PF6
as supporting electrolyte. An Amel 5000 system was used with a Pt
wire as the working electrode and a Pt plate (0.6 cm2) as the auxili-
ary electrode. The potentials were measured against Ag/AgCl and
are referenced against E1/2([Fe(C5H5)2]/[Fe(C5H5)2]ϩ) ϭ 0 V.
X-ray Structure Determination
Crystals suitable for X-ray structure determination were obtained
by gasphase diffusion of Et2O into a concentrated solution of
4aBPh4 in MeCN and by diffusion of an Et2O layer into a concen-
trated solution of 4bPF6 in CH2Cl2.
Single crystal X-ray diffraction studies of compound 4aBPh4 were
performed on a Hilger & Watts four circle diffractometer with
monochromated Mo-Kα radiation at 20 °C. For compound 4bPF6
a Bruker axs SMART CCD system was used (temperature
Ϫ120 °C; Mo-Kα radiation). Both structures were solved by direct
methods [25] and refined by SHELXTL [26, 27]. The crystal data
and the conditions for data collection and refinement are summar-
ized in Table 1. All atoms (except hydrogen) were refined using
anisotropic thermal parameters. The hydrogen atoms were placed
geometrically and refined using a riding model with isotropic ther-
mal parameters equal to 1.2 (CH) or 1.5 (CH3) Ueq of the carbon
atoms to which they are attached.
The crystallographic data for the structures reported in this paper
have been deposited at the Cambridge Data Centre as supplemen-
tary publication no. CCDC-207476 (4aBPh4), and CCDC-207477
(4bPF6). These data can be obtained free of charge at www.ccdc.ca-
m.ac.uk/conts/retrieving.html or from the Cambridge Crystallo-
graphic Centre, 12 Union Road, Cambridge CB2 1EZ, UK [fax:
(internat.) ϩ 44-1223/336-033; e-mail: deposit@ccdc.cam.ac.uk].
HRS measurements of the first hyperpolarisabilities
Hyper-Rayleigh scattering measurements were performed with a
pulsed Nd:YAG laser at a wavelength of λ ϭ 1064 nm. For the
experimental setup see ref. [17b]. Solutions of the complexes in
MeNO2 with concentrations in the range of 10Ϫ4 to 10Ϫ6 M were
used with p-nitroaniline as a reference [β(MeNO2) ϭ 34.6 x 10Ϫ30
esu] [28]. Fluorescence checks were made by replacing the inter-
ference filter in front of the photomultiplier tube with filters that
have transmittances at 400, 450, 500, 560, 600, and 700 nm [19].
Acknowledgments: This work was supported by the Deutsche For-
schungsgemeinschaft (DFG, HE 1309/3), by the European Com-
munity (COST D4/003/94, TMR FMRX-CT98-0166) and by the
Fonds der Chemischen Industrie. We thank the DEGUSSA AG for
a donation of RuCl3 and Sartorius GmbH for a donation of micro-
filters.
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