cis-dicyanoosmium(II) diimine complexes bearing phosphine or sulfoxide ligands: Spectroscopic and luminescent studies

Article abstract of DOI:10.1021/ic070290l

A series of cis-dicyanoosmium(II) complexes [Os(PPh₃) ₂(CN)₂(N∩N)] (N∩N = Ph₂phen (2a), bpy (2b), phen (2c), Ph₂bpy (2d), ^tBu₂bpy (2e)) and [Os(DMSO)₂(CN)₂(N∩N)] (3a-3e, N∩N = Br ₂phen (31), Clphen (3g)), were synthesized and their spectroscopic and photophysical properties were examined, and [Os(PMe₃) ₂(CN)₂(phen)] (4) with axial PMe₃ ligands was similarly prepared. The molecular structures of 2a, 2c, [2c·Zn(NO ₃)₂]_∞, 2d, 2e, 3b, 3d, 3e, and 4 were determined by X-ray crystallographic analyses. The two CN ligands are cis to each other with mean Os-C bond distance of 2.0 A. The two PR₃ (R = Ph, Me) or DMSO ligands are trans to each other with P/S-Os-P/S angles of ～77°. The UV-vis absorption spectra of 2a-2e display an intense absorption band at 268-315 nm (ε = ～(1.54-4.82) × 10⁴ M^-1 cm^-1) that are attributed to π → π*(N∩N) and/or π → π*(PPH₃) transitions. The moderately intense absorption bands with λ_max at 387-460 nm (ε = ～ (2.4-11.3) × 10³ M^-1 cm^-1) are attributed to a ¹MLCT transition. A weak, broad absorption at 487-600 nm (ε = ～390-1900 M^-1 cm^-1) is assigned to a ³MLCT transition. Excitation of 2a-2e in dichloromethane at 420 nm gives an emission with peak maximum at 654-703 nm and lifetime of 0.16-0.67 μs. The emission energies, lifetimes, and quantum yields show solvatochromic responses, and plots of ν_max, τ, and Φ, respectively, versus E_T (solvent polarity parameter) show linear correlations, indicating that the emission is sensitive to the local environment. The broad structureless solid-state emission of 2a-2e at 298 (λ_max 622-707 nm) and 77 (λ_max 602-675 nm) K are assigned to ³MLCT excited states. The 77 K MeOH/EtOH (1:4) glassy solutions of 2a-2e also exhibit ³MLCT emissions with λ_max = 560-585 nm. The ¹MLCT absorption and ³MLCT emission of 3a-3g occur at λ_max = 332-390 nm and 553-644 nm, respectively. In the presence of Zn(NO₃)₂, both the ¹MLCT absorption and ³MLCT emission of 2c in acetonitrile blue-shift from 397 to 341 nm and 651 to 531 nm, respectively. The enhancement of emission intensity (I/I_o) of 2e at 531 nm reached a maximum of ～810 upon the addition of two equivs of Zn(NO₃) ₂. The crystallographic and spectroscopic evidence suggests that 2c undergoes binding of Zn²⁺ ions via the cyano moieties.

Full text of DOI:10.1021/ic070290l

Inorg. Chem. 2007, 46, 11003−11016
cis-Dicyanoosmium(II) Diimine Complexes Bearing Phosphine or
Sulfoxide Ligands: Spectroscopic and Luminescent Studies
Siu-Wai Lai,* Queenie K.-W. Chan, Nianyong Zhu, and Chi-Ming Che*
Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular
Technology for Drug DiscoVery and Synthesis, and HKU-CAS Joint Laboratory on New Materials,
The UniVersity of Hong Kong, Pokfulam Road, Hong Kong SAR, China
Received February 13, 2007
A series of cis-dicyanoosmium(II) complexes [Os(PPh3)2(CN)2(N∩N)] (N∩N
Ph2bpy (2d), tBu2bpy (2e)) and [Os(DMSO)2(CN)2(N∩N)] (3a-3e, N∩N
Br2phen (3f), Clphen (3g)), were synthesized
and their spectroscopic and photophysical properties were examined, and [Os(PMe3)2(CN)2(phen)] (4) with axial
PMe3 ligands was similarly prepared. The molecular structures of 2a, 2c, [2c Zn(NO3)2]∞, 2d, 2e, 3b, 3d, 3e, and
4 were determined by X-ray crystallographic analyses. The two CN ligands are cis to each other with mean Os
bond distance of 2.0 Å. The two PR3 (R Ph, Me) or DMSO ligands are trans to each other with P/S Os P/S
315 nm (
) Ph2phen (2a), bpy (2b), phen (2c),
)
‚
−C
)
−
−
angles of
∼
177
4.82)
°
. The UV
×
−
vis absorption spectra of 2a
−
2e display an intense absorption band at 268
−
ꢀ
1
) ∼(1.54
−
104 M- cm-1) that are attributed to π f π*(N∩N) and/or π f π*(PPh3) transitions. The
1
moderately intense absorption bands with λmax at 387
−460 nm (ꢀ ) ∼ (2.4
−
11.3)
−
×
103 M- cm-1) are attributed
to a 1MLCT transition. A weak, broad absorption at 487
3MLCT transition. Excitation of 2a
654 703 nm and lifetime of 0.16 0.67
responses, and plots of νmax , and
indicating that the emission is sensitive to the local environment. The broad structureless solid-state emission of
2a 2e at 298 (λmax 622 707 nm) and 77 (λmax 602
675 nm) K are assigned to 3MLCT excited states. The 77 K
MeOH/EtOH (1:4) glassy solutions of 2a 560
2e also exhibit 3MLCT emissions with λmax 585 nm. The 1MLCT
absorption and 3MLCT emission of 3a
3g occur at λmax 332 390 nm and 553 644 nm, respectively. In the
−
600 nm (ꢀ ) ∼390
1900 M- cm-1) is assigned to a
1
−2e in dichloromethane at 420 nm gives an emission with peak maximum at
−
−
µs. The emission energies, lifetimes, and quantum yields show solvatochromic
,
τ
Φ, respectively, versus ET (solvent polarity parameter) show linear correlations,
−
−
−
−
−
)
−
)
−
−
presence of Zn(NO3)2, both the 1MLCT absorption and 3MLCT emission of 2c in acetonitrile blue-shift from 397 to
341 nm and 651 to 531 nm, respectively. The enhancement of emission intensity (I/Io) of 2e at 531 nm reached
a maximum of
∼
810 upon the addition of two equivs of Zn(NO3)2. The crystallographic and spectroscopic evidence
+
suggests that 2c undergoes binding of Zn2 ions via the cyano moieties.
Introduction
chemosensory,3,4 electroluminescent (in organic light-emitting
devices),5,6 and photovoltaic (in solar cells)7 materials. In
Transition-metal complexes that display intense phos-
phorescence from metal-to-ligand charge transfer (MLCT)
excited states have been widely investigated,1 including inter
alia for photoinduced electron-transfer reactions2 and as
(2) (a) Loiseau, F.; Marzanni, G.; Quici, S.; Indelli, M. T.; Campagna, S.
Chem. Commun. 2003, 286-287. (b) Bergamini, G.; Saudan, C.;
Ceroni, P.; Maestri, M.; Balzani, V.; Gorka, M.; Lee, S.-K.; van Heyst,
J.; Vo¨gtle, F. J. Am. Chem. Soc. 2004, 126, 16466-16471. (c) Laine´,
P. P.; Bedioui, F.; Loiseau, F.; Chiorboli, C.; Campagna, S. J. Am.
Chem. Soc. 2006, 128, 7510-7521.
(3) (a) Beer, P. D.; Szemes, F.; Balzani, V.; Sala`, C. M.; Drew, M. G. B.;
Dent, S. W.; Maestri, M. J. Am. Chem. Soc. 1997, 119, 11864-11875.
(b) Beer, P. D. Acc. Chem. Res. 1998, 31, 71-80. (c) Beer, P. D.;
Cadman, J. New J. Chem. 1999, 23, 347-349. (d) Beer, P. D.;
Cadman, J. Coord. Chem. ReV. 2000, 205, 131-155.
* To whom correspondence should be addressed. Email: cmche@hku.hk
(C.-M.C.), swlai@hku.hk (S.-W.L.).
(1) (a) Lehn, J.-M. Supramolecular Chemistry; VCH Publishers: Wein-
heim, Germany, 1995. (b) Fabbrizzi, L.; Licchelli, M.; Pallavicini, P.
In Transition Metals in Supramolecular Chemistry; Sauvage, J.-P.,
Ed.; Wiley & Sons: New York, 1999. (c) Sauvage, J.-P.; Collin, J.-
P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.; Balzani, V.; Bari-
gelletti, F.; De Cola, L.; Flamigni, L. Chem. ReV. 1994, 94, 993-
1019.
(4) (a) Prodi, L.; Bolletta, F.; Montalti, M.; Zaccheroni, N. Coord. Chem.
ReV. 2000, 205, 59-83. (b) Keefe, M. H.; Benkstein, K. D.; Hupp, J.
T. Coord. Chem. ReV. 2000, 205, 201-228. (c) Hu, Y.-Z.; Xiang, Q.;
Thummel, R. P. Inorg. Chem. 2002, 41, 3423-3428.
10.1021/ic070290l CCC: $37.00
Published on Web 11/22/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 26, 2007 11003

Lai et al.
the literature, studies in this area are mainly confined to d6
metal ions containing polypyridyl ligands,8,9 which display
intense absorption and emission in the visible region.
Previous reports have shown that d6 metal complexes
containing cyanide and polypyridyl ligands can non-
covalently interact with solvent molecules, and their emission
properties are sensitive to the polarity of the local medium.10-12
The observation of solvatochromic charge-transfer ab-
sorption spectra for metal-cyanide complexes such as
[Fe(diimine)2(CN)2] was first described by Burgess.13 Sub-
sequently, La Mar and co-workers noted that intermolecular
O-H(solvent)‚‚‚NtC and C-H‚‚‚NtC interactions could
affect the electronic properties of dicyano(porphyrinato)-
ferrate(III).14 Furthermore, complexes bearing protonated,15
metalated,16,17 and Lewis-acid (BF3)18 adducts of cyano
ligands with spectral properties that are significantly different
from counterparts with free cyano moieties have been
reported.
Luminescent osmium(II) complexes are relatively under-
developed19-21 when compared to the ruthenium(II) ana-
logues with polypyridyl ligands,22 yet practical applications
can nevertheless be envisaged. For example, it has been
reported that luminescent osmium(II) derivatives such as
[Os(diimine)3]2+ can potentially function as oxygen sensors,23
whereas [Os(N∩N)2(L∧L)]2+ (N∩N ) substituted phenan-
throline; L∧L ) strong π-acid ligand, e.g., Ph2AsCHd
CHAsPh2 or Ph2PCHdCHPPh2) and [Os(fptz)2(PPh2Me)2]
(fptzH ) 3-trifluoromethyl-5-(2-pyridyl)-1,2,4-triazole) have
been utilized as OLED materials.24 Here, we report a class
of solvatochromic dicyanoosmium(II) complexes containing
a variety of diimine ligands. Notably, the water-soluble
DMSO-derivatized osmium(II) complexes have been devel-
oped, thereby providing an entry to a new family of
phosphorescent sensory materials with applications in aque-
ous medium.
Experimental Section
(5) (a) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Sibley, S.;
Thompson, M. E.; Forrest, S. R. Nature 1998, 395, 151-154. (b)
Adachi, C.; Baldo, M. A.; Forrest, S. R.; Lamansky, S.; Thompson,
M. E.; Kwong, R. C. Appl. Phys. Lett. 2001, 78, 1622-1624. (c) Ma,
Y.; Zhang, H.; Shen, J.; Che, C. Synth. Met. 1998, 94, 245-248.
(6) (a) Welter, S.; Brunner, K.; Hofstraat, J. W.; De Cola, L. Nature 2003,
421, 54-57. (b) Kalyuzhny, G.; Buda, M.; McNeill, J.; Barbara, P.;
Bard, A. J. J. Am. Chem. Soc. 2003, 125, 6272-6283. (c) Slinker, J.;
Bernards, D.; Houston, P. L.; Abrun˜a, H. D.; Bernhard, S.; Malliaras,
G. G. Chem. Commun. 2003, 2392-2399.
(7) (a) Gra¨tzel, M. Nature 2001, 414, 338-344. (b) Wang, P.; Zakeer-
uddin, S. M.; Moser, J. E.; Humphry-Baker, R.; Comte, P.; Aranyos,
V.; Hagfeldt, A.; Nazeeruddin, M. K.; Gra¨tzel, M. AdV. Mater. 2004,
16, 1806-1811.
(8) (a) Balzani, V.; Scandola, F. In Supramolecular Photochemistry; Ellis
Horwood: New York, 1991. (b) Watanabe, S.; Onogawa, O.; Komatsu,
Y.; Yoshida, K. J. Am. Chem. Soc. 1998, 120, 229-230. (c) Mizuno,
T.; Wei, W.-H.; Eller, L. R.; Sessler, J. L. J. Am. Chem. Soc. 2002,
124, 1134-1135. (d) Anzenbacher, Jr. P.; Tyson, D. S.; Jurs´ıkova´,
K.; Castellano, F. N. J. Am. Chem. Soc. 2002, 124, 6232-6233.
(9) (a) Barigelletti, F.; Flamigni, L.; Calogero, G.; Hammarstro¨m, L.;
Sauvage, J.-P.; Collin, J.-P. Chem. Commun. 1998, 2333-2334. (b)
Rau, S.; Bu¨ttner, T.; Temme, C.; Ruben, M.; Go¨rls, H.; Walther, D.;
Duati, M.; Fanni, S.; Vos, J. G. Inorg. Chem. 2000, 39, 1621-1624.
(10) (a) Belser, P.; von Zelewsky, A.; Juris, A.; Barigelletti, F.; Balzani,
V. Gazz. Chim. Ital. 1985, 115, 723-729. (b) Simpson, N. R. M.;
Ward, M. D.; Morales, A. F.; Barigelletti, F. J. Chem. Soc., Dalton
Trans. 2002, 2449-2454.
(11) Curtis, J. C.; Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1983, 22,
224-236.
(12) Benniston, A. C.; Mackie, P. R.; Farrugia, L. J.; Smith, G.; Teat, S.
J.; McLean, A. J. New J. Chem. 2001, 25, 458-464.
(13) (a) Burgess, J. Spectrochim. Acta 1970, 26A, 1369-1374. (b) Burgess,
J. Spectrochim. Acta 1970, 26A, 1957-1962. (c) Podsiadla, M.;
Rzeszotarska, J.; Kalinowski, M. K. Monatsh. Chem. 1994, 125, 827-
831.
(14) (a) Frye, J. S.; La Mar, G. N. J. Am. Chem. Soc. 1975, 97, 3561-
3562. (b) La Mar, G. N.; Gaudio, J. D.; Frye, J. S. Biochim. Biophys.
Acta 1977, 498, 422-435. (c) Ikezaki, A.; Nakamura, M. Inorg. Chem.
2002, 41, 2761-2768. (d) Ikezaki, A.; Nakamura, M. Inorg. Chem.
2003, 42, 2301-2310.
(15) (a) Peterson, S. H.; Demas, J. N. J. Am. Chem. Soc. 1976, 98, 7880-
7881. (b) Peterson, S. H.; Demas, J. N. J. Am. Chem. Soc. 1979, 101,
6571-6577.
(16) Kinnaird, M. G.; Whitten, D. G. Chem. Phys. Lett. 1982, 88, 275-
280.
Synthesis and General Procedures. 4,7-Diphenyl-1,10-phenan-
throline (Ph2phen), 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen),
4,4′-diphenyl-2,2′-bipyridine (Ph2bpy), 4,4′-di-tert-butyl-2,2′-bi-
pyridine (tBu2bpy), and 5-chloro-1,10-phenanthroline (Clphen) were
purchased from Aldrich. Syntheses of 5,6-dibromo-1,10-phen-
anthroline (Br2phen),25 K2[OsVIO2(OH)4],26 and [OsO2(CN)2(N∩N)]
(N∩N ) Ph2phen,19,27 bpy,28 tBu2bpy)29 were prepared according
to literature procedures. Dichloromethane for photophysical studies
was washed with concentrated sulfuric acid, 10% sodium hydrogen
carbonate, and water, dried by calcium chloride, and distilled over
calcium hydride. Acetonitrile for photophysical measurements was
distilled over potassium permanganate and calcium hydride. All
of the other solvents were of analytical grade and purified according
to conventional methods.30
Instrumentation and Physical Measurements. Fast atom
bombardment (FAB) mass spectra were obtained on a Finnigan
Mat 95 mass spectrometer with a 3-nitrobenzyl alcohol matrix,
whereas electrospray mass spectra were obtained on a LCQ
1
quadrupole ion-trap mass spectrometer. H (500 MHz), 13C (126
(19) Cheng, J. Y. K.; Cheung, K.-K.; Che, C.-M. Chem. Commun. 1997,
623-624.
(20) El-ghayoury, A.; Harriman, A.; Ziessel, R. Chem. Commun. 1999,
2027-2028.
(21) Chen, Y.-L.; Lee, S.-W.; Chi, Y.; Hwang, K.-C.; Kumar, S. B.; Hu,
Y.-H.; Cheng, Y.-M.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H.; Yeh, S.-
J.; Chen, C.-T. Inorg. Chem. 2005, 44, 4287-4294.
(22) (a) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.;
von Zelewsky, A. Coord. Chem. ReV. 1988, 84, 85-277 and references
therein. (b) Derossi, S.; Adams, H.; Ward, M. D. Dalton Trans. 2007,
33-36.
(23) Xu, W.; Kneas, K. A.; Demas, J. N.; DeGraff, B. A. Anal. Chem.
1996, 68, 2605-2609.
(24) (a) Carlson, B.; Phelan, G. D.; Kaminsky, W.; Dalton, L.; Jiang, X.;
Liu, S.; Jen, A. K.-Y. J. Am. Chem. Soc. 2002, 124, 14162-14172.
(b) Tung, Y.-L.; Lee, S.-W.; Chi, Y.; Tao, Y.-T.; Chien, C.-H.; Cheng,
Y.-M.; Chou, P.-T.; Peng, S.-M.; Liu, C.-S. J. Mater. Chem. 2005,
15, 460-464. (c) Chou, P.-T.; Chi, Y. Eur. J. Inorg. Chem. 2006,
3319-3332.
(17) (a) Demas, J. N.; Addington, J. W. J. Am. Chem. Soc. 1974, 96, 3663-
3664. (b) Demas, J. N.; Addington, J. W.; Peterson, S. H.; Harris, E.
W. J. Phys. Chem. 1977, 81, 1039-1043. (c) Bartocci, C.; Bignozzi,
C. A.; Scandola, F.; Rumin, R.; Courtot, P. Inorg. Chim. Acta 1983,
76, L119-L121. (d) Bignozzi, C. A.; Scandola, F. Inorg. Chem. 1984,
23, 1540-1545. (e) Bignozzi, C. A.; Roffia, S.; Scandola, F. J. Am.
Chem. Soc. 1985, 107, 1644-1651. (f) Chow, C.-F.; Lam, M. H. W.;
Sui, H.; Wong, W.-Y. Dalton Trans. 2005, 475-484.
(25) Feng, M.; Chan, K. S. Organometallics 2002, 21, 2743-2750.
(26) Malin, J. M. Inorg. Synth. 1980, 20, 61-63.
(27) Cheng, J. Y. K.; Cheung, K.-K.; Che, C.-M.; Lau, T.-C. Chem.
Commun. 1997, 1443-1444.
(28) Sartori, C.; Preetz, W. Z. Anorg. Allg. Chem. 1989, 572, 151-163.
(29) Chin, K.-F.; Cheng, Y.-K.; Cheung, K.-K.; Guo, C.-X.; Che, C.-M. J.
Chem. Soc., Dalton Trans. 1995, 2967-2973.
(30) Perrin, D. D.; Armarego, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press: Oxford, U.K., 1980.
(18) Shriver, D. F.; Posner, J. J. Am. Chem. Soc. 1966, 88, 1672-1677.
11004 Inorganic Chemistry, Vol. 46, No. 26, 2007

cis-Dicyanoosmium(II) Diimine Complexes
MHz), and 31P (202 MHz) NMR measurements were performed
on a DPX 500 Bruker FT-NMR spectrometer with chemical shifts
(in ppm) relative to tetramethylsilane (1H and 13C) and H3PO4 (31P)
as references. Elemental analyses were performed by the Institute
of Chemistry at the Chinese Academy of Sciences, Beijing. Infrared
spectra were recorded on a Bio-Rad FTIR spectrophotometer. UV-
vis spectra were recorded on a PerkinElmer Lambda 19 UV/vis
spectrophotometer. Thermal analyses were performed on a Perkin-
Elmer TGA 7 thermogravimetric analyzer (heating rate ) 15 °C/
min, N2 atmosphere). Cyclic voltammetry was performed using a
Bioanalytical Systems model 100 B/W electrochemical analyzer.
The electrochemical cell was a conventional two-compartment cell
with a glassy carbon disk as the working electrode, an Ag|AgNO3
(0.1 M) electrode as the reference electrode, and a platinum wire
as the counter electrode. Tetrabutylammonium hexafluorophosphate
(0.1 M) was used as the supporting electrolyte. The ferrocenium/
ferrocene was used as internal reference and all of the potentials
were quoted with respect to Cp2Fe+/0. The E1/2 values were taken
as the average of the cathodic and anionic peak potentials for the
oxidative and reductive waves.
[OsO2(CN)2(phen)], 1c. Yield: 0.17 g, 72%. 1H NMR (DMSO-
d6): δ 8.47-8.50 (m, 2H), 8.55 (s, 2H), 9.34 (dd, J ) 8.3, 1.2 Hz,
2H), 9.99 (dd, J ) 5.1, 1.2 Hz, 2H). FAB-MS: m/z 457 [M +
H]+, 443 [M + H-N]+, 430 [M-CN]+, 414 [M-CN-O]+, 404
[M-2CN]+. Anal. Calcd for C14H8N4O2Os: C, 37.00; H, 1.77; N,
12.33. Found: C, 36.92; H, 1.90; N, 12.57. IR (KBr): ν 2157
(CtN), 861 (OsdO) cm-1
.
[OsO2(CN)2(Ph2bpy)], 1d. Yield: 0.27 g, 89%. 1H NMR
(DMSO-d6): δ 7.69-7.71 (m, 6H), 8.18-8.21 (m, 4H), 8.50 (d, J
) 6.0 Hz, 2H), 9.51 (s, 2H), 9.65 (d, J ) 5.9 Hz, 2H). FAB-MS:
m/z 585 [M + H]+, 569 [M + H-O]+, 558 [M-CN]+, 542
[M-CN-O]+. Anal. Calcd for C24H16N4O2Os: C, 49.48; H, 2.77;
N, 9.62. Found: C, 49.10; H, 2.87; N, 9.24. IR (KBr): ν 2162
(CtN), 851 (OsdO) cm-1
.
[OsO2(CN)2(Br2phen)], 1f. Yield: 0.12 g, 38%. 1H NMR
(DMSO-d6): δ 8.54-8.57 (m, 2H), 9.45 (d, J ) 8.2 Hz, 2H), 10.04
(d, J ) 4.4 Hz, 2H). FAB-MS: m/z 613 [M + H]+, 597 [M +
H-O]+, 581 [M + H-2O]+. Anal. Calcd for C14H6N4Br2O2Os:
C, 27.47; H, 0.99; N, 9.15. Found: C, 27.22; H, 1.13; N, 8.87. IR
(KBr): ν 2157 (CtN), 860 (OsdO) cm-1
.
Emission and Lifetime Measurements. Steady-state emission
spectra were recorded on a Fluorolog-3 Model FL3-21 spectro-
photometer. Solution samples for measurements were degassed with
at least four freeze-pump-thaw cycles. Low-temperature (77 K)
emission spectra for glassy solutions and solid-state samples were
recorded in 5 mm diameter quartz tubes, which were placed in a
liquid nitrogen Dewar flask equipped with quartz windows. The
emission spectra were corrected for monochromator and photo-
multiplier efficiency and for xenon lamp stability. Emission lifetime
measurements were performed with a Quanta Ray DCR-3 pulsed
Nd:YAG laser system (pulse output 355 nm, 8 ns). Errors for λ
values ((1 nm), τ ((10%), Φ ((10%) were estimated.
[OsO2(CN)2(Clphen)], 1g. Yield: 0.13 g, 51%. 1H NMR
(DMSO-d6): δ 8.49-8.58 (m, 2H), 8.87 (s, 1H), 9.25 (d, J ) 8.2
Hz, 1H), 9.43 (d, J ) 8.8 Hz, 1H), 9.97 (d, J ) 4.8 Hz, 1H), 10.07
(d, J ) 4.6 Hz, 1H). FAB-MS: m/z 491 [M + H]+, 476 [M + 2H
- O]+, 461 [M + 3H - 2O]+. Anal. Calcd for C14H7N4ClO2Os:
C, 34.40; H, 1.44; N, 11.46. Found: C, 34.28; H, 1.55; N, 11.67.
IR (KBr): ν 2159 (CtN), 853 (OsdO) cm-1
.
[Os(PPh3)2(CN)2(N∩N)] (N∩N ) Ph2phen (2a), bpy (2b), phen
t
(2c), Ph2bpy (2d), Bu2bpy (2e)). To a stirred solution of [OsO2-
(CN)2(N∩N)] (0.95 mmol) in dichloromethane (15 mL) was added
a solution of PPh3 (1.5 g, 5.73 mmol) in methanol (15 mL). The
mixture was transferred to a quartz tube, stirred, and exposed to
broad-band irradiation (λ > 290 nm) with a 400 W mercury arc
lamp under a nitrogen atmosphere for 4 h. The solvent was removed
under vacuum to give a brown solid. The crude product was purified
by chromatography on a silica gel column using dichloromethane
to remove excess PPh3 and the dioxoosmium(VI) precursor, and
the orange product was eluted with CH2Cl2/CH3OH (4:1 v/v)
mixture. Removal of the solvent under vacuum gave a deep-red
solid, which was recrystallized to give dark-red or brown crystals
by diffusion of diethyl ether into a dichloromethane solution.
Synthesis and characterization of 2a were reported previously.19
Luminescence quantum yields were determined using the method
of Demas and Crosby31 with [Ru(bpy)3]Cl2 in degassed acetonitrile
as a standard reference solution (Φr ) 0.062) and calculated
according to the following equation: Φs ) Φr(Br/Bs)(ns/nr)2(Ds/
Dr), where the subscripts s and r refer to sample and reference
standard solution respectively, n is the refractive index of the
solvents, D is the integrated intensity, and Φ is the luminescence
quantum yield. The quantity B was calculated by B ) 1 - 10-AL
,
where A is the absorbance at the excitation wavelength and L is
the optical path length. The radiative (kr) and nonradiative (knr) rate
constants were calculated by kr ) Φ0/τ0 and knr ) kr (1/Φ0 - 1),
respectively. Solid-state emission quantum yields were determined
by the method of Wrighton et al.,32 using KBr as the standard, and
calculated by Φ ) E/(Rstd - Rsmpl), where E is the area under the
corrected emission curve of the sample, and Rstd and Rsmpl are the
corrected areas under the diffuse reflectance curves of the non-
absorbing standard and the sample, respectively, at the excitation
wavelength.
[Os(PPh3)2(CN)2(bpy)], 2b. Yield: 0.64 g, 73%. 1H NMR
(CD3OD): δ 6.63 (t, J ) 7.0 Hz, 2H), 7.16-7.28 (m, 18H, PPh3),
7.45-7.51 (m, 12H, PPh3), 7.63 (t, J ) 7.6 Hz, 2H), 8.15 (d, J )
8.2 Hz, 2H), 8.31 (d, J ) 5.8 Hz, 2H). 13C{1H} NMR (CDCl3/
CD3OD 15:1 v/v): δ 120.8, 127.0, 127.8 (t, J ) 4.7 Hz), 129.2,
131.6 (t, J ) 23.9 Hz), 133.6 (t, J ) 5.1 Hz), 134.0, 154.0, 156.4,
Os-CN not resolved. 31P{1H} NMR (CDCl3/CD3OD 15:1 v/v): δ
4.53. FAB-MS: m/z 925 [M + H]+, 636 [M- PPh3-CN]+. Anal.
Calcd for C48H38N4P2Os: C, 62.46; H, 4.15; N, 6.07. Found: C,
[OsO2(CN)2(N∩N)] (N∩N ) Ph2phen (1a), bpy (1b), phen (1c),
Ph2bpy (1d), tBu2bpy (1e), Br2phen (1f), Clphen (1g)). K2[OsVIO2-
(CN)2(OH)2] was prepared by literature method.19 Previous reports
revealed that cis-dicyano dioxoosmium(VI) diimine complexes for
62.33; H, 4.03; N, 6.01. IR (KBr): ν 2048, 2070 (CtN) cm-1
.
[Os(PPh3)2(CN)2(phen)], 2c. Yield: 0.56 g, 62%. 1H NMR
(CDCl3): δ 6.82 (dd, J ) 8.1, 5.3 Hz, 2H), 7.03-7.13 (m, 18H,
PPh3), 7.26-7.33 (m, 12H, PPh3), 7.77 (s, 2H), 7.87 (d, J ) 8.0
Hz, 2H), 8.90 (d, J ) 5.3 Hz, 2H). 13C{1H} NMR (CDCl3): δ
125.5, 126.7, 127.7 (t, J ) 4.7 Hz), 128.9, 129.1, 131.6 (t, J )
23.8 Hz), 132.6, 133.6 (t, J ) 5.1 Hz), 148.3, 154.5, Os-CN not
resolved. 31P{1H} NMR (CDCl3): δ 4.77. FAB-MS: m/z 949 [M
+ H]+, 660 [M-PPh3-CN]+. Anal. Calcd for C50H38N4P2Os: C,
63.41; H, 4.04; N, 5.92. Found: C, 63.48; H, 3.91; N, 5.91. IR
t
N∩N ) Ph2phen (1a),19,27 bpy (1b),28 and Bu2bpy (1e)29 were
prepared by the addition of a N∩N ligand in dichloromethane to a
freshly prepared aqueous solution of K2[OsVIO2(CN)2(OH)2], in the
presence of tetrabutylammonium chloride and acetic acid at room
temperature. Similarly, 1c, 1d, 1f, and 1g were prepared according
to literature procedures.19,27-29
(31) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991-1024.
(32) Wrighton, M. S.; Ginley, D. S.; Morse, D. L. J. Phys. Chem. 1974,
78, 2229-2233.
(KBr): ν 2053, 2068 (CtN) cm-1
.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11005

Lai et al.
1
[Os(PPh3)2(CN)2(Ph2bpy)], 2d. Yield: 0.66 g, 65%. H NMR
[Os(DMSO)2(CN)2(tBu2bpy)], 3e. Yield: 0.34 g, 54%. 1H NMR
(CDCl3): δ 1.45 (s, 18H, Bu), 3.36 (s, 12H, SOMe2), 7.53 (dd, J
t
(CDCl3): δ 6.62 (d, J ) 6.0 Hz, 2H), 7.13-7.14 (m, 18H, PPh3),
7.53-7.57 (m, 22H, PPh3 and Ph), 7.92 (s, 2H), 8.64 (d, J ) 6.1
Hz, 2H). 13C{1H} NMR (CDCl3): δ 118.7, 124.7, 126.8, 127.7 (t,
J ) 4.7 Hz), 128.9, 129.5, 129.8, 132.1 (t, J ) 23.6 Hz), 133.8 (t,
J ) 5.2 Hz), 136.9, 146.6, 154.2, 157.0, Os-CN not resolved.
31P{1H} NMR (CDCl3): δ 3.63. FAB-MS: m/z 1075 [M-H]+,
998 [M-Ph-H]+, 814 [M-PPh3]+, 787 [M-PPh3-CN-H]+.
Anal. Calcd for C60H46N4P2Os: C, 67.03; H, 4.31; N, 5.21.
Found: C, 66.65; H, 4.30; N, 5.02. IR (KBr): ν 2052, 2072 (CtN)
) 6.0, 1.9 Hz, 2H), 8.05 (d, J ) 1.9 Hz, 2H), 9.56 (d, J ) 5.9 Hz,
2H). 13C{1H} NMR (CDCl3): δ 30.4 (CMe3), 35.6 (CMe3), 46.6
(SOMe2), 119.8, 124.7, 129.2 (CtN), 153.9, 158.5, 162.9. FAB-
MS: m/z 669 [M + H]+, 591 [M + H-SOMe2]+, 528 [M +
H-SOMe2-SOMe]+, 502 [M + H-SOMe2-SOMe-CN]+. Anal.
Calcd for C24H36N4S2O2Os: C, 43.22; H, 5.44; N, 8.40. Found:
C, 43.05; H, 5.64; N, 8.15. IR (KBr): ν 2064, 2087 (CtN) cm-1
.
[Os(DMSO)2(CN)2(Br2phen)], 3f. Yield: 0.33 g, 50%. 1H NMR
(CDCl3): δ 3.32 (s, 12H, SOMe2), 7.99 (dd, J ) 8.5, 5.2 Hz, 2H),
8.94 (dd, J ) 8.5, 1.3 Hz, 2H), 10.04 (dd, J ) 5.2, 1.3 Hz, 2H).
13C{1H} NMR (CDCl3): δ 46.5 (SOMe2), 126.5, 127.4, 127.8
(CtN), 130.8, 138.5, 149.8, 155.3. FAB-MS: m/z 739 [M + H]+,
659 [M + H-SOMe2]+, 596 [M + H-SOMe2-SOMe]+, 570 [M
+ H-SOMe2-SOMe-CN]+. Anal. Calcd for C18H18N4S2O2-
Br2Os: C, 29.36; H, 2.46; N, 7.61. Found: C, 28.95; H, 2.58; N,
cm-1
.
[Os(PPh3)2(CN)2(tBu2bpy)], 2e. Yield: 0.69 g, 70%. 1H NMR
(CDCl3): δ 1.28 (s, 18H, Bu), 6.40 (dd, J ) 6.1, 2.0 Hz, 2H),
t
7.08-7.14 (m, 18H, PPh3), 7.44-7.48 (m, 12H, PPh3), 7.58 (d, J
) 1.9 Hz, 2H), 8.39 (d, J ) 6.1 Hz, 2H). 13C{1H} NMR (CDCl3):
δ 30.6 (CMe3), 34.8 (CMe3), 116.6, 124.3, 127.6 (t, J ) 4.6 Hz),
128.7, 132.2 (t, J ) 23.5 Hz), 133.8 (t, J ) 5.2 Hz), 153.5, 156.4,
158.6, Os-CN not resolved. 31P{1H} NMR (CDCl3): δ 4.74. FAB-
MS: m/z 1035 [M-H]+, 959 [M-Ph]+, 774 [M-PPh3]+, 747
[M-PPh3-CN-H]+, 719 [M-PPh3-2CN-3H]+. Anal. Calcd for
C56H54N4P2Os: C, 64.97; H, 5.26; N, 5.41. Found: C, 64.59; H,
7.47. IR (KBr): ν 2076, 2090 (CtN) cm-1
.
[Os(DMSO)2(CN)2(Clphen)], 3g. Yield: 0.31 g, 56%. 1H NMR
(CDCl3): δ 3.30 (s, 6H, SOMe2), 3.33 (s, 6H, SOMe2), 7.93 (dd,
J ) 8.2, 5.2 Hz, 1H), 8.02 (dd, J ) 8.4, 5.2 Hz, 1H), 8.15 (s, 1H),
8.43 (dd, J ) 8.3, 1.3 Hz, 1H), 8.88 (dd, J ) 8.5, 1.3 Hz, 1H),
9.97 (dd, J ) 5.2, 1.3 Hz, 1H), 10.06 (dd, J ) 5.2, 1.3 Hz, 1H).
13C{1H} NMR (CDCl3): δ 46.4, 46.5 (SOMe2), 126.4, 126.6, 126.7,
127.9 (CtN), 128.0 (CtN), 129.3, 129.8, 132.3, 134.9, 136.4,
149.2, 150.6, 154.7, 155.4. FAB-MS: m/z 615 [M + H]+, 537 [M
+ H- SOMe2]+, 475 [M + 2H - SOMe2-SOMe]+, 448 [M +
H-SOMe2-SOMe-CN]+. Anal. Calcd for C18H19N4S2O2ClOs: C,
35.26; H, 3.12; N, 9.14. Found: C, 35.28; H, 3.45; N, 8.81. IR
5.60; N, 5.15. IR (KBr): ν 2055, 2074 (CtN) cm-1
.
[Os(DMSO)2(CN)2(N∩N)] (N∩N ) Ph2phen (3a), bpy (3b),
phen (3c), Ph2bpy (3d), tBu2bpy (3e), Br2phen (3f), Clphen (3g)).
A suspension mixture of [OsO2(CN)2(N∩N)] (0.95 mmol) in
dimethyl sulfoxide (30 mL) was transferred to a quartz tube, stirred,
and exposed to broad-band irradiation (λ > 290 nm) with a 400 W
mercury arc lamp under nitrogen atmosphere for 4 h. The solvent
was removed under vacuum to give a brown solid, which was
purified by chromatography on a silica gel column, using CH2Cl2
to remove SO2Me2. The orange product was eluted with CH2Cl2/
CH3OH (4:1 v/v) mixture, and recrystallization by diffusion of
diethyl ether into a dichloromethane solution gave dark-red or brown
crystals. Syntheses and characterization of 3a were reported
previously.19
(KBr): ν 2070, 2089 (CtN) cm-1
.
[Os(PMe3)2(CN)2(phen)], 4. Yield: 0.35 g, 68%. 1H NMR
(CDCl3): δ 1.02-1.04 (m, 18H, Me), 7.75 (dd, J ) 8.1, 5.3 Hz,
2H), 7.98 (s, 2H), 8.32 (d, J ) 8.1 Hz, 2H), 10.13 (d, J ) 4.5 Hz,
2H). 13C{1H} NMR (CDCl3): δ 13.2 (t, J ) 16.3 Hz, Me), 125.5,
127.5, 130.4, 133.6, 149.2, 154.0, Os-CN not resolved. 31P{1H}
NMR (CDCl3): δ -38.35. FAB-MS: m/z 578 [M + 2H]+, 501
[M + H- PMe3]+. Anal. Calcd for C20H26N4P2Os: C, 41.81; H,
4.56; N, 9.75. Found: C, 41.51; H, 4.69; N, 9.79. IR (KBr): ν
1
[Os(DMSO)2(CN)2(bpy)], 3b. Yield: 0.27 g, 51%. H NMR
(CDCl3): δ 3.34 (s, 12H, SOMe2), 7.59 (t, J ) 6.6 Hz, 2H), 8.04
(t, J ) 7.9 Hz, 2H), 8.15 (d, J ) 8.1 Hz, 2H), 9.74 (d, J ) 5.6 Hz,
2H). 13C{1H} NMR (CDCl3): δ 46.6 (SOMe2), 122.9, 127.6, 128.8
(CtN), 137.9, 154.6, 158.8. FAB-MS: m/z 557 [M + H]+, 479
[M + H- SOMe2]+, 417 [M + 2H - SOMe2- SOMe]+. Anal.
Calcd for C16H20N4S2O2Os: C, 34.65; H, 3.63; N, 10.10. Found:
2025, 2059 (CtN) cm-1
.
X-ray Crystallography. Crystals of 2a‚3CH2Cl2, 2c‚2CH2Cl2,
[2c‚Zn(NO3)2]∞, 2d‚CH2Cl2‚CH3CN, 2e‚CH2Cl2‚H2O, 3d‚0.5-
(CH2Cl2), 3e‚0.5(CH2Cl2)‚0.5(Et2O), and 4‚CH2Cl2‚2H2O were
obtained by slow diffusion of diethyl ether into dichloromethane
solutions, whereas that of 3b‚CH3OH was obtained by diffusion
of diethyl ether into a CH2Cl2/CH3OH (3:1) solution. The crystal
data and details of data collection and refinement are summarized
in Table 1 and Table S1 in the Supporting Information. The crystal
structure of 3a had previously been reported.19
Diffraction data for 2a‚3CH2Cl2, 2c‚2CH2Cl2, [2c‚Zn(NO3)2]∞,
2d‚CH2Cl2‚CH3CN, 2e‚CH2Cl2‚H2O, 3b‚CH3OH, 3d‚0.5(CH2Cl2),
and 3e‚0.5(CH2Cl2)‚0.5(Et2O) were collected on a MAR diffrac-
tometer with graphite monochromatized Mo KR radiation (λ )
0.71073 Å), whereas that of 4‚CH2Cl2‚2H2O was collected on a
Bruker Smart 1000 CCD diffractometer. The images were inter-
preted and intensities integrated using the program DENZO.33 The
structure was solved by direct method employing SHELXS-9734
(2e‚CH2Cl2‚H2O, 3d‚0.5(CH2Cl2), 3e‚0.5(CH2Cl2)‚0.5(Et2O), and
C, 33.32; H, 3.60; N, 9.99. IR (KBr): ν 2059, 2083 (CtN) cm-1
.
1
[Os(DMSO)2(CN)2(phen)], 3c. Yield: 0.31 g, 56%. H NMR
(CD3OD): δ 3.23 (s, 12H, SOMe2), 8.07-8.11 (dd, J ) 8.2, 5.2
Hz, 2H), 8.23 (s, 2H), 8.80-8.82 (dd, J ) 8.3, 1.4 Hz, 2H), 9.74-
9.76 (dd, J ) 5.2, 1.4 Hz, 2H). 13C{1H} NMR (CDCl3): δ 46.5
(SOMe2), 126.1, 127.8, 128.4 (CtN), 130.7, 137.3, 150.0, 154.7.
FAB-MS: m/z 581 [M + H]+, 518 [M + H-SOMe]+, 503 [M +
H-SOMe2]+. Anal. Calcd for C18H20N4S2O2Os: C, 37.36; H, 3.48;
N, 9.68. Found: C, 37.40; H, 3.55; N, 9.58. IR (KBr): ν 2060,
2091 (CtN) cm-1
.
[Os(DMSO)2(CN)2(Ph2bpy)], 3d. Yield: 0.32 g, 48%. 1H NMR
(CDCl3): δ 3.41 (s, 12H, SOMe2), 7.58-7.60 (m, 6H), 7.74-7.76
(m, 6H), 8.34 (d, J ) 1.7 Hz, 2H), 9.74 (d, J ) 5.9 Hz, 2H).
13C{1H} NMR (CDCl3): δ 46.7 (SOMe2), 120.9, 125.4, 127.3,
129.0 (CtN), 129.7, 130.7, 136.0, 150.8, 154.5, 159.1. FAB-MS:
m/z 709 [M + H]+, 646 [M + H-SOMe]+, 631 [M + H-SOMe2]+,
568 [M + H-SOMe2- SOMe]+, 542 [M + H-SOMe2-SOMe-
CN]+. Anal. Calcd for C28H28N4S2O2Os: C, 47.58; H, 3.99; N,
7.93. Found: C, 47.43; H, 4.02; N, 7.81. IR (KBr): ν 2068, 2089
(33) Otwinowski, Z.; Minor, W. In Processing of X-ray Diffraction Data
Collected in Oscillation Mode; Methods in Enzymology, Vol. 276,
Macromolecular Crystallography, part A, Carter, C. W., Jr.; Sweet,
R. M. Eds.; Academic Press: New York, 1997; pp 307-326.
(34) Sheldrick, G. M. SHELX 97, Programs for Crystal Structure Analysis;
University of Go¨ttingen: Go¨ttingen, Germany, 1997.
(CtN) cm-1
.
11006 Inorganic Chemistry, Vol. 46, No. 26, 2007

cis-Dicyanoosmium(II) Diimine Complexes
Table 1. Crystal Data
[2c‚Zn(NO3)2]∞
2d‚CH2Cl2‚CH3CN
3b‚CH3OH
4‚CH2Cl2‚2H2O
formula
fw
[C50H38N6O6OsP2Zn]∞
C63H51Cl2N5OsP2
1201.13
0.35 × 0.35 × 0.20
triclinic
P1h
12.015(2)
13.223(3)
17.861(4)
83.28(3)
87.84(3)
75.57(3)
2729.1(9)
2
1.462
25.38
50.92
9415
8417
651
0.032, 0.086
+0.81, -1.42
C17H24N4O3OsS2
586.72
0.60 × 0.25 × 0.15
triclinic
P1h
7.671(2)
9.465(2)
15.651(3)
102.86(3)
98.04(3)
104.78(3)
1047.6(4)
2
1.860
63.10
50.96
3523
3036
234
0.034, 0.086
+1.76, -2.56
C21H32N4O2OsP2Cl2
695.55
0.50 × 0.40 × 0.30
monoclinic
P2/n
10.882(3)
10.392(3)
12.466(4)
90
100.07(2)
90
1388.0(7)
2
1.664
49.25
51.34
1136.37
0.40 × 0.20 × 0.10
orthorhombic
Pnna
25.929(5)
14.953(3)
11.856(2)
90
cryst size (mm3)
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
90
90
4596.8(16)
4
1.642
34.10
51.32
4304
2978
295
0.034, 0.105
+0.74, -0.79
Z
Dc (g cm-3
)
µ (cm-1
)
2θmax (deg)
no. unique data
no. obsd. Data (I g 2σ(I))
no. variables
2636
2111
149
0.024, 0.065
+0.44, -1.20
b
Ra, Rw
residual F, eÅ-3
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b Rw ) [∑w(|Fo| - |Fc|)2/∑w|Fo| ]1/2
.
Scheme 1
4‚CH2Cl2‚2H2O) or SIR9735 program (2a‚3CH2Cl2, 2c‚2CH2Cl2,
[2c‚Zn(NO3)2]∞, 2d‚CH2Cl2‚CH3CN, and 3b‚CH3OH) on a PC.
For [2c‚Zn(NO3)2]∞, the two coordinated NO3 are disordered
-
into two sets of positions, each with half occupancy. One crystal-
lographic asymmetric unit consists of half of one formula unit,
which is the basic unit of a polymer. The atoms of the disordered
-
NO3 ligands were refined isotropically, the other non-hydrogen
atoms were refined anisotropically. For 2a‚3CH2Cl2, one crystal-
lographic asymmetric unit consists of one formula unit, including
three CH2Cl2 solvent molecules. For 2c‚2CH2Cl2, one crystal-
lographic asymmetric unit consists of half of a formula unit,
including one CH2Cl2 solvent molecule. For 2d‚CH2Cl2‚CH3CN,
one crystallographic asymmetric unit consists of one formula unit,
including one dichloromethane and one acetonitrile solvent mol-
ecule, which was disordered into two sets of positions. For
2e‚CH2Cl2‚H2O, one dichloromethane and one water molecule were
also located. One crystallographic asymmetric unit consists of one
formula unit.
For 3b‚CH3OH, one crystallographic asymmetric unit consists
of one formula unit, including one methanol solvent molecule. For
3d‚0.5(CH2Cl2), one crystallographic asymmetric unit consists of
one formula unit, including half of one dichloromethane solvent
molecule. For 3e‚0.5(CH2Cl2)‚0.5(Et2O), two formula units are in
the crystallographic asymmetric unit, including two independent
osmium complexes, and one dichloromethane and one diethyl ether
molecule. The Platon-squeeze method36 was used to subtract the
effect of unlocated solvent molecules. For 4‚CH2Cl2‚2H2O, one
crystallographic asymmetric unit consists of half of formula unit,
including half of dichloromethane and one water molecule.
complexes [OsO2(CN)2(N∩N)] (N∩N ) bpy (1b), phen (1c),
Ph2bpy (1d), Br2phen (1f), Clphen (1g)) were prepared by
the reaction of (nBu4N)2[OsO2(CN)2(OH)2] with N∩N ligands
in dichloromethane in the presence of acetic acid (the crystal
structure of 1a has been reported).27 Irradiation of a CH2Cl2/
CH3OH mixture (1:1 v/v) of [OsO2(CN)2(N∩N)] and PPh3
(6 equiv) using a 400 W mercury arc lamp (λ > 290 nm)
for 4 h gave [Os(PPh3)2(CN)2(N∩N)] (N∩N ) Ph2phen (2a),
t
bpy (2b), phen (2c), Ph2bpy (2d), Bu2bpy (2e)). The crude
products in each case were purified by chromatography on
a silica gel column, using CH2Cl2 as eluent to remove
greenish-yellow impurities, followed by a CH2Cl2/CH3OH
(4:1 v/v) mixture, to elute the product as an orange band.
Recrystallization by diffusion of diethyl ether into dichloro-
methane (with the exception of 2b) or dichloromethane with
10% methanol (2b) solutions yielded brown crystalline solids.
Similarly, [Os(PMe3)2(CN)2(phen)] (4) was prepared from
[OsO2(CN)2(phen)] and PMe3 in 68% yield (Scheme 1).
The complexes [Os(DMSO)2(CN)2(N∩N)] (N∩N ) Ph2phen
(3a), bpy (3b), phen (3c), Ph2bpy (3d), tBu2bpy (3e), Br2phen
(3f), Clphen (3g)) were obtained by the photolysis of 1a-
1g in degassed DMSO for 6 h. The above purification
procedure was followed to afford brown crystals of 3a-3g
in 50-60% yields. Scheme 2 depicts the molecular structures
of 2a-2e, 3a-3g, and 4. The absorption spectral traces of
1e (3.91 × 10-5 M) in DMSO solution versus time of
irradiation using a 400 W mercury arc lamp were recorded:
at 0 min, 1e in DMSO shows a band with λmax at 300-320
Results
Synthesis and Characterization. The synthesis of [OsO2-
(CN)2(N∩N)] (N∩N ) Me2bpy,29 Ph2phen (1a)19,27 and
tBu2bpy (1e))29 and [OsL2(CN)2(Ph2phen)] (L ) PPh3 (2a)
and DMSO (3a))19 have previously been communicated. The
(35) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. SIR97;
J. Appl. Crystallogr. 1998, 32, 115.
(36) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7-13.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11007

Lai et al.
Scheme 2. cis-Dicyanoosmium(II) Diimine Complexes 2a-2e, 3a-3g, and 4
nm; after 1 min, the λmax shifted to ∼288 nm with a broad
and intense absorption tailing from 350 to 450 nm, similar
to the UV-vis absorption spectrum of 3e (below), and no
isosbestic spectral changes were observed. After photolysis
for 6 h, column chromatography of the reaction mixture with
dichloromethane as eluent gave dimethyl sulfone (SO2Me2),37
which was characterized by 1H and 13C NMR (δ 2.99 and δ
41.7 respectively in CDCl3) and IR spectroscopy (ν(SdO)
1336 cm-1 in KBr). The yield of SO2Me2 (based on the dioxo
precursor), as analyzed by capillary gas chromatography, was
in slight excess of 100%, presumably because of the presence
of residual oxygen in the reaction atmosphere.
shift from 128.3 to 133.5 ppm was also observed by changing
the solvent from acetone-d6 to CD3OD. The 31P{1H} NMR
spectra show a singlet centered at δ 3.63-4.77 for 2a-2e
and δ -38.35 for 4, revealing that the two trans phosphine
ligands are chemically equivalent. Upon the addition of
Zn(NO3)2 to 2e in CD3CN, the 31P{1H} NMR signal shifted
from δ 3.86 (without Zn2+) to δ 4.88.
The IR spectra of 2a-2e reveal two ν(CtN) stretches of
equal intensity at ∼2050 and 2070 cm-1, consistent with the
cis coordination geometry of the CN ligands.38 For 3a-3g,
the two ν(CtN) bands appear at a higher frequency of
∼2060-2075 and 2083-2090 cm-1. This is consistent with
DMSO being a better π acceptor than PPh3. The two ν(CtN)
bands of 4 are at 2025 and 2059 cm-1, as can be expected
because PMe3 is a superior σ donor compared with DMSO
and PPh3. The reaction of 2c with excess Zn(NO3)2 in
acetonitrile afforded a greenish-yellow solid of [2c‚Zn(NO3)2]∞,
and the corresponding IR spectrum shows the ν(CtN)
doublet at 2065 and 2101 cm-1, which are at higher
frequencies than those (2053 and 2068 cm-1) for 2c. This is
consistent with the existence of binding between the cyano
moieties and electrophilic Zn2+ ions.39 Similar shifts of
ν(CtN) bands have also been observed upon the addition
of Zn(NO3)2 to 2a (from (2060, 2076) to (2071, 2105) cm-1)
and 2e (from (2055, 2074) to (2063, 2098) cm-1). The
shifting of ν(CtN) bands due to Zn2+ coordination was
reversible; upon the addition of excess sodium chloride to a
methanolic solution of [2c‚Zn(NO3)2]∞, the solution turned
from yellow to red, from which 2c was isolated and
characterized by its ν(CtN) stretching bands.
The positive FAB mass spectrum of [2e‚Zn(NO3)2]n shows
peaks at m/z 1037, 1163, and 1353, corresponding to the
[M + H]+, [M + H + ZnNO3]+, and [M + H + Zn(NO3)2
+ ZnNO3]+ ions, respectively. The electrospray ionization
mass spectrum of a methanolic solution of 2e upon addition
of 1000 equiv of Zn(NO3)2 (Figure S2 in the Supporting
Information) displayed similar peaks at m/z 1162.0 [M +
ZnNO3]+ and 1351.7 [M + Zn(NO3)2 + ZnNO3]+, and upon
dilution with methanol/H2O, their intensities gradually
diminished, whereas that of the parent [M + H]+ ion at m/z
1037.1 slowly increased. Similarly, the positive FAB mass
spectrum of [3a‚Zn(NO3)2]n displayed [M + H + Zn(NO3)2
+ ZnNO3]+ ions at m/z 1049, whereas the ESI mass spectrum
2a-2e and 3a-3g have a good solubility in common
organic solvents, and 3a-3g are soluble in water, whereas
the dioxo precursors (1a-1g) are insoluble in dichloro-
methane, chloroform, n-hexane, methanol, and acetonitrile
and are only sparingly soluble in DMF and DMSO. 2a-2e
and 3a-3g are stable in solid form. The TGA thermogram
of 2b (Figure S1 in the Supporting Information) revealed
that this complex is stable up to 419 °C, whereas 2e, 3a,
and 3c showed the first decomposition temperature at 182,
215, and 257 °C, respectively. All of the complexes are stable
in CH2Cl2, CHCl3, CH3CN, or CH3OH for 1 week, although
3a-3g are stable in aqueous solutions for 2 days.
The 1H NMR spectra of 2a-2e show multiplets at δ 7.03-
7.57 that are attributed to the phenyl protons of PPh3 and
N∩N ligands. The signals at δ 6.40-6.82 and 7.58-8.93
1
correspond to aryl protons of the diimine group. The H
NMR spectra of 3a-3g display a singlet at δ 3.23-3.41,
attributable to the dimethyl protons of coordinated DMSO
ligands, whereas the diimine aromatic protons appear at δ
7.53-10.06. The 13C{1H} NMR spectra of 2a-2e and 4 in
CDCl3 are well resolved except for the Os-C≡N resonances;
peaks at δ 116.6-158.6 are attributed to the aromatic carbon
atoms of PPh3 (with the exception of 4) and diimine ligands.
For 3a-3g, the 13C{1H} NMR spectra show the dimethyl
carbon atoms of the coordinated DMSO ligands at δ ∼46.6,
whereas peaks at δ 119.8-162.9 correspond to the carbon
atoms from the diimine and cyano ligands. The 13C{1H}
NMR spectra of 3e in the absence and presence of Zn(NO3)2
in CDCl3/CD3OD (2:1 v/v) have been recorded. The signals
of cyano carbon atoms shifted from δ 131.1 to δ 134.9 upon
the addition of Zn2+. A similar change in the C≡N chemical
(37) (a) Sharipov, A. K. Russ. J. Appl. Chem. 2003, 76, 108-113. (b)
Lyavinets, A. S.; Marushchak, N. T. Russ. J. Gen. Chem. 2004, 74,
885-889.
(38) (a) Schilt, A. A. Inorg. Chem. 1964, 3, 1323-1325. (b) Spaulding,
L.; Reinhardt, B. A.; Orchin, M. Inorg. Chem. 1972, 11, 2092-2094.
(39) Shriver, D. F. Struct. Bonding 1966, 1, 32-58.
11008 Inorganic Chemistry, Vol. 46, No. 26, 2007

cis-Dicyanoosmium(II) Diimine Complexes
S4 in the Supporting Information). The two CN ligands are
coordinated to [Zn(NO3)2], and the coordination sphere
around the zinc atoms can be described as a distorted trigonal
bipyramid, with one η2- (bidentate: Zn-O 1.91(1), 2.37(1)
Å) and one η1-nitrate (Zn-O 2.24(1) Å) ion, plus two
cyanide groups from [Os(PPh3)2(CN)2(phen)] molecules
(Zn-N 1.935(5) Å).
3b (Figure 3) shows a geometry similar to that of the PPh3
derivatives, 2a and 2c-2e. The mean Os-C, CtN, and
Os-N bond lengths are 2.02, 1.15, and 2.13 Å respectively,
which are comparable to those in 2a and 2c-2e. The mean
Os-S distance of 2.30 Å is comparable to those reported
for [OsX2(DMSO)4] (2.34-2.35 Å; X ) Cl-, Br-).43 Apart
from intermolecular interactions between the cyanide ligands
and solvent molecules (methanol), there are short inter-
molecular contacts (2.34-2.65 Å) from the coordinated
OdS(CH3)2 ligands to the aromatic C-H groups of bipyri-
dine and DMSO hydrogens.
Figure 1. Perspective view of 2d (30% probability ellipsoids).
Intermolecular interactions between the cyanide and phen
ligands (aryl C-H‚‚‚NtC intermolecular contact ) 2.587
Å) were observed in the crystal structure of 4 (Figure 4),
and water molecules are present between the methyl groups
of PMe3 and cyanide or aryl (C-H) groups of adjacent
molecules. The intermolecular CtN‚‚‚H2O, H2O‚‚‚H-
C(PMe3), and H2O‚‚‚H-C(phen) distances lie in the range
of 2.460-2.824 Å.
in H2O revealed peaks at m/z 857.8 [M + ZnNO3]+ and
1047.7 [M + Zn(NO3)2 + ZnNO3]+.
Crystal Structures. The crystal structures of 2d, [2c‚
Zn(NO3)2]∞, 3b, and 4 (ORTEP diagrams in Figures 1-4),
and 2a, 2c, 2e, 3d, and 3e (Figures S3-S7 in the Supporting
Information) have been determined; selected bond lengths
and angles are listed in Table 2 and Table S2 in the
Supporting Information. The two cyano ligands are cis to
each other, and the mean Os-C bond lengths of 2a and 2c-
2e are ∼2.02 Å, which are comparable to that in [OsO2-
(CN)2(pyridine)2] (2.039 Å)29 and [OsO2(CN)2(Ph2phen)]
(2.02 and 2.053 Å).27 The average cyano CtN distance is
1.14 Å, which is typical for the unbridged CtN termini (1.15
Å in [Fe(CN)4(CO)2]2- and [Mn(CN)3(CO)3]2-).40 The two
PPh3 ligands of 2a and 2c-2e are trans to each other with
a mean Os-P bond length of 2.36 Å, similar to Os-P
distances observed in [Os{PH(OMe)Ph}(CO)2(PPh3)2] (∼2.34
Å)41 and mer-[OsCl(SC6F5)(N2)(PMe2Ph)3] (∼2.38 Å for
Os-P distances not residing trans to SC6F5).42 For 2a, the
phenyl substituents of the Ph2phen ligand are displaced by
a mean angle of 54° from the plane of 1,10-phenanthroline
(Figure S3 in the Supporting Information). Similarly, for 2d,
the phenyl rings are displaced by ∼36° from the bpy plane
(Figure 1). There are intermolecular CtN‚‚‚H-CHCl2
hydrogen-bonding interactions (2.689 Å) and short contacts
(<3.35 Å) between PPh3 ligands and CH3CN solvent
molecules.
Absorption and Emission Spectroscopy. The UV-vis
absorption data of 2a-2e and 4 in CH2Cl2, and those of 3a-
3g in CH2Cl2 and H2O are listed in Table 3; the spectral
data measured in other solvents are given in the Supporting
Information (Table S3). All of the complexes are soluble in
common organic solvents with the exception of 2b, which
is sparingly soluble in dichloromethane, chloroform, and
methanol. 2a-2e display an intense absorption band with
λmax at 269-313 nm (ꢀ ) (2.50-4.55) × 104 M-1 cm-1),
together with a broad and moderately intense absorption at
λmax 406-446 nm (ꢀ ) (3.10-10.0) × 103 M-1 cm-1) and
tailing to 520-580 nm (ꢀ ) (600-1800) M-1 cm-1) in
CH2Cl2 solutions. In the literature, [Ru(bpy)3]2+ and
[Os(bpy)3]2+ have individually been reported to display an
intense low-energy absorption band with λmax at 450 and 480
nm, respectively, both of which have been assigned to MLCT
transitions.44 Thus, the low-energy absorptions of 2a-2e at
1
406-446 nm are assigned to MLCT: (dπ)Os f π*(N∩N)
transitions, whereas the tailings at 520-580 nm with ꢀ values
of (600-1800) M-1 cm-1 could be due to 3MLCT transitions.
The solvent effect on the absorption spectra of 2a-2e has
been investigated, and the data are given in the Supporting
Information (Table S3). For 2e, the high-energy absorption
The X-ray crystal structure of [2c‚Zn(NO3)2]∞ (Figure 2)
contains 1D zigzag polymeric chains with alternate [Os(PPh3)2-
(CN)2(phen)] and Zn(NO3)2 units. The N-C-Os (172.9(5)°)
and C-N-Zn angles (168.5(5)°) are slightly bent from 180°.
The structural parameters of the [Os(PPh3)2(CN)2(phen)]
units in [2c‚Zn(NO3)2]∞ are comparable to those in 2c (Figure
(43) (a) Robinson, P. D.; Hinckley, C. C.; Ikuo, A. Acta Crystallogr., Sect.
C 1989, 45, 1079-1080. (b) McDonagh, A. M.; Humphrey, M. G.;
Hockless, D. C. R. Aust. J. Chem. 1998, 51, 807-811.
(44) (a) Creutz, C.; Chou, M.; Netzel, T. L.; Okumura, M.; Sutin, N. J.
Am. Chem. Soc. 1980, 102, 1309-1319. (b) Pankuch, B. J.; Lacky,
D. E.; Crosby, G. A. J. Phys. Chem. 1980, 84, 2061-2067. (c)
Ferguson, J.; Herren, F.; Krausz, E. R.; Maeder, M.; Vrbancich, J.
Coord. Chem. ReV. 1985, 64, 21-39. (d) Meyer, T. J. Pure Appl.
Chem. 1986, 58, 1193-1206. (e) Johnson, S. R.; Westmoreland, T.
D.; Caspar, J. V.; Barqawi, K. R.; Meyer, T. J. Inorg. Chem. 1988,
27, 3195-3200.
(40) Contakes, S. M.; Hsu, S. C. N.; Rauchfuss, T. B.; Wilson, S. R. Inorg.
Chem. 2002, 41, 1670-1678.
(41) Bohle, D. S.; Jones, T. C.; Rickard, C. E. F.; Roper, W. R. J. Chem.
Soc., Chem. Commun. 1984, 865-867.
(42) Cruz-Garritz, D.; Gelover, S.; Torrens, H.; Leal, J.; Richards, R. L. J.
Chem. Soc., Dalton Trans. 1988, 2393-2396.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11009

Lai et al.
Figure 2. Perspective view of [2c‚Zn(NO3)2]∞ (30% probability ellipsoids).
to 6700 M-1 cm-1 at 398 nm in DMSO. 4 shows the
absorption peak maximum varying from 404 nm in methanol
to 465 nm in chloroform (Figure S9 in the Supporting
Information).
Upon excitation at 420 nm, 2a-2e show an intense
emission with λmax at 602-717 nm. The effect of solvents
on the emission properties has been examined. As an
example, the emission λmax of 2e (concentration ) 3 × 10-5
M) varies with the solvent (Table S3 in the Supporting
Information and Figure 6) from 627 nm in CH3OH to 707
nm in toluene (∆νmax ) 1800 cm-1); the emission quantum
yield (Φ) and lifetime (τ) decrease for lower emission
energies. The maximum Φ and τ values of 2e occur in
CH3OH (0.035 and 0.31 µs respectively (λmax ) 627 nm)),
and these values decrease to 0.017 and 0.19 µs in DMF (λmax
) 662 nm), and 0.003 and 0.09 µs in toluene (λmax ) 707
nm). The long emission lifetime in the microsecond regime
suggests triplet parentage for the emissive excited state.
Figure 3. Perspective view of 3b (30% probability ellipsoids).
For 2a, its emission λmax shows a similar bathochromic
shift from 637 nm in methanol to 712 nm in toluene. The
absorption (λabs ) 398-438 nm) and emission (λem ) 637-
712 nm) maxima of 2a in various solvents are red-shifted
from those of λabs ) 387-412 nm and λem ) 621-661 nm
observed for 2c. Because of its poor solubility, the photo-
physical properties of 2b can only be examined in methanol,
dichloromethane, and chloroform. 2d has a better solubility
than 2b, and its photophysical properties in different solvents
have been examined. The solvent effect on the emission λmax
for 2d is also evident, where λmax varies from 650 nm in
methanol to 717 nm in THF.
maximum shows a minor shift from λmax at 291 nm (ꢀ )
23000 M-1 cm-1) in CH3OH to 298 nm (ꢀ ) 28300 M-1
cm-1) in benzene, whereas the low-energy absorption bands
at λ > 400 nm display a substantial solvatochromism: the
largest shift of peak maximum is from 410 nm (ꢀ ) 3130
M-1 cm-1) in CH3OH to 460 nm (ꢀ ) 2500 M-1 cm-1) in
toluene (∆ν ) 2650 cm-1). The electronic absorption spectra
of 2e in different solvents at 298 K are depicted in part a of
Figure 5, and a plot of the absorption energies for 2e versus
the solvent polarity, as defined by the ET value (classified
with respect to the longest-wavelength solvatochromic
absorption band of the pyridinium N-phenolate betaine dye),45
affords a linear correlation, as shown in part b of Figure 5.
The absorption bands of 2a, 2c, and 2d at 387-440 nm show
similar solvatochromism, and the maximum shift in λmax
values are 750 cm-1 for 2d, 1570 cm-1 for 2c, and 2290
cm-1 for 2a when the solvent changes from methanol to THF
or toluene. The molar extinction coefficient for 2c changes
markedly from ꢀ ) 3200 M-1 cm-1 at 408 nm in pyridine
The solid-state emission of 2e at 298 K exhibits a
structureless band with λmax at 670 nm (τ ) 0.15 µs), which
blue-shifts to 632 nm with a lifetime of 1.06 µs at 77 K. In
a 77 K glassy MeOH/EtOH (1:4) solution, the emission λmax
blue-shifts to 560 nm (τ ) 16.1 µs). Similarly, the solid-
state emission of 2b exhibits a broad band at λmax 622 nm
with a quantum yield of 0.017 at room temperature.
Compared with the PPh3 counterpart (2c), the emissions λmax
of 4 are red-shifted and have lower quantum yields and
shorter lifetimes both in the solid state and in solutions.
Solvatochromism has also been observed for the emission
(45) (a) Dimroth, K.; Reichardt, C.; Siepmann, T.; Bohlmann, F. Justus
Liebigs Ann. Chem. 1963, 661, 1-37. (b) Marcus, Y. Chem. Soc. ReV.
1993, 22, 409-416.
11010 Inorganic Chemistry, Vol. 46, No. 26, 2007

cis-Dicyanoosmium(II) Diimine Complexes
Figure 4. (a) Perspective view of 4 (30% probability ellipsoids). (b) Crystal packing diagram.
Table 2. Selected Bond Lengths (Angstroms) and Angles (Degrees)
counterparts (387-460 nm). The emission λmax of 3a-3e
(583-640 nm) are at higher energies than those of 2a-2e
at 621-717 nm. The absorption and emission properties of
3a-3e are solvent-dependent. For 3b, its absorption λmax
varies from 341 nm in H2O to 376 nm in CH2Cl2, and its
emission λmax red-shifts from 563 nm in H2O to 630 nm in
DMF. The emission quantum yield and lifetime of 3e vary
from 0.03 and 0.22 µs in H2O to 0.27 and 0.96 µs in CHCl3,
respectively. The absorption and emission properties of 3a-
3e have been examined in aqueous solutions. As an example,
the UV-vis absorption and emission spectra of 3b in
aqueous solution are depicted in Figure 7. The excitation
spectrum of 3b in H2O, monitored at emission λmax 563 nm,
shows peak maxima at 296, 331, and 376 nm, which matches
the ground-state absorption spectrum. The room-temperature
solid-state emission of 3b shows a broad band at λmax 581
nm with a quantum yield of 0.37, the latter being significantly
higher than that of 0.017 for the PPh3 congener, 2b. For 3f
and 3g containing the Br2phen and Clphen ligands, respec-
tively, their absorption λmax at 376 and 363 nm are red-shifted
from that of 3c at 352 nm in CH2Cl2 solution. Similarly, the
emissions λmax of 3f and 3g at 626 and 615 nm respectively
are red-shifted from that of 3c at λmax 600 nm in CH2Cl2
solution.
[2c‚Zn(NO3)2]∞
Os(1)-C(1)
1.993(6)
Zn(1)-N(1)
1.935(5)
1.91(1)
2.37(1)
N(1)-C(1)
1.140(6)
2.124(4)
2.381(1)
97.9(3)
169.7(2)
92.3(2)
77.4(2)
178.81(7)
89.4(2)
Zn(1)-O(1)
Os(1)-N(2)
Os(1)-P(1)
Zn(1)-O(2)
Zn(1)-O(4)
2.24(1)
C(1)-Os(1)-C(1*)
C(1)-Os(1)-N(2)
C(1*)-Os(1)-N(2)
N(2)-Os(1)-N(2*)
P(1)-Os(1)-P(1*)
C(1)-Os(1)-P(1)
N(2*)-Os(1)-P(1*)
N(1)-C(1)-Os(1)
C(1)-N(1)-Zn(1)
N(1*)-Zn(1)-N(1)
O(4)-Zn(1)-O(2)
O(1)-Zn(1)-O(4)
N(1)-Zn(1)-O(4)
O(1)-Zn(1)-N(1)
172.9(5)
168.5(5)
123.5(3)
134.9(6)
75.1(7)
109.8(3)
112.3(4)
90.2(1)
2d‚CH2Cl2‚CH3CN
Os(1)-C(1)
2.030(4)
2.022(4)
1.145(5)
1.149(6)
94.2(2)
94.4(1)
171.5(1)
76.7(1)
Os(1)-N(3)
2.109(3)
2.118(3)
2.361(1)
2.387(1)
175.45(3)
86.7(1)
Os(1)-C(2)
Os(1)-N(4)
N(1)-C(1)
Os(1)-P(1)
Os(1)-P(2)
P(1)-Os(1)-P(2)
C(1)-Os(1)-P(2)
N(3)-Os(1)-P(2)
N(1)-C(1)-Os(1)
N(2)-C(2)
C(1)-Os(1)-C(2)
C(1)-Os(1)-N(3)
C(2)-Os(1)-N(3)
N(3)-Os(1)-N(4)
89.83(9)
175.3(4)
3b‚CH3OH
Os(1)-C(1)
2.019(8)
2.014(7)
1.141(9)
1.150(9)
90.7(3)
96.1(2)
173.1(2)
77.0(2)
Os(1)-N(3)
2.131(5)
2.303(2)
2.305(2)
1.468(5)
178.69(6)
88.9(2)
Os(1)-C(2)
Os(1)-S(1)
N(1)-C(1)
Os(1)-S(2)
S(1)-O(1)
S(1)-Os(1)-S(2)
C(1)-Os(1)-S(1)
N(3)-Os(1)-S(1)
N(1)-C(1)-Os(1)
N(2)-C(2)
C(1)-Os(1)-C(2)
C(1)-Os(1)-N(3)
C(1)-Os(1)-N(4)
N(3)-Os(1)-N(4)
90.9(2)
176.2(7)
Because the emission energy of the cis-dicyanoosmium(II)
complexes are solvent-dependent, it is pertinent to apply the
energy-gap law to this system.46 Figure 8 shows a plot of ln
4‚CH2Cl2‚2H2O
Os(1)-C(1)
N(2)-C(1)
C(1)-Os(1)-C(1*)
C(1)-Os(1)-N(1*)
C(1)-Os(1)-N(1)
N(1)-Os(1)-N(1*)
1.989(4)
1.169(6)
95.1(2)
93.4(2)
171.5(1)
78.2(2)
Os(1)-N(1)
2.105(3)
2.345(1)
173.78(6)
86.8(1)
93.11(9)
174.5(4)
Os(1)-P(1)
3
P(1)-Os(1)-P(1*)
C(1)-Os(1)-P(1)
N(1)-Os(1)-P(1)
N(2)-C(1)-Os(1)
knr against the MLCT emission energy of 2c at 298 K in
various solvents. There is a linear decrease in ln knr with
increasing energy gap (Eem/cm-1) between the ground and
excited states. The slope (-5.02 eV-1) and intercept (24 (
1) of the plot for 2c were obtained, and comparisons were
made with the values of ca. -7.5 eV-1 and 28-30,
of 4; its emission λmax varies from 701 nm in methanol with
a τ of 0.092 µs to 760 nm in ethyl acetate with a τ of 0.033
µs.
In nonaqueous solutions, the absorption λmax of 3a-3e
(332-390 nm) are blue-shifted from those of the 2a-2e
(46) (a) Caspar, J. V.; Kober, E. M.; Sullivan, B. P.; Meyer, T. J. J. Am.
Chem. Soc. 1982, 104, 630-632. (b) Caspar, J. V.; Meyer, T. J. J.
Phys. Chem. 1983, 87, 952-957.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11011

Lai et al.
Table 3. Photophysical Data of 2a-2e, 3a-3g, and 4
complex medium (T/K)
λabsa/nm (ꢀ / M-1cm-1
)
λ emb / nm; τ/µs
667; 0.67
Φem
2a
2b
2c
2d
2e
3a
CH2Cl2 (298)
solid (298)
solid (77)
284 (45 500), 323 (sh, 11 800), 416 (10 000), 447 (sh, 8500), 521 (sh, 1800)
0.063
707; 0.39
675; 2.66
582; 15.9
665; 0.16
622; 0.21
602; 3.06
575; 14.4
654; 0.53
622; 0.18
605; 2.85
562; 25.1
703; 0.16
663; <0.1
646; 0.57
585; 18.5
657; 0.27
670; 0.15
632; 1.06
560; 16.1
609; 1.42
563; 1.22
610; 0.18
578, 611; 1.58, 1.65
540; 12.4
613; 0.45
563; 0.33
581; 0.47
560; 4.67
532; 11.2
glassc (77)
CH2Cl2 (298)
solid (298)
solid (77)
296 (24 800), 328 (sh, 6300), 446 (3100), 555 (sh, 640)
0.012
0.017
glassc (77)
CH2Cl2 (298)
solid (298)
solid (77)
269 (33 300), 295 (sh, 18 600), 406 (6300), 430 (sh, 5900), 525 (sh, 1100)
313 (37 500), 348 (15 200), 431 (8800), 462 (sh, 8300), 580 (sh, 1400)
295 (28 400), 440 (3700), 550 (sh, 620)
0.046
0.010
0.022
glassc (77)
CH2Cl2 (298)
solid (298)
solid (77)
glassc (77)
CH2Cl2 (298)
solid (298)
solid (77)
glassc (77)
CH2Cl2 (298)
H2O (298)
solid (298)
solid (77)
271 (32 500), 291 (31 400), 313 (sh, 11 300), 361 (10 900), 406 (sh, 7020), 471 (sh, 1390)
288 (38 500), 328 (sh, 15 000), 380 (sh, 8500)
0.34
0.15
glassc (77)
CH2Cl2 (298)
H2O (298)
solid (298)
solid (77)
3b
3c
3d
3e
3f
3g
4
280 (18 300), 307 (sh, 6200), 316 (sh, 5000), 376 (3500), 393 (sh, 3100), 487 (sh, 520)
266 (23 000), 304 (14 600), 315 (13 900), 341 (5000), 411 (sh, 850)
0.070
0.085
0.37
glassc (77)
CH2Cl2 (298)
H2O (298)
solid (298)
solid (77)
260 (28 200), 274 (sh, 16 200), 290 (sh, 11 800), 352 (5320), 391 (sh, 4160), 462 (sh, 660) 600; 1.20
272 (24 500), 316 (sh, 6380), 348 (sh, 4480), 365 (4040), 409 (sh, 940)
0.22
0.068
553; 0.40
573; 0.45
552, 556; 7.20, 7.77
524, 550 (sh); 16.8
623; 0.55
574; 0.45
622; 0.15
561, 606; 0.44, 0.56
543; 13.5
598; 0.78
555; 0.22
589; 0.30
555; 3.86
530; 10.6
626; 0.61
579; 0.53
630; 0.11
611; 1.04
552; 9.37
615; 0.87
567; 0.69
609; 0.42
590; 4.15
551; 11.1
728; 0.072
678, 707 (max); 0.15
660; 2.41
glassc (77)
CH2Cl2 (298)
H2O (298)
solid (298)
solid (77)
258 (27 800), 298 (41 600), 323 (sh, 16 600), 386 (8910), 401 (sh, 8250), 498 (sh, 1210)
286 (24 500), 323 (sh, 10 700), 357 (5780)
0.13
0.085
glassc (77)
CH2Cl2 (298)
H2O (298)
solid (298)
solid (77)
255 (sh, 8400), 279 (15 500), 303 (sh, 6200), 313 (sh, 5200), 370 (3100), 464 (sh, 500)
255 (sh, 16 600), 270 (19 200), 302 (11 500), 312 (10 800), 340 (4500), 402 (sh, 1000)
0.16
0.030
glassc (77)
CH2Cl2 (298)
H2O (298)
solid (298)
solid (77)
269 (22 900), 286 (sh, 14 000), 313 (sh, 4600), 376 (4200), 403 (sh, 3500), 488 (sh, 850)
283 (26 000), 326 (sh, 7300), 360 (4300), 377 (sh, 3800)
0.10
0.14
glassc (77)
CH2Cl2 (298)
H2O (298)
solid (298)
solid (77)
264 (21 000), 279 (sh, 11 300), 288 (sh, 8800), 363 (3700), 399 (sh, 3000), 484 (sh, 740)
277 (23 600), 318 (sh, 7100), 355 (4000), 372 (sh, 3300), 412 (sh, 870)
0.19
0.22
glassc (77)
CH2Cl2 (298)
solid (298)
solid (77)
266 (38 100), 289 (sh, 11 100), 314 (sh, 2570), 435 (6400), 459 (6490), 558 (sh, 1190)
0.0017
glassc (77)
612; 11.7
a The bold number indicates λmax for the MLCT absorption band. b Excitation wavelength at 420 nm for 2a-2e and 4, and 370 nm for 3a-3g. c Measured
in MeOH/EtOH ) 1:4.
respectively, for the [OsX4L] and [OsX2L2] series
(X ) halides, nitrogen donors, phosphines, or CO;
L ) bpy or phen).47 Similarly, a plot of ln knr versus Eem for
3e in aprotic solvents afforded a straight line with slope of
-9.84 eV-1 and an intercept of 34 ( 2, and the data are
given as Supporting Information (Figure S10). The emission
spectrum of 3c in H2O recorded 0.2 ps after laser exci-
tation at 266 nm shows a broad band with λmax ∼470 nm,
which undergoes a single-exponential decay with a rate
constant k of ∼2 × 1012 s-1 to the 3MLCT excited state. We
1
assign the 470 nm emission to originate from the MLCT
excited state.
Effects of Metal Ions upon Photoluminescence. (I) In
Acetonitrile or Methanol Solution. Because the emission
energies of 2a-2e and 3a-3g are solvent-sensitive, we have
(47) (a) Caspar, J. V.; Meyer, T. J. J. Am. Chem. Soc. 1983, 105, 5583-
5590. (b) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J.
J. Phys. Chem. 1986, 90, 3722-3734.
11012 Inorganic Chemistry, Vol. 46, No. 26, 2007

cis-Dicyanoosmium(II) Diimine Complexes
Figure 5. (a) UV-vis absorption spectra of 2e in various solvents at 298 K. (b) Plot of absorption energies in cm-1 for 2e against ET value of solvents.
Figure 7. Absorption (solid) and emission (dash, λex ) 370 nm) spectra
of 3b in H2O at 298 K.
Figure 6. Emission spectra of 2e in various solvents at 298 K.
also examined the absorption and emission properties of this
class of complexes in the presence of metal ions (Mn+). For
2e, upon the addition of up to 2 equiv of Zn(NO3)2, the
absorption λmax gradually shifted from 424 to 367 nm and
the weak low-energy band at 526 nm diminished. When more
than 2 equiv of Zn2+ ions were added, a slight further red-
shift of the absorption maximum from 367 to 371 nm (with
10 equiv of Zn2+) was recorded. The absorption spectral
traces are not isosbestic, and the data are provided in the
Supporting Information.
n
The emission spectral traces of 2e in a 0.1 M Bu4NPF6
methanolic solution upon the addition of Zn(NO3)2 in
methanol at different concentrations were recorded (Figure
9). A plot of the emission intensity enhancement factor (I/
Figure 8. Plot of ln knr against Eem for 2c in various solvents at 298 K.
Io) at 531 nm versus the number of equivalents of Zn2+ is
given in the inset of Figure 9. Upon the addition of up to 2
equiv of Zn(NO3)2, the emission λmax significantly blue-shifts
to 531 nm, with concomitant enhancement of the I/Io value
(up to 810 at λ ) 531 nm) and emission lifetime (from 0.31
to 2.4 µs). Further addition of Zn(NO3)2 led to a slight
decrease in the emission intensity and a red-shift in the
emission λmax to 541 nm (at 10 equiv of Zn2+). When
Inorganic Chemistry, Vol. 46, No. 26, 2007 11013

Lai et al.
been evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-di-
phenyltetrazolium bromide (MTT) assay.48 Complex 3c
showed no significant cytotoxicity toward HepG2 and
SUNE1 cells, with more than 90% cell survival at a complex
concentration up to 50 µM and IC50 (inhibitory concentration)
values greater than 100 µM.
Electrochemistry. The cyclic voltammograms of 2c, 3c,
3f, 3g, and 4 in CH3CN solutions at 298 K were recorded at
a scan rate of 100 mV/s using 0.1 M nBu4NPF6 as a
supporting electrolyte. Complexes 2c, 3c, and 4 display one
reversible couple at E1/2 ) +0.53, +0.92, and +0.31 V,
respectively. There is also a reversible one-electron reduction
couple at E1/2 ) -1.97, -1.70, and -1.93 V for 2c, 3c, and
4, respectively. We assign the couples at E1/2 ) +0.31 to
+0.92 V to the metal-centered oxidation [Os(III) + e- f
Os(II)], whereas the reduction couples at E1/2 ) -1.70 to
-1.97 V are due to the reduction of diimine ligands.49 The
E1/2 (Os III/II) of 3c at +0.92 V is cathodically shifted from
that of +0.53 V for 2c, which is consistent with the fact
that DMSO is a better π acceptor than PPh3. The E1/2 (Os
III/II) of 4 at +0.31 V could be attributed to PMe3 being a
better σ donor than DMSO and PPh3. The E1/2 (Os III/II) values
of 3f (+0.96 V) and 3g (+0.91 V) are similar, consistent
with the metal-centered assignment for the electrochemical
oxidation.
Figure 9. Emission spectral traces and (inset) emission intensity enhance-
ment factor (I/Io, monitored at 531 nm) of 2e at increasing equivalents of
Zn(NO3)2 in 0.1 M nBu4NPF6 methanolic solution at 298 K (λex ) 420 nm,
[2e] ) 4.96 × 10-5 M).
monitoring at 541 nm, the excitation spectrum of 2e
in the presence of 10 equiv of Zn(NO3)2 is similar to that
of the ground-state absorption spectrum under the same
conditions.
The effect of other cations has also been investigated.
n
Addition of 2 equiv of Cu(ClO4)2 to a 0.1 M Bu4NPF6
The excited-state redox potentials of cis-dicyano-
osmium(II) diimine complexes can be estimated from the
acetonitrile solution of 2c led to a blue-shift of the absorption
maximum from 397 to 342 nm and complete quenching of
the emission. The presence of 100 equiv of LiClO4 or
NaClO4 did not cause a dramatic change in the emission
properties; the emission intensity only decreased by ∼50 and
10%, and the emission λmax slightly shifted to 645 and 650
nm, respectively. Blue shifts in emission λmax (∆νmax ) 3460
cm-1) and I/Io values of 200-1500 were also observed upon
addition of 200 equiv of Mg(ClO4)2, Cd(ClO4)2, or Zn(ClO4)2
to 2c in 0.1 M nBu4NPF6 acetonitrile solution. Similar
findings on the changes in the emission properties of 3a-
3e in acetonitrile solutions upon the addition of Zn(NO3)2
were also recorded. As an example, the emission of 3a in
electrochemical and spectroscopic data. The E1/2 (OsIII/II*
)
values can be expressed by E1/2 (OsIII/II*) ) E1/2 (OsIII/II) -
E0-0 (OsII*/II); the E0-0 value can be estimated from low-
temperature solid-state emission (2.06 eV for 2c; 2.26 eV
for 3c; 1.89 eV for 4), and the E1/2 (OsIII/II) value is obtained
from cyclic voltammetric data. Therefore, the E1/2 (OsIII/II*
)
were calculated to be -1.53, -1.34, and -1.58 V for 2c,
3
3c, and 4 respectively, revealing that the MLCT excited
states are strong reductants.50
Discussion
This work demonstrates that photolysis of [OsO2(CN)2-
(N∩N)] in the presence of PPh3, PMe3, or DMSO is a useful
method for the preparation of strongly luminescent cis-
dicyanoosmium(II) complexes bearing diimine (N∩N) ligands.
As dimethyl sulfone was detected after photolysis of
[OsO2(CN)2(N∩N)] in DMSO solutions, the photoreduction
of dioxoosmium(VI) to osmium(II) likely involves the
transfer of an oxygen atom from the electronic excited
state(s) of [OsO2(CN)2(N∩N)] to DMSO. The photochemical
reactions of [OsO2(CN)2(N∩N)] with PR3 and DMSO are
depicted in Scheme 1. Previous studies showed that trans-
n
0.1 M Bu4NPF6 acetonitrile solution shows a blue shift in
λmax from 626 to 540 nm and I/Io of 124 at 540 nm upon the
addition of up to 2 equiv of Zn(NO3)2.
(II) In Aqueous Solution. The addition of up to 10 equiv
of Zn(NO3)2 to an aqueous solution of 3a at 298 K did not
cause a notable blue-shift in emission λmax or a substantial
enhancement of emission intensity (maximum I/Io ) 1.5 at
562 nm with 2 equiv of Zn2+). This reveals that the binding
of Zn2+ to 3a is significantly diminished in aqueous medium.
Emission titration of 3a upon the addition of different
n
concentrations of Zn(NO3)2 in 0.1 M Bu4NPF6 aqueous
solution was undertaken; addition of Zn2+ (up to 3 equiv)
induced no shift in the emission λmax at 563 nm. The emission
intensity at λmax was slightly affected by the addition of
Zn(NO3)2, but the changes were sporadic and irregular.
Cytotoxicity. The cytotoxicity of 3c toward a panel of
several selected human cancer cell lines (human hepato-
cellular carcinoma (HepG2), human nasopharyngeal carci-
noma (SUNE1), and human breast cancer cells (MCF7)) has
(48) Mosmann, T. J. Immunol. Methods 1983, 65, 55-63.
(49) (a) Collison, D.; Mabbs, F. E.; McInnes, E. J. L.; Taylor, K. J.; Welch,
A. J.; Yellowlees, L. J. J. Chem. Soc., Dalton Trans. 1996, 329-334.
(b) Chan, S.-C.; Chan, M. C. W.; Wang, Y.; Che, C.-M.; Cheung,
K.-K.; Zhu, N. Chem.sEur. J. 2001, 7, 4180-4190.
(50) (a) Kober, E. M.; Marshall, J. L.; Dressick, W. J.; Sullivan, B. P.;
Caspar, J. V.; Meyer, T. J. Inorg. Chem. 1985, 24, 2755-2763. (b)
Kober, E. M.; Sullivan, B. P.; Dressick, W. J.; Caspar, J. V.; Meyer,
T. J. J. Am. Chem. Soc. 1980, 102, 7383-7385. (c) Kober, E. M.;
Caspar, J. V.; Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1988, 27,
4587-4598.
11014 Inorganic Chemistry, Vol. 46, No. 26, 2007

cis-Dicyanoosmium(II) Diimine Complexes
Scheme 3
dioxoosmium(VI) complexes supported by nitrogen donor
3
and/or CN ligands have a long-lived and emissive [(dxy)1
(dxz, dyz)1] excited state in solution and are powerful photo-
oxidants. Indeed, light-induced photochemical oxidation of
alkenes to epoxides by [OsO2(CN)2(tBu2bpy)] complexes had
previously been demonstrated.29 The [OsO2(CN)2(N∩N)]
complexes in this work have a long-lived emission in the
visible region. As an example, 1e shows an emission at 653
nm with a lifetime of 0.65 µs and a quantum yield of 6.3 ×
10-4 in CH3CN solution. The emission of 1e was found to
be quenched by DMSO with a quenching rate constant of
3.0 × 109 M-1 s-1. This suggests that the photodeoxygen-
ation of 1e probably occurs via the 3[(dxy)1 (dxz, dyz)1] excited
state. This assumption is supported by the finding that the
photoreduction of 1e to 3e in DMSO occurred efficiently
within 30 min upon light excitation at λ ) 450 nm, which
is the spectral region for the dxy f (dxz, dyz) transitions.28,29,51
In this work, the 3MLCT emission energy of cis-dicyano-
osmium(II) complexes are affected by: (1) substituent(s) on
the diimine ligand, (2) π-acceptor auxiliary ligands (PR3 and
DMSO), (3) solvent polarity, and (4) the presence of metal
cations. Derivatization of the diimine ligand with electron-
withdrawing substituents stabilizes the π* orbital, whereas
the electron-donating alkyl substituent increases the energy
than that of the ground state, and decreasing solvent polarity
leads to stabilization of the excited state to a greater degree.
This is consistent with the assignment of the emissive excited
state to be dπ(OsII) f π*(N∩N) in nature, as depicted in
Scheme 3.
The solvatochromic behavior of the emission of these
Os(II) complexes follows a linear correlation between ln knr
and Eem, as predicted by the energy-gap law. A plot of ln knr
3
against the emission energy of the MLCT excited state of
2c in various solvents afforded a linear correlation with a
slope of -5.02 eV-1 and an intercept of (24 ( 1), as depicted
in Figure 8. A simplified equation for the relationship
between ln knr and the emission energy, Eem is: ln knr ) (ln
â - SM) - (γ0 Eem/pωM), assuming a single acceptor
vibration.47a The â value relates to the spin-orbit coupling
constant for osmium(II) complexes. SM is a measure of
excited-state distortion and γ0 ) ln (Eem/SM pωM) - 1, where
pωM is the vibrational progression of the deactivating
mode(s). For 2c and 3e, variation in ln â should be small.
Well-revolved vibronic low-temperature (77 K) glassy emis-
sion spectra of 2c and 3e have not been obtained in this work,
therefore a quantitative discussion on SM and γ0 cannot be
made. The slope (-9.84 eV-1) of the plot for 3e is more
negative than that of 2c (-5.02 eV-1), and the intercept (34
( 2) for 3e is relatively larger than that of (24 ( 1) for 2c,
suggesting that the excited-state structural distortion (related
to SM and pωM values) of the former could be smaller than
that of the latter. For 3a-3f, the absorption and emission
maxima are in general at higher energies than those for 2a-
3
of the π* orbital. Thus, the MLCT emission energy in
acetonitrile decreases in the order: (i) for phen derivatives:
2c (λem ) 651 nm) > 2a (669 nm), whereas 3c (λem ) 613
nm) > 3a (626 nm) > 3g (628 nm) > 3f (644 nm), (ii) for
bpy derivatives: 2e (λem ) 653 nm) > 2b (656 nm) > 2d
(697 nm), whereas 3e (λem ) 613 nm) > 3b (626 nm) > 3d
(634 nm). The strong π-acceptor axial ligands (L) increase
the energy gap between the dπ(Os) and π* (N∩N) orbitals
as a result of dπ(Os) f L π backbonding. Because DMSO
is a better π acceptor than trimethyl- and triphenylphos-
phine,52 the emissions of 3a-3g are at higher energies (λem
) 613-644 nm in CH3CN) than those observed for 2a-2e
(λem ) 651-697 nm) and 4 (λem ) 731 nm).
3
2e. The emission excited states of 3a-3f contain more IL
In this work, intermolecular interactions between the
coordinated cyanide groups and solvent molecules affect the
3MLCT emission of the Os(II) complexes. For example, the
emission λmax of 2e blue-shifts from 707 nm in toluene to
627 nm in CH3OH. We attribute this to hydrogen-bonding
interactions between the protic solvent molecules such as
MeOH or EtOH and coordinated CN ligands, which is also
revealed by difference in chemical shifts of the cyano carbon
atoms of 3e recorded in CD3OD and acetone-d6 (δ 133.5 vs
δ 128.3). The cyanide-solvent hydrogen-bonding interaction
causes a shift of electron density away from Os(II). As a
result, the dπ(Os) level would be lowered, leading to increases
in 1MLCT absorption and 3MLCT emission energies in protic
solvents.53 Alternatively, the red-shift of the emission of cis-
dicyanoosmium(II) diimine complexes in less polar solvents
suggests that the dipole moment of the excited-state is lower
character, and, hence, the excited-state distortion of the
metal-ligand bond(s) in the case of 3e could be smaller than
3
that of 2c, the latter exhibits a MLCT excited state. The
data for 2c in protic solvents (MeOH and EtOH) show slight
deviations from a linear correlation, and this may be
rationalized by hydrogen-bonding interactions between the
solvent molecules and cyano groups in the excited state.19,50a
Similarly, the relatively low Φ and short τ of 3a-3e in
aqueous solution can be attributed to hydrogen-bonding
contacts between the DMSO ligands and water molecules.
The MLCT absorption and emission maximum of 2e
exhibit hypsochromic shifts upon the addition of metal
cations; this shift was also accompanied by an enhancement
of the emission intensity. The most-dramatic effect was
observed with Zn(NO3)2: upon the addition of up to 2 equiv
of Zn(NO3)2, the emission λmax in 0.1 M nBu4NPF6 in
methanol shifted from 627 to 531 nm with a 810-fold
increase in I/Io at λ of 531 nm. Analysis of the solution by
ESI mass spectrometry indicated the formation of [2e‚Zn-
(NO3)2‚ZnNO3] species. We propose that the cyanide ligands
(51) Miskowski, V. M.; Gray, H. B.; Hopkins, M. D. AdV. Transit. Met.
Coord. Chem. 1996, 1, 159-186.
(52) Cotton, F. A.; Wilkinson, G. In AdVanced Inorganic Chemistry, 3rd
ed.; Wiley & Sons: New York, 1972; p 720.
(53) Garc´ıa Posse, M. E.; Katz, N. E.; Baraldo, L. M.; Polonuer, D. D.;
Colombano, C. G.; Olabe, J. A. Inorg. Chem. 1995, 34, 1830-1835.
Inorganic Chemistry, Vol. 46, No. 26, 2007 11015

Lai et al.
of the osmium(II) complexes undergo binding to the elec-
trophilic Zn2+ ions, causing a decrease in electron density
at Os(II) and leading to destabilization of the 3MLCT excited
state and, hence, an increase in the 3MLCT emission energy.
The enhancement in emission intensity and blue shift in
emission λmax (from 627 to 531 nm) of 2e in the presence of
Zn(NO3)2 could likely be attributed to a change in the triplet
excited state from 3MLCT with λmax at 627 nm to that having
mixed 3IL and 3MLCT parentages with λmax at 531 nm. The
results of NMR experiments are consistent with the decrease
in electron density around Os(II) upon the addition of
Zn(NO3)2. The 13C chemical shift of the cyano carbon atoms
of 3e (δ 131.1 in CDCl3/CD3OD (2:1)) and the 31P chemical
shift of 2e (δ 3.86 in CD3CN) increase to δ 134.9 and δ
4.88, respectively, in the presence of Zn(NO3)2.
The two cyanide ligands of the cis-dicyanoosmium(II)
diimine complexes can bind metal ions. The MLCT absorp-
tion and emission bands undergo substantial blue shifts in
energy, and the emission intensity is significantly enhanced
upon complexation of metal ions. The emission enhancement
may be a consequence of increased molecular rigidity upon
the coordination of Zn2+ ions by cyanide groups. The water-
soluble Os(II) complexes [Os(DMSO)2(CN)2(N∩N)] (3a-
3g) are potentially applicable in luminescent signaling studies
involving molecules of biological interest. Their relatively
nontoxic nature, as observed for 3c, facilitates their future
development in biosensory applications. Very recently, we
have accomplished the synthesis of the cis-dicyano-
osmium(II) diimine complex bearing a functionalizable bpy
group, [Os(DMSO)2(CN)2(bpy(COOH)2)]. Treatment with
N-hydroxysuccinimide (NHS) is envisaged to give [Os-
(DMSO)2(CN)2(bpy(NHS)2)], which can readily undergo
covalent attachment to biomolecules, and we will publish
this work in due course.
We have determined the crystal structure of [2c‚Zn-
(NO3)2]∞ (Figure 2), which comprises [Zn(NO3)2] moieties
linked via the cyanide groups of 2c units to form an
alternating zigzag chain. The room-temperature solid-state
emission of [2e‚Zn(NO3)2]∞ shows a λmax at 548 nm, which
is significantly blue-shifted from that of 2e (λmax 670 nm).
This supports the rationale that the coordination of Zn2+ by
Acknowledgment. We are grateful for financial support
from the Research Grant Council of the Hong Kong SAR,
China (HKU 7030/06P, HKU 7011/07P), The University
of Hong Kong (URC-administered Seed Funding Grant
200511159176), and the National Natural Science Foundation
of China/Research Grants Council Joint Research Scheme
(N_HKU 742/04). We thank Prof. David L. Phillips and
Dr. Wai-Ming Kwok for performing time-resolved emission
spectroscopy experiments and helpful discussions and the
reviewers for their insightful comments.
3
the CN groups increases the MLCT emission energy.
Conclusion
The absorption and emission energies, emission quantum
yield, and lifetime of cis-dicyanoosmium(II) complexes
bearing diimine ligands exhibit remarkable solvatochromism.
A linear correlation between MLCT absorption energy and
solvent polarity (defined by ET values) was observed. The
energy-gap law was obeyed, as demonstrated by the plot of
the nonradiative rate constant against the emission energy.
The cyanide ligands are engaged in intermolecular hydrogen-
bonding interactions with solvent molecules, causing electron
density to shift away from osmium(II) and consequentially
Supporting Information Available: Characterization data of
2a and 3a; crystal data, bond lengths and angles, and perspective
view of 2a‚3CH2Cl2, 2c‚2CH2Cl2, 2e‚CH2Cl2•H2O, 3d‚0.5(CH2-
Cl2), and 3e‚0.5(CH2Cl2)‚0.5(Et2O); and selected photophysical
spectra. This material is available free of charge via the Internet at
http://pubs.acs.org.
3
higher MLCT emission energies. A previous report on the
IC070290L
solvatochromic properties of [Ru(bpy)(CN)4]2- has described
the interaction of the externally directed cyanide lone pairs
with solvent molecules.54
(54) Timpson, C. J.; Bignozzi, C. A.; Sullivan, B. P.; Kober, E. M.; Meyer,
T. J. J. Phys. Chem. 1996, 100, 2915-2925.
11016 Inorganic Chemistry, Vol. 46, No. 26, 2007