Synthesis and luminescence properties of [Pt{4′-(Np1)-trpy} (C≡CPh)]SbF6 and [Pt{4′-(Np1)-trpy}{C≡C(CH 2)2CH3}]SbF6 [4′-(Np1)-trpy = 4′-(1-naphthyl)-2,2′:6′,2″-terpyridine]

Article abstract of DOI:10.1016/j.ica.2005.06.085

The synthesis and characterisation of [Pt{4′-(Np1)-trpy}(C≡CPh) ]SbF₆ (1) and [Pt{4′-(Np1)-trpy}{C≡C(CH₂) ₂CH₃}]SbF₆ (2) [4′-(Np1)-trpy = 4′-(1-naphthyl)-2,2:6′,2′-terpyridine] are described. Complexes 1 and 2 exhibit unimolecular ³MLCT (MLCT = metal-to-ligand charge transfer) emission in acetonitrile and in a low concentration 77 K glass solution in butyronitrile. The high concentration glass emission as well as the emission in the solid state is from a ³MMLCT (MMLCT, metal-metal-to-ligand charge transfer) excited state, reflecting the presence of d_z²(Pt)-d_z²(Pt) interactions in these media.

Full text of DOI:10.1016/j.ica.2005.06.085

Inorganica Chimica Acta 358 (2005) 4567–4570
www.elsevier.com/locate/ica
Note
Synthesis and luminescence properties of
[Pt{40-(Np1)-trpy}(C„CPh)]SbF6 and
[Pt{40-(Np1)-trpy}{C„C(CH2)2CH3}]SbF6
[40-(Np1)-trpy = 40-(1-naphthyl)-2,20:60,200-terpyridine]
a,
a
b
John S. Field *, Raymond J. Haines , David R. McMillin ,
a
a
Orde Q. Munro , Grant C. Summerton
a
School of Chemistry, University of KwaZulu-Natal, Pietermaritzburg 3209, South Africa
b
Department of Chemistry, Purdue University, West Lafayette, IN 47907-2084 , USA
Received 6 May 2005; accepted 1 June 2005
Available online 31 August 2005
Abstract
The synthesis and characterisation of [Pt{40-(Np1)-trpy}(C„CPh)]SbF6 (1) and [Pt{40-(Np1)-trpy}{C„C(CH2)2CH3}]SbF6 (2)
[40-(Np1)-trpy = 40-(1-naphthyl)-2,2:60,20-terpyridine] are described. Complexes exhibit unimolecular 3MLCT
and
1
2
(MLCT = metal-to-ligand charge transfer) emission in acetonitrile and in a low concentration 77 K glass solution in butyronitrile.
The high concentration glass emission as well as the emission in the solid state is from a 3MMLCT (MMLCT, metal–metal-to-ligand
charge transfer) excited state, reflecting the presence of d2z ðPtÞ–dz2ðPtÞ interactions in these media.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Luminescence; Platinum complexes; Terpyridine complexes
1. Introduction
[Pt{40-(Np1)-trpy}{C„C(CH2)2CH3}]SbF6 (2) (Np1 =
1-naphthyl). These complexes are distinguished by the
presence of a 1-naphthyl group bonded to the 4-position
of the 2,20:60,200-terpyridyl moiety. As we have previously
reported, the naphthyl group can influence dramatically
the luminescence properties of terpyridyl ligand com-
plexes of platinum (II) [5].
Terpyridyl (trpy where trpy = 2,20:60,200-terpyridine)
ligand complexes of platinum (II) with a chloride ion as
the fourth ligand bonded to platinum have received con-
siderable attention insofar as their photoluminescence
properties are concerned [1–14]. However, only four re-
ports have appeared on the photophysics of complexes
where a terminal-acetylide ligand is bound to a Pt(trpy)
unit [15–18] and one report on the photophysics of
complexes where two Pt(trpy) units are linked by a bridg-
ing-acetylide ligand [19]. We report the synthesis and pho-
toluminescence properties of two new-acetylide
complexes, [Pt{40-(Np1)-trpy}(C„CPh)]SbF6 (1) and
2. Experimental
2.1. Materials
All organic reagents and solvents were purchased
from Aldrich Chemicals and used as received. The 40-
(1-naphthyl)-2,2:60,200-terpyridine was prepared as de-
scribed previously [5]. The [Pt(PhCN)2Cl2] and AgSbF6
*
Corresponding author. Tel.: +27 33 2605239; fax: +27 33 2605009.
E-mail address: fieldj@ukzn.ac.za (J.S. Field).
0020-1693/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2005.06.085

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J.S. Field et al. / Inorganica Chimica Acta 358 (2005) 4567–4570
were obtained from Strem Chemicals. The AgC„CA
[A = Ph or (CH2)2CH3] salts were prepared by reaction
of AgNO3 with the appropriate alkyne using the method
of Agawa [20]. The CD3CN used for recording NMR
spectra was of spectroscopic grade and obtained from
Merck Chemicals. For the UV–Vis absorption and solu-
tion emission measurements spectroscopic grade sol-
vents were used that were deoxygenated prior to use
by a stream of argon.
7.9–8.4 (7H), 7.5–7.8 (4H), 7.33 (m, 4H), 2.64 (t, 2H,
C„CCH2CH2CH3), 1.68 (m, 2H, CCH2CH2CH3), 1.11
(t, 3H, CCH2CH2CH3). UV–Vis (50 lM in CH3CN):
k
max/nm (e, Mꢀ1 cmꢀ1) 289(3.3 · 104); 312(1.5 · 103);
326(1.3 · 103); 341(1.6 · 103); 430(6.0 · 103).
2.3. Instrumentation
Microanalysis for carbon, hydrogen and nitrogen was
performed by Galbraith Laboratories, Knoxville, TN,
USA. Infrared spectra were recorded using a Shimadzu
2.2. Synthesis of [Pt{40-(Np1)-trpy}(C„CA)]SbF6
[A = Ph (1) and A = (CH2)2CH3 (2)]
1
FT IR 4300 spectrometer. H NMR spectra were re-
corded at 303 K using a Varian Gemini 200 MHz spec-
trometer. UV–Vis spectra were recorded at 295 K using
a Shimadzu UV-2101PC scanning spectrophotometer.
Emission spectra were recorded on a SLM-Aminco
SPF-500C spectrofluorometer. The cryostat was an Ox-
ford Instruments model DN1704 liquid-nitrogen-cooled
system complete with an Oxford Instruments model
ITC4 temperature controller. The excitation wavelength
was 330 nm, with the scattered light removed by a 400
nm long-wave-pass filter. The 337 nm line from a nitro-
gen laser served as the excitation source for the lifetime
measurements, with a 337 nm band pass filter used to re-
move stray light from the beam. Lifetime data were ana-
lysed as described previously [21,22].
A suspension of [Pt(PhCN)2Cl2] (100 mg, 0.21 mmol)
in acetonitrile (20 ml) was treated with an equimolar
amount of AgSbF6 (73 mg, 0.21 mmol) dissolved in ace-
tonitrile (5 ml). The reaction mixture was heated under
reflux for 16 h, the AgCl precipitate removed by filtra-
tion and one equivalent of 40-(1-naphthyl)-2,2:60,200-ter-
pyridine (76 mg, 0.21 mmol) added to the filtrate. The
reaction mixture was heated under reflux for a further
24 h after which the volume of the solution was reduced
in vacuo, resulting in the precipitation of [Pt{40-(Np1)-
trpy}Cl]SbF6. Subsequent purification involved washing
the product with a minimum of acetonitrile and drying
in vacuo. Yield: 0.12 g (70%). Anal. Calc. for
C25H17ClF6N3PtSb: C, 36.37; H, 2.08; N, 5.09. Found:
C, 36.71; H, 2.33; N, 5.30%. 1H NMR (CD3CN): d
8.92 (m, 2H), 8.49 (m, 2H), 8.0–8.4 (7H), 7.6–7.9 (6H).
A suspension of [Pt{40-(Np1)-trpy}Cl]SbF6 (100 mg,
0.12 mmol) and AgC„CA (0.15 mmol, 25% excess) in
pyridine (5 ml) was stirred for 48 h. Precipitation of
the product was effected by the addition of chloroform.
The solid material was washed thoroughly with chloro-
form and dried in vacuo. Purification of the crude prod-
uct was achieved by its extraction into a minimum
amount of boiling acetonitrile and subsequent filtration
of the hot solution. Allowing the filtrate to cool to room
temperature afforded both [Pt{40-(Np1)-trpy}(C„CPh)]
SbF6 and [Pt{40-(Np1)-trpy}{C„C(CH2)2CH3}]SbF6
as orange microcrystalline solids.
3. Results and discussion
The r-acetylide complexes 1 and 2 were synthesised
in good yields by means of a metathesis reaction in
which the chloro-analogue, [Pt{40-(Np1)-trpy}Cl]SbF6,
was reacted in pyridine with the silver salts AgC„CPh
and AgC„C(CH2)2CH3 respectively. Complexes 1 and
2 were isolated as orange microcrystalline solids by cool-
ing a solution of the compound in hot acetonitrile.
Unfortunately, despite repeated attempts, it was not
possible to grow single crystals of 1 and 2 for the pur-
poses of an X-ray diffraction study.
[Pt{40-(Np1)-trpy}(C„CPh)]SbF6. Yield: 78 mg
(73%). Anal. Calc. for C33H22F6N3PtSb: C, 44.77; H,
2.49; N, 4.71. Found: C, 44.40; H, 2.68; N, 4.81%. IR
(KBr, cmꢀ1): m(C„CPh) 2120w; m(trpy) 1608s, 1486m,
1477m, 1418m, 1394mw, 1034w; mðSbF6ꢀÞ 659vs. 1H
NMR (CD3CN): d 8.88 (m, 2H), 7.9–8.4 (8H), 7.5–7.8
(8H), 7.30 (m, 4H). UV–Vis (50 lM in CH3CN):
3.1. Photophysical properties of 1 and 2
The UV–Vis absorption spectra of 1 and 2 measured
in acetonitrile are very similar with a peak at ꢁ289 nm, a
vibrationally structured band between 300 and 350 nm,
and a broad band at ꢁ430 nm. As is the case for other
terpyridyl ligand complexes of platinum(II), the high
1
k
max/nm (e, Mꢀ1 cmꢀ1) 289(3.8 · 104); 310(1.7 · 103);
energy peaks are assigned to (p–p*) transitions of the
326(1.5 · 103); 341(1.7 · 103); 429(7.8 · 103).
40-(1-naphthyl)-2,2:60,2-terpyridyl ligand [2–19]. Two
possibilities exist for the assignment of the broad low en-
ergy band, a dp(Pt) ! p*(trpy) metal-to-ligand charge
transfer (MLCT) transition or an acetylide-to-terpyri-
dine ligand-to-ligand charge transfer (LLCT) transition.
We tentatively make the MLCT assignment, as indeed
have other workers for the broad band that is observed
[Pt{40-(Np1)-trpy}{C„C(CH2)2CH3}]SbF6. Yield:
50 mg (49%). Anal. Calc. for C30H24F6N3PtSb: C,
42.03; H, 2.82; N, 4.90. Found: C, 42.40; H, 2.96; N,
5.07%. m[C„C(CH2)2CH3] 2128w; m(trpy) 1603m,
1475w, 1415w, 1337m, 1031w, 788m, 779m, 752m;
1
mðSbF6ꢀÞ 661vs. H NMR (CD3CN): d 9.89 (m, 2H),

J.S. Field et al. / Inorganica Chimica Acta 358 (2005) 4567–4570
4569
in the 400–500 nm region of the absorption spectra of
mononuclear r-acetylide ligand complexes of platinum
terpyridines [15–18].
The emission spectra of 1 and 2 measured in CH2Cl2/
CH3CN (20:1) and CH2Cl2 solutions are shown in Fig. 1.
The emission spectra in the mixed solvent system consist
of a single asymmetric peak centred at 611 nm for 1 and
632 nm for 2, with excited state lifetimes of 1.80 and
0.55 ls, respectively. Both complexes exhibit more in-
tense emission maxima at slightly lower energies when re-
corded in pure CH2Cl2, occurring at 616 and 638 nm for
1 and 2, respectively. The excited state lifetimes (s) are
correspondingly longer, being 2.6 and 1.2 ls, respec-
tively. The decrease of the emission intensity when a
coordinating solvent (CH3CN) is added, the change in
emission energy with the polarity of the solvent and the
emission profile, are all consistent with a 3MLCT assign-
ment to the emitting state. The same assignment has been
made for the fluid emission exhibited by the r-acetylide
complexes, [Pt(trpy)(C„CPh)]PF6 [15], [Pt{40-R1-trpy)
(C„CR2)]ClO4 (R1 = p-tolyl; R2 = CH2OH, n-propyl,
C6H4Cl-4, C6H5, C6H4CH3-4) [16] and [Pt(trpy)(C„C
C6H4-4-R]X (R = N(CH3)2, X = BF4; R = N-15-mono-
azacrown-5, X = ClO4) [17]. We note that the emission
in dichloromethane exhibited by the analogous chloride
compound [Pt{40-(Np1)-trpy}Cl]SbF6 [5], has a similar
band profile to those shown in Fig. 1 for the r-acetylide
derivatives 1 and 2. However, the emission energy and
excited state lifetime are higher [kem(max) = 588 nm
and s = 16.6 ls]. The unexpectedly long excited state life-
time for the chloride compound has been explained in
terms of the configurational mixing of 3ILCT
(ILCT = intraligand charge transfer) character in an
emitting state that is primarily 3MLCT in origin [5]. This
does not appear to be the case for compounds 1 and 2;
moreover, the shorter lifetimes recorded for the r-acety-
lide derivatives are consistent with the energy gap law
[23,24] as their emission energies are lower than that re-
corded for [Pt{40-(Np1)-trpy}Cl]SbF6 [5].
Fig. 2. Solid state emission spectra of 1 as a function of cooling from
(a) 280 K to (f) 80 K in 40 K steps.
The solid state emission spectra of 1 and 2 were re-
corded at 40 K intervals over the temperature range
80–280 K. The spectra recorded for 1 are shown in
Fig. 2, those obtained for 2 being very similar.1 The solid
emission spectrum of 1 at 280 K consists of a relatively
broad asymmetric band centred at 703 nm (s = 360 ns).
On lowering the temperature to 80 K the band narrows
and systematically increases in intensity (s = 1.30 ls).
Furthermore, the emission maximum systematically
shifts to the red as the solid is cooled reaching a value
of 754 nm at 80 K. These features of the solid emission
3
exhibited by 1 are characteristic of a MMLCT (metal–
metal-to-ligand charge transfer) excited state as exhib-
ited in the solid state by, for example, [Pt(trpy)Cl]CF3
SO3 [2], [Pt{4-(o-CH3-Ph)-trpy}Cl]SbF6 [7], [Pt{4-(o-Cl-
Ph)-trpy}Cl]SbF6 [9] and [Pt(trpy)(C„CPh)]PF6 [15].
The implication is that d2z ðPtÞ–d2z ðPtÞ interactions are
present in the solid and that these grow stronger as the
solid is cooled [7,9,15]. However, in view of the absence
of a crystal structure determination of 1 or 2 to confirm
this conclusion, a study was made of the concentration
dependence of the 77 K butyronitrile glass emission
exhibited by 2; Fig. 3 gives the results. (The lower solubil-
ity of 1 in butyronitrile prevented the acquisition of a
clean set of spectra over the full concentration range
for this compound.) At the lowest concentration of
0.001 mM, a vibrationally structured band with compo-
nents at 527 and 558 nm is observed. A Huang-Rhys ra-
tio (I0–1/I0–0) of less than 1 is in line with an assignment
3
that is predominantly MLCT in character. Indeed, the
low concentration glass emission for 2 is very similar to
that measured at 77 K in a butyronitrile glass for
3
[Pt(trpy)(C„CPh)]PF6 and for which a MLCT assign-
ment was made [15]. When the concentration is increased
1
Fig. 1. Emission spectra of 1 in CH2Cl2/CH3CN (20:1) (a) and CH2Cl2
The solid emission maxima at 280 and 80 K for 2 occur at 680
(b). Emission spectra of 2 in CH2Cl2/CH3CN (20:1) (c) and CH2Cl2
(d).
(287 ns) and 729 nm (676 ns), respectively. (The lifetime of the emitting
state is given in brackets.)

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a new low energy band develops such that at 0.260 M it
appears as a broad, but well-pronounced band, centred
at 691 nm. This band is reminiscent of the bands that ap-
pear between 680 and 729 nm in the solid state emission
spectra of 21. Clearly, aggregation of the [Pt{40-(Np1)-
trpy}{C„C(CH2)CH3}]+ cations occurs at high
concentrations of the complex with, presumably, the
concomitant onset of d2z ðPtÞ–d2z ðPtÞ interactions that give
3
rise to MMLCT emission at a longer wavelength. Sim-
ilar behaviour has been reported for the concentration
dependence of the emission recorded in an EMD
(EMD = EtOH:MeOH:dimethylformamide) glass for
[Pt(trpy)Cl]PF6 [3].
In summary, complexes 1 and 2 exhibit photolumines-
3
cence from a unimolecular MLCT excited state when
the cationic luminophore is isolated; however, when
aggregation occurs (either in a high concentration glass
3
or in the solid state) emission is from a MMLCT state
because of the presence of d2z ðPtÞ–d2z ðPtÞ interactions.
Acknowledgements
We wish to thank the University of KwaZulu-Natal
and the South African National Research Foundation
for financial support.