The unique dodecanuclear cluster compound Re12CS17 was prepared and studied by X-ray, complex impedance method and density functional theory (DFT). The compound is amorphous, possesses semiconducting properties. Computer simulations showed that the Re and S atoms at the external borders of the neighboring molecules Re12CS17 can form sufficiently strong Re•••S intermolecular bonds, similar to the Mo•••S intermolecular bonds of cuboctahedron Mo6S8 molecules in the Chevrel phases. (doi: 10.5562/cca1973

Maxim Raisovich Rizhikov

Nikolay Favstovich Uvarov

Svetlana Gennad\u27evna Kozlova

Svyatoslav Petrovich Gabuda

Vladimir Efimovich Fedorov

Yakov Maksumovich Gayfulin

Yuri Vladimirovich Mironov

Croatica Chemica Acta - izd. tromjesečno Hrvatsko kemijsko društvo

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 † Presented at the 34th International Convention on Information and Communication Technology, Electronics and Microelectron-ics, May 23rd − 27th, 2011, Opatija, Croatia. * Author to whom correspondence should be addressed. (E-mail: fed@niic.nsc.ru) CROATICA CHEMICA ACTA CCACAA, ISSN 0011-1643, e-ISSN 1334-417X Croat. Chem. Acta 85 (1) (2012) 113–116.  http://dx.doi.org/10.5562/cca1973 Original Scientific Article  Synthesis of Molecular Dodecanuclear Carbon-centered  Rhenium Cluster Re12CS17 and its Conducting Properties† Vladimir Efimovich Fedorov,a,* Svyatoslav Petrovich Gabuda,a Svetlana Gennad'evna Kozlova,a Yakov Maksumovich Gayfulin,a Yuri Vladimirovich Mironov,a  Maxim Raisovich Rizhikov,a and Nikolay Favstovich Uvarovb aNikolaev Institute of Inorganic Chemistry, Siberian Branch of Russian Academy of Sciences, Novosibirsk, 630090, Russia bInstitute of Solid State Chemistry and Mechanochemistry, Siberian Branch of Russian Academy of Sciences,  Novosibirsk, 630128, Russia RECEIVED DECEMBER 21, 2011; ACCEPTED FEBRUARY 22, 2012   Abstract. The unique dodecanuclear cluster compound Re12CS17 was prepared and studied by X-ray, complex impedance method and density functional theory (DFT). The compound is amorphous, possesses semiconduct-ing properties. Computer simulations showed that the Re and S atoms at the external borders of the neighbor-ing molecules Re12CS17 can form sufficiently strong Re···S intermolecular bonds, similar to the Mo···S inter-molecular bonds of cuboctahedron Mo6S8 molecules in the Chevrel phases. (doi: 10.5562/cca1973)  Keywords: rhenium cluster, Chevrel phase, DFT, conductivity  INTRODUCTION The interest to the cluster chalcogenides of transition metals (M = Mo, Re, etc.) is associated with the prospects of their use for the development of superconducting sole-noids, cathode materials, molecular "machines", etc.1 The most famous representatives of cluster chalcogenides are Chevrel phase type MMo6Q8 (Q = S, Se), based on the parent structure Mo6Q8.1 Detailed studies of the lower chalcogenides of molybdenum have shown that in these systems, in addition to octahedral clusters Mo6Q8, larger clusters of Mo9Q11 and Mo12Q14 may be generated; these clusters can be viewed as the condensation products of Mo6 octahedra via common triangular faces.2 Cluster chemistry of rhenium is very similar to the chemistry of molybdenum. Thus, in addition to well-known octahedral complexes with the cluster core {Re6Q8}, some con-densed complexes like [Re9Se11Br6]2– and K6[Re12C-S17(CN)6] were obtained too.3,4 Last complex is consid-ered as promising monomolecular switch.5,6 Drawing an analogy between the crystallochemi-cal properties of chalcogenide cluster complexes of molybdenum and rhenium, it is interesting to note the following examples. The reaction of Mo6Se8 with mol-ten KCN leads to the complex K6[Mo6Se8(CN)6], which recalls a complex K6[Re12CS17(CN)6]. These two chalcocyanide complexes of molybdenum and rhenium can be conventionally written as [Mo6Se8]·6KCN, and [Re12CS17]·6KCN. Similar description of these com-plexes suggests that if Mo6Se8 exists as a neutral stable phase, perhaps, Re12CS17 can exist too. This idea was the basis for developing a method of synthesis of rheni-um cluster molecular complex Re12CS17 without termi-nal ligands, in order to obtain a molecular switch. For realization of this idea the reactions of succes-sive substitution of terminal ligands in the basic com-plex K6[Re12CS17(CN)6] were carried out using follow-ing steps: K6[Re12CS17(CN)6] → K6[Re12CS17(OH)6] → [Re12CS17(H2O)6] → [Re12CS17(OH)6].   EXPERIMENTAL AND CALCULATIONS  Synthesis Synthesis of Re12CS17 was carried out using two-steps procedure. Step 1. Synthesis of [Re12CS17(H2O)6]·4H2O. 0.1 M aqueous solution of H2SO4 was added dropwise to aqueous solution of K6[Re12CS17(OH)6]·4H2O (400 mg, 0.128 mmol) until bleaching solution. Black precipitate was deposited. The solution was decanted, the precipi-tate was washed with water and dried in air. Yield: 370 114 V. E. Fedorov et al., Synthesis of Molecular Re12CS17 Cluster and its Conducting Properties Croat. Chem. Acta 85 (2012) 113. mg. EDS: Re:S = 12.0:16.9. The presence of potassium in the solid was not found. Number of water molecules was determined according to thermogravimetric analy-sis (Figure 1). On the thermogram in the range from 25 to 150° C a single broad endothermic peak was record-ed, which corresponds to the mass loss of 6.1 %. Such a mass (6.1 % = 177 amu) corresponds to the loss of about 10 water molecules per molecule of the cluster complex. The calculation shows that in a cluster  complex with empirical formula [Re12CS17(H2O)6], w(H2O) = 3.7 %. Consequently, the compound obtained can be de-scribed by the formula [Re12CS17(H2O)6]·4H2O, subject to the special feature of coordination of cluster core. Resulting anhydrous compound Re12CS17 is stable up to 400 °C. Step 2. Synthesis of Re12CS17. 300 mg (0.103 mmol) [Re12CS17(H2O)6]·4H2O was placed in a glass boat and held for 2 hours at 250 °C in a tube furnace under vacu-um. A black crumbly powder is formed. Yield: 280 mg. EDS: Re:S = 12.0:17.0. IR (KBr) ν/cm–1: 411. According to X-ray diffraction study the bulk phase of the cluster compound Re12CS17 is amorphous. As evidence that the substance contains the Re12-fragment the proper hydroxocomplex has been synthesized starting from Re12CS17. For this, 0.2 g Re12CS17 was dissolved in boil-ing KOH solution. The solution was evaporated until the onset of crystallization and cooled. The precipitated crys-tals were filtered and the precipitate was dried in air. Yield: 0.185 g (85 %).   X-ray Analysis  The structure of compound K6[Re12CS17(OH)6]·9H2O is solved by X-ray single crystal diffraction analysis. Sin-gle crystals suitable for XRD analysis were selected manually from reaction product. X-ray diffraction data (a = 14.1085 (7) Å, c = 14.1784 (7) Å, V = 2444.1 (2) Å3, Z = 2, space group P6 3/m, ρcalc = 4.4375 g/cm3) were obtained at 150 K by the standard four-circle diffractometer Bruker-Nonius X8 Apex (MoKα radia-tion, graphite monochromator, a two-coordinate CCD-detector). According to crystal structure data the result-ing hexahydroxocomplex is described by formula K6[Re12CS17(OH)6]·9H2O. The structure of the cluster core in this compound is the same as that in cluster complex K6[Re12CS17(OH)6]·4H2O described previous-ly, the main interatomic distances correspond to known values for this cluster anion.7 The slight discrepancy is observed at distances of Re–O: 2.063(9) Å is in the compound synthesized here and 2.091(14) Å in pub-lished previously.7 We should also note a slight differ-ence in the unit cell parameters. The reason for these discrepancies, we associate with a different number of water molecules in the structure of compounds.  Electrical Measurements  Re12S17 conductivity measurements were carried out on pelletized samples, pressed under a pressure of 400 MPa with pressed into silver electrodes. Conductivity meas-urements were performed by two-electrode scheme in forevacuum (6.67 Pa) at temperatures of 20 to 200 ºC on an alternating current with a precision measuring elec-trical parameters of the Hewlett Packard HP 4284A in the frequency range from 20 Hz to 1 MHz. Conductivity values were calculated from the frequency dependence of conductivity by the method of complex impedance.  Quantum-chemical Analysis Analysis of the intermolecular interactions carried out by numerical simulation of the binding of two mole-cules Re12CS17 using known data about the location of molecules in Mo6S8 Chevrel phases.1 The density func-tional theory method was used with software package ADF2008.8 Analysis of interatomic interactions were carried out using a topological method of "Atoms in the molecule" (AIM).9 For the analysis of electron density by AIM program was used DGrid 4.5.10  Figure 1. Thermogravimetric curves of [Re12CS17(H2O)6]·4H2O.  Figure 2. Temperature dependence of the conductivity of the pelletized sample Re12CS17. V. E. Fedorov et al., Synthesis of Molecular Re12CS17 Cluster and its Conducting Properties 115 Croat. Chem. Acta 85 (2012) 113. DISCUSSION  According to conductivity study, tablet samples of Re12CS17 have stable semiconducting properties at tem-peratures below 400 K (Figure 2). The experimental value of conduction activation energy Eact, determined from the Arrhenius dependence of σ = (A/T)∙exp(Eаct/kT) is the Eact = 0.28 ± 0.02 eV. The obtained value of ≈ 3 times less energy-electron excitation calculated for the cluster molecule Re12CS17 (Eexc = 0.8 eV) (Figure 3). This result may reflect the fact that the experimental Eact is not connected with the one-electron excitation of molecules, and the measured value of the barrier corre-sponds to the activation energy of electron hopping on the intermolecular contacts Re···Re. At temperatures above 400 K an irreversible increase in conductivity, due to, apparently, with the dehydration of compounds that might partially hydrated during storage in air. Most likely, water molecules are located close to the cations and block electron transfer between them. When dehy-dration opens a path of electron transfer, this leads to an increase in conductivity on the order. At the same time, the intermolecular distance cation-cation decreases, which leads to a slight decrease in the conduction acti-vation energy Eact from 0.30 to 0.28 eV. Computer simulations showed that the Re and S atoms at the external borders of the neighboring mole-cules Re12CS17 can form sufficiently strong intermo-lecular bonds Re···S (Figure 4), similar to the intermo-lecular bonds of Mo···S cuboctahedron Mo6S8 mole-cules in the Chevrel phases.1 The binding energy be-tween two molecules Mo6S8 is –1.71 and –1.55 eV for the two molecules Re12CS17. Topological quantum anal-ysis of the intermolecular interaction of molecules Mo6S8 and Re12CS17 showed that the interactions are a four-center and are characterized by a ring critical point (rcp) with density of energy –0.37 and –0.53 eV Å–3, respectively. The emergence of one-dimensional zigzag chains Re12CS17–Re12CS17, as well as chains of atoms –S–S–S– in the amorphous sulfur, can explain the ab-sence of X-ray reflections of the bulk phase of the com-pound.  CONCLUSION Molecular cluster complex of composition Re12CS17 with stable semiconducting properties is synthesized for the first time. The structure of the Re12CS17 is identified as amorphous. It is shown that the molecule Re12CS17 can form a bound state, like the molecules Mo6S8 in Chevrel phases. It is assumed that this sample can be used as a basis for creating monomolecular electrical device. Acknowledgement. The study was supported by Russian Foundation for Basic Research (Grants 10-03-01040 and 11-03-00637) and by Division of Material Sciences of Russian Academy of Science.  REFERENCES 1. Ø. Fischer and M. B .Maple (Eds.), Superconductivity in Ternary Compounds I;.Springer: Berlin, 1982.  2. R. Chevrel, M. Potel, M. Sergent, M. Decroux, and Ø. Fischer,  J. Solid State Chem. 34 (2) (1980) 247. 3. V. E. Fedorov, M. R. J. Elsegood, S. S. Yarovoi, and Y. V. Mironov, Chem. Commun. 17 (1998) 1861. 4. Yu. V. Mironov, N. G. Naumov, S. G. Kozlova, Sung-Jin Kim, and V. E. Fedorov, Angew. Chem. Int. Ed. 44 (2005) 6867. 5. S. P. Gabuda, S. G. Kozlova, Yu. V. Mironov, and V. E. Fedorov, Nanoscale Res. Lett. 4 (9) (2009) 1110. 6. V. E. Fedorov, S. P. Gabuda, S. G. Kozlova, Y. V. Mironov, N. G. Naumov, S.-J. Kim, and N. F. Zakharchuk, “Electronic switch of metal conductivity in μ6-carbon centered [Re12(μ6-С)S17(CN)6]n– nano cluster”, in: P. Biljanovic and K. Skala (Eds.), Proceedings 33-rd International Convention MIPRO (Microelectronics, Elec-tronics and Electronic Technology/ MEET Grid and Visualizations Systems/GVS), Opatija, Croatia, 2010, p. 29. 7. Yu. V. Mironov, S. G. Kozlova, Kim Sung-Jin, W. S. Sheldrick,   Figure 3. Energy levels of MOs for Re12СS17. Estimated image of bonding highest occupied molecular orbital  (HOMO) and of antibonding lowest unoccupied molecular orbital (LUMO).   Figure 4. The structure of two interacting molecules Re12CS17 (simulation results). 116 V. E. Fedorov et al., Synthesis of Molecular Re12CS17 Cluster and its Conducting Properties Croat. Chem. Acta 85 (2012) 113. and V. E. Fedorov, Polyhedron 29 (2010) 3283. 8. Amsterdam Density Functional (ADF) program, Release 2008.02; Vrije Universteit: Amsterdam, The Netherlands, 2008. 9. R. F. Bader, Atoms in Molecules: A Quantum Theory, Claren-don, New York, 1990. 10. M. Kohout, DGrid, version 4.5, Radebeul, 2009. 

Synthesis of Molecular Dodecanuclear Carbon-centered Rhenium Cluster Re12CS17 and its Conducting Properties

Svetlana Gennad'evna Kozlova

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Synthesis of Molecular Dodecanuclear Carbon-centered Rhenium Cluster Re12CS17 and its Conducting Properties

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