Metal complexes of 4′-(3-phenylpropoxy)-2,2′:6′,2″-terpyridine and 4′-(3-propoxy)-2,2′:6′,2″-terpyridine

Article abstract of DOI:10.1016/S0277-5387(01)00905-6

Reaction of 4′-chloro-2,2′:6′,2″-terpyridine with 3-phenyl-n-propanol or n-propanol in the presence of excess KOH in dmso, respectively, yields 4′-(3-phenylpropoxy)-2,2′:6′,2″-terpyridine (L²) and 4′-(3-propoxy)-2,2′:6′,2″-terpyridine (L^3<

Full text of DOI:10.1016/S0277-5387(01)00905-6

Polyhedron 20 (2001) 2889–2900
www.elsevier.com/locate/poly
Metal complexes of 4%-(3-phenylpropoxy)-2,2%:6%,2¦-terpyridine and
4%-(3-propoxy)-2,2%:6%,2¦-terpyridine
Xiaoming Liu a,*, Eric J.L. McInnes b, Colin A. Kilner a, Mark Thornton-Pett a,
Malcolm A. Halcrow a,*
a School of Chemistry, Uni6ersity of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK
b Department of Chemistry, CW EPR Ser6ice Centre, Uni6ersity of Manchester, Oxford Road, Manchester M13 9PL, UK
Received 25 May 2001; accepted 3 August 2001
Abstract
Reaction of 4%-chloro-2,2%:6%,2¦-terpyridine with 3-phenyl-n-propanol or n-propanol in the presence of excess KOH in dmso,
respectively, yields 4%-(3-phenylpropoxy)-2,2%:6%,2¦-terpyridine (L2) and 4%-(3-propoxy)-2,2%:6%,2¦-terpyridine (L3). The following
complexes of these two ligands have been prepared: [{Cu(m-Cl)L}2](BF4)2, [Cu(NCMe)(L)](BF4)2, [PdCl(L)]BF4 and [PtCl(L)]BF4
(L=L2, L3). Recrystallisation of [Cu(NCMe)(L2)](BF4)2 from PhCN/Et2O yields [Cu(NCPh)(L2)](BF4)2, whose crystal structure
shows a square planar Cu(II) ion with substantial disorder in the PhCN ligand and 3-phenylpropoxy tail. The single crystal
structure of [PdCl(L2)]BF4·2CH3NO2 contains a square planar Pd(II) centre. Neither of these structures, nor the solution
spectroscopic or electrochemical data from the complexes, provide any evidence for intramolecular p–p interactions between the
terpyridine ring and phenylpropoxy substituent. (Non-SI unit employed: 1 G=10−4 T.) © 2001 Elsevier Science Ltd. All rights
reserved.
Keywords: Cu(II) complexes; UV–Vis; EPR spectra
attributable to oxidation of the L1 dimethoxyphenyl
1. Introduction
moiety to a radical cation. These are unique examples
of heteroarene dimer cation species that are stable
enough to be characterised by standard synthetic meth-
ods, rather than by pulse radiolysis [3,4].
We have recently reported a structural and electro-
chemical study of the complexes [Cu(L1)(TpR)]BF4
(L1=1-{pyrid-2-yl}-3-{2%,5%-dimethoxyphenyl}pyrazole;
[TpR]−=tris-{3-phenylpyrazolyl}borate
tris-{3-[4-methylphenyl]pyrazolyl}borate
tris-{3-[4-fluorophenyl]pyrazolyl}borate
{[TpPh]−},
{[TpTol]−},
{[TpPhF]−};
Following on from this initial work, we were keen to
investigate more generally the effects of p–p interac-
tions on the properties of redox-active and/or photoac-
tive arenes and their complexes. Ideally, one should
prepare bis-aryl ligands containing intramolecular p–p
interactions so as not to rely on serendipitous, and
difficult to design, inter-ligand interactions to achieve
the desired p–p stacking [1,2,5,6]. As an initial study,
we have chosen to investigate terpyridyl ligands bearing
tethered aryl substituents, to examine the effects of p–p
interactions on the well-known reductive ligand-based
electrochemistry and fluorescent behaviour of their
Pt(II) complexes [7,8]. This paper describes our initial
efforts towards this goal.
Scheme 1), which exhibit an intramolecular p–p inter-
action involving the dimethoxyphenyl moiety of L1 and
a [TpR]− aryl substituent [1,2]. The cyclic voltam-
mograms of these complexes in CH2Cl2/0.5
M
NnBu4PF6 at room temperature contain a fully re-
versible one-electron oxidation by cyclic voltammetry,
* Corresponding authors. Tel.: +44-113-233-6506; fax: +44-113-
233-6565.
E-mail address: m.a.halcrow@chem.leeds.ac.uk (X. Liu).
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00905-6

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X. Liu et al. / Polyhedron 20 (2001) 2889–2900
2. Experimental
2.2. 4%-(Propoxy)-2,2%:6%,2¦-terpyridine (L3)
Unless otherwise stated, all manipulations were car-
ried out in air using commercial grade solvents. 4%-
Method as for L2, using 4%-chloro-2,2%:6%,2¦-ter-
pyridine (0.86 g, 3.2×10−3 mol) and propan-1-ol (0.25
g, 4.2×10−3 mol). The product formed colourless
needles from hot hexanes (yield 0.74 g, 64%). Anal.
Found: C, 73.9; H, 6.0; N, 14.6. Calc. for C18H17N3O:
Chloro-2,2%:6%,2¦-terpyridine,
3-phenylpropan-1-ol,
propan-1-ol, HBF4 (48 wt.% in water), hydrated
Cu(BF4)2, (Aldrich), CuCl2·2H2O, PdCl2 and K2PtCl4
(Avocado) were used as supplied, while 2,6-bis-(pyrid-
2-yl)-4-pyridone [9] was prepared by the literature
procedures.
1
C, 73.2; H, 5.8; N, 14.2%. M.p. 105–107 °C. H NMR
(CDCl3): l 8.67 (2H, d, J=4.8 Hz, Py H6/6¦), 8.61 (2H,
d, J=8.0 Hz, Py H3/3¦), 7.98 (2H, s, Py H3%/5%), 7.92
(2H, dd, J=7.6 and 8.0 Hz, Py H4/4¦), 7.42 (2H, d,
J=7.6 Hz, Py H5/5¦), 4.18 (2H, t, J=6.5 Hz, OCH2),
1.73 (2H, m, CH2CH2CH3), 1.07 (3H, t, J=7.5 Hz,
CH3). EI MS; m/z: 291 [M+], 276 [M−CH3]+, 262
[M−C2H5]+, 248 [M−C3H7]+, 233 [M−OC3H7+
H]+.
2.1. 4%-(3-Phenylpropoxy)-2,2%:6%,2¦-terpyridine (L2)
2.1.1. Method A
Freshly ground KOH (1.40 g, 2.5×10−2 mol) was
suspended in dmso (20 cm3), to which 2,6-bis-(pyrid-2-
yl)-4-pyridone (0.80 g, 3.2×10−3 mol) and 1-bromo-3-
phenylpropane (0.80 g, 4.0×10−3 mol) were added in
that order. The reaction mixture was then stirred for 16
h at 60 °C. Addition of water (20 cm3) to the resultant
orange solution gave a milky suspension, which after
standing at −10 °C, yielded a yellowish white solid
which was collected and washed with water. The solid
was dried over P2O5 overnight. Recrystallisation from
hot hexane gave a white crystalline solid (yield 0.65 g,
55%).
2.3. 4%-(3-Phenylpropoxy)-2,2%:6%,2¦-terpyridindionium
ditetrafluoroborate ([H2L2][BF4]2)
A mixture of L2 (0.50 g, 1.4×10−3 mol) and
aqueous HBF4 (0.76 cm3 of a 5.5 M solution, 4.2×
10−3 mol) in MeOH (10 cm3) was allowed to evaporate
slowly, yielding colourless crystals (yield 0.44 g, 58%).
Anal. Found: C, 53.2; H, 4.3; N, 7.6. Calc. for
1
C24H23B2F8N3O: C, 53.1; H, 4.3; N, 7.7%. H NMR
({CD3}2SO): l 8.87 (4H, m, Py H6/6¦+Py H3/3¦), 8.38
(2H, pseudo-t, 7.7 Hz, Py H4/4¦), 8.16 (2H, s, Py H3%/5%),
7.82 (2H, pseudo-t, 7.5 Hz, Py H5/5¦), 7.27 (5H, m, Ph
H2–5), 4.33 (2H, t, J=6.3 Hz, OCH2), 2.81 (2H, t,
J=7.3 Hz, PhCH2), 2.12 (2H, dd, J=6.3 and 7.3 Hz,
CH2CH2CH2).
2.1.2. Method B
The procedure in method A was followed, using
3-phenylpropan-1-ol (0.54 g, 4.0×10−3 mol) and 4%-
chloro-2,2%:6%,2¦-terpyridine (0.86 g, 3.2×10−3 mol)
(yield 1.1 g, 93%). Anal. Found: C, 78.5; H, 5.8; N,
11.7. Calc. for C24H21N3O: C, 78.5; H, 5.8; N, 11.4%.
1
M.p. 103–105 °C. H NMR (CDCl3): l 8.71 (2H, d,
2.4. [PdCl(L2)]BF4 (1)
J=4.8 Hz, Py H6/6¦), 8.64 (2H, d, J=7.9 Hz, Py H3/3¦),
8.05 (2H, s, Py H3%/5%), 7.86 (2H, pseudo-t, 7.5 Hz, Py
A suspension of PdCl2 (0.08 g, 5.0×10−4 mol), L2
(0.18 g, 5.0×10−4 mol) and NaBF4 (0.17 g, 1.5×10−3
mol) were suspended in MeNO2 (10 cm3). This mixture
was refluxed for 5 h. Insoluble solid was filtered off and
the filtrate was reduced to approximately 2 cm3 volume.
Vapour diffusion of Et2O into this solution gave a pale
yellow crystalline solid (yield 0.27 g, 90%). Anal.
H
4/4¦), 7.32 (7H, m, Py H5/5¦+Ph H2–5), 4.25 (2H, t,
J=6.1 Hz, OCH2), 2.88 (2H, t, J=7.6 Hz, PhCH2),
2.20 (2H, dd, J=6.1 and 7.6 Hz, CH2CH2CH2). EI
MS; m/z: 367 [M+], 276 [M−CH2Ph]+, 262 [M−
C2H4Ph]+, 248 [M−C3H6Ph]+, 233 [M−OC3H6Ph+
H]+.
Scheme 1.

X. Liu et al. / Polyhedron 20 (2001) 2889–2900
2891
Found: C, 47.3; H, 3.5; N, 6.8. Calc. for
2.9. [{Cu(v-Cl)(L3)}2](BF4)2 (6)
C24H21BClF4N3OPd: C, 48.3; H, 3.5; N, 7.0%. FAB
MS; m/z: 508 ([106Pd35Cl(L2)]+), 473 ([106Pd(L2)]+), 354
Method as for 5, using L3 (0.15 g, 5.0×10−4 mol).
The product formed blue needles from MeCN/Et2O
(yield 0.23 g, 98%). Anal. Found: C, 45.4; H, 3.7; N,
9.0. Calc. for C36H34B2Cl2Cu2F8N6O2: C, 45.3; H, 3.6;
N, 8.8%. FAB MS; m/z: 865 [63Cu235Cl2(L3)211BF4]+, 389
[63Cu35Cl(L3)]+, 373 [63CuF(L3)]+, 354 [63Cu(L3)]+, 311
[63Cu(L3ꢀC3H7)]+ with correct isotopic distributions.
([106Pd(L2ꢀC3H6C6H5)]+
distributions.
with
correct
isotopic
2.5. [PdCl(L3)]BF4 (2)
Method as for 1, using L3 (0.15 g, 5.0×10−4 mol).
The product is a pale yellow solid (yield 0.23 g, 89%).
Anal. Found: C, 41.6; H, 3.5; N, 7.9. Calc. for
C18H17BClF4N3OPd: C, 41.6; H, 3.3; N, 8.1%. FAB
MS; m/z: 432 [106Pd35Cl(L3)]+, 397 [106Pd(L3)]+, 354
2.10. [Cu(NCMe)(L2)](BF4)2 (7)
[
106Pd(L3ꢀC3H7)]+ with correct isotopic distributions.
A solution of Cu(BF4)2·6H2O (0.70 g, 2.0×10−3
mol) and L2 (0.73 g, 2.0×10−3 mol) in MeCN (20 cm3)
was stirred at room temperature for 1 h. The blue
solution was filtered and concentrated to approximately
5 cm3, resulting in the precipitation of a blue solid.
Slow addition of Et2O to the mixture afforded further
precipitation. The solid was collected, washed with
Et2O and dried in vacuo. Recrystallisation by vapour
diffusion of Et2O into a MeCN solution of the complex
afforded a blue–purple crystalline solid (yield 1.00 g,
77%). Anal. Found: C, 48.4; H, 3.8; N, 8.6. Calc. for
C26H24B2CuF8N4O: C, 48.4; H, 3.7; N, 8.7%. FAB MS;
m/z: 449 [63CuF(L2)]+, 430 [63Cu(L2)]+, 311
[63Cu(L2ꢀC3H6C6H5)]+ with correct isotopic distribu-
tions. IR spectrum (cm−1, Nujol mull): 2324w, 2297w.
2.6. [PtCl(L2)]BF4 (3)
A suspension of K2PtCl4 (0.21 g, 5.0×10−4 mol), L2
(0.18 g, 5.0×10−4 mol) and NaBF4 (0.11 g, 1.0×10−3
mol) in MeNO2 (20 cm3) was refluxed for 21 h. The
NaCl precipitate was removed by hot filtration, and the
filtrate was concentrated. Addition of Et2O to this
solution afforded a red solid which was collected,
washed with diethyl ether and dried in vacuo (yield 0.17
g, 50%). Anal. Found: C, 41.3; H, 3.6; N, 5.9. Calc. for
C24H21BClF4N3OPt: C, 41.0; H, 3.3; N, 6.0%. FAB
MS; m/z: 597
[ [
195Pt35Cl(L2)]+, 478 195Pt35Cl(L2ꢀ
C3H6C6H5)]+, 443 [195Pt(L2ꢀC3H6C6H5)]+ with correct
isotopic distributions.
2.7. [PtCl(L3)]BF4 (4)
2.11. [Cu(NCMe)(L3)](BF4)2 (8)
Method as for 3, using L3 (0.15 g, 5.0×10−4 mol).
The product was a red microcrystalline solid (yield 0.16
g, 53%). Anal. Found: C, 35.7; H, 2.9; N, 6.6. Calc. for
C18H17BClF4N3OPt: C, 35.5; H, 2.8; N, 6.9%. FAB
MS; m/z: 521 [195Pt35Cl(L3)]+, 486 [195Pt(L3)]+, 478
Method as for 7, using L3 (0.60 g, 2.0×10−3 mol).
The complex formed deep blue microcrystals from
MeCN/Et2O (yield 0.96 g, 84%). Anal. Found: C, 42.0;
H, 3.6; N, 9.8. Calc. for C20H20B2CuF8N4O: C, 42.2; H,
3.5; N, 9.8%. FAB MS: m/z 373 [63CuF(L3)]+, 354
[63Cu(L3)]+, 311 [63Cu(L3ꢀC3H7)]+ with correct isotopic
distributions. IR spectrum (cm−1, Nujol mull): 2331w,
2301w.
[
195Pt35Cl(L3ꢀC3H7)]+, 443 [195Pt(L3ꢀC3H7)]+ with cor-
rect isotopic distributions.
2.8. [{Cu(v-Cl)(L2)}2](BF4)2 (5)
A mixture of CuCl2·2H2O (0.085 g, 5.0×10−4 mol),
L2 (0.18 g, 5.0×10−4 mol) and NaBF4 (0.055 g, 5.0×
10−4 mol) was refluxed in MeNO2 (20 cm3) for 4 h.
The pale blue solution was filtered and concentrated to
approximately 2 cm3, and the product precipitated with
Et2O. Vapour diffusion of Et2O into a solution of the
complex in MeCN yielded blue microcrystals (yield 0.21
g, 75%). Anal. Found: C, 52.2; H, 3.9; N, 7.6. Calc. for
C48H42B2Cl2Cu2F8N6O2: C, 52.1; H, 3.8; N, 7.6%. FAB
MS; m/z: 1017 [63Cu235Cl2(L2)211BF4]+, 465 [63Cu35Cl-
(L2)]+, 449 [63CuF(L2)]+, 430 [63Cu(L2)]+, 311
2.12. Single crystal X-ray structure determinations
Yellow
blocks
of
[PdCl(L2)]BF4·2CH3NO2-
(1.2CH3NO2) were obtained from a hot MeNO2 solu-
tion of the complex. Storage of a benzonitrile solution
of 7 at −30 °C yielded blue crystals of formula
[Cu(NCPh)(L2)](BF4)2 (9: Anal. Found: C, 53.4; H, 3.9;
N, 8.2. Calc. for C31H26B2CuF8N4O: C, 52.6; H, 3.7; N,
7.9%). Experimental details from the structure determi-
nations are given in Table 1. Both structures were
solved by standard heavy atom methods (SHELXS-97
[10]) and refined by full-matrix least-squares on F2
[63Cu(L2ꢀC3H6C6H5)]+
with
correct
isotopic
distributions.
(SHELXL-97 [11]).

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X. Liu et al. / Polyhedron 20 (2001) 2889–2900
Table 1
Crystal data and structure refinement parameters for [PdCl(L1)]BF4·2CH3NO2 (1.2CH3NO2) and [Cu(NCPh)(L1)](BF4)2 (9)
[PdCl(L1)]BF4·2CH3NO2 (1.2CH3NO2)
[Cu(NCPh)(L1)](BF4)2 (9)
Empirical formula
Formula weight
Temperature (K)
C26H27BClF4N5O5Pd
718.19
150(2)
C31H26B2CuF8N4O
707.72
293(2)
,
u (A)
Crystal habit
0.71073
0.71073
blue lath
0.24×0.13×0.07
triclinic
yellow block
0.75×0.51×0.36
orthorhombic
Pna21
Crystal size (mm)
Crystal class
Space group
(
P1
Unit cell dimensions
,
a (A)
19.3958(6)
22.8909(5)
6.6562(1)
13.0402(3)
13.8065(4)
8.6891(3)
87.6469(16)
,
b (A)
,
c (A)
h (°)
i (°)
83.2172(18)
k (°)
76.7599(17)
1511.98(8)
2
3
,
V (A )
2955.27(12)
4
0.789
Z
v (Mo Ka) (mm−1
Diffractometer
)
0.805
Enraf–Nonius KappaCCD
Enraf–Nonius KappaCCD
Measured reflections
Independent reflections
Rint
19 947
6431
0.087
24 570
6865
0.053
Absorption correction
Min/max transmission
Observed reflections (I\2|(I))
Range in 2q (°)
multi-scan
0.589, 0.764
5567
5.50BqB54.98
multi-scan
0.830, 0.946
5666
5.52BqB54.94
Index ranges
−24BhB25, −29BkB27, −8BlB8
−16BhB16, −17BkB17, −11BlB11
Number of parameters
Number of restraints
R(F) a, wR(F2) b
396
7
0.055, 0.150
583
182
0.044, 0.116
Goodness-of-fit on F2
Weighting scheme c
Max. shift/e.s.d.
1.038
1.023
w=1/[|2(Fo2)+(0.0854P)2+3.3986P]
w=1/[|2(Fo2)+(0.0565P)2+0.6657P]
0.051
0.017
Dzmin, Dzmax
Flack parameter
−1.41, 0.58
0.39(7)
−0.87, 0.42
a R=ꢀ[ꢁFoꢁ−ꢁFcꢁ]/ꢀꢁFoꢁ.
b wR=[ꢀw(Fo2−Fc2)/ꢀwFo4]1/2
c P=(Fo2+2Fc2)/3.
.
2.13. X-ray structure determination of
[PdCl(L2)]BF4·2CH3NO2(1.2CH3NO2)
occupied orientations C(33A)–C(37A) and C(33B)–
C(37B), by rotation about the bridgehead atom C(32).
All CꢀC bonds within both phenyl rings were con-
strained to be the same. The L2 3-phenylpropoxy sub-
stituent is also disordered over two different
conformations O(20A)ꢀC(29A) and O(20B)ꢀC(29B),
which were also modelled as equally occupied. Equiva-
lent CꢀO or CꢀC bond lengths in each conformation
were constrained to be the same. The anion centred on
B(43) is disordered by rotation about the B(43)ꢀF(44)
bond. Three orientations of this anion were modeled,
with all BꢀF distances constrained to be the same:
F(45A)–F(47A), with occupancy 0.5; and F(45B)–
F(47B) and F(45C)–F(47C), each with occupancy 0.25.
All the constraints in the final model had a sum of 0.03
This crystal was refined as a racemic twin. No disor-
der was detected in the complex cation or the anion.
However, the O atoms of the solvent molecule centred
on N(41) were disordered over three equally occupied
orientations, with all NꢀO distances restrained to
,
1.27(2) A. All wholly occupied non-H atoms with occu-
pancy ]0.5 were refined anisotropically, and all H
atoms were placed in calculated positions.
2.14. X-ray structure determination of
[Cu(NCPh)(L2)](BF4)2 (9)
,
Both ligands in the complex cation, and one of the
BF4− anions, suffer from disorder. The phenyl ring of
the benzonitrile ligand is disordered over two equally
A. All wholly occupied non-H atoms with occupancy
]0.5 were refined anisotropically, and H atoms were
placed in calculated positions.

X. Liu et al. / Polyhedron 20 (2001) 2889–2900
2893
2.15. Other measurements
Cl(L)]BF4 (L=L2, 5; L=L3, 6) were prepared from
these ligands, using similar synthetic methods to those
previously reported for [MCl(terpy)]+ (M=Cu, Pd, Pt)
compounds [15–17]. The complexes [Cu(NCMe)(L)]-
(BF4)2 (L=L2, 7; L=L3, 8) were also synthesised, by
complexation of the appropriate tridentate ligand with
1 molar equivalent of hydrated Cu(BF4)2 in MeCN.
Microanalyses for all of the complexes were consis-
tent with the proposed formulations, while the IR
spectra of 1–6 showed the presence of BF4− and the
appropriate tridentate ligand only. For 7 and 8 addi-
tional IR absorptions were exhibited corresponding to
Infra-red spectra were obtained as Nujol mulls
pressed between KBr windows, or in NaCl solution
cells, between 400 and 4000 cm−1 using a Nicolet
Avatar 360 spectrophotometer. UV–Vis spectra were
obtained with a Perkin–Elmer Lambda 900 spec-
trophotometer operating between 200 and 1100 nm, in
1 cm quartz cells. All NMR spectra were run on a
Bruker ARX250 spectrometer, operating at 250.1 MHz
(1H) and 62.9 MHz (13C). Mass spectra were performed
on a VG AutoSpec spectrometer, the fast atom bom-
bardment spectra employing a 3-NOBA matrix. CHN
microanalyses were performed by the University of
Leeds School of Chemistry microanalytical service.
EPR spectra were obtained using a Bruker ESP300E
spectrometer; X-band spectra (approximately 9.5 GHz)
employed an ER4102ST resonator and ER4111VT
cryostat, while for S-band spectra (approximately 4
GHz) a ER4118SM-S-5W1 resonator and a ER4118VT
cryostat were used. Melting points are uncorrected.
Conductivity measurements were obtained with a
Jenway 4310 analyser, at a concentration of 1.0×10−3
mol dm−3. All electrochemical measurements were car-
ried out using an Autolab PGSTAT30 voltammetric
analyser, in CH2Cl2 containing 0.5 M NnBu4BF4 (pre-
pared from NnBu4OH and aqueous HBF4 in water,
followed by two recrystallisations from hot MeOH) as
supporting electrolyte. Voltammetric experiments in-
volved the use of platinum disk working and platinum
wire counter electrodes, and an Ag/AgCl reference elec-
trode. All potentials quoted are referenced to an inter-
nal ferrocene/ferrocenium standard and were obtained
at a scan rate of 100 mV s−1, unless otherwise stated.
the wCꢁN vibration of the MeCN ligand (for 7, wCꢁN
=
2324, 2297 cm−1; for 8, wCꢁN=2331, 2301 cm−1) [18].
However, while precedent suggests that 1–4 and 7 and
8 can safely be described as mononuclear complexes, 5
or 6 could in principle exist as monomeric complexes,
or as [{Cu(m-Cl)(L)}2](BF4)2 (L=L2, L3) dimers
analogous to the crystallographically characterised
[{Cu(m-Cl)(terpy)}2](PF6)2 [15]. The latter possibility is
favoured by the FAB MS of these two compounds,
which exhibit weak molecular ions corresponding to
[{63Cu(m-35Cl)(L)}2(11BF4)]+ (L=L2, M+=1017; L=
L3, M+=865); none of the other complexes exhibit
dimer peaks by mass spectrometry. The dimeric molec-
ular structures of 5 and 6 were confirmed by the
spectroscopic studies described below.
Single crystals of X-ray quality of formula
[PdCl(L2)]BF4·2CH3NO2 (1.2CH3NO2) were grown by
vapour diffusion of Et2O into a MeNO2 solution of the
complex. Recrystallisation of [Cu(NCMe)(L2)](BF4)2
from PhCN/Et2O yielded deep blue crystals analysing
as [Cu(NCPh)(L2)](BF4)2 (9). The presence of PhCN in
these crystals was suggested by both microanalysis and
IR spectroscopy (wCꢁN=2279, 2226 cm−1) [18], and
subsequently confirmed by the crystal structure analysis
described below. Views of the molecular structures of
these two complexes in the crystal are shown in Figs. 1
and 3, while selected metric parameters are given in
Tables 2–4.
3. Results and discussion
Molecular models suggested that a 4-atom chain
between two aryl groups is an optimum length to allow
a geometrically favourable p–p interaction [12] to form
between the linked rings. With this in mind, the ligand
4%-(3-phenyl-n-propoxy)-2,2%:6%,2¦-terpyridine (L2) was
synthesised either from 3-phenylpropan-1-ol and 4%-
chloro-2,2%:6%,2¦-terpyridine, or from 1-bromo-3-phenyl-
propane and 2,6-(pyrid-2-yl)pyrid-4-one, in
a
KOH/dmso suspension according to the method of
Constable and Newkome [13,14]. For comparison, an
equivalent ligand lacking a phenyl substituent, 4%-pro-
poxy-2,2%:6%,2¦-terpyridine (L3), was also prepared by an
analogous synthesis using 4%-chloro-2,2%:6%,2¦-ter-
pyridine and propan-1-ol. Both ligands were isolated
from the reaction mixtures by precipitation with water,
yielding white solids that were recrystallised from hot
hexanes. The complexes [PdCl(L)]BF4 (L=L2, 1; L=
L3, 2) [PtCl(L)]BF4 (L=L2, 3; L=L3, 4) and [Cu-
Fig. 1. Solid state structure of the complex cation in the crystal of
[PdCl(L2)]BF4·2CH3NO2(1.2CH3NO2), showing the atom numbering
scheme employed. For clarity, all hydrogen atoms have been omitted.

2894
X. Liu et al. / Polyhedron 20 (2001) 2889–2900
Table 2
Table 4
,
,
Selected bond lengths (A) and bond angles (°) for the structure of
Unfavourable intermolecular H···H and H···F distances (A) involving
[PdCl(L2)]BF4·2CH3NO2 (1.2CH3NO2)
the disordered regions of the crystal structure of [Cu(NCPh)-
(L1)](BF4)2 (9)
Bond lengths
a
,
Pd(1)ꢀCl(2)
Pd(1)ꢀN(3)
Pd(1)ꢀN(10)
Pd(1)ꢀN(16)
2.2948(10)
1.924(4)
2.035(3)
2.036(3)
Symmetry relation
dH···X (A)
H(21D)···H(35B%)
H(25A)···H(36B%)
H(25A)···H(37B¦)
H(25B)···H(33B§)
H(26A)···H(35A¨)
H(26B)···H(27A¨%)
H(35A)···H(36A¨¦)
x, 1+y, z
2.3
2.0
1.6
2.2
2.1
2.2
1.7
2−x, 2−y, 2−z
2−x, 2−y, 2−z
2−x, 2−y, 1−z
1+x, 1+y, z
3−x, 3−y, 1−z
1−x, 1−y, 2−z
Bond angles
Cl(2)ꢀPd(1)ꢀN(3)
Cl(2)ꢀPd(1)ꢀN(10)
Cl(2)ꢀPd(1)ꢀN(16)
N(3)ꢀPd(1)ꢀN(10)
N(3)ꢀPd(1)ꢀN(16)
N(10)ꢀPd(1)ꢀN(16)
178.1(3)
98.02(10)
100.28(11)
81.46(14)
80.16(15)
161.49(16)
H(25B)···F(45C¨§)
H(25B)···F(46A¨§)
H(25B)···F(46C¨§)
H(33B)···F(46A¨¨)
H(33B)···F(46C¨¨)
H(37A)···F(45B¨¨)
1+x, y, z
1+x, y, z
1+x, y, z
1−x, 2−y, 1−z
1−x, 2−y, 1−z
1−x, 2−y, 2−z
2.5
2.5
2.4
2.5
2.5
2.3
Table 3
,
Selected bond lengths (A) and bond angles (°) for the structure of
[Cu(NCPh)(L1)](BF4)2 (9)
All contacts are shorter than the sum of the van der Waals radii of
,
,
two H atoms (2.4 A), or of a H atom and a F atom (2.6 A) [21].
Bond lengths
a X=H, F
Cu(1)ꢀN(2)
Cu(1)ꢀN(9)
Cu(1)ꢀN(15)
Cu(1)ꢀN(30)
Cu(1)ꢀF(39)
Cu(1)ꢀF(44)
1.908(2)
2.021(2)
2.023(2)
1.949(2)
2.4981(15)
2.3712(15)
planes of the terpyridyl skeletons on adjacent
molecules, [N(3)ꢀC(19)] and [N(3%)ꢀC(19%)], is 0.9(2)°.
There is an edge-to-face CꢀH–p interaction between
H(12) of one molecule and the phenyl substituent
of a neighbouring cation [C(25¦)–C(30)¦] related by
−1/2+x, 3/2−y, z, with H(12)ꢀX(1¦)=2.5 A and
C(12)ꢀH(12)···X(1¦)=157° [X(1¦)=centroid of
C(25¦)–C(30¦)]. The phenyl substituent of each cation
[C(25)–C(30)] also forms a p–p interaction with that of
the neighbouring cation [C(25§)–C(30§)] related by
2−x, 2−y, −1/2+z, the dihedral angle between the
two rings being 1.7(2)°, the inter-planar distance 3.1 A
and the centroids of the two rings being offset by 4.5 A
Bond angles
N(2)ꢀCu(1)ꢀN(9)
N(2)ꢀCu(1)ꢀN(15)
N(2)ꢀCu(1)ꢀN(30)
N(2)ꢀCu(1)ꢀF(39)
N(2)ꢀCu(1)ꢀF(44)
N(9)ꢀCu(1)ꢀN(15)
N(9)ꢀCu(1)ꢀN(30)
N(9)ꢀCu(1)ꢀF(39)
N(9)ꢀCu(1)ꢀF(44)
N(15)ꢀCu(1)ꢀN(30)
N(15)ꢀCu(1)ꢀF(39)
N(15)ꢀCu(1)ꢀF(44)
N(30)ꢀCu(1)ꢀF(39)
N(30)ꢀCu(1)ꢀF(44)
F(39)ꢀCu(1)ꢀF(44)
80.55(8)
80.50(8)
171.99(8)
86.38(7)
97.32(7)
161.04(8)
99.82(8)
87.43(7)
93.72(7)
98.99(8)
91.70(7)
88.37(7)
85.65(7)
90.65(7)
176.26(6)
,
,
,
[12].
The Cu ion in 9 is almost perfectly planar, with
Cu···N distances that are normal for tetragonal Cu(II)
species [20]. There is one long Cu···F contact to each
anion
[Cu(1)ꢀF(39)=2.4981(15),
Cu(1)ꢀF(44)=
,
2.3712(15) A], leading to a distorted octahedral [4+
1+1] coordination sphere (Table 3, Fig. 3). In contrast
to the structure of 1, the L2 3-phenylpropoxy group in
9 is disordered over two equally occupied conforma-
tions. In one conformation [O(20A)ꢀC(29A)] the pro-
poxy tether exhibits exclusively anti XꢀCꢀCꢀC (X=C,
O) torsion angles, while the other conformation
[O(20B)ꢀC(29B)] contains a gauche C(21B)ꢀC(22B)ꢀ
C(23B)ꢀC(24B) torsion. The PhCN phenyl substituent
is also disordered over two equally occupied orienta-
tions [C(33A)ꢀC(37A) and C(33B)ꢀC(37)B], by rotation
about the C(31)ꢀC(32) bond. Finally, the anion centred
on B(43) is disordered over three orientations by rota-
tion about the B(43)ꢀF(44) bond.
The asymmetric unit of 1.2CH3NO2 contains one
complex cation lying on a general position, with one
anion and two lattice solvent molecules that do not
interact with the metal centre. The coordination at
Pd(1) is essentially planar (Table 2, Fig. 1), the Pd(1)ꢀN
bond lengths and ClꢀPd(1)ꢀN and NꢀPd(1)ꢀN angles
being within the ranges found for other [PdX(terpy)]+
(X−=halide, pseudohalide or alkyl anion) complexes
[19]. The L2 3-phenylpropoxy substituent adopts a sin-
gle conformation in the crystal, with all CH2 groups
being anti to each other.
The cations in 1.2CH3NO2 pack into stacks (Fig. 2),
each molecule within the stack being related by 2−x,
1−y, −1/2+z. Within these columns of cations, each
Adjacent molecules in the lattice of 9 interact by van
der Waals contacts only. The packing diagram of this
structure reveals several unfavourable intermolecular
,
molecule is separated by Pd(1)···Pd(1%)=3.459(1) A
while the dihedral angle between the least-squares

X. Liu et al. / Polyhedron 20 (2001) 2889–2900
2895
H···H contacts between individual disorder orientations
of neighbouring cations (Table 4). Clearly, therefore,
the conformation of any individual molecule in the
lattice will be dictated by those adopted by its neigh-
bours. There are also several close intermolecular H···F
contacts from the disordered regions of the cation to
the disordered anion of neighbouring molecules (Table
4), so that the anion disorder in this structure is dic-
tated, at least in part, by the ligand disorder.
while those of 7 and 8 are larger at approximately 190
−1 cm2 mol−1. These data are all somewhat smaller
than the ‘typical’ values quoted for a 1:1 (140
−1 cm2 mol−1) or 2:1 (220 V−1 cm2 mol−1) elec-
V
V
trolyte in MeCN [22], which may reflect some ion
pairing in solution. However, from comparison with
1–4 it seems clear that 7 and 8 are better described as
2:1 electrolytes, and that the chloride ligands in 5 and 6
remain coordinated to the Cu atoms. As discussed
below, 5 and 6 are in fact better described as 2:1
electrolytes, [{Cu(m-Cl)L}2](BF4)2 (L=L2, L3).
Conductivity measurements of the complexes in this
study were run in MeCN (Table 5). Complexes 1–6
exhibit conductivities in the range 89–110
UV–Vis data for the ligands and complexes were run
in MeCN at 290 K, and are listed in Table 5. It is clear
V
−1 cm2 mol−1 (per mole of empirical formula units),
Fig. 2. Partial packing diagram for [PdCl(L2)]BF4·2CH3NO2(1.2CH3NO2), showing the arrangement of cations into 1D stacks. For clarity all
hydrogen atoms, anions and solvent molecules have been omitted.
Fig. 3. Solid state structure of the complex molecule in the crystal of [Cu(NCPh)(L2)](BF4)2 (9) showing the atom numbering scheme employed.
All orientations of the disordered ligands and anion are shown (see Section 2). For clarity, all hydrogen atoms have been omitted, while the
numbers of disordered F atoms are not shown.

2896
X. Liu et al. / Polyhedron 20 (2001) 2889–2900
Table 5
and MeCN in the spectrochemical series [23] and sug-
gests that the molecular structures of 5/6 and 7/8 are
not comparable.
Conductivity and UV–Vis spectroscopic data for the compounds in
this study (MeCN, 290 K) a
\
,
umax, nm (mmax, 103 M cm−1
)
X-band EPR spectra of the Cu(II) complexes were
run as powders, and in frozen 10:1 MeCN–toluene
solution (Table 6). Interestingly in the light of their
similar solution UV–Vis spectra, the EPR spectra of
solid 5 and 6 are markedly different. Both compounds
show the gꢂ\gÞ\ge pattern that is typical of tetrago-
M
(V−1 cm2 mol−1
)
L2
L3
240 (23.7), 277 (21.1)
241 (26.8), 277 (24.7)
243 (31.0), 281 (29.3), 333
(sh), 350 (sh)
243 (32.2), 281 (28.8), 302
(sh), 333 (sh), 350 (sh)
225 (27.8), 255 (26.5), 284
(37.2), 303 (14.3), 316 (14.3),
330 (17.5), 395 (3.9)
226 (27.2), 256 (35.3), 284
(33.9), 304 (14.2), 316 (14.7),
330 (17.7), 392 (3.9)
241 (27.8), 263 (33.73), 276
(30.2), 316 (12.1), 328 (11.1),
692 (0.12)
224 (36.2), 263 (31.6), 275
(28.2), 317 (12.1), 328 (11.2),
693 (0.12)
242 (29.0), 250 (sh), 260 (27.8)
277 (28.6), 316 (12.1), 329
(12.2), 625 (0.13)
242 (29.3), 251 (28.0), 260
(27.8), 277 (28.8), 317 (12.8),
329 (12.8), 629 (0.13)
[PdCl(L2)]BF4 (1) 93
[PdCl(L3)]BF4 (2) 103
[PtCl(L2)]BF4 (3) 89
nal Cu(II) ions with a {dx
2}1 or {dxy}1 ground state
2
[24], but with different g-v−alyues. In addition, while the
spectrum of 5 is essentially invariant between 290 and
120 K, the spectrum of 6 changes markedly from being
axial at 290 K, to rhombic at 120 K. For 6 only, a weak
‘half-field’ resonance near 1500 G is also apparent,
which arises from a DmS= 92 transition and is a
characteristic of an exchange-coupled dicopper species
with negligible zero-field splitting [24]. This observation
was confirmed by re-running the spectrum at S-band,
which shows the expected increase in relative intensity
of this signal, which now resonates near 600 G. In
frozen solution, 5 and 6 give visually identical, broad-
ened spectra in which the gꢂ component is too broad to
be resolved. At S-band only, ‘half-field’ resonances are
also observed in the solution spectra of both com-
pounds at 120 K.
[PtCl(L3)]BF4 (4) 110
[{Cu(m-Cl)(L2)}2]- 196 a
(BF4)2 (5)
[{Cu(m-Cl)(L3)}2]- 196 a
(BF4)2 (6)
[Cu(NCMe)(L2)]- 199
(BF4)2 (7)
[Cu(NCMe)(L3)]- 188
(BF4)2 (8)
The EPR spectra of 7 in the solid and in frozen
solution are well resolved and very similar (Table 6),
and are consistent with the presence of isolated, tetrag-
onal Cu(II) centres [24]. The solution spectrum of 8
closely resembles that of 7, showing that the molecular
structures of the two compounds in solution are essen-
tially the same. The powder spectra of 8 and 9 visually
resemble that of 7 but are broader, so that the gꢂ
component cannot be unambiguously resolved.
From these spectroscopic and conductivity data, we
conclude that 7 and 8 adopt mononuclear structures
analogous to crystalline 9, based on the tetragonal
[Cu(NCMe)L]2+ (L=L2, L3) dication. For 5 and 6, we
a For comparison with 1–4, conductivity values calculated per mole
of copper ion are \M=98 V−1 cm2 mol−1; see text.
that the spectra of each pair of complexes (1/2, 3/4, 5/6
and 7/8) are essentially identical, showing differences
within each pair that are small-to-insignificant. This
strongly implies that the presence of the potentially p–p
stacking pendant arm in the L2-containing complexes
has an undetectable effect on their electronic structures.
The Cu(II) complexes 5–8 each exhibit a single well-
defined d–d band. This lies at approximately 65 nm
shorter wavelength for 5 and 6, compared to 7 and 8,
which is inconsistent with the relative positions of Cl−
Table 6
X-band EPR data for the Cu(II) complexes in this study
g1
g2
g3
A1
[{Cu(m-Cl)(L2)}2](BF4)2 (5)
[{Cu(m-Cl)(L3)}2](BF4)2 (6)
Powder a
MeCN a
Powder b
Powder a
MeCN a
Powder
MeCN
Powder
MeCN
Powder
2.259
2.052
2.063
2.056
2.058
2.057
2.056
2.058
2.057
2.059
2.056
2.052
2.063
2.056
2.028
2.057
2.056
2.058
2.057
2.059
2.056
2.178
2.182
[Cu(NCMe)(L2)](BF4)2 (7)
[Cu(NCMe)(L3)](BF4)2 (8)
[Cu(NCPh)(L2)](BF4)2 (9)
2.185
2.181
171
186
2.193
193
Unless otherwise stated, all spectra were obtained at 120 K. Hyperfine couplings are to 63,65Cu and are in G.
a Spectrum exhibits an additional ‘half-field’ resonance near 1500 G (X-band) and/or 600 G (S-band); see text.
b Spectrum run at 290 K.

X. Liu et al. / Polyhedron 20 (2001) 2889–2900
2897
Table 7
Voltammetric data for the compounds in this study
Solvent
M(II/I)
E1/2 (V)
M(I/0)
Epc (V)
L/L−
E1/2 (V)
L
−/L2−
E1/2 (V)
[H2L2](BF4)2
CH2Cl2
dmf
dmf
dmf
dmf
MeCN
MeCN
MeCN
MeCN
−0.92
−1.20 a,b
−1.20 a,b
−1.35
−1.36
−0.70
−0.72
−0.68
−0.69
[PdCl(L2)]BF4 (1)
[PdCl(L3)]BF4 (2)
[PtCl(L2)]BF4 (3)
−1.83
−1.84
−0.58 a
−0.51 a
−0.17
−0.18
−2.45 b
−2.49 b
[PtCl(L3)]BF4 (4)
[{Cu(m-Cl)(L2)}2](BF4)2 (5)
[{Cu(m-Cl)(L3)}2](BF4)2 (6)
[Cu(NCMe)(L2)](BF4)2 (7)
[Cu(NCMe)(L3)](BF4)2 (8)
−0.99 a
−0.96 a
−0.94 a
−0.91 a
Data were obtained in CH2Cl2/0.5 M NnBu4PF6, dmf/0.1 M NnBu4PF6 or MeCN/0.1 M NnBu4PF6 at 298 K. Potentials are quoted vs. an internal
ferrocene/ferrocenium standard, at scan rate 100 mV s−1
a Irreversible process, Epc value quoted.
.
b Additional Pd-based reductions are also observed, at Epc=−1.6, −2.0, −2.4 and −2.5 V.
propose dimeric [{Cu(m-Cl)L}2](BF4)2 (L=L2, L3)
structures in the solid state and in solution. Consistent
with this, the EPR spectra of 5 and 6 closely parallel to
those reported for salts of [{Cu(m-Cl)(terpy)}2]2+ have
been previously reported [25]. In addition, the proposal
of mononuclear structures for 7–9, and dimeric struc-
tures for 5 and 6, reconciles the anomalous relative d–d
absorption energies of these two series of compounds
(see above).
Voltammetric experiments were run in CH2Cl2/0.5 M
NnBu4BF4, MeCN/0.1 M NnBu4BF4 or dmf/0.1 M
NnBu4BF4 at 298 K (Table 7). All potentials in the
following discussion are quoted against an internal
ferrocene/ferrocenium standard, and were measured at
a scan rate of 100 mV s−1. Both L2 and L3 are electro-
chemically inert in CH2Cl2 and MeCN within the avail-
able window for these solvents. In order to more
accurately quantify the electrochemical behaviour that
might be expected upon coordination of these ligands,
the doubly protonated ligand [H2L2](BF4)2 was pre-
pared by treatment of L2 with three molar equivalents
of HBF4 in MeOH, and its electrochemical behaviour
examined. This ligand salt exhibited a quasi-reversible
reduction at E1/2= −0.92 V in CH2Cl2. Hence, both
metal- and ligand-based reactivity was anticipated in
the voltammograms of 1–8.
position products formed following this ligand
reduction.
The CVs of 3 and 4 exhibit three quasi-reversible
reductions (Fig. 4(a)). By analogy with the cyclic
voltammogram of [PtCl(terpy)]+, which contains three
processes at similar potentials to those here [8], we
assign the first reduction to a L/L− (L=L2, L3) couple.
The second reduction may be a Pt(II/I) wave, although
this was not definitively proven [8], while no assignment
of the third reduction of [PtCl(terpy)]+ has been made.
Differential pulse voltammetry showed that the first
For solubility reasons, cyclic voltammograms (CVs)
of 1–4 were run in dmf. The Pd(II) complexes 1 and 2
exhibit complex CVs, containing two principle pro-
cesses: an irreversible reduction at Epc= −1.20 V; and
a more intense irreversible reduction at Epc= −2.5 V,
whose peak current is approximately twice that of the
first reduction. Several other weak irreversible reductive
waves also appear between these two values. We tenta-
tively assign the first reduction to a L/L− (L=L2, L3)
couple, owing to its proximity to the analogous reduc-
tion shown by 3 and 4 (see below), and the other
reductions to Pd-based processes arising from decom-
Fig. 4. (a) Cyclic voltammograms and (b) differential pulse voltam-
mograms of [PtCl(L2)]BF4 (3) in dmf/0.1 M NnBu4BF4 at 298, 273
and 223 K. The potential scale is referenced to the internal ferrocene/
ferrocenium standard.

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X. Liu et al. / Polyhedron 20 (2001) 2889–2900
On the basis of these data, and by analogy to the
voltammetric behaviour of other Cu/terpyridyl com-
plexes [26], the first, second and third reduction waves
were, respectively, assigned to Cu(II/I), L/L− (L=L2,
L3) and Cu(I/0) reductions (Table 5). That the L/L−
and Cu(I/0) processes occur at essentially identical po-
tentials for 5–8 suggests that initial reduction of 5 and
6 might lead to rapid dissociation of Cl− from the Cu
ions; this would also account for the irreversibility of
this reduction for 5 and 6. However, this hypothesis
cannot account for the different Cu(I/II) reoxidation
behaviour exhibited by the two sets of compounds.
Hence, further experiments are required to quantify the
structures of the reduction products of 5–8, which
might be monomeric or dimeric in nature [26,27].
Given that the CVs of 3 and 4 match that of [Pt-
Cl(terpy)]+ very closely, it is interesting that 5–8 show
an apparently ligand-based reduction at such a positive
potential as −0.7 V, when other Cu/terpyridyl com-
plexes exhibit irreversible terpy-based reduction reac-
tions at EpcB −1.8 V [26,28]. We note that, in all these
literature cases, the ligand-based reduction potential is
substantially anodic of the Cu(I/0) couple, and lies
close to the reduction potential of the relevant non-co-
ordinated terpyridine derivative. Hence, it appears that
the unusually positive and reversible L/L− (L=L2, L3)
reductions shown by 5–8 reflect the fact that the ligand
‘L’ is still coordinated to Cu(I) ions when this reduction
takes place. In the literature compounds, the more
negative ligand-based reduction is of free terpyridine,
decoordinated following reduction of the complex to
metallic copper.
Fig. 5. Cyclic voltammograms of [{Cu(m-Cl)(L2)}2](BF4)2 (5, dashed
line) and [Cu(NCMe)(L2)](BF4)2 (7, solid line) in MeCN/0.1 M
NnBu4BF4 at 298 K. The potential scale is referenced to the internal
ferrocene/ferrocenium standard. The irreversible third reduction ex-
hibited by these compounds (Table 7) is not shown.
and third reduction waves actually contain two closely
overlapping processes; this splitting becomes more pro-
nounced at lower temperatures (Fig. 4(b)). Although
such splitting was not detected in the CV of [Pt-
Cl(terpy)]+ [8], it is known that [PtCl(terpy)]+ and
[PtCl(terpy)] both undergo monomer/dimer equilibria
in solution with K:10 M−1 [8]. Hence, we suggest
that the overlapping reduction peaks for 3 and 4 corre-
spond to reduction of monomeric and dimeric species
at a given oxidation level.
We can make the following additional observations
about the CVs of 3 and 4. First, the assignment of the
second reduction as a Pt-based process is supported by
the lack of splitting on this peak. A Pt(II/I) reduction
will involve insertion of an electron into a dx
2
2
−y
orbital, which lies perpendicular to the intradimer
Pt···Pt vector and so will have essentially identical
energies in the monomeric and dimeric species. Second,
the observation of overlapping peaks on the third re-
duction wave of 3 and 4 both suggests its assignment as
a ligand-based process, and implies that [PtClL]− (L=
L2, L3) also exists as a mixture of monomers and
dimers, with a similar equilibrium constant to those for
the less reduced species.
Complexes 5–8 each exhibit three electrochemical
reduction processes in MeCN (Table 7, Fig. 5). It is
only the first of these that varies significantly between
the compounds. For 5 and 6 this is an irreversible
reduction, occurring near Epc= −0.55 V; while for 7
4. Concluding remarks
We have prepared a terpyridine derivative L2, bear-
ing a flexible 3-phenylpropoxy side chain that, in princi-
ple, could readily form an intramolecular p–p
interaction with the terpyridine moiety that introduces
little or no conformational strain onto the propoxy
linker. Unfortunately, however, there is no evidence
that such a p–p interaction is formed by L2, or any of
its complexes we have examined, in the solid state or in
solution. Evidently the p–p interaction on its own,
which is likely to have an enthalpy of no more than 20
kJ mol−1 [29], is insufficient to overcome other weak
intermolecular interactions involving the terpyridine
and/or phenyl groups that prevent it from forming.
Hence, in order to accomplish our aim of preparing an
intramolecularly p–p-stacked polypyridine, we must
and 8 a quasi-reversible wave is observed at E1/2
=
−0.18 V. The latter process exhibits an abnormal
lineshape, however, with an unusually sharp return
wave that may be indicative of partial adsorption of the
reduced species onto the electrode. The second and
third reductions for 5–8 are essentially identical for all
four compounds, occurring as a quasi-reversible wave
at E1/2= −0.7090.02 V; and an irreversible peak in
the range Epc= −0.9590.04 V. The most negative
reduction exhibits a daughter desorption spike charac-
teristic of the adsorption of Cu metal at the electrode.
use
a more rigid linker group that forces the
polypyridine and aryl units to adopt a face-to-face
geometry. We are actively pursuing this challenge.

X. Liu et al. / Polyhedron 20 (2001) 2889–2900
2899
Moorefield, A.M.W. Cargill Thompson, J. Chem. Soc., Chem.
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 164048 and 164049 for
1.2CH3NO2 and 9, respectively. Copies of this informa-
tion may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336033; e-mail: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
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Acknowledgements
The authors gratefully acknowledge funding by The
Royal Society (M.A.H.), the EPSRC (X.L.) and the
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