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Synthesis, crystal structure and properties of the new semiconductor (EVT)4·[Pt(CN)4]
Synthetic Metals 140 (2004) 171–176
Synthesis, crystal structure and properties of the new semiconductor (EVT)4 ·[Pt(CN)4 ] A.D. Dubrovskii a , N.G. Spitsina a,∗ , A.N. Chekhlov a , O.A. Dyachenko a , L.I. Buravov a , A.A. Lobach a , Jose Vidal Gancedo b , Concepcio Rovira b a
b
Institute of Problems of Chemical Physics RAS, Moscow District, Chernogolovka 142432, Russia Institut de Ciència de Materials de Barcelona, CSIC, Campus de la U.A.B., E-08193 Bellaterra, Spain Received 18 April 2003; accepted 21 May 2003
Abstract A novel radical cation salt based on of the donor (4,5-ethylenedithio-4 ,5 -vinylenedithio)tetrathiafulvalene (EVT) with the square planar anion Pt(CN)4 2− has been synthesized: (EVT)4 ·[Pt(CN)4 ] (1). According to the X-ray analysis its crystal structure includes EVT cation layers alternating with anion layers along the a-axis of the unit cell. The radical cation layer is formed by EVT stacks with -packing type, the donors in stacks are tetramerized. The EPR spectra of a plate-like crystal of (EVT)4 ·[Pt(CN)4 ] salt shows a very weak signal with typical parameters of TTF derivative. The room temperature conductivity of salt 1 is 8 × 10−2 −1 cm−1 and the temperature dependence of the conductivity exhibits semiconducting character. © 2003 Elsevier B.V. All rights reserved. Keywords: Radical cation salts; (4,5-Ethylenedithio-4 ,5 -vinylenedithio)tetrathiafulvalene; Tetracyanoplatinate(II) anion; X-ray crystal structure; EPR spectroscopy
1. Introduction Synthesis, crystal structure and conducting properties of organic conductors based on TTF and some of its unsymmetrical (methylenedithio)tetrathiafulvalene (MDT-TTF), (ethylenedithio)tetrathiafulvalene (EDT-TTF) and symmetrical derivatives such as (tetramethyl)tetraselenafulvalene (TMTSF), bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) with tetracyanoplatinate(II) anion have been reported earlier [1–7]. Radical cation salts with tetracyanoplatinate(II) anions display a wide spectrum of conducting properties ranging from semiconductors [3,5,6] to metals [1–4] and even superconductors [7].The anionic part alongside with the Pt(CN)4 2− might include either molecules of a solvent or water due to different synthesis conditions [3,5,7]. For studying the impact of the donor molecular structure on the properties of radical cation salts:
∗ Corresponding author. Tel.: +7-095-785-7048; fax: +7-096-515-5420. E-mail address: [email protected] (N.G. Spitsina).
0379-6779/03/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0379-6779(03)00353-9
we synthesized and studied the salt based on dehydrated derivative of ET ((4,5-ethylenedithio-4 ,5 -vinylenedithio)tetrathiafulvalene (EVT)) with tetracyanoplatinate(II) anion. This work presents data concerning the crystal structure, EPR spectroscopy and conducting properties of radical cation salt (EVT)4 ·[Pt(CN)4 ].
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A.D. Dubrovskii et al. / Synthetic Metals 140 (2004) 171–176
2. Experimental 2.1. Synthesis
Table 1 Atomic coordinates (×10−4 ) and equivalent isotropic displacement parameters for (EVT)4 ·[Pt(CN)4 ] Atom
Crystals of the (EVT)4 ·[Pt(CN)4 ] salt were obtained by electro-chemical oxidation of neutral EVT (C1 = 1 × 10−3 M) in an H-shaped electrochemical cell with separated anode and cathode spaces. The reaction was performed in fresh distillated benzonitrile (C6 H5 CN, Aldrich chemical) with 10 vol.% of absolute ethyl alcohol in the mode of direct current (I = 0.75 mA) in Ar atmosphere at 25 ◦ C. The tetrabutylammoniun salt (Bu4 N)2 ·Pt(CN)4 was used as electrolyte. Within 8 days black plates-shaped crystals with characteristic metallic shine were growing on the Pt anode. The crystals were filtered, washed in acetone and dried in the air. The correlation between S and Pt according to the local X-ray analysis is equal to 32:1 which corresponds to the formula (EVT)4 ·[Pt(CN)4 ] for salt 1, that composition was confirmed by the X-ray study. 2.2. X-ray study A single crystal of 1 in the form of a thin plate resembling a parallelepiped with dimensions of 0.4 mm × 0.25 mm × 0.05 mm was selected for the X-ray study. The main crystallographic data of the crystal structure of salt 1 are: C44 H24 N4 S32 Pt, M = 1829.7, a = 15.860(2) Å, b = 11.822(2) Å, c = 16.490(3) Å, β = 101.00(2)◦ , V = 3035.0(8) Å3 , monoclinic, the group P21 /m, Z = 2, dcalc = 2.00 g/cm3 . The unit cell parameters were determined and specified by the least square method (LSM) using 25 strong automatically centered reflections on the four-circle automatic diffractometer CAD-4 (graphite-monochromatized Mo K␣ radiation, λ = 0.7107 Å). Five thousand six hundred and six independent reflections (among them 4301 with I ≥ 2σ(I)) were registered by ω/2θ scanning within the angle range of 2.52◦ ≤ 2θ ≤ 49.94◦ . The structure was solved by a direct method and a number of successive Fourier syntheses using SHELX-86 program [8]. Hydrogen atoms were not localized. The refinement was done with the LSM with the anisotropic approximation for all non-hydrogen atoms using SHELX-97 program [9]. The final R factor value is 0.047 for 4301 reflections with I ≥ 2σ (I). The absorption was not considered (µ(Mo K␣) = 3.46 mm−1 ). The atom coordinates and their equivalent isotropic thermal parameters are given in Table 1. The bond lengths and angles are presented in Tables 2 and 3, respectively. 2.3. EPR spectroscopy The EPR spectra have been performed in a plate-like crystal on a Bruker ESP-300 E spectrometer operating in the X-band (9.3 GHz) and equipped with a TE102 microwave cavity, a Field Frequency lock system BRUKER ER 033 M and a NMR Gaussmeter BRUKER ER 035 M. The microwave power was kept well below saturation.
Pt(1) C(1) N(1) C(2) N(2) S(1A) S(2A) S(3A) S(4A) C(1A) C(2A) C(3A) C(4A) C(5A) C(6A) S(1B) S(2B) S(3B) S(4B) C(1B) C(2B) C(3B) C(4B) C(5B) C(6B) S(1C) S(2C) S(3C) S(4C) C(1C) C(2C) C(3C) C(4C) C(5C) C(6C) S(1D) S(2D) S(3D) S(4D) C(1D) C(2D) C(3D) C(4D) C(5D) C(6D)
x −83(1) −16(3) 20(3) −150(3) −169(3) 1589(1) 3501(1) 5403(1) 7019(1) 902(2) 2524(2) 4063(3) 4843(3) 6259(2) 7820(4) 2482(1) 4160(1) 6071(1) 7858(1) 1579(3) 3259(2) 4710(3) 5520(3) 7008(2) 8737(3) 1683(1) 3457(1) 5372(1) 7030(1) 805(3) 2538(3) 4013(4) 4818(4) 6244(2) 7941(3) 1641(1) 3417(1) 5252(1) 6912(1) 789(3) 2510(2) 3960(3) 4710(3) 6126(2) 7722(3)
y
z
Beq (Å2 × 103 )
2500 1262(5) 517(4) 1272(5) 557(4) −1112(1) −1252(1) −1256(1) −1023(1) −1938(4) −1939(3) −2500 −2500 −1937(3) −1952(5) 1040(1) 1270(1) 1271(1) 1044(1) 1937(5) 1934(3) 2500 2500 1928(3) 1952(5) 1058(1) 1269(1) 1265(1) 1064(1) 1939(5) 1933(4) 2500 2500 1938(3) 1935(4) 1099(1) 1249(1) 1256(1) 1032(1) 1950(4) 1935(3) 2500 2500 1931(3) 1932(5)
2609(1) 1824(3) 1378(3) 3428(3) 3890(3) 3908(1) 4557(1) 5697(1) 6900(1) 4406(3) 4164(2) 4874(3) 5362(3) 6343(2) 7395(6) 5335(1) 6451(1) 7535(1) 8438(1) 5147(4) 5883(2) 6753(4) 7249(4) 8009(2) 8450(4) −2626(1) −1660(1) −554(1) 621(1) −2552(4) −2179(3) −1356(3) −871(4) 68(2) 758(5) −300(1) 719(1) 1955(1) 3079(1) −83(3) 161(2) 1067(4) 1593(4) 2550(2) 3523(5)
44(1) 61(2) 70(1) 56(2) 72(2) 46(1) 38(1) 41(1) 54(1) 49(1) 34(1) 29(1) 31(1) 33(1) 141(3) 54(1) 39(1) 39(1) 55(1) 87(2) 36(1) 32(1) 34(1) 36(1) 86(2) 60(1) 40(1) 40(1) 57(1) 83(2) 42(1) 32(1) 34(2) 35(1) 99(3) 51(1) 42(1) 46(1) 68(1) 57(1) 35(1) 33(1) 32(1) 38(1) 97(2)
3. Results and discussion The crystal structure of salt (EVT)4 ·[Pt(CN)4 ] is layered: the layers of radical cations alternate with the anion layers along the a-directions of the unit cell (Figs. 1 and 2). The Pt atom of crystallographically independent anion Pt(CN)4 2− is located in a special position on the symmetry plane m and carbon atoms of the central C=C bond of the four EVT crystallographically independent radical cations (further on marked as A–D) are also located in special positions on the symmetry plane m. The asymmetric part of the unit cell contains half of anion and half of all the four radical cations.
A.D. Dubrovskii et al. / Synthetic Metals 140 (2004) 171–176 Table 2 Bond lengths (d) for (EVT)4 ·[Pt(CN)4 ]
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Table 3 Selected angles (ω) for (EVT)4 ·[Pt(CN)4 ]
Bond
d (Å)
Bond
d (Å)
Angle
ω (◦ )
Angle
ω (◦ )
Pt(1)–C(1) Pt(1)–C(1)I Pt(1)–C(2)I Pt(1)–C(2) C(1)–N(1) C(2)–N(2) S(1A)–C(2A) S(1A)–C(1A) S(2A)–C(3A) S(2A)–C(2A) S(3A)–C(4A) S(3A)–C(5A) S(4A)–C(5A) S(4A)–C(6A) C(1A)–C(1A)II C(2A)–C(2A)II C(3A)–C(4A) C(3A)–S(2A)II C(4A)–S(3A)II C(5A)–C(5A)II C(6A)–C(6A)II S(1B)–C(2B) S(1B)–C(1B) S(2B)–C(3B) S(2B)–C(2B) S(3B)–C(4B) S(3B)–C(5B) S(4B)–C(5B) S(4B)–C(6B) C(1B)–C(1B)I C(2B)–C(2B)I C(3B)–C(4B) C(3B)–S(2B)I
1.970(6) 1.970(6) 1.999(5) 1.999(5) 1.156(7) 1.142(7) 1.759(4) 1.776(5) 1.751(3) 1.759(4) 1.752(3) 1.754(4) 1.744(4) 1.758(6) 1.328(10) 1.326(8) 1.340(7) 1.751(3) 1.752(3) 1.331(8) 1.296(12) 1.742(4) 1.761(5) 1.720(3) 1.739(4) 1.715(3) 1.726(4) 1.745(4) 1.756(5) 1.330(11) 1.337(8) 1.384(7) 1.720(3)
C(4B)–S(3B)I C(5B)–C(5B)I C(6B)–C(6B)I S(1C)–C(2C) S(1C)–C(1C) S(2C)–C(3C) S(2C)–C(2C) S(3C)–C(4C) S(3C)–C(5C) S(4C)–C(5C) S(4C)–C(6C) C(1C)–C(1C)I C(2C)–C(2C)I C(3C)–C(4C) C(3C)–S(2C)I C(4C)–S(3C)I C(5C)–C(5C)I C(6C)–C(6C)I S(1D)–C(2D) S(1D)–C(1D) S(2D)–C(3D) S(2D)–C(2D) S(3D)–C(5D) S(3D)–C(4D) S(4D)–C(6D) S(4D)–C(5D) C(1D)–C(1D)I C(2D)–C(2D)I C(3D)–C(4D) C(3D)–S(2D)I C(4D)–S(3D)I C(5D)–C(5D)I C(6D)–C(6D)I
1.715(3) 1.352(8) 1.296(11) 1.753(4) 1.761(6) 1.725(3) 1.731(4) 1.732(3) 1.748(4) 1.737(4) 1.753(5) 1.327(12) 1.341(9) 1.371(8) 1.725(3) 1.732(3) 1.329(8) 1.335(10) 1.746(4) 1.775(5) 1.752(3) 1.753(4) 1.732(4) 1.750(3) 1.720(5) 1.740(4) 1.299(10) 1.335(8) 1.333(7) 1.752(3) 1.750(3) 1.346(8) 1.342(11)
C(1)–Pt(1)–C(1)I C(1)–Pt(1)–C(2)I C(1)I –Pt(1)–C(2)I C(1)–Pt(1)–C(2) C(1)I –Pt(1)–C(2) C(2)I –Pt(1)–C(2) N(1)–C(1)–Pt(1) N(2)–C(2)–Pt(1) C(2A)–S(1A)–C(1A) C(3A)–S(2A)–C(2A) C(4A)–S(3A)–C(5A) C(5A)–S(4A)–C(6A) C(1A)II –C(1A)–S(1A) C(2A)II –C(2A)–S(1A) C(2A)II –C(2A)–S(2A) S(1A)–C(2A)–S(2A) C(4A)–C(3A)–S(2A)II C(4A)–C(3A)–S(2A) S(2A)II –C(3A)–S(2A) C(3A)–C(4A)–S(3A) C(3A)–C(4A)–S(3A)II S(3A)–C(4A)–S(3A)II C(5A)II –C(5A)–S(4A) C(5A)II –C(5A)–S(3A) S(4A)–C(5A)–S(3A) C(6A)II –C(6A)–S(4A) C(2B)–S(1B)–C(1B) C(3B)–S(2B)–C(2B) C(4B)–S(3B)–C(5B) C(5B)–S(4B)–C(6B) C(1B)I –C(1B)–S(1B) C(2B)I –C(2B)–S(2B) C(2B)I –C(2B)–S(1B) S(2B)–C(2B)–S(1B) C(4B)–C(3B)–S(2B) C(4B)–C(3B)–S(2B)I S(2B)–C(3B)–S(2B)I C(3B)–C(4B)–S(3B)I C(3B)–C(4B)–S(3B) S(3B)I –C(4B)–S(3B)
95.9(3) 178.6(2) 85.5(2) 85.5(2) 178.6(2) 93.1(3) 178.3(5) 178.1(5) 98.5(2) 94.78(19) 95.33(19) 102.9(2) 123.35(16) 123.76(13) 117.50(13) 118.3(2) 122.54(14) 122.54(14) 114.8(3) 122.90(14) 122.90(14) 114.2(3) 128.28(13) 117.35(13) 114.4(2) 128.7(2) 101.3(2) 95.4(2) 95.3(2) 100.9(2) 127.07(18) 116.85(14) 127.41(13) 115.7(2) 122.24(15) 122.24(15) 115.4(3) 121.95(16) 121.95(16) 115.8(3)
C(5B)I –C(5B)–S(3B) C(5B)I –C(5B)–S(4B) S(3B)–C(5B)–S(4B) C(6B)I –C(6B)–S(4B) C(2C)–S(1C)–C(1C) C(3C)–S(2C)–C(2C) C(4C)–S(3C)–C(5C) C(5C)–S(4C)–C(6C) C(1C)I –C(1C)–S(1C) C(2C)I –C(2C)–S(2C) C(2C)I –C(2C)–S(1C) S(2C)–C(2C)–S(1C) C(4C)–C(3C)–S(2C) C(4C)–C(3C)–S(2C)I S(2C)–C(3C)–S(2C)I C(3C)–C(4C)–S(3C)I C(3C)–C(4C)–S(3C) S(3C)I –C(4C)–S(3C) C(5C)I –C(5C)–S(4C) C(5C)I –C(5C)–S(3C) S(4C)–C(5C)–S(3C) C(6C)I –C(6C)–S(4C) C(2D)–S(1D)–C(1D) C(3D)–S(2D)–C(2D) C(5D)–S(3D)–C(4D) C(6D)–S(4D)–C(5D) C(1D)I –C(1D)–S(1D) C(2D)I –C(2D)–S(1D) C(2D)I –C(2D)–S(2D) S(1D)–C(2D)–S(2D) C(4D)–C(3D)–S(2D) C(4D)–C(3D)–S(2D)I S(2D)–C(3D)–S(2D)I C(3D)–C(4D)–S(3D)I C(3D)–C(4D)–S(3D) S(3D)I –C(4D)–S(3D) C(5D)I –C(5D)–S(3D) C(5D)I –C(5D)–S(4D) S(3D)–C(5D)–S(4D) C(6D)I –C(6D)–S(4D)
116.76(13) 126.76(13) 116.5(2) 127.66(17) 100.5(2) 95.5(2) 95.3(2) 102.1(2) 126.22(19) 116.95(14) 126.16(14) 116.8(2) 122.45(15) 122.45(15) 115.0(3) 122.57(16) 122.57(16) 114.8(3) 126.49(13) 117.06(13) 116.4(2) 125.98(18) 99.1(2) 94.8(2) 95.4(2) 104.0(2) 124.53(16) 124.46(13) 117.57(13) 117.8(2) 122.35(15) 122.35(15) 115.2(3) 122.80(14) 122.80(14) 114.4(3) 117.42(13) 127.62(13) 115.0(2) 128.19(19)
Symmetry transformations used to generate equivalent atoms: I x, (1/2) − y, z; II x, −1/2 − y, z.
As the anion charge is equal to −2, in principle the formal charge on each radical cation is equal to +1/2. The Pt(CN)4 2− anion has a square planar form typical to Pt(II) complexes with unequal bond lengths Pt(1)–C(1) makes 1.970(6) and Pt(1)–C(2) 1.999(5) Å [10]. The bond angles Pt(1)–C(1)–N(1) and Pt(1)–C(2)–N(2) are equal to 178.3(5) and 178.1(5)◦ , respectively. The structure of salt 1 has two short contacts (shorter than van der Waals (VDW) radii sum ) between the cation and anion layers: Pt(1). . . C(6A) makes 3.647 Å (VDW radii Pt and C are 2.1 and 1.7 Å, respectively [11]).
Fig. 1. Projection of crystal structure of (EVT)4 ·[Pt(CN)4 ] on ab plane.
Symmetry transformations used to generate equivalent atoms: I x, (1/2) − y, z; II x, −1/2 − y, z.
Fig. 2. Structure of Pt(CN)4 2− anion (symmetry transformations used to generate equivalent atoms: x, (1/2) − y, z).
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A.D. Dubrovskii et al. / Synthetic Metals 140 (2004) 171–176 Table 4 Shortened intermolecular contacts S. . . S between radical cations Contact S2A. . . S3A(I)
S2A. . . S4A(I) S1A. . . S1B(II) S2A. . . S1B(II) S1C. . . S4D(III) S2C. . . S4D(III) S3C. . . S2D(III) S4C. . . S1D(III)
R (Å)
Contact
R (Å)
3.502 3.596 3.569 3.519 3.503 3.564 3.577 3.418
S4A. . . S3B(II)
3.364 3.591 3.579 3.377 3.502 3.412 3.503 3.535
S4A. . . S4B(II) S1B. . . S4D(I) S2B. . . S4D(I) S4C. . . S2D(III) S2C. . . S4C(III) S2B. . . S2C(IV) S2B. . . S3C(IV)
Symmetry transformations: I 1 − x, −y, 1 − z; II x, y, z; III 1 − x, −y, −z; IV x, y, 1 + z.
Fig. 3. View of a cation layer in (EVT)4 ·[Pt(CN)4 ] showing the short S. . . S contacts as dashed lines.
The radical cation layer is formed by EVT stacks held together by short S. . . S contacts being the packing of EVT donors of the -type [12]. Fig. 3 shows EVT radical cation packing in the organic layer. The stacking axis is practically parallel to the c-axis of the unit cell and the donors in the stack alternate in the following way: . . . A. . . B. . . C. . . D. . . A. . . B. . . C. . . D. . . (Fig. 4). The distances between the radical cations middle planes (the planes are drawn through the central TTF-fragment) make the following values: 3.67(1) Å (A. . . B), 3.53(2) Å (B. . . C), 3.75(1) Å (C. . . D) and 4.07(2) Å (D. . . A ) and are almost parallel (the angle between the middle planes of TTF-fragments does not exceed 4.5(1)◦ ). Taking into account the interplanar distances radical cations in the stack are tetramerized. Inside the tetramers, A, B and C, D
Fig. 4. View of the alternation of the EVT molecules in the stack.
molecules are shifted with respect to each other along the long molecule axis around one half of the central C=C bond length and between C and B molecules there is practically no shift. EVT donors of the neighboring stacks are connected by short intermolecular S. . . S contacts (3.364–3.596 Å), which are shorter than the sum of the VDW radii of sulfur atom (3.6 Å [13]). Radical cations A–D have 16, 12, 14 and 10 intermolecular contacts respectively. Alongside with the short contacts between the stacks, there are short intermolecular intrastacks S. . . S contacts (3.503–3.535 Å), in particular between B and C cations (four contacts). Taking into account short intermolecular contacts between B and C radical cations inside the stack, one can speak about their dimerization in the tetramer. The list of short intermolecular contacts is given in Table 4. EVT radical cations have a non-planar structure. The twist angle along the S. . . S line of terminated vinylenedithio fragment and the adjacent tetrathioethylene fragment in all molecules is around 53◦ . The external carbon atoms of all cations in 1 show large values of the equivalent isotropic thermal parameters and as a result C–C bond lengths of ethylene and vinylene fragments have approximately equal values not exceeding 1.343(8) Å. This fact might be accounted for by positional disordering of EVT molecules. The bond lengths and angles of the TTF internal fragment of the EVT molecules in salt 1 are similar in general to those earlier found for neutral EVT [14,15] and (EVT)2 ·AsF6 salt [16]. Table 5 summarizes the bond lengths of the neutral EVT0 molecule, EVT+1/2 and the four independent molecules of EVT in the crystal structure of (EVT)4 ·[Pt(CN)4 ] 1. From the values on Table 5 and according to the fact that the length of the central C=C bond grows with the increase of the radical cation charge, it can be assumed that EVT molecules A and B in salt 1 are neutral and all charge is localized in molecules B and C. Indeed, B and C molecules have the bond lengths a and d longer and b and c shorter than those of (EVT)2 ·AsF6 salt. EPR studies were performed on a plate-like single crystal at room temperature. The crystal was rotated in three orthogonal planes corresponding to the ab, bc, and ac crystallographic planes. EPR parameters (g factor, and peak-to-peak linewidth, Hpp ), in three orientations of the crystal with
A.D. Dubrovskii et al. / Synthetic Metals 140 (2004) 171–176
175
Table 5 Comparative bonds lengths (Å) in EVT molecules
a b c d Reference
A
B
C
D
EVT0
EVT+1/2
1.340(7) 1.752(3) 1.752(4) 1.329(8)
1.384(7) 1.718(3) 1.742(4) 1.345(8) This work
1.371(7) 1.729(3) 1.740(4) 1.335(8)
1.333(7) 1.751(3) 1.743(4) 1.341(8)
1.336 1.755 1.753 1.329 [14,15]
1.359 1.739 1.743 1.333 [16]
Table 6 Room temperature EPR parameters for (EVT)4 ·[Pt(CN)4 ] Compound
(EVT)4 ·[Pt(CN)4 ]
EPR parameters gmax.
Hppmax(G)
gint
Hppint(G)
gmim
Hppmim(G)
2.0104
6.9
2.0054
6.9
2.0025
6.9
respect to the external magnetic field are reported in Table 6. The EPR spectra confirm the diamagnetic character of the anion as only display a narrow EPR lorentzian signal with g-values typical of the organic donor. In accordance with the crystal structure, the g-factor maximum value is observed when the magnetic field is applied along the a-axis which correspond with the EVT molecular largest axis, and the g-factor minimum value when the magnetic field is parallel to the c-axis, the EVT radical cation staking direction. (EVT)4 ·[Pt(CN)4 ] salt display a very weak EPR signal in accordance with the X-ray and conductivity measurements that points out towards strong dimerization of the radical-cation molecules B and C. In fact the EPR signal should be attributed to defects on the crystal due to non-dimerized radical cations and in accordance with this the linewidth is narrow and do not present anisotropy. The conductivity of (EVT)4 ·[Pt(CN)4 ] crystals at room temperature is relatively low (8 × 10−2 −1 cm−1 ) and shows semiconducting character. This result is in accordance with the previous EPR results and the X-ray characteristics showing short contacts between B and C radical cations (namely their dimerization) in the stack as well as by charge localization on these radicals. In conclusion, on changing the donor from ET to EVT in (D)4 [Pt(CN)4 ] salts, strong changes in the physical properties are observed. Even though the (EVT)4 ·[Pt(CN)4 ] crystals have similar -like packing than the (ET)4 ·[Pt(CN)4 ] salt with  -packing type of radical cations, the transport properties are different since ET salt is metallic [2–4] whereas EVT salt 1 is semiconductor. This result is due to the fact that
in the (ET)4 ·[Pt(CN)4 ] salt the average interplane distances between the ET molecules in the stack are approximately equal whereas in (EVT)4 ·[Pt(CN)4 ] salt a strong dimerization with charge localization is observed.
Acknowledgements This work was partially supported by grants from the INTAS No 2001-2212, RFBR No 02-03-33218, DGI-Spain BQU2000-1157 and DURSI-Catalunya 2001SGR-00362.
References [1] R.P. Shibaeva, R.M. Lobkovskaya, V.E. Korotkov, N.D. Kushch, E.B. Yagubskii, M.K. Makova, Synth. Met. 27 (1988) A457. [2] R.M. Lobkovskaya, N.D. Kushch, R.P. Shibaeva, E.B. Yagubskii, M.A. Simonov, Kristallografiya 34 (1989) 1158. [3] L. Ouahab, J. Padiou, D. Grandjean, Ch. Garrigou-Lagrange, P. Delhaes, M. Bencharif, Chem. Commun. (1989) 1038. [4] M. Fettouhi, L. Ouahab, D. Grandjean, Acta Crystallogr. Sect. B 48 (1992) 275. [5] L. Ouahab, M. Fettouhi, J.F. Halet, V.M. Yartsev, C. GarrigouLagrange, P. Delhaes, C. Sourisseau, New J. Chem. 17 (1993) 399. [6] M. Fettouhi, L. Ouahab, D. Grandjean, L. Ducasse, J. Amiell, R. Canet, P. Delhaes, Chem. Mater. 7 (1995) 461. [7] H. Mori, I. Hirabayashi, S. Tanaka, T. Mori, Y. Maruyama, H. Inokuchi, Solid State Commun. 80 (1991) 411. [8] G.M. Sheldrick, SHELXS-86, Program for Crystal Structure Determination, University of Cambrige, UK, 1986. [9] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structure. University of Gottingen, Germany, 1997.
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[10] D.M. Wascheck, S.W. Peterson, A.H. Rels, J.M. Williams, Inorg. Chem. 15 (1976) 74. [11] S.S. Batsanov, Russ. J. Inorg. Chem. 36 (1991) 3015. [12] T. Mori, Bull. Chem. Soc. Jpn. 71 (1998) 2509. [13] S.S. Batsanov, Russ. Chem. Bull. 44 (1995) 24. [14] H. Nakano, K. Miyawaki, T. Nogami, Y. Shirota, S. Harada, N. Kasai, Bull. Chem. Soc. Jpn. 62 (1989) 2604.
[15] V.E. Korotkov, R.P. Shibaeva, K.A. Balodis, V.Yu. Khodorkovskii, O.Ya. Neiland, Kristallografiya 36 (1991) 113. [16] H. Nakano, K. Miyawaki, T. Nogami, Y. Shirota, S. Harada, N. Kasai, A. Kobayashi, R. Kato, H. Kobayashi, Bull. Chem. Soc. Jpn. 63 (1990) 2281.
Synthesis, crystal structure and properties of the new semiconductor (EVT)4 ·[Pt(CN)4 ] A.D. Dubrovskii a , N.G. Spitsina a,∗ , A.N. Chekhlov a , O.A. Dyachenko a , L.I. Buravov a , A.A. Lobach a , Jose Vidal Gancedo b , Concepcio Rovira b a
b
Institute of Problems of Chemical Physics RAS, Moscow District, Chernogolovka 142432, Russia Institut de Ciència de Materials de Barcelona, CSIC, Campus de la U.A.B., E-08193 Bellaterra, Spain Received 18 April 2003; accepted 21 May 2003
Abstract A novel radical cation salt based on of the donor (4,5-ethylenedithio-4 ,5 -vinylenedithio)tetrathiafulvalene (EVT) with the square planar anion Pt(CN)4 2− has been synthesized: (EVT)4 ·[Pt(CN)4 ] (1). According to the X-ray analysis its crystal structure includes EVT cation layers alternating with anion layers along the a-axis of the unit cell. The radical cation layer is formed by EVT stacks with -packing type, the donors in stacks are tetramerized. The EPR spectra of a plate-like crystal of (EVT)4 ·[Pt(CN)4 ] salt shows a very weak signal with typical parameters of TTF derivative. The room temperature conductivity of salt 1 is 8 × 10−2 −1 cm−1 and the temperature dependence of the conductivity exhibits semiconducting character. © 2003 Elsevier B.V. All rights reserved. Keywords: Radical cation salts; (4,5-Ethylenedithio-4 ,5 -vinylenedithio)tetrathiafulvalene; Tetracyanoplatinate(II) anion; X-ray crystal structure; EPR spectroscopy
1. Introduction Synthesis, crystal structure and conducting properties of organic conductors based on TTF and some of its unsymmetrical (methylenedithio)tetrathiafulvalene (MDT-TTF), (ethylenedithio)tetrathiafulvalene (EDT-TTF) and symmetrical derivatives such as (tetramethyl)tetraselenafulvalene (TMTSF), bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET) with tetracyanoplatinate(II) anion have been reported earlier [1–7]. Radical cation salts with tetracyanoplatinate(II) anions display a wide spectrum of conducting properties ranging from semiconductors [3,5,6] to metals [1–4] and even superconductors [7].The anionic part alongside with the Pt(CN)4 2− might include either molecules of a solvent or water due to different synthesis conditions [3,5,7]. For studying the impact of the donor molecular structure on the properties of radical cation salts:
∗ Corresponding author. Tel.: +7-095-785-7048; fax: +7-096-515-5420. E-mail address: [email protected] (N.G. Spitsina).
0379-6779/03/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0379-6779(03)00353-9
we synthesized and studied the salt based on dehydrated derivative of ET ((4,5-ethylenedithio-4 ,5 -vinylenedithio)tetrathiafulvalene (EVT)) with tetracyanoplatinate(II) anion. This work presents data concerning the crystal structure, EPR spectroscopy and conducting properties of radical cation salt (EVT)4 ·[Pt(CN)4 ].
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2. Experimental 2.1. Synthesis
Table 1 Atomic coordinates (×10−4 ) and equivalent isotropic displacement parameters for (EVT)4 ·[Pt(CN)4 ] Atom
Crystals of the (EVT)4 ·[Pt(CN)4 ] salt were obtained by electro-chemical oxidation of neutral EVT (C1 = 1 × 10−3 M) in an H-shaped electrochemical cell with separated anode and cathode spaces. The reaction was performed in fresh distillated benzonitrile (C6 H5 CN, Aldrich chemical) with 10 vol.% of absolute ethyl alcohol in the mode of direct current (I = 0.75 mA) in Ar atmosphere at 25 ◦ C. The tetrabutylammoniun salt (Bu4 N)2 ·Pt(CN)4 was used as electrolyte. Within 8 days black plates-shaped crystals with characteristic metallic shine were growing on the Pt anode. The crystals were filtered, washed in acetone and dried in the air. The correlation between S and Pt according to the local X-ray analysis is equal to 32:1 which corresponds to the formula (EVT)4 ·[Pt(CN)4 ] for salt 1, that composition was confirmed by the X-ray study. 2.2. X-ray study A single crystal of 1 in the form of a thin plate resembling a parallelepiped with dimensions of 0.4 mm × 0.25 mm × 0.05 mm was selected for the X-ray study. The main crystallographic data of the crystal structure of salt 1 are: C44 H24 N4 S32 Pt, M = 1829.7, a = 15.860(2) Å, b = 11.822(2) Å, c = 16.490(3) Å, β = 101.00(2)◦ , V = 3035.0(8) Å3 , monoclinic, the group P21 /m, Z = 2, dcalc = 2.00 g/cm3 . The unit cell parameters were determined and specified by the least square method (LSM) using 25 strong automatically centered reflections on the four-circle automatic diffractometer CAD-4 (graphite-monochromatized Mo K␣ radiation, λ = 0.7107 Å). Five thousand six hundred and six independent reflections (among them 4301 with I ≥ 2σ(I)) were registered by ω/2θ scanning within the angle range of 2.52◦ ≤ 2θ ≤ 49.94◦ . The structure was solved by a direct method and a number of successive Fourier syntheses using SHELX-86 program [8]. Hydrogen atoms were not localized. The refinement was done with the LSM with the anisotropic approximation for all non-hydrogen atoms using SHELX-97 program [9]. The final R factor value is 0.047 for 4301 reflections with I ≥ 2σ (I). The absorption was not considered (µ(Mo K␣) = 3.46 mm−1 ). The atom coordinates and their equivalent isotropic thermal parameters are given in Table 1. The bond lengths and angles are presented in Tables 2 and 3, respectively. 2.3. EPR spectroscopy The EPR spectra have been performed in a plate-like crystal on a Bruker ESP-300 E spectrometer operating in the X-band (9.3 GHz) and equipped with a TE102 microwave cavity, a Field Frequency lock system BRUKER ER 033 M and a NMR Gaussmeter BRUKER ER 035 M. The microwave power was kept well below saturation.
Pt(1) C(1) N(1) C(2) N(2) S(1A) S(2A) S(3A) S(4A) C(1A) C(2A) C(3A) C(4A) C(5A) C(6A) S(1B) S(2B) S(3B) S(4B) C(1B) C(2B) C(3B) C(4B) C(5B) C(6B) S(1C) S(2C) S(3C) S(4C) C(1C) C(2C) C(3C) C(4C) C(5C) C(6C) S(1D) S(2D) S(3D) S(4D) C(1D) C(2D) C(3D) C(4D) C(5D) C(6D)
x −83(1) −16(3) 20(3) −150(3) −169(3) 1589(1) 3501(1) 5403(1) 7019(1) 902(2) 2524(2) 4063(3) 4843(3) 6259(2) 7820(4) 2482(1) 4160(1) 6071(1) 7858(1) 1579(3) 3259(2) 4710(3) 5520(3) 7008(2) 8737(3) 1683(1) 3457(1) 5372(1) 7030(1) 805(3) 2538(3) 4013(4) 4818(4) 6244(2) 7941(3) 1641(1) 3417(1) 5252(1) 6912(1) 789(3) 2510(2) 3960(3) 4710(3) 6126(2) 7722(3)
y
z
Beq (Å2 × 103 )
2500 1262(5) 517(4) 1272(5) 557(4) −1112(1) −1252(1) −1256(1) −1023(1) −1938(4) −1939(3) −2500 −2500 −1937(3) −1952(5) 1040(1) 1270(1) 1271(1) 1044(1) 1937(5) 1934(3) 2500 2500 1928(3) 1952(5) 1058(1) 1269(1) 1265(1) 1064(1) 1939(5) 1933(4) 2500 2500 1938(3) 1935(4) 1099(1) 1249(1) 1256(1) 1032(1) 1950(4) 1935(3) 2500 2500 1931(3) 1932(5)
2609(1) 1824(3) 1378(3) 3428(3) 3890(3) 3908(1) 4557(1) 5697(1) 6900(1) 4406(3) 4164(2) 4874(3) 5362(3) 6343(2) 7395(6) 5335(1) 6451(1) 7535(1) 8438(1) 5147(4) 5883(2) 6753(4) 7249(4) 8009(2) 8450(4) −2626(1) −1660(1) −554(1) 621(1) −2552(4) −2179(3) −1356(3) −871(4) 68(2) 758(5) −300(1) 719(1) 1955(1) 3079(1) −83(3) 161(2) 1067(4) 1593(4) 2550(2) 3523(5)
44(1) 61(2) 70(1) 56(2) 72(2) 46(1) 38(1) 41(1) 54(1) 49(1) 34(1) 29(1) 31(1) 33(1) 141(3) 54(1) 39(1) 39(1) 55(1) 87(2) 36(1) 32(1) 34(1) 36(1) 86(2) 60(1) 40(1) 40(1) 57(1) 83(2) 42(1) 32(1) 34(2) 35(1) 99(3) 51(1) 42(1) 46(1) 68(1) 57(1) 35(1) 33(1) 32(1) 38(1) 97(2)
3. Results and discussion The crystal structure of salt (EVT)4 ·[Pt(CN)4 ] is layered: the layers of radical cations alternate with the anion layers along the a-directions of the unit cell (Figs. 1 and 2). The Pt atom of crystallographically independent anion Pt(CN)4 2− is located in a special position on the symmetry plane m and carbon atoms of the central C=C bond of the four EVT crystallographically independent radical cations (further on marked as A–D) are also located in special positions on the symmetry plane m. The asymmetric part of the unit cell contains half of anion and half of all the four radical cations.
A.D. Dubrovskii et al. / Synthetic Metals 140 (2004) 171–176 Table 2 Bond lengths (d) for (EVT)4 ·[Pt(CN)4 ]
173
Table 3 Selected angles (ω) for (EVT)4 ·[Pt(CN)4 ]
Bond
d (Å)
Bond
d (Å)
Angle
ω (◦ )
Angle
ω (◦ )
Pt(1)–C(1) Pt(1)–C(1)I Pt(1)–C(2)I Pt(1)–C(2) C(1)–N(1) C(2)–N(2) S(1A)–C(2A) S(1A)–C(1A) S(2A)–C(3A) S(2A)–C(2A) S(3A)–C(4A) S(3A)–C(5A) S(4A)–C(5A) S(4A)–C(6A) C(1A)–C(1A)II C(2A)–C(2A)II C(3A)–C(4A) C(3A)–S(2A)II C(4A)–S(3A)II C(5A)–C(5A)II C(6A)–C(6A)II S(1B)–C(2B) S(1B)–C(1B) S(2B)–C(3B) S(2B)–C(2B) S(3B)–C(4B) S(3B)–C(5B) S(4B)–C(5B) S(4B)–C(6B) C(1B)–C(1B)I C(2B)–C(2B)I C(3B)–C(4B) C(3B)–S(2B)I
1.970(6) 1.970(6) 1.999(5) 1.999(5) 1.156(7) 1.142(7) 1.759(4) 1.776(5) 1.751(3) 1.759(4) 1.752(3) 1.754(4) 1.744(4) 1.758(6) 1.328(10) 1.326(8) 1.340(7) 1.751(3) 1.752(3) 1.331(8) 1.296(12) 1.742(4) 1.761(5) 1.720(3) 1.739(4) 1.715(3) 1.726(4) 1.745(4) 1.756(5) 1.330(11) 1.337(8) 1.384(7) 1.720(3)
C(4B)–S(3B)I C(5B)–C(5B)I C(6B)–C(6B)I S(1C)–C(2C) S(1C)–C(1C) S(2C)–C(3C) S(2C)–C(2C) S(3C)–C(4C) S(3C)–C(5C) S(4C)–C(5C) S(4C)–C(6C) C(1C)–C(1C)I C(2C)–C(2C)I C(3C)–C(4C) C(3C)–S(2C)I C(4C)–S(3C)I C(5C)–C(5C)I C(6C)–C(6C)I S(1D)–C(2D) S(1D)–C(1D) S(2D)–C(3D) S(2D)–C(2D) S(3D)–C(5D) S(3D)–C(4D) S(4D)–C(6D) S(4D)–C(5D) C(1D)–C(1D)I C(2D)–C(2D)I C(3D)–C(4D) C(3D)–S(2D)I C(4D)–S(3D)I C(5D)–C(5D)I C(6D)–C(6D)I
1.715(3) 1.352(8) 1.296(11) 1.753(4) 1.761(6) 1.725(3) 1.731(4) 1.732(3) 1.748(4) 1.737(4) 1.753(5) 1.327(12) 1.341(9) 1.371(8) 1.725(3) 1.732(3) 1.329(8) 1.335(10) 1.746(4) 1.775(5) 1.752(3) 1.753(4) 1.732(4) 1.750(3) 1.720(5) 1.740(4) 1.299(10) 1.335(8) 1.333(7) 1.752(3) 1.750(3) 1.346(8) 1.342(11)
C(1)–Pt(1)–C(1)I C(1)–Pt(1)–C(2)I C(1)I –Pt(1)–C(2)I C(1)–Pt(1)–C(2) C(1)I –Pt(1)–C(2) C(2)I –Pt(1)–C(2) N(1)–C(1)–Pt(1) N(2)–C(2)–Pt(1) C(2A)–S(1A)–C(1A) C(3A)–S(2A)–C(2A) C(4A)–S(3A)–C(5A) C(5A)–S(4A)–C(6A) C(1A)II –C(1A)–S(1A) C(2A)II –C(2A)–S(1A) C(2A)II –C(2A)–S(2A) S(1A)–C(2A)–S(2A) C(4A)–C(3A)–S(2A)II C(4A)–C(3A)–S(2A) S(2A)II –C(3A)–S(2A) C(3A)–C(4A)–S(3A) C(3A)–C(4A)–S(3A)II S(3A)–C(4A)–S(3A)II C(5A)II –C(5A)–S(4A) C(5A)II –C(5A)–S(3A) S(4A)–C(5A)–S(3A) C(6A)II –C(6A)–S(4A) C(2B)–S(1B)–C(1B) C(3B)–S(2B)–C(2B) C(4B)–S(3B)–C(5B) C(5B)–S(4B)–C(6B) C(1B)I –C(1B)–S(1B) C(2B)I –C(2B)–S(2B) C(2B)I –C(2B)–S(1B) S(2B)–C(2B)–S(1B) C(4B)–C(3B)–S(2B) C(4B)–C(3B)–S(2B)I S(2B)–C(3B)–S(2B)I C(3B)–C(4B)–S(3B)I C(3B)–C(4B)–S(3B) S(3B)I –C(4B)–S(3B)
95.9(3) 178.6(2) 85.5(2) 85.5(2) 178.6(2) 93.1(3) 178.3(5) 178.1(5) 98.5(2) 94.78(19) 95.33(19) 102.9(2) 123.35(16) 123.76(13) 117.50(13) 118.3(2) 122.54(14) 122.54(14) 114.8(3) 122.90(14) 122.90(14) 114.2(3) 128.28(13) 117.35(13) 114.4(2) 128.7(2) 101.3(2) 95.4(2) 95.3(2) 100.9(2) 127.07(18) 116.85(14) 127.41(13) 115.7(2) 122.24(15) 122.24(15) 115.4(3) 121.95(16) 121.95(16) 115.8(3)
C(5B)I –C(5B)–S(3B) C(5B)I –C(5B)–S(4B) S(3B)–C(5B)–S(4B) C(6B)I –C(6B)–S(4B) C(2C)–S(1C)–C(1C) C(3C)–S(2C)–C(2C) C(4C)–S(3C)–C(5C) C(5C)–S(4C)–C(6C) C(1C)I –C(1C)–S(1C) C(2C)I –C(2C)–S(2C) C(2C)I –C(2C)–S(1C) S(2C)–C(2C)–S(1C) C(4C)–C(3C)–S(2C) C(4C)–C(3C)–S(2C)I S(2C)–C(3C)–S(2C)I C(3C)–C(4C)–S(3C)I C(3C)–C(4C)–S(3C) S(3C)I –C(4C)–S(3C) C(5C)I –C(5C)–S(4C) C(5C)I –C(5C)–S(3C) S(4C)–C(5C)–S(3C) C(6C)I –C(6C)–S(4C) C(2D)–S(1D)–C(1D) C(3D)–S(2D)–C(2D) C(5D)–S(3D)–C(4D) C(6D)–S(4D)–C(5D) C(1D)I –C(1D)–S(1D) C(2D)I –C(2D)–S(1D) C(2D)I –C(2D)–S(2D) S(1D)–C(2D)–S(2D) C(4D)–C(3D)–S(2D) C(4D)–C(3D)–S(2D)I S(2D)–C(3D)–S(2D)I C(3D)–C(4D)–S(3D)I C(3D)–C(4D)–S(3D) S(3D)I –C(4D)–S(3D) C(5D)I –C(5D)–S(3D) C(5D)I –C(5D)–S(4D) S(3D)–C(5D)–S(4D) C(6D)I –C(6D)–S(4D)
116.76(13) 126.76(13) 116.5(2) 127.66(17) 100.5(2) 95.5(2) 95.3(2) 102.1(2) 126.22(19) 116.95(14) 126.16(14) 116.8(2) 122.45(15) 122.45(15) 115.0(3) 122.57(16) 122.57(16) 114.8(3) 126.49(13) 117.06(13) 116.4(2) 125.98(18) 99.1(2) 94.8(2) 95.4(2) 104.0(2) 124.53(16) 124.46(13) 117.57(13) 117.8(2) 122.35(15) 122.35(15) 115.2(3) 122.80(14) 122.80(14) 114.4(3) 117.42(13) 127.62(13) 115.0(2) 128.19(19)
Symmetry transformations used to generate equivalent atoms: I x, (1/2) − y, z; II x, −1/2 − y, z.
As the anion charge is equal to −2, in principle the formal charge on each radical cation is equal to +1/2. The Pt(CN)4 2− anion has a square planar form typical to Pt(II) complexes with unequal bond lengths Pt(1)–C(1) makes 1.970(6) and Pt(1)–C(2) 1.999(5) Å [10]. The bond angles Pt(1)–C(1)–N(1) and Pt(1)–C(2)–N(2) are equal to 178.3(5) and 178.1(5)◦ , respectively. The structure of salt 1 has two short contacts (shorter than van der Waals (VDW) radii sum ) between the cation and anion layers: Pt(1). . . C(6A) makes 3.647 Å (VDW radii Pt and C are 2.1 and 1.7 Å, respectively [11]).
Fig. 1. Projection of crystal structure of (EVT)4 ·[Pt(CN)4 ] on ab plane.
Symmetry transformations used to generate equivalent atoms: I x, (1/2) − y, z; II x, −1/2 − y, z.
Fig. 2. Structure of Pt(CN)4 2− anion (symmetry transformations used to generate equivalent atoms: x, (1/2) − y, z).
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A.D. Dubrovskii et al. / Synthetic Metals 140 (2004) 171–176 Table 4 Shortened intermolecular contacts S. . . S between radical cations Contact S2A. . . S3A(I)
S2A. . . S4A(I) S1A. . . S1B(II) S2A. . . S1B(II) S1C. . . S4D(III) S2C. . . S4D(III) S3C. . . S2D(III) S4C. . . S1D(III)
R (Å)
Contact
R (Å)
3.502 3.596 3.569 3.519 3.503 3.564 3.577 3.418
S4A. . . S3B(II)
3.364 3.591 3.579 3.377 3.502 3.412 3.503 3.535
S4A. . . S4B(II) S1B. . . S4D(I) S2B. . . S4D(I) S4C. . . S2D(III) S2C. . . S4C(III) S2B. . . S2C(IV) S2B. . . S3C(IV)
Symmetry transformations: I 1 − x, −y, 1 − z; II x, y, z; III 1 − x, −y, −z; IV x, y, 1 + z.
Fig. 3. View of a cation layer in (EVT)4 ·[Pt(CN)4 ] showing the short S. . . S contacts as dashed lines.
The radical cation layer is formed by EVT stacks held together by short S. . . S contacts being the packing of EVT donors of the -type [12]. Fig. 3 shows EVT radical cation packing in the organic layer. The stacking axis is practically parallel to the c-axis of the unit cell and the donors in the stack alternate in the following way: . . . A. . . B. . . C. . . D. . . A. . . B. . . C. . . D. . . (Fig. 4). The distances between the radical cations middle planes (the planes are drawn through the central TTF-fragment) make the following values: 3.67(1) Å (A. . . B), 3.53(2) Å (B. . . C), 3.75(1) Å (C. . . D) and 4.07(2) Å (D. . . A ) and are almost parallel (the angle between the middle planes of TTF-fragments does not exceed 4.5(1)◦ ). Taking into account the interplanar distances radical cations in the stack are tetramerized. Inside the tetramers, A, B and C, D
Fig. 4. View of the alternation of the EVT molecules in the stack.
molecules are shifted with respect to each other along the long molecule axis around one half of the central C=C bond length and between C and B molecules there is practically no shift. EVT donors of the neighboring stacks are connected by short intermolecular S. . . S contacts (3.364–3.596 Å), which are shorter than the sum of the VDW radii of sulfur atom (3.6 Å [13]). Radical cations A–D have 16, 12, 14 and 10 intermolecular contacts respectively. Alongside with the short contacts between the stacks, there are short intermolecular intrastacks S. . . S contacts (3.503–3.535 Å), in particular between B and C cations (four contacts). Taking into account short intermolecular contacts between B and C radical cations inside the stack, one can speak about their dimerization in the tetramer. The list of short intermolecular contacts is given in Table 4. EVT radical cations have a non-planar structure. The twist angle along the S. . . S line of terminated vinylenedithio fragment and the adjacent tetrathioethylene fragment in all molecules is around 53◦ . The external carbon atoms of all cations in 1 show large values of the equivalent isotropic thermal parameters and as a result C–C bond lengths of ethylene and vinylene fragments have approximately equal values not exceeding 1.343(8) Å. This fact might be accounted for by positional disordering of EVT molecules. The bond lengths and angles of the TTF internal fragment of the EVT molecules in salt 1 are similar in general to those earlier found for neutral EVT [14,15] and (EVT)2 ·AsF6 salt [16]. Table 5 summarizes the bond lengths of the neutral EVT0 molecule, EVT+1/2 and the four independent molecules of EVT in the crystal structure of (EVT)4 ·[Pt(CN)4 ] 1. From the values on Table 5 and according to the fact that the length of the central C=C bond grows with the increase of the radical cation charge, it can be assumed that EVT molecules A and B in salt 1 are neutral and all charge is localized in molecules B and C. Indeed, B and C molecules have the bond lengths a and d longer and b and c shorter than those of (EVT)2 ·AsF6 salt. EPR studies were performed on a plate-like single crystal at room temperature. The crystal was rotated in three orthogonal planes corresponding to the ab, bc, and ac crystallographic planes. EPR parameters (g factor, and peak-to-peak linewidth, Hpp ), in three orientations of the crystal with
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Table 5 Comparative bonds lengths (Å) in EVT molecules
a b c d Reference
A
B
C
D
EVT0
EVT+1/2
1.340(7) 1.752(3) 1.752(4) 1.329(8)
1.384(7) 1.718(3) 1.742(4) 1.345(8) This work
1.371(7) 1.729(3) 1.740(4) 1.335(8)
1.333(7) 1.751(3) 1.743(4) 1.341(8)
1.336 1.755 1.753 1.329 [14,15]
1.359 1.739 1.743 1.333 [16]
Table 6 Room temperature EPR parameters for (EVT)4 ·[Pt(CN)4 ] Compound
(EVT)4 ·[Pt(CN)4 ]
EPR parameters gmax.
Hppmax(G)
gint
Hppint(G)
gmim
Hppmim(G)
2.0104
6.9
2.0054
6.9
2.0025
6.9
respect to the external magnetic field are reported in Table 6. The EPR spectra confirm the diamagnetic character of the anion as only display a narrow EPR lorentzian signal with g-values typical of the organic donor. In accordance with the crystal structure, the g-factor maximum value is observed when the magnetic field is applied along the a-axis which correspond with the EVT molecular largest axis, and the g-factor minimum value when the magnetic field is parallel to the c-axis, the EVT radical cation staking direction. (EVT)4 ·[Pt(CN)4 ] salt display a very weak EPR signal in accordance with the X-ray and conductivity measurements that points out towards strong dimerization of the radical-cation molecules B and C. In fact the EPR signal should be attributed to defects on the crystal due to non-dimerized radical cations and in accordance with this the linewidth is narrow and do not present anisotropy. The conductivity of (EVT)4 ·[Pt(CN)4 ] crystals at room temperature is relatively low (8 × 10−2 −1 cm−1 ) and shows semiconducting character. This result is in accordance with the previous EPR results and the X-ray characteristics showing short contacts between B and C radical cations (namely their dimerization) in the stack as well as by charge localization on these radicals. In conclusion, on changing the donor from ET to EVT in (D)4 [Pt(CN)4 ] salts, strong changes in the physical properties are observed. Even though the (EVT)4 ·[Pt(CN)4 ] crystals have similar -like packing than the (ET)4 ·[Pt(CN)4 ] salt with  -packing type of radical cations, the transport properties are different since ET salt is metallic [2–4] whereas EVT salt 1 is semiconductor. This result is due to the fact that
in the (ET)4 ·[Pt(CN)4 ] salt the average interplane distances between the ET molecules in the stack are approximately equal whereas in (EVT)4 ·[Pt(CN)4 ] salt a strong dimerization with charge localization is observed.
Acknowledgements This work was partially supported by grants from the INTAS No 2001-2212, RFBR No 02-03-33218, DGI-Spain BQU2000-1157 and DURSI-Catalunya 2001SGR-00362.
References [1] R.P. Shibaeva, R.M. Lobkovskaya, V.E. Korotkov, N.D. Kushch, E.B. Yagubskii, M.K. Makova, Synth. Met. 27 (1988) A457. [2] R.M. Lobkovskaya, N.D. Kushch, R.P. Shibaeva, E.B. Yagubskii, M.A. Simonov, Kristallografiya 34 (1989) 1158. [3] L. Ouahab, J. Padiou, D. Grandjean, Ch. Garrigou-Lagrange, P. Delhaes, M. Bencharif, Chem. Commun. (1989) 1038. [4] M. Fettouhi, L. Ouahab, D. Grandjean, Acta Crystallogr. Sect. B 48 (1992) 275. [5] L. Ouahab, M. Fettouhi, J.F. Halet, V.M. Yartsev, C. GarrigouLagrange, P. Delhaes, C. Sourisseau, New J. Chem. 17 (1993) 399. [6] M. Fettouhi, L. Ouahab, D. Grandjean, L. Ducasse, J. Amiell, R. Canet, P. Delhaes, Chem. Mater. 7 (1995) 461. [7] H. Mori, I. Hirabayashi, S. Tanaka, T. Mori, Y. Maruyama, H. Inokuchi, Solid State Commun. 80 (1991) 411. [8] G.M. Sheldrick, SHELXS-86, Program for Crystal Structure Determination, University of Cambrige, UK, 1986. [9] G.M. Sheldrick, SHELXL-97, Program for the Refinement of Crystal Structure. University of Gottingen, Germany, 1997.
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[10] D.M. Wascheck, S.W. Peterson, A.H. Rels, J.M. Williams, Inorg. Chem. 15 (1976) 74. [11] S.S. Batsanov, Russ. J. Inorg. Chem. 36 (1991) 3015. [12] T. Mori, Bull. Chem. Soc. Jpn. 71 (1998) 2509. [13] S.S. Batsanov, Russ. Chem. Bull. 44 (1995) 24. [14] H. Nakano, K. Miyawaki, T. Nogami, Y. Shirota, S. Harada, N. Kasai, Bull. Chem. Soc. Jpn. 62 (1989) 2604.
[15] V.E. Korotkov, R.P. Shibaeva, K.A. Balodis, V.Yu. Khodorkovskii, O.Ya. Neiland, Kristallografiya 36 (1991) 113. [16] H. Nakano, K. Miyawaki, T. Nogami, Y. Shirota, S. Harada, N. Kasai, A. Kobayashi, R. Kato, H. Kobayashi, Bull. Chem. Soc. Jpn. 63 (1990) 2281.