Complexes of ruthenium(III) and chromium(III) with a new tetradentate N2O2-donor ligand: Crystal structures, redox properties and spectroelectrochemistry

Article abstract of DOI:10.1016/S0277-5387(01)00938-X

Reaction of 3-(2-methoxyphenyl)pyrazole with 1,2- bis(bromomethyl) benzene under phase-transfer conditions, followed by demethylation of the methoxyphenyl units with BBr₃, affords the new ligand H₂L in which two bidentate chelating units (pyrazolyl -phenol) are separated by a o-xylyl spacer. Reaction of H₂L with [M(acac)₃] (M = Cr, Ru) afforded in each case two mononuclear products [M(L)(acac)] and [M(L)(HL)]. Crystal structure determinations of [M(L)(acac)] for both M = Cr and Ru show that the complexes have similar structures, with the ligand L^2- folded such that it coordinates as a tetradentate chelate in a cis-N₂, cis-O2 manner with the remaining two coordination sites at the metal occupied by the acac ligand. Neither complex [M(L)(HL)] formed X-ray quality crystals but we assume a similar mononuclear structure in which one L^2- is coordinated as a tetradentate chelate, and the second (HL)^- is coordinated via one bidentate N,O-binding site with the second site pendant and remaining protonated. [Ru(L)(acac)] undergoes reversible oxidation to Ru(IV) and an irreversible reduction to Ru(II); in contrast, for [Ru(L)(HL)] the Ru(III)-Ru(IV) and Ru(II)-Ru(III) couples are both reversible. A UV-Vis-NIR spectroelectrochemical study of [Ru(L)(HL)] was accordingly carried out, and shows that in the Ru(IV) state the spectrum develops intense, low-energy charge-transfer transitions in the near-IR region.

Full text of DOI:10.1016/S0277-5387(01)00938-X

Polyhedron 20 (2001) 3231–3237
www.elsevier.com/locate/poly
Complexes of ruthenium(III) and chromium(III) with a new
tetradentate N2O2-donor ligand: crystal structures, redox properties
and spectroelectrochemistry
Guido D. Frey, Zo¨e R. Bell, John C. Jeffery, Michael D. Ward *
School of Chemistry, Uni6ersity of Bristol, Cantock’s Close, Bristol BS8 1TS, UK
Received 16 July 2001; accepted 10 September 2001
Abstract
Reaction of 3-(2-methoxyphenyl)pyrazole with 1,2-bis(bromomethyl)benzene under phase-transfer conditions, followed by
demethylation of the methoxyphenyl units with BBr3, affords the new ligand H2L in which two bidentate chelating units
(pyrazolyl–phenol) are separated by a o-xylyl spacer. Reaction of H2L with [M(acac)3] (M=Cr, Ru) afforded in each case two
mononuclear products [M(L)(acac)] and [M(L)(HL)]. Crystal structure determinations of [M(L)(acac)] for both M=Cr and Ru
show that the complexes have similar structures, with the ligand L2− folded such that it coordinates as a tetradentate chelate in
a cis-N2,cis-O2 manner with the remaining two coordination sites at the metal occupied by the acac ligand. Neither complex
[M(L)(HL)] formed X-ray quality crystals but we assume a similar mononuclear structure in which one L2− is coordinated as a
tetradentate chelate, and the second (HL)− is coordinated via one bidentate N,O-binding site with the second site pendant and
remaining protonated. [Ru(L)(acac)] undergoes reversible oxidation to Ru(IV) and an irreversible reduction to Ru(II); in contrast,
for [Ru(L)(HL)] the Ru(III)–Ru(IV) and Ru(II)–Ru(III) couples are both reversible. A UV–Vis–NIR spectroelectrochemical
study of [Ru(L)(HL)] was accordingly carried out, and shows that in the Ru(IV) state the spectrum develops intense, low-energy
charge-transfer transitions in the near-IR region. © 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Tetradentate chelate; Pyrazolyl–phenol; Ligands; Spectroelectrochemical
1. Introduction
We have recently investigated the coordination be-
haviour of ligand L1 (Scheme 1) which contains two
pyrazolyl–pyridine termini separated by an o-xylyl
spacer, and found that this ligand can bridge two metal
ions to result in either dinuclear helicates [with Cu(I)]
Ligands containing two bidentate compartment sepa-
rated by a spacer group have been extensively used in
self-assembly recently [1]. In particular, formation of
dinuclear triple helicates with stoichiometry M2L3 [2],
and edge-bridged tetrahedral cages of stoichiometry
M4L6 [3,4], arise from reaction of these ligands (having
four donor atoms) with labile metal ions having a
preference for octahedral geometry, such that a ratio of
1.5 ligands for each metal ion is required to satisfy both
the coordination preference of each metal ion and the
tendency of a polydentate ligand to use all of its donor
atoms.
* Corresponding author. Tel.: +44-117-928-7655; fax: +44-117-
929-1295.
E-mail address: mike.ward@bristol.ac.uk (M.D. Ward).
Scheme 1.
0277-5387/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0277-5387(01)00938-X

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G.D. Frey et al. / Polyhedron 20 (2001) 3231–3237
ods (see Section 3) it gave X-ray quality crystals from
CH2Cl2ꢀEt2O and the crystal structure is shown in Fig.
1. The steric bulk of the methoxy group results in a
substantial twist between the pyrazolyl and adjacent
methoxyphenyl rings (torsion angles of 31 and 47°).
Deprotection of Me2L with BBr3 afforded H2L in 89%
1
yield; in its H NMR spectrum a broad singlet at 10.64
ppm is characteristic of the phenol protons which each
form an OꢀH···N hydrogen-bonding interaction with
the adjacent pyrazolyl ring, as we have observed with a
variety of pyridine–phenol chelating ligands [7].
Fig. 1. Crystal structure of Me2L1.
2.2. Preparation and characterisation of complexes with
Cr(III) and Ru(III)
[5] or tetrahedral cages [with Co(II)] [4]. However, it is
also capable of coordination to a single metal ion as a
tetradentate chelate, giving simpler mononuclear com-
plexes [5], and in the dinuclear complex [{(L1)Ni} (m-
L1){Ni(L1)]4+ both terminal (tetradentate) and
bridging (bis-bidentate) coordination modes were ob-
served [4].
In seeking to extend our studies on potentially bridg-
ing ligands of this type we wished to prepare a ligand
having a similar architecture but a different donor set.
To that end we report in this paper the synthesis and
some coordination chemistry with the new ligand H2L
(Scheme 1) which contains two potentially N,O-chelat-
ing sites, based on pyrazolyl–phenolate units, linked by
an o-xylyl spacer. The harder donor set of these ligands
compared to L1 is expected to result in stabilisation of
metal complexes in higher oxidation states, and we
describe our initial studies of the coordination be-
haviour of H2L with Cr(III) and Ru(III).
Complexes with Cr(III) and Ru(III) were prepared
by reaction of H2L with the appropriate [MIII(acac)3] in
a 3:2 stoichiometry, in ethylene glycol at higher temper-
atures. Under these conditions the acidic protons of the
phenol donors protonate the anionic acac ligands to
form neutral Hacac which evaporates from the reaction
mixture [8].
The reaction with [Cr(acac)3] afforded a clear, dark
green solution. TLC examination revealed the presence
of two principal products and several trace products.
Extraction of the reaction mixture with CH2Cl2 and
purification by column chromatography allowed isola-
tion of the two main products, one in much higher yield
than the other. On the basis of their electron-impact
mass spectra these were readily identified as the
mononuclear complexes [Cr(L)(acac)] (major product)
and [Cr(L)(HL)] (minor product). Assuming the usual
octahedral coordination, the former of these must have
L2− coordinated as a tetradentate chelate, whereas the
latter will have one tetradentate chelating ligand L2−
and one ‘hypodentate’ (HL)− which is acting as only a
bidentate, mono-anionic ligand through one bidentate
binding site with the other bidentate site pendant.
[Cr(L)(acac)] formed X-ray quality crystals by slow
evaporation of a CH2Cl2 solution, and the structure is
shown in Fig. 2. The ligand L2− is folded such that it
coordinates as a tetradentate chelate in a cis-N2,cis-O2
manner with the remaining two coordination sites occu-
pied by the acac ligand. The pyrazolyl–phenolate units
form six-membered chelate rings with the Cr(III) cen-
tre, with torsion angles of 21° between rings 1 and 2,
and 19° between rings 3 and 4 [where ring 1 contains
atoms N(11)ꢀC(15), and so on]. The bond distances are
unremarkable.
2. Results and discussion
2.1. Ligand synthesis
The synthesis of the new ligand H2L follows the
general method used to prepare L1, viz. preparation of
a
pyrazole with a suitable substituent (here, 2-
methoxyphenyl) attached, followed by reaction of 2
equiv. of the pyrazole with 1,2-bis(bromomethyl)-
benzene under phase-transfer conditions [5]. The only
variation required in this method for its use in the
synthesis of H2L is that the phenols are protected as
their methyl ethers during synthesis of the backbone,
and then deprotection at the end with BBr3 liberates the
two pyrazolyl–phenol sites. The appropriate 3-(2-
methoxyphenyl)pyrazole has been described by us be-
fore, when it was used to make a tris(pyrazolyl)borate
[6], and reaction of this with 1,2-bis(bromomethyl)-
benzene afforded the protected precursor Me2L in 55%
yield. In addition to characterisation by standard meth-
Reaction of H2L with [Ru(acac)3] in a similar way
afforded a dark blue solution from which two products
were isolated after chromatographic purification. These
were identified by mass spectrometry and elemental
analysis as [Ru(L)(acac)] (major product) and
[Ru(L)(HL)] (minor product). The crystal structure of
[Ru(L)(acac)] is shown in Fig. 3; it is very similar to the

G.D. Frey et al. / Polyhedron 20 (2001) 3231–3237
3233
ture could form in each case even if the initially-formed
complex was not ideal. In these Ru(III) and Cr(III)
complexes however, initial formation of a complex in
which 1 equiv. of L2− is acting as a tetradentate chelate
effectively prevents formation of higher nuclearity cage
structures. The largest structures that are likely to form
in significant amounts under these conditions are there-
fore the dinuclear complexes [LMIII(m-L)MIIIL], and it
is clear that [Cr(L)(HL)] and [Ru(L)(HL)] are ‘en route’
to this and would form such complexes by reaction of
the pendant bidentate site with a second equivalent of
[ML(acac)] (M=Cr, Ru respectively). However, no
significant amounts of such dinuclear complexes could
be detected.
Interestingly, the residue left at the top of the column
after chromatographic separation of [Ru(L)(HL)] and
[Ru(L)(acac)] was examined by FAB mass spectrometry
and revealed the presence of higher oligomers: weak
peaks at m/z 2506 and 1984 can be assigned as {Ru4L5}
and {Ru3L4} species respectively, suggesting that for-
mation of cages with stoichiometry {Ru4L6} might be
accessible under sufficiently forcing conditions. How-
ever, these fractions were present in only tiny amounts
and could not be separated chromatographically.
Cr(III) analogue described above, with torsion angles
of 25 and 22° within each bidentate pyrazolyl–pheno-
late unit [involving rings 1/2 and 3/4 respectively, fol-
lowing the notation used for the Cr(III) analogue].
Again, L2− is folded and acting as a tetradentate
chelate with a cis-N2,cis-O2 coordination mode, and
unremarkable bond distances which are all slightly
longer in the Ru(III) complex than in the Cr(III)
complex.
It is presumably the kinetic inertness of these metal
ions that prevents formation of higher oligomers such
as the tetrahedral (metal)4(ligand)6 cages that we ob-
served with ligand L1. As mentioned earlier, the pyri-
dine-based ligand L1 can adopt either bridging or
terminal binding modes [4,5], but since the metal ions
to which it was coordinated [e.g. Ni(II), Co(II), Cu(I)]
were labile, the most thermodynamically stable struc-
2.3. Redox and spectroscopic properties
The Cr(III) complexes showed no significant redox
behaviour, with only irreversible processes at extreme
negative potentials. This is not surprising: the redox
chemistry of Cr(III) complexes is often associated with
ligand-centred processes, as in the three reductions of
[Cr(bipy)3]3+ [9], or with Cr(III)–Cr(II) couples if the
donor set will stabilise the Co(II) state. In these com-
plexes however, there are no reducible ligands and a
hard donor set.
Both Ru(III) complexes however are redox active
(Fig. 4). [Ru(L)(acac)] in CH2Cl2 shows a reversible
Ru(III)–Ru(IV) couple at +0.20 V versus Fc/Fc+, and
an irreversible process which we assume to be a
Ru(II)–Ru(III) couple at approximately −1.4 V versus
Fc/Fc+. In contrast, for [Ru(L)(HL)] both Ru(III)–
Ru(IV) and Ru(II)–Ru(III) couples are fully reversible,
and occur at +0.14 and −1.47 V, respectively versus
Fc/Fc+. Despite the difference in donor sets—N2O4 for
[Ru(L)(acac)] and N3O3 for [Ru(L)(HL)]—the poten-
tials for reversible oxidation to Ru(IV) are very similar.
The value of +0.14 V versus Fc/Fc+ for this redox
process in [Ru(L)(HL)] is also identical to that of
[RuIII(no)3] [Hno=2-(2-hydroxyphenyl)pyridine] which
has a (pyridine)3(phenolate)3 donor set [8a].
Fig. 2. Crystal structure of [Cr(L)(acac)].
Because of the reversibility of both Ru(III)–Ru(IV)
and Ru(II)–Ru(III) processes of [Ru(L)(HL)] we car-
ried out a UV–Vis–NIR spectroelectrochemical study
(CH2Cl2, −30 °C) to determine the electronic spectra
in all three accessible oxidation states; the results are in
Fig. 3. Crystal structure of [Ru(L)(acac)].

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G.D. Frey et al. / Polyhedron 20 (2001) 3231–3237
known Ru(II) complexes with pyridine-based ligands
[10].
On oxidation of the metal to the Ru(IV) state, the
phenolate“Ru(III) LMCT at 575 nm is replaced by a
series of intense lower-energy transitions: the most in-
tense is at 860 nm, and lower-intensity bands are visible
at approximately 1100 and 1550 nm. We assign the
intense 860 nm transition to a phenolate“Ru(IV)
LMCT process. Compared to the Ru(III) complex, this
transition is more intense as the metal is more electron-
deficient, and is red-shifted because the metal d(p)
manifold will be lowered in energy on oxidation. Ex-
actly similar behaviour is seen in e.g. a series of
oxoꢀMo(V) complexes with phenolate ligands, in which
oxidation to Mo(VI) results in the phenolate“Mo
LMCT process being increased in intensity and lowered
in energy for the same reasons [11]. The nature of the
two lower-energy transitions is less obvious. They could
have pyrazolyl“Ru(IV) LMCT character, or could
arise because the d(p) orbital set is not degenerate; with
a low-spin d4 configuration there are two holes in the
d(p) orbital set such that for each donor atom two
LMCT transitions at different energies are possible.
Whatever their exact assignment however, it is appar-
ent that these intense, low-energy transitions—which
span much of the near-IR region—are relevant to our
current work on near-IR electrochromic dyes [11,12].
Materials which can be switched electrochemically be-
tween transparent and strongly absorbing in this region
of the spectrum are of possible technological interest
for at least two reasons: (i) they could be used in ‘smart
windows’ to filter out the part of the solar spectrum
which is felt as heat; and (ii) they could be used for
switching data transmission along silica fibre-optic ca-
bles which operate in the near-IR region [13]. To date
we have concentrated on systems based on ruthenium-
dioxolene [12] and tris(pyrazolyl)borato-oxoꢀMo(V)
chromophores [11] which show strong, low-energy
charge-transfer transitions in some oxidation states but
not others. This new work indicates that charge-trans-
fer transitions in simple Ru(IV) complexes are also
worth further study in this respect.
Fig. 4. Cyclic voltammograms of (a) [Ru(L)(acac)]; and (b)
[Ru(L)(HL)] in CH2Cl2 at a Pt-bead electrode (scan rate, 0.2 V s−1).
Fig. 5. Results of the spectroelectrochemical study on [Ru(L)(HL)]
(CH2Cl2, 243 K). (a) Spectra recorded during reduction of Ru(III) to
Ru(II); (b) spectra recorded during oxidation of Ru(III) to Ru(IV). In
(b), the discontinuity (*) at 860 nm arises from the detector change.
3. Experimental
3.1. General details
Fig. 5. In the starting Ru(III) state the lowest-energy
feature, at 575 nm, may be assigned as phenolate“
Ru(III) ligand-to-metal charge-transfer (LMCT) by
analogy with related complexes [8]. On reduction to the
Ru(II) state, this LMCT transition collapses and is
replaced by a transition at higher energy (440 nm)
which we tentatively ascribe to a Ru(II)“pyrazolyl(p*)
MLCT process, by analogy with the much more well-
3-(2-Methoxyphenyl)pyrazole was prepared accord-
ing to the previously described route [6]. Other starting
materials and reagents were obtained from the usual
commercial sources (Aldrich, Avocado, Lancaster) and
used as received. The following instruments were used
for routine spectroscopic analyses: H NMR spectra, a
JEOL Lambda 300 MHz spectrometer; EI and FAB
mass spectra, a VG-Autospec instrument; X-band EPR
1

G.D. Frey et al. / Polyhedron 20 (2001) 3231–3237
3235
spectra, a Bruker ESP-300E spectrometer. Instrumenta-
tion used for electrochemical measurements, and for the
spectroelectrochemical study with an OTTLE cell, has
been described before [14].
dried over MgSO4, and evaporated to dryness. Purifica-
tion by column chromatography (silica, CH2Cl2) af-
forded pure H2L as a white solid (1.62 g, 89%). EIMS:
1
m/z 422 [M+], 262. H NMR (300 MHz, CDCl3): l
10.62 (2H, br s; OH), 7.54 (2H, dd, J=7.7, 1.5 Hz;
hydroxyphenyl H3), 7.36 (2H, m; phenyl), 7.32 (2H, d,
J=2.6 Hz; pyrazolyl H5), 7.17–7.23 (4H, m; hydrox-
yphenyl H5, and phenyl), 7.00 (2H, dd, J=8.0, 1.0 Hz;
hydroxyphenyl H6), 6.90 (2H, td, J=7.4, 1.3; hydrox-
yphenyl H4), 6.62 (2H, d, J=2.5 Hz; pyrazolyl H4),
5.33 (4H, s; CH2). Anal. Found: C, 73.7; H, 5.4; N,
13.1. Calc. C, 73.9; H, 5.2; N, 13.3%.
3.2. Synthesis of H2L
A two-phase mixture of 3-(2-methoxyphenyl)pyrazole
(3.13 g, 18 mmol), 1,2-bis-(bromomethyl)benzene (2.25
g, 8.5 mmol), toluene (150 cm3) Bu4NOH (25 drops of
n
40% aqueous solution) and aqueous NaOH (10 molar
concentration, 35 cm3) was heated to 85 °C and stirred
vigorously at this temperature for 24 h. After cooling,
the yellow–orange organic phase was separated,
washed with water, and dried over MgSO4. Filtration
and removal of the solvent afforded a brown solid.
Purification by column chromatography (silica,
CH2Cl2) afforded pure Me2L as a white solid (2.22 g,
55%). EIMS: m/z 450 (M+), 276 {M+−[3-(2-
methoxyphenyl)pyrazole]}. 1H NMR (300 MHz,
CDCl3): l 7.96 (2H, dd, J=7.6, 1.9 Hz; anisyl H3),
7.27–7.31 (6H, m; anisyl H5, phenyl, and pyrazolyl H5),
7.15 (2H, m; phenyl), 6.91–7.03 (4H, m; anisyl H4 and
H6), 6.79 (2H, d, J=2.7 Hz; pyrazolyl H4), 5.46 (4H, s;
CH2), 3.89 (6H, s; OMe). Anal. Found: C, 74.6; H, 5.7;
N, 12.2. Calc. C, 74.7; H, 5.8; N, 12.4%.
Deprotection of Me2L was carried out as follows. To
a solution of Me2L (1.94 g, 4.3 mmol) in dry CH2Cl2
(30 cm3) under N2 was added BBr3 (10.8 g, 4 cm3, 10
equiv.) and the mixture was stirred at 30 °C for 5 h.
After this period, aqueous NaOH (pH 9) was carefully
added dropwise to afford a white precipitate and a
yellow aqueous phase. This mixture was extracted with
several portions of CH2Cl2, which were combined,
3.3. Syntheses of complexes
A mixture of H2L and [M(acac)3] (M=Cr, Ru; 0.67
equiv. with respect to H2L) in ethylene glycol was
heated to 170 °C (M=Cr) or 140 °C (M=Ru) whilst
bubbling a stream of N2 slowly through the mixture;
this was maintained for 6 h. For M=Cr the reaction
mixture became dark green after 20 min; for M=Ru a
dark blue-violet colour was observed. After allowing
the reaction mixture to cool to room temperature (r.t.),
excess water was added and the mixture was extracted
with several portions of CH2Cl2 which were combined,
dried (MgSO4) and evaporated to dryness. Purification
by column chromatography (silica, CH2Cl2 containing
1–1.5% added MeOH) afforded two main products in
each case whose characterisation data are as follows.
[Cr(L)(acac)] (dark green): EIMS: m/z 571 (80%,
M+), 472 (100%, M+−acac). Found: C, 53.7; H, 4.3;
N, 7.2. Calc. for [Cr(L)(acac)]·2CH2Cl2: C, 53.4; H, 4.3;
N, 7.6%.
Table 1
Crystallographic data for the three crystal structures
Compound
Me2L
[Cr(L)(acac)]·2CH2Cl2
[Ru(L)(acac)]·CH2Cl2
Chemical formula
Formula weight
C28H26N4O2
450.53
C33H31Cl4CrN4O4
741.42
C31H29Cl2N4O4Ru
705.56
System, space group
monoclinic, P21/n
7.9949(19)
12.330(3)
23.989(6)
91.37(3)
2364.2(10)
4
1.266
monoclinic, P21/c
8.853(4)
15.325(7)
24.741(8)
90.07(2)
3357(2)
4
1.467
0.703
0.3×0.2×0.2
21199, 7651, 0.0496
7651, 0, 415
0.0474, 0.1277
+0.625, −0.578
monoclinic, P21/c
10.392(5)
13.312(6)
21.454(8)
90.38(4)
2968(2)
4
1.579
0.753
0.5×0.2×0.05
12032, 5997, 0.0776
5997, 0, 390
0.0471, 0.0970
+0.464, −0.542
,
a (A)
,
b (A)
,
c (A)
i(°)
V (A )
3
,
Z
Dcalc (Mg m−3
)
v (Mo Ka) (mm−1
)
0.081
Crystal size (mm)
0.4×0.3×0.2
12557, 4156, 0.0307
4156, 0, 317
0.0423, 0.1145
+0.204, −0.258
Reflections collected: total, independent, Rint
Data, restraints, parameters
a,b
Final R1, wR2
−3
,
Largest residuals (e A
)
a Structure was refined on Fo2 using all data; the value of R1 is given for comparison with older refinements based on Fo with a typical threshold
of F]4|(F).
b wR2=[ꢀ[w(Fo2−Fc2)2]/ꢀ[w(Fo2)2]1/2 where w−1=[|2(Fo2)+(aP)2+bP] and P=[max(Fo2,0)+2Fc2]/3.

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G.D. Frey et al. / Polyhedron 20 (2001) 3231–3237
Table 2
collected in Table 2. None of the structural determina-
tions presented any significant problems.
,
Selected inter-atomic lengths (A) and angles (°) for [Cr(L)(acac)]·
2CH2Cl2 and Ru(L)(acac)]·CH2Cl2
Bond lengths
4. Supplementary data
Cr(1)ꢀO(42)
Cr(1)ꢀO(22)
Cr(1)ꢀO(62)
Cr(1)ꢀO(64)
Cr(1)ꢀN(31)
Cr(1)ꢀN(11)
1.921(2)
1.931(2)
1.963(2)
1.964(2)
2.087(2)
2.100(2)
Ru(1)ꢀO(42)
Ru(1)ꢀO(22)
Ru(1)ꢀO(64)
Ru(1)ꢀO(62)
Ru(1)ꢀN(11)
Ru(1)ꢀN(31)
1.983(3)
2.008(3)
2.015(3)
2.028(3)
2.061(4)
2.077(4)
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC No. 167121–167123. Copies of
this information may be obtained free of charge from
The Director, CCDC, 12 Union Road, Cambridge,
CB2 1EZ, UK (fax: +44-1223-336033; email: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Bond angles
O(42)ꢀCr(1)ꢀO(22)
O(42)ꢀCr(1)ꢀO(62)
91.30(9) O(42)ꢀRu(1)ꢀO(22)
92.19(9) O(42)ꢀRu(1)ꢀO(64)
93.58(14)
84.20(14)
88.05(14)
89.39(14)
O(22)ꢀCr(1)ꢀO(62) 176.50(8) O(22)ꢀRu(1)ꢀO(64)
O(42)ꢀCr(1)ꢀO(64)
O(22)ꢀCr(1)ꢀO(64)
O(62)ꢀCr(1)ꢀO(64)
O(42)ꢀCr(1)ꢀN(31)
O(22)ꢀCr(1)ꢀN(31)
O(62)ꢀCr(1)ꢀN(31)
O(64)ꢀCr(1)ꢀN(31) 172.05(9) O(62)ꢀRu(1)ꢀN(11)
O(42)ꢀCr(1)ꢀN(11) 173.65(9) O(42)ꢀRu(1)ꢀN(31)
O(22)ꢀCr(1)ꢀN(11)
O(62)ꢀCr(1)ꢀN(11)
O(64)ꢀCr(1)ꢀN(11)
N(31)ꢀCr(1)ꢀN(11)
91.36(8) O(42)ꢀRu(1)ꢀO(62)
90.31(9) O(22)ꢀRu(1)ꢀO(62) 176.71(14)
89.30(9) O(64)ꢀRu(1)ꢀO(62) 93.66(13)
84.77(9) O(42)ꢀRu(1)ꢀN(11) 171.19(14)
96.71(9) O(22)ꢀRu(1)ꢀN(11)
83.92(9) O(64)ꢀRu(1)ꢀN(11)
Acknowledgements
83.71(16)
87.33(14)
93.56(16)
86.96(15)
94.31(15)
We thank the EPSRC for financial support (Z.R.B),
the European Union for an ERASMUS scholarship
(G.D.F), and Dr John P. Maher for recording the EPR
spectra.
83.14(9) O(22)ꢀRu(1)ꢀN(31)
93.36(9) O(64)ꢀRu(1)ꢀN(31) 170.97(15)
85.63(9) O(62)ꢀRu(1)ꢀN(31) 84.43(15)
98.88(9) N(11)ꢀRu(1)ꢀN(31) 101.58(16)
References
[1] (a) B.J. Holliday, C.A. Mirkin, Angew Chem., Int. Ed. Engl. 40
(2001) 2023;
(b) D. Philp, J.F. Stoddart, Angew. Chem., Int. Ed. Engl. 35
(1996) 1155;
(c) C. Piguet, G. Bernardinelli, G. Hopfgartner, Chem. Rev. 97
(1997) 2005.
[Cr(L)(HL)] (grass green): FABMS: m/z 894 (100%,
M+), 916 (80%, M+Na+). Found: C, 67.6; H, 5.0; N,
12.0. Calc. for [Cr(L)(HL)]·0.5CH2Cl2: C, 67.3; H, 4.5;
N, 12.0%.
[Ru(L)(acac)] (blue-green): EIMS: m/z 621 (100%,
M+), 521 (10%, M+−acac). Found: C, 54.9; H, 4.4;
N, 7.3. Calc. for [Ru(L)(acac)]·CH2Cl2: C, 54.4; H, 4.3;
N, 7.9%. EPR (CH2Cl2–thf glass, 105 K): g1=2.413
(positive-going signal), g2=2.106 (inflexion), g3=1.818
(negative-going signal).
[Ru(L)(HL)] (blue-violet): FABMS: m/z 943 (100%,
M+), 966 (15%, M+Na+). Found: C, 64.0; H, 4.8; N,
11.0. Calc. for [Ru(L)(HL)]·0.5CH2Cl2: C, 64.0; H, 4.3;
N, 11.4%. EPR (CH2Cl2–thf glass, 105 K): g1=2.291
(positive-going signal), g2=2.161 (inflexion), g3=1.862
(negative-going signal).
[2] (a) M. Albrecht, O. Blau, R. Fro¨hlich, Chem. Eur. J. 5 (1999) 48;
(b) J. Xu, T.N. Parac, K.N. Raymond, Angew. Chem., Int. Ed.
Engl. 38 (1999) 2878;
(c) M. Albrecht, M. Schneider, H. Ro¨ttele, Angew. Chem., Int.
Ed. Engl. 38 (1999) 557;
(d) N. Fatin-Rouge, S. Blanc, E. Leize, A. van Dorsselaer, P.
Baret, J.-L. Pierre, A.-M. Albrecht-Gary, Inorg. Chem. 39 (2000)
5771;
(e) H. Cheng, D. Chun-ying, F. Chen-jie, M. Qing-jan, J. Chem.
Soc., Dalton Trans. (2000) 2419;
(f) M. Albrecht, Chem. Eur. J. 6 (2000) 3485;
(g) C.R. Rice, S. Wo¨rl, J.C. Jeffery, R.L. Paul, M.D. Ward, J.
Chem. Soc., Dalton Trans. (2001) 550.
[3] (a) R.W. Saalfrank, N. Lo¨w, F. Hampel, H.-D. Stachel, Angew.
Chem., Int. Ed. Engl. 35 (1996) 2209;
(b) T. Beissel, R.E. Powers, K.N. Raymond, Angew. Chem., Int.
Ed. Engl. 35 (1996) 1084;
(c) T. Beissel, R.E. Powers, T.N. Parac, K.N. Raymond, J. Am.
Chem. Soc. 121 (1999) 4200;
3.4. X-ray crystallography
Suitable crystals were quickly transferred from the
mother liquor to a stream of cold N2 (173 K) on a
Siemens SMART diffractometer fitted with a CCD-type
area detector. In all cases a full sphere of data was
collected at 173 K using graphite-monochromatised Mo
Ka radiation. Empirical absorption corrections were
applied using SADABS [15], and structure solution and
refinement was performed with the SHELX suite of
programs [16]. Table 1 contains a summary of the
crystal parameters, data collection and refinement de-
tails; selected bond distances for the structures are
(d) M. Scherer, D.L. Caulder, D.W. Johnson, K.N. Raymond,
Angew. Chem., Int. Ed. Engl. 38 (1999) 1588;
(e) R.L. Paul, S.M. Couchman, J.C. Jeffery, J.A. McCleverty,
Z.R. Reeves, M.D. Ward, J. Chem. Soc., Dalton Trans. (2000)
845.
[4] J.S. Fleming, K.L.V. Mann, C.-A. Carraz, E. Psillakis, J.C.
Jeffery, J.A. McCleverty, M.D. Ward, Angew. Chem., Int. Ed.
Engl. 37 (1998) 1279.
[5] J.S. Fleming, K.L.V. Mann, S.M. Couchman, J.C. Jeffery, J.A.
McCleverty, M.D. Ward, J. Chem. Soc., Dalton Trans. (1998)
2047.
[6] P.L. Jones, K.L.V. Mann, J.C. Jeffery, J.A. McCleverty, M.D.
Ward, Polyhedron 16 (1997) 2435.

G.D. Frey et al. / Polyhedron 20 (2001) 3231–3237
3237
McCleverty, M.A. Cowin, C.N. Morgan, R. Varrazza, R.V.
Penty, I.H. White, Chem. Mater. 12 (2000) 2523;
(b) S.R. Bayly, E.R. Humphrey, H. de Chair, C.G. Paredes, Z.R.
Bell, J.C. Jeffery, J.A. McCleverty, M.D. Ward, F. Totti, D.
Gatteschi, S. Courric, C.G. Screttas, J. Chem. Soc., Dalton
Trans. (2001) 1401.
[7] (a) J.C. Jeffery, E. Schatz, M.D. Ward, J. Chem. Soc., Dalton
Trans. (1992) 1921;
(b) B.M. Holligan, J.C. Jeffery, M.D. Ward, J. Chem. Soc.,
Dalton Trans. (1992) 3337;
(c) B.M. Holligan, J.C. Jeffery, M.K. Norgett, E. Schatz, M.D.
Ward, J. Chem. Soc., Dalton Trans. (1992) 3345;
(d) J.C. Jeffery, C.S.G. Moore, E. Psillakis, M.D. Ward, P.
Thornton, Polyhedron 14 (1995) 599.
[12] (a) A.M. Barthram, R.L. Cleary, R. Kowallick, M.D. Ward,
Chem. Commun. (1998) 2695;
(b) A.M. Barthram, M.D. Ward, New J. Chem. 24 (2000) 501.
[13] (a) D.R. Rosseinsky, R.J. Mortimer, Adv. Mater. 13 (2001) 783;
(b) R.J. Mortimer, Chem. Soc. Rev. (1997) 147;
(c) R.J. Mortimer, Electrochim. Acta 44 (1999) 2971.
[14] S.-M. Lee, R. Kowallick, M. Marcaccio, J.A. McCleverty, M.D.
Ward, J. Chem. Soc., Dalton Trans. (1998) 3443.
[15] G.M. Sheldrick, SADABS, A Program for Absorption Correction
with the Siemens SADABS Area-Detector System; University of
Go¨ttingen, Germany, 1996.
[8] (a) D.A. Bardwell, D. Black, J.C. Jeffery, E. Schatz, M.D. Ward,
J. Chem. Soc., Dalton Trans. (1993) 2321;
(b) G.K. Lahiri, S. Bhattacharya, B.K. Ghosh, A. Chakravorty,
Inorg. Chem. 26 (1987) 4324;
(c) K.S. Finney, G.W. Everett, Inorg. Chim. Acta 11 (1974)
185.
[9] J.T. Hupp, M.J. Weaver, Inorg. Chem. 23 (1984) 3639.
[10] A. Juris, V. Balzani, F. Barigeletti, S. Campagna, P. Belser, A.
von Zelewsky, Coord. Chem. Rev. 84 (1988) 85.
[11] (a) A. McDonagh, S.R. Bayly, D.J. Riley, M.D. Ward, J.A.
[16] G.M. Sheldrick, SHELXS-97 and SHELXL-97, University of Go¨t-
tingen, Germany, 1997.