Excited states of Ru(II) and Re(I) bipyridyl complexes attached to cyclotriphosphazenes: A synthetic, spectroscopic, and computational study

Article abstract of DOI:10.1021/ic902171j

A series of new cyclotriphosphazene ligands substituted with pendant 2,2′-bipyridyl moieties, namely, bis[(1,′-biphenyl)-2,2′- dioxy](2,2′-bipyridyl-3,3′-dioxy)cyclotriphosphazene (L ¹), bis[(1,′-biphenyl)-2,2′-dioxy][bis{4-(2,2′- bipyridin)-4-yl-phenyoxy}]cyclotriphosphazene (L²), (pentaphenoxy)[4-(2,2′-bipyridin)-4-yl-phenyoxy]cyclotriphosphazene (L³), and (pentaphenoxy) [4-{6-phenyl(2,2′-bipyridin)-4-yl}- phenoxy]cyclotriphosphazene (L⁴), has been used to synthesize the ruthenium(II) and rhenium(I) complexes, [(L)Ru(bpy)₂](PF ₆)₄ (L = L¹ or L³), [(L²) {Ru(bpy)₂}₂](PF₆)₄, [(L)Re(CO) ₃Cl] (L = L¹, L³ or L⁴), and [(L²) {Re(CO)₃Cl}₂]. Single crystal X-ray structures of [(L¹)Re(CO)₃Cl] and [(L⁴)Re(CO) ₃Cl] show the bipyridyl component of the cyclotriphosphazene substituted ligands is bound to the Re(I) giving a distorted octahedral N₂C₃Cl coordination sphere in both cases. Density functional theory (DFT) methods were employed to model the ground-state vibrational properties of the molecules, and their accuracies verified using vibrational spectroscopy. Electronic transitions were identified using UV-visible and resonance Raman spectroscopic techniques, aided by time-dependent (TD) DFT methods. Transient resonance Raman spectra of the excited states of the compounds were acquired and found to be comparable to those reported for studied metal bipyridyl units lacking the cyclotriphosphazene substituents. The cyclotriphosphazene unit has little effect on the properties of the metal bipyridyl chromophore.

Full text of DOI:10.1021/ic902171j

Inorg. Chem. 2010, 49, 4073–4083 4073
DOI: 10.1021/ic902171j
Excited States of Ru(II) and Re(I) Bipyridyl Complexes Attached to
Cyclotriphosphazenes: A Synthetic, Spectroscopic, and Computational Study
Raphael Horvath,† Carl A. Otter,‡ Keith C. Gordon,*,† Andrew M. Brodie,*,‡ and Eric W. Ainscough*,‡
†MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Chemistry,
University of Otago, Dunedin, New Zealand, and ‡Chemistry-Institute of Fundamental Sciences,
Massey University, Palmerston North, New Zealand
Received November 3, 2009
A series of new cyclotriphosphazene ligands substituted with pendant 2,20-bipyridyl moieties, namely, bis[(1,10-biphenyl)-2,20-
dioxy](2,20-bipyridyl-3,30-dioxy)cyclotriphosphazene (L1), bis[(1,10-biphenyl)-2,20-dioxy][bis{4-(2,20-bipyridin)-4-yl-phenyoxy}]-
cyclotriphosphazene (L2), (pentaphenoxy)[4-(2,20-bipyridin)-4-yl-phenyoxy]cyclotriphosphazene (L3), and (pentaphenoxy) [4-
{6-phenyl(2,20-bipyridin)-4-yl}-phenoxy]cyclotriphosphazene (L4), has been used to synthesize the ruthenium(II) and rheni-
um(I) complexes, [(L)Ru(bpy)2](PF6)4 (L = L1 or L3), [(L2) {Ru(bpy)2}2](PF6)4, [(L)Re(CO)3Cl] (L = L1, L3 or L4), and [(L2)
{Re(CO)3Cl}2]. Single crystal X-ray structures of [(L1)Re(CO)3Cl] and [(L4)Re(CO)3Cl] show the bipyridyl component of the
cyclotriphosphazene substituted ligands is bound to the Re(I) giving a distorted octahedral “N2C3Cl” coordination sphere in both
cases. Density functional theory (DFT) methods were employed to model the ground-state vibrational properties of the
molecules, and their accuracies verified using vibrational spectroscopy. Electronic transitions were identified using UV-visible
and resonance Raman spectroscopic techniques, aided by time-dependent (TD) DFT methods. Transient resonance Raman
spectra of the excited states of the compounds were acquired and found to be comparable to those reported for studied metal
bipyridyl units lacking the cyclotriphosphazene substituents. The cyclotriphosphazene unit has little effect on the properties of the
metal bipyridyl chromophore.
Introduction
cyclic phosphazenes (Chart 1) are classes of compounds where
such control is possible. A wide range of substituents can be
attached to the phosphazene scaffold, allowing many possibi-
lities for derivatization. For example, we have recently explored
the reactions of cyclic phosphazenes substituted with pyridine,
phenanthroline, and phosphine ligand moieties and found them
to have a rich metal-ion coordination chemistry.6-12 There are
also many other examples of metal containing cyclic phospha-
zene compounds in which pyrazolyl, nitrile, or ferrocenyl
ligands, to name a few, have been incorporated.13,14 The
Complexes of heavy transition metals such as rhenium and
ruthenium are suitable for use as dyes in Gratzel cells as well as
emitting centers in organic light emitting diodes (OLEDs).1-4
As such devices become commercialized, improved materials
technologies and production methods become more important.
OLEDs have great potential in display technology; however,
currently they suffer from limited lifetimes and are thus largely
unsuitable for commercial use. It has been determined that both
emissive and charge-transporting layers and their communica-
tion can have an effect on the degradation rate.5 For example
the rates of diffusion of radicals as well as the stability of the host
material are important. It is therefore advantageous to utilize
materials in the construction of OLEDs where parameters such
as the glass transition temperature (Tg) and stability against
various influences can be carefully controlled. Polymeric and
(6) Ainscough, E. W.; Brodie, A. M.; Depree, C. V.; Moubaraki, B.;
Murray, K. S.; Otter, C. A. Dalton Trans. 2005, 3337–3343.
(7) Ainscough, E. W.; Brodie, A. M.; Depree, C. V.; Jameson, G. B.;
Otter, C. A. Inorg. Chem. 2005, 44, 7325–7327.
(8) Ainscough, E. W.; Brodie, A. M.; Chaplin, A. B.; O’Connor, J. M.;
Otter, C. A. Dalton Trans. 2006, 1264–1266.
(9) Ainscough, E. W.; Brodie, A. M.; Jameson, G. B.; Otter, C. A.
Polyhedron 2007, 26, 460–471.
(10) Ainscough, E. W.; Brodie, A. M.; Derwahl, A.; Kirk, S.; Otter, C. A.
Inorg. Chem. 2007, 46, 9841–9852.
(11) Ainscough, E. W.; Brodie, A. M.; Davidson, R. J.; Otter, C. A. Inorg.
Chem. Commun. 2008, 11, 171–174.
(12) Ainscough, E. W.; Brodie, A. M.; Davidson, R. J.; Moubaraki, B.;
Murray, K. S.; Otter, C. A.; Waterland, M. R. Inorg. Chem. 2008, 47, 9182–
9192.
*To whom correspondence should be addressed. E-mail: kgordon@chemistry.
otago.ac.nz (K.C.G.), a.brodie@massey.ac.nz (A.M.B.), e.ainscough@massey.
ac.nz (E.W.A.).
(1) O’Regan, B.; Graetzel, M. Nature 1991, 353, 737–740.
(2) Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913–915.
(3) Lundin, N. J.; Blackman, A. G.; Gordon, K. C.; Officer, D. L. Angew.
Chem., Int. Ed. 2006, 45, 2582–2584.
(4) Welter, S.; Brunner, K.; Hofstraat, J. W.; DeCola, L. Nature 2003,
421, 54–57.
(5) Kondakov, D. Y.; Lenhart, W. C.; Nichols, W. F. J. Appl. Phys. 2007,
101, 024512/1–024512/7.
(13) Chandrasekhar, V.; Thilagar, P.; Murugesa Pandian, B. Coord.
Chem. Rev. 2007, 251, 1045–1074.
(14) Pertici, P.; Vitulli, G.; Gleria, M.; Facchin, G.; Milani, R.; Bertani, R.
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r
2010 American Chemical Society
Published on Web 04/08/2010
pubs.acs.org/IC

4074 Inorganic Chemistry, Vol. 49, No. 9, 2010
Horvath et al.
Chart 1. Generic Polyphosphazene and Cyclotriphosphazene (CTP)
Structures
Synthesis. [N3P3(biph)2(O2bpy)] (L1). A mixture of [N3P3-
(biph)2Cl2] (0.391 g, 0.68 mmol), Cs2CO3 (1 g, 3.07 mmol), and
(HO)2bpy (0.128 g, 0.68 mmol) in acetone (30 mL) was heated at
reflux over 5 h. The mixture was taken to dryness, and the
residue was extracted with CH2Cl2. The extract was filtered
through Celite and taken to dryness on a rotary evaporator.
Chromatography of the residue on silica using CH2Cl2/MeOH
(98:2) as eluent gave the product as a white solid (0.320 g) which
was recrystallized from CH2Cl2/hexane. Yield: 0.280 g (60%).
Anal. Required for C34H22N5O6P3: C, 59.23; H, 3.22; N,
10.16%. Found: C, 58.70; H, 3.32; N, 10.20%. ESMS: m/z 690
[MþH]þ. 31P{1H} NMR (CDCl3): δ 24.9-27.5 (m, 3P) 1H
NMR (CDCl3): δ 8.72 (br m, 2H), 7.71 (m, 2H), 7.51 (m, 4H),
7.48-7.38 (m, 6H), 7.37-7.28 (m, 8H).
binding of metal ions that have valuable photophysical proper-
ties, such as ruthenium and rhenium, have been reported in
some of these systems.13 A recent report details the preparation
of an OLED device that incorporates an iridium complex
bonded to a cyclotriphosphazene dendrimer.15 In some cases
the chemistry has also been extended to the polyphosphazene
analogues, yielding the metal-rich macromolecular species. Since
the flexibility of the polymer backbone can be controlled by the
choice of the substituents incorporated, properties such as Tg
can also be controlled.16 Hence, the polymeric and cyclic phos-
phazene systems are promising candidates to explore as hosts for
dyes in OLED or photochemical energy cell systems. To allow
the efficient design of devices it is advantageous to know in detail
the effect of phosphazene attachment on fluorophore behavior.
This study examines the properties of transition-metal fluoro-
phores attached to cyclotriphosphazene (CTP) in comparison
to the free fluorophores with reference to their photophysical
properties. It has been carried out using a variety of ground and
excited state spectroscopic techniques including FT-Raman,
resonance Raman, and transient resonance Raman (TR2) and
has been supplemented by density functional theory (DFT)
calculations to obtain a theoretical insight. The compounds
studied here are derivatives of the well-known ruthenium tris-
(bipyridyl)ruthenium(II) cation, [Ru(bpy)3]2þ, and bipyridyl-
tricarbonylchlororhenium(I), [Re(bpy)(CO)3Cl], fluorophores.
This is the first time cyclic phosphazene systems containing
these species have been reported. It is interesting to determine if
the attachment of metal units to the CTP function dramatically
alters the emissive properties imbued by the metal complex or
does the CTP unit act as an electronically mute scaffold?
[N3P3(biph)2(OPhbpy)2] 0.25CH2Cl2 (L2). To a solution of
3
HOPhbpy (0.40 g, 1.6 mmol) in THF (30 mL) was added NaH
(0.65 g of a 60% dispersion in oil, 1.6 mmol NaH). The solution
was stirred at room temperature over 3 h, and TBAB (0.03 g)
and [N3P3(biph)2Cl2] (0.462 g, 0.8 mmol) were added. The
mixture was heated at reflux over 15 h, allowed to cool, and
the THF removed on a rotary evaporator. The crude residue was
extracted with CH2Cl2 and filtered through Celite. The CH2Cl2
extract was taken to dryness, and the residue purified by column
chromatography on silica using MeOH (0-4%) in CH2Cl2 as
eluent. Recrystallization from CH2Cl2/hexane and drying at
70 °C under vacuum afforded the product as a white solid. Yield:
0.700 g (87%). Anal. Required for C56.25H38.5Cl0.5N7O6P3: C,
66.23; H, 3.78; N, 9.61%. Found: C, 66.44; H, 3.85; N, 9.83%.
ESMS: m/z 998 [MþH]þ. 31P{1H} NMR (CDCl3): δ 25.43 (d, 2P,
J
PP = 93 Hz, phosphazene), 9.67 (t, P, JPP = 95 Hz, phosphazene).
1H NMR (CDCl3): δ 9.25 (s, 2H), 9.10 (d, 2H), 8.89 (m, 4H), 8.24
(m, 2H), 8.03 (m, 4H), 7.94 (m, 2H), 7.69 (m, 2H), 7.59 (m, 4H),
7.50 (m, 4H), 7.40 (m, 4H), 7.31 (m, 4H), 7.15 (m, 4H).
[N3P3(OPh)5(OPhbpy)] (L3). To a solution of HOPhbpy
(0.145 g, 0.60 mmol) in THF (30 mL) was added NaH (0.024 g
of a 60% dispersion in oil, 0.60 mmol NaH), and the mixture was
stirred over 0.5 h. [N3P3(OPh)5Cl] (0.373 g, 0.60 mmol) and
TBAB (0.050 g, 0.16 mmol) were added, and the mixture was
heated at reflux overnight. The THF was removed on a rotary
evaporator, and the residue was extracted into CH2Cl2. The
organic extract was filtered through Celite and taken to dryness
on a rotary evaporator. Chromatography of the residue on silica
using CH2Cl2/MeOH (98:2) as eluent afforded the product as an
oil which was dried under vacuum at 50 °C to give a waxy solid.
Yield: 0.350 g (70%). Anal. Required for C46H36N5O6P3:
C, 65.17; H, 4.28; N, 8.26%. Found: C, 65.04; H, 4.47; N, 8.29%.
ESMS: m/z 848 [MþH]þ. 31P{1H} NMR (CDCl3): δ 10.9-9.2
(m, 3P). 1H NMR (CDCl3): δ 8.74 (m, 2H), 8.68 (br s, H), 8.55
(m, H), 7.89 (m, H), 7.55 (m, 2H), 7.50 (m, H), 7.37 (m, H),
7.21-7.06 (m, 15H), 7.03 (m, 2H), 6.99-6.86 (m, 10H).
Experimental Section
General Procedures. Analytical grade solvents were used without
further purification with the exception of tetrahydrofuran (THF)
which was distilled from sodium/benzophenone. [Re(CO)5Cl] was
obtained from Pressure Chemicals (Pittsburgh) and tetrabutyl-
ammonium bromide (TBAB) was obtained from Merck. [N3P3-
(biph)2Cl2] (biph =2,20-oxybiphenyl),17 [N3P3(OPh)2Cl] (OPh =
oxyphenyl),18 3,30-dihydroxybipyridine [(HO)2bpy],19 4-(4-hydro-
xyphenyl)-2,20-bipyridine (HOPhbpy),20 4-(4-hydroxyphenyl)-6-
phenyl-2,20-bipyridine21 (HOPhbpyPh), and [Ru(bpy)2Cl2]2H2O22
were prepared according to literature procedures.
[N3P3(OPh)5(OPhbpyPh)] (L4). A mixture of HOPhbpyPh
(0.163 g, 0.5 mmol) and NaH (0.020 g of a 60% dispersion in oil,
0.5 mmol NaH) in THF (35 mL) was allowed to stir at room
temperature over 1 h. [N3P3(OPh)5Cl] (318 mg, 0.5 mmol) and
TBAB (20 mg) were added, and the mixture was heated at reflux
overnight. The THF was removed on a rotary evaporator, the
residue extracted with CH2Cl2, and the extract filtered through
Celite. Chromatography on silica using MeOH (0-2%) in
CH2Cl2 as eluent yielded the product as a clear oil, which was
dried under vacuum. Yield: 0.401 g (87%). Anal. Required for
C51H40N6O6P3: C, 67.61; H, 4.36; N, 7.58%. Found: C, 67.74;
H, 4.57; N, 7.56%. ESMS: m/z = 924 [MþH]þ. 31P{1H} NMR
(CDCl3): δ 9.71-7.98 (m, 3P). 1H NMR (CDCl3): δ 8.71 (m, H),
8.67 (m, H), 8.57 (s, H), 8.18 (m, 2H), 7.88-7.83 (m, 2H),
7.60-7.49 (m, 4H), 7.45 (m, H), 7.33 (m, H) 7.20-7.06 (m, 15H),
7.03 (m, 2H), 6.99-6.88 (m, 10H).
(15) Bolink, H. J.; Santamaria, S. G.; Sudhakar, S.; Zhen, C.; Sellinger, A.
Chem. Commun. 2008, 618–620.
(16) Allcock, H. R. Chemistry and Applications of Polyphosphazenes;
Wiley: New York, 2003; p 774.
(17) Carriedo, G. A.; Fernandez-Catuxo, L.; Alonso, F. J. G.; Gomez-
Elipe, P.; Gonzalez, P. A. Macromolecules 1996, 29, 5320–5325.
(18) Allcock, H. R.; Laredo, W. R.; deDenus, C. R.; Taylor, J. P.
Macromolecules 1999, 32, 7719–7725.
(19) Tiecco, M.; Testaferri, L.; Tingoli, M.; Chianelli, D.; Montanucci,
M. Synthesis 1984, 736–738.
(20) Hayes, M. A.; Meckel, C.; Schatz, E.; Ward, M. D. J. Chem. Soc.,
Dalton Trans. 1992, 703–708.
(21) Neve, F.; Ghedini, M.; Francescangeli, O.; Campagna, S. Liq. Cryst.
1998, 24, 673–680.
(22) Godwin, J. B.; Meyer, T. J. Inorg. Chem. 1971, 10, 2150–2153.
[(L1)Ru(bpy)2](PF6)2 0.5CH2Cl2 (1). A mixture of L1 (0.050 g,
3
0.073 mmol) and [Ru(bpy)2Cl2] 2H2O (0.038 g, 0.073 mmol)
3
in MeOH (30 mL) was heated at reflux overnight. The red

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4075
solution was allowed to cool and filtered through Celite. A
solution of NH4PF6 in MeOH was added to the filtrate to
produce a red precipitate that was collected by filtration and
washed with Et2O. The product was purified by chromatogra-
phy on alumina using MeCN as eluent and recrystallized from
CH2Cl2/hexane. Yield: 0.050 g (48%). Anal. Required for
C54.5H39ClF12N9O6P5Ru: C, 45.60; H, 2.72; N, 8.78%. Found:
C, 45.33; H, 2.92; N, 8.62%. ESMS: m/z 1248 [MþPF6]þ, 522
[M]2þ. 1H NMR (d6-DMSO): δ 8.79 (m, 4H), 8.29 (m, 2H), 8.13
(m, 4H), 7.89 (m, 2H), 7.33-7.62 (m, 8H), 7.60 (m, 2H), 7.57-
7.41 (m, 12H), 7.37 (m, 2H), 7.30 (m, 2H). 31P{1H} NMR
(d6-DMSO): δ 24.9-24.3 (m, 2P), 22.0-20.8 (m, P), -144.0
(sept, 2P, JPF = 729 Hz).
Table 1. Crystal and Refinement Data for Compounds 4 3CHCl3 and
3
7 0.26H2O
3
4 3CHCl3
3
7 0.26H2O
3
empirical formula
C
40H25Cl10-
N5O9P3Re
C
55H42.52ClN5-
O9.26P3Re
1234.18
M
T (K)
1353.26
190(2)
triclinic
P1
8.5198(6)
14.6205(10)
20.7929(14)
105.593(2)
98.725(2)
98.796(2)
2414.3(3)
2
3.229
1.862
50.7
8413
8413/0/613
R1 = 0.0379,
wR2 = 0.0914
R1 = 0.0493,
wR2 = 0.0976
1.047
190(2)
triclinic
P1
crystal system
space group
˚
a (A)
11.6960(6)
11.7241(6)
21.3092(11)
76.201(3)
83.228(3)
66.364(3)
2598.8(2)
2
2.545
1.577
50.7
9399
9399/274/683
R1 = 0.0502,
wR2 = 0.1147
R1 = 0.0624,
wR2 = 0.1221
1.126
˚
b (A)
˚
c (A)
R (deg)
β (deg)
γ (deg)
[(L3)Ru(bpy)2](PF6)2 (2). A mixture of L3 (0.204 g, 0.24 mmol)
and [Ru(bpy)2Cl2] 2H2O (0.125 g, 0.24 mol) was heated at reflux in
3
3
˚
V (A )
Z
MeOH (25 mL) over 24 h. A solution of NH4PF6 in MeOH was
added to produce an orange precipitate which was collected by
filtration and washed with Et2O. Yield: 0.250 g (67%). Anal.
Required for C66H52F12N9O6P5Ru: C, 51.11; H, 3.38; N, 8.13%.
μ (MoKR) (mm-1
)
F
calc (g cm-3
)
2θ max (deg)
Found: C, 50.56; H, 3.54; N, 8.04%. ESMS: m/z1058 [Mþ2PF6]2þ
,
no. of unique reflections
data/restraints/parameters
final R indices [I > 2σ(I)]
657 [MþPF6]3þ, 457 [M]4þ. H NMR (d6-DMSO): δ 9.08 (m,
2H), 8.83 (m, 4H), 8.16 (m, 5H), 7.93 (m, 2H), 7.81 (m, 2H), 7.72
(m, 5H), 7.51 (m, 5H), 7.29-7.15 (m, 13H), 7.15-7.03 (m, 4H),
6.91 (m, 4H), 6.81 (m, 6H). 31P{1H} NMR (d6-DMSO): δ 9.0 (m,
3P), -144.1 (sept, 2P, JPF = 709 Hz).
1
R indices (all data)
goodness of fit on F2
[(L2){Ru(bpy)2}2](PF6)4 CH2Cl2 (3). A mixture of L2 (0.100
3
g, 0.100 mmol) and [Ru(bpy)2 Cl2] 2H2O (0.104 g, 0.200 mmol)
was a mixture of singly and doubly substituted material
(approximately 1:10). The precipitate was dissolved in a solution
of CH2Cl2 (20 mL) and CHCl3(10 mL) which was allowed to
evaporate slowly over 2 weeks. Two microcrystalline crops of
clean doubly substituted material were collected during this
time. Yield: 0.075 g (44%). Anal. Required for C63H40Cl4N7-
O12P3Re2: C, 44.66; H, 2.38; N, 5.79%. Found: C, 44.55; H,
2.31; N, 5.85%. 31P{1H} NMR (d6-DMSO): δ 25.07 (d, 2P,
3
was heated at reflux in MeOH (25 mL) over 24 h. A solution of
NH4PF6 in MeOH was added to produce an orange precipitate
which was collected by filtration and washed with Et2O. The
precipitate was dissolved in CH2Cl2 and hexane was added,
producing a red oil that formed a glassy solid upon standing in a
freezer. Yield: 0.160 g (64%). Anal. Required for C97H72Cl2-
F24N15O6P7Ru2: C, 46.80; H, 2.92; N, 8.44%. Found: C, 46.78;
H, 2.81; N, 8.48%. ESMS: m/z 1406 [MþPF6]þ, 630 [M]2þ. 1H
NMR (d6-DMSO): δ 9.14 (s, 2H), 9.08 (m, 2H), 8.82 (m, 8H),
8.26-8.09 (m, 14H), 7.89 (m, 2H), 7.79 (m, 2H), 7.75-7.62 (m,
14H), 7.56 (m, 4H), 7.53-7.45 (m, 14H), 7.42 (m, 4H), 7.15 (m,
4H). 31P{1H} NMR (d6-DMSO): δ 25.3 (d, 2P, JPP = 92 Hz),
9.86 (m, P), -144.1 (sept, 4P, JPF = 732 Hz).
1
JPP = 92 Hz), δ 10.01 (t, P, JPP = 92 Hz). H NMR (d6-
DMSO): δ 9.09 (s, 2H), 9.07-9.02 (m, 6H), 8.38 (m, 2H), 8.32
(m, 4H), 8.13 (m, 2H), 7.80 (m, 2H), 7.70 (m, 4H), 7.64 (m, 4H),
7.54 (m, 4H), 7.46 (m, 4H), 7.23 (m, 4H).
[(L4)Re(CO)3Cl] (7). A suspension of L4 (0.050 g, 0.054 mmol)
and [Re(CO)5Cl] (0.194 g, 0.054 mmol) in toluene (10 mL) was
heated at reflux over 5 h. The resulting orange solution was filtered,
and the toluene removed on a rotary evaporator. The residue was
dissolved in CH2Cl2 (ca. 3 mL) and filtered through a plug of Celite.
Hexane was added to the filtrate, and a crop of crystalline material
developed over 48 h. A crystal suitable for X-ray diffraction data
collection was selected, and the bulk was collected by filtration and
dried under vacuum. Yield: 0.045 g (68%). Anal. Required for
C55H40ClN5O9P3Re: C, 53.73; H, 3.28; N, 5.70%. Found: C, 53.76;
H, 3.38; N, 5.63%. 1H NMR (CDCl3): δ 9.14 (m, H), 8.31 (m, H),
8.25 (m, H), 8.09 (m, H), 7.76-7.64 (m, 3H), 7.64-7.58 (m, 3H),
7.56-7.48 (m, 3H), 7.25-7.07 (m, 17H), 7.07-7.01 (m, 4H),
6.97-6.85 (m, 6H). 31P{1H} NMR (CDCl3): δ 9.6-9.0 (m, 3P).
Crystallography. Vapor diffusion of pentane into a CDCl3
[(L1)Re(CO)3Cl] 0.5C7H8 (4). A mixture of L1 (0.050 g, 0.073
3
mmol) and [Re(CO)5Cl] (0.026 g, 0.072 mmol) was heated at
reflux in toluene (25 mL) over 5 h. The yellow solution was
concentrated on a rotary evaporator to approximately 5 mL and
the yellow precipitate that formed was collected by filtration,
washed with Et2O, and dried under vacuum at 40 °C. Yield:
0.057 g (76%). Anal. Required for C40.5H26ClN5O9P3Re: C,
46.67; H, 2.64; N, 6.72%. Found: C, 46.94; H, 2.54; N,
6.81%.31P{1H} NMR (CDCl3): δ 9.13 (m, 3P). 1H NMR
(CDCl3): δ 8.98 (m, 2H), 7.98 (m, 2H), 7.67 (m, 2H), 7.57 (m,
4H), 7.47 (m, 4H), 7.41-7.34 (m, 8H).
[(L3)Re(CO)3Cl] (5). A mixture of L3 (0.050 g, 0.059 mmol)
and [Re(CO)5Cl] (0.018 g, 0.049 mmol) in toluene (10 mL) was
heated at reflux over 5 h and stirred at room temperature overnight.
The orange solution was filtered, taken to dryness on a rotary
evaporator, and the residue was dissolved in CH2Cl2 (ca. 10 mL).
Hexane was added to this solution, and the volume was reduced to
produce a yellow precipitate that was collected by filtration and
dried under vacuum at 40 °C. Yield 0.040 g (59%). Anal. Required
for C49H36ClN5O9P3Re: C, 51.02; H, 3.15; N, 6.07%. Found: C,
51.17; H, 3.19; N, 6.11%. 31P{1H} NMR (CDCl3): δ9.55-8.97 (m,
3P). 1H NMR (CDCl3): δ 9.11 (m, H), 9.06 (m, H), 8.27 (m, H),
8.21 (s, H), 8.09 (m, H), 7.59 (m, 2H), 7.50 (m, 2H), 7.25-7.10 (m,
17H), 7.04 (m, 4H), 6.98-6.86 (m, 6H).
solution of 4 afforded yellow blocks of 4 3CDCl3, and yellow
plates of 7 0.26H2O were grown from CH2Cl2/hexane solution.
3
3
The X-ray data were collected on a Siemens P4 four circle
diffractometer, using a Siemens SMART 1K CCD area detec-
tor. The crystals were mounted in an inert oil and irradiated with
˚
graphite-monochromated Mo-KR (λ = 0.71073 A) X-rays.
The data were collected by the SMART program and processed
with SAINT to apply Lorentz and polarization corrections to
the diffraction spots (integrated 3 dimensionally). Crystal data
are given in Table 1. The structures were solved by direct
methods and refined using the SHELXTL program.23 Hydro-
gen atoms were calculated at ideal positions.
[(L2){Re(CO)3Cl}2] CH2Cl2 (6). A mixture of L2 (0.100 g,
3
0.100 mmol) and [Re(CO)5Cl] (0.072 g, 0.199 mmol) in toluene
(15 mL) was heated at reflux over 3 h then stirred at room
temperature overnight. A yellow precipitate formed that was
collected by filtration and washed with Et2O. The precipitate
(23) Sheldrick, G. M. SHELXL Suite of Programs for Crystal Structure
€
€
€
Analysis; Institut f€ur Anorganische Chemie der Universitat Gottingen: Gottingen,
Germany, 1998.

4076 Inorganic Chemistry, Vol. 49, No. 9, 2010
Horvath et al.
Instrumentation. Microanalyses were performed by the
Campbell Microanalytical Laboratory, University of Otago. H
All calculations employed the B3LYP functional using the 6-31G(d)
basis set for the ligands, while heavy metal centers were approxi-
mated using LANL2DZ effective core potentials.29 The output
frequencies were scaled by a factor of 0.97530 and IR and Raman
spectra generated using a Lorentzian line-shape with a half-width at
half-maximum (HWHM) of 3 cm-1. The vibrational modes and
molecular orbitals were visualized using Molden31 and GaussView
v4.1 (Gaussian, Inc.) respectively after extraction from the output
files using GaussSum.32 The accuracy of the calculations was moni-
tored using mean absolute deviation (MAD) values, which are ob-
tained by averaging the absolute difference in cm-1 of the 5-10 most
prominent experimental peaks to the corresponding calculated peaks
in the spectral range 400 cm-1 to 1800 cm-1. Carbonyl stretches
require different scale-factors33 and were therefore omitted in the
MAD calculations. Unambiguous assignment of vibrational modes
from visual comparison of spectra was possible for most peaks. TD-
DFT calculations were carried out in a dichloromethane solvent field
using the IEF-PCM method,34,35 which treats the solvent as a
continuum containing the solute as a series of interlocking spheres.
Geometry optimizations were not carried out in a solvent field, as
these are very difficult to achieve for molecules this size; however,
correlation is found to be better than for calculations where solvent
contributions have been completely neglected.36,37
1
NMR spectra were recorded at 162 MHz and 31P{1H} NMR
spectra were recorded at 400 MHz on a Bruker Avance 400
spectrometer. Electrospray mass spectra were obtained from
CH3CN solutions on a Micromass ZMD spectrometer run in
the positive ion mode. Listed peaks correspond to the most
abundant isotopomer; assignments were made by a comparison
of observed and simulated spectra. All ground-state vibrational
measurements were taken in solid-state KBr disks. FT-IR mea-
surements were obtained using a Perkin-Elmer BX FT-IR spec-
trometer with Spectrum v2.00 software. The spectra were
acquired as 64 co-added scans with a resolution of 4 cm-1. FT-
Raman spectra were obtained using a Bruker Equinox 55 inter-
ferometer coupled with a FRA-106 Raman module and a D418T
liquid-nitrogen-cooled Germanium detector, controlled by the
Bruker OPUS v5.5 software package. A Nd:YAG laser operating
at 1064 nm and 450 mW was used. The spectra were acquired as
256-2024 co-added scans with a resolution of 4 cm-1. UV-
visible absorption spectra of 10-4 mol L-1 solutions of the
compounds were acquired in the range 190-600 nm using a Jasco
V-550 spectrophotometer controlled by Spectrum Measurement
v1.53.00. Emission spectra were obtained using the setup
described by Howell et al.24,25 In short, the excitation beam from
a continuous-wave Innova I-302 krypton-ion laser (Coherent, Inc.)
operating at 350.7 nm and collection lens are arranged in a 135°
backscattering geometry, which focuses the emission on an Acton
Research SpectraPro500i spectrograph. A notch filter is used to
remove the laser excitation line. Using a 300 grooves mm-1
diffraction grating and four acquisition windows, a wavelength
range of 300-950 nm was observed. A similar setup using a 1200
grooves mm-1 diffraction grating was used to perform resonance
Raman (RR) spectroscopy at excitation wavelengths of 350.7,
406.7, and 413.1 nm.26,27 Furthermore, a diode-pumped laser
(CrystaLaser) at 444.3nm anda Melles Griot Omnichrome model
543-MAP argon laser at 457.9 and 488.0 nm were used to obtain
spectra at these excitation wavelengths. Excited-state transient
resonance Raman (TR2) measurements were performed using
354.7 nm third-harmonic radiation from a Brilliant (Quantel) Nd:
YAG pulse laser at power outputs of 0.96, 1.84, and 3.10 mJ/pulse
and a repetition rate of 10 Hz. For both RR and TR2 compounds
were in 10-3 mol L-1 CH2Cl2 solutions, which had been degassed
using argon for 20 min prior to measurement. The excited state
lifetime of argon-purged 10-3 mol L-1 CH2Cl2 solutions was
measured using excitation from the Brilliant Nd:YAG laser des-
cribed above. Emission signals were measured by a Hamamatsu
H5783-04 photomultiplier at 580, 620, 660, and 700 nm and read
out on a Tektronix TDS 3032B model digital oscilloscope. For
each trace the natural logarithm of the emission intensity was
plotted against time, and typically these data could be fit linearly
with R2 values greater than 0.95. The errors were estimated using
the standard deviation of measurements between each wave-
length. No sample degradation was observed for any of the com-
plexes for either TR2 or emission lifetime measurements.
Results and Discussion
Syntheses. The new phosphazene ligands, L1, L2, L3,
and L4, were prepared by the reaction of 1 or 2 equiv of the
phenolic bipyridine precursors with [N3P3(biph)2Cl2] or
[N3P3(OPh)5 Cl] in the presence of a base (Scheme 1). The
reaction of (HO)2bpy with [N3P3(biph)2Cl2] in acetone using
Cs2CO3 gives the ligand L1. The treatment of HOPhbpy with
NaH in THF followed by the reaction with [N3P3(biph)2Cl2]
at reflux overnight in the presence of the catalyst TBAB gives
the ligand L2. The reaction of the sodium salt of HOPhbpy
or HOPhbpyPh in THF with [N3P3(OPh)5Cl] using TBAB
as a catalyst affords the ligands L3 and L4. All four ligands
were purified by chromatography and L1 and L2 were ob-
tained as white solids after recrystallization from CH2Cl2/
hexane. L3 and L4 were obtained as oils after drying under
vacuum at 50 °C. Ruthenium tris-bipyridyl derivatives of
L1-L3 were obtained by reacting the ligands with [Ru-
(bpy)2Cl2] in refluxing MeOH followed by metathesis with
NH4PF6. The complexes all show characteristic MLCT
transitions between 446 and 454 nm and ε per Ru(II) ranges
between 11600 and 17300 dm3 mol-1 cm-1. The half wave
potentials for the Ru(II)/Ru(III) couple (with respect to the
ferrocene/ferrocinium couple) are 0.86 and 0.87 V respec-
tively for [(L3)Ru(bpy)2](PF6)2 and [(L2){Ru(bpy)2}2](PF6)4
with a value slightly higher for [(L1)Ru(bpy)2](PF6)2 at
0.98 V. The rhenium complexes were prepared from the
reaction between [Re(CO)5Cl] and L1-L4 in refluxing
Computational Details. Density functional theory (DFT)
calculations were carried out using the Gaussian 03 Package28
(Gaussian, Inc.). Frequency and time-dependent (TD) calculations
were performed on the optimized ground-state structures. To in-
vestigate the triplet state structure of 7, geometry optimization of the
model compound [Re(4,6-dpb)(CO)3Cl] (4,6-dpb =4,6-diphenyl-
2,20-bipyridine) in a triplet-state configuration were also performed.
(29) Howell, S. L.; Scott, S. M.; Flood, A. H.; Gordon, K. C. J. Phys.
Chem. A 2005, 109, 3745–3753.
(30) Walsh, P. J.; Gordon, K. C.; Officer, D. L.; Campbell, W. M. J. Mol.
Struc., THEOCHEM 2006, 759, 17–24.
(31) Schaftenaar, G.; Noordik, J. H. J. Comput.-Aided Mol. Des. 2000, 14,
123–134.
(32) O’Boyle, N. M.; Tenderholt, A. L.; Langner, K. M. J. Comput. Chem.
2008, 29, 839–845.
(33) Howell, S. L.; Gordon, K. C.; Waterland, M. R.; Leung, K. H.;
Phillips, D. L. J. Phys. Chem. A 2006, 110, 11194–11199.
(34) Chipman, D. M. J. Chem. Phys. 2000, 112, 5558–5565.
(35) Tomasi, J.; Mennucci, B.; Cances, E. J. Mol. Struc., THEOCHEM
1999, 464, 211–226.
(24) Howell, S. L.; Gordon, K. C. J. Phys. Chem. A 2004, 108, 2536–2544.
(25) Howell, S. L.; Matthewson, B. J.; Polson, M. I. J.; Burrell, A. K.;
Gordon, K. C. Inorg. Chem. 2004, 43, 2876–2887.
(26) Walsh, P. J.; Gordon, K. C.; Lundin, N. J.; Blackman, A. G. J. Phys.
Chem. A 2005, 109, 5933–5942.
(27) Lind, S. J.; Gordon, K. C.; Waterland, M. R. J. Raman Spectrosc.
2008, 39, 1556–1567.
(28) Frisch, M. J. et al. Gaussian 03; Gaussian,Inc.: Wallingford, CT, 2003.
(36) Charlot, M.-F.; Aukauloo, A. J. Phys. Chem. A 2007, 111, 11661–
11672.
(37) Vlcek, A. J.; Zalis, S. J. Phys. Chem. A 2005, 109, 2991–2992.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4077
Scheme 1. Synthesis Schemes for the Ligands L1-L4 and Numbering for the Ruthenium and Rhenium Complexes
toluene. The materials were purified by recrystallization.
Retention of solvent molecules by aromatic phosphazene-
based ligands and their complexes is a common occur-
rence in our experience (even after prolonged drying
under vacuum). The presence of solvent is confirmed by
shows the expected ligand bipyridine coordination mode with
the Re(I) coordination sphere being composed of a “N2C3Cl”
donor set. Selected bond lengths and angles are given in
Table 2. The Re(I) ion lies in a distorted octahedral environ-
ment with three Re-C bonds of between 1.907(6) and
1
˚
the microanalytical data, H NMR spectra, and X-ray
1.940(7) A to the carbonyl ligands and two similar Re-N
˚
bonds of 2.180(4) and 2.192(4) A to the bipyridine nitrogen
data where possible. There is a precedent for this behavior
in phosphazene chemistry, and it has been exploited in the
design of clathrate systems.38
˚
donors. The Re-Cl bond length is 2.4731(14) A. The 7-mem-
bered ring containing the O-P-O linkage that fuses the pyri-
dyl rings of the bipyridyl ligand causes some distortion from
the ideal ligand plane. Hence the mean planes of the coordi-
nating pyridine rings are rotated by approximately 25° to one
another, although the biphenyl moieties bound to the remain-
ing two phosphorus atoms in the molecule have considerably
larger interannular torsion angles of approximately 45°.
[(L4)Re(CO)3Cl] 0.26H2O (7 0.26H2O). The crystal
X-ray Crystallography. [(L1)Re(CO)3Cl] 3CDCl3 (4
3CDCl3). The crystal structure of the complex (Figure 1)
3
3
(38) (a) Allcock, H. R.; Sunderland, N. J.; Primrose, A. P.; Rheingold, A.
L.; Guzei, I. A.; Parvez, M. Chem. Mater. 1999, 11, 2478–2485. (b) Cameron,
T. S.; Borecka, B. Phosphorus Sulfur 1992, 64, 121–128. (c) Allcock, H. R.;
Levin, M. L. Acc. Chem. Res. 1985, 18, 1324–1330. (d) Haddon, R. C.;
Chichester-Hicks, S. V.; Mayo, S. L. Inorg. Chem. 1988, 27, 1911–1915. (e)
Allcock, H. R. Acc. Chem. Res. 1978, 11, 81–87.
3
3
structure of the complex (Figure 2) shows essentially the

4078 Inorganic Chemistry, Vol. 49, No. 9, 2010
Horvath et al.
Figure 2. View of complex, [(L4)Re(CO)3Cl] (7), with the hydrogen
atoms removed for clarity.
Figure 1. View of complex [(L 1)Re(CO)3Cl] (4), with the hydrogen
atoms removed for clarity.
1
4
˚
˚
Table 2. Selected Bond Lengths (A) and Angles (deg) for [(L )Re(CO)3Cl] (4)
Table 3. Selected Bond Lengths (A) and Angles (deg) for [(L )Re(CO)3Cl] (7)
Re(1)-C(35)
Re(1)-C(36)
Re(1)-C(37)
1.925(6)
1.907(6)
1.940(7)
Re(1)-N(4)
Re(1)-N(5)
Re(1)-Cl(1)
2.192(4)
2.180(4)
2.4731(14)
Re(1)-C(53)
Re(1)-C(54)
Re(1)-C(55)
1.921(7)
1.900(7)
1.919(7)
Re(1)-N(4)
Re(1)-N(5)
Re(1)-Cl(1)
2.181(6)
2.171(5)
2.4932(16)
P(1)-N(1)
P(1)-N(3)
P(2)-N(1)
1.560(5)
1.567(5)
1.586(5)
P(2)-N(2)
P(3)-N(2)
P(3)-N(3)
1.576(5)
1.572(5)
1.594(4)
P(1)-N(1)
P(1)-N(3)
P(2)-N(1)
1.566(7)
1.593(6)
1.580(7)
P(2)-N(2)
P(3)-N(2)
P(3)-N(3)
1.585(7)
1.571(7)
1.579(6)
C(35)-Re(1)-C(37)
C(36)-Re(1)-C(35)
C(36)-Re(1)-C(37)
C(35)-Re(1)-N(4)
C(36)-Re(1)-N(4)
C(37)-Re(1)-N(4)
C(35)-Re(1)-N(5)
C(36)-Re(1)-N(5)
87.8(3)
87.2(3)
88.9(3)
98.3(2)
173.5(2)
94.8(2)
174.0(2)
98.8(2)
C(37)-Re(1)-N(5)
N(5)-Re(1)-N(4)
C(35)-Re(1)-Cl(1)
C(36)-Re(1)-Cl(1)
C(37)-Re(1)-Cl(1)
N(4)-Re(1)-Cl(1)
N(5)-Re(1)-Cl(1)
91.9(2)
75.8(2)
96.3(2)
93.8(2)
175.2(2)
82.1(1)
83.8(1)
C(54)-Re(1)-C(53)
C(54)-Re(1)-C(55)
C(55)-Re(1)-C(53)
C(53)-Re(1)-N(4)
C(54)-Re(1)-N(4)
C(55)-Re(1)-N(4)
C(53)-Re(1)-N(5)
C(54)-Re(1)-N(5)
89.4(3)
91.3(3)
86.1(3)
169.8(3)
97.7(2)
101.0(2)
97.5(3)
94.7(2)
C(55)-Re(1)-N(5)
N(5)-Re(1)-N(4)
C(53)-Re(1)-Cl(1)
C(54)-Re(1)-Cl(1)
C(55)-Re(1)-Cl(1)
N(4)-Re(1)-Cl(1)
N(5)-Re(1)-Cl(1)
173.1(2)
74.7(2)
91.7(2)
178.3(2)
90.0(2)
81.0(1)
83.9(1)
same coordination mode for the distorted octahedral Re(I)
coordination sphere as 4. Selected bond lengths and angles
are given in Table 3. In this case the Re-C bonds range
hypodentate rings and the nearest carbonyl ligands (3.082
˚
and 3.067 A respectively for [Re(tpy)(CO)3Cl] and 7). The
˚
oxygen atoms of these carbonyl ligands lie 3.254 and 3.204 A
˚
between 1.900(7) and 1.921(7) A, and there are two similar
from the centroid of the phenyl ring in 7 and pyridine ring in
[Re(tpy)(CO)3Cl] and could be considered as participating
in intramolecular forms of π-carbonyl interactions that have
been reported elsewhere.41
˚
Re-N bonds of 2.171(5) and 2.181(6) A to the bipyridine
˚
nitrogen donors. The Re-Cl bond length is 2.4932(16) A.
The geometries about the coordinated/Re(I) centers in 4
and 7 are similar to those seen in [Re(phen)(CO)3Cl]
(phen =1,10-phenanthroline);39 however, the binding in 7
more closely resembles [Re(tpy)(CO)3Cl] (tpy =2,20,200-
terpyridine) in which the tpy ligand acts in a bidentate man-
ner.40 The steric hindrance offered by the uncoordinated
aromatic rings causes the bipyridine moiety to approach the
metal at a slight angle. Hence, in [Re(tpy)(CO)3Cl] and 7 the
mean planes of coordinated bipyridine moieties lie at angles
of 20 and 21°, respectively, to the mean coordination planes
in which the nitrogen atoms bind. The torsion angle between
the coordinated and the uncoordinated pyridine ring in
[Re(tpy)(CO)3Cl] is 130° and similar to the torsion angle
of 129° between the coordinated pyridine ring and the
6-phenyl ring in 7. This twisting still leaves short intra-
molecular contacts between the ipso-carbon atoms on the
Vibrational Spectra. FT-IR spectra are dominated by
aromatic ring deformations and are thus mostly similar
for compounds of ligands with similar phosphazene-
substitution (i.e., L1 and L2 are similar, as are L3 and L4).
Carbonyl stretching frequencies, available for 4-7, are
however quite informative (Table 4). Most notably, the
symmetric stretching mode of 4 at 2026 cm-1 appears red-
shifted in 5-7 to 2021 cm-1, which is consistent with
decreased πL* f dπ back-donation and suggests a slightly
more electron-poor bipyridine unit.42-44 Representative
(41) (a) Egli, M.; Sarkhel, S. Acc. Chem. Res. 2007, 40, 197–205. (b)
Gambaro, A.; Ganis, P.; Manoli, F.; Polimeno, A.; Santi, S.; Venzo, A. J.
Organomet. Chem. 1999, 583, 126–130.
(42) Worl, L. A.; Duesing, R.; Chen, P.; Della Ciana, L.; Meyer, T. J. J.
Chem. Soc., Dalton Trans. 1991, 849–858.
(43) Alsindi, W. Z.; Easun, T. L.; Sun, X. Z.; Ronayne Kate, L.; Towrie,
M.; Herrera, J.-M.; George, M. W.; Ward, M. D. Inorg. Chem. 2007, 46,
3696–3704.
(44) Gamelin, D. R.; George, M. W.; Glyn, P.; Grevels, F.-W.; Johnson,
F. P. A.; Klotzbuecher, W.; Morrison, S. L.; Russell, G.; Schaffner, K.;
Turner, J. J. Inorg. Chem. 1994, 33, 3246–3250.
(39) Haddad, S. F.; Marshall, J. A.; Crosby, G.; Twamley, B. Acta
Crystallogr., Sect. E 2002, E58, m559–m561.
(40) Civitello, E. R.; Dragovich, P. S.; Karpishin, T. B.; Novick, S. G.;
Bierach, G.; O’Connell, J. F.; Westmoreland, T. D. Inorg. Chem. 1993, 32,
237–241.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4079
Table 4. Carbonyl Stretching Frequencies Found in the FT-IR Spectra of
Compounds 4-7a
The absorption spectra of 2 and 3 are very similar to the
,
spectrum of [Ru(bpy)3]2þ 45,46
where the band around 450
ν(CO)/cm-1
nm has been attributed to a (HOMO-2, HOMO-1) f
(LUMOþ1, LUMOþ2) MLCT transition,46 correspond-
ing to the reduction of a single bipyridine ligand.47 This is
largely consistent with our assignment of the lowest-
energy transition calculated at 414 nm (Supporting In-
formation, Table S1). Although transitions with signifi-
cant HOMO f LUMO character are calculated at lower
energies, they show far lower oscillator strengths. They
perhaps contribute to the red edge of the absorption
band. In comparison, compound 1 shows a red-shift of
the lowest-energy band to 468 nm. This is due to a
lowering of the π* molecular orbital energy with respect
to the metal dπ orbital, indicating electron-deficiency
caused by substitution with CTP.42 Here the transition
is calculated to originate from the HOMO-3 orbital,
terminating on the HOMO and HOMOþ2 orbitals.
The decrease compared to 2 offsets the effect of the
geometric constraints imposed by substitution of the
bpy at two points, which increases the dihedral angle of
the two pyridine rings from planarity to ∼8° according to
DFT geometry calculations. The resulting decrease in
conjugation is expected to slightly increase the π* orbital
energy and thus the energy of the MLCT transition;
however, this is not observed. It should be noted that
the increase is far greater for the equivalent rhenium
compound (4), with a dihedral angle of ∼25°. From
DFT calculations, the bpy 3,30-H atoms of 1 are approxi-
4
5
6
7
symmetry
2026
1910
2021
1916
1894
2021
1916
1896
2021
1921
1886
a0
a00
a0
a All measurements are in KBr. Symmetry assignments are from
ref 44.
˚
mately 2.68 A from the N atoms of the ancillary bpy
Figure 3. FT-Raman spectra of compounds 1, 2, 4, 5, and 7 acquired in
KBr. Spectra of 3 and 6 are represented by those of 2 and 7.
ligands, which is shorter than the sum of their van der
Waals radii. This suggests that perhaps intramolecular
CH-π interactions are responsible for the decreased bi-
pyridine dihedral angle of 1 compared to 4, where ancil-
lary bipyridine ligands are absent.
FT-Raman spectra are shown in Figure 3. The spectra of
3 and 6 share most of their main features with those of 2
and 7, respectively, and are therefore omitted. As with
FT-IR, spectra are dominated by aromatic ring deforma-
tions, most notably characteristic bpy and biphenyl
stretches at about 1610 cm-1 as well as bpy breathing
modes at about 1030 cm-1. A number of minor peaks are
highlighted, as they correspond to significant vibrational
modes in resonance Raman (vide infra). It is important to
quantify the quality of the calculated spectra, as this
ensures that the calculations are producing an accurate
picture of the electronic structure and allows other calcu-
lated data to be trusted. We do this by comparing the
calculated vibrational spectra to the experimentally ob-
served data; good correlation gives confidence in calcu-
lated quantities, such as structure, vibrational modes, and
energetics.30 The mean absolute deviations calculated lie
between 8 and 10 cm-1 for Raman and IR spectra
respectively, which is quite satisfactory considering a
Compounds 5-7 show broad bands at about 392 nm,
which are calculated by TD-DFT at about 410 nm as
MLCT transitions originating predominantly in the
HOMO-1 orbitals and terminating in the LUMO orbitals.
A similar transition for [Re(bpy)(CO)3Cl] has previously
been measured at 388 nm (in CH2Cl2)48 and calculated at
403 nm (in MeCN, at the B3LYP/cc-pvdz level).49 Molecular-
orbital pictures (Figure 5) show that the relevant LUMOs
are mostly localized on the bipyridine unit rather than the
phenyl linker, indicating that conjugation with substituents
plays only a small role in the lowest-energy excitation. The
same applies to the 6-phenyl substituent of compound 7. In
the spectrum of 4 a similar band is found at a wavelength of
405 nm, mostly because of a HOMO-1 f LUMO transition
calculated at 428 nm (Supporting Information, Table S1).
As with 1, a shift to higher wavelengths is due to an energy-
decrease of the ligand π* orbital. Compounds 3 and 6 each
contain two metal-fluorophores, and for the UV-visible
spectrum the extinction coefficient values for each are
spectrometer resolution of 4 cm-1
.
Electronic Spectra. The electronic absorption spectra
of 1-7 are shown in Figure 4, and the lowest-energy
peaks are summarized in Table 5. The first eight calcu-
lated transitions with nonzero oscillator strengths can
be found in the Supporting Information, Table S1. It
should be noted that for the bimetallic compounds 3
and 6 the same low-energy transitions are calculated
for each metal center, therefore essentially doubl-
ing each transition observed for compounds 2 and 5
respectively.
(45) de Carvalho, I. M. M.; Moreira, I. d. S.; Gehlen, M. H. Polyhedron
2005, 24, 65–73.
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4080 Inorganic Chemistry, Vol. 49, No. 9, 2010
Horvath et al.
Figure 4. UV-visible spectra of (a) the ruthenium compounds and (b) the rhenium compounds. All spectra were acquired in dichloromethane.
Table 5. UV-Visible Absorption, Emission, and Lifetime Dataa
Making the assumption that the emission energy is com-
parable to the energy gap (i.e., ΔE ≈ Eem),54 the change in
λ
abs(ε)/nm
lifetime is not inconsistent with the energy-gap law.55,56
However, factors such as molecular rigidity or spin-orbit
effects have to be considered as well to fully explain this.
Shorter time-dynamics have been elucidated by Cannizzo
et al. for [Ru(bpy)3]2þ57 and [Re(bpy)(CO)3Cl].49 For
[Ru(bpy)3]2þ, population of a single 3MLCT state is
reported to occur on a 20 fs time scale through inter-
compound
(103 M-1 cm-1
)
λem/nm
τ/ns
1
2
3
4
5
6
7
468 (sh) (11)
455 (17)
454 (32)
405 (3.5)
392 (6.0)
392 (12)
392 (4.9)
452 (13)
388 (2.1)
647
614
613
659
629
630
634
597
598
380 ( 40
590 ( 60
670 ( 70
8 ( 1
47 ( 5
40 ( 10
27 ( 3
680
1
[Ru(bpy)3]2þb
system crossing (ISC) via the initially excited MLCT
state. For [Re(bpy)(CO)3Cl], ISC occurs to two 3MLCT
states in about 85-160 fs. Both states radiatively decay on
a time scale of nanoseconds; however, since conversion
from the higher to the lower 3MLCT state occurs in less
than 0.5 ps, phosphorescence is in practice only observed
from the latter.
[Re(bpy)(CO)3Cl]c
39
a All measurements are at room temperature in dichloromethane.
b From ref 52. c From ref 48.
essentially added, which is especially apparent at about
300 nm and higher wavelengths in comparison with 2 and
5. This is strong evidence that there is no communication via
CTP. The linear addition of absorbance breaks down around
240 nm, as this region corresponds to a π fπ* LC transition
of the biphenyl moieties.50,51 Therefore relatively little
change in the UV-visible properties of compounds 1-7 is
Resonance Raman (RR) Spectroscopy. RR shows selec-
tive enhancement of modes within active chromophores,
where the excitation wavelength (λex) determines which
particular chromophore is being probed. This makes
vibrational mode assignment by direct comparison to
calculated spectra very difficult; however, it is possible
via FT-Raman spectra, which show near-identical fre-
quencies. The spectra of representative compounds ac-
quired at 350.7 and 444.3 nm are shown in Figure 6a and
Figure 6b and correspond to ligand-centered π f π* and
MLCT transitions respectively. Although spectra were
also acquired at other wavelengths, these are omitted as
they display band positions and intensities that are almost
identical to the 444.3 nm spectrum. 444.3 nm was chosen
as it gave a good signal-to-noise ratio, and it corresponds
to transitions that are well into the MLCT regime for all
compounds. Again, 3 and 6 are omitted as they show
almost identical spectra to 2 and 5 respectively. The most
significant vibrational modes are summarized in Table 6.
observed compared to [Re(bpy)(CO)3Cl] and [Ru(bpy)3]2þ
.
Some electron-withdrawing properties are observed in the
lowering of the π*L orbitals.
Generally the observed lifetimes and emission maxima
are similar to those of the reference complexes [Ru-
(bpy)3]2þ 52 and [Re(bpy)(CO)3Cl].48,53 For both com-
plexes the emission is attributed to decay from a 3MLCT
state.48,52,53 The fact that, for each sample, the emission
spectra shows a single exponential (as a function of
3
emission λ) is consistent with a single MLCT emitting
state for compounds 1-7. The excited-state lifetimes are
somewhat lower for compounds in which the bpy-CTP
attachment is more intimate, compounds 1 and 4, while
their maximum emission wavelengths are increased.
(50) Mulazzi, E.; Ripamonti, A.; Athouel, L.; Wery, J.; Lefrant, S. Phys.
Rev. B 2002, 65, 085204/1–085204/9.
(51) Beenken, W. J. D.; Lischka, H. J. Chem. Phys. 2005, 123, 144311/
1–144311/9.
(54) Caspar, J. V.; Kober, E. M.; Sullivan, B. P.; Meyer, T. J. J. Am.
Chem. Soc. 1982, 104, 630–632.
(55) Treadway, J. A.; Loeb, B.; Lopez, R.; Anderson, P. A.; Keene, F. R.;
Meyer, T. J. Inorg. Chem. 1996, 35, 2242–2246.
(52) Durham, B.; Caspar, J. V.; Nagle, J. K.; Meyer, T. J. J. Am. Chem.
Soc. 1982, 104, 4803–4810.
(53) Sato, S.; Sekine, A.; Ohashi, Y.; Ishitani, O.; Blanco-Rodriguez, A.
M.; Vlcek, A. J.; Unno, T.; Koike, K. Inorg. Chem. 2007, 46, 3531–3540.
(56) Damrauer, N. H.; Boussie, T. R.; Devenney, M.; McCusker, J. K. J.
Am. Chem. Soc. 1997, 119, 8253–8268.
(57) Cannizzo, A.; van Mourik, F.; Gawelda, W.; Zgrablic, G.; Bressler,
C.; Chergui, M. Angew. Chem., Int. Ed. 2006, 45, 3174–3176.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4081
Figure 5. MO pictures of MLCT transitions of compounds 2 (a) and 7 (b) as calculated in a dichloromethane solvent field. The fluorophores on the
ruthenium and rhenium compounds respectively show very similar MO pictures. The CTP units are omitted for clarity.
Figure 6. Resonance Raman (RR) spectra of compounds 1, 2, 4, 5, and 7 at excitation wavelengths (a) 350.7 nm and (b) 444.3 nm. All spectra were
acquired in dichloromethane. The solvent peaks are marked by asterisks.
Table 6. Vibrational Modes Corresponding to Significant Peaks in the FT-Raman and Resonance Raman Spectraa
a Compounds displaying these or similar modes are listed.
At an excitation wavelength of 350.7 nm compound 1shows
resonance-enhancement of the modes at 1565 and 1080
cm-1, and especially at 1456 cm-1. While a vibration of
the ancillary bpy ligands is responsible for the former, the
latter two modes correspond to vibrations of the CTP-
attached bpy ligand, which implies significant involvement
in the transition of this moiety. In 2 (and thus 3) resonance
enhancement is seen in both CTP-attached and ancillary
bpy ligands, for example, peaks at 1541 and 1563 cm-1
respectively. At 444.3 nm excitation, however, the features
corresponding to ancillary bpy increase in relative intensity
for compounds 1-3. Especially marked in this respect are
the peaks at about 1489 and 1317 cm-1. This suggests
that MLCT transitions involve predominantly the CTP-
attached ligands while the more energetic π f π* transitions
occur on both CTP-attached and ancillary bipyridine li-
gands. The few peaks seen in the RR spectrum of 4 all
correspond to bpy vibrations while, in comparison with the
spectrum of 1 (Figure 6b), all vibrations due to ancillary bpy
ligands are obviously absent. The mode at 1456 cm-1 is very
similar to the one observed for 1, and its absence at 444.3 nm
supports the π f π* assignment. The spectra of 5-7 are
very similar to the RR spectrum of [Re(bpy)(CO)3Cl] mea-
sured by Smothers and Wrighton,58 who assign the ob-
served modes to vibrations of bpy. Comparison with DFT-
calculated Raman modes confirms this (Table 6). Some
differences exist between the spectra, however; compounds
(58) Smothers, W. K.; Wrighton, M. S. J. Am. Chem. Soc. 1983, 105,
1067–1069.

4082 Inorganic Chemistry, Vol. 49, No. 9, 2010
Horvath et al.
excited-state localization of the electron in compounds 2 and
3. The modes observed for 1 are slightly red-shifted in
comparison, indicating weaker binding within the bipyridine
moiety in the triplet-state of this compound. This is good
evidence for the localization of the excited-state electron on a
single bipyridine moiety in compounds 1-3. Compounds
4-7 generally show weaker excited-state features due to the
lower excited-state population because of the decreased
lifetimes; however, they are still visible. For example, 4
-
3
displays bpy
features at 1558, 1431 (observed in the
solvent-subtracted spectrum) and 1279 cm-1. Compounds
5 and 6 show excited-state features at about 1286, 1210 and
as a shoulder at 1019 cm-1, while similar peaks are observed
at 1289, 1240, and 1013 cm-1 for 7. They are again attribu-
table to the bipyridine radical anion58,60 and again deviations
from literature-values of [Re(bpy)(CO)3Cl] exist, indicating
involvement of the phenyl and therefore partial localization
of the excited state on this moiety. As with the ruthenium
compounds above, the peak at about 1603 cm-1 appears
enhanced relative to the resonance Raman spectra, which
supports this conclusion.
Figure 7. Transient resonance Raman spectra of some compounds
acquired in dichloromethane at energies of 3.10 mJ/pulse. The solvent
peaks have been subtracted for clarity.
5 and 6 show a bpy-deformation peak at 1330 cm-1, while a
similar mode is observed at 1372 cm-1 in the spectrum of 7
(Figure 6a). Accordingly, for 7 this mode involves the
6-substituted phenyl. Also observed is a totally symmetric
carbonyl stretch at 2031 cm-1 for 4and about 2026 cm-1 for
5-7. This is further evidence for the presence of a MLCT
state at wavelengths of 444.3 nm and higher as the relative
intensity of these modes is stronger at these excitation-
wavelengths.
Conclusion
New cyclotriphosphazene ligands, L1, L2, L3 and L4, have
been prepared from the reaction of sodium or cesium salts of the
hydroxy species, (HO)2bpy, HOPhbpy, and HOPhbpyPh with
the appropriate cyclotriphosphazene precursors. The ruthe-
nium- and rhenium-containing fluorophores attached to phos-
phazenes in the compounds 1-7 were obtained from the
reactions of the free ligands with [Ru(bpy)2Cl2] or [Re(CO)5-
Cl]. All the compounds were characterized by elemental ana-
lyses, 31P and 1H NMR, and, in some cases, electrospray mass
spectrometry. Two of the rhenium complexes, 4 and 7, were also
characterized by single crystal X-ray crystallography and shown
to have the bipyridyl moiety coordinated giving a distorted
octahedral “N2C3Cl” coordination sphere around the metal.
Using resonance Raman, it was found that the transitions res-
ponsible for the bands at about 460 and 390 nm for the ruthe-
nium and rhenium compounds, respectively, are metal to ligand
charge-transfer in character, while the higher-energy bands are
π f π*. This is in accordance with TD-DFT calculations, which
were used to visualize the transition in terms of a HOMO/
HOMO-1 f LUMO MLCT. Direct observation of the excited
state bpy•- radical anion with transient resonance Raman
spectroscopy confirmed the localized nature of the excited states,
Transient Resonance Raman (TR2) Spectroscopy. TR2
enables the examination of the excited-state structure in a
similar fashion that RR is used for the ground-state. The
leading edge of an intense laser pulse is used to generate
molecules in the excited state, and the rest of the pulse then
probes this state, provided the excited-state population is
sufficiently high. Various pulse-energies (0.96 mJ/pulse, 1.84
mJ/pulse, and 3.10 mJ/pulse) were used to examine the
variation in the amount of excited state generated. The
photon to molecule ratio is about 30 for the highest pulse
energy.59 As with RR, the metal-bipyridyl unit is mostly
responsible for the observed peaks. Therefore the TR2
spectra of 3 and 6 are represented by those of 2 and 5,
respectively, in Figure 7. Identification of excited-state fea-
tures is carried out by comparison to the ground state (λex =
351 nm) resonance Raman spectra. A significant number of
ground-state features are observed; however, also clearly
visible are excited-state features corresponding to the radical
similarly to [Re(bpy)(CO)3Cl] and [Ru(bpy)3] 2þ
.
In conclusion, the study shows that the emissive properties
of Ru(bpy) and Re(bpy) luminophores are not greatly
perturbed when attached to CTP units if the covalent bond-
ing is through a bpy linker substituent (such as a phenoxy
group in L2, L3, and L4). If the bpy luminophore is bound to
the CTP unit directly through the 6,60 positions (L1), then the
emissive properties are somewhat altered; however, they are
not severely compromised. Generally, compounds 1-7 were
shown to behave similarly to the corresponding metal bipyridyl-
units without the CTP unit. This lack of interaction between
fluorophore and chemically robust CTP unit has significance
with respect to the potential applications of substituted cyclic
phosphazenes in devices such as OLEDs. In principle, robust
polymers may be formed from cyclic phosphazene that do
anion of 2,20- bipyridine (bpy -).47,58 Characteristic bpy
-
3
3
peaks are observed at about 1430, 1283, 1208, and 1013 cm-1
for 2 and 3.47 These values represent no obvious trend in
terms of their differences from literature values for
[Ru(bpy)3]2þ; however, all are within 6 cm-1. The peaks at
about 1603 cm-1 occur with a higher relative intensity
compared to the resonance Raman spectra. They appear
similar to the peak at 1599 cm-1 in the excited-state reso-
nance Raman spectrum of [Ru(dpb)3]2þ (dpb = 4,40-
diphenyl-2,2-bipyridine), measured by Damrauer et al.,56
which suggests some phenyllinker involvement exists in the
(59) Calculated by comparison of the number of photons in a single pulse
(5.5 ꢀ 1015 photons at 350.7 nm) with the number of molecules in the sample.
At a spot-size of approximately 300 μm and a penetration depth of 1 mm, the
irradiated volume of sample is 2.83 ꢀ 10-7 L, which corresponds to 1.70 ꢀ
1014 molecules.
(60) Lewis, J. D.; Clark, I. P.; Moore, J. N. J. Phys. Chem. A 2007, 111,
50–58.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4083
not affect the electronic properties of the metal complex.
Effectively the phosphazene polymer could act as a highly
chemically and thermally robust lattice holding electronic
materials, such as luminophores and hole- and electron-
transport units, within this matrix.
and UOO0611). The support of the University of Otago,
Foundation of Research Science and Technology, the
Royal Society of New Zealand, and the MacDiarmid
Institute for Advanced Materials and Nanotechnology is
gratefully acknowledged.
Acknowledgment. We thank Dr. K. Wagner for assis-
tance with electrochemical measurements and gratefully
acknowledge financial support from the Massey Univer-
sity Research Fund and RSNZ Marsden Funds (MAU208
Supporting Information Available: Crystallographic informa-
tion for compounds 4 3CDCl3 and 7 in CIF format. TD-DFT
transitions calculated for compounds 1-7. This material is
available free of charge via the Internet at http://pubs.acs.org.
3