New [M(R,R′timdt)2] Metal-Dithiolenes
J. Am. Chem. Soc., Vol. 121, No. 30, 1999 7105
Table 3. Calculateda Mulliken Charges (e) for 1-3, 11-13,
14-16 (Atom Numbering as in Figure 1)
thebasisoftheirdepolarizationratiosin11and[Pd(dmit)2]-0.5(17),
since [Pd(dmit)2] had never been isolated. The calculated
frequencies of the ag modes (134, 341, 368, 499, 500, 962, 1122,
1385 cm-1 and 119, 340, 365, 494, 503, 945, 1121, 1384 cm-1
for 11 and 12, respectively) are in good agreement with those
found in the experimental Raman spectra of 11 and 17 (140,
343, 364, 488, 496, 950, 1051, 1399 cm-1 and 140, 345, 364,
485, 515, 1078, 1354 cm-1). These assignments are similar to
those proposed by Ramakumar et al.47 on the basis of ab initio
calculations.48
compd
M
S(1,2)
C(1,2) X(1,2)b
C(3)
S(3)
1
2
3
11
12
13
14d
15
16
-0.060c -0.014 -0.028
-0.186
-0.247
0.022 -0.031
0.029 -0.021
-0.005 -0.008 -0.094
0.233 -0.205 -0.053
0.231 -0.204 -0.053
0.230 -0.203 -0.053
-0.142
-0.206
-0.013 -0.060
-0.154 -0.019
-0.233 -0.008
0.036 -0.103
0.045 -0.093
0.056 -0.072
0.074 -0.196
0.074 -0.196
0.074 -0.202
0.043 -0.071
0.058 -0.074
Coming to our dithiolenes, the most intense band, originated
from a b3u bending mode, falls at 434, 429, and 431 cm-1 for
14, 15, and 16, respectively. These values are in very good
agreement with the experimental bands found at average values
of 435(2), 427(3), and 425(3) cm-1 for 7a-i, 8a-j, and 9a-j,
respectively. The calculated b2u stretching mode is expected to
be not very intense and to fall at 380, 334, and 319 cm-1 in 14,
15, and 16, respectively. As seen in the Vibrational Spectroscopy
section, this band appears as a medium band at an average value
of 380(2) cm-1 for [Ni(R,R′timdt)2] and as a very weak band
at 339(2) cm-1 for [Pd(R,R′timdt)2], but it is not visible in Pt
complexes. As regards the Raman peaks, DFT calculations
predict the ag stretching mode at 312, 325, and 353 cm-1 in 14,
15, and 16 in quite good agreement with the average experi-
mental values found for 7a-i, 8a-j, and 9a-j [330(4), 342-
(2), and 377(3) cm-1, respectively].49 This is the most intense
band, since it is resonance enhanced (excitation energy of the
Nd:YAG laser 1064 cm-1).16 The shift toward higher energies
on passing from Ni to Pt had already been observed in
[M(mnt)2]2- [mnt ) maleonitriledithiolate;50 ν(ag) ) 335, 349,
378 cm-1 for M ) Ni, Pd, and Pt, respectively] and was
attributed to an increased metal-d/ligand-π orbital overlap.51 The
second Raman peak falling at average values of 434(1), 429-
(2), and 422(1) cm-1 for Ni, Pd, and Pt (only visible in 9d and
9e) complexes, respectively, might be attributed either to ag or
b1g bending modes (calculated frequencies 444, 439, and 440
cm-1 and 443, 443, and 444 cm-1 for 14, 15, and 16
respectively).
a pVDZ Basis set by Schafer, Horn, and Ahlrichs35 for C, H, N, S
atoms; Hay and Wadt LANL2DZ basis set with ECP36 used for the
metal atoms. b X ) S for 11-13; X ) N for 14-16. c The Mulliken
charge calculated on the Ni atom using a simpler HF method was
-0.070 e. See: Fischer-Hjalmars, I.; Henriksson-Enflo, A. Int. J.
Quantum Chem. 1980, 18, 409. d The Mulliken charges calculated for
7a are -0.003, -0.084, 0.070, -0.221, 0.115, and -0.222 e.
The calculated energies of the HOMOs of the three series
explain the differences in oxidation processes, which are
achievable only in our dithiolenes (see the Cyclic Voltammetry
section). Moreover, since the HOMO does not involve the metal
orbitals, it is not surprising that the change of the metal does
not affect the oxidation potentials. This agrees with the structural
features of the only oxidized dithiolene in this series isolated
so far, which shows that the oxidation is ligand-centered.16
The calculated Mulliken charges42 (Table 3) show that in all
series the metal becomes remarkably more negative on passing
from Ni to Pd and Pt, while the charges on the sulfur donor
atoms tend to become less negative or neutral. The charges on
the N-C(dS)-N and S-C(dS)-S groups of H2timdt and dmit
ligands are unaffected by the change in the metal. Accordingly,
the chemical shift of the C(3) carbon (Mulliken charge +0.074
e) is very similar in 7a-i, 8a-j, and 9a-j.
Finally, the DFT calculations help understand the nature and
type of the vibrational bands observed with FT-IR and FT-
Raman techniques in the far-IR region (500-50 cm-1; Table
4). In 1-3, almost pure normal modes are found, and the
assignments based on DFT-calculations only partially agree with
the previously published43,44 normal coordinate analyses, which
were not complete in the far-IR region, and led to conflicting
assignments. As far as the dmit derivatives are concerned,
despite the large amount of publications regarding their proper-
ties, only a few spectroscopic studies have been reported.45
Recently,46 the Raman-active ag bands have been identified on
Conclusions
Due to their photochemical and thermal stabilities and to their
very strong absorption in the NIR region, which is close to the
Nd:YAG excitation energy (1064), [Ni(R2timdt)2] dithiolenes
have proved to be ideal candidates for Q-switching this type of
laser. With the aim of getting closer to the desired wavelength,
several Ni (7a-i), Pd (8a-j), and Pt (9a-j) dithiolenes
belonging to the general [M(R,R′timdt)2] class of compounds
have been synthesized and fully characterized by means of
several techniques. In the case of asymmetric ligands, vibrational
spectroscopies support a trans orientation, confirmed for 7c by
an X-ray crystal structure determination. Therefore, all the
considered dithiolenes belong to the centrosymmetric D2h (R
) R′) or C2h (R * R′) point groups. Electrochemical measure-
ments demonstrate that while the oxidation of Pd-dithiolenes
over the neutral state is achievable and quasi-reversible, it is
irreversible both in Ni and Pt analogues. The syntheses of these
(42) In the present case, the slight difference in Ni charge magnitude
(-0.013 e) compared to the previously reported value for 14 (-0.017 e18)
depends on the change in basis set and on the use of effective core potentials.
(43) Adams, D. M.; Cornell, J. B. J. Chem. Soc. A 1968, 1299.
(44) Siimann, O.; Fresco, J. Inorg. Chem. 1971, 10, 2.
(45) (a) Papavassiliou, G.; Cotsilios, A. M.; Jacobsen, C. S. J. Mol. Struct.
1984, 115, 41. (b) Tajima, H.; Naito, T.; Tamura, M.; Kobayashi, A.; Kato,
R.; Kobayashi, H.; Clark, R. A.; Underhill, A. E. Mol. Cryst. Liq. Cryst.
1990, 181, 233. (c) Tajima, H.; Naito, T.; Tamura, M.; Takahashi, A.;
Toyoda, S.; Kobayashi, A.; Kuroda, H.; Kato, R.; Kobayashi, H.; Clark, R.
A.; Underhill, A. E. Synth. Metals 1991, 41, 2417. (d) Tamura, M.; Masuda,
R.; Tajima, H.; Kuroda, H.; Kobayashi, A.; Yakushi, K.; Kato, R.;
Kobayashi, H.; Tokumoto, M.; Kinoshita, N.; Anzai, H. Synth. Metals 1991,
41, 2499. (e) Underhill, A. E.; Clark, R. A.; Marsden, I. J. Phys. Condens.
Matter 1991, 3, 933. (f) Jacobsen, C. S.; Yartsev, V. M.; Tanner, D. B.;
Bechgaard, K. Synth. Metals 1993, 55-57, 1925. (g) Nakamura, T.;
Underhill, A. E.; Coomber, A. T.; Friend, R. H.; Tajima, H.; Kobayashi,
A.; Kobayashi, H. Inorg. Chem. 1995, 34, 870. (h) Liu, H. L.; Tanner, D.
B.; Pullen, A. E.; Abboud, K. A.; Reynolds, J. R. Phys. ReV. 1996, B53,
10557.
(47) Ramakumar, R.; Tanaka, Y.; Yamaji, K. Phys. ReV. 1997, B56, 795.
(48) Seger, D. M.; Korzenietski, C.; Kowalchik, W. J. Phys. Chem. 1991,
95, 69.
(49) In the case of [Ni(Pri2timdt)2], this band (346 cm-1) has similarly
been attributed to the ag totally symmetric stretching mode.16
(50) (a) Gray, H. B.; Billig, E. J. Am. Chem. Soc. 1963, 85, 2019. (b)
Davidson, A.; Edelstein, N.; Holm, R. H.; Maki, A. H. ibidem 1963, 85,
2029; Inorg. Chem. 1963, 2, 1227.
(46) Pokhodnya, K. I.; Faulmann, C.; Malfant, I.; Andreu-Solano, R.;
Cassoux, P.; Mlayah, A.; Smirnov, D.; Leotin, J. Private comunication. The
paper will be published in the Proceedings of the International Conference
on Science and Technology of Synthetic Metals, 1998.
(51) Clark, R. J. H.; Turtle, P. C. J. Chem. Soc., Dalton Trans. 1977,
2142
Aragoni, Maria Carla
