Structural basis for unusually long wavelength charge transfer transitions in complexes [MCl(ECH2CH2NME2)(PR3)] (E = Te, Se; M = Pt, Pd): Experimental results and TD-DFT calculations

Article abstract of DOI:10.1021/ic011210v

A series of new complexes, the blue compounds [PdCl(TeCH₂CH₂NMe₂)(PR₃)] (PR₃ = PEt₃, PPrⁿ₃, PBUⁿ₃, PMe₂Ph, PMePh₂, PPh₃, PTol₃) and the red [PtCl(TeCH₂CH₂NMe₂)(PR₃)] (PR₃ = PMe₂Ph, PMePh₂), were synthesized and studied spectroscopically (¹H and ³¹P NMR, UV/vis) and by cyclic voltammetry. The structures of [PdCl(TeCH₂-CH₂NMe₂) (PPrⁿ₃)] (2b) [PdCl(TeCH₂CH₂NMe₂)(PMePh₂)] (2e), [PtCl(TeCH₂CH₂NMe₂)(PMePh₂)] (2i), and the related [PtCl(SeCH₂CH₂NMe₂)(PEt₃)] (3) were determined crystallographically, revealing a typical pattern of trans-positioned neutral N and P donor atoms in an approximately square planar setting. The molecules 2b, 2e, and 2i were calculated by TD-DFT methodology to understand the origin of the weak (ε ≈ 200 M^-1 cm^-1) long-wavelength bands at about 600 nm for Pd/Te complexes such as 2b or 2e, at ca. 460 nm for Pt/Te systems such as 2i, and at about 405 nm for Pt/Se analogues such as 3. These transitions are identified as charge transfer transitions from the selenolato or tellurolato centers to unoccupied orbitals involving mainly the phosphine coligands for the Pt^II compounds and more delocalized MOs for the Pd^II analogues. Calculations and electrochemical data were used to rationalize the effects of metal and chalcogen variation.

Full text of DOI:10.1021/ic011210v

Inorg. Chem. 2002, 41, 2864−2870
Structural Basis for Unusually Long Wavelength Charge Transfer
Transitions in Complexes [MCl(ECH CH NMe2)(PR )] (E ) Te, Se; M )
2
2
3
Pt, Pd): Experimental Results and TD-DFT Calculations
,†
,‡
Sandip Dey,† Vimal K. Jain,* Axel Kno1dler,‡ Axel Klein,‡ Wolfgang Kaim,* and Stanislav Za´lisˇ§
NoVel Materials and Structural Chemistry DiVision, Bhabha Atomic Research Centre,
Trombay, Mumbai 400085, India, Institut fu¨r Anorganische Chemie, UniVersita¨t Stuttgart,
Pfaffenwaldring 55, D-70550 Stuttgart, Germany, and J. HeyroVsky Institute of Physical
Chemistry, Academy of Sciences of the Czech Republic, DolejsˇkoVa 3,
CZ-18223 Prague, Czech Republic
Received November 28, 2001
A series of new complexes, the blue compounds [PdCl(TeCH CH NMe2)(PR )] (PR ) PEt3, PPrn3, PBun3, PMe2Ph,
2
2
3
3
PMePh2, PPh3, PTol3) and the red [PtCl(TeCH CH NMe2)(PR )] (PR ) PMe2Ph, PMePh2), were synthesized and
2
2
3
3
studied spectroscopically (1H and 31P NMR, UV/vis) and by cyclic voltammetry. The structures of [PdCl(TeCH -
2
CH NMe2)(PPrn3)] (2b) [PdCl(TeCH CH NMe2)(PMePh2)] (2e), [PtCl(TeCH CH NMe2)(PMePh2)] (2i), and the related
2
2
2
2
2
[PtCl(SeCH CH NMe2)(PEt3)] (3) were determined crystallographically, revealing a typical pattern of trans-positioned
2
2
neutral N and P donor atoms in an approximately square planar setting. The molecules 2b, 2e, and 2i were
calculated by TD-DFT methodology to understand the origin of the weak (ꢀ ≈ 200 M-1 cm-1) long-wavelength
bands at about 600 nm for Pd/Te complexes such as 2b or 2e, at ca. 460 nm for Pt/Te systems such as 2i, and
at about 405 nm for Pt/Se analogues such as 3. These transitions are identified as charge transfer transitions from
the selenolato or tellurolato centers to unoccupied orbitals involving mainly the phosphine coligands for the PtII
II
compounds and more delocalized MOs for the Pd analogues. Calculations and electrochemical data were used
to rationalize the effects of metal and chalcogen variation.
Introduction
been reviewed recently.2d In this work we present a study
which involves PdII- or PtII-bound selenolate or tellurolate
donors and triorganophosphines as acceptors in complexes
[MCl(ECH2CH2NMe2)(PR3)] (E ) Se, Te; M ) Pd, Pt). This
combination of heavier elements for main group donor,
acceptor, and transition metal mediator poses a formidable
challenge for quantum chemical calculations which we
sought to interpret the unusual long-wavelength absorptions
in a more quantitative way; corresponding methods such as
relativistic time-dependent density functional theory (TD-
DFT) have only recently become applicable to such large
systems containing heavy elements.3
Metal-mediated interaction between coordinated ligands
is an important aspect of coordination chemistry. As an
example, the charge transfer interactions between metal-
bound donor and acceptor centers have been recognized and
described qualitatively in planar complexes of group 10
metals with thiolato donors and R-diimine acceptors.1,2a-c
The possible function of organophosphines as acceptor
components for charge transfer transitions in complexes has
* Authors to whom correspondence should be addressed. E-mail:
kaim@iac.uni-stuttgart.de (W.K.); jainvk@apsara.barc.ernet.in (V.K.J.).
† Bhabha Atomic Research Centre.
Based on the crystallographically determined structures
‡ Universita¨t Stuttgart.
of compounds [PdCl(TeCH2CH2NMe2)(PPrn )] (2b), [Pd-
§ Heyrovsky Institute.
3
(1) (a) Paw, W.; Lachicotte, R. J.; Eisenberg, R. Inorg. Chem. 1998, 37,
4139. (b) Cummings, S. D.; Eisenberg, R. J. Am. Chem. Soc. 1996,
118, 1949. (c) Connick, W. B.; Gray, H. B. J. Am. Chem. Soc. 1997,
119, 11620.
(2) (a) Vogler, A.; Kunkely, H. Top. Curr. Chem. 1990, 158, 1. (b)
Kunkely, H.; Vogler, A. J. Organomet. Chem. 1993, 453, 269. (c)
Kunkely, H.; Vogler, A. Inorg. Chim. Acta 1997, 264, 305. (d) Vogler,
A.; Kunkely, H. Coord. Chem. ReV., in press.
Cl(TeCH2CH2NMe2)(PMePh2)] (2e), and [PtCl(TeCH2CH2-
NMe2)(PMePh2)] (2i) we present TD-DFT calculations and
electrochemical measurements to understand the conspicuous
(3) Rosa, A.; Baerends, E. J.; van Gisbergen, S. J. A.; van Lenthe, E.;
Groeneveld, J. A.; Snijders, J. G. J. Am. Chem. Soc. 1999, 121, 10356.
2864 Inorganic Chemistry, Vol. 41, No. 11, 2002
10.1021/ic011210v CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/07/2002

Long-WaWelength Charge Transfer Transitions
and the residue was extracted with hexane (3 × 10 cm3). The
extracts were passed through a Florisil column to yield a blue
solution, which was concentrated and kept at -4 °C to yield air-
sensitive blue crystals in 60% yield (182 mg). The other palladium
and platinum complexes 2b-i were prepared in an analogous
manner. 2a: Anal. Calcd for C10H25ClNPdTe: C, 26.1; H, 5.5; N,
3.1. Found: C, 25.5; H, 5.2; N, 3.1. 1H NMR (CDCl3): δ 1.16 (td,
17.4 Hz (d), 7.6 Hz (t); PCH2Me); 1.83-1.94 (m, PCH2); 2.62 (d,
2.8 Hz, NMe2); 2.80 (t, 6.0 Hz, TeCH2); 3.49 (t, 5.0 Hz, NCH2).
31P{1H} NMR (CDCl3): δ 26.6 (s).
colors of the complexes. The comparison with corresponding
selenolato systems4a such as the now structurally character-
ized [PtCl(SeCH2CH2NMe2)(PEt3)] (3) serves to further
elucidate the electronic structures of these compounds.
Experimental Section
Materials and Instrumentation. All syntheses were carried out
under high-purity nitrogen in dry and distilled analytical grade
solvents. Tellurium (99.99%), tertiary phosphines (Strem Chemi-
cals), and Me2NCH2CH2Cl‚HCl were obtained from commercial
sources. The complexes Na2PdCl4, [M2Cl2(µ-Cl)2(PR3)2] (PR3 )
PEt3, PPrn , PBun , PMe2Ph, PMePh2, PPh3, or PTol3, Tol )
[PdCl(TeCH2CH2NMe2)(PPrn )] (2b): recrystallized from hex-
3
ane in 70% yield, mp 81 °C. Anal. Calcd for C13H3ClNPPdTe: C,
3
3
1
p-tolyl),4b and [PtCl(SeCH2CH2NMe2)(PEt3)] (3) were prepared
according to literature methods. Melting points were determined
in capillary tubes and are uncorrected. Elemental analyses were
31.1; H, 6.2; N, 2.8. Found: C, 31.5; H, 6.4; N, 2.7. H NMR
(CDCl3): δ 1.02 (t, 7.2 Hz, PCCMe); 1.53-1.84 (m, PCH2CH2-);
2.57 (d, 2.8 Hz, NMe2); 2.77 (t, 6.0 Hz, TeCH2); 3.46 (t, 6.0 Hz,
NCH2). 31P{1H} NMR (acetone-d6): δ 16.7 (s).
1
carried out by the Analytical Chemistry Division of BARC. H,
[PdCl(TeCH2CH2NMe2)(PBun )] (2c): recrystallized from hex-
13C{1H}, and 31P{1H} NMR spectra were recorded on a Bruker
DPX-300 NMR spectrometer operating at 300, 75.47, and 121.49
MHz, respectively. Chemical shifts are relative to internal solvent
peaks for 1H and 13C NMR resonances and to external 85% H3PO4
for 31P NMR signals. UV/vis absorption spectra were recorded in
CH2Cl2 on a Bruins Instruments Omega 10 spectrophotometer.
Cyclic voltammetry was carried at a 100 mV/s scan rate in
dichloromethane/0.1 M Bu4NPF6 using a three-electrode configu-
ration (glassy carbon working electrode, Pt counter electrode, Ag/
AgCl reference) and a PAR 273 potentiostat and function generator.
The ferrocene/ferrocenium couple served as internal reference.
All spectroscopic data of compounds 2a-i were obtained for
freshly prepared solutions; the colors of the solutions change (within
ca. 1 h for palladium complexes) when left at room temperature.
This behavior of tellurolate complexes of Pd or Pt is not uncom-
mon.5
3
ane in 74% yield. Anal. Calcd for C16H37ClNPPdTe: C, 35.3; H,
6.9; N, 2.6. Found: C, 35.5; H, 7.0; N, 2.5. 1H NMR (acetone-d6):
δ 0.93 (t, 7.2 Hz, PCCCMe); 1.41-1.90 (m, PCH2CH2CH2-); 2.57
(d, 2.8 Hz, NMe2); 2.78 (t, 3.0 Hz, TeCH2); 3.50 (m, NCH2). 31P-
{1H} NMR (acetone-d6): δ 18.1 (s).
[PdCl(TeCH2CH2NMe2)(PMe2Ph)] (2d): recrystallized from
CH2Cl2-Me2CO in 65% yield, mp 132 °C. Anal. Calcd for C12H21-
ClNPPdTe: C, 30.0; H, 4.4; N, 2.9. Found: C, 29.5; H, 3.9; N,
1
2.6. H NMR (CDCl3): δ 1.91 (d, 11.4 Hz, PMe2); 2.62 (d, 2.8
Hz, NMe2); 2.71 (br, TeCH2); 3.61 (t, 5.0 Hz, NCH2); 7.41 (m,
Ph), 7.62 (m, Ph). 31P{1H} NMR (CDCl3): δ -6.1 (s).
[PdCl(TeCH2CH2NMe2)(PMePh2)] (2e): recrystallized from
CH2Cl2-Me2CO in 58% yield, mp 172 °C. Anal. Calcd for C17H23-
ClNPPdTe: C, 37.7; H, 4.3; N, 2.6. Found: C, 37.3; H, 4.3; N,
2.4. 1H NMR (CDCl3): δ 2.26 (d, 11.4 Hz, PMe); 2.67 (merged in
NMe2 resonance, TeCH2); 2.68 (d, 2.8 Hz, NMe2); 3.73 (t, 5.0 Hz,
NCH2); 7.40 (m, Ph), 7.63 (m, Ph). 31P{1H} NMR (CDCl3): δ
8.7 (s).
[PdCl(TeCH2CH2NMe2)(PPh3)] (2f): (i) recrystallized from
CH2Cl2-Me2CO in 52% yield, mp 154 °C dec. Anal. Calcd for
C22H25ClNPPdTe: C, 43.7; H, 4.2; N, 2.3. Found: C, 42.9; H, 4.3;
N, 2.1. 1H NMR (CDCl3): δ 2.69 (merged in NMe2 protons,
TeCH2); 2.74 (d, 2.8 Hz, NMe2); 3.84 (t, 5.0 Hz, NCH2); 7.25-
7.35 (m, Ph), 7.80-7.85 (m, Ph). 31P{1H} NMR: δ 21.9 (s). (ii)
Solid PPh3 (330 mg, 1.26 mmol) was added to an acetone
suspension of (30 cm3) of 1 (428 mg, 1.25 mmol), and the mixture
was stirred for 3 h under N2. The green solution was filtered, and
the filtrate was dried in vacuo to give a greenish yellow solid. The
solid was washed with hexane, diethyl ether, and acetone to remove
unreacted PPh3 and recrystallized from dichloromethane-acetone
(yield 498 mg, 52%). Analytical and spectroscopic data are similar
to those of the sample prepared via route i.
Syntheses. (Me2NCH2CH2Te)2. Bis(2-dimethylaminoethyl)di-
telluride was prepared via the general method reported by Li et
al.,6 involving the reduction of Te powder with PhNHNH2 in DMF,
followed by treatment with Me2NCH2CH2Cl. The red, air- and
moisture-sensitive liquid was distilled in vacuo (110-118 °C, 0.01
mmHg). 1H NMR (CDCl3): δ 2.25 (s, 6H, NMe2); 2.56 (t, 7.4 Hz,
2H, SeCH2) and 3.27 (t, 7.4 Hz, 2H, NCH2).7 13C{1H} NMR
(CDCl3): δ 5.3 (s, TeCH2); 44.9 (s, NMe2); 62.0 (s, NCH2).
[PdCl(TeCH2CH2NMe2)]n (1). Solid Na2PdCl4 (1.86 g, 6.32
mmol) was added to a stirred methanolic solution of (Me2NCH2-
CH2Te)2 (1.26 g, 3.15 mmol) at room temperature, whereupon a
brownish yellow solid precipitated. The mixture was stirred for 4
h. The solid was washed with methanol, water, acetone, and diethyl
ether and dried in vacuo (yield: 1.51 g, 70%). It was recrystallized
from CH2Cl2 as a brown solid (370 mg, 25%); mp >180 °C dec.
Anal. Calcd for C4H10ClNPdTe: C, 14.0; H, 3.0; N, 4.1. Found:
C, 13.5; H, 2.6; N, 4.5.
[PdCl(TeCH2CH2NMe2)(PEt3)] (2a). To a methanolic solution
(10 cm3) of NaTeCH2CH2NMe2 as prepared from (Me2NCH2CH2-
Te)2 (194 mg, 0.33 mmol) and NaBH4 (26 mg, 0.68 mmol) was
added an acetone suspension (25 cm3) of [Pd2Cl2(µ-Cl)2(PEt3)2]
(194 mg, 0.33 mmol); the reaction mixture was then stirred for 3
h at room temperature. The solvents were evaporated in vacuo,
[PdCl(TeCH2CH2NMe2)(PTol3)] (2g): prepared similarly to 2f,
method ii, and recrystallized from acetone-hexane in 56% yield,
mp 108 °C. Anal. Calcd for C25H31ClNPPdTe: C, 46.5; H, 4.8; N,
2.2. Found: C, 44.8; H, 5.1; N, 1.7. 1H NMR (CDCl3): δ 2.68 (t,
merged with NMe2 protons, TeCH2); 2.72 (d, 2.8 Hz, NMe2); 3.78
(t, 5.0 Hz, NCH2); 7.15 (d, 7.5 Hz, C6H4), 7.62 (d, 7.5 Hz, C6H4).
31P{1H} NMR (CDCl3): δ 19.8 (s).
(4) (a) Dey, S.; Jain, V. K.; Knoedler, A.; Kaim, W.; Zalis, S. Eur. J.
Inorg. Chem. 2001, 2965. (b) Dey, S.; Jain, V. K.; Varghese, B. J.
Organomet. Chem. 2001, 623, 48.
(5) (a) Jain, V. K.; Kannan, S. J. Organomet. Chem. 1991, 418, 349. (b)
Kannan, S. Ph.D. Thesis, Mumbai University, 1992.
(6) Li, J. Q.; Bao, W. L.; Lue, P.; Zhou, X. Synth. Commun. 1996, 21,
799.
[PtCl(TeCH2CH2NMe2)(PMe2Ph)] (2h): recrystallized from
CH2Cl2-Me2CO in 68% yield, mp 148 °C. Anal. Calcd for C12H21-
ClNPPtTe: C, 25.4; H, 3.7; N, 2.5. Found: C, 25.4; H, 3.7; N,
2.5. 1H NMR (CDCl3): δ 1.92 (d, 11.3 Hz, 3J(Pt-H) 34 Hz, PMe2);
3
2.29 (t, 6.0 Hz, TeCH2); 2.74 (d, 2.8 Hz, with 14.0 Hz J(Pt-H),
NMe2); 3.36 (t, 6.0 Hz, NCH2); 7.38 (m, Ph), 7.67 (m, Ph). 31P-
(7) Srivastava, V.; Batheja, R.; Singh, A. K. J. Organomet. Chem. 1994,
484, 93.
1
{1H} NMR (CDCl3): δ -26.5, J(195Pt-31P) 3382 Hz.
Inorganic Chemistry, Vol. 41, No. 11, 2002 2865

Dey et al.
Table 1. Crystallographic and Structure Refinement Data of Complexes [MCl(ECH2CH2NMe2)(PR3)]
M/E/PR3
Pd/Te/PPrn3 (2b)
Pd/Te/PMePh2 (2e)
Pt/Te/PMePh2 (2i)
Pt/Se/PEt3 (3)
chem formula
fw
C13H31ClNPPdTe
501.81
C17H23ClNPPdTe
541.78
C17H23ClNPPtTe
630.47
C10H25ClNPtSe
499.78
cryst size (mm)
T/K
0.5 × 0.3 × 0.3
0.3 × 0.3 × 0.2
0.1 × 0.1 × 0.05
0.1 × 0.1 × 0.3
173(2)
173(2)
293(2)
173(2)
λ/Å
0.71073
triclinic
P1h
8.413(2)
10.709(3)
11.406(3)
74.096(17)
85.768(18)
72.795(19)
944.1(4)
0.71073
monoclinic
P21/c
11.627(2)
13.388(3)
11.859(2)
90
106.88(3)
90
0.71073
monoclinic
P21/c
11.682(2)
13.499(3)
12.926(3)
90
106.70(3)
90
0.71073
orthorhombic
P212121
9.6374(19)
11.5216(16)
13.917(2)
90
90
90
1545.3(4)
2.148
4
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
1766.5(6)
2.037
4
1952.6(7)
2.145
4
F
calcd, g cm-3
Z
1.765
2
2.711
µ/mm-1
2.907
8.866
11.687
reflns collected/unique
data/restraints/params
final R1, wR2 indices
R1, wR2 (all data)
5536/4663
4663/0/163
0.0332, 0.0799
0.0430, 0.0850
4974/4476
4476/0/200
0.0425, 0.1076
0.0561, 0.1147
13907/1968
1968/0/200
0.0301, 0.0768
0.0319, 0.0788
3801/3293
3293/0/136
0.0424, 0.0986
0.0557, 0.1064
[PtCl(TeCH2CH2NMe2)(PMePh2)] (2i): recrystallized from
acetone-hexane in 64% yield, mp 166 °C dec. Anal. Calcd for
C17H23ClNPPtTe: C, 32.4; H, 3.7; N, 2.2. Found: C, 32.2; H, 3.7;
N, 2.1. 1H NMR (CDCl3): δ 2.28 (d, 11.2 Hz, 3J(Pt-H) ) 32 Hz,
PMe2); 2.80 (TeCH2 merged in NMe2 resonance); 2.80 (d, 2.8 Hz,
3J(Pt-H) ) 18 Hz, NMe2); 3.48 (t, 6.0 Hz, NCH2); 7.39 (m, Ph),
propyl, and phenyl substituent groups and triple-ú quality for the
rest of the system were employed. The inner shells were represented
by the frozen core approximation (1s for C, N, 1s-2p for P and Cl,
1s-4p for Te, 1s-3d for Pd, and 1s-4d for Pt were kept frozen). The
following density functionals were used within ADF: the local
density approximation (LDA) with VWN parametrization of
electron gas data or the functional including Becke’s gradient
correction11 to the local exchange expression in conjunction with
Perdew’s gradient correction12 to the LDA expression (ADF/BP).
The scalar relativistic (SR) zero order regular approximation
(ZORA) was used within this study. The TD-DFT calculations were
done using the optimized geometries of the [MCl(TeCH2CH2-
NMe2)(L)] complexes.
1
7.58-7.66 (m, Ph). 31P{1H} NMR (CDCl3): δ -11.1, J(195Pt-
31P) 3491 Hz.
Crystallography. Single crystals of [PdCl(TeCH2CH2NMe2)-
(PMePh2)] (2e) and [PtCl(TeCH2CH2NMe2)(PMePh2)] (2i) were
obtained at -10 °C from CH2Cl2-acetone and acetone-hexane
mixtures, respectively, while single crystals of [PdCl(TeCH2CH2-
NMe2)(PPrn )] (2b) and [PtCl(SeCH2CH2NMe2)(PEt3)] (3) were
3
obtained from concentrated hexane solutions. X-ray data of 3,4a of
a purple-pink crystal of 2b, and of a blue crystal of 2e were collected
at 173(2) K on Siemens P4 and P3 diffractometers, using graphite-
monochromated Mo KR radiation (λ ) 0.71073 Å) and employing
the ω-2θ scan technique. X-ray data of a red crystal of 2i were
collected on a Nonius Kappa CCD diffractometer at room temper-
ature. The unit cell parameters (Table 1) were determined from 25
reflections measured by a random search routine. The intensity data
were measured for Lorentz polarization and absorption effects (ψ
scans). The structures of 2b, 2i, and 3 were solved by the Patterson
method while the structure of 2e was solved by direct methods
(program SHELXTL 5.18). The non-hydrogen atoms were refined
anisotropically, and the hydrogen atoms were introduced (riding
model).
Results and Discussion
Synthesis and NMR Spectroscopy. When Na2PdCl4 was
treated with a methanolic solution of (Me2NCH2CH2Te)2, a
brown insoluble product of the composition [PdCl(TeCH2-
CH2NMe2)]n (1) was isolated. The analogous selenolate
[PdCl(SeCH2CH2NMe2)]n exists as a structurally character-
ized trimeric molecule (n ) 3).13 When 1 was treated with
tertiary phosphines, complexes of the general formula [PdCl-
(TeCH2CH2NMe2)(PR3)] (2) were isolated. Compounds 2a-i
are also readily prepared by reacting [Pd2Cl2(µ-Cl)2(PR3)2]
with NaTeCH2CH2NMe2 in a 1:2 molar ratio. This reaction
can be extended for the preaparation of platinum analogues
(Scheme 1).
The 1H NMR spectra of 2 show characteristic resonances.
The NMe2 signal appears as a doublet due to J(Pt-H)
coupling. The resonances for the platinum complexes are
flanked by 195Pt satellites with the 3J(Pt-H) values compa-
rable to those of the corresponding selenolate complexes.4a
The 31P NMR spectra exhibit single resonances indicating
the formation of only one isomer. The magnitude of 1J(Pt-
DFT Calculations. Ground state electronic structure calculations
on complexes [MCl(TeCH2CH2NMe2)(PR3)] (M ) Pd, Pt, PR3 )
PPrn , PMe2Ph, PMePh2) have been done by density-functional
3
4
theory (DFT) methods using the ADF2000.029,10 program package.
The lowest excited states of the closed-shell complexes were
calculated by the time-dependent DFT (TD-DFT) method.
Within the ADF program, Slater type orbital (STO) basis sets
of double-ú quality with polarization functions within methyl,
(8) SHELXTL 5.1; Bruker Analytical X-Ray Systems: Madison, WI, 1998.
(9) Fonseca Guerra, C.; Snijders, J. G.; Te Velde, G.; Baerends, E. J.
Theor. Chem. Acc. 1998, 99, 391.
(10) van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J. Comput. Phys.
Commun. 1999, 118, 119.
(11) Becke, A. D. Phys. ReV. A 1988, 38, 3098.
(12) Perdew, J. P. Phys. ReV. A 1986, 33, 8822.
(13) Dey, S.; Jain, V. K.; Knoedler, A.; Lissner, F.; Kaim, W. J. Chem.
Soc., Dalton Trans. 2001, 723.
2866 Inorganic Chemistry, Vol. 41, No. 11, 2002

Long-WaWelength Charge Transfer Transitions
Scheme 1
Figure 1. Molecular structure of [PdCl(TeCH2CH2NMe2)(PPrn )] (2b) with
3
crystallographic numbering scheme.
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) of
[MCl(ECH2CH2NMe2)(PR3)]
M/E/PR3
Pd/Te/PPrn Pd/Te/PMePh2 Pt/Te/PMePh2 Pt/Se/PEt3
3
(2b)
(2e)
(2i)
(3)
M-E
2.5095(8)
2.3740(12)
2.2295(11)
2.172(3)
2.137(5)
1.457(5)
1.449(5)
1.509(6)
1.453(7)
2.5156(6)
2.3929(14)
2.2093(13)
2.143(4)
2.153(6)
1.409(6)
1.440(7)
1.481(7)
1.439(8)
2.5261(5)
2.3780(14) 2.356(2)
2.2189(12) 2.210(2)
2.182(4)
2.150(6)
1.447(6)
1.506(7)
1.467(7)
1.474(10)
2.3563(10)
M-Cl
M-P
M-N
E-C(1)
N-C(3)
N-C(4)
N-C(2)
C(1)-C(2)
2.160(7)
Figure 2. ORTEP plot [PtCl(TeCH2CH2NMe2)(PMePh2)] (2i) with
crystallographic numbering scheme.
1.945(11)
1.456(16)
1.497(14)
1.476(12)
1.483(16)
N-M-P
N-M-Cl
P-M-Cl
N-M-E
P-M-E
179.19(8)
91.89(9)
88.62(4)
87.85(9)
91.59(3)
176.22(3)
91.35(13)
178.89(13)
94.07(13)
86.84(5)
86.61(13)
92.56(4)
173.20(4)
92.36(17)
103.9(5)
109.3(4)
110.2(5)
109.2(3)
109.6(4)
114.2(4)
106.9(4)
116.7(4)
178.69(11) 175.9(4)
91.58(11)
87.52(5)
87.32(11)
93.66(4)
175.16(3)
91.88(17)
107.2(5)
114.2(5)
102.6(4)
108.6(3)
110.9(3)
113.0(3)
108.5(4)
116.3(5)
92.6(2)
87.12(10)
86.3(2)
93.86(7)
177.57(11)
97.0(3)
107.1(9)
110.4(10)
107.6(9)
107.0(7)
112.7(7)
111.9(6)
108.6(6)
113.7(9)
Cl-M-E
C(1)-E-M
C(3)-N-C(4) 109.9(4)
C(3)-N-C(2) 104.9(3)
C(4)-N-C(2) 110.1(4)
C(3)-N-M
C(4)-N-M
C(2)-N-M
C(2)-C(1)-E 109.2(3)
C(1)-C(2)-N 114.9(4)
111.2(3)
107.3(3)
113.5(3)
Figure 3. ORTEP plot [PtCl(SeCH2CH2NMe2)(PEt3)] (3) with crystal-
lographic numbering scheme.
P) for the platinum complexes suggests that the phosphine
ligand is trans to the nitrogen atom of the chelating
group,4a,14,15 which is confirmed by X-ray structural analysis.
Structures of Complexes 2b, 2e, 2i, and 3. Crystal-
lographic information on the four structurally characterized
complexes is summarized in Table 1, and the bond param-
eters are given in Table 2. Compounds 2e (Pd) and 2i (Pt)
are isostructural.
Figures 1-3 illustrate a coordination arrangement in which
an approximately square planar MII center is surrounded by
Te (or Se), N, Cl, and P atoms with the neutral group 15
donor atoms in trans position to each other. Consequently,
the charged donors (chloride and Te or Se) also adopt a
mutual trans arrangement. The five-membered chelate rings
exhibit a twist conformation with the carbon atoms lying on
opposite sides of the metal coordination plane. With the
unsymmetrical triorganophosphine PMePh2 in 2e and 2i the
P-C(phenyl) bonds to C(12) lie virtually in the best plane
PtTeNClP (Figure 2). The bond lengths (M-Te,16-18 Te-
(14) Narayan, S.; Jain, V. K.; Varghese, B. J. Chem. Soc., Dalton Trans.
1998, 2359.
(15) Jain, V. K.; Kannan, S.; Butcher, R. J.; Jasinski, J. P. Polyhedron
1995, 14, 3641.
Inorganic Chemistry, Vol. 41, No. 11, 2002 2867

Dey et al.
Table 3. UV/Vis Absorption Dataa of Complexes in CH2Cl2
complex
λmax (ꢀ)
[PdCl(TeCH2CH2NMe2)(PEt3)] (2a)
260 (27952), 288 (11050), 355(2500), 575 (140)
258 (34500), 288 (13970), 359(2700), 578 (290)
255 (27500), 287 (12000), 345 (2680), 573 (210)
225 (21500), 262 (29000), 287 (12700), 358 (2700), 587 (180)
223 (42180), 264 (41170), 359 (sh, 3570), 599 (280)
224 (32000), 269 (21650), 367 (sh), 623 (150)
240 (27400), 270 (sh), 349 (7542), 615 (141)
241 (20700), 265 (sh), 295 (sh), 452 (150)
243 (17200), 270 (sh), 300 (sh), 460 (140)
284, 405
[PdCl(TeCH2CH2NMe2)(PPrn )] (2b)
3
[PdCl(TeCH2CH2NMe2)(PBun )] (2c)
3
[PdCl(TeCH2CH2NMe2)(PMe2Ph)] (2d)
[PdCl(TeCH2CH2NMe2)(PMePh2)] (2e)
[PdCl(TeCH2CH2NMe2)(PPh3)] (2f)
[PdCl(TeCH2CH2NMe2){PTol3}] (2g)
[PtCl(TeCH2CH2NMe2)(PMe2Ph)] (2h)
[PtCl(TeCH2CH2NMe2)(PMePh2)] (2i)
[PtCl(SeCH2CH2NMe2)(PEt3)] (3)b
a Wavelengths λmax at the absorption maxima in nm, molar extinction coefficients ꢀ in M-1 cm-1
.
b From ref 4a.
Table 4. Electrochemical Dataa of Complexes
Epa(ox)
Epc(red)
[PdCl(TeCH2CH2NMe2)(PMePh2)]b
(2e)
(2b)
(2h)
(2h)
(2i)
0.25
0.27
0.07
0.01
0.07
0.03
0.28
0.34
0.30
0.55
-2.12
[PdCl(TeCH2CH2NMe2)(PPrn )]b
-2.35
3
[PtCl(TeCH2CH2NMe2)(PMe2Ph)]b
[PtCl(TeCH2CH2NMe2)(PMe2Ph)]c
[PtCl(TeCH2CH2NMe2)(PMePh2)]b
[PtCl(TeCH2CH2NMe2)(PMePh2)]c
[PtCl(SeCH2CH2NMe2)(PMePh2)]b,e
[PtCl(SeCH2CH2NMe2)(PMe2Ph)]b,e
[PtCl(SeCH2CH2NMe2)(PEt3)]b
d
-2.68
d
-2.63
f
f
f
(2i)
(3)
[PdCl(SeCH2CH2NMe2)(PPh3)]b,e
-2.04
a Scan rate 100 mV/s, peak potentials for irreversible processes in V vs
+
FeCp2/FeCp2
.
b Measurement in CH2Cl2/Bu4NPF6. c Measurement in DMF/
Bu4NPF6. d Not applicable. e From ref 4a. f Not observed (<-2.7 V).
Figure 4. UV/vis spectrum of [PdCl(TeCH2CH2NMe2)(PPrn )] (2b) in
CH2Cl2 solution.
an estimate for the relative positioning of the frontier orbitals.
Table 4 contains the relevant data for selected compounds.
In the series of the complexes with PMePh2 as a ligand,
the rather facile oxidation occurs most easily for the “PtTe”
complex 2i whereas the “PdTe” system 2e and the “PtSe”
compound 3 exhibit slightly, about 0.2 V higher anodic peak
potentials. A much stronger effect is apparent on the
reductive side. Whereas the “PdTe” compound 2e is reduced
at a fairly negative but still well-accessible potential, the
platinum complexes 2i and 3 display a large negative
potential shift >0.50 V relative to the Pd analogues. This
effect is in agreement with the hypsochromic shift of the
long-wavelength (HOMO-LUMO) transition when exchang-
ing Pd by Pt.
Calculations and Discussion of the Electronic Structure.
The DFT calculations essentially reproduce the experimental
structures of the palladium and the platinum compounds
(Table 5). The strongest discrepancies occur for the Te-C
and M-X (X ) Te, N) bonds which are calculated with too
long distances by about 0.05 Å.
Based on either the calculated or the experimental
geometries the DFT procedure yields MO situations where
the highest occupied orbitals are centered on the tellurolate
(with some metal contribution) whereas the lowest unoc-
cupied MOs are identified as more mixed orbitals involving
more (Pt) or less (Pd) contribution from the triorganophos-
phine ligand (Tables 6-8, Figure 5).
For instance, the ADF/BP calculated compositions of
molecular orbitals of [PdCl(TeCH2CH2NMe2)(PMePh2)] (2e)
are summarized in Table 6. The highest occupied molecular
orbital (HOMO), 71a, is predominantly formed by Te p
orbitals with contributing 4d orbitals of Pd. The Pd 4d and
3
C16-19) and bond angles are not unusual; obviously, the Pt-
Te bond is longer in 2i at 2.5261(5) Å than the Pt-Se bond
at 2.3563(10) Å in 3 or 2.3773(7) Å in the directly related
[PtCl(SeCH2CH2NMe2)(PMePh2)].4a
UV/Vis Absorption Spectra. All complexes described
here are distinctly colored, either blue (Pd compounds) or
red (Pt complexes). Well-separated, broad but relatively weak
(ꢀ ≈ 200 M-1 cm-1) bands in the visible are responsible for
this color. Figure 4 shows a representative example, and
Table 3 summarizes the absorption data in dichloromethane
solution; studies in acetone solution for selected examples
showed essentially similar absorption features within ex-
perimental uncertainty ((5 nm) of λmax. In the series of
palladium(II) complexes there is a clear trend for the long-
wavelength band. Its wavelength at the absorption maximum
decreases with increasing donor and decreasing acceptor
strength of the triorganophosphine, i.e., in the series
PPh3 > PMePh2 > PMe2Ph > P(alkyl)3 (Table 3). The plati-
num(II) complexes have their absorptions at much higher
energies, at about 460 nm (2.70 eV)4a as compared to about
600 nm (2.07 eV) for the palladium(II) analogues.
Cyclic Voltammetry. Although both the oxidation and
the reduction of the complexes occur irreversibly, the
comparison of electrochemical peak potentials can provide
(16) Jain, V. K.; Kannan, S.; Bohra, R. Polyhedron 1992, 11, 1551.
(17) Singh, A. K.; Srivastava, V.; Dhingra, S. K.; Drake, J. E.; Bailey, J.
H. Acta Crystallogr. 1992, C48, 655.
(18) Giolando, D. M.; Rauchfuss, T. B.; Rheingold, A. L. Inorg. Chem.
1987, 26, 1636.
(19) Drake, J. E.; Bailey, J. H. E.; Singh, A. K.; Srivastava, V. Acta
Crystallogr. 1993, C49, 684.
2868 Inorganic Chemistry, Vol. 41, No. 11, 2002

Long-WaWelength Charge Transfer Transitions
Table 5. Comparison of ADF/BP Calculated Bond Lengths and
Angles with Experimental Data for [MCl(TeCH2CH2NMe2)(L)]
(L ) PMePh2, PPr3)
Table 8. ADF/BP Calculated One-Electron Energies and Percentage
Composition of Frontier Molecular Orbitals of
[MCl(TeCH2CH2NMe2)(L)] Complexes Expressed in Terms of
Composing Fragments
Pd/Te/PMePh2
Pd/Te/PPrn
Pt/Te/PMePh2
3
(2e)
(2b)
(2i)
prevailing
complex
MO
E (eV)
character
M L Te Cl N
calcd
exptl
calcd
exptl
calcd
exptl
Pd/Te/PMePh2 LUMO (72a) -2.70 dPd + PMePh2 24 39 25
8
3
2
6
M-Te
M-Cl
M-P
2.567
2.399
2.232
2.205
2.199
2.516
2.393
2.209
2.143
2.153
2.580
2.401
2.247
2.213
2.192
2.510
2.374
2.230
2.172
2.137
2.585
2.409
2.222
2.206
2.196
2.526
2.378
2.219
2.182
2.150
(2e)
+ Te
HOMO (71a) -4.31 Te + dPd
18
70
9
4
Pt/Te/PMePh2 LUMO (79a) -2.27 dPt + PMePh2 18 60 10
M-N
(2i)
+ Te
HOMO (78a) -4.09 Te + dPt
LUMO (68a) -2.10 dPd + PPrn
+ Te
Te-C(1)
23
66
7
Pd/Te/PPrn
(2b)
30 20 29 10
N-M-P
N-M-Cl
P-M-Cl
N-M-Te
P-M-Te
C(1)-Te-M
C(2)-N-M
179.0
92.5
86.7
88.6
92.1
90.1
113.1
178.9
94.1
86.8
86.6
92.6
92.4
114.2
179.1
91.9
87.4
87.7
93.0
90.0
114.4
179.2
91.9
88.6
87.9
91.6
91.4
113.5
177.8
90.8
87.6
87.9
93.6
90.6
113.5
178.7
91.6
87.5
87.3
93.7
91.9
113.0
3
3
HOMO (67a) -4.11 Te + dPd
20 3 68
8
Table 9. Selected ADF/BP Calculated Lowest Singlet Excitation
1
Energies for [PdCl(TeCH2CH2NMe2)(PPrn )] (2b; A1 States)
3
main character
(% composition)
excn energy
(eV)
oscillator
strength
Table 6. ADF/BP Calculated One-Electron Energies and Percentage
Composition of Selected Highest Occupied and Lowest Unoccupied
Molecular Orbitals of [PdCl(TeCH2CH2NMe2)(PMePh2)] (2e) Expressed
in Terms of Composing Fragments
99 (67a f 68a) (HOMO f LUMO)
93 (66a f 68a)
95 (65a f 68a)
97 (67a f 69a)
60 (67a f 70a); 37 (63a f 68a)
95 (65a f 68a
1.98
3.15
3.20
3.65
3.84
4.03
4.27
0.0004
0.006
0.002
0.002
0.019
0.015
0.140
prevailing
character
MO
E (eV)
Pd
PMePh2 Te Cl
N
unoccupied
74a
73a
35 (63a f 68a); 29 (67a f 70a);
14 (61a f 68a); 6 (60a f 68a)
-1.98 PMePh2
-2.08 PMePh2
-2.70 dPd + PMePh2 24 (d)
+ Te
3 (d)
2 (d)
90
94
39
2
2
8
72a
25
3
2
Te/PPrn complex 2b. Variation of the central metal or L
3
affects mainly the composition of the LUMO, where the L
contribution varies from 20% to 60% on going from the Pd/
Te/PPrn3 system (2b) to the Pt/Te/PMePh2 complex 2i. The
composition of the set of highest occupied orbitals is only
moderately influenced.
These calculated variations of the HOMO/LUMO positions
in Table 8 confirm the shifts of redox potentials within this
series of complexes. Specifically, the changes within the
isostructural series 2e/2i, viz., ELUMO(2i) - ELUMO(2e) ) 0.43
eV and EHOMO(2i) - EHOMO(2e) ) 0.22 eV, show broad
agreement with the experimental peak potential differences
Epc(2e) - Epc(2i) ) 0.51 V and Epa(2e) - Epa(2i) ) 0.18 V
(Table 4).
occupied
71a
70a
69a
68a
-4.31 Te + dPd
-5.46 dPd
-5.58 Cl + dPd
-5.65 Cl + dPd
18 (d)
11 (s); 63 (d)
20 (d)
2 (s); 2 (p);
22 (d)
3 (p); 11 (d)
83 (d)
70
9
4
3
3
12 14
68
13 49
67a
66a
65a
-5.91 Cl + Te
-6.38 dPd
-6.60 PMePh2
2
10
62
41 38
1
4
1
6
18 (d)
7
Table 7. ADF/BP Calculated One-Electron Energies and Percentage
Composition of Selected Highest Occupied and Lowest Unoccupied
Molecular Orbitals of [PdCl(TeCH2CH2NMe2)(PPrn )] (2b) Expressed in
3
Terms of Composing Fragments
prevailing
character
MO
E (eV)
Pd
PPrn Te Cl
N
3
unoccupied
70a
69a
68a
occupied
67a
66a
65a
64a
63a
The TD-DFT calculated lowest excitation energies for
-0.13 PPrn3 + dPd
-0.44 Te
34 (d)
13 (d)
60
7
3
54
1
[PdCl(TeCH2CH2NMe2)(PPrn )] (2b) are listed in Table 9.
3
1
6
-2.10 dPd + PPrn3 + Te 30 (d)
20 29 10
Calculations for the PMe2Ph- and PMePh2-containing sys-
tems 2e and 2i produced many additional weak low-energy
transitions to unoccupied orbitals involving the phenyl
groups; we therefore restrict the discussion largely to that
of the trialkylphosphine-palladium complex 2b and its
calculated platinum analogue. In all cases, the lowest
calculated excitation corresponds to a transition from the
largely Te based HOMO into a more delocalized LUMO
with significant Te, metal, phosphine, and even some chloride
contributions. Although pure ligand-field (d-d) transitions
would also result in weak, broad absorptions, the remaining
empty metal d orbital of the d8 system is too high in energy
to be involved in low-energy transitions.
-4.11 Te + dPd
-5.24 dPd
20 (d)
12 (s); 63 (d)
24 (d)
25 (d)
4 (p); 7 (d)
87 (d)
3
3
3
68
11
8
4
1
-5.39 Cl + dPd
-5.53 Cl + dPd
-5.77 Cl + Te
-6.11 dPd
66
18 51
43 37
1
8
62
62a
61a
1
4
1
6
-6.78
18 (d)
7
Cl 3p orbitals contribute significantly to the next lower lying
occupied MOs 68a-70a. The lowest lying unoccupied
molecular orbital (LUMO) is delocalized over the system
with a large contribution from PMePh2 (39%). Several higher
lying unoccupied orbitals are present which largely involve
the phenyl groups of the PMePh2 fragment, an effect which
is absent in the otherwise similar trialkylphosphine system
2b (Table 7). Table 8 compares the energies and composi-
tions of frontier molecular orbitals within the structurally
characterized series of [MCl(TeCH2CH2NMe2)(L)] com-
plexes. Figure 5 shows the LUMO composition of the Pd/
According to Tables 8 and 9, the low-energy electronic
transitions responsible for the colors can thus be described
mainly as ligand(Te)-to-ligand(PR3) charge transfer transi-
tions in the case of Pt complexes whereas the target MO is
of more mixed character for the Pd analogues with their
Inorganic Chemistry, Vol. 41, No. 11, 2002 2869

Dey et al.
Summarizing, we have used both experiments and DFT
calculations for mixed-ligand complexes of PdII and PtII to
establish the nature of the remarkably low energy charge
transfer transitions from the p(Te) HOMO to unoccupied
orbitals of more (Pd) or less (Pt) mixed character with large
PR3 contributions. Due to the involvement of heavier
elements in the frontier orbitals we have validated the DFT
results through crystallographic confirmation of structure
calculations and through studies of the spectroscopic and
electrochemical response on variation of the organophosphine
acceptor ligands. In chemical terms, the stronger back-
bonding interaction between PtII vs PdII and the phosphine
acceptors destabilizes the LUMO (more negative reduction
potential) whereas the replacement of Se by Te causes the
expected destabilization of the HOMO (lower oxidation peak
potential). The variation of the phosphines confirms that the
LUMO is indeed an orbital with considerable PR3 contribu-
tions; the lower lying unoccupied orbitals of the aromatic
derivatives cause the bathochromic shift observed in Table
3. It is confirmed1 that the electronically rather inert PdII
and PtII centers are particularly suitable to allow observation
of ligand-ligand charge transfer processes, even with less
common combinations of donor and acceptor groups.
Figure 5. LUMO representation of [PdCl(TeCH2CH2NMe2)(PPrn )] (2b).
3
Donor atoms around PdII: Te, N, Cl, P (clockwise, starting from the top).
unusually low transition energies. The calculated value of
1.98 eV (626 nm) for 2b is in reasonable agreement with
the experimental absorption maximum at 2.14 eV (578 nm,
Table 3). The low intensity of this long-wavelength transition
is well reproduced by the TD-DFT procedure; the next
transitions for 2b (Table 9) which are well separated from
the HOMO-LUMO transition both experimentally (Figure
5, Table 3) and from the DFT calculation (Table 9) can be
characterized as excitations from Pd- or Cl-localized orbitals
into the L-localized LUMOs. The TD-DFT calculated lowest
transitions for Pd/Te/PMePh2 (2e), Pd/Te/PMe2Ph (2d), and
Acknowledgment. We thank Drs. J. P. Mittal and P. Raj
for encouragement of this work. We are grateful to Dr. P.
K. Mathur, Head, Analytical Chemistry Division BARC, for
providing microanalysis of the compounds. Support of this
work from BMBF (Project No. IND 99/060), the DFG, FCI,
the Ministry of Education of the Czech Republic, and the
DLR (Bonn) for KONTAKT Project CZE 00/013 is grate-
fully acknowledged.
Pd/Te/PPrn (2b) are 1.77, 1.93, and 1.98 eV, respectively.
3
Calculated values for Pt/Te/PMePh2 (2i), Pt/Te/PMe2Ph (2b),
and Pt/Te/PPrn are 1.88, 2.07, and 2.37 eV, respectively.
3
These calculated trends are in agreement with the experi-
mental variations of the lowest transitions resulting from PR3
ligand changes within both series of M/Te/PR3 complexes.
The shift of the lowest transition to higher energies on
replacement of Pd by Pt for individual members of the series
is underestimated but qualitatively reproduced.
Supporting Information Available: Details of the X-ray
structure determination (four compounds) in CIF format. This
material is available free of charge via the Internet at
http://pubs.acs.org.
IC011210V
2870 Inorganic Chemistry, Vol. 41, No. 11, 2002