Vectorial property dependence in bis{4′-(n-pyridyl)-2,2′: 6′,2″-terpyridine}iron(ii) and ruthenium(ii) complexes with n = 2, 3 and 4

Article abstract of DOI:10.1039/b714970k

A comparative structural and spectroscopic investigation of the complexes [M(1)₂]²⁺, [M(2)₂]²⁺ and [M(3) ₂]²⁺ in which M = Fe or Ru, and ligands 1, 2 and 3 are 4′-(2-pyridyl)-, 4′-(3-pyridyl)- and 4′-(4-pyridyl)-2, 2′:6′,2″-terpyridine, respectively, is reported. The complexes [Ru(1)₂]²⁺, [Ru(2)₂]²⁺ and [Ru(3)₂]²⁺ undergo mono- and bis-N-methylation. The consequences of methylation on the absorption spectra and electrochemical properties are discussed; the solid-state structure of the bis(N-methylated) derivative of [Ru(2)₂][PF₆]₂ is presented. This journal is The Royal Society of Chemistry.

Full text of DOI:10.1039/b714970k

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PAPER
www.rsc.org/dalton | Dalton Transactions
ꢀ
ꢀ
ꢀ
ꢀꢀ
Vectorial property dependence in bis{4 -(n-pyridyl)-2,2 :6 ,2 -
terpyridine}iron(II) and ruthenium(II) complexes with n = 2, 3 and 4†‡
Jonathon E. Beves, Emma L. Dunphy, Edwin C. Constable,* Catherine E. Housecroft,* Cameron J. Kepert,
Markus Neuburger, David J. Price and Silvia Schaffner
Received 28th September 2007, Accepted 13th November 2007
First published as an Advance Article on the web 12th December 2007
DOI: 10.1039/b714970k
2
+
2+
A comparative structural and spectroscopic investigation of the complexes [M(1)
2
] , [M(2) ] and
2
2
+
ꢀ
ꢀ
[
4
M(3)
2
]
in which M = Fe or Ru, and ligands 1, 2 and 3 are 4 -(2-pyridyl)-, 4 -(3-pyridyl)- and
ꢀ ꢀ ꢀꢀ 2+ 2+
ꢀ
-(4-pyridyl)-2,2 :6 ,2 -terpyridine, respectively, is reported. The complexes [Ru(1)
2
] , [Ru(2) ] and
2
2
+
[
Ru(3)
2
] undergo mono- and bis-N-methylation. The consequences of methylation on the absorption
spectra and electrochemical properties are discussed; the solid-state structure of the bis(N-methylated)
derivative of [Ru(2)
2
][PF
6
2
] is presented.
Introduction
Metallosupramolecular chemistry is built upon precepts of com-
1
mensurate metal ion–ligand interactions, and is a valuable
2–5
concept for the construction of functional materials and devices.
We have extended the principles to the use of metal complexes
as scaffolds bearing additional functionality. Our emphasis is
on well-defined {M(bpy)
3
} and {M(tpy) } motifs which may be
2
introduced directly using kinetically inert metal centres such as
ruthenium(II) or osmium(II), or constructed using self-assembly
processes of free bpy or tpy metal-binding domains with labile
metal centres such as cobalt(II) or iron(II). A particular application
of this principle involves the decoration of the scaffold with
additional metal-binding domains to give what we have termed
6–15
‘expanded ligands’.
We are currently investigating the self
Scheme 1 The concept of the expanded ligand exemplified by the change
assembly of molecular architectures with defined dimensional-
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢀ
from 3,3 -bipyridine to a bis{4 -(3-pyridyl)-2,2 :6 ,2 -terpyridine} metal
n+
ity based on the pendant coordinating ability of {M(1)
2
ꢀ
} ,
complex.
n+
n+
ꢀ
ꢀ
ꢀꢀ
{M(2)
2
}
and {M(3)
2
}
motifs where 1 = 4 -(2-pyridyl)-2,2 :6 ,2 -
ꢀ
ꢀ
ꢀ
ꢀꢀ
ꢀ
2+
2+
terpyridine, 2 = 4 -(3-pyridyl)-2,2 :6 ,2 -terpyridine, 3 = 4 -(4-
and compare the N-methylation reactions of [Ru(1) ] , [Ru(2) ]
and [Ru(3) ] .
2
2
ꢀ
ꢀ
ꢀꢀ
2+
2
pyridyl)-2,2 :6 ,2 -terpyridine (Scheme 1). We and others have
n+
6,7,16
reported the synthesis of {M(3)
2
}
complexes (n = 2, M = Fe,
Despite complexes of 3 being well established, those of 1 and 2
7,10
7
17
n+
n+
Ru,
Os, n = 3, M = Rh). The complexes {M(3)
2
}
are
are less well studied. Two reports of {M(1) } complexes have
2
ꢀ
20,21
usefully regarded as expanded 4,4 -bipyridines in which the N · · · N
appeared
and the photophysical properties of the isomeric
˚
3+
distance of the pendant 4-pyridyl donors is increased from ∼7 A
complexes [IrL2] (L = 1, 2 or 3) and some protonated and
18
22
˚
to ∼18 A. We have demonstrated that the pendant 4-pyridyl
alkylated derivatives have been studied in detail. Among the
n+
group in {M(3)
2
}
retains its characteristic reactivity and reacts
alkylating agents
products obtained from hydrothermal reactions of 1 with CuI and
KI is the mixed oxidation state compound [Cu (1) I ] [Cu (l-I) I ]
6
,7,14,16,19
6–9,16
12
with protons,
and metal ions. In this
2
2
2
2
2
2 2
ꢀ
paper we report the expanded ligand analogues of 2,2 -bipyridine
and 3,3 -bipyridine (Scheme 1) involving an {M(tpy)
containing a discrete mixed oxidation state cation comprising a
ꢀ
2+
II
2
2
}
scaffold
{Cu (7) } moiety in which one of the 2-pyridyl substituents is
I
20
n+
with pendant 2-pyridyl (1) and 3-pyridyl (2) ligands. We describe
coordinated to a {Cu I } unit. The complexes {M(2) } have
2
2
10,23
23
detailed comparative structural and spectroscopic studies of the
received little attention with only [Ru(2) ][PF ] ,
and [Ir(2) ][PF ] being reported to date.
[Fe(2) ][PF ]
2
6
2
2
6 2
2
+
2+
2+
21
complexes [M(1)
2
] , [M(2)
2
]
and [M(3)
2
]
with M = Fe or Ru,
2
6 3
Experimental
Department of Chemistry, University of Basel, Spitalstrasse 51, CH4056
Basel, Switzerland. E-mail: edwin.constable@unibas.ch; Fax: +41 61 267
General methods
1
018; Tel: +41 61 267 1001
†
This paper is dedicated to our mentor and colleague Professor Ken Wade
1
13
H and C NMR spectra were recorded on a Bruker Avance DRX
00 spectrometer; the numbering scheme adopted for the ligands is
on the occasion of his 75th birthday.
CCDC reference numbers 662661–662664 and 666047. For crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/b714970k
5
‡
1
13
shown in Scheme 2. Chemical shifts for H and C NMR spectra
3
86 | Dalton Trans., 2008, 386–396
This journal is © The Royal Society of Chemistry 2008

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3
and EtOH (3 × 15 cm ). Recrystallization from CHCl
3
–MeOH
gave 1 as a white crystalline solid (2.36 g, 7.60 mmol, 38.0%).
Spectroscopic and mass spectrometric data were consistent with
25
the literature. Found: C, 77.08; H, 4.68; N, 18.18. C20
requires C, 77.40; H, 4.55; N, 18.05.
H
14
N
4
Ligand 2
24
Ligand 2 was prepared by the procedure of Hanan reported
for 3. 2-Acetylpyridine (4.84 g, 40.0 mmol) was added to a
solution of pyridine-3-carbaldehyde (2.18 g, 20.4 mmol) in EtOH
3
(
(
100 cm ). KOH pellets (2.7 g, 50 mmol) and aqueous NH
3
3
60 cm , 25%, 0.85 mol) were added to the solution. This was
stirred at room temperature for 4 h, and the off-white solid that
formed was collected by filtration and washed with H
O (3 ×
5 cm ) and EtOH (3 × 15 cm ). Ligand 2 was isolated as a
white crystalline solid after recrystallization from CHCl –MeOH
2.72 g, 8.76 mmol, 43.8%). Spectroscopic and mass spectrometric
2
3
3
1
3
(
25
data were as previously reported. Found: C, 77.15; H, 4.62; N,
8.24. C20 requires C, 77.40; H, 4.55; N, 18.05.
1
H
14
N
4
[
Fe(1)
2
][PF
]
6 2
Ligand 1 (0.20 g, 0.64 mmol) and FeCl
2
·4H
were dissolved in MeOH (30 cm ) and stirred at room temperature
for 30 min. Excess aqueous NH PF was added and the resulting
purple precipitate was collected on Celite, washed with H O, EtOH
and Et O, and redissolved in MeCN. Solvent was removed to give
Fe(1) ][PF as a purple microcrystalline solid (0.18 g, 0.19 mmol,
2
O (0.064 g, 0.32 mmol)
3
4
6
2
2
[
5
(
8
1
4
1
1
2
1
6 2
]
B3
9%). H NMR (CD CN, 500 MHz) d/ppm 9.57 (s, 4H, H ), 9.01
d, J 4.2 Hz, 2H, H ), 8.65 (d, J 8.0 Hz, 4H, H ), 8.60 (d, J
.0 Hz, 2H, H ), 8.22 (dt, J 7.8, 1.7 Hz, 2H, H ), 7.92 (dt, J 8.0,
.3 Hz, 4H, H ), 7.69 (dd, J 7.2, 5.0, 2H, H ), 7.20 (d, J 5.5 Hz,
3
C6
A3
C3
C4
Scheme 2 Structures of ligands 1–6 and atom labelling for NMR spectra.
A4
C5
A6
A5
13
1
H, H ), 7.09 (t, J 6.6 Hz, 4H, H ). C{ H} NMR (CD
3
CN
3
,
are referenced to residual solvent peaks with respect to TMS =
d 0 ppm. For the NMR spectra of complexes containing ligands
B2
A2
A6
C2
25 MHz) d/ppm 161.5 (C ), 158.9 (C ), 154.1 (C ), 153.7 (C ),
C6
B4
A4
C4
A5
51.7 (C ), 149.8 (C ), 139.8 (C ), 139.2 (C ), 128.4 (C ), 126.5
1
, 2 or 3, Et N was added to the solution to confirm that the
3
C5
A3
C3
B3
(
PF
C ), 125.0 (C ), 123.1 (C ), 121.8 (C ). ES-MS: m/z 822 [M −
coordinated ligands were fully deprotonated. Electrospray (ES)
mass spectra were recorded using a Finnigan MAT LCQ mass
spectrometer. Electronic absorption spectra were recorded on an
Agilent 8453 UV-Visible Spectrophotometer.
Electrochemical measurements were performed with an Eco
Chemie Autolab PGSTAT 20 system using glassy carbon working
and platinum auxiliary electrodes with a silver wire as a pseudo-
+
2+
−5
−3
6
] , 339 [M − 2PF
6
] . UV/VIS kmax/nm (1.87 × 10 mol dm ,
3
−1
−1
MeCN) 571 (e/dm mol cm 27 700), 324 (48 700), 285 (76 800),
2
C
77 (63 600), 241 (34 800). Found: C, 48.57; H, 3.00; N, 11.40.
·1.5H O requires C, 48.36; H, 3.15; N, 11.28. See
Table 4 for electrochemical data.
40
H
28
F
12FeN
8
P
2
2
reference electrode; purified MeCN was used as the solvent and
[Fe(2)
2
][PF
]
6 2
n
0.1M [ Bu
4
N][PF ] as the supporting electrolyte; ferrocene was
6
The preparation of [Fe(2)
with 2 (0.20 g, 0.64 mmol) and FeCl
Fe(2) ][PF was isolated as a purple solid (0.20 g, 0.21 mmol,
64%). H NMR (CD CN, 500 MHz) d/ppm 9.50 (d, J 1.6 Hz,
2
][PF
6
]
2
was as for [Fe(1)
2
][PF ] , starting
6
2
added at the end of each experiment as an internal reference.
2
·4H O (0.064 g, 0.32 mmol).
2
Reactions were carried out under N
distilled before use.
Ligand 3 was prepared by the one-pot method of Hanan.
2
. Solvents were dried and
[
2
]
6 2
1
24
3
C2
B3
C6
2
H, H ), 9.21 (s, 4H, H ), 8.91 (d, J 4.8 Hz, 2H, H ), 8.64 (d,
C4
A3
J 8.4 Hz, 2H, H ), 8.61 (d, J 8.0 Hz, 4H, H ), 7.93 (t, J 7.8 Hz,
4
Ligand 1
Ligand 1 was prepared by modifying the procedure reported for 3
A4
C5
H, H ), 7.79 (dd, J 7.8, 4.9 Hz, 2H, H ), 7.19 (d, J 5.6 Hz,
A6
A5
13
1
4H, H ), 7.10 (t, J 6.6 Hz, 4H, H ). C{ H} NMR (CD
3
CN,
24
B2
A2
A6
C6
by Hanan. 2-Acetylpyridine (4.84 g, 40.0 mmol) was added to a
solution of pyridine-2-carbaldehyde (2.18 g, 20.4 mmol) in EtOH
125 MHz) d/ppm 161.5 (C ), 158.9 (C ), 154.1 (C ), 152.6 (C ),
C2
B4
A4
C4
C3
149.9 (C ), 148.6 (C ), 139.9 (C ), 136.3 (C ), 133.6 (C ), 128.4
3
3
A5
C5
A3
B3
(
100 cm ). KOH pellets (2.7 g, 50 mmol) and aqueous NH
3
(60 cm ,
(C ), 125.4 (C ), 124.9 (C ), 122.8 (C ). ES-MS: m/z 822 [M −
+
2+
−5
−3
2
5%, 0.85 mol) were added to the solution which was then stirred
PF
6
] , 339 [M − 2PF
6
] . UV/VIS kmax/nm (1.87 × 10 mol dm ,
3
−1
−1
at room temperature for 4 h. An off-white solid formed which
MeCN) 567 (e/dm mol cm 26 600), 322 (52 500), 284 (92 000),
3
was collected by filtration and washed with H
2
O (3 × 15 cm )
277 (78 400), 244 (40 700). Found: C, 49.41; H, 2.98; N, 11.75.
This journal is © The Royal Society of Chemistry 2008
Dalton Trans., 2008, 386–396 | 387

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1
0
−6
−3
C
40
H
28
F
12FeN
8
P
2
requires C, 49.71; H, 2.92; N, 11.59. See Table 4
reassigned. UV/VIS kmax/nm (8.90 × 10 mol dm , MeCN)
3
−1
−1
for electrochemical data.
489 (e/dm mol cm 30 800), 313 (70 700), 278 (78 800). See
Table 4 for electrochemical data.
[
Fe(3)
2
][PF
]
6 2
[
Ru(4)
2
][PF
6
]
4
and [Ru(1)(4)][PF
6 3
]
The preparation of [Fe(3)
with 2 (0.20 g, 0.64 mmol) and FeCl
Fe(3) ][PF was isolated as a purple solid (0.24 g, 0.25 mmol,
7%). Spectroscopic data differ slightly from those of the tetraflu-
2
][PF
6
]
2
was as for [Fe(1)
2
][PF
6
]
2
, starting
3
2
·4H O (0.065 g, 0.33 mmol).
2
Iodomethane (5.0 cm , 80 mmol) was added to a solution of
[Ru(1)
3
[
7
2
6
]
2
2
][PF
6
]
2
(0.20 g, 0.20 mmol) in MeCN (20 cm ). NH
4
PF
6
(0.1 g, 0.6 mmol) was added to prevent the precipitation of the
iodide salt. The mixture was heated at reflux and was monitored
by thin layer chromatography (SiO
aqueous KNO 7 : 2 : 2). This showed the formation of a yellow
product with high R value (assumed to be an organic derivative,
but remaining unidentified) in addition to the desired red products.
A further 5 cm of MeI was added after 24 h, and the solution
was heated to reflux for a further 24 h until chromatography
indicated that the formation of the yellow product was becoming
increasingly dominant. Solvent was removed from the reaction
mixture, and the residue was dissolved in a minimum amount
6
1
oroborate salt previously reported. H NMR (CD CN, 500 MHz)
3
B3
C2
d/ppm 9.23 (s, 4H, H ), 9.02 (d, J 6.0 Hz, 4H, H ), 8.63 (d, J
2
, MeCN : H O : saturated
2
A3
C3
8
4
.0 Hz, 4H, H ), 8.23 (d, J 6.0 Hz, 4H, H ), 7.93 (t, J 7.2 Hz,
H, H ), 7.18 (d, J 5.3 Hz, 4H, H ), 7.10 (t, J 6.6 Hz, 4H,
3
A4
A6
f
A5
13
1
B2
H ). C{ H} NMR (CD
3
CN, 125 MHz) d/ppm 161.7 (C ),
A2
A6
C2
C4
B4
3
1
1
58.7 (C ), 154.1 (C ), 152.3 (C ), 148.7 (C ), 145.0 (C ),
A4
A5
A3
C3
B3
40.0 (C ), 128.5 (C ), 125.1 (C ), 123.0 (C ), 122.7 (C ). ES-
+
2+
MS: m/z 822 [M − PF
6
] , 339 [M − 2PF
6
] . UV/VIS kmax/nm
−
5
−3
3
−1
−1
(
(
1.87 × 10 mol dm , MeCN) 569 (e/dm mol cm 25 000), 324
45 100), 284 (81 700), 276 (74 100), 245 (48 200). Found: C, 48.96;
H, 3.20; N, 12.39. C40
C, 49.31; H, 3.17; N, 12.13. See Table 4 for electrochemical data.
H
28
F
12FeN
8
P
2
·0.75MeCN·0.75H
2
O requires
of MeCN and purified by chromatography (SiO
saturated aqueous KNO 7 : 2 : 2). Three, well-separated red bands
were collected. The first was [Ru(1) ][PF . The second (major)
fraction was [Ru(1)(4)][PF ; the final fraction was [Ru(4) ][PF
Each was collected and excess aqueous NH PF added. Removal
of MeCN under reduced pressure gave a red precipitate which
was collected on Celite, washed well with H O, EtOH and Et
and then redissolved in MeCN. Removal of the solvent gave
[Ru(1)(4)][PF (81 mg, 0.069 mmol, 35%) and [Ru(4) ][PF
(22 mg, 0.017 mmol, 8.5%) as red powders. [Ru(1)(4)][PF
2
, MeCN : H
2
O :
3
2
]
6 2
6
]
3
2
6
4
] .
[
Ru(1)
2
][PF
6
]
2
4
6
Ligand 1 (0.30 g, 0.97 mmol) and RuCl
3
·3H
2
O (0.24 g, 0.92 mmol)
3
were suspended in ethane-1,2-diol (15 cm ) and the mixture was
heated in a microwave oven (800 W) for 4 min. Another equivalent
of 1 (0.30 g, 0.97 mmol) and 3 drops of N-ethylmorpholine were
added, and the solution was heated in the microwave oven (800 W)
2
2
O
6
]
3
2
6 4
1
]
6
]
3
: H
1
B3
for 5 min. The deep red solution was poured into aqueous NH
4
PF
150 cm ). A red precipitate formed and was collected on Celite,
washed with H O, EtOH and Et O, and redissolved in MeCN. The
product was purified by chromatography (SiO , MeCN : H O :
saturated aqueous KNO 7 : 2 : 2). Addition of aqueous NH PF
and removal of MeCN gave a red precipitate which was collected
on Celite, washed with H O, EtOH and Et O and redissolved in
MeCN. Removal of the solvent gave [Ru(1) ][PF as a red solid
CN, 500 MHz) d/ppm
6
NMR (CD
6.2 Hz, 1H, H
3
CN, 500 MHz) d/ppm 9.43 (s, 2H, H ), 9.01 (d, J
3
1/4C6
1/4C6
(
), 8.97 (d, J 4.2 Hz, 1H, H
), 8.84 (s, 2H,
4
B3
4C4
1A3
2
2
H ), 8.83 (t, J 7.9 Hz, 2H, H ), 8.70 (d, J 8.0 Hz, 2H, H ),
8.50 (d, J 8.3 Hz, 1H, H ), 8.48 (d, J 8.2 Hz, 2H, H ), 8.37
(d, J 7.3 Hz, 2H, H ), 8.29 (ddd, J 1.2, 7.5, 6.5 Hz, 2H, H ),
1
C3
4A3
2
2
4
C3
4C5
3
4
6
1
C4
8.18 (td, J 7.8, 1.7 Hz, 1H, H ), 7.66 (dd, J 4.9, 7.2 Hz, 1H,
1
C5
4A6
1A6
2
2
H
), 7.51 (d, J 5.4 Hz, 2H, H ), 7.46 (d, J 5.4 Hz, 2H, H ),
4
A5
2
6
]
2
7.24 (ddd, J 1.0, 7.1, 6.2 Hz, 2H, H ), 7.22 (ddd, J 1.0, 7.1,
1
1A5
13
1
(
9
0.34 g, 0.34 mmol, 37%). H NMR (CD
3
C6
6.1 Hz, 2H, H ), 4.51 (s, 3H, Me). C{ H} NMR (CD
3
CN,
B3
1A2
4C2
4A2
1C6
1,4B2
4C6
.41 (s, 4H, H ), 8.96 (d, J 4.0 Hz, 2H, H ), 8.68 (d, J 8.0 Hz, 4H,
125 MHz) d/ppm 159.1 (C ), 158.1, (C ), 157.0 (C ), 153.8
A3
C3
C4
1,4A6
1C2
H ), 8.49 (d, J 8.0 Hz, 2H, H ), 8.17 (dt, J 7.8, 1.7 Hz, 2H, H ),
(C ), 153.7 (C ), 152.8 (C ), 152.0 (C ), 148.5 (C ), 148.3
A4
C5
1B4
4C4
1C4
4A4
1A4
7
7
.96 (dt, J 8.0, 1.4 Hz, 4H, H ), 7.64 (dd, J 6.9, 4.8 Hz, 2H, H ),
(C ), 147.8 (C ), 139.4 (C ), 139.3 (C ), 139.1 (C ), 138.0
A6
A5
4B4
4C3
4C5
4A5
1A5
.44 (d, J 5.1 Hz, 4H, H ), 7.18 (ddd, J 7.2, 5.7, 1.1 Hz, 4H, H ).
(C ), 131.6 (C ), 129.6 (C ), 129.0 (C ), 128.6 (C ), 126.6
1
3
1
A2
1C5
1A3
4A3
4B3
1C3
C{ H} NMR (CD
3
CN, 125 MHz) d/ppm 159.1 (C ), 156.6
(C ), 125.8 (C ), 125.0 (C ), 124.5 (C ), 123.0 (C ), 122.1
B2
C2
A6
C6
B4
C4
1B3
Me
+
(
C ), 153.7 (C ), 153.5 (C ), 151.6 (C ), 147.6 (C ), 139.2 (C ),
(C ), 48.9 (C ). ES-MS: m/z 1027 [M − PF
6
3
] . UV/VIS kmax/nm
A4
A5
C5
A3
C3
−5
−3
−1
−1
139.0 (C ), 128.5 (C ), 126.2 (C ), 125.6 (C ), 122.9 (C ), 122.0
(1.22 × 10 mol dm , MeCN) 490 (e/dm mol cm 23 000),
B3
+
2+
(
k
2
C ). ES-MS: m/z 867 [M − PF
6
] , 361 [M − 2PF
6
3
] ; UV/VIS
328 (38 500), 313 (52 500), 278 (57 500). Found: C, 40.15; H, 2.89;
−
6
−3
−1
−1
max/nm (8.90 × 10 mol dm , MeCN) 492 (e/dm mol cm
N, 9.16. C41
H
31
F
18
N
8
P
3
+
Ru·2.5H
2
O requires C, 40.47; H, 2.98; N,
◦
7 200), 316 (56 000), 286 (58 700), 277 (57 800). Found: C, 46.28;
Ru·1.5H O requires C, 46.25; H,
.01; N, 10.79. See Table 4 for electrochemical data.
9.21. E /V vs. Fc/Fc : +1.02 (reversible), −1.32 (irreversible),
1
H, 2.88; N, 10.95. C40
3
H
28
F
12
N
8
P
2
2
−1.93 (irreversible). [Ru(4)
2
][PF
6
]
4
H NMR (CD CN, 500 MHz):
3
C6
B3
d/ppm 9.03 (d, J 6.1 Hz, 2H, H ), 8.95 (s, 4H, H ), 8.83 (t, J
C4
A3
7
2
7
.6 Hz, 2H, H ), 8.54 (d, J 8.1 Hz, 4H, H ), 8.42 (d, J 7.2 Hz,
H, H ), 8.29 (t, J 7.0 Hz, 2H, H ), 8.00 (t, J 7.3 Hz, 4H, H ),
C3
C5
A4
[
Ru(2)
2
][PF
]
6 2
A6
A5
.57 (d, J 5.3 Hz, 4H, H ), 7.28 (t, J 6.6 Hz, 4H, H ), 4.55 (s,
10
13
1
A2
[
Ru(2)
2
][PF
6
]
2
was prepared as previously described. Mass spec-
6H, Me). C{ H} NMR (CD
3
CN, 125 MHz) d/ppm 158.1 (C ),
1
B2
A6
C2
C6
C4
trometric data were consistent with those published; in the H
156.7 (C ), 154.0 (C ), 152.9 (C ), 148.4 (C ), 147.5 (C ), 139.6
B3
A4
B4
C3
C5
A5
A3
NMR spectrum, a NOESY cross peak between the signal for H
(C ), 138.9 (C ), 131.6 (C ), 129.7 (C ), 129.1 (C ), 126.1 (C ),
C4
C4
C6
B3
Me
+
and H allowed assignments of H at d 8.53 ppm and H at d
124.6 (C ), 49.3 (C ). ES-MS: m/z 1187 [M − PF
6
3
] . UV/VIS
1
3
−5
−3
−1
−1
8
.86 ppm, reassigned from our previous publication; C NMR
k
max/nm (3.49 × 10 mol dm , MeCN) 487 (e/dm mol cm
C4
C5
signals for C (d 135.2 ppm) and C (d 124.3 ppm) are also
22 900), 331 (18 300), 311 (24 400), 277 (31 400). Found: C 37.13,
3
88 | Dalton Trans., 2008, 386–396
This journal is © The Royal Society of Chemistry 2008

View Article Online
A4
A6
H 3.00, N 9.09; C42
H
34
F
24
N
8
P
4
Ru·2H
2
O·0.75CH
3
CN requires C
4H, H ), 7.45 (d, J 5.2 Hz, 4H, H ), 7.24 (ddd, J 7.2, 5.6, 1.1 Hz,
A5
13
1
37.30, H 3.04, N 8.75%. See Table 4 for electrochemical data.
4H, H ), 4.57 (s, 6H, Me). C{ H} NMR (CD
3
CN, 125 MHz)
A2
B2
A6
C6
d/ppm 158.5 (C ), 157.0 (C ), 153.7 (C ), 146.9 (C ), 145.5
C2
C4
B4
A4
C3
C5
(
1
C ), 144.9 (C ), 141.5 (C ), 139.5 (C ), 138.3 (C ), 129.8 (C ),
[
Ru(2)(5)][PF
6
]
3
A5
A3
B3
Me
29.0 (C ), 125.8 (C ), 123.0 (C ), 50.0 (C ). ESI-MS: 299 [M −
3
3+
2+
+
Iodomethane (0.50 cm , 8.0 mmol) was added to a solution of
3PF
6
] , 521 [M − 2PF
6
] , 1187 [M − PF
6
3
] . UV/VIS kmax/nm
3
−6
−3
−1
−1
[
Ru(2)
2
](PF
6
)
2
(0.22 g, 0.22 mmol) in MeCN (15 cm ). NH
4
PF
6
(8.90 × 10 mol dm , MeCN) 494 (e/dm mol cm 24 500),
(
0.05 g, 0.3 mmol) was then added to prevent the precipitation of
315 (39 000), 277 (58 600), 238 (31 300). Found: C 37.34, H 2.69, N
◦
the iodide salt. The mixture was heated to 50 C and monitored by
thin layer chromatography (SiO , MeCN : H O : saturated aqueous
KNO 7 : 2 : 2). After 15 min, the mono-methylated species was
8.45; C42
H
34
F
24
N
8
P
4
Ru·1.5H
2
O requires C 37.13, H 2.74, N 8.25%.
2
2
See Table 4 for electrochemical data.
3
the major product. Solvent was removed and the residue dissolved
in a minimum amount of MeCN and purified by chromatography
[
Ru(3)(6)][PF
6
]
3
3
(
SiO
portion of the major (middle) red band was collected and excess
aqueous NH PF added. Removal of the MeCN under reduced
pressure gave a red precipitate which was collected on Celite and
washed well with H O, EtOH and Et O. The solid was redissolved
in MeCN, and removal of the solvent gave [Ru(2)(5)][PF as
CN,
2
, MeCN : H
2
O : saturated aqueous KNO
3
7 : 2 : 2). The central
Iodomethane (0.25 cm , 4.0 mmol) was added to a solution of
[Ru(3)
(0.1 g, 0.6 mmol in 5 mL H
3
2
][PF
6
]
2
(0.10 g, 0.099 mmol) in MeCN (25 cm ). NH
4
PF
6
4
6
2
O) was added to prevent precipitation
] . The mixture was heated at reflux
2
+
of the iodide salt of [Ru(3)
and monitored by thin layer chromatography (SiO
saturated aqueous KNO 7 : 2 : 2). After 20 min, [Ru(3)(6)][PF
was the major species present. Solvent was removed and the
residue dissolved in a minimum amount of MeCN and purified by
column chromatography (SiO
KNO 7 : 2 : 2). The main (middle) red band was collected and
excess aqueous NH PF was added. Removal of MeCN gave a
red precipitate which was collected on Celite, washed with H O,
EtOH and Et O, and redissolved in MeCN. Removal of solvent
gave [Ru(3)(6) ][PF as a red powder (0.047 g, 0.040 mmol,
41%). The lowest R fraction from the chromatography column
was also collected and yielded [Ru(6) ][PF as a red powder
2
2
2
2
, MeCN : H O :
2
6
]
3
3
]
6 3
1
a red powder (0.020 g, 0.017 mmol, 7.7%). H NMR (CD
3
5
C2
2C2
5
9
8
(
8
00 MHz) d/ppm 9.49 (s, 1H, H ), 9.41 (d, J 2.0 Hz, 1H, H ),
5
C4
5B3
2B3
.22 (d, J 8.2 Hz, 1H, H ), 9.08 (s, 2H, H ), 9.06 (s, 2H, H ),
2
, MeCN : H
2
O : saturated aqueous
5
C6
2C6
.89 (d, J 6.1 Hz, 1H, H ), 8.87 (dd, 4.7, 1.3 Hz, 1H, H ), 8.66
3
2
,5A3
2C4
d, J 8.1 Hz, 4H, H ), 8.56 (ddd, J 7.9, 1.6, 2.2 Hz, 1H, H ),
.37 (dd, J 7.9, 6.3 Hz, 1H, H ), 8.00 (td, J 7.7, 1.4 Hz, 2H,
), 7.97 (td, J 8.0, 1.4 Hz, 2H, H ), 7.75 (dd, J 7.8, 5.0 Hz,
H, H ), 7.49 (d, J 5.5 Hz, 2H, H ), 7.42 (d, J 5.4 Hz, 2H, H ),
4
6
5
C5
2
5
A4
2A4
H
2
2
C5
5A6
2A6
1
7
2
2
]
6 3
5
A5
.24 (ddd, J 7.1, 6.3, 1.0 Hz, 2H, H ), 7.20 (ddd, J 7.2, 6.3, 1.0 Hz,
f
2
A5
Me
13
1
H, H ), 4.58 (s, 3H, H ). C{ H} NMR (CD
3
CN, 125 MHz)
2
6 4
]
2
A2
5A2
2B2
5B2
1
d/ppm 158.8 (C ), 158.6 (C ), 157.2 (C ), 156.4 (C ), 153.6
(0.020 g, 0.015 mmol, 15%, see below). H NMR and UV/VIS
spectroscopic and electrochemical data were consistent with the
2
5
2
2
,5A6
2C6
2C2
5C6
2B4
(
(
(
(
(
C
C
C
C
), 152.1 (C ), 149.7 (C ), 146.8 (C ), 146.7 (C ), 145.6
C2
5C4
5B4
2,5A4
5C3
7
13
1
), 144.8 (C ), 141.1 (C ), 139.3 (C ), 138.4 (C ), 136.3
), 133.7 (C ), 129.7 (C ), 128.8 (C ), 128.6 (C ), 125.7
literature data. C{ H} NMR (125 MHz, CD
3
CN) d/ppm 158.7
C4
2C3
5C5
5A5
2A5
6A2
6C4
3A2
3C2
6B2
3C4
3B2
6C2
3/6A6
(C ), 158.5 (C ), 157.3 (C ), 156.4 (C ), 153.6 (C
), 153.6
,5A3
2C5
2,5B3
Me
3B4
), 125.3 (C ), 122.9 (C ), 49.9 (C ). UV/VIS kmax/nm
(C ), 152.1 (C ), 147.4 (C ), 147.3 (C ), 144.9 (C ), 141.4
(C ), 139.4 (C ), 129.0 (C ), 128.7 (C ), 127.0 (C ), 125.9
(C ), 123.1 (C ), 123.0 (C ), 122.9 (C ), 49.2 (C ). Found
C 40.82, H 3.00, N 10.11; C41 Ru·2.5H O·0.75CH CN
requires C 40.92, H 3.09, N 9.82%.
−
5
−3
3
−1
−1
6B4
3,6A4
6A5
3A5
6C3
4.01 × 10 mol dm , MeCN) 491 (e/dm mol cm 27 000),
14 (60 200), 278 (64 400). Found: C, 39.75; H, 3.01; N, 9.05.
3
,6A3
3C3
6B3
3B3
Me
3
C
41
H
31
F
18
N
8
P
3
Ru·4H
2
O requires C, 39.59; H, 3.16; N, 9.01. ES-
H
31
F
18
N
8
P
3
2
3
−
MS: m/z 1027 [M − PF
6
] . See Table 4 for electrochemical data.
[
Ru(5)
2
][PF
6
]
4
[Ru(6)
2
][PF
]
6 4
3
Iodomethane (1.0 cm , 16 mmol) was added to a solution of
[Ru(6)
[Me O][BF
4.0 mmol) was added to a solution of [Ru(3)
2
][PF
6
] has previously been prepared in 34% yield using
4
3
7
3
[
Ru(2)
0.05 g, 0.3 mmol) was added to prevent the precipitation of the
iodide salt. The mixture was heated at reflux and monitored by thin
layer chromatography (SiO , MeCN : H O : saturated aqueous
KNO 7 : 2 : 2). After 6 h, no further reaction was observed
the reaction does not go to completion, even on addition of
2
](PF
6
)
2
(0.10 g, 0.10 mmol) in MeCN (10 cm ). NH
4
PF
6
3
4
] as methylating agent. Iodomethane (0.25 cm ,
](PF (0.048 g,
0.047 mmol) in MeCN (5 cm ). The mixture was heated at reflux
and monitored by thin layer chromatography (SiO , MeCN : H O :
saturated aqueous KNO 7 : 2 : 2). After 8 h, a red precipitate
had formed (assumed to be the iodide salt) and NH PF (0.02 g,
(
2
)
6 2
3
2
2
2
2
3
3
(
4
6
more MeI). Solvent was removed and the residue dissolved in
a minimum amount of MeCN and purified by chromatography
0.1 mmol) was added to give a soluble hexafluorophosphate salt.
After 10 h, no further reaction was observed; the reaction does
not go to completion, even on adding more MeI. Solvent was
removed and the residue was dissolved in a minimum amount of
(
SiO
main (lowest R
NH PF added. Removal of MeCN gave a red precipitate which
was collected on Celite, washed with H O, EtOH and Et O, and
redissolved in MeCN. Removal of the solvent gave [Ru(5) ][PF
as a red powder (0.068 g, 0.051 mmol, 52%). H NMR (CD CN,
2
, MeCN : H
2
O : saturated aqueous KNO 7 : 2 : 2). The
3
f
) red band was collected and excess aqueous
4
6
MeCN and purified by column chromatography (SiO
O : saturated aqueous KNO 7:2:2). The main (lowest R
red band was collected and excess aqueous NH PF was added.
Removal of MeCN gave a red precipitate which was collected
on Celite, washed with H O, EtOH and Et O, and redissolved in
MeCN. Removal of solvent gave [Ru(6) ][PF as a red powder
2
, MeCN :
2
2
H
2
3
f
)
2
6
]
4
4
6
1
3
C2
C4
5
9
4
00 MHz) d/ppm 9.40 (s, 2H, H ), 9.20 (d, J 8.2 Hz, 2H, H ),
2
2
B3
C6
.04 (s, 4H, H ), 8.89 (d, J 6.1 Hz, 2H, H ), 8.63 (d, J 8.1 Hz,
2
6 4
]
A3
C5
1
H, H ), 8.38 (dd, J 8.0, 6.3 Hz, 2H, H ), 8.02 (td, J 8.0, 1.3 Hz,
(0.025 g, 0.019 mmol, 40%). H NMR and UV/VIS spectroscopic
This journal is © The Royal Society of Chemistry 2008
Dalton Trans., 2008, 386–396 | 389

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Table 1 Crystal data for the complexes‡
{[Fe(1) ][PF
4
2
6
]
2
}·9H
2
O
[Fe(2)
2
][PF
6
]
2
[Fe(3)
2
][PF
6
]
2
·2MeCN
[Ru(1)
2
][PF
6
]
2
·2H
2
O
2{[Ru(5)
2
][PF
6
]
4
}·H
2
O
Formula
Formula weight
Crystal system
C
160
H
130
F
48Fe
4
N
32
O
9
P
8
C
40
H
28
F
12FeN
8
P
2
C
44
H
34
F
12FeN10
P
2
C
40
H
32
F
12
N
8
O
2
P
2
Ru
C
84
H
70
F
48
N
16OP
8
Ru
2
4028.08
Triclinic
P1
966.49
Triclinic
P1
1048.59
Tetragonal
I4 /a
8.7704(2)
8.7704(2)
56.525(1)
90
90
90
4347.9(2)
1.760
4
1047.75
Triclinic
P1
2679.41
Triclinic
P1
8.5631(1)
15.5219(2)
19.7088(2)
103.5494(7)
97.4740(7)
101.6026(6)
2451.09(5)
1.815
¯
¯
¯
¯
Space group
1
a/A˚
15.7521(6)
16.1814(6)
17.3664(6)
94.145(2)
99.444(2)
109.469(2)
4078.3(3)
1.640
9.3867(2)
10.4130(2)
21.3789(3)
93.680(1)
100.262(1)
110.4597(8)
1908.30(6)
1.682
16.124(4)
16.170(4)
17.526(4)
94.305(5)
99.731(4)
113.697(4)
4071.9(16)
1.768
b/A˚
c/A˚
◦
a/
b/
◦
◦
c /
U/A˚
3
−
3
D
Z
c
/Mg m
1
2
4
1
−
1
l(Mo-Ka)/mm
T/K
Refln collected
0.553
173
18 648
0.583
173
18 394
0.520
173
3188
0.574
150(2)
18 394
0.587
173
11 707
Refln for refinement (Rint) 12 869 (0.045)
13 834 (0.026)
1157
2431 (0.086
204
13 834 (0.018)
1157
8538 (0.025)
811
Parameters
1180
Threshold
R1 (R1 all data)
wR2 (wR2 all data)
I > 1.0r (I)
0.0776 (0.1172)
0.0842 (0.1214)
I > 2.0r (I)
0.0375 (0.0648)
0.0434 (0.0678)
I > 3.0r (I)
0.0998 (0.1160)
0.0578 (0.0590)
I > 2.0r (I)
0.0598 (0.0838)
0.1536 (0.1718)
I > 3.0r (I)
0.0364 (0.0539)
0.0378 (0.0481)
7
13
1
and electrochemical data matched the literature data. C{ H}
NMR (CD CN, 125 MHz) d/ppm 158.4 (C ), 157.0 (C ), 153.7
A2
B2
3
A6
C4
C2
B4
A4
A5
(
1
[
3
C ), 153.3 (C ), 147.3 (C ), 142.0 (C ), 139.6 (C ), 129.0 (C ),
C3
A3
B3
Me
27.1 (C ), 126.0 (C ), 123.3 (C ), 49.3 (C ). ES-MS: m/z 1187
−
M − PF
6
] . Found: C 36.67, H 2.80, N 8.61; C42
H
34
F
24
N
8
P
4
Ru·
H
2
O·0.5CH
3
CN requires C 36.73, H 2.97, N 8.47%.
Crystal structure determinations‡
Data for 4{[Fe(1) ][PF }·9H O, [Fe(2)
2
6
]
2
2
2
][PF
6
]
2
, [Fe(3)
2
][PF
6
]
2
·
2
MeCN and 2{[Ru(5) ][PF }·H O were collected on an Enraf
2
6
]
4
2
Nonius Kappa CCD instrument; data reduction, solution and
26
27
refinement used the programs COLLECT, SIR92, DENZO/
28
29
Scheme 3 The Hanan one-pot synthesis of ligands 1, 2 and 3.
SCALEPACK and CRYSTALS. Data for [Ru(1)
2
][PF
6
]
2
·4H
2
O
were collected on a Bruker SMART 1000 CCD diffractometer;
data reduction, solution (by Patterson map) and refinement used
7
[
[
[
Os(3)
2
][PF
][NO
][PF
6
]
2
,
as well as the single crystal structures of
30
31
the programs SAINT, SHELXS-97 and SHELXL-97. For
crystal data, see Table 1.
16
11
Fe(3)
Ru(2)
2
3
]
2
·3H
2
O·MeCN, [Ru(3)
2
][PF
6
][NO
3
]·DMSO and
10
2
6
]
2
.
Here, we report a systematic study of the iso-
2
+
2+
2+
meric hexafluorophosphate salts of [Fe(1)
2
] , [Fe(2)
2
] , [Fe(3) ] ,
2
2
+
2+
2+
Results and discussion
[Ru(1)
plexes [FeL
2
] , [Ru(2)
][PF
in good yields by treating FeCl
of ligand in MeOH under ambient conditions. The purple
hexafluorophosphate salts were precipitated by addition of excess
2
]
]
and [Ru(3)
where L = 1, 2 or 3 may be synthesized
O with two equivalents
2
] . The homoleptic iron(II) com-
2
6
2
Ligand synthesis
2
·4H
2
Ligand 1 has been previously prepared using the Kr o¨ hnke
32,33
25
23
methodology
and in PEG, but the Hanan one-pot method
aqueous NH
spectra of [Fe(1)
were assigned to [M − PF
m/z 339) corresponded to the ion [M − 2PF
isotope distributions for these peaks matched those simulated. No
4
PF
6
. The highest mass peaks in the electrospray mass
][PF , [Fe(2) ][PF and[Fe(3) ][PF (m/z 822)
] . In each spectrum, the base peak
(
Scheme 3) is more convenient and yields 1 in 38% yield from 2-
2
6
]
2
2
6
]
2
2
]
6 2
acetylpyridine and pyridine-2-carbaldehyde. Ligand 2 has been
prepared by a variety of methods from 2-acetylpyridine and
pyridine-3-carbaldehyde
obtain 2 in 44% yield. Hanan has previously reported the
synthesis of ligand 3 directly from 2-acetylpyridine and pyridine-
+
6
2
+
(
6
] . The observed
10,25,34
and using the Hanan method, we
1
13
fragmentation peaks were visible in the spectra. H and C NMR
spectra of acetonitrile solutions of [Fe(1) ][PF , [Fe(2) ][PF
and [Fe(3) ][PF were assigned using COSY, NOESY, HMQC
and HMBC techniques (see Scheme 2 for atom labelling). In the
]
2
2
]
6 2
24
2
6
4
-carbaldehyde (Scheme 3).
2
]
6 2
Synthesis and spectroscopic and structural characterization of
complexes
1
H NMR spectrum of [Fe(1)
2
][PF
6
]
2
, the proton signals for the
pendant pyridine ring (ring C) are easily assigned starting from
B3
C3
We have previously reported the syntheses and spectro-
scopic characterization of [Fe(3)
a cross peak in the NOESY spectrum between H and H . For
6
1
2
][BF
4
]
2
,
[Ru(3)
2
][PF
6
]
2
and
[Fe(2)
2
][PF
6
] , the H NMR resonances for ring C were assigned
2
3
90 | Dalton Trans., 2008, 386–396
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B3
beginning with cross peaks in the NOESY spectrum between H
ric unit. The structural parameters of cations A and B differ
C2
B3
C4
1
and H , and H and H (Scheme 2). The H NMR spectroscopic
signals for H , H , H and H show little variation in chemical
shifts along the series of complexes. Proton H responds to the
change in the position of heteroatom substitution in the pendant
pyridyl ring and the signal shifts from d 9.23 and 9.21 ppm in
little within the {Fe(tpy) } coordination spheres. They are also
2
A3
A4
A5
A6
similar in terms of the twisting of the pendant pyridine rings
with respect to the central ring of the tpy unit (angles between
the least squares planes of the rings containing N2 and N7,
B3
35
◦
and N5 and N8 = 25.3(2) and 4.2(2) in cation A, compared to
◦
[
[
Fe(3)
Fe(1)
2
][PF
][PF
6
]
]
2
and [Fe(2)
2
][PF
6
]
2
, respectively to d 9.57 ppm in
, consistent with the expected deshielding by the
corresponding angles of 24.8(2) and 6.8(2) in cation B). We have
ꢀ
ꢀ
ꢀ
ꢀꢀ
2
6
2
previously noted examples in which bis{4 -(4-pyridyl)-2,2 :6 ,2 -
1
3
pyridine nitrogen. The chemical shifts of the C NMR resonances
for the tpy carbon atoms vary little on going from [Fe(1) ][PF
. The H and C signals for
terpyridine} metal complexes suffer distortion from linearity along
ꢀ
11,14
2
6
]
2
the N · · · M · · · N axis.
In homoleptic complexes containing
1
13
ꢀ
to [Fe(2)
2
][PF
6
]
2
to [Fe(3)
2
][PF
6
]
2
ligands 1 and 2, the corresponding axis contains C · · · M · · · C
the pendant pyridine ring in each complex reflect the change in
position of attachment to the 4 -carbon atom of the tpy group and
atoms, and in both independent cations in 4[Fe(1)
2 6 2 2
][PF
the C · · · Fe · · · C angles are close to 180 (C34 · · · Fe1 · · · C39 =
176.56(4) and C84 · · · Fe2 · · · C89 = 176.92(7) ). Fig. 2 illustrates
that the [Fe(1)
]
·9H
O,
ꢀ
ꢀ
◦
◦
◦
the changes in symmetry.
2
+
36,37
[
Ru(1)
ing RuCl
followed by the addition of a second equivalent of 1 in the presence
of N-ethylmorpholine, and precipitation with [NH ][PF ]. Dark
red [Ru(1) ][PF was isolated in good yield after chromatographic
purification. The electrospray mass spectrum of the product
2
][PF
6
]
2
was prepared under microwave heating, by treat-
2
]
cations assemble with {Fe(tpy) } embraces,
2
3
·3H
2
O with one equivalent of 1 in ethane-1,2-diol,
interspersed by chains of hydrogen-bonded water molecules
(Table 2).
4
6
2
]
6 2
2
+
exhibited a base peak at m/z 361 assigned to [M − 2PF
the highest mass peak (m/z 867) corresponded to [M − PF
Both peak envelopes showed the correct isotope distributions, and
6
]
and
+
6
] .
1
13
no fragmentation peaks were observed. The H and C NMR
spectra were assigned using COSY, NOESY, HMQC and HMBC
techniques. The H NMR spectrum of an acetonitrile solution of
1
[
Ru(1)
2
][PF
6
2
] was generally similar to that of its iron(II) analogue.
One noticeable difference is the shift to higher frequency of the
A6
signal for H (the protons closest to the metal centre) on going
2
+
A6
2+
from [Fe(1)
2
]
(d 7.20 ppm for H ) to [Ru(1) ] (d 7.44 ppm) as
2
1
is also observed for the tpy analogues. A comparison of the H
NMR spectrum of [Ru(1)
10
2
][PF
6
]
2
with those of [Ru(2)
reveals the same pattern for the tpy proton signals
2
][PF
6
]
2
and
7
[
Ru(3)
2
][PF
6
]
2
B3
as is observed for the iron(II) complexes, viz. only proton H is
influenced by the change in substitution pattern of the pendant
B3
2+
pyridine ring (H d 9.41 ppm in [Ru(1)
2
][PF
and d 9.07 ppm in [Fe(3) ][PF
Single crystals of 4{[Fe(1) ][PF }·9H
evaporation of an MeCN–H O solution of [Fe(1)
6
]
2
versus d 9.04 ppm
Fig. 2 Packing of [Fe(1)2] cations and water molecules in 4[Fe(1) ][PF ] ·
2
6 2
10
7
in [Ru(2)
2
][PF
6
]
2
2
6
]
2
).
9H
2
O. Symmetry codes: i = 1 −x, 2 −y, −z; ii = x, y, 1 + z. Anions have
]
2
2
O were grown by slow
][PF . There
been omitted.
2
6
2
2
]
6 2
are two independent cations (A, Fig. 1, and B) in the asymmet-
Single crystals of [Fe(2)
2
][PF
6
]
2
were grown by slow evaporation
][PF . The coordination
of an MeCN–H
2
O solution of [Fe(2)
2
]
6 2
environment around the iron(II) centre is unexceptional (Fig. 3),
and the framework suffers little bending away from linearity
◦
as defined by the angle C34 · · · Fe1 · · · C40 = 171.11(3) . One
pendant pyridine ring is virtually coplanar with the tpy domain
to which it is attached, but the other is significantly twisted out
2
+
of plane, more so than in the [Fe(1)
2
]
cations described above
2
+
(for [Fe(2)
2
] , angles between the least squares planes of the
rings containing atoms N2 and N35, and N5 and N39 are 2.5(1)
◦
and 41.0(1) , respectively). The origin of this deviation from
coplanarity appears to be weak face-to-face p-stacking involving
the rings containing atoms N5 and N39 (Fig. 4). The separation
˚
between the planes of these rings is 3.99 A. At the other end of the
Fig. 1 Molecular structure of one (defined as cation A) of the two
ꢀ
cation, the approximately coplanar 4 -(3-pyridyl)-tpy ligand lies
2+
independent [Fe(1)
ellipsoids plotted at 40% probability level. Hydrogen atoms are omitted.
2
]
cations in 4{[Fe(1)
2
][PF
6
]
2
}·9H
2
O with thermal
over, but offset from, another such ligand in an adjacent cation of
the chain. The distance between the least squares planes of the 24
C and N atoms per ligand is 3.70 A, indicating the presence of
weak p-stacking. The chains lie parallel to one another and engage
Selected bond distances and angles: Fe1–N1 = 1.974(3), Fe1–N2 =
1
.877(2), Fe1–N3 = 1.978(3), Fe1–N4 = 1.983(3), Fe1–N5 = 1.877(3),
Fe1–N6 = 1.976(3) A˚ ; N1–Fe1–N2 = 81.2(1), N2–Fe1–N3 = 81.0(1),
◦
36,37
−
N4–Fe1–N5 = 81.1(1), N5–Fe1–N6 = 81.0(1) .
in rather loose {Fe(tpy)
2
} embraces,
with the [PF
6
]
ions
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Table 2 Hydrogen-bonded contacts involving water molecules and ligand 1 N atoms in 4{[Fe(1)
2
][PF
6
]
2
}·9H
2
O. The symmetry code refers to the atom
with the asterisk
D–H · · · A
D–H/A˚
H · · · A/A˚
D · · · A/A˚
D–H · · · A/◦
165
175
157
166
153
166
154
177
Symmetry code
—
—
—
—
—
—
O1–H1 · · · N7
O1–H2 · · · O2
O2–H4 · · · O3
O3–H5 · · · O4
O2–H14 · · · O1
O3–H15 · · · O2
O1–H12 · · · O1*
O4*–H8 · · · N57
0.82
0.82
0.83
0.82
0.83
0.82
0.82
0.82
2.06
1.99
2.02
1.73
2.05
2.00
2.13
1.86
2.865(4)
2.812(6)
2.803(6)
2.533(13)
2.812(6)
2.803(6)
2.892(5)
2.676(11)
1 − x, 2 − y, −z
x, y, 1 + z
residing in the cavities between the chains. The solid state structure
10
of [Fe(2)
2
][PF
6
]
2
essentially mimics that of [Ru(2)
2
][PF
6
]
2
although they are not isomorphous, since the unit cell expands
3
˚
from 1908.30(6) to 1920.8(3) A on going from the iron(II) to
ruthenium(II) complex to account for the increase in M–N bond
lengths.
X-Ray quality crystals of [Fe(3)
2
][PF
6
]
2
·2MeCN were grown by
][PF
cation (Fig. 5) lies on the special
position 4-bar inversion axis (Wyckoff letter b) of the I4 /a
slow evaporation of an aqueous MeCN solution of [Fe(3)
2
6
2
] .
2
+
The iron atom in the [Fe(3) ]
2
1
space group (origin choice 2), and the N3 · · · Fe1 · · · N3b vector is
constrained to being linear. The twisting of each pendant pyridine
◦
ring with respect to the central ring of the tpy unit is 32.9(2) .
Packing of the cations in the crystal is controlled by two factors:
p-stacking between pendant pyridine rings and face-to-face and
edge-to-face p-interactions involving the tpy domains. Fig. 6a
shows part of one infinite chain of p-stacked interactions (inter-
2
+
Fig. 3 Molecular structure of the [Fe(2)
2
]
2 6 2
cation in [Fe(2) ][PF ] with
thermal ellipsoids plotted at 40% probability level. Hydrogen atoms
are omitted. Selected bond distances and angles: Fe1–N1 = 1.982(2),
Fe1–N2 = 1.886(2), Fe1–N3 = 1.977(2), Fe1–N4 = 1.968(2), Fe1–N5 =
˚
ring separation = 3.63 A). The pendant pyridine rings on the
extremities of each chain engage in a second set of p-stacking
(Fig. 6b) with the result that the chains are interlocked into
a three-dimensional network. Fig. 6c shows a view down the
1
8
.878(2), Fe1–N6 = 1.969(2) A˚ ; N1–Fe1–N2 = 80.74(8), N2–Fe1–N3 =
◦
0.93(8), N4–Fe1–N5 = 80.87(8), N5–Fe1–N6 = 80.84(8) .
3
6,37
crystallographic c axis, illustrating {Fe(tpy)
2
} embraces
(face-
˚
to-face separation = 3.45 A and CH · · · centroid of ring containing
−
˚
N1 = 3.25 A). The [PF
6
] ions and acetonitrile solvent molecules
are disordered, and each has been modelled over two sites of equal
occupancies. Bothreside incavities between pendant pyridinerings
of adjacent molecules; three of these cavities are visible in Fig. 6b.
cation in [Fe(3)
MeCN makes it difficult to give a meaningful comparison
2
+
The high symmetry of the [Fe(3)
2
]
2
][PF
6
]
2
·
2
2
+
Fig. 5 Molecular structure of the [Fe(3)
2
2
]
cation in [Fe(3)
2
][PF
6
]
2
·
MeCN with thermal ellipsoids plotted at 40% probability level, and
Fig. 4 (a) Cations in [Fe(2)
p-stacking interactions between alternating pairs of pendant pyridine
rings. Two such interactions are shown. (b) Offset p-stacking between
2
][PF
6
]
2
assemble into chains with weak
hydrogen atoms omitted. Selected bond distances and angles: Fe1–N1 =
◦
1.983(2), Fe1–N2 = 1.882(2), N1–Fe1–N2 = 80.67(4) . Symmetry codes:
1
1
1
3
1
1
a = −x, −y + /
2
, −z + /
4
; b = −x + /
4
, y + /
4
, −z + /
4
; c = x + /
4
,
ꢀ
1
1
pairs of approximately planar 4 -(3-pyridyl)-tpy ligands.
−y + /
4
, −z + /
4
.
3
92 | Dalton Trans., 2008, 386–396
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Fig. 7 Molecular structure of one (cation A) of the crystallographically
2
+
independent [Ru(1)
2
]
cations in [Ru(1)
2
][PF
6
]
2
·4H
2
O. Thermal ellipsoids
are plotted at 40% probability level; H atoms are omitted. Selected bond
distances and angles: Ru1–N1 = 2.069(4), Ru1–N2 = 1.976(4), Ru1–N3 =
2
.064(4), Ru1–N4 2.078(4), Ru1–N5 = 1.980(4), Ru1–N6 = 2.077(4) A˚ ,
N1–Ru1–N2 = 79.04(15), N2–Ru1–N3 = 78.65(15), N4–Ru1–N5 =
◦
7
2
8.65(15), N5–Ru1–N6 = 78.97(15) . For Molecule B: Ru2–N7 =
.060(4), Ru2–N8 = 1.985(3), Ru2–N9 = 2.071(4), Ru2–N10 2.070(4),
Ru2–N11 = 1.973(4), Ru2–N12 = 2.076(4) A˚ , N7–Ru2–N8 = 79.23(14),
N8–Ru2–N9 = 78.46(15), N11–Ru2–N10 = 78.85(15), N11–Ru2–N12 =
◦
7
8.70(14) .
ble areas, indicating that the difference in complex : solvent ratios
between the iron(II) and ruthenium(II) complexes is real. Although
the packing of the cations and anions in 4{[Fe(1)
2
][PF
6
]
2
}·9H
2
O
and [Ru(1) ][PF O is extremely similar, the absence of the
2
6
]
2
·2H
2
extra water molecule in the unit cell of the ruthenium(II) complex
permits a change in the orientations of the pendant pyridine
rings and a slightly increased efficiency of cation packing. This
is apparent by the fact that, within experimental error, the unit cell
volumes of 4{[Fe(1)
2
][PF
6
]
2
}·9H
2
O and [Ru(1)
2
][PF
6
]
2
·2H
2
O are
3
3
˚
˚
the same within four esd’s (4078.3(3) A M = Fe, 4071.9(16) A
for M = Ru). In contrast, on going from [Fe(2)
2
][PF
6
]
2
and
2
+
[Ru(2) ][PF ] which are essentially isomorphous, the unit cell
Fig. 6 (a) Assembly of one chain of [Fe(3)
2
2
]
cations in [Fe(3)
2
][PF
6
]
2
·
2
6 2
MeCN and (b) interlocking of chains through p-stacking between
expands in response to the increase in M–N bond lengths on
going from Fe to Ru.
pendant pyridine rings. (c) A view down the c axis showing {Fe(tpy) }
2
embraces. Solvent molecules and anions have been omitted.
Methylation of the complexes
between the structures of the cation in this salt and in
16
¯
[
Fe(3)
2
][NO
3
]
2
·3H
2
O·MeCN. The latter crystallizes in the P1
We have previously reported the effects of protonation of the
pendant 4-pyridyl units in [M(3)
electrochemical and photophysical properties.
mono- and diprotonation of [Ru(3)
conclusion that protonation of the pendant 4-pyridyl group lowers
the energy of the lowest lying p* molecular orbitals, thereby
increasing the electron accepting ability of the complexes. The
absorption and luminescence bands of both complexes are red-
shifted to lower energy upon protonation, and protonation acts as
2
+
space group and therefore lacks the symmetry constraints imposed
on the [Fe(3)
X-Ray quality crystals of [Ru(1) ][PF ·2H O were grown by
slow evaporation of an MeCN–H O solution of [Ru(1) ][PF
The asymmetric unit contains two crystallographically indepen-
2
]
(M = Fe, Ru, Os) on their
2
+
6,7,19
2
]
cation in [Fe(3) ][PF
2
6
]
2
·2MeCN.
Studies of the
2
+
2+
2
6
]
2
2
2
]
and [Os(3)
2
]
lead to the
2
2
6
]
2
.
2
+
dent [Ru(1)
2
]
cations (labelled A, Fig. 7, and B). The bond
parameters in the coordination spheres of the ruthenium(II)
centres are similar in cations A and B, and the only significant
difference between them is the degree of twisting of the pendant
pyridine rings with respect to the tpy units to which they are
bonded. The angles between the least squares planes of the rings
containing N2 and N13, and N5 and N14 in cation A are 11.9(2)
2
+
a luminescent switch. For [Ru(3)
is increased by protonation, whereas the reverse is observed
2
] , the luminescence intensity
2
+
19
when [Os(3)
N-methylation of [Ru(3)
systematic study of the N-methylation of [Ru(1)
with a comparison of the data obtained for [Ru(3)
N-Methylation of [Ru(1) ][PF and [Ru(2)
achieved by treatment with MeI. The nitrogen atom of the pendant
pyridine unit in [M(1) ][PF is sterically more protected than
that in [M(2) ][PF , and so it is not surprising that methylation
requires harsher conditions than methylation of
2
]
is protonated. We have also investigated the
2
+ 7
2
] , and now describe the results of a
◦
2+
2+
and 32.4(3) , respectively, and between the least squares planes
2
]
and [Ru(2) ]
2
2
+
of pyridine rings containing N8 and N15, and N11 and N16 in
2
] .
][PF
◦
cation B are 3.0(2) and 13.3(3) , respectively. These twist angles
2
6
]
2
2
6
]
2
was
differ from those in the analogous iron(II) complex described
◦
◦
above (25.3(2) and 4.2(2) in cation A, and 24.8(2) and 6.8(2)
in cation B). Whereas [Fe(1) ][PF crystallizes as a 4 : 9 hydrate,
Ru(1) ][PF crystallizes as a dihydrate. A check using Platon for
voids in the [Ru(1) ][PF O did not reveal any solvent accessi-
·2H
2
6 2
]
2
6
]
2
2
]
6 2
38
2+
[
2
6
]
2
of [Ru(1) ]
2
2
+
2
6
]
2
2
[Ru(2)
2
] . In the former case, 25 h at reflux in the presence
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of >1000-fold excess of MeI resulted in a mixture of the
presence of N-methyl substituents, but rather from differences in
packing which are forced by the need to accommodate an increased
3
+
mono(methylated) derivative [Ru(1)(4)] and the bis(methylated)
4
+
−
4+
complex [Ru(4)
2
] . Longer reaction times did not result in
number of [PF
6
] ions. The two [Ru(5)
2
]
cations in the unit cell are
¯
complete methylation. In contrast, a four-fold excess of MeI and
related by the inversion centre of the P1 space group. All cations in
Fig. 9a are structurally identical, but the interactions between them
can be separated into two types. Adjacent blue and red cations
◦
3+
heating at 50 C for 15 min produced [Ru(2)(5)] , while the
4
+
formation of [Ru(5) ] required a 16-fold excess of MeI and reflux
2
conditions for 6 h. We have previously prepared [Ru(6)
2
][PF
6
]
4
in
in Fig. 9a engage in face-to-face and edge-to-face p-interactions
7
36,37
3
4% yield using [Me
3
O][BF
4
] as a methylating agent. The yield
that are typical of {M(tpy)
2
} embraces,
i.e. these involve the
can be improved slightly by using MeI under reflux conditions,
outer pyridine rings of the tpy domains of ligands 5. In contrast,
adjacent cations coloured red in Fig. 9a (and similarly, pairs of blue
cations) stack so that the tpy pyridine ring containing atom N3 lies
over, but offset from, the pendant N-methylpyridinium ring of the
adjacent cation (Fig. 9b). Although the distance from the centroid
◦
7
although the reaction fails to proceed at temperatures ≤40 C,
the boiling point of MeI. The NMR spectra of the methylated
derivatives were assigned using COSY, NOESY, HMQC and
HMBC techniques. The spectra for the homoleptic complexes
are superimpositions of the spectra of the component homoleptic
˚
of one ring to the plane containing the other is ≈3.6 A, the angle
1
◦
complexes. In the H NMR spectra, the signals affected most by
between the planes containing the rings is ≈18 , indicating that any
C4
C5
N-methylation are those for H and H with Dd values (Dd =
p-interactions are weak. Fig. 9b also shows the close proximity of
C4
C5
4+
d
methylated − dnon-methylated) of 0.66 and 0.65 ppm for H and H
the water solvent molecules tothe [Ru(5) ] cations. Short contacts
2
2
+
4+
on going from [Ru(1)
on going from [Ru(2)
2
]
to [Ru(4)
2
] , and 0.67 and 0.64 ppm
] ). The chemical shifts of
exist between each O1 atom and three C–H groups (C24H24 · · · O1
2
+
4+
◦
˚
2
]
to [Ru(5)
2
with C · · · O = 3.21(1) A, C–H · · · O = 173 , C27H27 · · · O1 with
◦
˚
the tpy protons are largely unaffected by N-methylation of the
C · · · O = 3.53(1) A, C–H · · · O = 171 , and C3H31 · · · O1i with
B3
◦
˚
pendant pyridine ring, with one exception. Proton H (Scheme 2)
C · · · O = 3.47(1) A, C–H · · · O = 169 , symmetry code i = 1 − x,
1 − y, −z).
2
+
4+
is little perturbed on going from [Ru(3)
2
]
to [Ru(6)
2
]
(d 9.07 to
7
2+
10
4+
9
.01 ppm ) and from [Ru(2)
2
]
(d 9.04 ppm ) to [Ru(5)
2
]
(d 9.04
4
+
ppm). However, methylation of [Ru(1)
H
2
]
results in the signal for
B3
shifting to lower frequency from d 9.41 ppm to d 8.95 ppm.
B3
This is presumably a shielding effect caused by the H protons
lying over the p-system of the pendant N-methylpyridinium group
which will twist so as to lie orthogonal to the plane of tpy ring
B3
B to reduce steric interactions between the Me group and H .
The signal for the N-methyl substituent (≈d 4.5 ppm) is similar
to those observed in N-methylpyridinium iodide (d 4.35 ppm) and
3
9
N-methylpyridinium tetrafluoroborate (d 4.31 ppm) in CD
3
CN.
(Fig. 8) was confirmed by single crys-
][PF O. The two
4
+
The structure of [Ru(5) ]
2
tal X-ray diffraction for the salt 2{[Ru(5)
2
6
]
4
}·H
2
ligands are crystallographically independent and each pendant N-
methylpyridinium ring is twisted out of the plane of the tpy unit to
which it is bonded. The angles between the least squares planes of
the rings containing atoms N2 and N7, and N5 and N8 are 24.3(1)
◦
◦
and 52.2(2) , respectively, compared with angles of 40.0 and 2.1
2
+ 10
for [Ru(2) ] . These differences do not arise directly from the
2
4
+
Fig. 8 Molecular structure of the [Ru(5)
2
]
cation in 2{[Ru(5)
2
][PF
6
]
4
}·
H
2
O with thermal ellipsoids plotted at 30% probability level. Hy-
4
+
drogen atoms are omitted. Selected bond distances and angles:
Fig. 9 Packing of [Ru(5)
2
]
cations in 2{[Ru(5)
2
][PF
6
]
4
}·H
2
O showing
Ru1–N1 = 2.075(2), Ru1–N2 = 1.975(2), Ru1–N3 = 2.076(2), Ru1–N4 =
(a) face-to-face and edge-to-face p-interactions between cations coloured
red and blue, and (b) a separate set of face-to-face interactions between
pairs of cations (red) related by an inversion centre. [PF
omitted for clarity.
2
.083(2), Ru1–N5 = 1.986(2), Ru1–N6 = 2.076(2), N7–C36 = 1.481(4),
N8–C42 = 1.482(4) A˚ ; N1–Ru1–N2 = 78.44(9), N2–Ru1–N3 = 79.10(9),
]
−
anions are
6
◦
N4–Ru1–N5 = 78.74(9), N5–Ru1–N6 = 78.66(9) .
3
94 | Dalton Trans., 2008, 386–396
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Electronic spectroscopy
with the consequence that the substituent is no longer conjugated
with the tpy. The competing influences of increased charge and
The complexes are all coloured and exhibit characteristic MLCT
absorptions in the visible region of the spectrum. The electronic
decreased conjugation essentially compensate resulting in a small
2+
blue shift of the MLCT band. In the case of [Ru(2) ] , the decrease
2
2
+
40–43
spectrum of [Fe(tpy)
2
]
exhibits three types of absorption.
in conjugation is expected to be less as the steric interaction with
Ligand p–p* absorptions are observed at ∼275 and 320 nm, an
MLCT band occurs at ∼560 nm and a weak and rarely reported
d–d transition occurs at ∼835 nm. The MLCT band is complex
and exhibits a shoulder corresponding to transitions to higher
energy ligand p* orbitals. The electronic spectra of the iron(II)
the tpy will be decreased and a red shift is observed. In the case of
2+
[
Ru(3) ] , there are expected to be no steric interactions between
2
the methyl group and the tpy and the significant red-shifting is a
consequence of both the increased charge and the conjugation of
the substituent and the tpy ring.
We are currently investigating the emission properties of the
ruthenium(II) complexes and will detail these results, along with
protonation studies, in a future paper.
2
+
2+
complexes [Fe(1)
the same as that of [Fe(3)
77 nm, 284–285 nm, 322–324 nm and 567–571 nm. The Hammett
r parameters for 2-, 3- and 4-pyridyl substituents of 0.71, 0.55 and
2
]
and [Fe(2)
2
+6
]
are within experimental error
exhibiting absorptions at 276–
2
2
]
2
44,45
0
.94 respectively
indicate that all the pyridyl groups are more
ꢀ
Electrochemistry
electron withdrawing than the proton at the 4 -position in the
parent tpy complexes. This is compatible with the red-shifting of
the MLCT bands which follows from a lowering of the tpy-based
p* levels in the complexes with 1–3. The broadness of the MLCT
bands makes a more detailed analysis of the relative kmax values
for the three complexes meaningless.
The ruthenium(II) complexes are of more interest as they are
luminescent and a combination of the absorption and emission
data gives direct information on the energies of the singlet and
triplet states. We have previously commented upon the difficulty
in making quantitative correlations of photophysical trends with
The electrochemical behaviour of the complexes is a subtle method
for investigating the synergic ligand metal interactions in this series
of complexes. Three influences are expected to be operative in any
given complex: (i) the metal centre present, (ii) the charge on
the complex and (iii) the substitution pattern of the ligand and
the degree of conjugation of the substituent. The electrochemical
orbitals may, with caution, be correlated with the spectroscopic
orbitals. A number of general observations may be made. In
2+
the series of [M(L)
3
2
]
complexes (M = Fe or Ru, L = 1, 2 or
), the metal(II)/metal(III) process becomes progressively more
positive. For a given ligand in the complex [ML ] the reversible
46
substituent effects in compounds of this type, but considered that
the close similarity of the species [Ru(L)
n+
2
2
+
2
]
(L = 1–6) might allow
Fe(II)/Fe(III) process is about 150 mV less positive than the
reversible Ru(II)/Ru(III) process as is also observed in the parent
meaningful comparisons to be made. Absorption spectroscopic
data are given in Table 3. Qualitatively, the absorption spectra of
n+
7
[
M(tpy)
2
] species.
2
+
2+
the complexes [Ru(1)
2
]
and [Ru(2)
2
]
are, within experimental
and exhibit absorptions
In the case of methylation, there are no ambiguities associated
2
+ 7,19
error, the same as that of [Ru(3)
2
]
with the equilibria between protonated and non-protonated
species as are observed in the studies of the parent complexes
with ligands 1–3. The methylation has two influences (Table 4).
Firstly, the overall increase in the charge of the complex is
expected to shift the ruthenium(II)/(III) process to a more positive
potential, and at the same time, shift the ligand reductions to a less
negative potential. The shift of the metal-centred process to more
positive potential is, however, extremely modest, varying between
at ∼275 nm, ∼310 nm and ∼490 nm. As expected, the latter
(
MLCT) transitions are red-shifted with respect to the absorption
2
+
7
in [Ru(tpy)
2
]
(475 nm). However, the electronic consequences
of alkylation are by no means so easy to clarify. Although the
change from 3 to 6 leads to the expected further significant red-
shifting of the MLCT band, this is not the case on changing from
1
to 4, or from 2 to 5. The spectroscopic orbitals involved in
the MLCT transition will be susceptible to two influences: the
increased positive charge on the substituent which is expected to
lower the energy, and changes in conjugation which could either
raise or lower the energy. In the case of the methylation of the
pendant 2-pyridyl substituent in [Ru(1)
N-alkyl substituent forces the ring to be near orthogonal to the tpy
2+
4+
6
0 mV on comparing [Ru(2)
2
]
with [Ru(5)
2
]
to 110 mV in the
2+
4+
case of [Ru(1)
2
]
with [Ru(4)
2
] . This insensitivity to the overall
charge is most likely a result of the pendant N-methylpyridinium
2
+
2
] , the steric bulk of the
Table 4 Redox potentials for [ML
2
][PF
6
]
2
ꢀ
(M = Fe, Ru; L = 1, 2, 3),
2 6 4 3
ꢀ
ꢀ
[
[
Ru(L)(L )][PF
6
]
3
(L = 4, 5, 6) and [Ru(L )
][PF ] in CH CN. Data for
2+
3+
4+
Ru(3)
2
2
] , [Ru(3)(6)] and [Ru(6) ] are from ref. 7. See the Experimental
Table 3 Absorption spectroscopic data for [RuL
2
][PF
in CH
are from ref. 7. Extinction
6
]
3
2
(L = 1, 2, 3),
for details of the reversibility of each process
ꢀ
ꢀ
ꢀ
2
[
Ru(L)(L )][PF
data for [Ru(3)
coefficients are given in the Experimental
6
]
2
3
(L = 4, 5, 6) and [Ru(L )
][PF
6
]
4
CN. Absorption
2+
3+
4+
] , [Ru(3)(6)] and [Ru(6)
2
]
2+
3+
M /M
Ligand reductions
2
2
2
+
+
+
[
Fe(1)
[Fe(2)2]
Fe(3)
[Ru(1)
[Ru(1)(4)]
2
]
+0.75
+0.78
+0.84
+0.90
+1.02
+1.01
+0.96
+0.98
+1.02
+0.95
+1.00
+1.03
−1.42
−1.3
—
—
—
—
—
−1.93
−1.90
−1.73
−1.93
−1.76
−1.80
−1.84
−1.56
−2.21
−2.23
−2.13
—
—
—
k
max/nm
−1.66
[
2
]
2
−1.35
−1.3
—
2
+
2+
[
[
[
[
[
[
[
[
[
Ru(1)
2
]
492
490
487
489
491
494
488
500
507
—
328
331
—
—
—
—
—
—
316
313
311
313
314
315
312
313
313
286
—
—
—
—
—
—
—
—
277
278
277
278
278
277
273
275
276
—
—
—
—
—
238
238
240
240
]
—
—
3+
3+
3+
3+
3+
3+
Ru(1)(4)]
−1.32
−1.34
−1.25
−1.32
−1.19
—
4
+
+
4+
Ru(4)
Ru(2)
2
]
]
[Ru(4)
[Ru(2)
2
]
]
−1.61
2
2+
2
2
—
—
—
Ru(2)(5)]
[Ru(2)(5)]
—
4
+
+
4+
Ru(5)
Ru(3)
2
]
]
[Ru(5)
[Ru(3)
2
]
]
−1.58
−1.54
−1.50
−1.16
−2.12
2
2+
2
2
—
Ru(3)(6)]
[Ru(3)(6)]
−1.09
—
−1.79
4+
4+
Ru(6)
2
]
[Ru(6)
2
]
−1.06
This journal is © The Royal Society of Chemistry 2008
Dalton Trans., 2008, 386–396 | 395

View Article Online
ring being orthogonal to the tpy plane and there being no
conjugation between the metal centre and the substituent. The
ligand reductions in the complexes are more difficult to rationalise
and we will discuss them in no further detail at this point.
11 E. C. Constable, C. E. Housecroft, M. Neuburger, S. Schaffner and F.
Schaper, Inorg. Chem. Commun., 2006, 9, 616.
2 J. E. Beves, E. C. Constable, C. E. Housecroft, C. J. Kepert and D. J.
1
Price, CrystEngComm, 2007, 9, 456.
13 J. E. Beves, E. C. Constable, C. E. Housecroft, M. Neuburger and S.
Schaffner, CrystEngComm, 2007, DOI: 10.1039/b713001e.
1
1
1
4 J. E. Beves, E. C. Constable, C. E. Housecroft, C. J. Kepert, M.
Neuburger, D. J. Price and S. Schaffner, CrystEngComm, 2007, 9, 1073.
5 E. C. Constable, E. L. Dunphy, C. E. Housecroft, M. Neuburger, S.
Schaffner, F. Schaper and S. R. Batten, Dalton Trans., 2007, 4323.
6 E. C. Constable, C. E. Housecroft, M. Neuburger, D. Phillips, P. R.
Raithby, E. Schofield, E. Sparr, D. A. Tocher, M. Zehnder and Y.
Zimmermann, J. Chem. Soc., Dalton Trans., 2000, 2219.
Conclusions
We have carried out a detailed study of the structural and spec-
troscopic trends among the iron(II) and ruthenium(II) complexes
2
+
2+
2+
[
3
M(1)
2
] , [M(2)
2
]
and [M(3)
2
]
in which ligands 1, 2 and
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀꢀ
are 4 -(2-pyridyl)-, 4 -(3-pyridyl)- and 4 -(4-pyridyl)-2,2 :6 ,2 -
17 J. Paul, S. Spey, H. Adams and J. A. Thomas, Inorg. Chim. Acta, 2004,
357, 2827.
2
+
terpyridine, respectively. From the methylation of [Ru(1) ] ,
2
1
1
8 E. C. Constable, Coord. Chem. Rev., 2007, in press.
9 E. C. Constable, C. E. Housecroft, A. Cargill Thompson, P. Passaniti,
S. Silvi, M. Maestri and A. Credi, Inorg. Chim. Acta, 2007, 360, 1102.
2
+
2+
[
Ru(2)
2
]
and [Ru(3) ] , both mono- and bis-N-methylated
2
derivatives can be isolated. Whereas, N-methylation results in
2
+
20 H. Feng, X.-P. Zhou, T. Wu, D. Li, Y.-G. Yin and S. W. Ng, Inorg.
Chim. Acta, 2006, 359, 4027.
a red shift in the absorption spectra on going from [Ru(3) ]
2
2
+
2+
to [Ru(3)(6)] and [Ru(6) ] , the effect is less significant for
2
2
1 K. J. Arm, W. Leslie and J. A. G. Williams, Inorg. Chim. Acta, 2006,
59, 1222.
22 W. Goodall and J. A. G. Williams, J. Chem. Soc., Dalton Trans., 2000,
893.
complexes involving ligands with the 3-pyridyl substituent, and
for the 3-pyridyl substituent, a slight blue shift is observed. This
is consistent with changes in the relative orientations of the tpy
and pendant N-pyridinium rings leading to decreased conjugation
as the position of N-substitution moves closer to the tpy unit.
While the overall increase in charge of the complex upon N-
3
2
2
3 C. M. Ollagnier, D. Nolan, C. M. Fitchett and S. M. Draper, Inorg.
Chem. Commun., 2007, 10, 1045.
24 J. Wang and G. S. Hanan, Synlett, 2005, 1251.
25 C. B. Smith, C. L. Raston and A. N. Sobolev, Green Chem., 2005, 7,
2
+
2+
2+
650.
methylation of [Ru(1)
2
] , [Ru(2)
2
]
or [Ru(3)
2
]
is expected to
2
2
6 COLLECT Software, Nonius BV, 1997–2001.
shift the ruthenium(II)/(III) oxidation process to a more positive
potential, we observe little change. We attribute this to the pendant
N-methylpyridinium ring being orthogonal to the tpy plane and
resulting in little or no conjugation between the metal centre and
the substituent.
7 A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M. C.
Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27,
4
35.
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8 Z. Otwinowski and W. Minor, Methods in Enzymology, ed. C. W. Carter,
Jr and R. M. Sweet, Academic Press, New York, USA, 1997, vol. 276,
p. 307.
9 P. W. Betteridge, J. R. Carruthers, R. I. Cooper, K. Prout and D. J.
Watkin, J. Appl. Crystallogr., 2003, 36, 1487.
Acknowledgements
30 Bruker Analytical X-ray Instruments Inc., Madison, WI, USA.
3
1 G. M. Sheldrick, SHELX97, Programs for Crystal Structure Analysis,
University of G o¨ ttingen, Instit u¨ t f u¨ r Anorganische Chemie der Uni-
versit a¨ t, Tammanstrasse 4, D-3400 G o¨ ttingen, Germany, 1998.
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Schnalke and J. Curtze, Angew. Chem., 1962, 74, 811.
We thank the Swiss National Science Foundation, the University
of Basel and the Australian Research Council for financial
support.
3
3
3 L.-X. Zhao, Y.-S. Moon, A. Basnet, E.-K. Kim, Y. Jahng, J. G. Park,
T. C. Jeong, W.-J. Cho, S.-U. Choi, C. O. Lee, S.-Y. Lee, C. S. Lee and
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96 | Dalton Trans., 2008, 386–396
This journal is © The Royal Society of Chemistry 2008