1
4'-Chloro-2,2':6',2"-terpyridine (L): ethyl sulfate salts of [H2L]2+ and the single crystal
structures of [H2L][EtOSO3]Cl.H2O and [ML2][PF6]2 with M = Fe and Ru
Jonathon E. Beves, Edwin C. Constable,* Catherine E. Housecroft,* Markus Neuburger, Silvia
Schaffner and Jennifer A. Zampese
Department of Chemistry, University of Basel, Spitalstrasse 51, CH-4056 Basel, Switzerland.
Fax: +41 61 267 1018; E-mail: [email protected]
Abstract
The preparation and characterization of [H21][EtOSO3]2 and the crystal structure of
[H21][EtOSO3]Cl.H2O are reported (1 = 4'-chloro-2,2':6',2"-terpyridine); extensive hydrogen
bonding dictates both the conformation of the tpy domain and the crystal packing. An efficient
microwave oven synthesis of [Ru(1)2][PF6]2is described; the method has general application for
[Ru(tpy)2]2+ derivatives. In the solid state, [Ru(1)2][PF6]2 and [Fe(1)2][PF6]2 are isostructural and
crystallize in the tetragonal P–421c space group.
Keywords: 4'-Chloro-2,2':6',2"-terpyridine; heterocyclic; coordination; iron; ruthenium;
protonation
4'-Chloro-2,2':6',2"-terpyridine, 1, (Scheme 1) was initially reported in 1990 [1] and is now
commercially available. Ligand 1 and homo- and heteroleptic complexes [M(1)2]n+ [2] and
[M(tpy)(1)]n+ (tpy = 2,2':6',2"-terpyridine ) have proven to be versatile building blocks, either for
simple derivatization [3,4] or for allowing access to derivatives including macrocyclic complexes
[5], metallorods and metallostars [6], dendritic wedges [7], metal-organic frameworks [8] and
incorporation into polymeric species [9]. Despite the synthetic utility of 1 and its homoleptic
complexes, crystallographic studies of 1 [10], [Fe(1)2][NO3]2.2H2O [11], [Fe(1)2]Cl2.4H2O [12]
and [Ni(1)2]Cl2.3H2O [12] have only recently been reported. In addition, structural data for
[H21][BF4]Cl and [H21][PF6]Cl have been presented [13]. As part of our ongoing studies of
2
derivatized homoleptic bis(tpy) iron(II) and ruthenium(II) complexes, we have developed an
efficient one-step approach to [Ru(1)2]2+ which has general applicability, and have investigated
the structures of [Fe(1)2][PF6]2 and [Ru(1)2][PF6]2. We combine this report of their single crystal
structures with a description of the synthesis of [H21][EtOSO3]2 and the crystal structure of
[H21][EtOSO3]Cl.H2O.
Scheme 1 Structures of ligand 1 and [H21]2+, with labelling scheme for NMR spectroscopic data.
We
have
recently
observed
that
syntheses
designed
to
produce
4'-(3,5-
dimethylpyrazol-1-yl)-2,2':6',2"-terpyridine [14] and 4'-hydrazone derivatives of tpy [15] and
carried out in MeOH or EtOH in the presence of concentrated H2SO4, yield alkyl sulfate salts
of the diprotonated ligands. When a few drops of concentrated H2SO4 are added to an ethanol
solution of compound 1 [1], a white solid immediately precipitates [16]. The 1H NMR
spectrum of the product exhibited broadened peaks, but the relative integrals of the signals
for the tpy protons to that of the ethyl signals in the [EtOSO3]– anion provided evidence for
diprotonation of 1. However, the electrospray mass spectrum of the product gave evidence
only for [H1]+ (m/z 268). In the presence of both concentrated HCl and H2SO4, X-ray quality
crystals of [H21][EtOSO3]Cl.H2O were obtained, structural analysis of which [17] confirmed
the diprotonation state. Figure 1 shows that the tpy ligand adopts a cis,cis-conformation. The
two outer pyridine rings are protonated, and a combination of hydrogen bonding interactions
to the central pyridine N-atom and to the chloride ion stabilize the dication. This general
motif is common to [H2tpy]2+ cations [13,15,18-23], and constrains the tpy domain to
planarity (angles between the least squares planes of the rings containing N1 and N2, and N2
and N3 = 8.10(9) and 1.24(9)o, respectively). Although the [H21]2+ cations all lie in planes
that are parallel to one another, there is no π-stacking, and the packing interactions are
dominated by hydrogen bonding involving cations, anions and water molecules (Figure 2).
3
Fig. 1 Molecular structure of the [H21]2+−Cl− ion pair in [H21][EtOSO3]Cl.H2O with thermal
ellipsoids plotted at the 40% probability level. Selected bond parameters: Cl1−C8 = 1.726(2),
N1H1...Cl2 = 2.28, N1...Cl2 = 3.049(2), N1H1...N2 = 2.28, N1...N2 = 2.658(2), N3H2...Cl2
= 2.27, N3...Cl2 = 3.042(1), N3H2...N2 = 2.27, N3...N2 = 2.651(2) Å; N1−H1...Cl2 = 148,
N1−H1...N2 = 107, N3−H2...Cl2 = 149, N3−H2...N2 = 107o.
Fig. 2 Part of the hydrogen bonding network in [H21][EtOSO3]Cl.H2O. Symmetry codes: i =
−x, 1 – y, 1 – z; ii = 1 − x, 1 – y, 1 – z; iii = 1 + x, y, z.
The literature synthesis of [Ru(1)2][PF6]2 is by the two-step reaction of RuCl3.3H2O with 1
[2]. We have found that the complex can be prepared more efficiently under microwave oven
4
conditions [24]. The reaction is complete within 5 minutes, and gives [Ru(1)2][PF6]2 in close
to 90% yield after purification. The 1H NMR spectroscopic data for the complex are in
accord with those previously published [2]. This methodology can be applied more widely
for the preparation of homoleptic bis(tpy) ruthenium(II) complexes, circumventing the need
for a more time-consuming two-step synthesis. X-Ray quality crystals of [Ru(1)2][PF6]2 were
grown by slow evaporation of an MeCN−H2O solution of the complex (see below). The
complex [Fe(1)2][PF6]2 is conveniently prepared by reaction of FeCl2.4H2O with 1 in ethanol
[25]. A yield of 73% compares to the 61% reported for the synthesis of [Fe(1)2]2+ from
Fe(NH4)2(SO4)2.6H2O with 1 [4]. The electrospray mass spectrum of the complex exhibited a
peak at m/z 295 assigned to [M − 2PF6]2+, and the 1H NMR spectroscopic signature was
typical for a homoleptic {Fe(tpy)2}2+ unit. Purple crystals of [Fe(1)2][PF6]2 suitable for X-ray
diffraction were grown by slow evaporation of an MeCN–H2O solution of the compound.
The complexes [Fe(1)2][PF6]2 [26] and [Ru(1)2][PF6]2 [27] are isostructural and
crystallize in the tetragonal space group P–421c. The cations have crystallographically
imposed symmetry and Figure 3 shows the structure of the [Fe(1)2]2+ cation; the Fe atoms
resides on the special position 4-bar inversion axis (Wyckoff letter a) of the P–421c space
group. Important bond parameters for the [Fe(1)2]2+ cation are listed in the figure caption,
and analogous Ru−N bond distances in the [Ru(1)2]2+ cation in [Ru(1)2][PF6]2 are 2.074(2)
and 1.974(2) Å with a unique N−Ru−N bond angle of 78.80(5)o. In [M(1)2][PF6]2 (M = Fe or
Ru), the [M(1)2]2+ cations are aligned with the C−Cl vectors running parallel to the
crystallographic c axis. The [PF6]− ions are ordered, and the packing falls into the 45o
stacking category defined by McMurtrie and Dance [29], as observed for [Cu(tpy)2][PF6]2
and [Ni(tpy)2][PF6]2, both of which crystallize in the P–421c space group [29].
In conclusion, we have prepared and characterized [H21][EtOSO3]2 and have determined
the crystal structure of [H21][EtOSO3]Cl.H2O; extensive hydrogen bonding dictates both the
conformation of the tpy (tpy = 2,2':6',2"-terpyridine) domain and the crystal packing. An
efficient microwave oven synthesis of [Ru(1)2][PF6]2 is presented, and this methodology can be
applied more generally to the synthesis of homoleptic bis(tpy) ruthenium(II) complexes.
Crystalline [Ru(1)2][PF6]2 and [Fe(1)2][PF6]2 are isostructural and crystallize in the P–421c space
group.
5
Fig. 3 Molecular structure of the [Fe(1)2]2+ cation in [Fe(1)2][PF6]2, with thermal ellipsoids
plotted at the 30% probability level. Hydrogen atoms are omitted. Selected bond parameters:
Fe1−N1 = 1.987(2), Fe1−N2 = 1.877(2), C8−Cl1 = 1.731(2) Å; N1−Fe1−N2 = 80.89(4)o.
Symmetry codes: i = −x, y, −z; ii = x, −y, −z; iii = −x, −y, z. (The structure of the [Ru(1)2]2+
cation in [Ru(1)2][PF6]2 is shown in Figure S1.)
Acknowledgements
We thank the Swiss National Science Foundation and the University of Basel for financial
support.
Appendix A. Supplementary data
CCDC 682749 ([H21][EtOSO3]Cl.H2O), 682750 ([Ru(1)2][PF6]2) and 682751 ([Fe(1)2][PF6]2)
contain the supplementary crystallographic data. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
[email protected].
Figure S1 Molecular structure of the [Ru(1)2]2+ cation in [Ru(1)2][PF6]2; hydrogen atoms are
omitted.
6
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[16]
[H21][EtOSO3]2: 1 (100 mg, 0.37 mmol) was dissolved in hot EtOH (30 cm3) and a few
drops of conc. H2SO4 were added. A white precipitate formed within 5 min which
dissolved on heating. The solution was heated at reflux for 30 min and the colourless
solution was then cooled to room temperature. Et2O (~50 cm3) was added until a white
precipitate was observed. The solution was cooled at −10oC to give [H21][EtOSO3]2 as
colourless block-like crystals (176 mg, 0.34 mmol, 91%). 1H NMR (500 MHz, DMSOd6) δ / ppm 8.80 (br, HA6), 8.72 (br, HA3), 8.51 (br, HB3), 8.15 (br, HA4), 7.64 (br, HA5),
3.73 (q, J 7.1 Hz, 4H, HCH2), 1.10 (t, J 7.1 Hz, 6H, HCH3). 13C{1H} NMR (125 MHz,
DMSO-d6) δ / ppm 148.6 (CA6), 138.8 (CA4), 125.6 (CA5), 121.9 (CB3), 121.0 (CA3), 61.1
(CCH2), 15.1 (CCH3), quaternary carbons not observed. ES-MS m/z 268 [H1]+.
8
[17]
[H21][EtOSO3]Cl.H2O: C17H19Cl2N3O5S, M = 448.33, triclinic, space group P–1, a =
7.1689(2), b = 10.5494(2), c = 13.7038(2) Å, α = 68.951(2), β = 88.146(1), γ =
86.576(2)o, U = 965.44(4) Å3, Z = 2, Dc = 1.542 Mg m–3, μ(Mo-Kα) = 0.480 mm−1, T =
173 K, 4629 reflections collected. Refinement of 3351 reflections (254 parameters) with I
>3σ (I) converged at final R1 = 0.0312 (R1 all data = 0.0462), wR2 = 0.0326 (wR2 all
data = 0.0485), gof = 1.106.
[18]
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L. Spjuth, C. Madic, J. Chem. Soc., Dalton Trans. (1998) 2973.
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[23]
M. G. B. Drew, P. B. Iveson, M. J. Hudson, J-O. Liljenzin, L. Spjuth, P.-Y. Cordier, Å.
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[24]
[Ru(1)2][PF6]2: 1 (0.20 g, 0.75 mmol) and RuCl3.3H2O (0.090 g, 0.34 mmol) were
suspended in ethane-1,2-diol (15 cm3) and a drop of N-ethylmorpholine was added. The
mixture was heated in a domestic microwave oven (800 W, 5 min) to give a deep red
solution. After cooling to room temperature , the solution was poured into an aqueous
solution (100 cm3) of excess NH4PF6. The resulting red precipitate was collected on
Celite and washed well with H2O, EtOH and Et2O. The residue was dissolved in MeCN
(50 cm3), and H2O (15 cm3) was added. Solvent volume was reduced and red
[Ru(1)2][PF6]2 precipitated. The product was collected by filtration and was washed with
H2O and EtOH. [Ru(1)2][PF6]2 was isolated as a red microcrystalline solid (0.28 g, 0.30
mmol, 88%). 1H NMR (500 MHz, CD3CN) δ / ppm 8.84 (s, 2H, HB3), 8.47 (ddd, J 8.1,
1.2, 0.7 Hz, 2H, HA3), 7.94 (td, J 8.2, 1.5 Hz, 2H, HA4), 7.39 (ddd, J 5.6, 1.4, 0.7 Hz, 2H,
HA6), 7.19 (ddd, J 7.6, 5.6, 1.3 Hz,2H, HA5). 13C{1H} (125 MHz, CD3CN) δ / ppm 158.0
9
(CA2), 157.2 (CB2), 153.8 (CA6), 144.1 (CB4), 139.3 (CA4), 129.0 (CA5), 125.9 (CA3), 125.1
(CB3). ES-MS m/z 318 [M − 2PF6]2+, 781 [M − PF6]+. Found: C 38.95, H 2.18, N 9.15;
C30H20Cl2F12N6P2Ru requires C 38.89, H 2.18, N 9.07 %
[25]
[Fe(1)2][PF6]2: 1 (100 mg, 0.37 mmol) was added to FeCl2.4H2O (37 mg, 0.19 mmol) in
EtOH (40 cm3) at room temperature for 20 min. Aqueous NH4PF6 (excess) was added to
the purple solution, resulting in the precipitation of [Fe(1)2][PF6]2 which was collected on
Celite and washed well with H2O, EtOH and Et2O. The residue was dissolved in
MeCN (100 cm3), and H2O (20 cm3) was added; the solvent volume was reduced until a
purple precipitate formed which was collected by filtration and washed with H2O to give
[Fe(1)2][PF6]2 as a purple microcrystalline solid (120 mg, 0.14 mmol, 73%). 1H NMR
(500 MHz, CD3CN) 9.00 (s, 2H, s, HB3), 8.45 (d, J 7.9 Hz, HA3), 7.90 (td, J 7.7, 1.3 Hz,
2H, HA4), 7.14 (d, J 5.0 Hz, 2H, HA6), 7.09 (ddd, J 6.9, 5.7, 1.3, 2H, HA5). 13C{1H}(125
MHz, CD3CN) δ / ppm 161.9 (CB2), 157.8 (CA2), 154.4 (CA6), 146.7 (CB4), 140.0 (CA4),
128.8 (CA5), 125.3 (CA3), 125.2 (CB2). ES-MS m/z 295 [M − 2PF6]2+. Found: C 40.98, H
2.31, 9.68; C30H20Cl2F12FeN6P2 requires C 40.89, H 2.29, N 9.54 %.
[26]
[Fe(1)2][PF6]2: C30H20Cl2F12FeN6P2, M = 881.21, tetragonal, space group P–421c, a = b =
9.0431(1), c = 19.8515(3) Å, U = 1623.41(4) Å3, Z = 2, Dc = 1.803 Mg m–3, μ(Mo-Kα) =
0.833 mm−1, T = 173 K, 1944 reflections collected. Refinement of 1430 reflections (123
parameters) with I >3σ (I) converged at final R1 = 0.0245 (R1 all data = 0.0341), wR2 =
0.0273 (wR2 all data = 0.0312), gof = 1.102.
[27]
[Ru(1)2][PF6]2: C30H20Cl2F12N6P2Ru, M = 926.43, tetragonal, space group P–421c, a = b
= 8.925(1), c = 20.242(4) Å, U = 1612.2(5) Å3, Z = 2, Dc = 1.908 Mg m–3, μ(Mo-Kα) =
0.857 mm−1, T = 173 K, 16957 reflections collected, merging r = 0.1013. Refinement of
122 parameters using all 1424 independent reflections against F2 converged at final R1 =
0.0231 (R1 all data = 0.0236), wR2 = 0.0588 (wR2 all data = 0.0594), gof = 1.172.
[28]
J. McMurtrie and I. Dance, CrystEngComm 7 (2005) 216.