Electrocrystallization, X-ray structure and electronic properties of the dmit-based salt [MePh3P] [Ni(dmit)2]3 Anthony E. Pullen,a Hsiang-Lin Liu,b D. B. Tanner,b Khalil A. Abbouda and John R. Reynolds*a aDepartment of Chemistry, Center forMacromolecular Science and Engineering, University of Florida, P.O. Box 117200, Gainesville, Florida 32611–7200, USA bDepartment of Physics, University of Florida, P.O.Box 118440, Gainesville, Florida 32611-8440, USA Electrooxidation of [Ni(dmit)2 ]-(dmit=C3S52-=4,5-dithiolate-2-thione-1,3-dithiole) in 351 acetonitrile–acetone at a Pt wire anode in the presence of methyltriphenylphosphonium bromide electrolyte yields the radical anion salt complex [MePh3P][Ni(dmit)2]3. Black shiny platelet crystals were harvested. They belong to the monoclinic space group P21/c, M= 1631.41, a=21.0872(1), b=17.4930(2), c=15.7203(2) A° , b=107.072(1)°, V=5543.4(1) A° 3 and Z=4.The crystal packing structure consists of columns of Ni(dmit)2 units of width one unit separated by columns of MePh3P+ counter-ions. The Ni(dmit)2 columns are composed of dimers of Ni(dmit)2 units with non-bonding interactions with six other pairs of Ni(dmit)2 units.The arrangement of the dimers with respect to each other in the columns has been seen in other phosphonium-based Ni(dmit)2 complexes and is similar to the packing of k-BEDT-TTF radical cation salts which have shown superconductivity. Single-crystal temperaturedependent conductivity measurements have shown that this material is semiconducting with a room-temperature conductivity of 0.1 S cm-1 and a thermal activation energy of 0.22 eV.Since the reported synthesis of the dmit (dmit=C3S52-=4,5- Ph4P+, we have replaced a phenyl group on the cation with a methyl group in order to study, not only the structural dithiolate-2-thione-1,3-dithiole) ligand,1 it has been utilized in differences, but also the electronic properties. Herein, we report an extensive amount of research along with the development the synthesis, X-ray structure analysis and temperature-depen- of a number of analogues.The research has encompassed the dent conductivity of [MePh3P][Ni(dmit)2]3 and compare its areas of coordination chemistry,2 organic chemistry3 and mateproperties to the [Me4P][Ni(dmit)2]2, [Ph4P][Ni(dmit)2 ]3 rials chemistry.4 Bis-chelate dmit complexes using squareand [(PhCH2)Ph3P][Ni(dmit)2]3 salts.6,7 planar coordinating metals (i.e.NiII, PdII, PtII ) have been used in the assembly of semiconducting, metallic and even superconducting materials. The planar structure and sulfur-rich nature Experimental of dmit allows it to form stackable close-packing structures when using square-planar coordinating metals.Also, the large Synthesis of [MePh3P][Ni(dmit)2 ]3 sulfur atomic orbitals allows for intermolecular non-bonding [Bu4N][Ni(dmit)2] was synthesized following the procedures orbital interactions.4 Currently seven different dmit-based sys- described by Hansen et al.8 The radical anion salt tems are known to have superconducting electrical properties. [MePh3P][Ni(dmit)2]3 was synthesized via constant-current The complex a-[EDT-TTF][Ni(dmit)2 ] is the latest dmit- electrocrystallization in a two-compartment glass H-cell based complex to show such electrical properties, with a Tc of equipped with Pt wire electrodes.A saturated solution of 1.3 K at ambient pressure.5 [Bu4N][Ni(dmit)2] was electrooxidized in 351 acetonitrile– The primary methods used in the search for dmit-based acetone with 0.06 mol dm-3 MePh3PBr under an argon atmos- conducting materials has been to change the counter-ion and phere.A current density of 0.9 mA cm-2 was applied over a the metal centre, with the Ni(dmit)2 system and the alkylam- period of 18 days. Black, shiny chunk-like and platelet crystals monium-based cations being the most widely studied.6 The were harvested.All solvents were degassed thoroughly prior complex [Me4N][Ni(dmit)2]2 shows superconducting behav- to use. Acetone was used as received (Aldrich) and acetonitrile iour under 7 kbar pressure with a Tc of 5.0 K.5 One class of was dried over type 4A molecular sieves (Fisher). closed-shell cations not thoroughly studied are the phosphonium- based cations.6,7 The first Ni(dmit)2 non-integer oxi- X-Ray structure determination dation state complex to be electrocrystallized using a phosphonium-based cation was [Me4P][Ni(dmit)2]2 by Kato Crystallographic data for [MePh3P][Ni(dmit)2]3 are shown and co-workers.6 The structure is composed of columns of in Table 1.Data were collected at 173 K on a Siemens SMART dimers of Ni(dmit)2 units separated by columns of Me4P+ PLATFORM equipped with a CCD area detector.A black cations. The salt exhibits semiconductivity with a single-crystal shiny platelet crystal (0.23×0.1×0.08 mm3) was chosen for room-temperature conductivity of 0.6 S cm-1. Recently we, study. along with Nakamura et al.,7 have synthesized and studied the The diffractometer was equipped with a graphite mono- 351 tetraphenylphosphonium-based complex [Ph4P][Ni- chromator utilizing Mo-Ka radiation (l=0.71073 A° ).Cell (dmit)2 ]3 . This complex exhibits a unique packing array of parameters were refined using 8192 reflections. A hemisphere Ni(dmit)2 units. The packing is characterized by stacks of of data (1381 frames) was collected using the v-scan method Ni(dmit)2 units separated by orthogonal Ni(dmit)2 spacer (0.3° frame width).The first 50 frames were remeasured at the units. The salt displays semiconducting behaviour with a end of data collection to monitor instrument and crystal single-crystal room-temperature conductivity of 7–10 S cm-1. stability (maximum correction on I<1%). Psi-scan absorption To further the understanding of phosphonium-based Ni(dmit)2 corrections were applied based on the entire data set.radical anion salts, we have synthesized the similar351 complex The structure was solved by direct methods in SHELXTL, and refined using full-matrix least-squares procedures. The [MePh3P][Ni(dmit)2]3 by electrocrystallization. Similar to J. Mater. Chem., 1997, 7(3), 377–380 377Table 1 Crystallographic data for [MePh3P][Ni(dmit)2]3 mined to be ±0.2 K or better over the temperature range measured.chemical formula C37H18Ni3PS30 formula mass 1631.41 space group P21 /c Results and Discussion a/A° 21.0872(1) b/A° 17.4930(2) Crystal structure of [MePh3P][Ni(dmit)2 ]3 c/A° 15.7203(2) The crystal structure of [MePh3P][Ni(dmit)2]3 † consists of b/degrees 107.072(1) one MePh3P+ cation and three crystallographically indepen- V /A° 3 5543.4(1) Z 4 dent Ni(dmit)2 units.The packing is characterized by columns Dc /g cm-3 1.955 of Ni(dmit)2 dimers separated by columns of MePh3P+ coun- F(000) 3276 ter-ions. The Ni(dmit)2 units are arranged in a dimeric fashion m(Mo-Ka)/cm-1 22.0 in the bc plane with the long axis of Ni(dmit)2 molecules in 2hmax/degrees 55.0 the a direction, as shown in Fig. 2. Each dimer is surrounded range of h, k, l -28–25; 0–22; 0–20 by six other dimers.Each of the dimers forms dihedral angles R1 ;a wR2b 0.034; 0.065 goodness-of-fit 1.131 of 44.5(1)° and 51.2(1)° with four other dimers along the c Drmax/e A° -3 0.545 direction and 6.7(1)° with two other dimers along the b Drmin/e A° -3 -0.499 direction. This packing motif is quite similar to both [Me4P][Ni(dmit)2]2,6 and the k-phase BEDT-TTF salts. aR1=.(||Fo|-|Fc||)/.|Fo|.bwR2=[.[w(Fo2-Fc2 )2]/.[w(Fo2 )2]]1/2; Currently the complex k-[BEDT-TTF]2{Cu[N(CN)2]Cl} w=1/[s2(Fo2)+(0.0370p)2+0.31p], p=[max(Fo2, 0)+2Fc2]/3. with this packing array has the highest superconducting transition temperature measured to date of a molecular material of 12.8 K.4 The Me4P+ complex also forms dimers of Ni(dmit)2 non-H atoms were treated anisotropically, whereas the hydro- units but in this instance, dihedral angles of 60° with four gen atoms were refined with isotropic thermal parameters. 713 other adjacent dimers and 0° with two other pairs of the six Parameters were refined in the final cycle of refinement using total surrounding dimers are observed. There are extensive 9941 reflections [with I>2s(I )] to yield R1 of 3.40%, and S,S non-bonding interdimer orbital interactions in a two- 12219 reflections to yield wR2 of 6.48%, respectively.dimensional array resulting from close contacts with distances Refinement was carried out using F2. less than the sum of the van der Waals radii (3.70 A° ). The Molecular numbering schemes for the three crystallograph- S,S distances range from 3.440 A° resulting from thiolate– ically independent Ni(dmit)2 units of [MePh3P][Ni(dmit)2]3 thiolate [S(4)–S(14)] interactions to 3.658 A° due to thiolate– are shown in Fig. 1. Selected bond lengths and angles are thiole [S(18)–S(25)] interactions. There are also several Ni located in Table 2 for [MePh3P][Ni(dmit)2]3. dz2,S non-bonding interdimer interactions observed in the crystal lattice.These range from 3.232 A° due to Ni dz2–thiole Conductivity measurements [Ni(3)–S(9)] orbital overlap to 3.856 A° due to Ni dz2–thiolate Temperature-dependent (300–150 K) resistances were meas- [Ni(2)–S(24)] orbital interactions. ured by a four-probe method using an ac technique. Two Within the dimers, the Ni(dmit)2 units stack in an eclipsed single-crystal platelets of [MePh3P][Ni(dmit)2]3 (typically fashion.Two of the three crystallographically independent 0.91×0.46×0.09 mm3) were measured in this study. Narrow- Ni(dmit)2 units are in dimers with the units being slightly gauge (0.02 mm diameter) gold wires were affixed to the crystal slipped (transverse offset) from perfectly eclipsed, as shown by using fast drying gold paint.The sample was anchored ther- the view down the c axis in Fig. 3. These Ni(dmit)2 units form mally to the cold head of a closed-cycle refrigerator (CTI dimers with intradimer spacings ranging from 3.443 to 3.652 A° . Cryogenics). A typical run was performed by first cooling the The third crystallographically independent Ni(dmit)2 forms a sample to the lowest temperature, and then taking the data dimer with a perfectly eclipsed stacking motif.This is mediated while warming. Temperature reproducibility has been deter- by strong Ni dz2,Ni dz2 orbital interactions which is shown by the solid line in the packing diagram in Fig. 2. The distance is only 2.7837(7) A° between the Ni atoms. This results in a fold-like dmit–Ni–dmit dihedral angle of 13.0° of the dmit ligand planes from 0° for a perfectly square-planar complex.To our knowledge, this very short Ni,Ni interaction resulting from dimers arranged in an eclipsed fashion is unique among Ni(dmit)2-based complexes. This has been observed in several instances with Pd(dmit)24–6,9 and Pt(dmit)2-based materials.4,10 The above-described packing of the anions and cations in [MePh3P][Ni(dmit)2]3 is significantly different from the other similar 351 phosphonium-based complexes [Ph4P] [Ni(dmit)2]3 and [(PhCH2)Ph3P][Ni(dmit)2]3 but very similar to the 251 salt [Me4P][Ni(dmit)2]2.6,7 The Ph4P+ salt displays a unique packing scheme amongst the Ni(dmit)2 complexes, with stacks of Ni(dmit)2 units separated by orthogonal spacer Ni(dmit)2 units.By simply adding a methylene spacer to one of the phenyl groups, all of the Ni(dmit)2 molecules of [(PhCH2)Ph3P][Ni(dmit)2]3 are arranged in parallel planes.By replacing a phenyl group with a methyl † Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Fig. 1 Thermal ellipsoid drawings (50% probability) and numbering Centre (CCDC).See Information for Authors, J. Mater. Chem., 1997, Issue 1. Any request to the CCDC for this material should quote the schemes for the three crystallographically independent Ni(dmit)2 moieties in [MePh3P][Ni(dmit)2]3 full literature citation and the reference number 1145/25. 378 J. Mater. Chem., 1997, 7(3), 377–380Table 2 Bond lengths (A° ) and angles (degrees) for the crystallographically independent Ni(dmit)2 units of [MePh3P][Ni(dmit)2]3 Ni(1)MS(7) 2.1856(8) S(9)MC(6) 1.732(3) S(15)MC(13) 1.707(3) S(22)MC(21) 1.730(3) Ni(1)MS(4) 2.1871(8) S(9)MC(5) 1,737(3) S(16)MC(14) 1.700(3) S(22)MC(22) 1.750(3) Ni(1)MS(5) 2.1890(8) S(10)MC(6) 1,640(3) S(17)MC(15) 1.697(3) S(23)MC(21) 1.741(3) Ni(1)MS(6) 2.2106(8) C(2)MC(3) 1.390(4) S(18)MC(16) 1.737(3) S(23)MC(23) 1.744(3) Ni(1)MNi(1)a 2.7837(7) C(4)MC(5) 1.394(4) S(18)MC(14) 1.743(3) S(24)MC(22) 1.713(3) S(1)MC(1) 1.634(3) Ni(2)MS(14) 2.1595(8) S(19)MC(16) 1.735(3) S(25)MC(23) 1.715(3) S(2)MC(1) 1.740(3) Ni(2)MS(15) 2.1660(8) S(19)MC(15) 1.739(3) S(26)MC(24) 1.696(3) S(2)MC(2) 1.745(3) Ni(2)MS(17) 2.1614(8) S(20)MC(16) 1.641(3) S(27)MC(25) 1.697(3) S(3)MC(3) 1.739(3) Ni(2)MS(16) 2.1614(8) C(12)MC(13) 1.382(4) S(28)MC(26) 1.738(3) S(3)MC(1) 1.746(3) S(11)MC(11) 1.650(3) C(14)MC(15) 1.388(4) S(28)MC(24) 1.741(3) S(4)MC(2) 1.693(3) S(12)MC(11) 1.729(3) Ni(3)MS(26) 2.1615(8) S(29)MC(26) 1.740(3) S(5)MC(3) 1.690(3) S(12)MC(12) 1.745(3) Ni(3)MS(27) 2.1670(8) S(29)MC(25) 1.742(3) S(6)MC(4) 1.695(3) S(13)MC(11) 1.741(3) Ni(3)MS(25) 2.1712(8) S(30)MC(26) 1.641(3) S(7)MC(5) 1.686(3) S(13)MC(13) 1.745(3) Ni(3)MS(24) 2.1749(8) C(22)MC(23) 1.372(4) S(8)MC(4) 1.744(3) S(14)MC(12) 1.705(3) S(21)MC(21) 1.654(3) C(24)MC(25) 1.393(4) S(8)MC(6) 1.746(3) S(7)MNi(1)MS(4) 170.92(3) C(2)MC(3)MS(3) 116.6(2) S(11)MC(11)MS(12) 123.3(2) C(21)MS(22)MC(22) 97.44(14) S(7)MNi(1)MS(5) 85.21(3) S(5)MC(3)MS(3) 122.0(2) S(11)MC(11)MS(13) 122.9(2) C(21)MS(23)MC(23) 97.11(14) S(4)MNi(1)MS(5) 92.20(3) C(5)MC(4)MS(6) 121.5(2) S(12)MC(11)MS(13) 113.7(2) C(22)MS(24)MNi(3) 101.69(10) S(7)MNi(1)MS(6) 92.29(3) C(5)MC(4)MS(8) 115.1(2) C(13)MC(12)MS(14) 120.9(2) C(23)MS(25)MNi(3) 102.18(10) S(4)MNi(1)MS(6) 88.89(3) S(6)MC(4)MS(8) 123.4(2) C(13)MC(12)MS(12) 115.6(2) C(24)MS(26)MNi(3) 102.94(10) S(5)MNi(1)MS(6) 170.71(3) C(4)MC(5)MS(7) 121.8(2) S(14)MC(12)MS(12) 123.5(2) C(25)MS(27)MNi(3) 102.76(10) S(7)MNi(1)MNi(1)a 101.01(3) C(4)MC(5)MS(9) 116.7(2) C(12)MC(13)MS(15) 120.9(2) C(26)MS(28)MC(24) 97.17(14) S(4)MNi(1)MNi(1)a 87.95(3) S(7)MC(5)MS(9) 121.5(2) C(12)MC(13)MS(13) 116.2(2) C(26)MS(29)MC(25) 97.27(14) S(5)MNi(1)MNi(1)a 97.09(3) S(10)MC(6)MS(9) 121.9(2) C(15)MC(13)MS(13) 122.9(2) S(21)MC(21)MS(22) 123.8(2) S(6)MNi(1)MNi(1)a 92.16(3) S(10)MC(6)MS(8) 124.4(2) C(15)MC(14)MS(16) 121.1(2) S(21)MC(21)MS(23) 122.8(2) C(1)MS(2)MC(2) 97.53(14) S(9)MC(6)MS(8) 113.7(2) C(15)MC(14)MS(18) 116.0(2) S(22)MC(21)MS(23) 113.5(2) C(3)MS(3)MC(1) 97.02(14) S(14)MNi(2)MS(15) 93.11(3) S(16)MC(14)MS(18) 122.9(2) C(23)MC(22)MS(24) 122.0(2) C(2)MS(4)MNi(1) 102.45(10) S(14)MNi(2)MS(17) 177.89(3) S(16)MC(14)MS(18) 122.9(2) C(23)MC(22)MS(22) 115.6(2) C(3)MS(5)MNi(1) 102.51(10) S(15)MNi(2)MS(17) 85.64(3) C(14)MC(15)MS(17) 121.1(2) C(22)MC(23)MS(25) 120.8(2) C(4)MS(6)MNi(1) 101.61(10) S(14)MNi(2)MS(16) 88.13(3) C(14)MC(15)MS(19) 115.7(2) C(22)MC(23)MS(23) 116.3(2) C(5)MS(7)MNi(1) 102.47(10) S(15)MNi(2)MS(16) 177.90(3) S(17)MC(15)MS(19) 123.2(2) S(25)MC(23)MS(23) 122.9(2) C(4)MS(8)MC(6) 97.34(14) S(17)MNi(2)MS(16) 93.07(3) S(20)MC(16)MS(19) 123.1(2) C(25)MC(24)MS(26) 120.8(2) C(6)MS(9)MC(5) 97.14(14) C(11)MS(12)MC(12) 97.50(14) S(20)MC(16)MS(18) 123.3(2) C(25)MC(24)MS(28) 116.1(2) S(1)MC(1)MS(2) 123.3(2) C(11)MS(13)MC(13) 96.16(14) S(19)MC(16)MS(18) 113.6(2) S(26)MC(24)MS(28) 123.1(2) S(1)MC(1)MS(3) 123.2(2) C(12)MS(14)MNi(2) 102.50(10) S(26)MNi(3)MS(27) 92.66(3) C(24)MC(25)MS(27) 120.8(2) S(2)MC(1)MS(3) 113.5(2) C(13)MS(15)MNi(2) 102.44(10) S(26)MNi(3)MS(25) 178.64(3) C(24)MC(25)MS(29) 115.7(2) C(3)MC(2)MS(4) 121.4(2) C(14)MS(16)MNi(2) 102.24(10) S(27)MNi(3)MS(25) 86.35(3) S(27)MC(25)MS(29) 123.5(2) C(3)MC(2)MS(2) 115.3(2) C(15)MS(17)MNi(2) 102.51(10) S(26)MNi(3)MS(24) 87.78(3) S(30)MC(26)MS(28) 122.7(2) S(4)MC(2)MS(2) 123.2(2) C(16)MS(18)MC(14) 97.09(14) S(27)MNi(3)MS(24) 176.61(3) S(30)MC(26)MS(29) 123.5(2) C(2)MC(3)MS(5) 121.4(2) C(16)MS(19)MC(15) 97.44(14) S(25)MNi(3)MS(24) 93.26(3) S(28)MC(26)MS(29) 113.8(2) aSymmetry transformations used to generate equivalent atoms: -x, -y, -z+2.Fig. 3 View perpendicular to the Ni(dmit)2 moieties showing intradimer quasi-eclipsed stacking arrangements of the moieties of [MePh3P][Ni(dmit)2 ]3.Also shown are the dimers packed in a columnar arrangement separated by MePh3P+ cations. Dashed lines represent S,S distances less than the sum of the van der Waals radii. Fig. 2 View along the long axis of the Ni(dmit)2 moieties showing a dimeric packing arrangement in [MePh3P][Ni(dmit)2 ]3 [MePh3P+ cations have been omitted for clarity]. Also shown are extensive S,S tivity decreases rapidly from its 300 K value of 0.1 S cm-1 with and Ni dz2,S (A) and Ni dz2,Ni dz2 (——) non-bonding orbital interactions. decreasing temperature.The temperature-dependent conductivity is well fit by eqn. (1), group, the material [MePh3P][Ni(dmit)2]3 results with the s(T )=s0 exp(-Ea/kBT ) same stoichiometry but with a very different packing. The with a thermal activation energy Ea of 220 meV.The room- complex [Me4P][Ni(dmit)2]2 with a 251 stoichiometry due temperature conductivity is two orders of magnitude smaller to the small size of the cation, has a packing of the Ni(dmit)2 than that of [Ph4P][Ni(dmit)2]37 and similar to the value moieties identical to that of [MePh3P][Ni(dmit)2]3. reported for [(PhCH2)Ph3P][Ni(dmit)2]3 (0.2 S cm-1) and [Me4P][Ni(dmit)2]2 (0.6 S cm-1).6 Moreover, the value of the Electrical conductivity thermal activation energy is about 20 times larger than that of [Ph4P][Ni(dmit)2]3.Thus, although both [MePh3P] The temperature dependence of the four-probe is shown in Fig. 4. Semiconducting behaviour is illustrated as the conduc- [Ni(dmit)2]3 and [Ph4P][Ni(dmit)2 ]3 have the same stoichio- J. Mater. Chem., 1997, 7(3), 377–380 3792 V.E. Shklover, S. S. Nagapetyan and Y. T. Struchkov, Usp. Khim., 1990, 59, 1179; R. M. Olk, B. Olk, W. Dietzsch, R. Kirmse and E. Hoyer, Coord. Chem. 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Kobayashi and H. Kobayashi, Inorg. Chem., 1995, been seen not only in this series of phosphonium-based 34, 870; T. Nakamura, A. E. Underhill, T. Coomber, R. H. Friend, Ni(dmit)2 salts, but also within other families (i.e. ammonium, H. Tajima, A. Kobayashi and H. Kobayashi, Synth.Met., 1995, 70, sulfonium) of Ni(dmit)2 salts.4,6,7 1061; H. L. Liu, D. B. Tanner, A. E. Pullen, K. A. Abboud and J. R. Reynolds, Phys. Rev. B, 1996, 53, 10557. This work was funded by grants from the Air Force Office of 8 T. K. Hansen, J. Becher, T. Jorgensen, K. S. Varma, R. Khedekar and M. P. Cava, Org. Synth., 1995, 73, 270. Scientific Research (F49620-96-1-0067 and F49620-93-1-0322) 9 C. Faulmann, J. P. Legros, P. Cassoux, J. Cornelissen, L. Brossard, for work completed in the Chemistry Department and the M. Inokuchi, H. Tajima and M. Tokumoto, J. Chem. Soc., Dalton National Science Foundation (DMR-9403894) for the work T rans., 1994, 249; R. Kato, Y. L. Liu, H. Sawa, S. 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