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  ISSN 00360244, Russian Journal of Physical Chemistry A, 2009, Vol. 83, No. 11, pp. 1883–1886. © Pleiades Publishing, Ltd., 2009.Original Russian Text © E.P. Grishina, L.M. Ramenskaya, A.M. Pimenova, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 11, pp. 2072–2075. 1883 INTRODUCTIONRoom temperature molten salts (RTMS) are acomparatively new continuously broadening class of compounds. One of the most extensively studiedgroups of lowtemperature melts (ionic liquids, ILs) isN,N'dialkylimidazolium chloride–  AlCl 3  systems [1].Depending on the ratio between melt components,these systems behave either as Lewis bases (if theorganic salt is present in excess) or as Lewis acids (inthe presence of excess  AlCl 3 ). In basic ILs, the  Al 3+ cation forms the mononuclear complex ion. Inacid ILs, polynuclear complex particles arepresent along with . When transition metal salts are dissolved in chloroaluminate ionic liquids, the form in which they existdepends on the composition of the solvent. For instance, the silver ion is incorporated into halidecomplexes in basic systems and exists as a free cationin acid media [2]. The formation of complex anions was observed in the solution of MoCl 5  [3], UCl 5   ⋅ SOCl 2  [4], and other metal chlorides in chloroaluminate ILs. According to [5], transition metal salts MеCl 2  (Me = Ni, Mn, and Co) can form with complex anions with the composition [Me(AlCl 4 ) 3 ] –  inacid ILs. Review [2] contains data on the electrochemical precipitation of In, Sb, Te, Cd, Cu, Ag, Pd, Au, Zn, and Sn from solutions of the correspondingmetal chlorides forming complex ions in basic andacid chloroaluminate ionic liquids. According to [6–10], there are lowtemperatureionic liquids with metalcontaining anions which, asdistinct from the well studied haloaluminate liquids,have higher moisture and air stability and are therefore  AlCl 4 –  Al 2 Cl 7 –  AlCl 4 –  AlCl 4 – more simple to use. As with chloroaluminate ILs, thecomposition of the anionic part of these melts dependson the molar ratio between mixture components. If thecontent of a metal salt does not exceed 50 mol %,mononuclear complex anions ( , ,, , , , etc.) are largely present, and if the fraction of the salt is higher than50mol %, polynuclear complex particles ( ,, , etc.) are formed.For several ionic liquids of the N,N'dialkylimidazolium chloride–metal chloride type, melting points were measured, phase diagrams constructed [1, 6],and the structure of melts determined [11, 12]. However, for many systems (except chloroaluminate ILs),such important physicochemical characteristics asdensity, viscosity, and electrical conductivity were notstudied. It was well established for hightemperature binary salt melts [13, 14] that these characteristics were very sensitive to the formation of complex compounds between IL solvents and dissolved metal salts.Lowtemperature bromide melts, in particular, those based on 1butyl3methylimidazolium bromide(BMImBr), were studied to a still lesser extent. At thesame time, the physicochemical properties mentionedabove are of great importance for creating technologies with the use of lowtemperature ionic melts.The purpose of this work was to study the influenceof temperature and the ratio between the componentson the physicochemical characteristics (density, glasstransition temperature, viscosity, and electrical conductivity) of the BMImBr–AgBr lowtemperatureliquid. FeCl 4 – InCl 4 – ZnCl 3 – CuCl 2 – NbF 6 – TaF 6 – Fe 2 Cl 7 – Zn 2 Cl 5 – Zn 3 Cl 7 – The Physicochemical Properties of the LowTemperature Ionic Liquid Silver Bromide–1Butyl3Methylimidazolium Bromide E. P. Grishina, L. M. Ramenskaya, and A. M. Pimenova Institute of the Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russiaemail: epg@iscras.ru Received July 18, 2008  Abstract —The physicochemical properties of the lowtemperature ionic liquid based on 1butyl3meth ylimidazolium bromide (BMImBr) and silver bromide were studied. Differential scanning calorimetry, Fourier transform IR spectroscopy, densimetry, viscometry, and conductometry measurements were performedto determine the dependences of the parameters under study on the concentration of AgBr. It was shown thatthe temperature and concentration behavior of the physicochemical properties of BMImBr–AgBr meltscharacterized the interaction between the system components with the formation of complex particles. DOI: 10.1134/S0036024409110132 PHYSICAL CHEMISTRY OF SOLUTIONS  1884 RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 11 2009 GRISHINA et al. EXPERIMENTAL Binary electrolyte systems were prepared by directly mixing the ionic liquid (BMImBr, water content 2.6 wt %, melting point 55°С  [15]) and silver bromide AgBr of kh. ch. (chemically pure) grade at atemperature insignificantly higher than the meltingpoint of the IL ( ~70°С ) [15]. Studies were performedfor mixtures with silver bromide contents  х   = 0.015–0.220mole fractions (0.072–1.225 mol AgBr/kgBMImBr).The IR transmission spectra were recorded for samples squeezed between two KRS5 plates (transmission range 4000–200 cm –1 ) on an Avatar 360FTIR ESP spectrophotometer.The density of melts was determined under isothermal conditions pycnometrically (pycnometer volumes1, 2, and 5 cm 3 ) with respect to water [16] using anME215S Sartorius analytical balance; the accuracy of  weighing was 1 ×  10 –5   g.The dynamic viscosity of BMImBr–AgBr ionicliquids was measured at 20°С  on a BROOKFIELDDVII + Pro viscometer in a special smallvolumecell, plate radius 7.5 mm, gap between plates 1 mm,range of angular rotation velocities 10–100 rpm. The viscometer was calibrated against glycerol [17] todetermine the correction coefficient taking intoaccount cell design characteristics.The vitrification of ionic liquid samples was studied by differential scanning calorimetry on a NETZCHDSC 204 F1 instrument using an Al capsule; sample weight was ≈ 20  mg, heating was performed in an N 2 atmosphere from –110 to 100°С , heating rate was10K/min. The capsule was prepared following thestandard procedure immediately before each measurement.The conductivity of lowtemperature BMImBr– AgBr melts was determined at 20 ±  0.1°С  using anE720 immitance meter in a hermetically closed temperaturecontrolled conductometric cell with smoothplatinum electrodes. Measurements were performedover the alternating current frequency range  f   = 1–20kHz using the procedure described in [18]. Conductivity G   was extrapolated to an infinite frequency inthe G  –1/  f   coordinates. The constant of the conductometric cell was determined using a 0.01 N solution of KCl [19], whose electrical conductivity was compara ble with that of the ionic liquid studied.RESULTS AND DISCUSSION The spectral characteristics.  The table containsdata on the IR Fourier transform transmission spectraof the BMImBr–AgBr (  x   = 0.188) ionic liquid over thefrequency range 4000–2500 cm –1  (similar transmission spectra were obtained for ILs with other compositions). The bands were assigned to atomic group vibrations according to [20]. A comparison with thespectrum of initial BMImBr [15] shows that the introduction of AgBr causes a bathochromic shift of thecharacteristic minimum at 3143 cm –1  correspondingto the Hbond between the C2 heteroring atom and Br.Clearly, the salts interact through the bromide ion withthe formation of the [BMImBr ⋅ (AgBr)] complex salt. Density.  Our studies showed that the density ( ρ ) of solutions of AgBr in BMImBr linearly increased as theconcentration of the silver salt grew. The dependenceof ρ  on the mole fraction of AgBr at 20°С  was approximated by the linear equation ρ  = 1.300 + 1.098  x   ( r   =0.998) . According to the literature data, density is not very sensitive to weak chemical interactions in melts.Chemical interactions are usually revealed using density temperature coefficient ( ∆ρ / ∆ t  )–compositiondependences [13]. Such a dependence for the AgBr–BMImBr system has an extremum at  x   ~ 0.13  (Fig. 1).The densities of solutions of AgBr in BMImBr wereused to calculate molar volumes V   ( V   = ( M  1  x  1  + M  2  x  2 )/ ρ , where M  1  and M  2  are the molecular weightsof the binary system components). It is shown in Fig. 2that the experimental molar volume–compositiondependence (  = 168.4 – 134.2  x  , r   = –1) has apositive deviation from additivity over the whole concentration range studied ( = 168.3 – 150.0  x  , r =–0.999). Additive values were calculated using thedensity of crystalline AgBr, whose melting point is 424°С  [21].The conclusion can be drawn that the BMImBr– AgBr system exhibits concentration and temperatureinduced density variations characteristic of  binary melts with chemical intercomponent interactions [13].  Vitrification.  According to the differential scanningcalorimetry data, the glass transition temperature of asupercooled BMImBr melt with water impurity islower than –70°С  [15]. For BMImBr–AgBr mixtures, V   molexpt V   molаdd Characteristics of the IR transmission spectrum (3500–2500 cm –1 ) of BMImBr–AgBr and BMImBr ionic liquids ν , cm –1  Atomic groupBond  ν , cm –1  [20]BMImBr– AgBr BMImBr [15]3473 ( ν s )3442H 2 OО–Н3500–32002958 ( ν as )2872 ( ν s )29602873–CH 3 C–H2975–29502885–28602933 ( ν as )2871 ( ν s )29292873–CH 2 –C–H2940–29152870–284527332733N–CH 3 C–H2820–27303137 ( ν )3087 ( ν )31433082–CH аром C–H3095–30103000–3100 Note:  ν s  denotes symmetrical and ν as  asymmetric stretching vibrations.  RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 11 2009 THE PHYSICOCHEMICAL PROPERTIES OF THE LOWTEMPERATURE IONIC LIQUID1885 this temperature is more positive and increases from –70.2°С  to –48.8°С  as the content of AgBr growsfrom 0.078 to 0.220 mole fractions. According to[13], an increase in the freezing temperature of  binary melt is evidence of binding of more than onehalide ion of the meltsolvent by dissolved salt molecules with the formation of the corresponding complex ions. Dynamic viscosity and electrical conductivity. Thedynamic viscosity η  values were calculated taking intoaccount the correction coefficient [15] as the slope of the straight line in the shear stress ( τ )–rate of shear ( D  )coordinates [22]. The dependences of η  on D   for BMImBr–AgBr ionic liquids with various compositions are shown in Fig. 3. At  x   AgBr   < 0.188, the system behaves like initial BMImBr and exhibits the proper 607890.050.100.150.20  x   AgBr  , mole fractions −(∆ρ / ∆ t  ) ×  10 4 , g/(cm 3  K) Fig. 1.  Dependence of ∆ρ / ∆ t   on the content of AgBr for BMImBr–AgBr melts. 01701500.10.2  x   AgBr  , mole fractions V  , сm 3 2 1 Fig. 2.  Dependences of the molar volume of BMImBr– AgBr binary melts on the content of AgBr at 20°С :( 1 )experimental dependence and ( 2  ) dependence basedon the additivity rule. η   ×  10 − 4 , сP1.201.00.820604080 D  , rad/s 4 3 2 1 Fig. 3.  Dependence of dynamic viscosity η  on the rate of shear D   in the BMImBr–AgBr system at AgBr contents  х  (mole fractions) of ( 1 ) 0, ( 2  ) 0.120, ( 3  ) 0.169, and ( 4  )0.188. η   ×  10 − 4 , сP1.401.00.60.20.050.100.150.20403020100 χ   ×  10 − 4 , Sm/сm  x   AgBr  , mole fractions Fig. 4.  Dependences of specific conductivity χ  anddynamic viscosity η  on the ratio between BMImBr–AgBr  binary melt components at 20°С .  1886 RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 83 No. 11 2009 GRISHINA et al. ties of Bengham liquids. Initially, they are characterized by an increase in viscosity. When the yield point isreached, the system behaves as a Newton liquid, and η is independent of D  . At  x   AgBr    ≥  0.188 , BMImBr–AgBr  binary melts behave like BMImBr (with a 1.78 wt % water content) [15], that is, like a highly structureddilatant liquid, and η  increases as D   grows [23].The influence of the composition (  x  ) on η  and specific conductivity ( χ ) of BMImBr–AgBr melts is shownin Fig. 4. We see that the saltsolvent (BMImBr) has alower conductivity at 20°С  than dilute solutions of  AgBr in it. At this temperature, BMImBr is in themetastable supercooled melt state (melting point 55°С  [15]) with a sharply decreased ability to experience viscous flow, whereas binary systems are liquidsunder these conditions. The viscosity isotherm in theregion of compositions under consideration passes aminimum. Such a concentration behavior of viscosity is characteristic of melts of salts in the associated state, which dissociate when mixed with other salts [13]. The χ  value sharply decreases as the content of AgBr inmelts increases. This can be related to the formation of largesized silvercontaining complex ions with lowmobility [14].To summarize, the experimental property–composition dependences for the lowtemperatureBMImBr–AgBr ionic liquid have the form characteristic of binary melts with intercomponent interactionof the complex formation type. ACKNOWLEDGMENTSThis work was financially supported by Programno. 9 of the Division of Chemistry and Materials Science, Russian Academy of Sciences, “New Approaches to Improvement of Corrosion and Radiation Resistance of Materials and RadioecologicalSafety,” project no. 1.REFERENCES 1.J. D. Holbrey and K. R. Seddon, Clean Products Process. 1 , 223 (1999).2.F. Endres, Chem. Phys. Chem. 3 , 144 (2002).3.T. R. Scheffler, C. L. Hussey, K. R. 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Sundheim (McGrawHill,New York, San Francisco, Toronto, London, 1964;Mir, Moscow, 1966).15.L. M. Ramenskaya, E. P. Grishina, A. M. Pimenova,etal., Zh. Fiz. Khim. 82 , 1246 (2008) [Russ. J. Phys.Chem. 82 , 1098 (2008)].16.P. I. Voskresenskii, Technology of Laboratory Works (Mir, Moscow, 1973) [in Russian].17.H. Sedek, A. M. Habez, and F. X. Khalil, Electrochim. Acta 14 , 1089 (1969).18.B. A. Lopatin, Theoretical Foundations of Electrochemical Analysis Methods  (Vyssh. Shkola, Moscow, 1975)[in Russian].19.K. W. Pratt, W. F. Koch, Y. C. Wu, et al., Pure Appl.Chem. 73 , 1783 (2001).20.K. Nakanisi, Infrared Absorption Spectroskopy (HoldenDay, Tokyo, 1962; Mir, Moscow, 1965).21.V. A. Rabinovich and Z. Ya. Khavin, Short Chemical Handbook   (Khimiya, Leningrad, 1991) [in Russian].22.V. K. Abrosimov, V. V. Korolev, V. N. Afanas’ev, et al., Experimental Methods of Solution Chemistry. Densimetry, Viscosimetry, Conductometry, and Other Methods (Nauka, Moscow, 1997) [in Russian].23. 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