Preparation of Pt-Tl clusters showing new geometries. X-ray, NMR and luminescence studies

Article abstract of DOI:10.1039/c4dt00536h

Square planar complexes [Pt(CNC)L] (CNC = C,N,C-2,6-NC₅H ₃(C₆H₄-2)₂; L = tht (tetrahydrothiophene, SC₄H₈, 1), L = CN^tBu (2)) react with TlPF₆ in different Pt/Tl molar ratios (3/1 in the case of 1 and 1/1 in the case of 2) yielding the complexes [{Pt(CNC)(tht)} ₃Tl](PF₆) (3) and [Pt(CNC)(CN^tBu)Tl](PF ₆) (4), respectively. The structures of 3 and 4 (X-ray) show the presence of Pt→Tl dative bonds unsupported by any bridging ligands. In complex 3, the only Tl centre is simultaneously bonded to three Pt atoms forming a perfect equilateral triangle with Pt-Tl distances of 2.9088(5) A, remarkably short. Complex 4 is formed by three Pt(CNC)(CN ^tBu)Tl units, disposed in a triangular fashion, linked together through η⁶-Tl-arene interactions, and showing Pt-Tl bonds with distances of ca. 3.04 A. The study of these crystal structures would seem to indicate that the difference between the Pt/Tl ratios found in the complexes 3 and 4 is due to the steric requirements of the L ligand bonded to Pt. NMR studies both in solution and in the solid state show that the Pt-Tl bond persists in solutions of 3 and 4. The UV-vis spectra of 3 and 4 in solution display the same profiles as those of 1 and 2, which may suggest a partial dissociation of the Pt-Tl bond in solution. However, by DFT calculations it was proved that in this case the formation of the Pt-Tl dative bond does not produce the expected blue-shift in the UV-vis absorptions. The emissive behaviour of 1-4 in the solid state and in frozen solutions is also studied and included in this work.

Full text of DOI:10.1039/c4dt00536h

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Preparation of Pt–Tl clusters showing new
geometries. X-ray, NMR and luminescence
studies†‡
Cite this: Dalton Trans., 2014, 43,
10828
Úrsula Belío, Sara Fuertes§ and Antonio Martín*
5 3 6 4 2
Square planar complexes [Pt(CNC)L] (CNC = C,N,C-2,6-NC H (C H -2) ; L = tht (tetrahydrothiophene,
t
SC
4
H
8
, 1), L = CN Bu (2)) react with TlPF
6
in different Pt/Tl molar ratios (3/1 in the case of 1 and 1/1 in the
t
case of 2) yielding the complexes [{Pt(CNC)(tht)}
3
Tl](PF
6
) (3) and [Pt(CNC)(CN Bu)Tl](PF
6
) (4), respectively.
The structures of 3 and 4 (X-ray) show the presence of Pt→Tl dative bonds unsupported by any bridging
ligands. In complex 3, the only Tl centre is simultaneously bonded to three Pt atoms forming a perfect
equilateral triangle with Pt–Tl distances of 2.9088(5) Å, remarkably short. Complex 4 is formed by three
t
6
“
Pt(CNC)(CN Bu)Tl” units, disposed in a triangular fashion, linked together through η -Tl–arene inter-
actions, and showing Pt–Tl bonds with distances of ca. 3.04 Å. The study of these crystal structures
would seem to indicate that the difference between the Pt/Tl ratios found in the complexes 3 and 4 is
due to the steric requirements of the L ligand bonded to Pt. NMR studies both in solution and in the solid
state show that the Pt–Tl bond persists in solutions of 3 and 4. The UV-vis spectra of 3 and 4 in solution
display the same profiles as those of 1 and 2, which may suggest a partial dissociation of the Pt–Tl bond
in solution. However, by DFT calculations it was proved that in this case the formation of the Pt–Tl dative
bond does not produce the expected blue-shift in the UV-vis absorptions. The emissive behaviour of 1–4
in the solid state and in frozen solutions is also studied and included in this work.
Received 20th February 2014,
Accepted 13th May 2014
DOI: 10.1039/c4dt00536h
www.rsc.org/dalton
5
,43
and is a typical case of “inert pair” species.
Examples of the
Introduction
8
44
following donor–Tl(I) couples are known: Ru(0)(d )→Tl(I),
8
45,46
8
47,48
8
5,10,49–66
Metallophilic interactions between closed or pseudo closed Rh(I)(d )→Tl(I),
Ir(I)(d )→Tl(I),
Pt(II)(d )→Tl(I),
1
0
8
10
2
10
67–70
8
71,72
10
shell transition metals (d , d , d , s ) have been used as a Pt(0)(d )→Tl(I),
Pd(II)(d )→Tl(I)
and Au(I)(d )→
4
3,73–83
tool in the field of crystal or molecular engineering, linking Tl(I),
Pt(II) and Au(I) being the two main donor centres.
different subassemblies. A wide array of structural types has With regard to Pt(II)→Tl(I) heteropolynuclear clusters specifi-
been reported for complexes with this kind of interaction, cally, several structural configurations have been reported,
1
0,50–53
49,54–56
from simple linear bimetallic compounds to infinite one- dinuclear PtTl discrete examples,
trinuclear PtTl2
1
–17
5,57–59
dimensional chains.
In many cases, complexes containing or
Pt Tl
“sandwiches”,
tetranuclear
“paired”
Often Pt–Tl
2
1
0,60–64
5,59,61,64–66
these metal–metal bonds have also been shown to exhibit (PtTl)
2
,
or infinite networks.
photophysical and photochemical properties, such as lumine- bonds are supported by bridging ligands between the two
scence, attributable to the existence of metallophilic metallic centres, and/or the thallium atoms bear additional
6
,16,18–42
interactions.
Tl(I) is a fairly representative acceptor in this sort of hetero-
ligands.
Furthermore, the use of cyclometallated planar aromatic
1
0
2
polynuclear clusters. It shows a d s electron configuration C^N ligands on the coordination sphere of the platinum(II) has
been one of the lines of research undertaken in our labora-
2
,3,16,42,84
tory.
characteristics to the complex. Firstly, they are strong field
ligands that cause the d platinum orbital to raise its energy
These planar ligands confer two interesting
Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Departamento de
Química Inorgánica, Universidad de Zaragoza – CSIC, 50009 Zaragoza, Spain.
E-mail: tello@unizar.es
This paper is dedicated to the memory of Professor María Pilar García and favour the formation of stronger Pt→M dative bonds.
Clemente.
Electronic supplementary information (ESI) available. CCDC 966072, 966073
z
2
8
5,86
†
In addition, the presence of aromatic rings coplanar with the
Pt square plane allows for the presence of intermolecular π⋯π
interactions between the planar ligands, establishing different
‡
and 987896. For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/c4dt00536h
2
,6,16,17,42,87,88
§
ARAID researcher.
types of supramolecular arrangements.
Along
10828 | Dalton Trans., 2014, 43, 10828–10843
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with hydrogen bonding, this kind of π⋯π stacking is one of
8
9–94
the most important secondary interactions
modern supramolecular chemistry,
in the field of
9
5–98
playing an important
role in processes such as molecular self-assembly and self-
recognition of aromatic entities in the crystal state and also
having an important role in the luminescent properties of
8
4
some compounds.
In this paper we report the use of Pt precursors containing
the tridentate cyclometallated 2,6-diphenylpyridinate (CNC)
ligand. Their use has allowed us to prepare and characterize
two clusters containing unsupported Pt(II)→Tl(I) bonds with
unprecedented geometries. Their photophysical properties
have also been studied.
Some of the results contained in this paper have been pre-
9
9
viously reported in the form of a short communication.
Results and discussion
Syntheses of [Pt(CNC)L] (L = tht (tetrahydrothiophene, SC H ,
4
8
t
1
), L = CN Bu (2))
The preparation and structural characterization of the starting Fig. 1 Molecular structure of complex 1. Ellipsoids are drawn at the
0% probability level. Hydrogen atoms have been omitted for clarity.
5
material [Pt(CNC)(dmso)] (dmso = dimethyl sulfoxide) have
already been reported.
1
00
Nevertheless, we have modified the
synthetic route since we experienced some problems in follow-
ing the reported method of preparation (see Experimental).
Table 1 Selected bond lengths (Å) and angles (°) for [Pt(CNC)-
tht)]·0.5Me CO (1·0.5Me CO)
(
2
2
Complexes [Pt(CNC)L] (CNC = C,N,C-2,6-NC
5 3 6 4 2
H (C H -2) (see
t
Pt–N
Pt–C(1)
1.983(2)
2.067(3)
Pt–C(13)
Pt–S
2.062(3)
2.2473(6)
Scheme 1); L = tht (tetrahydrothiophene, SC H , 1), L = CN Bu
4
8
(
2)) have been prepared by replacing the dimethyl sulfoxide
ligand in the precursor [Pt(CNC)(dmso)] with the corres- N–Pt–C(13)
80.69(10)
160.70(10)
95.32(7)
N–Pt–C(1)
N–Pt–S
C(1)–Pt–S
80.60(10)
174.77(7)
103.62(7)
C(13)–Pt–C(1)
C(13)–Pt–S
ponding L (see Experimental for details). This procedure has
1
01–104
already been used in the synthesis of similar [Pt(CNC)L],
−
+
[
Pt(CNC)X] (ref. 101) or [Pt(CNC)L] (ref. 104) complexes.
1
Both the IR and H NMR spectra of complexes 1 and 2 have
determined by X-ray diffraction. Fig. 1 shows a view of the
complex and Table 1 lists a selection of relevant bond dis-
tances and angles. As expected, the crystal structure of 1 shows
a square planar coordination for the platinum, with structural
parameters for the “Pt(CNC)” fragment that are very similar to
the corresponding signals attributable to the ligands present
in the complexes, with the expected relative intensity (see
Experimental). Furthermore the crystal structure of 1 has been
1
00
those reported for platinum complexes containing this
similar tridentate CNC ligands. The Pt–S distance is also
or
8
8
similar to that found in the similar complex [Pt(2,6-diphenyl-
8
8
isonicotinate)(tht)].
No intermolecular π⋯π interactions
between the aromatic rings of the CNC plane ligands are
present in 1.
Reactions of 1 and 2 with TlPF
6
Complexes 1 and 2 are suitable precursors for the synthesis of
new clusters containing Pt(II)→Tl(I) bonds. We have tested the
reactions of 1 and 2 toward TlPF6 in dichloromethane in
different Pt/Tl molar ratios. Both 1 and 2 always react in a
fixed Pt/Tl proportion, 3/1 in the case of 1 and 1/1 in the case
of 2. If other proportions are used, the corresponding
unreacted products are recovered.
Thus, the reaction of 3 equivalents of 1 with 1 equivalent of
TlPF6 results, after work-up of the solution, in a red solid
Scheme 1 Syntheses of complexes 3 and 4.
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Fig. 2 Molecular structure of the cation of complex 3. Ellipsoids are
drawn at the 50% probability level. Hydrogen atoms have been omitted
for clarity.
Fig. 3 Molecular structure of the cation of complex 4. Ellipsoids are
drawn at the 50% probability level. Hydrogen atoms have been omitted
for clarity.
whose spectroscopic and analytical data correspond to the
formula [{Pt(CNC)(tht)} Tl](PF ) (3). Similarly, the reaction of 1
3
6
6
equivalent of 2 with 1 equivalent of TlPF allowed us to obtain
3
Table 2 Selected bond lengths (Å) and angles (°) for [{Pt(CNC)(tht)} Tl]-
a
an orange solid whose spectroscopic and analytical data (PF ) (3)
6
t
correspond to the formula [Pt(CNC)(CN Bu)Tl](PF ) (4) (see
6
Pt–N
Pt–S
1.996(13)
2.262(4)
Pt–C(1)
Pt–Tl
2.072(10)
2.9088(5)
Scheme 1).
The complete understanding of the solid state structures of
these complexes has been achieved through single crystal X-ray N–Pt–C(1)
80.8(3)
C(1)#1–Pt–C(1)
C(1)–Pt–S
C(1)–Pt–Tl
Pt#2–Tl–Pt
159.9(6)
99.8(3)
87.8(3)
120.0
N–Pt–S
studies of both 3 and 4. Fig. 2 and 3 show views of the corres-
N–Pt–Tl
169.1(3)
100.2(3)
90.68(10)
ponding complexes and Tables 2 and 3 list a selection of rele-
vant bond distances and angles.
S–Pt–Tl
a
Symmetry transformations used to generate equivalent atoms: #1 x, y,
3
Complex 3 is a tetranuclear Pt Tl cluster in which the Tl(I)
−z + 3/2; #2 −y + 1, x − y + 1, z.
centre lies on a 6-fold axis and thus the three Pt atoms form a
perfect equilateral triangle with the thallium atom in the
centre, the Pt–Tl–Pt angles being exactly 120°. Due to the mole-
cular symmetry, the three Pt–Tl distances are the same, 2.9088(5)
Å. To the best of our knowledge, this value is the shortest
one reported so far for a Pt(II)–Tl(I) bond unassisted by any
Table 3 Selected bond lengths (Å) and angles (°) for [{PtTl(C17
H
11N)-
t
(CN Bu)}
3
](PF
6
)
3
·1.5n-C
6
H14 (4·1.5n-C
6
H
14
)
Pt(1)–C(18)
Pt(1)–C(1)
Pt(1)–Tl(1)
1.913(7)
2.055(6)
3.0143(3)
2.002(5)
2.071(7)
1.893(7)
2.062(7)
3.0460(3)
Pt(1)–N(1)
Pt(1)–C(13)
Pt(2)–C(40)
Pt(2)–C(35)
Pt(2)–Tl(2)
Pt(3)–N(5)
Pt(3)–C(45)
1.988(5)
2.075(7)
1.905(7)
2.070(7)
3.0488(3)
1.997(5)
2.078(6)
bridging ligand or by pairing (PtTl) metallocycle systems. The
2
trigonal environment of the Tl centre seems to indicate the Pt(2)–N(3)
2
Pt(2)–C(23)
Pt(3)–C(62)
Pt(3)–C(57)
steric inactivity of its lone 6s electron pair that is usually
1
05
stereoactive,
which is a feature that has been previously
5
,43
observed in some M→Tl(I) clusters.
Some M Tl(III) com- Pt(3)–Tl(3)
3
plexes with a symmetrical trigonal environment for the
thallium(III) centre are known and they involve low valent
C(18)–Pt(1)–N(1)
N(1)–Pt(1)–C(1)
177.1(3)
80.9(2)
80.1(2)
177.2(3)
80.7(2)
81.1(2)
81.65(19)
99.3(3)
99.4(3)
161.2(3)
96.07(15)
70.67(18)
C(18)–Pt(1)–C(1)
C(18)–Pt(1)–C(13)
C(1)–Pt(1)–C(13)
C(40)–Pt(2)–C(35)
C(40)–Pt(2)–C(23)
C(35)–Pt(2)–C(23)
C(62)–Pt(3)–N(5)
N(5)–Pt(3)–C(57)
N(5)–Pt(3)–C(45)
C(62)–Pt(3)–Tl(3)
C(57)–Pt(3)–Tl(3)
96.8(3)
102.2(3)
160.8(3)
101.7(3)
96.5(3)
161.8(3)
178.3(2)
80.6(2)
80.6(2)
85.54(19)
112.87(16)
metal carbonyl complexes with general formulae [{M(CO) - N(1)–Pt(1)–C(13)
x
1
06
44
107
C(40)–Pt(2)–N(3)
N(3)–Pt(2)–C(35)
N(3)–Pt(2)–C(23)
(
η-C
5
H
5
)}
3
(μ
4
3
-Tl)} (x = 3, M = Cr, Mo;
x = 2, M = Ru, Fe
)
n−
107
107
or [{M(CO) } (μ -Tl)} (n = 0, M = Cr;
n = 3, M = Fe ).
3
3
However, 3 is the first Tl(I) complex in which this striking C(40)–Pt(2)–Tl(2)
C(62)–Pt(3)–C(57)
trigonal environment is found. As far as we know, there are only
C(62)–Pt(3)–C(45)
another three reports of clusters in which three donor metal
C(57)–Pt(3)–C(45)
atoms are simultaneously bonded to a Tl(I) centre and their N(5)–Pt(3)–Tl(3)
C(45)–Pt(3)–Tl(3)
geometry clearly departs from a regular trigonal disposition.
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t
6
One is [{Pt(pda)(NHCO Bu)
2
}
4
Tl
4
][Pt(CN)
4
]
2
(pda = 1,2-propyl-
The η -Tl–arene interactions found in 4 are fairly sym-
6
6
t
diamine), in which infinite “{Pt(pda)(NHCO Bu) }Tl” chains metric. The maximum and minimum Tl–C distances are
2
4
are linked via half of the Tl with “Pt(CN) ” units acting as con- 3.361(7)–3.152(7) Å for Tl(1), 3.371(7)–3.223(6) Å for Tl(2) and
nectors, resulting in a three-dimensional network. Neverthe- 3.450(6)–3.221(7) Å for Tl(3). The distance of each thallium
less, in this case, the environment of the Tl connected to three centre to the calculated centroids of these rings is 2.959, 2.978
platinum atoms is not symmetric, with longer Pt–Tl bond dis- and 3.021 Å, respectively, and the Pt–Tl–centroid angles are
t
tances (range 2.986–3.250 Å) and NHCO Bu ligands bridging 140.7(1)° for Tl(1), 145.2(1)° for Tl(2) and 144.7(1)° for Tl(3),
Pt and Tl. The other two cases present a family of six gold(I) which seems to indicate, in this case, the stereoactivity of the
4
3
2
105
6
complexes: {NBu
Tl{Au(3,5-C Cl
4
[Tl
2
{Au(C
6
Cl
5
)
2
}{μ-Au(C
6
Cl
5
)
2
}
2
]}
n
,
{NBu
4
-
Tl(I) lone 6s electron pair.
η -Tl–arene interactions do not
4
3
[
6
2
F
3
)
2
}
2
]}
n
,
{NBu [Tl{Au(C
4
6
Cl
5 2
) }{Au(3,5- seem to be very frequent and a search in the CCDC structural
4
3
81
C Cl F ) }]} , {NBu [Tl {Au(2C F Br) } ]} , {NBu [Tl {Au(2- database (version 5.35, updated November 2013) revealed just
6
2
3 2
n
4
2
6
4
2 3
n
4
2
8
1
81
C
6
F
4
I)
2
}
3
]}
n
,
and {NBu
4
[Tl{Au(2-C
6
F
4
Br)
2
}
2
]}
n
.
These com- a couple of dozens of reported structures containing this
plexes are basically prepared by the incorporation of [AuR
into [AuTlR2]n (R = C Cl , 3,5-C Cl F , 2-C F Br, 2-C F I)
−
52,109–119
2
]
feature.
As in 3, the three Pt planes in 4 form an almost perfect
6
5
6
2
3
6
4
6 4
chains and the formation of a third Au–Tl bond. The Au–Tl equilateral triangle, with dihedral angles of ca. 60°. Neverthe-
distances range from 2.935 to 3.466 Å and the environments of less, the disposition of the planes is different from that
t
the Tl atoms are planar, but not symmetrical, being best observed for 3. In 4, the CN Bu ligands are pointing outwards
described as distorted T-shaped.
from the triangular core formed by the Pt planes, two in one
The three “Pt(CNC)(tht)” units in 3 are disposed in such a direction and the third in the opposite direction. The triangu-
way that the best square Pt planes form an equilateral triangle. lar “cavity” formed by the Pt planes is much smaller in 3 than
Each of the three tht ligands is pointing in the same direction. in 4 (see Fig. 4). An idea of this is given by the separation of
The Pt–Tl lines are perpendicular to their respective Pt plane, the Pt atoms, which is 5.038(1) Å for 3 and ca. 7.674(1) Å for 4.
which is an arrangement that is usually found in complexes Another indication that the triangular disposition of the
showing Pt→M dative bonds and which maximizes the overlap- Pt planes is less sterically stressed in 4 than in 3 is the ob-
z
ping of the full 5d 2 Pt(II) orbital and the empty orbitals of the servation that the CNC planes are much less distorted in the
5
,10,53,108
acidic metal centre.
It is more likely that the disposi- first complex than in the second complex.
All these observations seem to point to the difference
tion adopted by the three “Pt(CNC)(tht)” was the optimal (and
perhaps the only possible) one to accommodate these three between the Pt/Tl ratios found in the complexes 3 and 4 as
bulky groups. The tht rings are bent away from the interior of being due to the steric requirements of the L ligand bonded to
the Pt Tl core, thus minimizing the repulsion with the CNC Pt. Thus, in 3 the tht ligand seems to be very flexible and is
3
ligand of the adjacent unit. Moreover, the plane of the CNC able to adopt a disposition in which its carbon atoms move
ligands is distorted in such a way that their pyridine rings, the away from the crowded core formed by the three Pt planes. As
closest to the tht of the adjacent unit, are moved back from the a result of this, the cavity formed can only accommodate one
best Pt square plane, while the two phenylene rings, which
have less steric hindrance, move slightly inside the centre
of the core. It is noteworthy that despite the apparent steric
hindrance, the Pt–Tl distances are short for this kind of
complexes.
t
Complex 4 (see Fig. 3) is formed by three “Pt(CNC)(CN Bu)-
Tl” units, disposed in a triangular fashion and linked together
6
through η -Tl–arene interactions established with one of the
phenylene rings of a neighbouring moiety. Each of the three
units shows a direct Pt–Tl bond unassisted by any bridging
ligand. The intermetallic bond distances are Pt(1)–Tl(1)
3
.0143(3) Å, Pt(2)–Tl(2) 3.0488(3) Å and Pt(3)–Tl(3) 3.0460(3) Å,
which are in the short range of this kind of interactions. The
Pt–Tl lines are tilted by 16.3(1)° (Pt(1)), 20.6(1)° (Pt(2)) and
2
2.2(1)° (Pt(3)) with respect to the perpendicular to the best Pt
square planes. This deviation could be caused by the tri-
6
angular disposition of the complexes to establish the η -Tl–
arene interactions. Complexes in which the Pt–Tl moieties
are ordered in pairs through additional bonds or interactions
of the thallium centre to
a
neighbouring unit are
1
0,50,60–64
known,
but as far as we know, no other examples of
the triangular “trimeric” disposition of Pt–Tl units found in 4
have been previously reported.
Fig. 4 Superposition of the molecular structures of the cations of com-
plexes 3 (red) and 4 (blue).
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Tl(I) cation that fits snugly between the three Pt atoms and
t
bonds all three. On the other hand, the CN Bu ligands in 4 are
less flexible due to the CN triple bond and their compulsory
linear disposition, and the relatively bulky t-butyl ends prevent
t
the “Pt(CNC)(CN Bu)” units from approaching each other
further. Consequently, the inner cavity is big enough for three
Tl(I) cations and three different individual Pt–Tl bonds to exist,
and even allows the relative approximation of two PF6− anions
whose fluorine atoms make contact with the Tl centres.
The crystal structures of 3 and 4 have also revealed the pres-
ence of π⋯π intermolecular interactions established between
the aromatic rings of the CNC ligand of adjacent units, which
lie in parallel planes with interplanar distances of ca. 3.4 Å
(
see Fig. S1, ESI‡). As mentioned previously, these π⋯π inter-
1
95
Fig. 5
Pt NMR spectra of compounds: 3 + TlPF
6
exc. (a) and 1 (b) in
actions have been found for complexes containing planar
cyclometallated ligands.
CD Cl
2
2
at variable temperature.
2
,6,16,17,42,87,88,103,120
Thus, in the case
of 3, the final result is a three-dimensional network linked by
π⋯π interactions (see Fig. S1a‡), whereas for 4 a two-dimen-
sional “sheet” of triangles is formed (see Fig. S1b‡).
1
95
1
Variable temperature
Pt{ H} NMR experiments were per-
formed on a CD Cl solution of 3 with TlPF6 in excess (see
2
2
Fig. 5a). At 193 K, the spectrum shows a doublet at −3100 ppm
1
due to Pt–Tl couplings ( JPt–Tl = 8.9 kHz) which collapse to a
broad signal at 243 K. This coupling constant value is similar
NMR studies
1
The H NMR spectra of 1 and 2 in CD Cl show the corres- to that observed in reported compounds with Pt(II)→Tl(I)
2
2
t
50,51,124
1
1
ponding signals for the CNC and tht or CN Bu ligands, respecti- dative bonds.
The separate J195 203 , J195 205 coupling
Pt– Tl Pt– Tl
vely (see Experimental). On the NMR time scale, both halves constants cannot be measured due to the broadness of the
of the CNC ligands are equivalent, and thus six signals are signals. Furthermore, at 193 K the 195Pt NMR spectrum of 1
observed for this ligand. In the case of 1, the two halves of the barely changes, displaying a singlet at −3901 ppm (see
1
95
tht ligands are also equivalent and two signals are present. For Fig. 5b). Both
2
Pt resonances appear downfield shifted with
, all the methyl groups of the CN Bu ligand are equivalent, respect to those at RT and the difference between them
giving rise to one singlet.
increases up to 801 ppm. It is worth noting that the sample
t
1
1
The H NMR spectrum of 3 is very similar to that of its pre- with an excess of TlPF showed an identical H NMR spectrum
6
cursor 1. The most significant shift of the signals observed in to that of compound 3.
1
95
the spectrum of 3 is that corresponding to the ortho phenyl
In order to confirm that the Pt NMR spectra obtained in
proton (H ) of the CNC ligand, which moves upfield 0.66 ppm solution reflect the structure revealed by the X-ray diffraction
2
1
195
with respect to 1. The H NMR spectra of 2 and 4 display studies, solid state
Pt NMR spectra of 1 and 3 were
almost identical profiles and thus there is no evidence of per- measured. For compound 1, spectra were registered at spin-
6
sistence in solution of the η -Tl–arene interactions found in ning speeds of 8 and 12 kHz (see Fig. S2, ESI‡). The isotropic
the crystals of 4.
In order to establish whether Pt(II)→Tl(I) dative bonds
remain in solution, we have conducted several
chemical shift of −3816 ppm agrees well with the solution
1
95
Pt NMR value at 193 K (−3901 ppm) (see Fig. 6).
1
95
1
Pt{ H} NMR
experiments (see Fig. 5). In CD Cl solution at room tempera-
2
2
1
95
ture, compound 1 shows a slightly structured
Pt resonance
1
4
at −3914 ppm, due to the quadrupolar nature of N of the
1
21
CNC ligand.
However, the spectrum of 3 under the same
conditions does not show any signal, probably because this
cluster dissociates in solution giving rise to a mixture of
1
95
different Pt/Tl species which are in equilibrium on the
NMR time scale. However, upon the addition of excess TlPF
Pt
6
, a
1
95
Pt NMR signal is observed at −3157 ppm. The downfield
shift with respect to the signal in the starting material 1 is
57 ppm, consistent with the formation of Pt→M dative bonds
7
in solution. This downfield shift is caused by the decrease of
electron density around the Pt centre upon coordination to
+
4,15–17,122,123
M .
Exactly the same dissociation process at the
Fig. 6 Comparison between the solid state (above) and solution
1
95
Pt NMR time scale was formerly observed in solutions of
195
(
below)
Pt NMR spectra of compounds 1 (blue) and 3 (red). Solid state
4
15,123
195
compounds containing Pt→Cd and Pt→Ag
dative bonds.
Pt NMR spectra are registered at spinning speeds of 12 kHz.
10832 | Dalton Trans., 2014, 43, 10828–10843
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1
95
Compound 3 was studied at 5, 8 and 12 kHz spinning
In an attempt to identify and confirm the Pt resonances,
speeds (see Fig. S3, ESI‡). At 5 kHz, the broad spectrum solid state NMR experiments were carried out on compounds 2
affords a rather low resolution; however, at 8 and 12 kHz the and 4. The spectra of 2 were recorded at spinning speeds of 5,
1
95
Pt NMR spectra displayed a better resolved pattern with 8 and 12 kHz (see Fig. S5, ESI‡). The isotropic chemical shift
1
95
195
clear evidence of splitting due to the Pt–Tl coupling. The Pt of −4020 ppm agrees well with the solution Pt NMR value at
signal appears as a doublet centered at −3088 ppm with a 193 K (−4076 ppm). Compound 4 was also studied at the same
coupling constant of 9.0 kHz, which is in close agreement with spinning speeds but a well resolved pattern was not obtained
1
95
1
the solution Pt NMR data at 193 K (−3100 ppm and J
=
at any spinning rate. Nevertheless, the moderate downfield
Pt–Tl
8
.9 kHz).
shifts (>280 ppm) in relation to its precursor (2) observed in
The remarkable downfield shifts (>750 ppm) in relation to CD
2
2
Cl at room and low (263 K) temperature are in agreement
its precursor 1 and the extraordinarily high value of the Pt(II)– with the existence of Pt→Tl dative bonds in solution for com-
Tl(I) coupling constant (8.9 kHz) are indicative of a fairly pound 4, but ones that are significantly weaker than those
strong Pt→Tl dative bond in solution for 3. Furthermore, from observed in compound 3.
1
95
the
Pt resonances obtained either at RT or low temperature
for 3 it is clear that only one Pt/Tl species is present and that it
Photophysical properties
matches with the solid state structure perfectly, as shown by
1
95
the solid
Pt NMR spectra. Hence, the excess of thallium in
Absorption spectra and theoretical calculations. UV-vis
the media just prevents the dissociation process and the only spectra data of compounds 1–4 in solution are summarized in
5
species formed is the tetranuclear one.
Table S1 (see ESI‡). In diluted solution (10− M), compounds 1
1
95
4
−1
Likewise, the same Pt NMR studies were performed on 2 and 2 display structured bands at 330–350 nm (ε > 10 M
1
95
−1
and 4. Compound 4 shows a very broad and weak
nance at −3795 ppm in CD Cl solution at room temperature. ligand and the solvent polarity (see Fig. S6 and S7, ESI‡).
Since the signal is very weak, even after 30 000 acquisition These are typical of metal-perturbed ligand centered tran-
Pt reso- cm ) that appear to be fairly insensitive to the ancillary
2
2
1
95
1
17,88,93,101,104,125
scans, the Pt NMR spectrum was repeated adding an excess sitions ( IL, CNC).
In addition, they all show
Pt signal was recorded in weak shoulder bands at lower energies: 410–440 nm (ε ∼
the same spectral region (−3766 ppm), as seen in Fig. S4 10 M cm ) as shown in the inset of Fig. S6.‡ On the basis
ESI‡). Since the H NMR spectrum of this sample is identical of previous studies on closely related derivatives [Pt(ethyl-2,6-
1
95
of TlPF
6
. In this case, a stronger
3
−1
−1
1
(
t
88
to that recorded for 4, it was used in the following experi- diphenylisonicotinate)(L)]; L = tht, CN Bu], and literature
1
95
17,88,93,101,104,125,126
ments. Thus, when the
Pt resonance of 4 is compared with reports,
these weak shoulder absorptions
1
that obtained in compound 2 (−4051 ppm), a downfield shift are attributed to a MLCT [5d(Pt)→π*(CNC)] transition. Com-
of 285 ppm is observed (see Fig. 7). This is in line with obser- pounds 3 and 4 exhibit very similar absorption profiles to
vations for 1 and 3 and also with previously reported those of the precursor. Unlike other reported compounds con-
4
,15–17,122,123
195
1,2,16
results.
{
Following the same procedure, the
H} NMR spectra of 2 and 4 were recorded in a solution of bands in 3 and 4 do not display any significant blue shift
CD Cl at 193 K. The spectrum of 2 displays a sharp singlet at compared to those of 1 and 2, respectively (Table S1, ESI‡). A
Pt- taining Pt→M dative bonds,
the low energy absorption
1
2
2
−
4076 ppm, whereas that corresponding to 4 does not show very similar behaviour was observed in the heterotrinuclear
+
any signal at all. The experiment was repeated at 263 K and a clusters [{(ethyl-2,6-diphenylisonicotinate)Pt(dmpyz)}
much weaker and broader signal appears downfield shifted Cu, Ag). This blue shift is normally attributed to the exist-
2
M] (M =
1
7
(
(
−3675 ppm) compared to that observed at room temperature ence of dative Pt→M bonds which increases the electrophilicity
see Fig. 7). This behaviour is similar to that described of the Pt centre and lowers the energy of the HOMO, resulting
1
for compound 3 (see above). However, unlike compound 3, no in an increase of the energy gap of the MLCT transition.
Pt–Tl coupling was observed in the case of 4.
Solid state diffuse reflectance spectra of 1–4 are depicted in
Fig. 8. The mononuclear complexes 1 and 2 exhibit identical
profiles to those of the solution. In compounds 3 and 4 the
low-energy bands (432 nm (3); 420 and 443 nm (4)), also
present in 1 and 2 (solid state) and in solution, are greatly
enhanced when compared to their corresponding precursors.
1
These bands were attributed to MLCT [5d(Pt)→π*(CNC)] tran-
sitions but in the case of 3 and 4 they are clearly perturbed by
5
,51,61
the existence of Pt–Tl bonds,
especially in 3 that displays
rather short Pt–Tl separations (2.9086(5) Å). There are also
weaker shoulder bands at ca. 540 nm possibly due to π⋯π
interactions between the CNC fragments, as shown in the
X-ray structures (see Fig. S1, ESI‡). The absence of π⋯π con-
tacts between the CNC ligands in the crystal structure of 1
would be in agreement with this assignment.
1
95
Fig. 7
Pt NMR spectra of compounds: 4 + TlPF
6
exc. (a) and 2 (b) in
CD Cl
2
2
at variable temperature.
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Fig. 8 Normalized Diffuse Reflectance spectra of 1–4 in the solid state
at room temperature.
To shed some light on the nature of low-energy transitions,
time-dependent density functional theory (TD-DFT) calcu-
lations were carried out using the hybrid density functional
M06 for 2 and 4′ (4′ is a model complex derived from one of
t
the units “Pt(CNC)(CN Bu)Tl” that forms the crystal structure
in 4). The geometric parameters of the optimized structures
(Tables S2–S4 and Fig. S8–S10 in the ESI‡) are in good agree-
ment with the X-ray structural analysis data. Relevant data on
the calculated low-energy electronic transitions in the gas
phase and the frontier molecular orbital (MOs) involved in
these are listed in Tables S5 and S6 (ESI‡).
The calculated low-energy transitions are in close agree- Fig. 9 (a) Normalized UV-vis spectra in dichloromethane (10− M) at
4
2
98 K and calculated transitions of 2 and 4’ (bars). (b) The most impor-
tant transitions (≥85%) involved in lower energy excited calculated states
S1 and S3).
ment, within the accuracy of the method, with the experi-
mentally observed absorption maxima (Fig. 9). In both
complexes, the lowest lying absorption (S1) involves the
HOMO→LUMO transition [λ: 433.5 nm (98.5%), 2; 452.9 nm
(
1
(
97.6%), 4′]. The HOMO is mostly located on the CNC (74% absorption S3 arises from a metal perturbed intraligand [ IL,
8
8
2
–86% 4′) and the platinum centre (24% 2–14% 4′) whereas π–π* (CNC)] transition. When comparing the DFT analysis of
t
88
the LUMO is constructed from orbitals located on the CNC 2 with that of [Pt(ethyl-2,6-diphenylisonicotinate) (CN Bu)],
a
(
79% 2–62% 4′), the platinum centre (13% 2–16% 4′), the iso- few differences can be observed. The LUMO is mostly located
cyanide ligand (8% 2–8% 4′) and the thallium centre (14%, 4′). on the isonicotinic moiety of the CNC ligand with considerable
Thus, the formation of the Pt(II)–Tl(I) bond produces a signifi- participation of the ethyl acetate, an electron-withdrawing
cant change in the nature of the lower unoccupied orbitals group, which lowers the LUMO energy. As a consequence of
(
LUMO and L+1), which now have a significant contribution this, both calculated and experimental absorptions are shifted
from the thallium orbitals, as previously reported else- to lower energies in relation to those of 2, as indicated in the
5
4,56,64
where.
The S1 calculated absorptions are assigned to an UV-vis section.
1
intraligand [ IL, π–π* (CNC)] transition mixed with some
metal-to-ligand charge transfer [ MLCT, (5d(Pt)→π*(CNC)] CNC (92%), more precisely on the phenyl ring opposite to the
character for both 2 and 4′ but, moreover, in the case of 4′, Pt–Tl bond. The electronic transition S3 is associated with
with an additional contribution of a ligand-to-metal charge the same metal perturbed intraligand [ IL, π–π* (CNC)] transition
transfer [ LMM′CT, π (CNC)→(d/s(Pt,Tl)].
The occupied orbital H−1 in 4′ is also largely located on the
1
1
1
1
mixed with a ligand-to-metal [ LMM′CT, π (CNC)→(d/s (Pt,Tl)]
Nonetheless, as seen in Fig. 9, the most important low charge transfer. All these calculated results are in close
energy absorptions (S3) calculated for 2 and 4′ are 330.5 and agreement with former assignments made in the absorption
3
53.3 nm, respectively. They mainly involve the following tran- spectroscopy section.
sitions: H → L+1 (87.1%, 2) and H−1 → L (84.8%, 4′). The fron-
Hence, the formation of the Pt–Tl dative bond certainly
tier orbitals involved in them are very similar to those of S1. leads to the stabilization of the HOMO (2.95 eV), reducing the
The unoccupied orbital L+1 in 2 (see Fig. S11, ESI‡) is mostly weight of the Pt orbitals (14%, 4′ vs. 24%, 2), but it also pro-
based on the CNC ligand (97%). Therefore, in 2 the calculated duces an even greater stabilization in the LUMO (3.18 eV).
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Table 4 Emission data for complexes 1–4
Comp.
Media (T [K])
λem (λex) [nm]
τ [μs]
a
1
Solid (298)
Solid (77)
561, 585, 666max (441)
680max (441)
508max, 547, 591, 637 (460)
507max, 546, 586 (405)
538sh, 565, 600max (439)
637 (439)
635 (420)
476, 514, 560sh, 620max (336)
604 (441)
601 (401)
610 (407)
509, 546, 610max (340–460)
735 (550)
735 (508)
2.7 (680)
23.2 (508), 4 (637)
a22.6 (507), 21.0 (546), 18.6 (586)
b
CH
CH
2
Cl
Cl
2
(77)c
2
2
(77)
2
3
4
Solid (298)
Solid (77)
2.7 (637)
2.7 (635)
a39.5 (476)
b
CH
CH
2
Cl
Cl
2
(77)c
2
2
(77)
Solid (298)
Solid (77)
1.4 (601)
3.1 (610)
a30.9 (509); 5.0 (610)
b
CH
CH
2
Cl
Cl
2
(77)c
2
2
(77)
Solid (298)
Solid (77)
2.5 (735)
3.8 (615)
b
c
CH Cl
2 2
(77)
615, 690sh (<440)
6
7
15, 700 (450–500)
20 (>500)
3.4 (720)
46.7 (476)
CH Cl
2 2
(77)
476, 514, 558, 612max (336)
a
Too weak to be measured. 10−3 M. 10−5 M.
b
c
9
3,104
Nevertheless, the overall effect in the transition energy is small neutral complexes [Pt(CNC)L]
(
and [Pt(2,6-diphenyliso-
t
88
H–L gap: 3.83 eV, 4′ vs. 4.06 eV, 2) and not always nicotinate)(CN Bu)]. Hence, the emissive behaviour of the
accompanied by the expected hypsochromic shift, as observed mononuclear complexes 1 and 2 is correspondingly attributed
3
in the UV-vis spectra and in related examples found in the to ππ* excimeric emissions.
1
7,84
literature.
The heteropolynuclear complexes 3 and 4 display unstruc-
To further evaluate this Pt–Tl interaction and its impor- tured bands with the corresponding maxima at ca. 600 and
tance in the nature of the emission, the structure of the first 735 nm and with barely any changes in shape or energy upon
excited state T of 4′ was optimized (see Fig. S10 and Table S4 cooling to 77 K. However, the emissive behaviour (energy shift-
1
1 0
in the ESI‡). T shows a similar structure to that of the S state ings) of the Pt–Tl derivatives compared to their own precursors
but with significant differences: the Pt–Tl distance increased is totally different, as shown in Fig. 10. The emission in 3 is
from 3.062 Å (S ) to 3.146 Å (T ), and the CNC ligand deviates substantially blue shifted, whereas that in 4 is red shifted
0
1
slightly from planarity.
when compared to the corresponding starting materials 1 and
In addition, both NBO and Mayer bond order analyses were 2. In line with earlier published results of Pt→M dative
2
,3,22
carried out in the S0 and T1 states. In the ground state (S0) bonds,
there is substantial bonding interaction between the Pt–Tl which holds the thallium centre tightly between the Pt
atoms (bond order = 0.240), as shown in the image of H−5 with a rather short donor–acceptor Pt–Tl bond distance, would
Fig. S12, ESI‡). As mentioned above, this Pt–Tl interaction is induce a remarkable hypsochromic shift in the emission
significantly weakened in the first excited state (T ), showing a
it seems that the structural arrangement in 3,
3
core
(
1
bond order of 0.1365, which is in accordance with the longer
Pt–Tl distance with respect to the ground state (see above).
This also agrees with the slight Pt–Tl antibonding character of
the LUMO. Therefore, the Pt–Tl bond is expected to have a
certain contribution in the excited state and consequently in
emissive properties.
Emission spectroscopy. All complexes are photoluminescent
in the solid state and in glassy solutions of CH Cl at 77 K.
2
2
The corresponding emission data are shown in Table 4.
Solid state emissions of 1–4 are rather weak at room temp-
erature, but they turn out to be brightly emissive upon cooling
to 77 K. The mononuclear complexes 1 and 2 show very broad
and slightly structured bands at room temperature with
maxima at 666 and 600 nm respectively. These emissions
became less structured with reduced bandwidths and red-
shifted when cooled down to 77 K (see Fig. S13, ESI‡). With
regard to emission shape and energies along with their
Fig. 10 Normalized solid state emission spectra. Pictures of solid
respective lifetimes, these were comparable to those of the samples of 3 (left) and 4 (right) at 77 K under UV light.
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band. Unlike compound 3, the emission band in 4 seems to
come from a different emissive state. Considering the energy
and shape of the band, its lifetime and the close Pt⋯Tl, π⋯π
and Tl⋯π contacts found in the extended lattice of the crystal
structure, it seems reasonable to attribute the emission to an
excimeric transition.
2 2
Glassy solutions of 1 in CH Cl at 77 K display strongly
structured emissions with vibronic spacings that match the
skeletal vibrational frequencies of the CNC ligand at concen-
−
5
−3
trations ranging from 10 M up to 10 M (Fig. S14‡). On the
other hand, the emission profile of glassy solutions of 2 in
2 2
CH Cl shows a low-energy (LE) unstructured band with
maxima at ca. 630 nm regardless of the concentration
10 M–10 M). It is only in the diluted solutions (10−5 M)
−
5
−3
(
that an additional and extremely weak structured emission
appears at higher energies (HE; 476, 514 nm). The lifetime Fig. 12 Normalized excitation (dashed line) and emission (solid line)
spectra of 4.
measurements determined for the high energy (HE) fit one
rather long component (τ ∼ 21 µs (1); 39 µs (2)) whereas the
low-energy (LE) bands give short lifetimes (τ ∼ 4 µs (1); 2.7 µs
(
2)). Therefore, considering all these data, the excitation When exciting at λex < 360 nm, the emission comprises two
spectra and the good concordance with previous “Pt(CNC)” distinct bands, one strong low energy band with maxima at
1
7,88,93,101,104,125
studies,
it can be considered that the HE band, 610 nm and one structured high-energy band (509, 546 nm).
which is the predominant one in 1, comes from a metal per- Upon exciting at longer wavelengths (λex > 380 nm), the HE
3
turbed ILCT excited state involving the CNC ligand whilst the band becomes significantly less intense, being the one at
3
LE band, mainly observed in 2, is most probably due to ππ* 610 nm the predominant over the entire spectrum. The life-
excimeric transitions.
time measurements, the excitation and emission profiles of
In line with what has been reported in the DFT and UV-vis this HE band resemble those found in 1. In concentrated solu-
section, the emissions of the analogous derivatives with the tions (10− M) of 3, there is no evidence of this HE band. Both
substituted R-CNC ligand (2,6-diphenylisonicotinate, R = excitation and emission spectra show low energy bands that
3
8
8
COOEt) are substantially red-shifted in relation to those perfectly match those observed in the solid state and also the
recorded in compounds 1 and 2 whether in the solid state or a LE emission (610 nm) recorded in 10− M solution. Lifetime
5
rigid matrix.
measurements fit to a single exponential (λem 610 nm: 3.1 μs
In the heteropolynuclear compounds 3 and 4, the emissive (10 M) and 5 μs (10 M)) and are typical of phosphorescent
behaviour of glassy solutions is different from that observed in processes.
−
3
−5
the corresponding precursors (1 and 2); see Fig. 11 and 12.
Similarly to compound 3, the emission of 4 in CH Cl
2 2
The emission spectra of diluted solutions (10 M) of 3 are (10−5 M) at 77 K consists of two bands (see Fig. 12). In this
−5
slightly dependent on the excitation wavelength, see Fig. 11. case, regardless of the excitation wavelength, the spectrum
shows
a very intense low-energy emission centered at
ca. 612 nm and a HE structured emission that is barely notice-
able (HE; 476, 514 nm). However, upon increasing the concen-
tration to 10− M, the excitation and emission profiles become
wavelength-dependent, which once again suggests the pres-
ence of different emissive states. The emission spectra moni-
tored at λex < 440 nm show an unstructured band at 615 nm,
with a modest shoulder at 690 nm. Upon excitation with wave-
lengths between 450–500 nm, this incipient shoulder led to
the formation of a second unstructured band shifted to lower
energies (720 nm) that co-exists with the former one (see
3
Fig. S15, ESI‡). Finally, the emission spectra recorded at λex
>
500 nm only display this second band, which agrees well with
the solid state emission. Taking all this into account and also
the differences in the excitation spectra (see Fig. 12), it seems
plausible to propose two different emissive states associated
with excimers and/or aggregates based on the different degrees
of Pt⋯Tl interactions within the Pt–Tl moeities. Furthermore,
the structured HE bands that are extremely weak and only
Fig. 11 Normalized excitation (dashed line) and emission (solid line)
spectra of 3.
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noticeable in diluted solutions of 3 and 4 seem to be compar- Pt–Tl coupling. This fact could be due to the greater robust-
able to those of 1 and 2, since their lifetime measurements, ness of the Pt–Tl bonds for 3 than for 4, and that the trigonal
excitation and emission profiles are very much alike. Thus, the Pt
same ILCT (CNC) excited state is proposed for these
3
Tl disposition found in 3 is remarkably stable.
The DFT studies on compounds 2 and 4′ correlate well with
3
emissions.
Following a similar procedure to the
ments, an excess of TlPF
the UV-vis experiments. The formation of Pt–Tl dative bonds
Pt NMR experi- does not produce the expected blue-shift in the absorption
was added to solutions of 3 and 4. bands since not only the HOMO but also the LUMO undergo
1
95
6
The corresponding UV-vis and emission spectra were recorded, an energy stabilization, producing an almost unnoticeable
and no changes were observed; they exhibited the same bands overall effect. In the solid state, the emission of 3 is consider-
as those of 3 and 4 (see Fig. S16 and S17, ESI‡). Therefore, no ably shifted to higher energies whereas that of 4 is shifted to
other Pt–Tl species were detected either by NMR, UV-vis or lower energies when compared to the corresponding starting
photoluminescence spectroscopic techniques.
materials. The emissive behaviour of 3 and 4 in concentrated
According to all these results, it could be concluded that solutions is comparable to that observed in the solid state,
−3
the emissions of 3 and 4 in concentrated (10 M) solutions where the existence of the Pt–Tl bond was established by
−
5
and, in the case of 3, in diluted (10 M) solutions too, are ana- different techniques.
logous to those obtained in the solid state, where the Pt–Tl
bond existence was confirmed by several characterization and
1
95
spectroscopic techniques (X-ray diffraction, solid state
NMR, diffused reflectance).
Pt
Experimental
General considerations
1
00
A modification of the method reported in the literature was
used to prepare the starting material [Pt(CNC)(dmso)] (CNC =
Conclusions
The square planar Pt(II) complexes 1 and 2 have proved to be 2,6-diphenylpyridinate) (see below). Elemental analyses were
adequate precursors in the preparation of complexes contain- carried out with a Perkin-Elmer 2400 CHNS analyzer. IR
ing Pt→Tl dative bonds unsupported by any bridging ligand spectra were recorded on a Perkin-Elmer Spectrum 100 FT-IR
3 and 4). The solid state geometries of these clusters are strik- spectrometer (ATR in the range 250–4000 cm− ). Mass spectro-
1
(
ing, since the platinum moieties adopt a triangular disposition metry was performed with the Microflex matrix-assisted
that gives rise to a cavity in which the thallium centres are laser desorption ionization-time-of-flight (MALDI-TOF) Bruker
1
195
located. It seems that the size of this cavity is determined by or an Autoflex III MALDI-TOF Bruker instrument. H and Pt
1
the steric requirements of the ligand bonded in the “fourth” { H} NMR spectra were recorded on a Bruker AV-400 spectro-
1
coordination position of the platinum. The tht ligand is meter using the standard references: SiMe for H and
4
t
195
195
smaller and more flexible than the CN Bu and thus it is able to Na
2
PtCl
6
in D
2
O for the
Pt. Solid state
Pt NMR experi-
bend away. Hence the triangular cavity in 3 is only able to host ments were acquired using a Bruker AV-400 WB and were refer-
a Tl centre, resulting in a trigonal environment for it and the enced to Na PtCl . The crystalline samples of 1–4 were packed
2
6
formation of three Pt–Tl bonds involving a single Tl atom. All in 4 mm o.d. zirconium oxide rotors and were placed within a
three Pt–Tl distances are 2.9086(5) Å, the shortest reported so 4 mm MAS BB-H1 probe at 25 °C. Solid state NMR spectra of
far for a Pt(II)–Tl(I) bond unassisted by any bridging ligand or 1–4 were recorded at different spinning speeds: 5, 8 and
2
by pairing (PtTl) metallocycle systems. Furthermore, the size 12 kHz using the hpdec pulse program. Molar conductances
of the cavity in 4 allows three Tl atoms to be accommodated, were carried out on a Philips PW9509 conductimeter in
resulting again in three Pt–Tl bonds that are slightly longer acetone solution (5 × 10− M). Diffuse reflectance UV-vis
than in 3 (3.0143(3), 3.0488(3) and 3.0460(3) Å), but still (DRUV) spectra were recorded on a Jasco electron corporation
4
6
remarkably short. The presence of the η -Tl–arene interactions evolution V670 spectrophotometer equipped with a Praying
in 4 is also noteworthy since they are responsible for the integ- Mantis integrating sphere. The solid samples were homo-
rity of the (PtTl)
3
cluster.
geneously diluted with silica. The mixtures were placed in a
The NMR studies support the idea that the Pt–Tl bonds homemade cell equipped with a quartz window. Steady-state
persist in solution. The best evidence is obtained for 3 in photoluminescence spectra were recorded on a Jobin-Yvon
terms of a downfield shift of the signal and presence of Pt–Tl Horiba Fluorolog FL-3–11 Tau 3 spectrofluorimeter using band
1
95
1
coupling in its
2 2
Pt{ H} NMR spectra in CD Cl solution. In pathways of 3 nm for both excitation and emission. Phosphor-
the case of 4, only a less pronounced downfield shift was escence lifetimes were recorded with a Fluoromax phosphori-
observed. Nevertheless, it seems clear that these clusters dis- meter accessory containing a UV xenon flash tube with a flash
sociate in solution to give equilibrium mixtures of different rate between 0.05 and 25 Hz. Phase shift and modulation were
1
95
Pt/Tl species on the
can be tuned up by adding an excess of TlPF
the temperature, but in the case of 4 this is not enough to a nanoLED controller and the software DAS6. The nanoLED
Pt NMR time scale. These equilibria recorded over the frequency range of 0.1–100 MHz. Nano-
6
or by lowering second lifetimes were recorded with a Datastation HUB-B with
1
95
produce a greater downfield shift of the
Pt signal or a clear employed for lifetime measurements was of 483 nm with pulse
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Paper
Dalton Transactions
2
2
lengths of <1.4 ns. The lifetime data were fitted using the 167.3 (s, JC–Pt = 73.7, C8), 150.5 (s, JC–Pt = 47.1, C9), 140.4 (s,
2
3
Jobin-Yvon software package and the Origin Pro 8 program.
C7), 136.7 (s, J
= 44.7, C2), 130.9 (s, J
= 29.0, C3), 124.6
C–Pt
C–Pt
3
4
Preparation of [Pt(CNC)(dmso)]. Potassium tetrachloroplati- (s, JC–Pt = 26.4, C5), 124.3 (s, C4), 115.3 (s, JC–Pt = 37.4, C6),
nate (0.638 g, 1.540 mmol) previously pulverized was added to 40.6 (s, C-α-tht), 30.4 (s, C-β-tht) ppm.
1
95
1
Pt{ H} NMR
a solution of 2,6-diphenylpyridine (0.463 g, 2.000 mmol) in (85.679 MHz, CD Cl ): δ = −3914 (t, J = 264.4 Hz) (293 K),
2
2
Pt–N
95
1
1
glacial acetic acid (125 mL). The reaction mixture was stirred at −3901 (s) (193 K) ppm. Solid state
Pt{ H} NMR (85.6 MHz):
1
26 °C under an Ar atmosphere until the red platinum salt was δ = −3816 ppm. Mass spectra MALDI+ DIT: m/z = 513
+
no longer visible (2 days). The reaction mixture was filtered, [Pt(C H N)(C H S)H] .
yielding the product [Pt(CNC-H)(μ-Cl)]
1
7
11
4
8
t
2
as an insoluble yellow
Preparation of [Pt(CNC)(CN Bu)] (2). To a solution of
powder which was washed with water, MeOH and diethyl ether [Pt(CNC)(dmso)] (0.20 g, 0.398 mmol) in MeOH (20 mL) at
(0.644 g, 91%).
room temperature, 54.0 µL of tht (0.477 mmol, 20% excess)
This [Pt(CNC-H)(μ-Cl)]
2
(0.250 g, 0.271 mmol) was dissolved was added. After 4 days of stirring the solution was concen-
in hot dmso (6 mL) and the reaction was stirred at 100 °C for trated until ca. 2 mL. The yellow precipitate which appeared
min. The solution obtained was filtered through celite and was filtered off, washed with n-hexane (10 mL) and air dried
washed with hot dmso (110 °C). The solution was then allowed (0.169 g, 83%). Anal. found: C, 52.02; H, 3.90; N, 5.62. Calcd
5
−
1
to reach room temperature and was added 40 mL of H
2 20 2
O and for C22H N Pt: C, 52.07; H, 3.97; N, 5.52%. IR (νmax/cm ):
Na CO (0.040 g, 0.377 mmol). The resulting yellow suspen- 2164 s (NC), 1597m (NC), 1576w (NC), 1560w (NC), 1543w
2
3
(acetone) = 1.08 Ω− cm mol
Cl , 293 K): δ = 7.62 (2H, dd,
= 7.0 Hz, J
1
2
−1
. H NMR
1
sion was stirred for 1 h and then filtered off, washed with H
and re-dissolved in CH Cl . To this solution, MgSO and acti- (400.132 MHz, CD
vated carbon were added and the mixture was stirred for 32.1 Hz, J
min, after which it was filtered through celite and evaporated
to dryness. Diethyl ether (10 mL) was added to the solid, and (2H, d, JH6–H7 = 8.0 Hz, JPt–H6 = 7.9 Hz, H6), 7.19 (2H, ddd,
the resulting suspension was filtered off and air dried (0.204,
5%).
Preparation of [Pt(CNC)(tht)] (1). To a solution of [Pt(CNC)- H4), 1.69 (9H, s, H- BuCN) ppm. C{ H} NMR (100.624 MHz,
dmso)] (0.103 g, 0.205 mmol) in MeOH (30 mL) at room temp- CD Cl , 293 K): δ = 168.8 (s, J = 665.6, C1), 168.5 (s, C8),
erature, 36.2 µL of tht (0.410 mmol, 100% excess) was added. 150.4 (s, C9), 141.3 (s, C7), 139.8 (s, JC–Pt = 69.7, C2), 131.7 (s,
After 4 days of stirring the solution was concentrated until
2
O
(NC), 1205w. Λ
M
3
2
2
4
2
2
Pt–H
J =
3
4
= 0.8 Hz, H2), 7.61 (1H, t,
H2–H4
JH7–H6 = 8.0 Hz, H7), 7.44 (2H, d, JH5–H4 = 7.6 Hz, H5), 7.29
H2–H3
3
3
5
3
4
3
3
4
JH3–H4 = 7.3 Hz, J
= 7.0 Hz, J
= 1.2 Hz, H3), 7.07
H3–H2
H3–H5
3
3
4
7
(2H, ddd, JH4–H5 = 7.6 Hz, JH4–H3 = 7.3 Hz, JH4–H2 = 1.3 Hz,
t
13
1
(
2
2
C–Pt
2
3
3 or 4
3 or 4
J
C–Pt = 36.7, C3), 124.6 (s,
J
C–Pt = 26.4,
= 30.5, C6), 58.4 (s, CuN), 31.1 (s, C–Me3)
Pt{ H} NMR (85.679 MHz, CD Cl ): δ = −4051 (s)
2 2
JC–Pt = 24.0, C5
4
ca. 2 mL. The yellow precipitate which appeared was filtered y C4), 115.7 (s, J
C–Pt
1
95
1
off, washed with n-hexane (10 mL) and air dried (0.086 g, ppm.
2%). Anal. found: C, 49.01; H, 3.71; N, 2.85; S, 5.77. Calcd for (293 K), −4076 (s) (193 K) ppm. Solid state
C H NPtS: C, 49.21; H, 3.74; N, 2.73; S, 6.26%. IR (νmax/ (85.6 MHz): δ = −4020 ppm. Mass spectra MALDI+ DIT: m/z =
1
95
1
8
Pt{ H} NMR
2
1
−
19
1
+
+
cm ): 1598w (NC), 1575w (NC), 1561w (NC), 1542w (NC), 508 [Pt(C17
H
11N)(C
Preparation of [{Pt(CNC)(tht)}
H NMR (400.132 MHz, CD Cl , 293 K, see Scheme 2 for the H tion of 1 (0.100 g, 0.193 mmol) in CH Cl (20 mL) at room
5
H
9
N)H] , 452 [Pt(C17
H11N)(NC)H] .
−
1
2
−1
1
267w (SC), 1251w (SC). Λ
M
(acetone) = 2.64 Ω cm mol
.
3
Tl](PF ) (3). To a yellow solu-
6
1
2
2
2
2
3
numbering scheme): δ = 7.61 (1H, t, JH7–H6 = 8.0 Hz, H7), 7.52 temperature, TlPF
2H, dd, JPt–H = 21.6 Hz, JH2–H3 = 7.5 Hz, JH2–H4 = 1.3 Hz, tion turns orange and after 90 min of stirring the solution was
H2), 7.48 (2H, dd, J
2H, d, JH6–H7 = 8.0 Hz, JPt–H6 = 10.4 Hz, H6), 7.22 (2H, ddd, orange solid, and the resulting suspension was filtered off,
H3–H4 = 7.4 Hz, JH3–H2 = 7.5 Hz, JH3–H5 = 1.1 Hz, H3), 7.07 washed with n-hexane (10 mL) and air dried (0.110 g, 90%).
2H, ddd, J
H4), 3.56 (4H, t, JPt–Hα = 52.9 Hz, JHα–Hβ = 6.5 Hz, H-α-tht),
.16 (4H, t,
100.624 MHz, CD Cl , 293 K): δ = 169.0 (s, J
6
(0.023 g, 0.064 mmol) was added. The solu-
3
3
4
(
3
4
= 7.5 Hz, J
= 1.1 Hz, H5), 7.31 evaporated to dryness. Diethyl ether (10 mL) was added to the
H5–H4
H5–H3
3
4
(
3
3
4
J
3
3
4
(
= 7.4 Hz, J
= 7.5 Hz, J
= 1.3 Hz, Anal. found: C, 39.69; H, 3.04; N, 2.39; S, 4.91. Calcd for
C H F N PPt S Tl: C, 40.10; H, 3.04; N, 2.23; S, 5.10%. IR
63 57 6 3 3 3
JHβ–Hα = 6.5 Hz, H-β-tht) ppm. C{ H} NMR (νmax/cm ): 1596w (NC), 1580w (NC), 1559w ν(NC), 1542w
H4–H3
H4–H5
H4–H2
3
3
3
13
1
−1
2
(
+
+
= 714.4, C1), (NC), 1272w (SC), 1252w (SC), 833s (PF ), 555m (PF ). Λ
2
2
C–Pt
6 6 M
(
acetone) = 256.96 Ω− cm mol
1
2
−1
. H NMR (400.132 MHz,
, 293 K): δ = 7.72 (1H, t, JH7–H6 = 8.0 Hz, H7), 7.51 (2H,
= 1.1 Hz, H5), 7.38 (2H, d, J
.0 Hz, JPt–H6 = 9.7 Hz, H6), 7.15 (2H, ddd, JH4–H3 = 7.4 Hz,
H4–H5 = 7.6 Hz, JH4–H2 = 1.1 Hz, H4), 7.05 (2H, ddd, JH3–H4
= 1.1 Hz, H3), 6.86 (2H, dd,
Pt–H = 19.7 Hz, JH2–H3 = 7.3 Hz, JH2–H4 = 1.1, H2), 3.36 (4H, t,
Pt–H = 54.5 Hz, JHα–Hβ = 6.2, H-α-tht), 1.98 (4H, b, H-β-tht)
ppm. C{ H} NMR (100.624 MHz, CD Cl , 293 K): δ = 167.2 (s,
C–Pt = 46.0, C9), 140.9 (s, C7),
38.4 (s, JC–Pt = 42.2, C2), 131.7 (s, JC–Pt = 28.7, C3), 125.2 (s,
1
3
CD
dd, J
2
Cl
2
3
4
3
= 7.6 Hz, J
=
H5–H4
H5–H3
H6–H7
4
3
8
3
4
3
J
=
3
4
7
.4 Hz, J
= 7.3 Hz, J
H3–H2
H3–H5
3
3
4
J
3
3
J
1
3
1
2
2
2
C8), 165.0 (s, C1), 150.1 (s,
J
2
3
3
1
Scheme 2
H
-2)
numbering scheme for the ligand C,N,C-2,6-
or 4
3 or 4
4
NC
5
H
3
(C
6
H
4
2
.
JC–Pt = 27.9,
JC–Pt = 24.6, C5 and C4), 116.0 (s, J
=
C–Pt
10838 | Dalton Trans., 2014, 43, 10828–10843
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Paper
1
9
195
1
3
7.6, C6), 43.1 (s, C-α-tht), 30.5 (s, C-β-tht) ppm. F NMR CD
2
Cl
2
): δ = −144.1 (sept, JP–F = 716.1 Hz) ppm. Pt{ H} NMR
(
376.489 MHz, CD Cl ): δ = -73.0 (d, J
= 711.6 Hz) ppm. (85.679 MHz, CD Cl ): δ = −3795 (s) (293 K) ppm. Mass spectra
2
2
F–P
2
2
3
1
+
P NMR (161.992 MHz, CD
11.6 Hz) ppm. Solid state
2
Cl
2
): δ = −144.4 (sept, JP–F
=
MALDI+ DIT: m/z
=
711 [Pt(C17
H
H
11N)(C
11N)(C
5
H
H
9
N)Tl] , 655
N)H] , 452
1
95
1
+
+
7
−
Pt{ H} NMR (85.6 MHz): δ = [Pt(C17
H
11N)(NCH)Tl] , 508 [Pt(C17
5
9
+
3088 (d, JPt–Tl = 9.0 kHz) ppm. Mass spectra MALDI+ DIT: [Pt(C H N)(NC)H] .
17 11
+
+
m/z = 1477 [TlPt
3
(C17
H
11N)
3
] , 1053 [TlPt
2
(C17
H
11N)
2
] , 849
+
+
X-ray structure determinations
Crystal data and other details of the structure analyses are pre-
(4). To a sented in Table 5. Suitable crystals for X-ray diffraction studies
Cl (20 mL) were obtained by slow diffusion of n-hexane into concentrated
[Pt
2
(C17
H
11N)
2
] , 717 [TlPt(C17
H
11N)(C H S)] , 513 [Pt-
4 8
+
(
C H N)(C H S)H] .
17 11 4 8
t
Preparation of [{PtTl(C17
H
11N)(CN Bu)}
3
](PF
6
)
3
yellow solution of 2 (0.100 g, 0.199 mmol) in CH
2
2
at room temperature, TlPF (0.070 g, 0.199 mmol) was added. solutions of the complexes in 3 mL of Me CO (1) or CH Cl (3,
6
2
2
2
After 60 min of stirring the solution was concentrated until 4). Crystals were mounted at the end of quartz fibres. The radi-
ca. 2 mL. The orange precipitate which appeared was filtered ation used in all cases was graphite monochromated MoKα (λ =
off, washed with n-hexane (10 mL) and air dried (0.129 g, 0.71073 Å). X-ray intensity data were collected on an Oxford
7
C
2
1
6%). Anal. found: C, 30.45; H, 2.07; N, 3.46. Calcd for Diffraction Xcalibur diffractometer. The diffraction frames
H F N PPtTl: C, 30.84; H, 2.07; N, 3.46%. IR (νmax/cm ): were integrated and corrected from absorption by using the
22 20 6 2
−1
1
27
168m (NC), 1598w (NC), 1577w (NC), 1560w (NC), 1543w (NC), CrysAlis RED program.
The structures were solved by the
+
+
−1
2
6 6 M
197w, 831s (PF ), 554s (PF ). Λ (acetone) = 231.65 Ω cm
Patterson and Fourier methods and refined by full-matrix least
, 293 K): δ = 7.63 (1H, t, squares on F with SHELXL-97.
were assigned anisotropic displacement parameters and
.2 Hz, JH2–H4 = 1.3 Hz, H2), 7.44 (2H, dd, JH5–H4 = 7.6 Hz, refined without positional constraints, except as noted below.
−
1
1
2
128
mol . H NMR (400.132 MHz, CD
2
Cl
2
All non-hydrogen atoms
3
3
3
JH7–H6 = 8.0 Hz, H7), 7.60 (2H, dd, J
= 30.9 Hz, J
=
H2–H3
Pt–H
4
3
7
4
3
4
J
H5–H3 = 1.2 Hz, H5), 7.29 (2H, d, JH6–H7 = 8.0 Hz, JPt–H6
=
All hydrogen atoms were constrained to idealized geometries
= 7.2 Hz, and assigned isotropic displacement parameters equal to 1.2
H3–H2
3
3
7
.8 Hz, H6), 7.20 (2H, ddd, J
= 7.5 Hz, J
H3–H4
4
3
3
J
H3–H5 = 1.2 Hz, H3), 7.09 (2H, ddd, JH4–H5 = 7.6 Hz, JH4–H3
=
times the Uiso values of their attached parent atoms (1.5 times
.5 Hz, JH4–H2 = 1.3 Hz, H3), 1.67 (9H, s, H- BuCN) ppm. for the methyl hydrogen atoms). For 1·0.5Me CO, the acetone
C{ H} NMR (100.624 MHz, CD Cl , 293 K): δ = 168.1 (s, C8), solvent molecule is disordered over two positions which were
4
t
7
2
1
3
1
2
2
1
J
66.6 (s, JC–Pt = 710.1, C1), 150.3 (s, C9), 141.7 (s, C7), 139.2 (s, refined with the same occupancy. In the structure of 3, the
2
C–Pt = 66.7, C2), 132.1 (s, JC–Pt = 36.1, C3), 125.4 (s, C4), 125.1 axial fluorine atoms of the PF6− anion are disordered over two
3
3
4
(s, J
= 24.7, C5), 116.1 (s, J
= 30.7, C6), 58.8 (s, CuN), positions which were refined with the same occupancy. In the
C–Pt
C–Pt
1
9
3
−
0.9 (s, C–Me
3
) ppm. F NMR (376.489 MHz, CD
2
2
6
Cl ): δ = structure of 4, the fluorine atoms of one of the PF anions are
3
1
70.0 (d, JF–P = 716.1 Hz) ppm. P NMR (161.992 MHz, badly disordered over three sets of positions, which were
Table 5 Crystal data and structure refinement for complexes [Pt(CNC)(tht)]·0.5Me
2 2 3 6
CO (1·0.5Me CO), [{Pt(CNC)(tht)} Tl](PF ) (3) and [{PtTl(C17H11N)-
t
(
3 6 3 6 6 14
CN Bu)} ](PF ) ·1.5n-C H14 (4·1.5n-C H )
1
·0.5Me
2
CO
3
6 14
4·1.5n-C H
CCDC number
Formula
966072
19NPtS·0.5Me
966073
987896
C
21
H
2
CO
C
63 57
H F
6 3 3
N PPt S
3
Tl
C
66 60
H F
18
6 3
N P Pt
Tl
3 3
6 14
·1.5n-C H
M
541.56
Monoclinic
C2/c
1886.91
Hexagonal
P ˉ6 2c
2699.75
Monoclinic
C2/c
Crystal system
Space group
a/Å
b/Å
c/Å
β/°
V/Å
T/K
42.5046(14)
9.9891(3)
9.0748(3)
101.875(3)
3770.6(2)
100(1)
15.6681(8)
15.6681(8)
13.2867(8)
90
2824.8(3)
100(1)
2
31.2557(7)
22.8837(3)
24.1734(3)
107.275(2)
16 510.0(5)
100(1)
3
Z
8
8
−
1
M(Mo-Kα)/mm
7.562
1.908
10.453
2.218
11.042
2.172
−
3
D
c
/g cm
F(000)
2096
8.4–57.8
23 519
1776
10 056
8.3–51.0
83 127
2θ range/°
8.5–52.0
14 729
1939
No. of data collected
No. of unique data
4560
15 322
R
R
R
int
0.0398
0.0364
0.0421
a
a
1
, wR
, wR
2
(I > 2σ(I))
b(all data)
0.0182, 0.0456
0.0188, 0.0460
1.071
0.0331, 0.0889
0.0341, 0.0984
1.043
0.0293, 0.0686
0.0373, 0.0725
1.074
1
2
2
GOF (F )
Absolute structure parameter
—
0.02(2)
—
a
2
2 2
2 2 1/2
b
2
2 2
1/2
R
1
= ∑(|F
o
c o
| − |F |)/∑|F |. wR
2
= [∑w (F
o
− F
c
) /∑w(F
o
) ]
.
Goodness-of-fit = [∑w (F
o
– F
c
) /(nobs − nparam)]
.
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Paper
Dalton Transactions
refined with partial occupancy 0.5/0.3/0.2. A common set of
anisotropic thermal parameters was used for the equivalent
fluorine atoms of each set. One of the n-hexane moieties was
refined with partial occupancy 0.5 and their C–C distances
constrained to reasonable values. A common set of anisotropic
thermal parameters was used for all the C atoms of this mole-
cule. Another n-hexane unit was disordered in such a way that
the γ carbon atom lies on an inversion centre, and thus the
external α methyl carbon atom is disordered over two positions
5 L. R. Falvello, J. Forniés, R. Garde, A. García, E. Lalinde,
M. T. Moreno, A. Steiner, M. Tomás and I. Usón, Inorg.
Chem., 2006, 45, 2543–2552.
6 J. R. Berenguer, A. Díez, J. Fernández, J. Forniés, A. García,
B. Gil, E. Lalinde and M. T. Moreno, Inorg. Chem., 2008,
47, 7703–7716.
7 L. R. Falvello, J. Forniés, A. Martín, V. Sicilia and
P. Villarroya, Organometallics, 2002, 21, 4604–
4610.
(
0.5/0.5). A common set of anisotropic thermal parameters was
8 E. Alonso, J. Forniés, C. Fortuño, A. Martín and
A. G. Orpen, Organometallics, 2003, 22, 5011–5019.
9 F. D. Rochon and R. Melanson, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1988, 44, 474–477.
used for all the C atoms of this molecule. Restraints in the geo-
metry of the PF
refinement of these models against F converged to final
−
6
anion were used. Full-matrix least-squares
2
residual indices given in Table 5.
10 J. Forniés, S. Fuertes, A. Martín, V. Sicilia, B. Gil and
E. Lalinde, Dalton Trans., 2009, 2224–2234.
Computational details
11 J. M. Casas, J. Forniés, S. Fuertes, A. Martín and V. Sicilia,
Organometallics, 2007, 26, 1674–1685.
12 L. R. Falvello, J. Forniés, C. Fortuño, F. Durán and
A. Martín, Organometallics, 2002, 21, 2226–2234.
Density functional calculations were performed using the
1
29
130
M06
hybrid functional under the Gaussian 09 package.
1
31
The SDD pseudopotential and the associated basis set
were
1
1
1
3 I. Ara, L. R. Falvello, J. Forniés, J. Gómez, E. Lalinde,
R. I. Merino and I. Usón, J. Organomet. Chem., 2002, 663,
used for the platinum and thallium atoms and the 6-31G-
1
32,133
(d)
basis set was used for all other atoms. Geometry
284–288.
optimisations were performed in the gas phase without sym-
metry restrictions, using initial coordinates derived from X-ray
data. Atomic coordinates (x, y, z) for the optimized structures
are shown in Tables S2–S4 (see ESI‡). The time-dependent
density-functional (TD-DFT) calculations were also carried out
using the Gaussian 09 package. Mulliken population, Natural
4 L. R. Falvello, J. Forniés, E. Lalinde, B. Menjón,
M. A. Garcia Monforte, M. T. Moreno and M. Tomás,
Chem. Commun., 2007, 3838–3840.
5 T. Yamaguchi, F. Yamazaki and T. Ito, J. Am. Chem. Soc.,
2001, 123, 743–744.
1
34
135
16 J. Forniés, S. Ibáñez, E. Lalinde, A. Martín, M. T. Moreno
and A. C. Tsipis, Dalton Trans., 2012, 41, 3439–3451.
17 S. Fuertes, C. H. Woodall, P. R. Raithby and V. Sicilia,
Organometallics, 2012, 31, 4228–4240.
Bond Orbital (NBO) and Mayer bond order analyses were
carried out using the Gaussian 09 package for interpretation
1
36
137
purposes. Molekel and ChemissianLab program packages
were used for the analysis and graphical representation of
molecular structures and orbitals.
1
1
2
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