Syntheses and crystal structures of dinuclear complexes containing d-block and f-block luminophores. Sensitization of NIR luminescence from Yb(III), Nd(III), and Er(III) centers by energy transfer from Re(I)- and Pt(II)-bipyrimidine metal centers

Article abstract of DOI:10.1021/ic048875s

Mononuclear complexes [Re(bpym)(CO)₃Cl] and [Pt(bpym)(CC-C ₆H₄CF₃)₂] (bpym = 2,2′-bipyrimidine), in which one of the bipyrimidine sites is vacant, have been used as complex ligands to prepare heterodinuclear d-f complexes in which a lanthanide tris(1,3-diketonate) unit is attached to the secondary bipyrimidine site to evaluate the ability of d-block chromophores to act as antennae for causing sensitized near-infrared (NIR) luminescence from adjacent lanthanide(III) centers. The two sets of complexes so prepared are [Re(CO)₃Cl(μ-bpym)Ln(fod)₃] (abbreviated as Re-Ln; where Ln = Yb, Nd, Er) and [(F₃C-C₆H₄-CC) ₂Pt(μ-bpym)Ln(hfac)₃] (abbreviated as Pt-Ln; where Ln = Nd, Gd). Members of both series have been structurally characterized; the metal-metal separation across the bipyrimidine bridge is ≈6.3 A in each case. In these complexes, the ³MLCT (MLCT = metal to ligand charge-transfer) luminescences of the mononuclear [Re(bpym)(CO)₃Cl] and [Pt(bpym)(CC-C₆H₄CF₃)₂] complexes are quenched by energy transfer to those lanthanides (Ln = Yb, Nd, Er) that have low-lying f-f states capable of NIR luminescence; as a result, sensitized NIR luminescence is seen from the lanthanide center following excitation of the d-block unit. In the solid state, quenching of the luminescence from the d-block chromophore is complete, indicating efficient d → f energy transfer, as a result of the short metal-metal separation across the bipyrimidine bridge. In a CH₂Cl₂ solution, partial dissociation of the dinuclear complexes into the mononuclear units occurs, with the result that some ³MLCT luminescence is observed from mononuclear [Re(bpym)(CO)₃Cl] or [Pt(bpym)(CC-C₆H₄CF ₃)₂] present in the equilibrium mixture. Solution UV-vis and luminescence titrations, carried out by the addition of portions of Ln(fod)₃(H₂O)₂ or Ln(hfac)₃(H ₂O)₂ to the d-block complex ligands, indicate that binding of the lanthanide tris(1,3-diketonate) unit at the secondary bipyrimidine site to give the d-f dinuclear complexes occurs with an association constant of ca. 10⁵ M^-1.

Full text of DOI:10.1021/ic048875s

Inorg. Chem. 2005, 44, 61−72
Syntheses and Crystal Structures of Dinuclear Complexes Containing
d-Block and f-Block Luminophores. Sensitization of NIR Luminescence
from Yb(III), Nd(III), and Er(III) Centers by Energy Transfer from Re(I)
and Pt(II) Bipyrimidine Metal Centers
−
−
Nail M. Shavaleev,† Gianluca Accorsi,‡ Dalia Virgili,‡ Zo
1
e R. Bell,† Theodore Lazarides,§
Giuseppe Calogero,| Nicola Armaroli,*,‡ and Michael D. Ward*,†,§
School of Chemistry, UniVersity of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K., Laboratorio di
Fotochimica, Istituto per la Sintesi Organica e la FotoreattiVita` del CNR, Via P. Gobetti 101,
I-40129 Bologna, Italy, Department of Chemistry, UniVersity of Sheffield, Sheffield S3 7HF, U.K.,
and Istituto per i Processi Chimico Fisici del CNR, Sezione de Messina, Via La Farina 237,
I-98123 Messina, Italy
Received August 16, 2004
Mononuclear complexes [Re(bpym)(CO)3Cl] and [Pt(bpym)(CC
one of the bipyrimidine sites is vacant, have been used as “complex ligands” to prepare heterodinuclear d
−
C6H4CF3)2] (bpym
)
2,2
′
-bipyrimidine), in which
f complexes
−
in which a lanthanide tris(1,3-diketonate) unit is attached to the secondary bipyrimidine site to evaluate the ability
of d-block chromophores to act as antennae for causing sensitized near-infrared (NIR) luminescence from adjacent
lanthanide(III) centers. The two sets of complexes so prepared are [Re(CO)3Cl(
Re Ln; where Ln Yb, Nd, Er) and [(F3C C6H4 CC)2Pt( -bpym)Ln(hfac)3] (abbreviated as Pt
Nd, Gd). Members of both series have been structurally characterized; the metal metal separation across the
bipyrimidine bridge is metal to ligand charge-
6.3 Å in each case. In these complexes, the 3MLCT (MLCT
transfer) luminescences of the mononuclear [Re(bpym)(CO)3Cl] and [Pt(bpym)(CC C6H4CF3)2] complexes are
quenched by energy transfer to those lanthanides (Ln Yb, Nd, Er) that have low-lying f f states capable of NIR
µ
-bpym)Ln(fod)3] (abbreviated as
−
)
−
−
µ
−Ln; where Ln
)
−
≈
)
−
)
−
luminescence; as a result, sensitized NIR luminescence is seen from the lanthanide center following excitation of
the d-block unit. In the solid state, quenching of the luminescence from the d-block chromophore is complete,
indicating efficient d
bridge. In a CH2Cl2 solution, partial dissociation of the dinuclear complexes into the mononuclear units occurs, with
the result that some 3MLCT luminescence is observed from mononuclear [Re(bpym)(CO)3Cl] or [Pt(bpym)(CC
C6H4CF3)2] present in the equilibrium mixture. Solution UV vis and luminescence titrations, carried out by the
addition of portions of Ln(fod)3(H2O)2 or Ln(hfac)3(H2O)2 to the d-block complex ligands, indicate that binding of the
f f energy transfer, as a result of the short metal−metal separation across the bipyrimidine
−
−
lanthanide tris(1,3-diketonate) unit at the secondary bipyrimidine site to give the d
−f dinuclear complexes occurs
1
with an association constant of ca. 105 M-
.
Introduction
biological assays1 to display devices,2 and as such, their
photophysical properties have received a huge amount of
attention. In contrast, the longer wavelength emission of
lanthanides such as Yb(III), Nd(III), Dy(III), Pr(III), and Er-
The intense, long-lived, and line-like emission of lan-
thanides such as Eu(III) and Tb(III) in the visible region has
made them of interest for a range of applications, from
(1) (a) Mayer, A.; Neuenhofer, S. Angew. Chem., Int. Ed. Engl. 1994,
33, 1044. (b) Faulkner, S.; Matthews, J. L. In ComprehensiVe
Coordination Chemistry, 2nd ed.; Ward, M. D., Ed.; Elsevier: Oxford,
U.K., 2004; Vol. 9, p 913.
(2) (a) Silver, J. In ComprehensiVe Coordination Chemistry, 2nd ed.;
Ward, M. D., Ed.; Elsevier: Oxford, U.K., 2004; Vol. 9 p 689. (b)
Kido, J.; Okamoto, Y. Chem. ReV. 2002, 102, 2357.
* To whom correspondence should be addressed. E-mail: m.d.ward@
sheffield.ac.uk (M.D.W.); armaroli@isof.cnr.it (N.A.).
† University of Bristol.
‡ ISOF-CNR.
§ University of Sheffield.
| IPCF-CNR.
10.1021/ic048875s CCC: $30.25
Published on Web 11/20/2004
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 1, 2005 61

Shavaleev et al.
(III) in the near-infrared (NIR) region has been less well
studied, although this situation is being remedied.3 Recent
interest in the photophysical properties of these lanthanide
ions stems from their possible use in medical diagnostics,
because the longer emission wavelengths (and hence, pos-
sibly, longer excitation wavelengths) penetrate human tissue
far more effectively than does UV or visible light.1b In
addition, NIR luminescence from metals such as Dy(III), Nd-
(III), and Er(III) is used as the basis for the optical amplifiers
used in fiber-optic systems based on silica fibers that transmit
their signals in the 1300-1550 nm region.4
Since lanthanide ions are very poor at absorbing light
directly, because of the low extinction coefficients of the
Laporte forbidden f-f transitions, energy transfer from an
adjacent strongly absorbing chromophore is usually used to
stimulate luminescence from lanthanides. Often, this is an
aromatic ligand that strongly absorbs UV light, and being
directly coordinated to the lanthanide center, it can effect
fast energy transfer from the resulting ligand-based triplet
state. This is the usual basis for achieving sensitized emission
from Eu(III) and Tb(III).1,2,5 However, the use of UV light
to perform excitation of lanthanides with lower-energy
luminescent levels is undesirable from two points of view.
First, it is inefficient; the use of a 300 nm photon to stimulate
1500 nm emission from Er(III) is inelegant and wasteful of
energy. Second, from the point of view of biological probes,
the incident radiation must be able to penetrate the tissue
sample to reach the chromophore, which rules out UV light
and much of the visible spectrum.1b Both of these points
suggest that it is desirable to design NIR-luminescent
lanthanide complexes that can undergo sensitized lumines-
cence following absorption of light at longer wavelengths.
To this end, there has been a recent effort directed at
attaching chromophores with relatively long wavelength
absorption maxima to NIR-emissive lanthanide ions. van
Veggel and co-workers have prepared complexes in which
a fluorescein-based chromophore, with an absorption maxi-
mum at about 500 nm, is used to stimulate NIR luminescence
from lanthanides.6 We have demonstrated a similar behavior
with lanthanide complexes of a tetrazine-based ligand having
an absorption maximum at ≈500 nm.7
For optimum control and tunability of absorption maxima,
however, having transition-metal chromophores as the energy
donors offers numerous advantages. Transition-metal com-
plexes can meet all of the following criteria: (i) a strong
absorption maximum that can be selected almost anywhere
in the visible or NIR region; (ii) a heavy metal ion that will
facilitate intersystem crossing and give a high triplet quantum
yield of the energy donor following excitation; (iii) relatively
long-lived triplet excited states that will facilitate energy
transfer to the adjacent lanthanide; (iv) kinetic inertness and
photochemical stability; (v) in many cases, luminescence
from the (unquenched) triplet state that will allow energy
transfer to the lanthanide to be followed by both quenching
of the donor and the appearance of sensitized emission from
the lanthanide; and (vi) synthetic convenience, for example,
the presence of a vacant coordination site at the periphery
of the complex (“complexes-as-ligands”) to which a lan-
thanide fragment can be attached. All of these criteria have
been exploited in the field of supramolecular photochemistry
of d-block metal fragments. The first examples of sensitized
NIR emission from lanthanide complexes using a covalently
attached d-block complex unit as the sensitizer were de-
scribed only a few years ago, by the groups of van Veggel
(using a [Ru(bipy)3]2+ or ferrocenyl unit as the energy donor)8
and Parker (using a Pd-porphyrin unit as the energy donor).9
More recently, Cr(III) chromophores have been used as
energy donors to luminescent lanthanides in heterodinuclear
helicate complexes10 and in oxalate-bridged dinuclear com-
plexes.11 Other heterodinuclear assemblies incorporating a
metal polypyridyl unit connected to a lanthanide, which show
d-f energy transfer and subsequent NIR luminescence from
the lanthanide, have been described recently by the groups
of Faulkner and Coe,12 Yanagida,13 Pikramenou,14 and Beer.15
(3) Representative recent papers describing NIR luminescence from
lanthanide complexes: (a) Hebbink, G. A.; Klink, S. I.; Grave, L.;
Oude Alink, P. G. B.; van Veggel, F. C. J. M. ChemPhysChem 2002,
3, 1014. (b) Faulkner, S.; Pope, S. J. A. J. Am. Chem. Soc. 2003, 125,
10526. (c) Magennis, S. W.; Ferguson, A. J.; Bryden, T.; Jones, T.
S.; Beeby, A.; Samuel, I. D. W. Synth. Met. 2003, 138, 463. (d)
Dickins, R. S.; Aime, S.; Batsanov, A. S.; Beeby, A.; Botta, M.; Bruce,
J.; Howard, J. A. K.; Love, C. S.; Parker, D.; Peacock, R. D.;
Buschmann, H. J. Am. Chem. Soc. 2002, 124, 12697. (e) Kamenskikh,
I. A.; Guerrasimova, N.; Dujardin, C.; Garnier, N.; Ledoux, G.; Pedrini,
C.; Kirm, M.; Petrosyan, A.; Spassky, D. Opt. Mater. (Amsterdam)
2003, 24, 267. (f) Wong, W. K.; Liang, H. Z.; Wong, W. Y.; Cai, Z.
W.; Li, K. F.; Cheah, K. W. New J. Chem. 2002, 26, 275. (g) Silva,
F. R. G. E.; Malta, O. L.; Reinhard, C.; Gu¨del, H. U.; Piguet, C.;
Moser, J. E.; Bu¨nzli, J.-C. G. J. Phys. Chem. A 2002, 106, 1670. (h)
Faulkner, S.; Beeby, A.; Carrie, M. C.; Dadabhoy, A.; Kenwright, A.
M.; Sammes, P. G. Inorg. Chem. Commun. 2001, 4, 187. (i) Hebbink,
G. A.; Klink, S. I.; Oude Alink, P. G. B.; van Veggel, F. C. J. M.
Inorg. Chim. Acta 2001, 317, 114. (j) Voloshin, A. I.; Shavaleev, N.
M.; Kazakov, V. P. J. Lumin. 2001, 93, 199.
(6) (a) Hebbink, G. A.; Grave, L.; Woldering, L. A.; Reinhoudt, D. N.;
van Veggel, F. C. J. M. J. Phys. Chem. A 2003, 107, 2483. (b) Wolbers,
M. P. O.; van Veggel, F. C. J. M.; Peters, F. G. A.; van Beelen, E. S.
E.; Hofstraat, J. W.; Geurts, F. A. J.; Reinhoudt, D. N. Chem.sEur.
J. 1998, 4, 772.
(7) Shavaleev, N. M.; Pope, S. J. A.; Bell, Z. R.; Faulkner, S.; Ward, M.
D. J. Chem. Soc., Dalton Trans. 2003, 808.
(8) Klink, S. I.; Keizer, H.; van Veggel, F. C. J. M. Angew. Chem., Int.
Ed. 2000, 39, 4319.
(9) Beeby, A.; Dickins, R. S.; FitzGerald, S.; Govenlock, L. J.; Maupin,
C. L.; Parker, D.; Riehl, J. P.; Siligardi, G.; Williams, J. A. G. Chem.
Commun. (Cambridge) 2000, 1183.
(10) Imbert, D.; Cantuel, M.; Bu¨nzli, J.-C. G.; Bernardinelli, G.; Piguet,
C. J. Am. Chem. Soc. 2003, 125, 15698.
(11) Subhan, M. A.; Nakata, H.; Suzuki, T.; Choi, J.-H.; Kaizaki, S. J.
Lumin. 2003, 101, 307.
(12) (a) Pope, S. J. A.; Coe, B. J.; Faulkner, S.; Bichenkova, E. V.; Yu,
X.; Douglas, K. T. J. Am. Chem. Soc. 2004, in press. (b) Pope, S. J.
A.; Coe, B. J.; Faulkner, S. Chem. Commun. (Cambridge) 2004, 1550.
(13) Guo, D.; Duan, C.-Y.; Lu, F.; Hasegawa, Y.; Meng, Q.-J.; Yanagida,
S. Chem. Commun. (Cambridge) 2004, 1486.
(14) Glover, P. B.; Ashton, P. R.; Childs, L. J.; Rodger, A.; Kercher, M.;
Williams, R. M.; De Cola, L.; Pikramenou, Z. J. Am. Chem. Soc. 2003,
125, 9918.
(4) (a) Tanabe, S. C. R. Chim. 2002, 5, 815. (b) Meinardi, F.; Colombi,
N.; Destri, S.; Porzio, W.; Blumstengel, S.; Cerminara, M.; Tubino,
R. Synth. Met. 2003, 137, 959. (c) Tanabe, S. Glass Sci. Technol.
(Frankfurt/Main) 2001, 74, 67. (d) Schweizer, T.; Goutaland, R.;
Martins, E.; Hewak, D. W.; Brocklesby, W. S. J. Opt. Soc. Am. B
2001, 18, 1436. (e) Hasegawa, Y.; Sogabe, K.; Wada, Y.; Yanagida,
S. J. Lumin. 2003, 101, 235.
(5) Sabbatini, N.; Guardigli, M.; Lehn, J.-M. Coord. Chem. ReV. 1993,
(15) Beer, P. D.; Szemes, F.; Passaniti, P.; Maestri, M. Inorg. Chem. 2004,
13, 3965.
123, 201.
62 Inorganic Chemistry, Vol. 44, No. 1, 2005

Dinuclear d/f-Block Complexes
Chart 1
an energy donor. In both series, 2,2′-bipyrimidine is used as
the bridging ligand connecting the two metal sites in order
to keep the metal-metal separation short and to facilitate
energy transfer. We describe the syntheses and structural
characterization of the complexes and their photophysical
properties, in particular, the occurrence of d f f energy
transfer leading to quenching of the luminescence from the
d-block unit and sensitized NIR luminescence from the
lanthanide unit. Some of the synthesis (of dinuclear Re/
lanthanide complexes) was outlined briefly in a preliminary
communication.16
Results and Discussion
Preparation and Photophysical Properties of the Pt(II)
Complexes. As a d-block energy-donor fragments, we
investigated the known complex [Re(bpym)(CO)3Cl] (bpym
) 2,2′-bipyrimidine),20 which is weakly luminescent from
its metal to ligand charge-transfer (MLCT) excited state; this
would allow us to use the extent of quenching of this
luminescence as a probe for studying energy transfer in the
dinuclear complexes. We also investigated the new series
of complexes [Pt(bpym)(CCAr)2]. We were interested in
using the Pt-diimine-diacetylide unit as an energy donor
for two reasons. First, complexes of this type show strong
luminescence from their MLCT excited states, which, as with
[Re(bpym)(CO)3Cl], provides a convenient handle for study-
ing energy transfer.21 Second, they are synthetically conve-
nient because the terminal diimine ligand (usually bipyridine
or phenanthroline) could be replaced with bipyrimidine,
therefore generating the necessary external binding site for
the lanthanide unit; additionally, they are neutral and
therefore soluble in the low-polarity solvents necessary to
achieve optimal association of the lanthanide fragment.21
Reaction of [Pt(bpym)Cl2]22 with the phenylacetylene
derivatives HCC-C6H4X (X ) H, Me, CF3) in CH2Cl2, in
We have recently described the syntheses, structures, and
photophysical properties of a series of d-f dinuclear
complexes that show sensitized NIR luminescence from Yb-
(III), Nd(III), or Er(III) following absorption of light by the
d-block chromophore in the visible region of the electro-
i
magnetic spectrum.16-19 In many of these complexes,16-18
a
the presence of Pr2NH and a catalytic amount of CuI,
afforded the complexes (bpym)PtH, (bpym)PtMe, and
(bpym)PtCF3 in good yield (see Chart 1 for abbreviations).
Of these, (bpym)PtH and (bpym)PtCF3 were structurally
characterized; the molecular structures are shown in Figures
1 and 2, respectively, and selected structural parameters are
collected in Tables 1 and 2. Both complexes have essentially
square-planar geometry around the Pt(II), with minor distor-
tions arising from the limited bite angle of the bipyrimidine
ligand (78.9° in each case). The (unconstrained) C-Pt-C
angles are 87.6° and 91.9° for (bpym)PtH and (bpym)PtCF3,
respectively. In both cases, the Pt-N distances (2.06-2.07
Å) are significantly longer than the Pt-C distances (1.94-
1.96 Å), in agreement with related structures.21
mononuclear, kinetically inert d-block complex fragment was
prepared with a peripheral, vacant diimine binding site;
reaction of the “complex ligand” with a lanthanide tris-
(diketonate) dihydrate [Ln(dik)3(H2O)2] (dik ) diketonate)
resulted in an immediate attachment of the {Ln(dik)3}
fragment to the vacant N,N′-bidentate site of the d-block
complex to give the heterodinuclear species. The syntheses
are facile and high-yielding, and the method is very general,
allowing a wide range of d-block chromophores and f-block
luminophores to be combined.
In this paper, we describe further studies in this area based
on the two series of d-f complexes shown in Chart 1, one
based on a {Re(CO)3Cl(diimine)} unit as an energy donor
and the other based on a Pt-diimine-bis(acetylide) unit as
The conformations of the molecules are different, however,
with the molecules of (bpym)PtH being significantly distorted
(16) Shavaleev, N. M.; Bell, Z. R.; Ward, M. D. J. Chem. Soc., Dalton
Trans. 2002, 3925.
(17) Shavaleev, N. M.; Bell, Z. R.; Accorsi, G.; Ward, M. D. Inorg. Chim.
Acta 2003, 351, 159.
(18) (a) Shavaleev, N. M.; Moorcraft, L. P.; Pope, S. J. A.; Bell, Z. R.;
Faulkner, S.; Ward, M. D. Chem.sEur. J. 2003, 9, 5283. (b)
Shavaleev, N. M.; Moorcraft, L. P.; Pope, S. J. A.; Bell, Z. R.;
Faulkner, S.; Ward, M. D. Chem. Commun. (Cambridge) 2003, 1134.
(19) Miller, T. A.; Jeffery, J. C.; Ward, M. D.; Adams, H.; Pope, S. J. A.;
Faulkner, S. J. Chem. Soc., Dalton Trans. 2004, 1524.
(20) Vogler, A.; Kisslinger, J. Inorg. Chim. Acta 1986, 115, 193.
(21) (a) Whittle, E. C.; Weinstein, J. A.; George, M. W.; Schanze, K. S.
Inorg. Chem. 2001, 40, 4053. (b) Hissler, M.; Connick, M.; Geiger,
D. K.; McGarrah, J. E.; Lipa, D.; Lachiotte, R. J.; Eisenberg, R. Inorg.
Chem. 2000, 39, 447. (c) Chan, S.-C.; Chan, M. C. W.; Wang, Y.;
Che, C.-M.; Cheung, K.-K.; Zhu, N. Chem.sEur. J. 2001, 7, 4180.
(d) James, S. L.; Younus, M.; Raithby, P. R.; Lewis, J. J. Organomet.
Chem. 1997, 543, 233.
(22) Kiernan, P. M.; Ludi, A. J. Chem. Soc., Dalton Trans. 1978, 1127.
Inorganic Chemistry, Vol. 44, No. 1, 2005 63

Shavaleev et al.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for (bpym)PtH
Pt(1)-C(11)
Pt(1)-N(21)
1.954(4)
2.073(3)
C(11)-C(12)
1.206(5)
C(11)-Pt(1)-C(11A) 91.9(2)
C(11)-Pt(1)-N(21A) 170.14(13) C(12)-C(11)-Pt(1) 175.2(3)
N(21A)-Pt(1)-N(21) 78.94(16) C(22)-N(21)-Pt(1) 115.2(2)
C(11)-Pt(1)-N(21) 95.05(13)
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
(bpym)PtCF3
Pt(1)-C(31)
Pt(1)-C(41)
Pt(1)-N(11)
1.936(8)
1.956(6)
2.060(5)
Pt(1)-N(21)
C(31)-C(32)
C(41)-C(42)
2.074(5)
1.210(10)
1.198(9)
C(31)-Pt(1)-C(41)
C(31)-Pt(1)-N(11)
C(41)-Pt(1)-N(11)
C(31)-Pt(1)-N(21)
C(41)-Pt(1)-N(21)
N(11)-Pt(1)-N(21)
87.6(3)
175.8(2)
96.6(2)
97.0(2)
175.2(2)
78.9(2)
C(12)-N(11)-Pt(1)
C(16)-N(11)-Pt(1)
C(26)-N(21)-Pt(1)
C(22)-N(21)-Pt(1)
C(32)-C(31)-Pt(1)
C(42)-C(41)-Pt(1)
116.2(4)
127.0(4)
126.1(5)
115.0(4)
177.4(6)
177.9(6)
Table 3. Photophysical Properties of the Mononuclear Complexes,
Recorded in Air-Equilibrated CH2Cl2 at 298 K
absorption
luminescence
λmax
ꢀ
λmax
τ
complex
(nm) (M-1 cm-1
)
(nm)a
(ns)
Φ × 102
(bpym)PtMe
430b
327
7 000
11 000
62 000
7 100
11 400
57 000
7 800
58 000
2 680
24 700
612
4.8
0.01
264c
425b
323
(bpym)PtH
600
15.2
0.12
263c
415b
269c
(bpym)PtCF3
575
689
107
2.1
3.7
Figure 1. (a) Molecular structure of (bpym)PtH using thermal ellipsoids
at the 40% probability level. (b) Packing in the crystal of (bpym)PtH.
[Re(bpym)(CO)3Cl] 403b
234c
0.011
a Value corrected for instrumental response where necessary. b MLCT
absorption maximum. c Ligand-centered absorption maximum.
with one phenyl ring lying above the mean Pt-bpym plane
and the other below it. A consequence of this is the absence
of well-defined columnar stacks that often arise in crystals
of planar Pt(II) complexes. The closest Pt‚‚‚Pt separation is
5.066 Å; the nearest interactions between each Pt center and
its neighboring molecules above and below it are at H(18)
and H(26), with Pt‚‚‚H separations of 3.19 and 3.29 Å,
respectively. In contrast, the molecules of (bpym)PtCF3 are
nearly coplanar, with an angle of only 1.7° between the PtNN
and PtCC planes. This results in the molecules forming
stacked pairs in the crystal with a pair of molecules related
by an inversion center having a Pt‚‚‚Pt separation of 3.392
Å (Figure 2b).
UV-vis absorption spectra and luminescence data on the
mononuclear complexes are collected in Table 3. All three
complexes show a MLCT transition in the 415-430 nm
region, as well as more intense transitions in the UV region
characteristic of ligand-centered transitions. The MLCT
transitions are red-shifted compared to those of the analogous
complexes with bipy or phen as the diimine ligand,21 which
is because of the lower energy of the lowest unoccupied
molecular orbital of bipyrimidine arising from the two
additional electronegative N atoms in the π system. Upon
excitation of the MLCT transition, all three complexes show
luminescence in an air-equilibrated CH2Cl2 solution. Like
the absorption maxima, the emission maxima (between 575
and 612 nm) are also red-shifted compared to the bipy and
Figure 2. (a) Molecular structure of (bpym)PtCF3 using thermal ellipsoids
at the 40% probability level. (b) Packing in the crystal of (bpym)PtCF3.
from planarity, as shown by the angle between the PtNN
and PtCC planes of 11°. Thus, the molecule is “bowed”,
64 Inorganic Chemistry, Vol. 44, No. 1, 2005

Dinuclear d/f-Block Complexes
phen analogues; for example, emission from [(phen)Pt(CC-
C6H4Me)2] (phen ) 1,20-phenanthroline) in a fluid solution
occurs at 578 nm,21 whereas (bpym)PtMe emits at 612 nm.
The previously observed variations in emission intensity and
lifetime that occur as the substituents on the phenyl rings
are changed are clear for the bpym complexes; as these
substituents become more electron-withdrawing, the absorp-
tion and emission maxima are blue-shifted and the emission
quantum yield and lifetime increase. Thus, whereas (bpym)-
PtMe and (bpym)PtH are weakly luminescent (τ ) 4.8 and
15 ns, respectively), (bpym)PtCF3 has a luminescence
lifetime (107 ns) and quantum yield (3.7%) comparable to
[Ru(bipy)3]2+ (bipy ) 2,2′-bipyridine) under the same
conditions (Table 3). The luminescence from these com-
plexes is less intense and shorter-lived than those previously
observed from the bipy and phen analogues,21 which may
be ascribed, in part, to the energy-gap law (lower-energy
luminescence tends to be weaker because of the greater
likelihood of quenching by molecular vibrations); however,
the previously reported measurements were performed in the
absence of O2, which will have a substantial effect, so the
data are not directly comparable.
We note that aggregation of the complexes in solution is
not an issue here. Planar Pt(II) complexes with diimine or
related ligands are well-known to associate in the solid state
(cf. some of the crystal structures described above), which
has a substantial effect on their luminescence properties, with
low-energy luminescence features arising either from exci-
mers (if there is π-π stacking of the aromatic ligands) or
from the metal-metal-bond to ligand charge-transfer
(MMLCT) excited state (if there is a Pt‚‚‚Pt interaction).23
In some cases, this association can occur in solution;
however, in these cases, the photophysical properties of the
complexes in solution are strongly concentration-dependent
and the association requires relatively high concentrations.24
For our mononuclear Pt(II) complexes, neither the UV-vis
absorption spectra nor the steady-state luminescence spectra
showed any change in their shape as samples were diluted
from 10-4 to 10-6 M, spanning the concentration range that
we used for photophysical studies. Also, all time-resolved
measurements in solution showed only a single-exponential
luminescence decay, indicating the presence of only one Pt-
based emitting species.
Figure 3. Molecular structure of Re-Yb using thermal ellipsoids at the
40% probability level (F atoms from the “fod” ligands are omitted for
clarity). The elongated thermal ellipsoid of C(81) reflects slight, unresolved
disorder of that CO ligand with the trans ligand Cl(1).
t
(H2O)2] (fod ) BuC(O)CH2C(O)CF2CF2CF3; see Chart 1)
in CH2Cl2 were combined, giving an immediate darkening
of the color of the Re chromophore; the addition of hexane,
followed by slow evaporation, afforded crystals of [Re-
(CO)3Cl(µ-bpym)Yb(fod)3] (Re-Yb) in good yield. The
analogous complexes Re-Nd and Re-Er were obtained in
the same way. Similarly, equimolar amounts of (bpym)PtCF3
and [Nd(hfac)3(H2O)2] (hfac ) CF3C(O)CH2C(O)CF3; see
Chart 1) dissolved in benzene were combined, giving an
immediate color change of the Pt chromophore from orange
to red as the dinuclear complex formed; the addition of
heptane, followed by slow evaporation of the solvent,
afforded a good crop of crystals of [(F3C-C6H4-CC)2Pt-
(µ-bpym)Nd(hfac)3] (Pt-Nd); the complex Pt-Gd was
prepared in the same way. The complexes are air stable and
were characterized on the basis of correct elemental analyses.
Mass spectrometry was unhelpful, showing only peaks for
the mononuclear metal species and their fragments. Several
of the complexes were also characterized by X-ray crystal-
lography.
The molecular structure of Re-Er was described in the
recent preliminary communication and is not reproduced
here.16 The structure of Re-Yb is very similar and is shown
in Figure 3; selected bond lengths and angles are in Table
4. The Re center has its usual fac-octahedral geometry with
unremarkable bond distances and angles.17,25 The Yb center
is in a distorted-square antiprismatic eight-coordinate ge-
ometry, characteristic of [Ln(dik)3(diimine)] species.17,18 The
atoms comprising the approximate square planes are N(11)/
N(21)/O(46)/O(44) (average deviation of these from the mean
plane through them: 0.286 Å) and O(54)/O(56)/O(36)/O(34)
(average deviation of these from the mean plane through
them: 0.238 Å); these mean planes are nearly coplanar, with
an angle of 2.4° between them. The Re‚‚‚Yb distance is 6.23
Å; the bridging bipyrimidine ligand is near-planar.
Preparation and Structures of d-f Dinuclear Com-
plexes. On the basis of the above results, we decided to use
(bpym)PtCF3 as the energy-donor component for incorpora-
tion into dinuclear complexes with lanthanides, along with
[Re(CO)3Cl(bpym)]. The dinuclear complexes were simply
prepared by reaction of either [Re(CO)3Cl(bpym)] or (bpym)-
PtCF3 with the appropriate Ln(dik)3(H2O)2 in CH2Cl2. Thus,
equimolar amounts of [Re(CO)3Cl(bpym)] and [Yb(fod)3-
(23) (a) Houlding, V. H.; Miskowski, V. M. Coord. Chem. ReV. 1991, 111,
145. (b) Kato, M.; Kosuge, C.; Morii, K.; Ahn, J. S.; Kitagawa, H.;
Mitani, T.; Matsushita, M.; Kato, T.; Yano, S.; Kimura, M. Inorg.
Chem. 1999, 38, 1638. (c) Connick, W. B.; Henling, L. M.; Marsh,
R. E.; Gray, H. B. Inorg. Chem. 1996, 35, 6261.
(24) (a) Arena, G.; Calogero, G.; Campagna, S.; Scolaro, L. M.; Ricevuto,
V.; Romeo, R. Inorg. Chem. 1998, 37, 2763. (b) Bailey, J. A.; Hill,
M. G.; Marsh, R. E.; Miskowski, V. M.; Schaefer, W. P.; Gray, H. B.
Inorg. Chem. 1995, 34, 4591.
(25) Shavaleev, N. M.; Barbieri, A.; Bell, Z. R.; Ward, M. D.; Barigelletti,
F. New J. Chem. 2004, 28, 398.
Inorganic Chemistry, Vol. 44, No. 1, 2005 65

Shavaleev et al.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for Re-Yb
Yb(1)-O(36)
Yb(1)-O(54)
Yb(1)-O(44)
Yb(1)-O(34)
Yb(1)-O(46)
Yb(1)-O(56)
Yb(1)-N(21)
Yb(1)-N(11)
2.223(6)
2.235(6)
2.240(6)
2.269(7)
2.284(6)
2.298(7)
2.517(7)
2.568(7)
Re(1)-C(81)
Re(1)-C(71)
Re(1)-C(61)
Re(1)-N(23)
Re(1)-N(13)
Re(1)-Cl(1)
1.74(3)
1.925(12)
1.931(13)
2.172(8)
2.187(8)
2.465(3)
C(81)-Re(1)-C(71)
C(81)-Re(1)-C(61)
C(71)-Re(1)-C(61)
C(81)-Re(1)-N(23)
C(71)-Re(1)-N(23)
C(61)-Re(1)-N(23)
C(81)-Re(1)-N(13)
C(71)-Re(1)-N(13)
88.8(6)
92.2(7)
87.5(5)
94.3(5)
98.3(4)
171.3(4)
97.6(5)
170.6(4)
C(61)-Re(1)-N(13)
N(23)-Re(1)-N(13)
C(81)-Re(1)-Cl(1)
C(71)-Re(1)-Cl(1)
C(61)-Re(1)-Cl(1)
N(23)-Re(1)-Cl(1)
N(13)-Re(1)-Cl(1)
98.9(4)
74.5(3)
175.5(5)
94.8(4)
90.7(5)
82.5(2)
78.5(2)
The molecular structures of Pt-Gd and Pt-Nd are shown
in Figures 4 and 5; selected bond lengths and angles are in
Tables 5 and 6. The structures are very similar to each other.
The coordination environment around the Pt center is not
substantially perturbed by attachment of the lanthanide unit
at the secondary site; in particular, the Pt-N bond distances
are not significantly different from their values in the
mononuclear unit (bpym)PtCF3. The lanthanide centers,
however, are now nine-coordinate, with a water molecule
coordinated in addition to the four bidentate chelating ligands.
This is unusual because the crystal structures of Ln(dik)3-
(diimine) complexes, including many that we have structur-
ally characterized,16-18 are eight-coordinate; the presence of
the ninth ligand in these crystal structures is presumably a
kinetic effect, arising from the favorable crystallization of
Figure 5. Molecular structure of one of the two crystallographically
independent molecules of Pt-Nd using thermal ellipsoids at the 40%
probability level (F atoms from the “hfac” ligands are omitted for clarity).
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
Pt-Gd‚(C6H6)
Gd(1)-O(66)
Gd(1)-O(71)
Gd(1)-O(76)
Gd(1)-O(56)
Gd(1)-O(51)
Gd(1)-O(61)
Gd(1)-O(1)
2.338(6)
2.351(5)
2.375(5)
2.388(6)
2.397(6)
2.412(5)
2.475(6)
Gd(1)-N(11)
Gd(1)-N(21)
Pt(1)-C(41)
Pt(1)-C(31)
Pt(1)-N(13)
Pt(1)-N(23)
2.660(6)
2.680(6)
1.932(9)
1.944(8)
2.067(7)
2.069(6)
C(41)-Pt(1)-C(31)
C(41)-Pt(1)-N(13)
C(31)-Pt(1)-N(13)
91.7(3)
173.1(3)
94.4(3)
C(41)-Pt(1)-N(23)
C(31)-Pt(1)-N(23)
N(13)-Pt(1)-N(23)
94.6(3)
173.3(3)
79.2(2)
Table 6. Selected Bond Lengths (Å) and Angles (deg) for
Pt-Nd‚(C6H6)
Nd(1)-O(71)
Nd(1)-O(61)
Nd(1)-O(77)
Nd(1)-O(57)
Nd(1)-O(67)
Nd(1)-O(51)
Nd(1)-O(1)
Nd(1)-N(21)
Nd(1)-N(11)
Pt(1)-C(31)
Pt(1)-C(41)
Pt(1)-N(23)
Pt(1)-N(13)
2.367(7)
2.420(7)
2.421(6)
2.425(7)
2.442(6)
2.476(7)
2.507(6)
2.712(7)
2.787(7)
1.937(9)
1.947(9)
2.052(7)
2.073(7)
Nd(2)-O(167)
Nd(2)-O(171)
Nd(2)-O(177)
Nd(2)-O(161)
Nd(2)-O(151)
Nd(2)-O(157)
Nd(2)-O(2)
Nd(2)-N(111)
Nd(2)-N(121)
Pt(2)-C(131)
Pt(2)-C(141)
Pt(2)-N(113)
Pt(2)-N(123)
2.404(6)
2.426(6)
2.428(6)
2.432(6)
2.432(6)
2.484(6)
2.534(6)
2.683(7)
2.708(7)
1.943(8)
1.945(8)
2.061(7)
2.075(7)
C(31)-Pt(1)-C(41)
C(31)-Pt(1)-N(23)
C(41)-Pt(1)-N(23)
C(31)-Pt(1)-N(13)
C(41)-Pt(1)-N(13)
N(23)-Pt(1)-N(13)
89.1(4)
94.2(3)
176.3(3)
173.3(3)
97.5(3)
79.3(3)
C(131)-Pt(2)-C(141)
C(131)-Pt(2)-N(113)
C(141)-Pt(2)-N(113)
C(131)-Pt(2)-N(123)
C(141)-Pt(2)-N(123)
N(13)-Pt(2)-N(123)
90.1(4)
95.7(3)
173.5(3)
174.3(3)
94.3(3)
79.7(3)
this particular form, even if it is not the dominant structure
in solution. The Pt‚‚‚Gd distance across the planar bipyri-
midine ligand is 6.263 Å. As we saw for (bpym)PtCF3, the
planar Pt fragments (angle between the PtNN and PtCC
planes: 3.6°) stack across an inversion center, giving an axial
Pt‚‚‚Pt contact of 3.497 Å between adjacent molecules in a
stacked pair. Pt-Nd has a very similar molecular structure
but a different crystal structure with two independent
complex molecules in the asymmetric unit. As with Pt-Gd,
each molecule of Pt-Nd stacks with its symmetry equivalent
across an inversion center; the Pt(1)‚‚‚Pt(1′) separation is
3.758 Å, and the Pt(2)‚‚‚Pt(2′) separation is 3.348 Å. Within
Figure 4. (a) Molecular structure of Pt-Gd using thermal ellipsoids at
the 40% probability level (F atoms are omitted for clarity). (b) Packing in
the crystal of Pt-Gd.
66 Inorganic Chemistry, Vol. 44, No. 1, 2005

Dinuclear d/f-Block Complexes
the two independent molecules, the Pt‚‚‚Nd separations are
6.335 and 6.286 Å.
Solution Behavior of the Dinuclear Complexes: UV-
Vis Spectra, Steady-State Luminescence, and Association
Constants. Binding of a [Ln(dik)3(H2O)2] unit to diimines
(NN), according to eq 1, to give the eight-coordinate diimine
adduct with liberation of two molecules of water is known
to be a reversible process, with equilibrium constants of up
to ≈107 M-1 for NN ) 2,2′-bipyridine or 1,10-phenanthro-
line in hydrocarbon solvents.26
[Ln(dik)3(H2O)2] + NN ) [Ln(dik)3(NN)] + 2H2O (1)
With less-basic NN ligands, the equilibrium constant is
correspondingly reduced. For example, we recently observed
binding constants on the order of 104 M-1 in CH2Cl2 for the
association of [Ln(dik)3(H2O)2] to the vacant NN site of
complexes such as [Cl2Pt(dppz)] [dppz ) 2,3-di(2-pyridyl)-
pyrazine] in which one of the vacant N donors is a pyrazine
rather than a pyridine ring.18a The result is that, at the
concentrations typically used for luminescence and UV-
vis spectroscopic studies, partial dissociation of the dinuclear
d-f complexes occurs, which complicates the luminescence
analysis in solution. Given the relatively low basicity of
pyrimidine compared to that of pyridine (pKa values in water
of 1.3 and 5.2, respectively), it was felt that this was likely
to be an issue with these complexes, and accordingly, UV-
vis and luminescence titrations on representative systems
were carried out. A representative example is shown in
Figure 6.
The addition of portions of [Ln(hfac)3(H2O)2] (Ln ) Gd,
Yb) to a solution of (bpym)PtCF3 in dry CH2Cl2 resulted in
a deepening of the orange color of the Pt chromophore, which
is associated with the MLCT transition being reduced in
energy and shifted more into the visible region, from 415 to
425 nm (Figure 6a). A graph of absorbance at a selected
wavelength versus the amount of [Ln(hfac)3(H2O)2] added
gave a smooth curve that fitted well to a 1:1 binding isotherm
(Figure 6c), from which the association constant for binding
of the lanthanide fragment to the diimine site (equilibrium
constant for eq 1) could be determined; the values obtained
were 3.5 ((0.3) × 105 M-1 for Pt-Yb and 1.2 ((0.2) ×
105 M-1 for Pt-Gd. These are rather low compared to the
values obtained for other lanthanide-diimine adducts with
ligands such as bipyridine and phenanthroline,26 and they
are low as a consequence of the poor basicity of bipyrimidine.
The slightly higher Ka value for Pt-Yb compared to that of
Pt-Gd presumably reflects the smaller ionic radius and
higher charge density of Yb(III). It is not appropriate to
overanalyze these binding constants because we found that
they are very sensitive to traces of moisture in the solvent;
the use of ordinary undried CH2Cl2 from a fresh bottle
afforded binding constants 2 orders of magnitude lower. The
important point is that, with Ka values of ca. 105 M-1,
significant dissociation is to be expected at the concentrations
typically used for luminescence measurements in solution
(≈10-5 M).
Figure 6. Titration of (bpym)PtCF3 with Yb(hfac)3(H2O)2 in a CH2Cl2
solution: (a) red shift in the MLCT absorption maximum of (bpym)PtCF3;
(b) quenching of Pt-based luminescence; (c) absorbance values at 500 nm
during titration (dots) fitted to a 1:1 binding isotherm (line) to give Ka )
3.5 × 105 M-1
.
Figure 7. Electronic absorption spectra of [Re(bpym)(CO)3Cl] (red),
(bpym)PtCF3 (green), [Nd(tta)3(H2O)2] (black), and [Yb/Er(fod)3(H2O)2]
(blue). Above 400 nm, the spectra are multiplied by a factor of 7.5. Inset:
phosphorescence spectra of [Gd(fod)3(H2O)2] at 77 K in CH2Cl2, λexc
294 nm.
)
Luminescence spectra were also recorded during the
titrations. With Ln ) Yb, binding of the lanthanide fragment
results in complete quenching of the luminescence of free
(bpym)PtCF3 (Figure 6b). In contrast, when Ln ) Gd, there
is some quenching of the (bpym)PtCF3 luminescence, but
this is not complete, and about 15% of the original
luminescence intensity remains after the addition of excess
[Gd(hfac)3(H2O)2]. This implies two things. First, binding
(26) Yajima, S.; Hasegawa, Y. Bull. Chem. Soc. Jpn. 1998, 71, 2825.
Inorganic Chemistry, Vol. 44, No. 1, 2005 67

Shavaleev et al.
of a lanthanide fragment to the secondary site of (bpym)-
PtCF3 provides an additional pathway for quenching of the
Pt-based luminescence, either by providing additional vi-
brational pathways for deactivation of the excited state or
3
by perturbation of the MLCT level that is due to the
presence of a +3 charge. These effects alone do not result
in complete quenching, as shown by the Pt-Gd system,
where there is residual luminescence; it is important to note
that Gd(III) cannot act as an energy acceptor because its first
electronically excited state is far too high in energy (≈32 000
cm-1). In contrast, in the Pt-Yb system, quenching is
complete because of the ability of Yb(III) to act as an energy
2
Figure 8. Electronic absorption spectra of Re-Yb/Er (black), Re-Nd
(red), and Pt-Nd (blue) in a CH2Cl2 solution. Above 400 nm, the spectra
are multiplied by a factor of 10. The dinuclear complexes undergo partial
dissociation; therefore, the spectra reflect a mixture of dissociated and
undissociated samples (see text).
acceptor through its low-lying F5/2 level. The presence of
incomplete quenching of the Pt-based luminescence when
Ln ) Gd but complete quenching when Ln ) Yb indicates
that Pt f Yb photoinduced energy transfer is taking place
in the latter case and we should see sensitized luminescence
from Yb(III) following excitation of the (bpym)PtCF3 center.
From this energy level description, the dinuclear com-
plexes Re-Ln and Pt-Ln possess an energy gradient
allowing energy transfer from the d-block to the f-block
moiety. The absorption spectra of Re-Ln and Pt-Nd in a
CH2Cl2 solution are depicted in Figure 8. The UV spectral
range is characterized by ligand-centered transitions. The
contribution of the bpym chelating ligand is of minor
importance and only observable in the peak/shoulders around
235 nm (see the spectrum of [Re(bpym)(CO)3Cl] in Figure
7). The remarkable differences observed in the various cases
are related to the presence of the three different diketonate
ligands (fod, tta, and hfa) that exhibit distinct UV absorption
profiles (Figure 7); these are the origin of the absorption
between 300 and 400 nm. For dinuclear complexes, by
inspecting the absorption spectra of mononuclear compounds
in Figure 8, one can assign the absorption features at
wavelengths longer than 400 nm to MLCT transitions of the
Re- or Pt-complexed moiety. The intensity of the Pt(II) r
bpym MLCT absorption band is substantially stronger than
that of the Re(I) r bpym absorption. Of course, in these
conditions, there will be some dissociation of the dinuclear
complex (eq 1), but the main features of the complexes [viz.,
the diketonate-centered transitions at 300-400 nm and the
MLCT transition of the d-block fragment at λ > 400 nm]
are only slightly affected by this, and apart from the shift in
the MLCT absorption of the d-block unit in the dinuclear
complexes, the spectra of the dinuclear complexes are
approximately the sum of the spectra of the two chro-
mophores.
A similar titration experiment was performed on the [Re-
(bpym)(CO)3Cl]/ Yb(fod)3 system with similar results. Bind-
ing of the Yb(fod)3 fragment at the vacant diimine site results
in a red shift of the MLCT absorption in the UV-vis
spectrum, from 403 nm to a shoulder at ca. 440 nm. From
the changes in the spectral data, an association constant for
lanthanide binding in Re-Yb of 1.9 ((0.2) × 105 M-1 cm-1
was determined, comparable to the values obtained for the
Pt-Ln complexes.
Photophysical Properties of the Dinuclear Complexes.
Photophysical properties of dinuclear Re-Ln (Ln ) Nd, Yb,
and Er) and Pt-Nd complexes were investigated in a CH2-
Cl2 solution. For the sake of comparison, mononuclear
compounds [Re(bpym)(CO)3Cl], (bpym)PtCF3, [Nd(tta)3-
(H2O)2] (tta ) 2-thenoyltrifluoroacetone), [Yb(fod)3(H2O)2],
and [Er(fod)3(H2O)2] have also been studied; the absorption
spectra are depicted in Figure 7. For the Nd(III) complexes,
the light-absorbing antenna unit is the diketonate ligand tta
or hfac; for Yb(III) and Er(III) analogues, this role is played
by fod. The presence of different ligands is reflected in the
different UV absorption profiles.
As mentioned above, the lowest electronic excited states
of [Re(bpym)(CO)3Cl]20,27 and (bpym)PtCF3 are of a
21
3MLCT nature, and they are located at 2.19 eV for the
former20 and 2.39 eV for the latter (determined from the
emission maximum of 518 nm in a frozen MeOH/EtOH
glass). For the mononuclear lanthanide complexes, UV
excitation of the ligand-centered bands results in typical
luminescence of the corresponding Ln(III) ion in the NIR
spectral region, with energy levels below 1.4 eV. This is a
consequence of an energy-transfer process from the diketo-
nate ligand to the corresponding metal ion. The sensitization
process in lanthanide complexes occurs from the ligand triplet
levels5 that, for fod/hfa and tta, are positioned at 2.80 and
2.57 eV, respectively, according to the phosphorescence
spectra of the reference Gd(III) complexes5 (see, for example,
the inset of Figure 8).
Upon excitation of the MLCT band of the Re moiety at
460 nm, all of the dinuclear Re-Ln complexes exhibit the
NIR emission features of the lanthanide ion (Figure 9).
Because no direct excitation of the lanthanide moiety occurs
at this wavelength, the observed NIR emission signals can
only arise by sensitization of the lanthanide ions from the
Re-complexed moiety, following energy transfer.8,12-15,19 As
expected, three emission bands were observed for Nd(III)
4
at 866, 1060, and 1330 nm (4I9/2, I11/2
,
4I13/2
r
4F3/2,
respectively), one for Yb(III) at 975 nm (2F7/2 r 2 F5/2), and
4
one for Er(III) at 1535 nm (4I15/2 r I13/2) (Figure 10).28
Following the measurements of association constants de-
scribed above, it is to be expected that partial dissociation
(27) Armaroli, N.; Accorsi, G.; Felder, D.; Nierengarten, J. F. Chem.s
Eur. J. 2002, 8, 2314.
68 Inorganic Chemistry, Vol. 44, No. 1, 2005

Dinuclear d/f-Block Complexes
Table 7. Lanthanide Emission Properties for the Dinuclear Complexes
in Solution and in the Solid State at 298 K
CH2Cl2
solid state
λ
max (nm)a τ (µs)b
λ
max (nm)a Φem × 10-4 c τ (µs)b
Re-Yb
Re-Er
Re-Nd
Pt-Nd
975
975d
6.7
<0.5
<0.5
975
79
9.6
1.6
0.9
1.0
975d
1534
1538d
1061
1061d
1061
1061d
1534
1538d
1061
1061d
1061
1061d
2
24
27
0.44e
<0.5
a λexc ) 460 nm. λexc ) 355 nm, laser excitation. c Φem for metal-based
luminescence only, calculated from eq 2 (see the main text). d Corrected
values for instrumental response. e Measured with a UV-vis detector at
λem ) 880 nm.
b
Figure 9. Corrected and normalized emission spectra from Re-Nd (red),
Re-Yb (blue), Re-Er (green), and Pt-Nd (red, inset) in CH2Cl2 solutions,
λexc ) 460 nm, absorbance at excitation wavelength ) 0.2.
compared to the intensity detected in mononuclear species
[Nd(tta)3(H2O)2] and [Yb(fod)3(H2O)2] (in the case of Re-
Er, the emission is so weak that quantitative considerations
are prevented). This is probably related to the replacement
of solvent molecules by N,N′-bipyrimidine in the Ln(III)
coordination sphere, which could depress nonradiative
deactivation pathways through vibrational quenching, as we
have seen before when comparing [Ln(dik)3(H2O)2] and [Ln-
(dik)3(diimine)] luminophores.29
Excitation of Pt-Nd into the MLCT Pt-based band (460
nm) in CH2Cl2 also gives rise to Nd(III) emission in the NIR
region, confirming that Pt f Nd energy transfer occurs.
However, in this case, an intense MLCT emission band at
λmax ) 575 nm is also observed, and the band’s low-energy
tail partially overlaps the sharp emission features of the Nd-
(III) center (inset of Figure 9). As mentioned above, residual
3MLCT luminescence has been observed in many cases in
dinuclear d-f complexes with Ru(II)-polypyridine-type
sensitizing units, and on the basis of lifetime measurements,
this has been related to a slow Ru f Ln energy-transfer
process that undergoes competition from intrinsic deactiva-
tion of the 3MLCT level of the Ru-complexed moi-
ety.8,12,13,15,19 However, upon excitation at 460 nm, we find
identical 3MLCT lifetimes for (bpym)PtCF3 and Pt-Nd (107
ns), indicating that, for the latter, we are seeing luminescence
from free (bpym)PtCF3 as a result of partial dissociation of
the complex into its mononuclear components. For intact Pt-
Nd, the Pt-based luminescence should be completely quenched,
as shown by the titration measurements (above) and by the
solid-state luminescence data (below). The inherently strong
luminescence of free (bpym)PtCF3 accounts for the sensitized
NIR luminescence from Nd(III) being partially obscured by
Figure 10. Approximate energy levels for Nd(III), Er(III), and Yb(III).
of the Re-Ln complexes into their mononuclear complexes
will occur (eq 1). Indeed, weak 3MLCT luminescence from
[Re(bpym)(CO)3Cl] was observed, with a quantum yield
corresponding to about 20% dissociation of the dinuclear
Re-Ln complexes. The lifetime of this excited state (2.1
ns) is the same as that of free [Re(bpym)(CO)3Cl]. No
shorter-lived 3MLCT luminescence component was detected,
indicating that, in the intact Re-Ln complexes, the Re-based
luminescence is completely quenched (or is reduced to a
subnanosecond lifetime) because of fast Re f Ln energy
transfer (Ln ) Yb, Nd, Er). The quenching is therefore
stronger than that observed in some other dinuclear lan-
thanide complexes with [Ru(bpy)n]2+-type moieties as energy
donors, where residual 3MLCT luminescence from the
d-block unit is observed.8,12,13,15,19 In the present case, the
close proximity of the two metal centers allows a very fast
energy transfer, which can compete successfully with the
fast intrinsic 3MLCT deactivation. Fortunately, the weakness
of the residual 3MLCT luminescence from free [Re(bpym)-
(CO)3Cl] means that its low-energy tail does not significantly
interfere with the lanthanide luminescence measurements of
the Re-Ln series in the NIR region (Figure 9).
3
the tail of the MLCT luminescence.
To avoid the dissociation process and get “clean” lumi-
nescence data in the NIR region, we also measured emission
spectra (λexc ) 460 nm) and lifetimes of the dinuclear
complexes in the solid state as powders; data are reported
in Table 7. In the solid state, no residual MLCT emission is
observed for any complex, of either Re or Pt type, confirming
that, in the intact dinuclear complexes, the energy-transfer
process from the d-block to the f-block metal centers is very
To test whether any change of the emission yield of the
Ln moiety occurs in the dinuclear complexes, we compared
the emission yields of the Re-Ln compounds with that of
the corresponding mononuclear lanthanide complex upon
excitation in the UV region. A small increase of the NIR
emission intensity in Re-Nd and Re-Yb was detected when
(28) Werts, M. H. V.; Hofstraat, J. W.; Geurts, F. A. J.; Verhoeven, J. W.
(29) Shavaleev, N. M.; Pope, S. J. A.; Bell, Z. R.; Faulkner, S.; Ward, M.
Chem. Phys. Lett. 1997, 276, 196.
D. J. Chem. Soc., Dalton Trans. 2003, 808.
Inorganic Chemistry, Vol. 44, No. 1, 2005 69

Shavaleev et al.
efficient. On the basis of eq 2, taking the measured values
of solid samples (τobs) and the radiative (“natural”) lifetimes
of Nd(III), Yb(III), and Er(III) ions (τR) as reported in the
literature,30 we obtain emission quantum yield values of the
lanthanide ion for dinuclear compounds. Such values are
comparable to those previously reported for NIR-emitting
Ln(III) complexes in the solid state.27
to the 4F3/2 and 4S3/2 levels is theoretically forbidden because
|∆J| ) 3. The short metal-metal distance and the conjugated
bridging ligand, which will provide an orbital coupling
pathway, mean that both Fo¨rster and Dexter energy-transfer
mechanisms are perfectly feasible; together with the large
number of possible energy-acceptor levels on Nd(III), it is
3
not surprising that the Pt-diimine MLCT donor state is
completely quenched by Nd(III).
For Er(III), the ground state is I15/2. Energy transfer to
Φem ) τobs/τR
(2)
4
4I13/2 at 6500 cm-1, although allowed by the Dexter mech-
anism, can be ruled out because of the large difference in
energy between donor and acceptor states, which would give
a very poor spectral overlap and make the process slow.
Energy transfer to 4I11/2 at 10 000 cm-1 is, however, Fo¨rster-
allowed (|∆J| ) 2). The only other two states that have
Discussion of Possible Energy-Transfer Mechanisms.
The mechanisms operative for d f f energy-transfer
processes are not clearly known. The energy transfer is
principally determined by the distance between energy-donor
and lanthanide units, as well as by the normalized overlap
between the emission spectrum of the donor and the
absorption spectrum of the lanthanide ion.31,32 The acceptor
level(s) on the lanthanide should be sufficiently below the
3MLCT level of the donor to provide a good driving force
for energy transfer and prevent back energy transfer33 but
not so much as to prevent good spectral overlap. In addition,
there are separate selection rules for Fo¨rster and Dexter
energy transfer, with the former requiring |∆J| ) 2, 4, or 6
at the lanthanide and the latter requiring |∆J| ) 0 or 1 (with
the exception of J ) J′ ) 0, which is forbidden).34 It is also
known that Dexter energy transfer also requires electronic
coupling (orbital overlap) between energy-donor and -ac-
ceptor components,31 whereas Fo¨rster energy transfer does
not.32 In the complexes described here, the emission spectrum
of the donor unit in the dinuclear complexes is not exactly
known because the donor luminescence is quenched, but we
can take the emission spectra of the mononuclear Pt and Re
complexes as guides. Taking their emission maxima and
allowing 1000-2000 cm-1 as a minimum gradient for energy
transfer, we need to consider energy-acceptor levels of up
to ca. 16 000 cm-1 for Pt-Nd and slightly less for the Re-
Ln diads.
4
4
appropriate energies are I9/2 and F9/2 (Figure 10), which
have |∆J| ) 3, and energy transfer to these is not allowed
by either the Fo¨rster or Dexter mechanism. This leaves the
4I11/2 level, which will overlap poorly with the weak tail end
of the 3MLCT donor emission spectrum, as the sole energy
acceptor. It is, on the face of it, surprising that the d f f
energy transfer in Re-Er is fast; of course, it may be much
slower than that in Re-Nd and Pt-Nd, where energy transfer
is more favorable, but it is still faster than our equipment
can resolve (300 ns).
A similar argument applies to Re-Yb, for which there is
4
also only a single acceptor level: energy transfer to F5/2,
lying at 10 200 cm-1, is Dexter-allowed (|∆J| ) 1 with
respect to the ground state). As with Re-Er, this acceptor
level will overlap only poorly with the long-wavelength tail
3
of the MLCT donor, and such a situation in other d-f
systems containing Yb(III) as an energy acceptor is known
to result in incomplete energy transfer.8,19 Yet, the Re-based
luminescence in Re-Yb is completely quenched, and the
rise time for Yb(III) luminescence is faster than our instru-
ment could detect. The combination of short metal-metal
separation and strong electronic coupling provided by the
bridging ligand may counteract the other limitations to energy
transfer in this system.
In Pt-Nd, there are seven closely spaced energy levels
on Nd(III) between ca. 11 000 and 16 000 cm-1 (Figure 10)
3
that will overlap with the low-energy side of the broad -
Thus, energy transfer in these complexes could plausibly
occur by either Fo¨rster or Dexter mechanisms, or [for Nd-
(III)] both. The occurrence of Dexter energy transfer has been
recently demonstrated for sensitized Sm(III) luminescence
by Bu¨nzli and co-workers.35 Contrarily, the occurrence of
energy transfer between lanthanide(III) ions and d-block ions
in dinuclear complexes where the metal complex fragments
are well separated and connected only by hydrogen bonds
between their respective ligands suggests a Fo¨rster mecha-
nism.36 It is worth pointing out that the situation regarding
d f f energy transfer is further confused by a variety of
other factors. The selection rules alluded to above are not
absolute but may be circumvented by the involvement of
4f-5d transitions;34 thus, for example, the 4I9/2 and 4F9/2 levels
MLCT luminescence from the Pt unit; for Re-Nd, the
highest of these is probably not relevant. If the Pt chro-
mophores in Pt-Nd have additional MMLCT or excimer
π-π* levels in the solid state arising from the crystal packing
(which would be lower than the 3MLCT state in energy; see
Figure 4b),23 then these would provide additional spectral
overlap with the Nd(III) f-f levels. The ground state of Nd-
(III) is 4I9/2, which means that the 2H11/2, 4F9/2, 4F7/2, and 2H9/2
levels could be populated by Dexter energy transfer (|∆J|
) 1, 0, 1, and 0, respectively, from the ground state) and
the 4F5/2 level could be populated by Fo¨rster energy transfer
(|∆J| ) 2 with respect to the ground state). Energy transfer
(30) Martinus, H.; Werts, V.; Ronald, Y.; Jukes, T. F.; Verhoeven, J. W.
Phys. Chem. Chem. Phys. 2002, 4, 1542.
(31) Dexter, D. L. J. Chem. Phys. 1953, 21, 836.
(32) Fo¨rster, T. Discuss. Faraday Soc. 1959, 27, 7.
(33) Sato, S.; Wada, M. Bull. Chem. Soc. Jpn. 1970, 43, 1955.
(34) de Sa´, G. F.; Malta, O. L.; de Mello Donega´, C.; Simas, A. M.; Longo,
R. L.; Santa-Cruz, P. A.; da Silva, E. F. Coord. Chem. ReV. 2000,
196, 165.
(35) Gonc¸alves e Silva, F. R.; Malta, O. L.; Reinhard, C.; Gu¨del, H.-U.;
Piguet, C.; Moser, J. E.; Bu¨nzli, J.-C. G. J. Phys. Chem. 2002, 106,
1670.
(36) Brayshaw, P. A.; Bu¨nzli, J.-C. G.; Froidevaux, P.; Harrowfield, J. M.;
Kim, Y.; Sobolev, A. N. Inorg. Chem. 1995, 34, 2069.
70 Inorganic Chemistry, Vol. 44, No. 1, 2005

Dinuclear d/f-Block Complexes
at 455 nm as the excitation source; the time resolution of the
instrument was 1 ns. Luminescence quantum yields were obtained
from dilute samples (≈10-5 M) using the method of Demas and
Crosby,40 employing [Ru(bipy)3][PF6]2 in air-equilibrated water as
the standard (φ ) 0.028).41
of Er(III) may play a role in acting as energy acceptors
despite having |∆J| ) 3 with respect to the ground state.
For Yb(III), an alternative energy-transfer mechanism has
been suggested by Horrocks and co-workers;37 this involves
a two-step forward-and-back electron-transfer process and
relies on the fact that Yb(III) may be transiently reduced to
Yb(II) if the sensitizer is a good electron donor in its excited
state. Gu¨del and co-workers suggested that “phonon-assisted”
energy transfer could occur from the ligand to Yb(III) in
[Yb(dipic)3]3-, where there is zero spectral overlap between
the phosphorescence of dipicolinate and the f-f absorption
of Yb(III); in this case, the excess energy is dissipated as
vibrations of the strongly mechanically coupled chro-
mophore-quencher system.38 This is a possibility in Re-
Yb, in which the two metal ions share a common bridging
ligand.
The steady-state NIR luminescence spectra were obtained with
an Edinburgh FLS920 spectrometer equipped with a Hamamatsu
R5509-72 supercooled photomultiplier tube at 193 K and a TM300
emission monochromator with NIR grating blazed at 1000 nm. An
Edinburgh Xe900 450 W xenon arc lamp was used as the excitation
light source. Corrected spectra were obtained via a calibration curve
supplied with the instrument. The NIR emission lifetimes were
obtained by using the third harmonic (355 nm) of a Nd:YAG laser
(JK Lasers) with a 20 ns pulse and 1-2 mJ of energy per pulse as
the source. The detector was a liquid-nitrogen-cooled germanium
and preamplifier (Northcoast Scientific Corp. model EO-817L). The
solid-state luminescence lifetimes were obtained by spreading some
sample in the powder state on a quartz support (25 × 25 mm).
Experimental uncertainties in the photophysical measurements
are estimated to be (8% for lifetime determinations, (2 and (5
nm for absorption and emission peaks, respectively, and (20% for
luminescence quantum yields.
Conclusions
The luminescent mononuclear d-block complexes [Re-
(bpym)(CO)3Cl] and (bpym)PtCF3, which contain 2,2′-
bipyrimidine as a ligand, act as “complex ligands”, allowing
the formation of d-f heterodinuclear complexes by the
addition of a Ln(diketonate)3 unit at the second diimine site.
In the resulting series of compounds Re-Ln and Pt-Ln,
where Ln is a NIR-luminescent lanthanide complex of Yb-
(III), Nd(III), or Er(III), excitation of the MLCT absorption
of the d-block chromophore results in fast Re f Ln or Pt f
Ln energy transfer with concomitant sensitized luminescence
from the lanthanide unit. In the dinuclear complexes, the
Syntheses. (A) General Procedure for the Synthesis of Pt-
Acetylide Complexes. Pt(bpym)Cl2 (0.15 g, 0.35 mmol), anhydrous
i
CuI (7 mg), and dry Pr2NH (2 cm3) were added to dry, degassed
dichloromethane (30 cm3) under N2, and the mixture was stirred
for 10 min, after which the appropriate acetylene (2.8 mmol, 8
equiv) was added. The resulting suspension was stirred under N2
at room temperature and protected from light for 2-5 days. The
reaction mixture could be sonicated to facilitate the reaction. By
the end of reaction, the suspension had dissolved to give a yellow-
deep-red solution that was evaporated to dryness. The solid residue
was dried under vacuum, and the product was purified by column
chromatography on alumina, eluting with CH2Cl2. The fraction
containing the product was collected and reduced in volume to 5
cm3. The complex was precipitated by the addition of hexane,
filtered, washed with hexane and ether, and dried under vacuum.
The complexes are air- and moisture-stable solids of an orange-
red color that are soluble in CH2Cl2, acetone, and tetrahydrofuran
and are insoluble in ether and hexane.
3
characteristic MLCT luminescence of the d-block chro-
mophore is completely quenched in each case in the solid
state.
Experimental Section
General Details. The following materials were prepared ac-
cording to published procedures: [Re(bpym)(CO)3Cl],20 [Pt(bpym)-
Cl2],22 [Nd(hfac)3(H2O)2], and [Gd(hfac)3(H2O)2].39 The reagents
[Yb(fod)3(H2O)2], R,R,R-trifluoro-4-ethynyl-toluene, 2,2′-bipyri-
midine, K2PtCl4, and Re(CO)5Cl were purchased from Aldrich and
used as received. 1H NMR spectra were recorded on a JEOL GX-
400 instrument at 400 MHz, IR spectra were recorded on a Perkin-
Elmer Spectrum One spectrophotometer, and luminescence titrations
were measured on a Perkin-Elmer LS-50 fluorimeter.
Photophysical Studies. Solution spectroscopic investigations
were carried out in dichloromethane (Carlo Erba, spectrofluorimetric
grade) using 1-cm-path-length cuvettes. Absorption spectra were
recorded with a Perkin-Elmer λ40 spectrophotometer. Uncorrected
emission spectra were obtained with an Edinburgh FLS920
spectrometer (continuous 450 W Xe lamp) equipped with a peltier-
cooled Hamamatsu R928 photomultiplier tube (185-900 nm) or
with a Perkin-Elmer LS-50B spectrofluorimeter equipped with a
Hamamatsu R3896 photomultiplier. Emission lifetimes of the Pt
complexes in the visible region were obtained with an IBH time-
correlated single-photon-counting spectrometer using a nano-LED
(1) Data for (bpym)PtH. Color: dark red. Yield: 73%. FAB-
MS m/z: 578 (22%, [M + Na]+), 555 (50%, M+). Anal. Calcd for
C24H16N4Pt: C, 51.9; H, 2.9; N, 10.1. Found: C, 51.6; H, 2.6; N,
1
9.8. H NMR (CD2Cl2): δ 9.96 (2H, dd, bpym H4 or H6), 9.27
(2H, dd, bpym H6 or H4), 7.77 (2H, t, bpym H5), 7.47 (4H, d, phenyl
H2/H6), 7.30 (4H, t, phenyl H3/H5), 7.20 (2H, m, phenyl H4).
(2) Data for (bpym)PtMe. Color: red. Yield: 67%. FAB-MS
m/z: 606 (24%, [M + Na]+), 583 (60%, M+). Anal. Calcd for
C26H20N4Pt: C, 53.5; H, 3.5; N, 9.6. Found: C, 54.0; H, 3.5; N,
1
9.3. H NMR (CD2Cl2): δ 9.97 (2H, dd, bpym H4 or H6), 9.26
(2H, dd, bpym H6 or H4), 7.76 (2H, t, bpym H5), 7.37 (4H, d,
phenyl), 7.11 (4H, d, phenyl), 2.35 (6H, s, Me).
(3) Data for (bpym)PtCF3. Color: orange. Yield: 80%. FAB-
MS m/z: 714 (4%, [M + Na]+), 691 (14%, M+). Anal. Calcd for
C26H14F6N4Pt: C, 45.2; H, 2.0; N, 8.1. Found: C, 44.8; H, 1.8; N,
1
8.1. H NMR (CD2Cl2): δ 9.88 (2H, dd, bpym H4 or H6), 9.30
(2H, dd, bpym H6 or H4), 7.79 (2H, t, bpym H5), 7.56 (8H, m,
phenyl).
(37) Horrocks, W. D.; Bolender, J. P.; Smith, W. D.; Supkowski, R. M. J.
Am. Chem. Soc. 1997, 119, 5972.
(38) Reinhard, C.; Gu¨del, H. U. Inorg. Chem. 2002, 41, 1048.
(39) Hasegawa, Y.; Kimura, Y.; Murakoshi, K.; Wada, Y.; Kim, J.;
Nakashima, N.; Yamanaka, T.; Yanagida, S. J. Phys. Chem. 1996,
100, 10201.
(B) Synthesis of Heterodinuclear Pt(II)-Ln(III) Complexes
Pt-Nd and Pt-Gd. These complexes were obtained by slow (3-5
(40) Demas, J. N.; Crosby, G. A. J. Phys. Chem. 1971, 75, 991.
(41) Nakamuru, K. Bull. Chem. Soc. Jpn. 1982, 55, 2697.
Inorganic Chemistry, Vol. 44, No. 1, 2005 71

Shavaleev et al.
Table 8. Crystal, Data Collection, and Refinement Details for Crystal Structuresa
complex
formula
(bpym)PtH
(bpym)PtCF3
Re-Yb
Pt-Gd‚(C6H6)
Pt-Nd‚(C6H6)
C24H16N4Pt
555.5
C26H14F6N4Pt
691.5
C41H36ClF21N4O9ReYb
1522.4
C47H23F24GdN4O7Pt
1564.0
C47H23F24N4NdO7Pt
1551.0
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
orthorhombic
Pbcn
17.316(3)
10.919(2)
10.0939(19)
90
90
90
1908.5(6)
4
1.933
monoclinic
C2/c
29.101(4)
7.3072(9)
28.224(4)
90
120.644(11)
90
5163.6(12)
8
triclinic
P1h
11.791(4)
12.177(3)
18.722(4)
81.78(2)
monoclinic
P2(1)/c
19.9826(17)
11.2877(12)
25.436(3)
90
109.142(6)
90
5420.1(9)
4
triclinic
P1h
11.325(3)
20.578(3)
23.106(4)
90.358(12)
95.917(12)
103.55(2)
5204.3(16)
4
R, deg
â, deg
88.31(2)
γ, deg
82.889(17)
2639.7(13)
2
V, Å3
Z
F, g cm-3
cryst size, mm3
µ, mm-1
data, restraints, params
final R1, wR2b
1.779
1.915
1.917
1.980
0.5 × 0.2 × 0.2
0.5 × 0.15 × 0.15
0.3 × 0.1 × 0.1
0.5 × 0.3 × 0.1
0.5 × 0.3 × 0.15
7.370
5.499
4.230
3.926
3.812
2192, 0, 132
0.0184, 0.0445
5883, 0, 319
0.0407, 0.1191
12024, 0, 712
0.0598, 0.1609
12397, 0, 674
0.0536, 0.1541
23673, 0, 1454
0.0684, 0.1661
a All data sets were collected on a Bruker SMART diffractometer with Mo KR radiation (λ ) 0.710 73 Å, 2θ limit ) 55°) at 173 K. b The value of R1
is based on selected data with F > 4σ(F); the value of wR2 is based on all data.
days) partial evaporation of a mixed benzene/heptane solution (4:
1, v/v; initial volume approximately 10 cm3) containing (bpym)-
PtCF3 and Ln(hfac)3‚2H2O (Ln ) Nd or Gd) in a 1:1 molar ratio
(ca. 50 µmol of each). The dark-red crystals of the heterodinuclear
complex that formed were filtered off, washed with hexane, and
vacuum-dried at room temperature. The complexes are air- and
moisture-stable solids of a dark-red color. Attempts at a similar
synthesis using heavier lanthanides (Ln ) Er or Yb) gave only
crystals of the starting materials.
(1) Data for Pt-Nd. Yield: 64%. Anal. Calcd for C41H17F24N4-
NdO6Pt: C, 33.8; H, 1.2; N, 3.9. Found: C, 34.2; H, 1.4; N, 3.7.
(2) Data for Pt-Gd (as Benzene Solvate). Yield: 65%. Anal.
Calcd for C47H23F24N4GdO6Pt: C, 36.1; H, 1.5; N, 3.6. Found: C,
36.0; H, 1.6; N, 3.7.
integration of the raw data and merging of equivalent reflections,
an empirical absorption correction was applied based on comparison
of multiple symmetry-equivalent measurements.42 The structures
were solved by direct methods and refined by full-matrix least
squares on weighted F2 values for all reflections using the SHELX
suite of programs.43
The structural determinations of (bpym)PtH and (bpym)PtCF3
were straightforward. The structural determinations of the dinuclear
complexes were complicated by disorder involving the F atoms
associated with the CF2CF2CF3 chains in Re-Yb and by rotational
disorder of the CF3 groups of the hfac ligands in Pt-Nd and Pt-
Gd. In Pt-Gd, the F atoms of three of the CF3 groups [involving
F(91)-F(93), F(31)-F(33), and F(71)-F(73)] could be refined in
two alternate positions with approximately 50:50 site occupancy
in each. In the other cases, the disorder could not be resolved, and
the F atoms accordingly have rather high thermal parameters; the
highest residual electron density peaks are close to these F atoms.
To keep the refinements stable, some of these F atoms and their
associated C atoms were refined with isotropic thermal parameters.
These problems are typical of complexes of this type containing
peripheral fluorocarbon chains.18
(C) Synthesis of Heterodinuclear Re(I)-Yb(III) Complex
Re-Yb. [Re(CO)3Cl(bpym)] (0.030 g, 65 µmol) and Yb(fod)3-
(H2O)2 (0.073 g, 65 µmol) were dissolved in CH2Cl2 (15 cm3),
and the red solution was stirred for 10 min. Hexane (15 cm3) was
added to the solution. Concentration of the solution resulted in the
precipitation of the orange-red dinuclear complex Re-Yb, which
was filtered, washed with a small amount of hexane, and vacuum-
dried. The complex is an air-stable orange solid, obtained in 67%
yield; it is soluble in benzene, CH2Cl2, and acetone and insoluble
in hexane. Large needlelike crystals suitable for X-ray analysis were
readily formed by slow evaporation of a mixed CH2Cl2/hexane
solution of the complex. Anal. Calcd for C41H36ClN4O9ReYbF21:
C, 32.4; H, 2.4; N, 3.7. Found: C, 33.0; H, 2.1; N, 3.8. IR (CH2-
Acknowledgment. We thank the Royal Society, London,
U.K. (postdoctoral fellowship to N.M.S.), and EPSRC,
Swindon, U.K. (Ph.D studentship to T.L. and postdoctoral
fellowship to Z.R.B.), for financial support. We thank Dr.
G. Di Marco as a proponent of Dr. G. Calogero’s research
activity program, entitled “Synthesis and Study of Lumi-
nescent Compounds Based on Transition-Metal Complexes
for Sensor Applications” and supported by the CNR short-
term mobility program, 2003.
Cl2): 2033, 1936, 1915 cm-1
.
The analogous complexes Re-Nd and Re-Er were prepared in
the same way.
(1) Data for Re-Er. Yield: 77%. Anal. Calcd for C41H36-
ClN4O9ReErF21: C, 32.5; H, 2.4; N, 3.7. Found: C, 32.4; H, 2.1;
Supporting Information Available: CIF file containing data
for the five crystal structures Re-Yb, Re-Nd, Re-Er, Pt-Nd,
and Pt-Gd. This material is available free of charge via the Internet
at http://pubs.acs.org.
N, 3.9. IR (CH2Cl2): 2033, 1936, 1915 cm-1
.
(2) Data for Re-Nd. Yield: 71%. Anal. Calcd for C41H36-
ClN4O9ReNdF21: C, 33.0; H, 2.4; N, 3.7. Found: C, 32.6; H, 2.2;
N, 3.8. IR (CH2Cl2): 2032, 1935, 1914 cm-1
.
X-ray Crystallography. Suitable crystals were mounted on a
Bruker SMART-CCD diffractometer equipped with graphite-
monochromatized Mo KR radiation. Crystallographic measurements
were carried out at 173 K; details of the crystal, data collection,
and refinement parameters are summarized in Table 8, and selected
structural parameters are collected in Tables 1, 2, and 4-6. After
IC048875S
(42) Sheldrick, G. M. SADABS: A Program for Absorption Correction with
the Siemens SMART System; University of Gottingen: Gottingen,
Germany, 1996.
(43) SHELXTL Program System, version 5.1; Bruker Analytical X-ray
Instruments Inc.: Madison, WI, 1998.
72 Inorganic Chemistry, Vol. 44, No. 1, 2005