Synthesis and characterization of heteroleptic cyclometalated divalent osmium Os[P(C6H5)3]2(CO) (Na?C-)Cl complexes

Article abstract of DOI:10.1016/j.inoche.2013.09.022

Simple synthetic procedure, reaction of Os[P(C₆H ₅)₃]₂(CO)₂Cl₂ with 2-phenylpyridine (or other similar Na?CH chelating ligands) in boiling 2-(2-ethoxyethoxy)ethanol solution leads to Os[P(C

Full text of DOI:10.1016/j.inoche.2013.09.022

Inorganic Chemistry Communications 37 (2013) 26–29
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis and characterization of heteroleptic cyclometalated divalent
osmium Os[P(C6H5)3]2(CO)(N∩C−)Cl complexes
b
Agnieszka Woźna a, Andrzej Kapturkiewicz a,b, , Gonzalo Angulo
⁎
a
Institute of Chemistry, Faculty of Sciences, University of Siedlce, 3 Maja 54, 08–110 Siedlce, Poland
Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01–224 Warsaw, Poland
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 April 2013
Accepted 12 September 2013
Available online 21 September 2013
Simple synthetic procedure, reaction of Os[P(C6H5)3]2(CO)2Cl2 with 2-phenylpyridine (or other similar N∩CH
chelating ligands) in boiling 2-(2-ethoxyethoxy)ethanol solution leads to Os[P(C6H5)3]2(CO)(N∩C−)Cl com-
plexes. Structures of the obtained species have been elucidated by means of 31P NMR and FT-IR techniques as
well as elemental analysis data. The UV–vis absorption and emission properties of the newly synthesized com-
plexes reveal the MLCT character of their lowest singlet and triplet excited states.
Keywords:
Osmium carbonyls
© 2013 Elsevier B.V. All rights reserved.
Chelating cyclometalated base ligands
31P NMR
FT-IR and UV–vis spectroscopy
Luminescent transition–metal complexes have received in recent
years a great deal of attention due to their rich photophysical properties
as well as their potential applications in light-to-electricity (dye-
sensitized solar cells) [1–3] and electricity-to-light (OLED or PLED) [4–6]
conversion devices. Among many possible metal–ligand(s) combinations,
the transition–metal complexes with d6 or d8 electron configuration with
various bi- or poly-dentate cyclometalated ligands (e.g., 2-phenylpyridine
ppy and its derivatives) forming metal–carbon bonds [7] are particularly
interesting because of their well pronounced emissive properties with
high quantum efficiency already at room temperature [8–14]. Strong
spin–orbit coupling in these d6 and d8 complexes results in efficient
intersystem crossing of the singlet state to the triplet manifold because
the presence of heavy metal ion removes the spin forbidden nature of
phosphorescence that results in emission from their lowest excited state.
Generally, depending on the nature of central metal ion as well as on
the coordinated ligand(s) the phosphorescence may originate from the
intra-ligand (IL) excited states or from the metal-to-ligand charge-
transfer (MLCT) excited state [15]. The latter case seems to be especially
interesting, because, upon variation of the substituents or even the
skeletal designs the coordinated ligand(s), one can tune the luminescent
properties of organometallic phosphors, particularly the emission wave-
lengths, efficiencies, and life-times [16]. This can be done changing the
main coordinated chromophore involved into the MLCT transition and/
or the auxiliary ligand(s). In particular cases it may result in design of
phosphors showing efficient luminescence in the near infrared (NIR) re-
gion at wavelengths longer than 700 nm as well as in saturated blue or
even near-UV phosphorescent materials. In this latter respect the pres-
ence of the auxiliary ligands like CO or phosphines may distinctly im-
prove the photophysical properties of organometallic emitters because
ligands with great π-accepting character stabilize the occupied metal-
based orbitals with parallel destabilization of the metal-centered excited
states due to the strong back-bonding properties of π-acid ligands. The
first of these effects usually leads to hypsochromic shifts of the 3⁎MLCT
emission whereas the second may block undesirable non-radiative deac-
tivation of the 3⁎MLCT state via 3⁎MLCT → dd inter-system crossing.
Both of the above mentioned effects may result in essential enhance-
ment of the emission quantum yield as it, for example, was observed
for the Os(bpy)23+ complex where one of the coordinated 2,2′-bipirydyl
molecule was replaced by the bidentate phosphine ligand cis-1,2-
bis(diphenylphosphino)ethylene
–
dppv [17,18]. The resulting
Os(bpy)2(dppv)2+ chelate, unlike Os(bpy)23+, shows very intense
room-temperature luminescence with an emission quantum yield
three orders of magnitude greater than that of Os(bpy)23+. Extremely
large emission quantum efficiencies have also been found for
Os(N∩N)(P∩P)(CO)Cl+ cations where N∩N and P∩P are coordinated
1,10-phenanthroline derivatives and bidentate phosphine ligands,
respectively. In a similar way the cyclometalated Os2+ complexes
with auxiliary CO and/or phosphine ligands are strongly emissive
organometallic phosphors [19–22]. Likewise to reported for Ir3+ and
Pt2+ complexes with various cyclometalated chromophores the emis-
sion properties of less elaborated osmium(II) chelates can be modified
by introducing appropriate changes in the cyclometalated ligands coor-
dinating the Os2+ ion [23–26].
Usually the cyclometalated Os2+ complexes can been prepared
using Os3(CO)12 as starting reactant [23–26]. Typical procedures involve
heating of a mixture of the carbonyl reagent and an appropriate
⁎
Corresponding author at: Institute of Physical Chemistry, Polish Academy of Sciences,
Kasprzaka 44/52, 01-224 Warsaw, Poland. Tel.: +48 22 6323221; fax: +48 22 6323333.
E-mail address: akapturkiewicz@ichf.edu.pl (A. Kapturkiewicz).
1387-7003/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2013.09.022

A. Woźna et al. / Inorganic Chemistry Communications 37 (2013) 26–29
27
chelating ligand L giving rise to cis-dicarbonyl complexes Os(CO)2 L2.
The obtained intermediates Os(CO)2L2 can be further converted, after
decarbonylation with freshly sublimed (CH3)3NO, to the Os(P)(CO)L2,
Os(P)2 L2 or Os(P∩P)L2 products by the substitution with appropriate
mono- (P) or bidentate phosphines (P∩P), correspondingly. Despite
that three steps are required to complete the synthesis, the final prod-
ucts are affordable with high yields up to 70%. On the other hand one
can expect that the above described procedure can be somewhat simpli-
fied if other reactants, namely Os(P)2(CO)2Cl2 or Os(P∩P)(CO)2Cl2,
would be applied as starting materials. To check this possibility we
have performed the reaction of Os(P(C6H5)3)2(CO)2Cl2 complex with a
series of the cyclometalated ligands N∩C−. Somewhat unexpectedly, in-
stead of the anticipated Os[P(C6H5)3](CO)(N∩C−)2 or Os[P(C6H5)3]2
(N∩C−)2 products we have obtained chelates with general formulae
of Os[P(C6H5)3]2(CO)(N∩C−)Cl. The obtained products have been iso-
lated and characterized. Here we present the preliminary results of
our investigations.
conversions have occurred with lower, ca. 20–35% yields. Noteworthy,
analogously performed reactions of Os[P(C6H5)3]2(CO)2Cl2 with all three
ligands from the parental 2-phenyl-benzazole family were unsuccessful,
contrary to their difluoro substituted derivatives. Evidently the presence
of the electron withdrawing substituents is essential for an efficient for-
mation of the Os−C bond. Perhaps, application of more drastic synthesis
conditions would result in the analogous products also in the cases of
unreactive 2-phenyl-benzazoles.
Products of the performed syntheses have been separated from
unreacted Os[P(C6H5)3)]2(CO)2Cl2 intermediate by means of column
chromatography. In most cases the synthesized complexes have been
separated and purified applying silica gel with CH2Cl2/n-hexane (1:1
or 2:1) mixtures as eluent. However, in the cases of the products
obtained in the reaction with 3,5-F2-pbi and 2,4-F2-pbi ligands a combi-
nation of neutral alumina with pure CH2Cl2 was more effective.
The isolated substances have been further characterized by means of
FT-IR spectra recorded in KBr matrices. In all investigated substances
only one band in the stretching region of carbonyl group has been
found with a value of νCO intrinsically depending on the nature of the li-
gand used in each specific case (cf. data in Table 1) indicating that the
synthesized species must contain at least one ligand molecule in the
Os2+ coordination sphere. This conclusion remains in nice agreement
with the different emission colours observed when crude as well as iso-
lated reaction products are irradiated with handheld UV lamp. Taking
into account the above described observations one can anticipate molec-
ular structures of the synthesized species. Assuming monomeric nature
of the synthesized complexes with octahedral coordination of the central
Os2+ ion, the two following structures, Os[P(C6H5)3]2(CO)(N∩C−)Cl or
Os[P(C6H5)3](CO)2(N∩C−)Cl, seem to be the most probable with two
equivalent P(C6H5)3 ligands in the first or two equivalent CO molecules
in the second alternative [32]. Such assignment arises from single signal
and single carbonyl band in the recorded 31P NMR and FT-IR spectra
but lack of uncoordinated triphenylphosphine (or triphenylphosphine
oxide) among the isolated reaction products permits to prefer the struc-
ture with two coordinated P(C6H5)3 ligands.
The elemental analysis results, especially the ratio of C vs. N contents
point unambiguously to this option. For example in the case of the com-
plex synthesized with use of 2,4-F2-pbo ligand it has been found C, 59.67;
H, 3.85; N, 1.45; Cl, 3.76; whereas Os[P(C6H5)3]2(CO)(2,4-F2-pbo)Cl
requires C, 59.55; H, 3.60; N, 1.39; Cl, 3.52%, respectively. Similar agree-
ment has also been found for other investigated complexes. All investi-
gated complexes seem to contain CO, Cl− and N∩C− ligands located in
one horizontal plane whereas two P(C6H5)3 molecules occupy both
axial position.
From two possible isomers (containing CO molecule in the trans po-
sition vs. N or C− subunits of the coordinated N∩C− ligand, respectively)
only one of them is affordable within the used synthetic procedure. Lack
of crystallographic data does not allow to directly specify which one of
the possible isomers is obtainable under the applied synthetic conditions.
However, the available IR data allow us to prefer isomers with localization
of CO molecule in the trans position vs. hetero-aromatic fragments of the
coordinated N∩C− ligands. This assignment is based on the observed cor-
relation of νCO frequency with electron withdrawing character of the
The not commercially available Os[P(C6H5)3]2(CO)2Cl2 complex can
be straightforwardly synthesized by refluxing of mixture K2OsCl6 with
two-fold excess of P(C6H5)3 in deoxygenated N,N-dimethylfomamide
solutions for 1.5 h [27]. The resulting solution was cooled to room tem-
perature and then precipitated into water. The precipitated white solid
was filtered, dried and purified by means of column chromatography on
neutral Al2O3 with CH2Cl2 and further precipitated from the eluent solu-
tion by adding n-hexane. It allows to remove traces of unreacted
P(C6H5)3. The obtained colourless crystalline solid product (obtained
with a yield up to 85%) has been identified as identical to the already de-
scribed in literature trans-cis-cis-Os[P(C6H5)3]2(CO)2Cl2 by means of 31
P
NMR (singlet at −10.2 ppm) and FT-IR (two bands in CO vibration re-
gion at 1955 and 2027 cm−1) spectroscopy [28–30]. The applied syn-
thetic procedure seems to be more convenient than the previously
reported one because gaseous CO is not required.
The isolated Os(P(C6H5)3)2(CO)2Cl2 intermediate successfully re-
acted with some N∩CH cyclometalated ligands (structures depicted
in Fig. 1). The reactions were carried out in the deoxygenated boiling
2-(2-ethoxyethoxy)-ethanol solutions containing Os[P(C6H5)3]2(CO)2Cl2
with equimolar amount of the investigated ligand for 8–9 h [31]. The
resulting reaction mixtures were then cooled to room temperature and
precipitated into water. In some cases, syntheses performed with ppy
or 2,4-F2-ppy ligands, the reaction products can be also precipitated
using an excess of diethyl ether. The obtained strongly luminescent solids
were filtered, dried and tentatively analyzed using 31P NMR spectrosco-
py. In the recorded 31P NMR spectra two dominant signals have been ob-
served, the first one corresponding to unreacted Os[P(C6H5)3]2(CO)2Cl2
and the second (singlet located in the range 3–7 ppm) attributed to the
reaction product. Noteworthy no significant signals characteristic for
free P(C6H5)3 or possible PO(C6H5)3 by-product has been detected. This
fact suggests that both of P(C6H5)3 molecules present in the starting Os
[P(C6H5)3]2(CO)2Cl2 intermediate remain in the synthesized species. The
ratio of the recorded 31P NMR signals characteristic for the investigated
reactions substrate and product allows also estimating the conversion ef-
ficiency. Efficiencies as high as ca. 70–85% have been found in the case of
ppy or 2,4-F2-ppy co-reactants, whereas in the other reported cases
Fig. 1. Structural formulae of the ligands studied and their acronyms used in the text.

28
A. Woźna et al. / Inorganic Chemistry Communications 37 (2013) 26–29
Table 1
Summary of spectroscopic and photophysical data for the investigated Os(PPh3)2(CO)
Cl(N∩C−) complexes. Positions of 31P NMR signal, CO stretching vibration frequencies
e
ν
CO, UV–vis absorption maxima (νabs ), molar extinction coefficients (εM), 77 K lumines-
e
cence maxima (νem ), and 77 K luminescence life-times (τem). Data in CHCl3 solutions
(
31P NMR), KBr pellets (IR), acetonitrile solutions (UV–vis absorption), and butyronitrile
glasses (77 K luminescence).
31P NMRa) νCO
(ppm)
νabs
εM
(M−1 cm−1
νem
τem
(μs)
b)
c)
d)
e)
f)
e
e
Ligand
N∩C−
(cm−1
)
(cm−1
)
)
(cm−1
)
2,4-F2-pbi 4.32
3,5-F2-pbi 3.58
2,4-F2-ppy 4.89
2,4-F2-pbo 4.02
1916
1916
1915
1914
1904
1902
1891
25,850 2250
25,200 2500
24,700 2140
24,600 2580
24,200 1820
23,010 2550
20,950 3470
21,950, 20,670 12.9
20,220, 18,860 17.3
21,600, 20,450 11.1
21,100, 19,650 9.0
20,480, 19,350 17.0
20,150, 18,800 12.0
17,100, 16,050 18.4g)
ppy
6.15
2,4-F2-pbt 4.65
piq
6.04
Chemical shifts are referenced to 85% phosphoric acid; corresponding 31P NMR value
a)
for Os(PPh3)2(CO)2Cl2 = −10.15 ppm.
b)
Only one band has been observed in CO stretching vibration region of IR spectra;
corresponding νCO values for Os(PPh3)2(CO)2Cl2 are 1955 and 2028 cm−1
.
c)
Bands assigned to 1⁎MLCT ←S0 transition.
d)
e
ε
M values at wavenumber of UV–vis absorption maxima (column under νabs).
e)
f)
3⁎MLCT→ S0 emission with resolved vibronic structure.
Mono-exponential decays.
g)
Room temperature data in acetonitrile solutions: νem = 16,550 cm−1, ϕem = 0.14,
Fig. 2. UV–vis absorption (left) and emission (right) spectra of Os(P(C6H5)2)2(CO)(ppy)Cl
complex in room temperature acetonitrile solutions and 77 K butyronitrile glasses, re-
spectively (solid lines). Lower part of absorption spectrum (dotted line) expanded by factor
100. Emission spectrum is presented in an arbitrary intensity scale.
e
τem = 5.1 μs.
coordinated N∩C− ligand as it can be straightforwardly deduced from the
monotonic relationships between νCO and 1*MLCT←S0 absorption
or 3*MLCT→S0 emission maxima (cf. data in Table 1). Increase of the
electron-withdrawing properties of the coordinated bidentate N∩C− li-
gand results in bathochromic shift of νCO from 1916 to 1890 cm−1 in
the investigated Os[P(C6H5)3]2(CO)(N∩C−)Cl series indicating weaken-
ing of the C−O bond as well as strengthening of the Os−C bond in the
Os−C≡O fragment of the complexes. The larger the effect, the more pro-
nounced is the electron withdrawing character of the coordinated N∩C−
ligand. Because the observed changes in νCO values arise from the shift
of electron density from the C−O bond to the Os−C in bond one can
conclude that in the studied complexes trans position vs. CO molecule is
occupied by an electron-accepting moiety. Because the investigated
cyclometalating N∩C− ligands consist of two, electron-donating (∩C−)
and electron-accepting (N∩) subunits one can also conclude that the
second one is trans located to the coordinating CO molecule in the studied
Os[P(C6H5)3]2(CO)(N∩C−)Cl complexes.
resulted in the appearance of emission with longer life-time τem and re-
solved vibronic structure. Taking into account the measured emission
quantum yield ϕem = 0.14 at room temperature and the observed
change of τem from 5.1 to 18.4 μs one can conclude that at liquid nitrogen
temperature Os[P(C6H5)3]2(CO)(piq)Cl complex is strongly emissive
with ϕem as large as ca. 0.50. Other investigated complexes, despite lack
of emissive properties in room temperature solutions, emit strongly in
77 K butyronitrile glasses. In all investigated cases the observed struc-
tured emissions were, similarly to Os[P(C6H5)3]2(CO)(piq)Cl, very in-
tense with τem in the range of 10–20 μs. @Such long emission life-
e
times together with the mentioned above dependence of the νem on
the N∩C− ligand nature point undoubtedly to the 3*MLCT character of
the lowest excited state in Os[P(C6H5)3]2(CO)(N∩C−)Cl molecules.
Very long emission lifetimes correspond also to very low, lower than
Due to different electronic properties of N∩C− chelates coordinated
to the Os2+ core, the synthesized complexes display also well pro-
nounced changes in their photo-physical properties reflected in the
recorded UV–vis absorption and emission spectra. Representative exam-
ples of the recorded UV/Vis absorption and emission spectra are
presented in Figs. 2 and 3, while the numerical photophysical data are
summarized in Table 1. The intra-ligand absorption bands, located in
the 200–400 nm region, are broad without well-defined maxima where-
as a quite well separated additional low intensity band tail into the visible
accounting for the observed colours of the synthesized species. The posi-
tion of this band is nicely correlated with the electron affinity of N∩C− li-
gands what enables qualifying the lowest energy bands as 1*MLCT ← S0
transitions. The corresponding 3*MLCT ← S0 transitions, however, have
not been observed in the recorded UV–vis absorption spectra, possibly
due to very low values of their molar extinction coefficients.
In a similar way the investigated substances are emissive in different
ranges of UV–vis radiation, from deep red for Os[P(C6H5)3]2(CO)(piq)Cl
to cyan for Os[P(C6H5)3]2(CO)(2,4-F2-pbi)Cl chelate. This observation al-
lows to attribute the observed emission to a 3*MLCT → S0 transition as it
has been further supported by emission life-time measurements (vide
infra). Somewhat unexpectedly, however, the synthesized complexes
are emissive only in solid phase or low temperature matrices. At room
temperature solutions only in the case of Os[P(C6H5)3]2(CO)(piq)Cl de-
Fig. 3. UV–vis absorption (left) and emission (right) spectra of Os(P(C6H5)2)2(CO)(piq)Cl
complex in room temperature acetonitrile solutions and 77 K butyronitrile glasses, re-
spectively (solid lines). Lower part of absorption spectrum (dotted line) expanded by factor
50. Emission spectrum is presented in an arbitrary intensity scale.
rivative quite intense broad emission centred at νem = 16,550 cm−1
e
has been observed. Lowering of measurement temperature to 77 K has

A. Woźna et al. / Inorganic Chemistry Communications 37 (2013) 26–29
29
temperature to 77 K leads to intense emission because thermal activa-
tion of a “loose bolt” effect might take place only at room temperature.
One can also speculate that the second possible isomers of the investi-
gated complexes (with CO molecule located in trans position vs. C− in
N∩C−) will better emit because trans interaction with stronger electron
donating C− fragment of N∩C− ligands should result in stronger Os−CO
bond that could prevent non-radiative room temperature deactivation of
the excited Os[P(C6H5)3]2(CO)(N∩C−)Cl species. This hypothesis, how-
ever, remains only a plausible option until necessary further synthetic
works will be completed.
Shortly summing up, osmium(II) chlorocarbonyl complexes with ad-
ditional phosphine ligand(s) are quite interesting precursors in the syn-
theses of novel luminescent materials. The results presented in this
communication indicate that such precursors can be successfully applied
for the syntheses with cyclometalated N∩C− ligands in a similar way as
it was previously reported for a neutral N∩N chelates. Depending on na-
ture of the N∩C− ligand attached to Os(CO)(P)22+ or Os(CO)(P∩P)2+
cores, one can markedly tune photophysical properties of quite easy af-
fordable heteroleptic Os2+ complexes. From this point of view such ma-
terials, promising alternative for the famous cyclometalated iridium(III)
chelates, need more attention.
Fig. 4. Relationship between emission maxima νem of Os[P(C6H5)3]2(CO)(N∩C−)Cl and
e
Ir(N∩C−)(acac) complexes. Values of νem from measurements performed at 77 K in
e
References
butyronitrile matrices and room temperature solutions in acetonitrile/dioxane 1:1 mixtures
for osmium(II) and iridium(III) derivatives, respectively. The data for Ir(N∩C−)(acac) che-
lates are from measurements done in our laboratory (partly published in refs [35,36]).
The dotted line with slope equal unity does not represent any theoretical fit and is drawn
only for illustration.
[1] K. Kalyanasundaram, M. Grätzel, Coord. Chem. Rev. 177 (1998) 347.
[2] P.-T. Chou, Y. Chi, M.-W. Chung, C.-C. Lin, Coord. Chem. Rev. 255 (2011) 2653.
[3] S. Ardo, G.J. Meyer, Chem. Soc. Rev. 38 (2009) 115.
[4] E. Holder, B.M.W. Langeveld, U.S. Schubert, Adv. Mater. 17 (2005) 1109.
[5] R.C. Evans, P. Douglas, C.J. Winscom, Coord. Chem. Rev. 250 (2006) 2093.
[6] P.-T. Chou, Y. Chi, Chem. Eur. J. 13 (2007) 380.
[7] M. Albrecht, Chem. Rev. 110 (2010) 576.
[8] Y. Chi, P.-T. Chou, Chem. Soc. Rev. 39 (2010) 638.
[9] P.G. Bomben, K.C.D. Robson, B.D. Koivisto, C.P. Berlinguette, Coord. Chem. Rev.
256 (2012) 1438.
105 s−1, values for the radiative rate constants that do not allow direct
observation of 3*MLCT←S bands in ordinary UV–vis spectra.
Depending on the chemical nature of the coordinated bidentate
N∩C− ligand, the MLCT emission from Os[P(C6H5)3]2(CO)(N∩C−)Cl
species can be tuned over a broad UV–vis radiation range, similarly
as it was found for the famous Ir(N∩C−)(acac) chelates [33–38].
The observed correlation (cf. Fig. 4) between emission maxima of
Ir(N∩C−)2(acac) and Os[P(C6H5)3]2(CO)(N∩C−)Cl luminophores sup-
ports additionally the postulated MLCT nature of the lowest, singlet
and triplet excited states of the Os2+ chelates reported in this commu-
nication. As compared to Ir(N∩C−)2(acac) complexes, emission maxima
of Os[P(C6H5)3]2(CO)(N∩C−)Cl derivatives with the same N∩C− ligand
are hipsochromically shifted by ca. 1300 cm−1 suggesting that true-
blue luminophores can be also affordable within this particular class of
osmium(II) complexes after appropriate modification of the N∩C− li-
gand present in Os[P(C6H5)3]2(CO)(N∩C−)Cl structure.
[10] J. Kalinowski, V. Fattori, M. Cocchi, J.A.G. Williams, Coord. Chem. Rev. 255 (2011) 2401.
[11] C. Ulbricht, B. Beyer, C. Friebe, A. Winter, U.S. Schubert, Adv. Mater. 21 (2009) 4418.
[12] Y. You, S.Y. Park, Dalton Trans. 38 (2009) 1267.
[13] Y. Chi, P.-T. Chou, Chem. Soc. Rev. 36 (2007) 1421.
[14] P.-T. Chou, Y. Chi, Eur. J. Inorg. Chem. (2006) 3319.
[15] X. Wang, A. Del Guerzo, R.H. Schmehl, J. Photochem. Photobiol. C 5 (2004) 55.
[16] V.W.-W. Yam, K.M.-C. Wong, Chem. Commun. 47 (2011) 11579.
[17] E.M. Kober, B.P. Sullivan, W.J. Dressick, J.V. Caspar, T.J. Meyer, J. Am. Chem. Soc.
102 (1980) 7383.
[18] J.V. Caspar, E.M. Kober, B.P. Sullivan, T.J. Meyer, J. Am. Chem. Soc. 104 (1982) 630.
[19] B.P. Sullivan, J.V. Caspar, S.R. Johnson, T.J. Meyer, Organometallics 3 (1984) 1241.
[20] B. Carlson, G.D. Phelan, W. Kaminsky, L. Dalton, X. Jiang, S. Liu, A.K.-Y. Jen, J. Am.
Chem. Soc. 124 (2002) 14162.
[21] B. Carlson, G.D. Phelan, J. Benedict, W. Kaminsky, L. Dalton, Inorg. Chim. Acta
357 (2004) 3967.
[22] S. Anastasova, A. Kapturkiewicz, J. Nowacki, Inorg. Chem. Commun. 8 (2005) 1177.
[23] K.-C. Hwang, J.-L. Chen, Y. Chi, C.-W. Lin, Y.-M. Cheng, G.-H. Lee, P.-T. Chou, S.-Y. Lin,
C.-F. Shu, Inorg. Chem. 47 (2008) 3307.
Taking into account the relatively long emission lifetimes measured
at 77 K one can straightforwardly explain the lack of room temperature
emission assuming the presence of effective non-radiative deactivation
of the investigated 3*MLCT states. Although the lowest triplet states in
the studied Os[P(C6H5)3]2(CO)(N∩C−)Cl luminophores have similar na-
ture, the observed differences in Os−CO bond energies (as it is seen from
[24] Y.-L. Tung, P.-C. Wu, C.-S. Liu, Y. Chi, J.-K. Yu, Y.-H. Hu, P.-T. Chou, S.-M. Peng, G.-H.
Lee, Y. Tao, A.J. Carty, C.-F. Shu, F.-I. Wu, Organometallics 23 (2004) 3745.
[25] Y.-M. Cheng, G.-H. Lee, P.-T. Chou, L.-S. Chen, Y. Chi, C.-H. Yang, Y.-H. Song, S.-Y.
Chang, P.-I. Shih, C.-F. Shu, Adv. Funct. Mater. 18 (2008) 183.
[26] B.-S. Du, J.-L. Liao, M.-H. Huang, C.-H. Lin, H.-W. Lin, Y. Chi, H.-A. Pan, G.-L. Fan, K.-T.
Wong, G.-H. Lee, P.-T. Chou, Adv. Funct. Mater. 22 (2012) 3491.
[27] In typical experiment 0.5 g of K2OsCl6 (1.04 mmol) and 1.09 g of P(C6H5)3 (4.16 mmol)
have been dissolved in 35 ml of N, N-dimethylformamide. After completing the reaction
mixture refluxing 60 ml of H2O has been used to precipitate reaction product.
[28] L.A.W. Hales, R.J. Irving, J. Chem. Soc. A (1967) 1932.
[29] J.P. Collman, W.R. Roper, J. Am. Chem. Soc. 88 (1966) 3504.
[30] H.C.S. Clark, K.S. Coleman, J. Fawcett, J.H. Holloway, E.G. Hope, J. Redding, D.R.
Russell, Polyhedron 18 (1999) 1207.
[31] In typical experiment 0.1 g of trans-cis-cis-Os[P(C6H5)3]2(CO)2Cl2 (0.12 mmol) and
equimolar amount of the given ligand have been dissolved in 10 ml of
2-(2-ethoxyethoxy)ethanol. After completing the reaction mixture refluxing 25 ml
of H2O has been used to precipitate reaction product.
νCO values) can explain the different (as compared to other complexes
reported in this study) photo-physical behaviour of Os[P(C6H5)3]2
(CO)(piq)Cl complex. Populating the 3*MLCT (as well as of 1*MLCT) ex-
cited state causes a shift of the electron density from Os2+ center to
the N∩C− moiety, which results in a weakening of Os−CO bonding in-
teractions. This enables radiationless deactivation through facile metal–
ligand bond stretching or even CO elimination [39]. The latter seems to
be likely because at room temperature the investigated chelates are
emissive in solid phases. In the case of Os[P(C6H5)3]2(CO)(piq)Cl the
lowest energy of the excited 3*MLCT state together with relatively strong
Os−CO bond seems to be responsible for the observation of room tem-
perature emission in solutions. In the other investigated complexes
3*MLCT energies are higher and the Os−CO bond energies are lower as
compared to Os[P(C6H5)3]2(CO)(piq)Cl chelate that results in extremely
operative radiationless deactivation at room temperature. Lowering of
[32] E.W. Abel, F.G.A. Stone, Q. Rev. Chem. Soc. 23 (1969) 325.
[33] S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, R. Kwong, I. Tsyba, M. Bortz,
B. Mui, R. Bau, M.E. Thompson, Inorg. Chem. 40 (2001) 1704.
[34] X. Gu, T. Fei, H. Zhang, H. Xu, B. Yang, Y. Ma, X. Liu, Eur. J. Inorg. Chem. (2009) 2407.
[35] W.-C. Chang, A.T. Hu, J.-P. Duan, D.K. Rayabarapu, C.-H. Cheng, J. Organomet. Chem.
689 (2004) 4882.
[36] T.-R. Chen, J. Organomet. Chem. 693 (2008) 3117.
[37] A. Kapturkiewicz, J. Nowacki, P. Borowicz, Z. Phys. Chem. 220 (2006) 525.
[38] A. Kapturkiewicz, J. Nowacki, P. Borowicz, Electrochim. Acta 50 (2005) 3395.
[39] M. Wrighton, Chem. Rev. 74 (1974) 401.