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Preparation and characterization of Ni(dpedt)(pddt) and Ni(dpedt)(pddt)·CS2, where dpedt is diphenylethylenedithiolate and pddt is 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate
Polyhedron 29 (2010) 969–974
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Polyhedron journal homepage: www.elsevier.com/locate/poly
Preparation and characterization of Ni(dpedt)(pddt) and Ni(dpedt)(pddt)CS2, where dpedt is diphenylethylenedithiolate and pddt is 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate George C. Anyfantis a,*, George C. Papavassiliou a,*, Aris Terzis b, Catherine P. Raptopoulou b, Vassilis Psycharis b, Patrina Paraskevopoulou c a
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48, Vassileos Constantinou Avenue, Athens 116 35, Greece Institute of Materials Science, NCSR, Demokritos, Athens 15310, Greece c Department of Inorganic Chemistry, Faculty of Chemistry, Panepistimioupoli Zografou, Athens 15771, Greece b
a r t i c l e
i n f o
Article history: Received 21 September 2009 Accepted 19 November 2009 Available online 23 November 2009 Keywords: Metal 1,2-dithiolenes Crystal structure Optical properties Redox properties
a b s t r a c t The unsymmetrical nickel 1,2-dithiolene complex based on diphenylethylenedithiolate (dpedt) and 6,7dihydro-5H-1,4-dithiepin-2,3-dithiolate (pddt) was prepared and characterized. Depending on the conditions of crystallization, it is possible to obtain the complex in two different crystalline forms. X-ray structure studies recognize these forms as Ni(dpedt)(pddt) and Ni(dpedt)(pddt)CS2. The experimental optical and electrochemical parameters are in a good agreement with the calculated ones, using the corresponding parameters of the symmetrical complexes, Ni(dpedt)2 and Ni(pddt)2. The HOMO and LUMO energy levels, obtained from optical and electrochemical measurements, are very close to the Fermi energy of (metallic) Au. The chemical and electrochemical properties of both forms showed that they are stable in air and could be candidate materials for optics and electronics. Ó 2009 Published by Elsevier Ltd.
1. Introduction During the last four decades a large number of metal 1,2-dithiolenes (M 1,2-DTs) have been prepared and studied [1–20]. The intense interest on dithiolene complexes is the result of their properties, mainly their remarkable reversible redox behavior and their unique electronic structures. Dithiolene chemistry has spanned a wide range of areas such as reactive [2], conductive [3], optical [4,5,19,20], photoconductive [5], and bioinorganic [6] materials. Recent experimental results involve this kind of complexes as promising materials for optics [4,8,19] and electronics [7]. Especially, the complexes of gold (Au 1,2-DTs) [10b,20] exhibit optical absorption maxima close to the lines of telecommunication lasers (e.g., 1550 nm) [19–21]. The majority of these studies is dedicated to symmetrical complexes. The preparation of mixed-ligand M 1,2-DTs (unsymmetrical) reveals some difficulties. However, by combination of several ligands, we can create a large number of complexes. For example, the combinations of the 15 dithiolene ligands, which are presented in Scheme 1 generates 105 neutral unsymmetrical dithiolene compounds, only for one metal. It is obvious that the vast number of * Corresponding authors. Tel.: +30 210 7273827; fax: +30 210 7273794 (G.C. Papavassiliou). E-mail addresses: [email protected] (G.C. Anyfantis), [email protected] (G.C. Papavassiliou). 0277-5387/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.poly.2009.11.014
the dithiolene ligands and the choice of the metal produce a large number of unsymmetrical dithiolenes. Our effort is focused on the preparation and characterization of unsymmetrical mixed-ligand M 1,2-DTs mainly for two reasons: first, because with combination of the dithiolene ligands we can achieve desirable properties (e.g., stability and solubility) [9] and second, because the mixed-ligand complexes could be candidate materials for second-order non-linear optical properties [8b,13,22]. In this paper, the preparation and characterization of the unsymmetrical complexes Ni(dpedt)(pddt) and Ni(dpedt)(pddt) CS2, based on the ligands diphenylethylenedithiolate (dpedt) and 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate (pddt), are described. These forms based on the same ligands are referred herein as 1 and 2, respectively. The new complexes were prepared by the procedure of Scheme 2.
2. Experimental 2.1. Materials and physical measurements The starting materials dpdto, ttdeo were prepared by methods reported elsewhere [23]. Elemental analysis was performed on a Perkin 2400 (II) autoanalyser. Electronic optical absorption (OA) UV–Vis–NIR spectra in CS2 and the spectra of the complex deposited on quartz plates were recorded on a Perkin–Elmer, Lambda
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S
S
S
S
dmedt D D D D
S
S
Ph
S
S
S
dddt
S
S
O
S
S
S
S
S
S
S
O
S
S
S
S
S
S
S
edo C10 H21 S
S S
C10 H21 S
pddt
S
S
dpedt
tmedt
D4-dddt
S
Ph
mdddt S
S
S
S
S
S
dmit
S
S
S
S
S
S
S
S
S
S
O
S
dcdt
dt
dmdddt
dmio
S
S
S
S
S
S
dmdt
S
S
S
S
tmdt
Scheme 1. Formulae of several 1,2-dithiolene ligands.
Scheme 2.
19 spectrophotometer, in the range 200–2200 nm. The Raman spectra were recorded on a in Via Reflex Renishaw confocal micro-Raman spectrophotometer, in the range 2500–100 cm1. Cyclic voltammetry measurements were carried out with a Bipotentiostat AFCBP1 from Pine Instrument Company and controlled with the PINECHEM 2.7.9 software, using a gold disk working electrode (2 mm diameter) and a Ag/Ag+ (0.01 M AgNO3 and 0.5 M nBu4NPF6 in acetonitrile) non-aqueous reference electrode (Bioanalytical Systems, Inc.) with a prolonged bridge (0.5 M n-Bu4NPF6 in acetonitrile). A Pt foil or gauge (8 cm2, Sigma–Aldrich) was employed as counter electrode. The working electrode was polished using successively 6, 3, 1 mm diamond paste on a DP-Nap polishing cloth (Struers, Westlake, OH), washed with water, acetone and air dried. The Pt foil and gauge electrodes were cleaned in a H2O2/H2SO4 (conc.) solution (1:4 v:v) and oven-dried. The concentration of the samples varied between 1 and 3 mM and that of supporting electrolyte (n-Bu4NPF6) was 0.5 M. The potential sweep rate varied between 40 and 1000 mV/s. All potentials are reported versus the ferrocenium/ferrocene (Fþ c /Fc) couple. 2.2. Synthesis of compounds [Ni(dpedt)(pddt)] (1) and [Ni(dpedt)(pddt)]CS2 (2) In a two-necked 250 mL flask, a solution-suspension of dpdto (270 mg, 1 mmol) and ttdeo (222 mg, 1 mmol) in dry MeOH (20 mL) was prepared with stirring under nitrogen atmosphere. Then, a solution of NaOMe, freshly prepared from Na (115 mg, 5 mmol) and MeOH (10 mL) was added and the mixture stirred at room temperature for 30 min. To the obtained yellow solution, a solution of NiCl2H2O (238 mg, 1 mmol) in deoxygenated MeOH (80 mL) was added slowly within 15 min. The solution was stirred
under nitrogen atmosphere for 1 h at room temperature, whereupon the color turned brown. Then, aq. HCl (2 mL, 35%) was added and the mixture was transferred to a beaker and stirred in air overnight. The precipitate was filtered, washed with water and MeOH and dried in air. The green-brown solid was extracted with CS2 and chromatographed on a silica gel, using CS2 as eluent. The second green fraction contained Ni(dpedt)(pddt)CS2 (2) (84 mg, 35%). M.p.: 238 °C (dec.). Anal. Calc. for C20H16S8Ni (MW 571.6): C, 42.03; H, 2.82. Found: C, 41.50; H, 2.61%. Raman 1398 (cm1) (C@C). Solute diffusion crystallization of 2 using CS2 and n-hexane as solvents gave form 1. M.p.: 253 °C (dec.). Anal. Calc. for C19H16S6Ni (MW 495.41): C, 46.06; H, 3.26. Found: C, 45.99; H, 3.10%. Raman 1383 (cm1) (C@C). 1 and 2 showed identical 1H NMR (300 MHz, CS2/CDCl3 2:2): d = 7.18–7.54 (m, 10H CH), 3.28 (m, 4H CH2), 2.42 (m, 2H CH2). 2.3. X-ray crystallography A single crystal of 1 (0.06 0.133 0.49 mm) was mounted in an oil drop and a single crystal of 2 (0.2 0.3 0.5 mm) was mounted in air. Diffraction measurements for 1 were made under the continuous flow of Nitrogen gas cooled at 93 °C using the X-Stream 2000 (Rigaku MSC) cryogenic crystal cooler system on a Rigaku R-AXIS SPIDER Image Plate diffractometer using graphite monochromated Mo radiation. Data collection (x-scans) and processing (cell refinement, data reduction and empirical absorption correction) were performed using the CRYSTALCLEAR program package [24]. Diffraction measurements for 2 were made on a Crystal Logic Dual Goniometer diffractometer using graphite monochromated Mo radiation. Unit cell dimensions were determined and refined by using the angular settings of 25 automatically centered reflec-
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tions in the range 11 < 2h < 23° and they appear in Table 1. Three standard reflections monitored every 97 reflections showed less than 3% variation and no decay. Lorentz, polarization corrections were applied using CRYSTAL LOGIC software. The structures were solved by direct methods using SHELXS-97 [25] and refined by fullmatrix least-squares techniques on F2 with SHELXL-97 [26]. All hydrogen atoms were located by difference maps and were refined isotropically. All non-hydrogen atoms were refined anisotropically. 3. Results and discussion 3.1. Formation of compounds 1 and 2 By applying the pseudo cross-coupling method [12] for the synthesis of mixed-ligand M 1,2-DTs, the complex Ni(dpedt)(pddt) was obtained. This method gave better yields than the ligand exchange reaction and other methods [1b,1c,2,3c,13]. The success of the preparation of the complex under the strong oxidation conditions of Scheme 2 indicates its stability in air. The new complex is soluble in CS2, CH2Cl2 and other organic solvents. Among the organic solvents, CS2 was found to be the best for chromatography separation. Recrystallization by the solute diffusion method using CS2 and n-hexane as solvents, long black needles of Ni(dpedt)(pddt) (form 1) were obtained, while recrystallization from CS2 black blocks of Ni(dpedt)(pddt)CS2 (form 2) were obtained. Also, crystals of 1 were obtained by recrystallization from CH2Cl2. The corresponding symmetrical complexes (CSC) were obtained from these reactions in smaller yields, 11% for Ni(dpedt)2 and 3% for Ni(pddt)2. 3.2. Structural information Form 1 crystallizes in a non-centrosymmetric orthorhombic space group, indicating that this is a candidate material for second Table 1 Crystal data and structure refinement for 1 and 2.
Empirical formula Formula weight T (°C) Wavelength (Å) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g/cm3) l (mm1) 2hmax (°) Reflections collected Unique reflections Reflections used Rint Parameters refined (D/r)max (De)max (e/Å3) (De)min (e/Å3) R/Rw (all data) R1a wR2a
1
2
C19H16NiS6 495.39 93 0.71073 Pab21 8.1933(2) 13.9461(2) 18.3349(4) 90.0 90.0 90.0 2095.03(7) 4 1.571 1.526 52 24 739 4101 4101 0.0448 299 0.009 0.418 0.295 0.0394/0.0576 0.0285b 0.0523b
C20H16NiS8 571.52 25 0.71073 P21/n 9.344(5) 18.023(9) 14.756(7) 90.0 95.72(2) 90.0 2473(2) 4 1.535 1.467 48 4046 3879 3879 0.0305 303 0.001 0.879 0.489 0.0782/0.1709 0.0607c 0.1555c
a w = 1/[r2(F 2o ) + (aP)2 + bP] and P = ((max)F 2o ,0)+2F 2c )/3; a = 0.0257, b = 0.07 for 1 P P P and a = 0.0739, b = 5.12 for 2. R1 = (|Fo||Fc|)/ (|Fo|) and wR2 = { [w(F 2o F 2c )2]/ P [w(F 2o )2]}1/2. b For 3464 reflections with I > 2r(I). c For 3031 reflections with I > 2r(I).
harmonic generation in the solid state [8f,22]. Form 2 crystallizes in a monoclinic centrosymmetric one. In this form covalent molecules enter the crystal structure. Form 1 is isostructural with the complex Ni(dpedt)(dddt) [10a]. In all cases, the structures present square planar geometry. Table 1 shows selected bond lengths and bond angles in NiS4C4 core of 1 and 2. It is worth mentioning that the co-crystallized molecule of CS2 does not alter the geometry of the core and the distances in both cases are almost the same. But the co-crystallized molecule affects drastically the packing of molecules (Table 2). Fig. 1 shows the ORTEP diagrams of Ni(dpedt)(dddt) molecule in the structures of compounds 1 and 2. The numbering scheme for atoms is also given. Fig. 2 shows the stacking in columns along the c-axis of Ni(dpedt)(dddt) molecules in the structure of 1. In this non-centrosym-
Table 2 Selected bond lengths (Å) and bond angles (°) for Ni(dpedt)(pddt) (1) and Ni(dpedt)(pddt)(CS2) (2).
Ni–S(3) Ni–S(4) Ni–S(5) Ni–S(6) S(3)–C(5) S(4)–C(4) S(5)–C(7) S(6)–C(6) C(4)–C(5) C(6)–C(7) S(5)–Ni–S(6) S(3)–Ni–S(4) C(5)–S(3)–Ni C(4)–S(4)–Ni C(7)–S(5)–Ni C(6)–S(6)–Ni C(5)–C(4)–S(4) C(4)–C(5)–S(3) C(7)–C(6)–S(6) C(6)–C(7)–S(5)
1
2
2.1291(8) 2.1219(7) 2.1288(7) 2.1289(8) 1.720(3) 1.710(3) 1.704(3) 1.716(3) 1.389(4) 1.396(4) 91.41(3) 91.05(3) 105.82(10) 105.79(9) 105.42(9) 105.11(10) 119.3(2) 118.0(2) 118.7(2) 119.02(19)
2.1276(18) 2.1387(19) 2.1239(18) 2.1291(18) 1.707(6) 1.701(6) 1.713(6) 1.716(6) 1.396(9) 1.407(7) 90.91(7) 90.91(7) 105.3(2) 105.6(2) 106.5(2) 105.89(19) 118.3(5) 119.4(4) 118.7(4) 117.9(4)
Fig. 1. ORTEP plot of Ni(dpedt)(dddt) molecule in 1 (a) and 2 (b) at the 50% probability level.
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Absorbance (a. u.)
877
945
(I)
993
(a) (b)
(c)
310
(II) 977
λonset = 1400
Fig. 2. Columns formed by Ni(dpedt)(dddt) molecules in the structure of compound 1. The shortest SS distances are also shown.
metric structure, there is not a pseudo-centrosymmetrical arrangement of metal 1,2-dithiolene molecules. The shortest SS distance, (S3S5) (x, 0.5y, 0.5 + z) = 3.738 Å, is a little larger than the sum of van der Waals radii (3.7 Å). The needle axis of the crystal is the aaxis. There are two such columns per cell, the second of these is generated from the one shown in Fig. 2 by applying the twofold screw axis operation which is parallel to the c-axis and is passing through (0.5, 0.5, 0). Fig. 3 shows the packing diagram of Ni(dpedt)(dddt) and CS2 molecules in the structure of 2. Ni(dpedt)(dddt) forms centrosymetrically related ‘‘dimers” which are situated in rows along the b-axis and couples of CS2 molecules form rows which are extended parallel to the row of dimers. Both are repeated alternatively along the a -axis and so a layer of CS2 couples and Ni(dpedt)(dddt) ‘‘dimers” is formed parallel to the (0 0 1) plane. These type of layers are packed normal the ab plane. Fig. 3 shows the packing of layers normal to (0 0 1) plane. There are two such layers per cell, and the second of these is generated from the one shown in Fig. 2 by applying the twofold screw axis operation which is parallel to the b-axis and is passing through (0.75, 0.0, 0.75) point. Also, in the form 2
250
500
750
1000
1250
1500
λ (nm) Fig. 4. (I) Electronic spectra of Ni(dpedt)2 (a), Ni(dpedt)(pddt) (b) and Ni(pddt)2 (c) solutions in CS2; (II) optical absorption spectrum of a thin deposit of Ni(dpedt)(pddt) on quartz plate.
there are no SS contacts smaller than the sum of the van der Walls radii. 3.3. The electronic optical absorption spectra Fig. 4I shows the electronic OA spectra of Ni(dpedt)(pddt) as well as the spectra of the symmetrical complexes Ni(dpedt)2 and Ni(pddt)2 in CS2. The electronic spectrum of [Ni(dpedt)(pddt)] in CS2 exhibits a strong band at 945 nm, which is typical for dithiolene complexes. This band is assigned to a p ? p* (b1u ? b2g) transition between the HOMO and LUMO levels [13]. Knowing the kmax
Fig. 3. Packing diagram of Ni(dpedt)(dddt) and CS2 molecules in the structure of compound 2. The layer formed by Ni(dpedt)(dddt) dimers and CS2 couples as seen normal to the (0 0 1) plane.
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of the symmetrical ones, it is possible to predict the kmax of the unsymmetrical by applying the empirical equation kmax(AB) = [kmax(AA) + kmax(BB)]/2 (AA, BB symmetrical and AB the corresponding unsymmetrical dithiolene). Even though this equation is an empirical one, it is a powerful tool in dithiolene chemistry mainly for two reasons: (a) we can design unsymmetrical dithiolenes with desirable absorption and (b) we can characterize them from their absorption. Low frequency bands are discrete in the solid state spectra. Fig. 4II shows the spectrum of 1 deposited on quartz plate from solution in CH2Cl2, by the spin coating technique. The electronic OA spectra of 2 do not show any considerable difference from those of 1, even in the solid state.
3.4. Electrochemical results Fig. 5 shows the cyclic voltammogram of Ni(dpedt)(pddt) in CH2Cl2. The electrochemical data are listed in Table 3 together with those of the corresponding symmetrical complexes. One can see that the redox potential and other values of the unsymmetrical compound lie in between those of the corresponding symmetrical ones. The voltammogram of Fig. 5 shows the presence of two reduction waves in the recorded region. The first wave with E1/2(2/1) at 1.154 V versus Fþ c /Fc corresponds to the redox couple [Ni(dpedt)(pddt)]2/[Ni(dpedt)(pddt)]1 and the second wave with E1/2(1/0) at 0.327 V corresponds to the couple [Ni(dpedt) (pddt)]1/[Ni(dpedt)(pddt)]0. There is also an oxidation wave with E1/2(0/1+) at ca. 0.622 V, which is suggesting that the complex can be further oxidized to a cationic species. The LUMO energy level (ELUMO) values were calculated from the reduction onset (Erd onset ) value for the 1e process via the equation: ELUMO = 4.8 + Erd onset [4b,5,6]. This is 4.60 eV for Ni(dpedt)(pddt). The HOMO energy level (EHOMO) values was calculated from the oxidation onset 10
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ox (Eox onset ) values for 1e process via the equation: EHOMO = 4.8 + Eonset [4b,5,6]. This is 5.30 eV for Ni(dpedt)(pddt). One can see that the LUMO level of Ni(dpedt)(pddt) is lower (more negative) than ca. 4.40 eV and the HOMO level is lower (more negative) than ca. 5.20 eV. The obtained values are little different from those of the corresponding symmetrical ones. These values indicate [6,15,27] that the complexes are stable in air, and could be candidate materials for fabrication of field-effect transistors [7g].
4. Conclusions The new unsymmetrical mixed-ligand nickel 1,2-dithiolene complexes, Ni(dpedt)(pddt) and Ni(dpedt)(pddt)CS2 have been prepared and characterized. Electronic and electrochemical measurements reveal intermediate values between those of the corresponding symmetrical ones. The combination of the dpedt ligand with the pddt ligand results to generate the soluble and air-stable complex in the neutral form. The main advantage from the combination of ligands is the possibility to manipulate the ELUMO and EHOMO levels of the complex. With ELUMO and EHOMO values well aligned with the Fermi energy of (metallic) Au, the stability in air and solubility in organic solvents allow us to create thin deposits. The complexes could be candidate materials for fabrication of field-effect transistors and/or materials for non-linear optics. Supplementary data CCDC 746476 and 746477 contain the supplementary crystallographic data for compounds 1 and 2, respectively. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336033; or e-mail: [email protected]. Acknowledgement
0.684 This work was carried out as part of the ‘‘Excellence in Research Institutes” project no. 64769, supported by GSRT/Ministry of Greece.
-0.266 ox
5
E
I (μA)
-1.095
= 0.500 onset
References 0 rd
E
onset
= -0.200 0.561
-5
-0.390 -1.213 -10
-1.5
-1.0
-0.5
0.0
0.5
1.0
+
E (V vs. Fc /Fc) Fig. 5. Cyclic voltammogram of Ni(dpedt)(pddt) solution in CH2Cl2/0.5 M n-Bu4NPF6 with Au disk electrode; scan rate 100 mV/s. Solid arrow indicates direction of scan.
Table 3 Electrochemical data of Ni(dpedt)(pddt), Ni(dpedt)2 and Ni(pddt)2. Complex
E1/2(1/0) (V)
E1/2(0/1+) (V)
Erd onset (V)
Eox onset (V)
ELUMO (eV)
EHOMO (eV)
Ni(dpedt)2 Ni(dpedt)(pddt) Ni(pddt)2
0.369 0.327 0.284
0.710 0.622 0.548
0.250 0.200 0.150
+0.600 +0.500 +0.400
4.55 4.60 4.65
5.40 5.30 5.20
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[6] [7]
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[11] (a) M. Mas-Torrent, C. Rovira, Chem. Soc. Rev. 37 (2008) 827; (b) J. Zaumseil, H. Sirringhaus, Chem. Rev. 107 (2007) 1296; (c) C. Reese, Z. Bao, Mater. Today 10 (2007) 20; (d) A. Faccheti, Mater. Today 10 (2007) 28. [12] (a) G.C. Papavassiliou, G.C. Anyfantis, Z. Naturforsch. 60b (2005) 811; (b) G.C. Anyfantis, G.C. Papavassiliou, A. Terzis, C.P. Raptopoulou, Y.F. Weng, H. Yoshino, K. Murata, Z. Naturforsch. 61b (2006) 1007. [13] (a) S. Curreli, P. Deplano, C. Faulmann, A. Ienco, C. Mealli, M.L. Mercuri, L. Pilia, G. Pintus, A. Serpe, E.F. Trogu, Inorg. Chem. 43 (2004) 5069; (b) F. Bigoli, P. Deplano, M.L. Mercuri, M.A. Pellinghelli, L. Pilia, G. Pintus, A. Serpe, E.F. Trogu, Inorg. Chem. 41 (2002) 5241. [14] M.K. Johnson, Prog. Inorg. Chem. 52 (2004) 213. [15] (a) K.I. Pokhodnya, C. Faulman, I. Maltfant, R. Andreu-Solano, P. Gassoux, A. Mlayh, D. Smirnov, J. Leotin, Synth. Met. 103 (1999) 2016; (b) H.H. Wang, S.B. Fox, E.B. Yagubskii, L.A. Kushch, A.I. Kotov, M.-H. Whangbo, J. Am. Chem. Soc. 119 (1997) 7601. [16] (a) C.W. Schlapfer, K. Nakamoto, Inorg. Chem. 14 (1975) 1338; (b) M.C. Aragoni, M. Arca, F. Demartin, F.A. Devillanova, A. Garau, F. Isaia, F. Lelj, V. Lippolis, G. Verani, J. Am. Chem. Soc. 121 (1999) 7098. [17] D. Sartain, M.R. Truter, J. Chem. Soc. A (1967) 1264. [18] (a) M. Megnamisi-Belombe, B. Nuber, Bull. Chem. Soc. Jpn. 62 (1989) 4092; (b) U. Geiser, S.F. Tytko, T.J. Allen, H.H. Wang, A.M. Kini, J.M. Williams, Acta Crystallogr., Sect. C 47 (1991) 1164. [19] Q. Dai, C.X. Feng, C. Hong, G. Xing, Z.X. Ping, C. Zhusheng, Supermol. Sci. 5 (1998) 531. [20] (a) G.C. Papavassiliou, G.C. Anyfantis, C.P. Raptopoulou, V. Psycharis, N. Ioannidis, V. Petrouleas, P. Paraskevopoulou, Polyhedron 28 (2009) 3368; (b) G.C. Papavassiliou, G.C. Anyfantis, G. Kakarantzas, Unpublished work concerning optical properties of Au 1,2-DTs similar to those obtained from carbon nanotube system (see Ref. [21] herein). [21] A.G. Rozhihn, V. Scardaci, F. Wang, F. Hennrich, I.H. White, W.I. Milne, A.C. Ferrari, Phys. Stat. Sol. 243 (2001) 3551. [22] K. Yu Supanitsky, T.V. Timofeeva, M.Yu. Antipin, Russ. Chem. Rev. 75 (2006) 457. [23] (a) A.K. Bhattacharya, A.G. Hortmann, J. Org. Chem. 39 (1974) 95; (b) K. Hartka, T. Kissel, J. Quante, R. Matsusch, Chem. Ber. 113 (1980) 1898. [24] Rigaku/MSC, CRYSTAL CLEAR. Rigaku/MSC Inc., The Woodlands, Texas, USA, 2005. [25] C.M. Sheldrick, SHELXS-97, Program for the Solution of Crystal Structures, University of Göttingen, Göttingen, Germany, 1997. [26] G.M. Sheldick, SHELXL-97, Program for the Refinement of Crystal Structures, University of Göttingen, Göttingen, Germany, 1997. [27] H. Sirringhaus, Adv. Mater. 21 (2009) 3859.
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Preparation and characterization of Ni(dpedt)(pddt) and Ni(dpedt)(pddt)CS2, where dpedt is diphenylethylenedithiolate and pddt is 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate George C. Anyfantis a,*, George C. Papavassiliou a,*, Aris Terzis b, Catherine P. Raptopoulou b, Vassilis Psycharis b, Patrina Paraskevopoulou c a
Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, 48, Vassileos Constantinou Avenue, Athens 116 35, Greece Institute of Materials Science, NCSR, Demokritos, Athens 15310, Greece c Department of Inorganic Chemistry, Faculty of Chemistry, Panepistimioupoli Zografou, Athens 15771, Greece b
a r t i c l e
i n f o
Article history: Received 21 September 2009 Accepted 19 November 2009 Available online 23 November 2009 Keywords: Metal 1,2-dithiolenes Crystal structure Optical properties Redox properties
a b s t r a c t The unsymmetrical nickel 1,2-dithiolene complex based on diphenylethylenedithiolate (dpedt) and 6,7dihydro-5H-1,4-dithiepin-2,3-dithiolate (pddt) was prepared and characterized. Depending on the conditions of crystallization, it is possible to obtain the complex in two different crystalline forms. X-ray structure studies recognize these forms as Ni(dpedt)(pddt) and Ni(dpedt)(pddt)CS2. The experimental optical and electrochemical parameters are in a good agreement with the calculated ones, using the corresponding parameters of the symmetrical complexes, Ni(dpedt)2 and Ni(pddt)2. The HOMO and LUMO energy levels, obtained from optical and electrochemical measurements, are very close to the Fermi energy of (metallic) Au. The chemical and electrochemical properties of both forms showed that they are stable in air and could be candidate materials for optics and electronics. Ó 2009 Published by Elsevier Ltd.
1. Introduction During the last four decades a large number of metal 1,2-dithiolenes (M 1,2-DTs) have been prepared and studied [1–20]. The intense interest on dithiolene complexes is the result of their properties, mainly their remarkable reversible redox behavior and their unique electronic structures. Dithiolene chemistry has spanned a wide range of areas such as reactive [2], conductive [3], optical [4,5,19,20], photoconductive [5], and bioinorganic [6] materials. Recent experimental results involve this kind of complexes as promising materials for optics [4,8,19] and electronics [7]. Especially, the complexes of gold (Au 1,2-DTs) [10b,20] exhibit optical absorption maxima close to the lines of telecommunication lasers (e.g., 1550 nm) [19–21]. The majority of these studies is dedicated to symmetrical complexes. The preparation of mixed-ligand M 1,2-DTs (unsymmetrical) reveals some difficulties. However, by combination of several ligands, we can create a large number of complexes. For example, the combinations of the 15 dithiolene ligands, which are presented in Scheme 1 generates 105 neutral unsymmetrical dithiolene compounds, only for one metal. It is obvious that the vast number of * Corresponding authors. Tel.: +30 210 7273827; fax: +30 210 7273794 (G.C. Papavassiliou). E-mail addresses: [email protected] (G.C. Anyfantis), [email protected] (G.C. Papavassiliou). 0277-5387/$ - see front matter Ó 2009 Published by Elsevier Ltd. doi:10.1016/j.poly.2009.11.014
the dithiolene ligands and the choice of the metal produce a large number of unsymmetrical dithiolenes. Our effort is focused on the preparation and characterization of unsymmetrical mixed-ligand M 1,2-DTs mainly for two reasons: first, because with combination of the dithiolene ligands we can achieve desirable properties (e.g., stability and solubility) [9] and second, because the mixed-ligand complexes could be candidate materials for second-order non-linear optical properties [8b,13,22]. In this paper, the preparation and characterization of the unsymmetrical complexes Ni(dpedt)(pddt) and Ni(dpedt)(pddt) CS2, based on the ligands diphenylethylenedithiolate (dpedt) and 6,7-dihydro-5H-1,4-dithiepin-2,3-dithiolate (pddt), are described. These forms based on the same ligands are referred herein as 1 and 2, respectively. The new complexes were prepared by the procedure of Scheme 2.
2. Experimental 2.1. Materials and physical measurements The starting materials dpdto, ttdeo were prepared by methods reported elsewhere [23]. Elemental analysis was performed on a Perkin 2400 (II) autoanalyser. Electronic optical absorption (OA) UV–Vis–NIR spectra in CS2 and the spectra of the complex deposited on quartz plates were recorded on a Perkin–Elmer, Lambda
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S
S
S
S
dmedt D D D D
S
S
Ph
S
S
S
dddt
S
S
O
S
S
S
S
S
S
S
O
S
S
S
S
S
S
S
edo C10 H21 S
S S
C10 H21 S
pddt
S
S
dpedt
tmedt
D4-dddt
S
Ph
mdddt S
S
S
S
S
S
dmit
S
S
S
S
S
S
S
S
S
S
O
S
dcdt
dt
dmdddt
dmio
S
S
S
S
S
S
dmdt
S
S
S
S
tmdt
Scheme 1. Formulae of several 1,2-dithiolene ligands.
Scheme 2.
19 spectrophotometer, in the range 200–2200 nm. The Raman spectra were recorded on a in Via Reflex Renishaw confocal micro-Raman spectrophotometer, in the range 2500–100 cm1. Cyclic voltammetry measurements were carried out with a Bipotentiostat AFCBP1 from Pine Instrument Company and controlled with the PINECHEM 2.7.9 software, using a gold disk working electrode (2 mm diameter) and a Ag/Ag+ (0.01 M AgNO3 and 0.5 M nBu4NPF6 in acetonitrile) non-aqueous reference electrode (Bioanalytical Systems, Inc.) with a prolonged bridge (0.5 M n-Bu4NPF6 in acetonitrile). A Pt foil or gauge (8 cm2, Sigma–Aldrich) was employed as counter electrode. The working electrode was polished using successively 6, 3, 1 mm diamond paste on a DP-Nap polishing cloth (Struers, Westlake, OH), washed with water, acetone and air dried. The Pt foil and gauge electrodes were cleaned in a H2O2/H2SO4 (conc.) solution (1:4 v:v) and oven-dried. The concentration of the samples varied between 1 and 3 mM and that of supporting electrolyte (n-Bu4NPF6) was 0.5 M. The potential sweep rate varied between 40 and 1000 mV/s. All potentials are reported versus the ferrocenium/ferrocene (Fþ c /Fc) couple. 2.2. Synthesis of compounds [Ni(dpedt)(pddt)] (1) and [Ni(dpedt)(pddt)]CS2 (2) In a two-necked 250 mL flask, a solution-suspension of dpdto (270 mg, 1 mmol) and ttdeo (222 mg, 1 mmol) in dry MeOH (20 mL) was prepared with stirring under nitrogen atmosphere. Then, a solution of NaOMe, freshly prepared from Na (115 mg, 5 mmol) and MeOH (10 mL) was added and the mixture stirred at room temperature for 30 min. To the obtained yellow solution, a solution of NiCl2H2O (238 mg, 1 mmol) in deoxygenated MeOH (80 mL) was added slowly within 15 min. The solution was stirred
under nitrogen atmosphere for 1 h at room temperature, whereupon the color turned brown. Then, aq. HCl (2 mL, 35%) was added and the mixture was transferred to a beaker and stirred in air overnight. The precipitate was filtered, washed with water and MeOH and dried in air. The green-brown solid was extracted with CS2 and chromatographed on a silica gel, using CS2 as eluent. The second green fraction contained Ni(dpedt)(pddt)CS2 (2) (84 mg, 35%). M.p.: 238 °C (dec.). Anal. Calc. for C20H16S8Ni (MW 571.6): C, 42.03; H, 2.82. Found: C, 41.50; H, 2.61%. Raman 1398 (cm1) (C@C). Solute diffusion crystallization of 2 using CS2 and n-hexane as solvents gave form 1. M.p.: 253 °C (dec.). Anal. Calc. for C19H16S6Ni (MW 495.41): C, 46.06; H, 3.26. Found: C, 45.99; H, 3.10%. Raman 1383 (cm1) (C@C). 1 and 2 showed identical 1H NMR (300 MHz, CS2/CDCl3 2:2): d = 7.18–7.54 (m, 10H CH), 3.28 (m, 4H CH2), 2.42 (m, 2H CH2). 2.3. X-ray crystallography A single crystal of 1 (0.06 0.133 0.49 mm) was mounted in an oil drop and a single crystal of 2 (0.2 0.3 0.5 mm) was mounted in air. Diffraction measurements for 1 were made under the continuous flow of Nitrogen gas cooled at 93 °C using the X-Stream 2000 (Rigaku MSC) cryogenic crystal cooler system on a Rigaku R-AXIS SPIDER Image Plate diffractometer using graphite monochromated Mo radiation. Data collection (x-scans) and processing (cell refinement, data reduction and empirical absorption correction) were performed using the CRYSTALCLEAR program package [24]. Diffraction measurements for 2 were made on a Crystal Logic Dual Goniometer diffractometer using graphite monochromated Mo radiation. Unit cell dimensions were determined and refined by using the angular settings of 25 automatically centered reflec-
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tions in the range 11 < 2h < 23° and they appear in Table 1. Three standard reflections monitored every 97 reflections showed less than 3% variation and no decay. Lorentz, polarization corrections were applied using CRYSTAL LOGIC software. The structures were solved by direct methods using SHELXS-97 [25] and refined by fullmatrix least-squares techniques on F2 with SHELXL-97 [26]. All hydrogen atoms were located by difference maps and were refined isotropically. All non-hydrogen atoms were refined anisotropically. 3. Results and discussion 3.1. Formation of compounds 1 and 2 By applying the pseudo cross-coupling method [12] for the synthesis of mixed-ligand M 1,2-DTs, the complex Ni(dpedt)(pddt) was obtained. This method gave better yields than the ligand exchange reaction and other methods [1b,1c,2,3c,13]. The success of the preparation of the complex under the strong oxidation conditions of Scheme 2 indicates its stability in air. The new complex is soluble in CS2, CH2Cl2 and other organic solvents. Among the organic solvents, CS2 was found to be the best for chromatography separation. Recrystallization by the solute diffusion method using CS2 and n-hexane as solvents, long black needles of Ni(dpedt)(pddt) (form 1) were obtained, while recrystallization from CS2 black blocks of Ni(dpedt)(pddt)CS2 (form 2) were obtained. Also, crystals of 1 were obtained by recrystallization from CH2Cl2. The corresponding symmetrical complexes (CSC) were obtained from these reactions in smaller yields, 11% for Ni(dpedt)2 and 3% for Ni(pddt)2. 3.2. Structural information Form 1 crystallizes in a non-centrosymmetric orthorhombic space group, indicating that this is a candidate material for second Table 1 Crystal data and structure refinement for 1 and 2.
Empirical formula Formula weight T (°C) Wavelength (Å) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (g/cm3) l (mm1) 2hmax (°) Reflections collected Unique reflections Reflections used Rint Parameters refined (D/r)max (De)max (e/Å3) (De)min (e/Å3) R/Rw (all data) R1a wR2a
1
2
C19H16NiS6 495.39 93 0.71073 Pab21 8.1933(2) 13.9461(2) 18.3349(4) 90.0 90.0 90.0 2095.03(7) 4 1.571 1.526 52 24 739 4101 4101 0.0448 299 0.009 0.418 0.295 0.0394/0.0576 0.0285b 0.0523b
C20H16NiS8 571.52 25 0.71073 P21/n 9.344(5) 18.023(9) 14.756(7) 90.0 95.72(2) 90.0 2473(2) 4 1.535 1.467 48 4046 3879 3879 0.0305 303 0.001 0.879 0.489 0.0782/0.1709 0.0607c 0.1555c
a w = 1/[r2(F 2o ) + (aP)2 + bP] and P = ((max)F 2o ,0)+2F 2c )/3; a = 0.0257, b = 0.07 for 1 P P P and a = 0.0739, b = 5.12 for 2. R1 = (|Fo||Fc|)/ (|Fo|) and wR2 = { [w(F 2o F 2c )2]/ P [w(F 2o )2]}1/2. b For 3464 reflections with I > 2r(I). c For 3031 reflections with I > 2r(I).
harmonic generation in the solid state [8f,22]. Form 2 crystallizes in a monoclinic centrosymmetric one. In this form covalent molecules enter the crystal structure. Form 1 is isostructural with the complex Ni(dpedt)(dddt) [10a]. In all cases, the structures present square planar geometry. Table 1 shows selected bond lengths and bond angles in NiS4C4 core of 1 and 2. It is worth mentioning that the co-crystallized molecule of CS2 does not alter the geometry of the core and the distances in both cases are almost the same. But the co-crystallized molecule affects drastically the packing of molecules (Table 2). Fig. 1 shows the ORTEP diagrams of Ni(dpedt)(dddt) molecule in the structures of compounds 1 and 2. The numbering scheme for atoms is also given. Fig. 2 shows the stacking in columns along the c-axis of Ni(dpedt)(dddt) molecules in the structure of 1. In this non-centrosym-
Table 2 Selected bond lengths (Å) and bond angles (°) for Ni(dpedt)(pddt) (1) and Ni(dpedt)(pddt)(CS2) (2).
Ni–S(3) Ni–S(4) Ni–S(5) Ni–S(6) S(3)–C(5) S(4)–C(4) S(5)–C(7) S(6)–C(6) C(4)–C(5) C(6)–C(7) S(5)–Ni–S(6) S(3)–Ni–S(4) C(5)–S(3)–Ni C(4)–S(4)–Ni C(7)–S(5)–Ni C(6)–S(6)–Ni C(5)–C(4)–S(4) C(4)–C(5)–S(3) C(7)–C(6)–S(6) C(6)–C(7)–S(5)
1
2
2.1291(8) 2.1219(7) 2.1288(7) 2.1289(8) 1.720(3) 1.710(3) 1.704(3) 1.716(3) 1.389(4) 1.396(4) 91.41(3) 91.05(3) 105.82(10) 105.79(9) 105.42(9) 105.11(10) 119.3(2) 118.0(2) 118.7(2) 119.02(19)
2.1276(18) 2.1387(19) 2.1239(18) 2.1291(18) 1.707(6) 1.701(6) 1.713(6) 1.716(6) 1.396(9) 1.407(7) 90.91(7) 90.91(7) 105.3(2) 105.6(2) 106.5(2) 105.89(19) 118.3(5) 119.4(4) 118.7(4) 117.9(4)
Fig. 1. ORTEP plot of Ni(dpedt)(dddt) molecule in 1 (a) and 2 (b) at the 50% probability level.
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Absorbance (a. u.)
877
945
(I)
993
(a) (b)
(c)
310
(II) 977
λonset = 1400
Fig. 2. Columns formed by Ni(dpedt)(dddt) molecules in the structure of compound 1. The shortest SS distances are also shown.
metric structure, there is not a pseudo-centrosymmetrical arrangement of metal 1,2-dithiolene molecules. The shortest SS distance, (S3S5) (x, 0.5y, 0.5 + z) = 3.738 Å, is a little larger than the sum of van der Waals radii (3.7 Å). The needle axis of the crystal is the aaxis. There are two such columns per cell, the second of these is generated from the one shown in Fig. 2 by applying the twofold screw axis operation which is parallel to the c-axis and is passing through (0.5, 0.5, 0). Fig. 3 shows the packing diagram of Ni(dpedt)(dddt) and CS2 molecules in the structure of 2. Ni(dpedt)(dddt) forms centrosymetrically related ‘‘dimers” which are situated in rows along the b-axis and couples of CS2 molecules form rows which are extended parallel to the row of dimers. Both are repeated alternatively along the a -axis and so a layer of CS2 couples and Ni(dpedt)(dddt) ‘‘dimers” is formed parallel to the (0 0 1) plane. These type of layers are packed normal the ab plane. Fig. 3 shows the packing of layers normal to (0 0 1) plane. There are two such layers per cell, and the second of these is generated from the one shown in Fig. 2 by applying the twofold screw axis operation which is parallel to the b-axis and is passing through (0.75, 0.0, 0.75) point. Also, in the form 2
250
500
750
1000
1250
1500
λ (nm) Fig. 4. (I) Electronic spectra of Ni(dpedt)2 (a), Ni(dpedt)(pddt) (b) and Ni(pddt)2 (c) solutions in CS2; (II) optical absorption spectrum of a thin deposit of Ni(dpedt)(pddt) on quartz plate.
there are no SS contacts smaller than the sum of the van der Walls radii. 3.3. The electronic optical absorption spectra Fig. 4I shows the electronic OA spectra of Ni(dpedt)(pddt) as well as the spectra of the symmetrical complexes Ni(dpedt)2 and Ni(pddt)2 in CS2. The electronic spectrum of [Ni(dpedt)(pddt)] in CS2 exhibits a strong band at 945 nm, which is typical for dithiolene complexes. This band is assigned to a p ? p* (b1u ? b2g) transition between the HOMO and LUMO levels [13]. Knowing the kmax
Fig. 3. Packing diagram of Ni(dpedt)(dddt) and CS2 molecules in the structure of compound 2. The layer formed by Ni(dpedt)(dddt) dimers and CS2 couples as seen normal to the (0 0 1) plane.
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of the symmetrical ones, it is possible to predict the kmax of the unsymmetrical by applying the empirical equation kmax(AB) = [kmax(AA) + kmax(BB)]/2 (AA, BB symmetrical and AB the corresponding unsymmetrical dithiolene). Even though this equation is an empirical one, it is a powerful tool in dithiolene chemistry mainly for two reasons: (a) we can design unsymmetrical dithiolenes with desirable absorption and (b) we can characterize them from their absorption. Low frequency bands are discrete in the solid state spectra. Fig. 4II shows the spectrum of 1 deposited on quartz plate from solution in CH2Cl2, by the spin coating technique. The electronic OA spectra of 2 do not show any considerable difference from those of 1, even in the solid state.
3.4. Electrochemical results Fig. 5 shows the cyclic voltammogram of Ni(dpedt)(pddt) in CH2Cl2. The electrochemical data are listed in Table 3 together with those of the corresponding symmetrical complexes. One can see that the redox potential and other values of the unsymmetrical compound lie in between those of the corresponding symmetrical ones. The voltammogram of Fig. 5 shows the presence of two reduction waves in the recorded region. The first wave with E1/2(2/1) at 1.154 V versus Fþ c /Fc corresponds to the redox couple [Ni(dpedt)(pddt)]2/[Ni(dpedt)(pddt)]1 and the second wave with E1/2(1/0) at 0.327 V corresponds to the couple [Ni(dpedt) (pddt)]1/[Ni(dpedt)(pddt)]0. There is also an oxidation wave with E1/2(0/1+) at ca. 0.622 V, which is suggesting that the complex can be further oxidized to a cationic species. The LUMO energy level (ELUMO) values were calculated from the reduction onset (Erd onset ) value for the 1e process via the equation: ELUMO = 4.8 + Erd onset [4b,5,6]. This is 4.60 eV for Ni(dpedt)(pddt). The HOMO energy level (EHOMO) values was calculated from the oxidation onset 10
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ox (Eox onset ) values for 1e process via the equation: EHOMO = 4.8 + Eonset [4b,5,6]. This is 5.30 eV for Ni(dpedt)(pddt). One can see that the LUMO level of Ni(dpedt)(pddt) is lower (more negative) than ca. 4.40 eV and the HOMO level is lower (more negative) than ca. 5.20 eV. The obtained values are little different from those of the corresponding symmetrical ones. These values indicate [6,15,27] that the complexes are stable in air, and could be candidate materials for fabrication of field-effect transistors [7g].
4. Conclusions The new unsymmetrical mixed-ligand nickel 1,2-dithiolene complexes, Ni(dpedt)(pddt) and Ni(dpedt)(pddt)CS2 have been prepared and characterized. Electronic and electrochemical measurements reveal intermediate values between those of the corresponding symmetrical ones. The combination of the dpedt ligand with the pddt ligand results to generate the soluble and air-stable complex in the neutral form. The main advantage from the combination of ligands is the possibility to manipulate the ELUMO and EHOMO levels of the complex. With ELUMO and EHOMO values well aligned with the Fermi energy of (metallic) Au, the stability in air and solubility in organic solvents allow us to create thin deposits. The complexes could be candidate materials for fabrication of field-effect transistors and/or materials for non-linear optics. Supplementary data CCDC 746476 and 746477 contain the supplementary crystallographic data for compounds 1 and 2, respectively. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/ retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336033; or e-mail: [email protected]. Acknowledgement
0.684 This work was carried out as part of the ‘‘Excellence in Research Institutes” project no. 64769, supported by GSRT/Ministry of Greece.
-0.266 ox
5
E
I (μA)
-1.095
= 0.500 onset
References 0 rd
E
onset
= -0.200 0.561
-5
-0.390 -1.213 -10
-1.5
-1.0
-0.5
0.0
0.5
1.0
+
E (V vs. Fc /Fc) Fig. 5. Cyclic voltammogram of Ni(dpedt)(pddt) solution in CH2Cl2/0.5 M n-Bu4NPF6 with Au disk electrode; scan rate 100 mV/s. Solid arrow indicates direction of scan.
Table 3 Electrochemical data of Ni(dpedt)(pddt), Ni(dpedt)2 and Ni(pddt)2. Complex
E1/2(1/0) (V)
E1/2(0/1+) (V)
Erd onset (V)
Eox onset (V)
ELUMO (eV)
EHOMO (eV)
Ni(dpedt)2 Ni(dpedt)(pddt) Ni(pddt)2
0.369 0.327 0.284
0.710 0.622 0.548
0.250 0.200 0.150
+0.600 +0.500 +0.400
4.55 4.60 4.65
5.40 5.30 5.20
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