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Copper quadrupole coupling constants in binary mixtures of acetonitrile with some other nitriles at 298 K
Journal of Molecular Liquids 111 (2004) 85–93
Copper quadrupole coupling constants in binary mixtures of acetonitrile with some other nitriles at 298 K Dip Singh Gilla,*, T.I. Quickendenb, L. Byrneb, Vivek Pathaniaa, B.K. Vermania b
a Department of Chemistry, Panjab University, Chandigarh-160 014, India School of Biomedical and Chemical Sciences, University of Western Australia, Crawley, Western Australia-6009, Australia
Received 7 April 2003; accepted 16 August 2003
Abstract 63 Cu and 65Cu nuclear magnetic resonance (NMR) and viscosity studies of 0.064 M CuClO4 have been made in binary mixtures of acetonitrile (AN) with succinonitrile (SN), adiponitrile (ADN), n-butyronitrile (n-BTN) and iso-butyronitrile (isoBTN) as co-solvents at 298 K using 500 MHz NMR spectrometer and an Ubbelohde viscometer, respectively. Chemical shift (d) and linewidth (D) for both 63Cu and 65Cu signals have been recorded relative to 0.064 M CuClO4 solution in pure anhydrous AN. Quadrupole relaxation rates (1yT2 )Q , reorientational correlation times (tR ) and copper quadrupole coupling constants (e 2Qqy h) have been calculated in all cases. The variation of these NMR parameters has been examined as a function of molecular percent co-solvent to compare the relative effects of these co-solvents on the solvation behaviour of Cuq and hence on the stabilization of copper (I) complexes formed. The (e 2 Qqyh) values in all ANqnitrile mixtures are larger than the values in pure AN and increase with the increase of molecular percent co-solvent. The strong increase of (e 2 Qqyh) values in all ANqnitrile mixtures with the increase of molecular percent co-solvent indicates the formation of mixed complexes of the form wCu(CH3CN)4yx(S)xxq (xs1y4) due to the replacement of AN molecules from the original complex wCu(CH3CN)4 xq formed in pure AN by the co-solvent molecules (S). The results also show that mixed copper (I) complexes in all cases remain stable even at high co-solvent compositions. The (e 2 Qqyh) values also indicate that the effect of dinitriles is relatively stronger than that of mononitriles, the effect of 63Cu isotope is relatively stronger than that of 65 Cu and the effect of iso-BTN is relatively stronger than that of n-BTN in the formation of mixed copper (I) complexes. 䊚 2003 Elsevier B.V. All rights reserved.
Keywords:
63
Cu;
65
Cu; NMR; Acetonitrile; Other nitriles
1. Introduction Stabilization of copper (I) salts in solution leads to applications in the hydrometallurgical purification of copper and silver w1–6x. Therefore, stabilization of concentrated copper (I) solutions is industrially a useful subject. Copper has two stable isotopes, 63Cu and 65Cu, which have high quadrupole moments and very favourable sensitivities w7x. Because of its large natural abundance (69.1%), 63Cu has been preferred for NMR studies w8–11x. Although, 63Cu NMR studies are very interesting but such studies are still meagre due to several difficulties. Firstly, Cu NMR studies can be made using only diamagnetic copper salts. For this purpose, copper (I) salts have to be used, the preparation *Corresponding author. Fax: q91-172-2545074. E-mail address: [email protected] (D.S. Gill).
of which, in the pure state, is difficult. Secondly, copper (I) solutions are stable only in a limited number of solvents, therefore, the choice of an appropriate solvent or solvent mixture is generally very laborious and difficult. Thirdly, 63Cu and 65Cu nuclei have large quadrupole moments (y0.211=10y28 m2 and y0.195=10y28 m2, respectively) due to which Cu NMR signals are usually very broad in pure solvents and become even broader in mixed solvents w8–12x because of the strong field gradient. Fourthly, the Cu NMR signal can be observed only in those cases where Cuq has tetrahedral symmetry at the copper nucleus. Tetrahedrally coordinated cuprous complexes such as Cu(CH3CN)4ClO4 or Cu(CH3CN)4BF4 which produce tetra-coordinated copper (I) complex ions in solution are shown to be very suitable salts for 63Cu NMR studies w8–10,12x. For bi-coordinated and tri-coordinat-
0167-7322/04/$ - see front matter 䊚 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.molliq.2003.08.022
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D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
ed copper (I) complexes in solution, the 63Cu NMR signal, however, cannot be observed w13,14x. The symmetry at the copper site is thus very important for Cu NMR measurements. 63Cu or 65Cu NMR chemical shifts (d) and linewidths (D) are very sensitive to the solvent medium. By measuring such parameters, significant information about the solvation behaviour of Cuq in mixed solvents can be obtained w8–10x. In this paper, we present some interesting Cu NMR results in binary mixtures of acetonitrile (AN) with some other nitriles (dinitriles and mononitriles) to throw light on the following three important aspects: (1) Which of the two isotopes 63Cu or 65Cu gives more symmetrical copper (I) complexes and hence better NMR signals? (2) Whether or not nitriles with two-C^ N groups in the same molecule are better solvents for the stabilization of copper (I) salts as compared to nitriles with a single–C^ N group? (3) Whether or not two isomers, e.g. n-butyronitrile (n-BTN) and iso-butyronitrile (isoBTN) have a similar effect on Cu NMR parameters? 2. Experimental Copper (I) perchlorate tetraacetonitrile Cu(CH3CN)4 ClO4 used for all NMR measurements was prepared by the method reported earlier w8,15x. The salt was stored in a dry box and was handled under anhydrous conditions. Water free AN (Unichrom, 99.7%), n-BTN (Fluka)99%), iso-BTN (Merck)98%) and adiponitrile (ADN) (Aldrich, 99%) were stored over well dried ˚ for several days before use. molecular sieves (4 A)
Succinonitrile (SN) (BDHLR)99%) was used as received. 63Cu and 65Cu NMR measurements were made ¨ at 298"1 K using 10 mm NMR tubes on a Bruker 500 MHz spectrometer using a broadband probe head at 132.612 MHz and 142.057 MHz frequencies. Copper (I) solutions were prepared by fixing the salt concentration as 0.064 M. All chemical shifts (d) and linewidths (D) were measured relative to 0.064 M CuClO4 in pure anhydrous AN, which was taken as a reference solution for all other measurements. For the reference solution, D for 63Cu and 65Cu was 482 Hz and 422 Hz, respectively, and d values in all cases were set as 0.0 ppm. The reference solution was measured from time to time to ensure consistency of all NMR results. The reproducibility d and D values was estimated as "2% and "3%, respectively. Densities and viscosities of all binary mixtures and 0.064 M CuClO4 solutions were measured at 298.15"0.01 K using Anton Paar Digital Densitimeter and Ubbelohde suspended level viscometer, respectively. The reproducibility of density measurements was within "2.0=10y3% and of viscosity measurements within "0.3%. 3. Results and discussion The linewidth of the 63Cu NMR signal at 482 Hz in the present measurement for 0.064 M CuClO4 solution in pure AN is in good agreement with the previous values between 480 to 550 Hz reported in the literature w7–10,12,13x. The linewidth of the 65Cu NMR signal 422 Hz, however, is smaller than that obtained for 63Cu.
Fig. 1. Chemical shift (d), plot (a) and linewidth (D), plot (b) for 63Cu NMR signal from 0.064 M CuClO4 solutions vs. mol % co-solvent in ANqco-solvent mixtures at 298 K ⽧ – ANqSN;j – ANqADN; D – ANqn-BTN; = – ANqiso-BTN.
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
87
Fig. 2. Chemical shift (d), plot (a) and linewidth (D), plot (b) for 65Cu NMR signal from 0.064 M CuClO4 solutions versus mol % co-solvent in ANqco-solvent mixtures at 298 K ⽧ – ANqSN;j – ANqADN; D – ANqn-BTN; = – ANqiso-BTN.
The linewidth found in both cases increased significantly with the water content of the AN. Trace amounts of copper (II) as impurity in CuClO4 also increased the linewidth of the copper signal considerably. It was, therefore ensured that AN used was completely water free and the trace amounts of copper (II) salt were absent. The linewidths of the 63Cu and 65Cu NMR signals in pure AN from various samples were reproducible within the experimental error. The chemical shift (d) and linewidth (D) have been measured for 63Cu and 65Cu NMR signals using 0.064 M CuClO4 solutions in binary mixtures of AN with SN, ADN, n-BTN and iso-BTN at different compositions of the mixtures (relative to 0.064 M CuClO4 solution in pure AN) and these NMR parameters as a function of molecular percent co-solvent for 63Cu and 65Cu are plotted in Figs. 1 and 2, respectively. It is observed from Figs. 1 and 2 that CuClO4 in binary mixtures of AN with other nitriles shows positive chemical shift and this shift becomes more positive with the increase of cosolvent composition in AN. In our previous 63Cu NMR studies also w7–11x, we observed that the chemical shift (d) in binary mixtures of AN with benzonitrile (BN), propionitrile (PN), 3-hydroxypropionitrile (3HPN) and 3-methoxypropionitrile (3MPN) were positive w9–11x and increased with the increase of molecular percent cosolvent. In each case, stable mixed complex ions of the form wCu(CH3CN)4yx(S)x xq (xs1y4) were formed due to the replacement of AN from the original complex
wCu(CH3CN)4xq formed in pure AN by the co-solvents. Negative d values for 63Cu NMR signals, however, were observed in binary mixtures of AN with many other organic solvents w7–11x. In such solvent systems, the mixed complexes wCu(CH3CN)4yx(S)x xq (xs1y4) were not very stable over the entire solvent composition range due to the fast replacement of AN by the cosolvent w7–11x. Even the complexes of the form wCu(P)4xq where P is co-solvent were not stable in all cases except for the cases where pyridine (Py) or triethylphosphite (C2H5O)3P were used as co-solvents w7,8x. A comparison of 63Cu and 65Cu NMR parameters (d and D) has been made by plotting these parameters against molecular percent co-solvent in all cases. d values in various solvent systems are almost identical for 63Cu and 65Cu but D values are relatively different. For illustration, the plot of these NMR parameters vs. molecular percent co-solvent in ANqn-BTN mixtures is shown in Fig. 3. The physical constants of all these binary mixtures used in the present work were not available in the literature, therefore an attempt was made to measure these parameters at different compositions of the mixtures. The measured dielectric constant (´0), density (r0) and viscosity (h0) of the binary mixtures of the solvent systems used at various compositions are presented in Table 1 and rs and hs parameters for 0.064 M copper (I) perchlorate solutions required for the calcu-
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
88
Fig. 3. Chemical shift (d), plot (a) and linewidth (D), plot (b) for BTN in ANqn-BTN mixtures at 298 K ⽧ – 63Cu;j – 65Cu
63
Cu and
65
Cu NMR signals from 0.064 M CuClO4 solutions vs. mol% n-
Table 1 Dielectric constant (´0), density (r0 in g cmy3) and viscosity (h0 in cP) for ANqco-solvent mixtures at 298.15 K
Table 2 Density (rs in g cmy3) and viscosity (hs in cP) for 0.064 M CuClO4 solutions in ANqco-solvent mixtures at 298.15 K
ANqSN
ANqSN
ANqn-BTN
ANqn-BTN
mol.% SN
´0
r0
h0
mol.% n-BTN
´0
r0
h0
mol.% SN
rs
hs
mol.% n-BTN
rs
hs
0.00 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
36.0 36.5 37.0 37.4 39.2 41.0 43.5 46.5 51.5 54.0
0.77685 0.78787 0.79689 0.80595 0.82401 0.85986 0.88738 0.90755 0.93813 0.97260
0.343 0.388 0.409 0.432 0.545 0.678 0.858 1.039 1.528 2.054
0.00 2.45 7.58 13.10 19.00 28.60 47.40 60.70 70.60 87.40 97.70 100.00
36.0 35.5 35.0 34.5 34.0 33.0 31.5 30.0 29.2 28.1 26.9 24.5
0.77685 0.77819 0.77884 0.77948 0.78013 0.78077 0.78228 0.78379 0.78463 0.78547 0.78605 0.78662
0.343 0.363 0.376 0.389 0.402 0.415 0.445 0.474 0.501 0.527 0.539 0.551
0.00 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
0.77783 0.79811 0.80692 0.81574 0.83436 0.87008 0.89687 0.91267 0.94848 0.98333
0.373 0.410 0.429 0.451 0.567 0.705 0.890 1.089 1.595 2.133
0.00 2.45 7.58 13.10 19.00 28.60 47.40 60.70 70.60 87.40 97.70 100.00
0.77783 0.78902 0.79007 0.79014 0.79037 0.79064 0.79153 0.79390 0.79453 0.79619 0.79626 0.79638
0.373 0.382 0.400 0.419 0.428 0.437 0.469 0.501 0.529 0.538 0.545 0.557
r0
h0
r0
h0
rs
hs
0.77685 0.79361 0.81858 0.84124 0.85446 0.86767 0.87308 0.87849 0.95850
0.343 0.411 0.506 0.634 0.724 0.800 0.901 0.983 5.99
0.77685 0.77641 0.77538 0.77498 0.77466 0.77349 0.77183 0.77016 0.76916 0.76815 0.76752 0.76688
0.343 0.373 0.379 0.387 0.394 0.401 0.418 0.436 0.457 0.478 0.483 0.487
0.77783 0.80574 0.82938 0.85109 0.85989 0.88443 0.90119 0.91796 0.97526
0.373 0.432 0.553 0.686 0.755 0.848 0.940 1.115 6.058
ANqADN mol% ´0 ADN 0.00 36.0 3.88 35.8 10.40 35.5 17.93 35.2 23.63 34.9 27.08 34.7 32.68 34.4 34.88 34.2 100.00 32.4
ANqiso-BTN ´0 mol% iso-BTN 0.00 36.0 2.40 35.2 7.44 34.4 12.85 33.6 18.65 32.8 28.22 31.5 46.93 29.3 60.25 27.4 70.22 26.3 87.15 25.2 97.69 24.6 100.00 23.8
ANqADN mol.% ADN 0.00 3.88 10.40 17.93 23.63 27.08 32.68 34.88 100.00
ANqiso-BTN rs mol.% BTN 0.00 0.77783 2.40 0.78870 7.44 0.78724 12.85 0.78638 18.65 0.78553 28.22 0.78514 46.93 0.78371 60.25 0.78199 70.22 0.78059 87.15 0.77973 97.69 0.76930 100.00 0.76866
hs 0.373 0.392 0.404 0.416 0.422 0.427 0.450 0.473 0.479 0.483 0.486 0.490
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
lation of quadrupole coupling constants and the molar volumes of the solvent systems used for the estimation of solvent radii (rs) are reported in Table 2. 3.1. Evaluation of quadrupole relaxation rates (1yT2)Q, reorientational correlation times (tR) and quadrupole coupling constants (e 2Qqyh) The spin lattice relaxation of copper nuclei is essentially governed by the quadrupole relaxation rate (1y T2)Q, which is extracted from the linewidth (D) and depends on the asymmetry factor of the solvation sphere (h) and the reorientational correlation time (tR) according to the relations w16x: B
C
1E F spD D T2 GQ
(1)
1E 3p2 Ž2Iq3. w h2 zw e2Qq z2 F s x1q |x | tR 2 D T2 GQ 10I Ž2Iy1. y 3 ~y h ~
(2)
B
C
where D represents the linewidth at half the height of the signal, I the is nuclear spin for the Cu nucleus and (e 2Qqyh) is the quadrupole coupling constant. Eq. (1) is applicable when NMR line shapes are Lorentzian. Eq. (2) is applicable for the limit of extreme narrowing when v2t2R<1. The h values for all these systems are not available, therefore, it was not possible to evaluate the factor (1qh2 y3) in Eq. (2). For the symmetrical complex wCu(CH3CN)4 xq formed in pure AN, where copper had tetrahedral symmetry at the Cu nucleus, the value of h is zero. In mixed solvents, the replacement of AN by any of the other analogous nitriles having identical shape and almost similar size and forming tetrahedral complexes of the type wCu(CH3CN)4yx(S)x xq (xs1y4), h can have a value which may not be zero but is too small to be significant. Setting Is3y2 for the 63Cu and 65Cu nuclei and (1q h2 y3)s1 as before w9,11x, Eq. (2) simplifies to Eq. (3) from which (e 2Qqyh) can be calculated. B
w 2 1E e Qq z2 F s3.9478x | tR D T2 GQ h ~ y
C
(3)
When the size of the solute molecule is much larger than that of the solvent molecule, the reorientational correlation time tR in Eq. (3) can be calculated by using the relation w16x: tRs
4pr3i hS 3kT
(4)
where ri is the radius of the spherical solvated ion or solute molecule and hS is the viscosity of the solution.
89
When the size of the solute and the solvent molecules, however, becomes comparable, Eq. (4) is no longer valid. Gierer and Wirtz w17x proposed a method of calculating tR values of the solute molecules when the solute molecules are of comparable size to the solvent molecules. This model takes into account the microviscosity factor, f GW, given by: w
fGWsx6 y
rS B 2rS Ey3zy1 F | qC1q ri D ri G ~
(5)
where ri is the radius of the solute or solvated ion and rS is the radius of the solvent molecule. In the macroscopic limit when ri4rS, this microviscosity factor becomes equal to unity but in case of neat liquids where ri;rS, its value lies between 0.06 and 0.17 w18x. For the ions and molecules of comparable size, the actual reorientational correlation time tR can be calculated by applying microviscosity correction to tR in Eq. (4). The following relation then becomes valid for the calculation of actual tR values w17,19x. tRs
4pri3hS w rS B 2r Ey3zy1 x6 qC1q S F | 3kT y ri D ri G ~
(6)
Using Eqs. (1), (3) and (6) and the solution viscosity (hS) for 0.064 M CuClO4 from Table 2, the copper quadrupole coupling constants (e 2Qqyh) in various solvent systems have been calculated. By taking solvated radii for Cuq (ri) from conductance data in pure solvents and the averaged ri values at various compositions in different solvent mixtures using these ri values, the tR values have been calculated using Eq. (6). These tR values are reported in Tables 3 and 4. The solvent radii (rs) were estimated by calculating the averaged molar volumes of the mixed solvents by using densities (r0) of the solvent mixtures from Table 1 and hs values from Table 2. The microviscosity factor f GW of Eq. (5) was found to lie between 0.24 and 0.29 in the present systems. The copper quadrupole coupling constants for 63 Cu and 65Cu complexes evaluated by this method are reported in Table 3. The quadrupole coupling constant usually increases with the formation of mixed complexes w10x. It can be seen from Table 3 that the quadrupole coupling constant values in all ANqnitrile mixtures are larger than the values in pure AN and increase with the increase of molecular percent co-solvent. The increase in these values with molecular percent co-solvent is larger in nitriles having double–C^ N groups as compared to nitriles having a single–C^ N group. The (e 2Qqyh) values at definite composition for 65Cu isotope are relatively smaller than the values for 63Cu at the corresponding compositions of the solvent mixtures. The (e 2Qqyh) values for copper (I) complexes in n-BTN
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
90
Table 3 Reorientational correlation times (tR ) and quadrupole coupling constants (e2 Qqyh) of 63 Cu and in AN q co-solvent mixtures at 298 K
65
Cu complexes from 0.064M CuClO4 solutions
ANqSN 63
65
Cu NMR
Cu NMR
mol.% SN
tR.10 (s)
e Qqyh(MHz)
mol.% SN
tR.1011(s)
e 2Qqyh(MHz)
0 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
1.39 1.40 1.47 1.53 1.91 2.15 2.78 3.00 3.46 4.33 ANqADN
5.26 5.48 5.44 5.86 5.62 6.86 7.29 7.92 9.09 10.67
0 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
1.39 1.40 1.47 1.53 1.91 2.15 2.48 3.00 3.94 4.33
4.92 5.08 5.06 5.41 5.18 6.31 7.09 7.22 7.70 9.65
e 2Qqyh(MHz) 5.26 5.92 6.31 7.00 7.49 7.81 8.44 8.73
mol.% ADN 0 3.88 10.4 17.93 23.63 27.08 32.68 34.88
65 Cu NMR tR.1011(s) 1.39 1.49 1.76 2.10 2.30 2.48 2.71 2.92
e 2Qqyh(MHz) 4.92 5.51 5.98 6.83 7.11 6.97 7.78 7.66
e 2Qqyh(MHz) 5.26 5.34 5.43 5.57 5.59 6.08 6.56 6.65 6.94 7.74 8.01
mol.% n-BTN 0 2.45 7.58 13.1 19 28.6 47.4 60.7 70.6 87.4 97.7
e 2Qqyh(MHz) 5.26 5.18 5.30 5.47 5.71 5.84 6.54 7.00 7.17 8.05 8.54
mol.% iso-BTN 0 2.4 7.44 12.85 18.65 28.22 46.93 60.25 70.22 87.15 97.69
mol.% ADN 0 3.88 10.4 17.93 23.63 27.08 32.68 34.88
11
63 Cu NMR tR.1011(s) 1.39 1.49 1.83 2.35 2.59 2.36 2.71 2.78 ANqn-BTN 63
mol.% n-BTN 0 2.45 7.58 13.1 19 28.6 47.4 60.7 70.6 87.4 97.7
65
Cu NMR
tR.1011(s) 1.39 1.42 1.46 1.52 1.66 1.67 1.87 2.11 2.19 2.17 2.33 ANqiso-BTN 63
mol.% iso-BTN 0 2.4 7.44 12.85 18.65 28.22 46.93 60.25 70.22 87.15 97.69
2
Cu NMR e 2Qqyh(MHz) 4.92 4.96 5.00 5.18 5.18 5.62 6.04 6.13 6.40 7.10 7.33
65
Cu NMR
tR.1011(s) 1.39 1.45 1.48 1.51 1.52 1.64 1.67 1.72 1.85 1.86 1.94
tR.1011(s) 1.39 1.42 1.46 1.52 1.66 1.67 1.87 2.11 2.19 2.17 2.33 Cu NMR
tR.1011(s) 1.39 1.45 1.48 1.51 1.52 1.64 1.67 1.72 1.85 1.82 1.94
e 2Qqyh(MHz) 4.92 4.86 4.94 5.11 5.36 5.47 6.11 6.56 6.74 7.57 7.88
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93 Table 4 Reorientational correlation times (tR) and 65Cu quadrupole coupling constants (e 2Qqyh) of copper (I) complexes from CuClO4 solutions in iso-BTN at different salt concentrations (C, in mol dmy3) at 298 K C
tR.1011(s)
e 2Qqyh(MHz)
0.032 0.064 0.128 0.256 0.411 0.512
1.88 1.93 2.23 2.54 2.68 2.78
7.90 7.89 7.89 7.87 7.81 7.81
are relatively smaller than those in iso-BTN at the same composition of the solvent mixtures. The result shows that in each case, stable mixed complexes of the form wCu(CH3CN)4yx(S)x xq (xs1y4) are formed due to the replacement of AN by co-solvents (S) from the original complex wCu(CH3CN)4 xq formed in pure AN. The mixed copper (I) complexes remain stable at all compositions of the solvent mixtures, if the co-solvents used are nitriles. The evidence for the stability of these complexes comes from the systematic increase of the (e 2Qqyh) values with the increase of co-solvent composition. If the co-solvents, however, are other organic solvents, the mixed complex ions do not remain stable beyond certain compositions of the co-solvents. A sudden jump of (e 2Qqyh) values after a certain co-solvent composition in these cases indicates the instability of the complexes w11x. The quadrupole coupling constant for 63Cu has a value of 5.26 MHz in pure AN which increases to 8.01 MHz at 97.7 mol.% n-BTN and 8.54 MHz at 97.69 mol.% iso-BTN. The (e 2Qqyh) for both
91
63
Cu and 65Cu nuclei at all compositions of AN with two isomeric nitriles n-BTN and iso-BTN differ slightly from each other. The value is relatively more in isoBTN than in n-BTN. The quadrupole coupling constant (e 2Qqyh) values in ANqSN mixture and ANqADN mixture increases largely by the increase of co-solvent composition. The value becomes 10.67 MHz at 69.4 mol.% SN and 8.39 MHz at 34.88 mol.% ADN. For 65 Cu also, the quadrupole coupling constant values increase largely by the increased composition of the cosolvent. The increase in the value of the quadrupole coupling constant is much stronger in case of SN and ADN, i.e. in nitriles having two –C^ N groups. Dinitriles are chelating ligands and form more asymmetric complexes as compared to those formed by mononitriles and thus, the larger (e 2Qqyh) values are obtained using dinitriles as co-solvents. The (e 2Qqyh) values for 65Cu in all ANqnitrile mixtures are relatively smaller in comparison to 63Cu values and the ratio of the (e 2Qqy h)2 values for 65Cu to 63Cu in all cases are in good agreement with the ratio of their corresponding linewidths (D). The linewidth data for CuClO4 in binary mixtures of AN with BN, PN, 3HPN and 3MPN were available from the previous work reported by Gill et al. w9–11x. Using these data, the copper quadrupole coupling constants (e 2Qqyh) for 63Cu complexes have been calculated and reported in Table 5 and for better comparison with the present values (from Table 3) have been plotted in Fig. 4. It is observed from this figure that the (e 2Qqyh) values in all cases increase with the increase of molecular percent co-solvent in ANqcosolvent mixtures. The increase is maximum in case of ANqADN mixtures and minimum for ANq3MPN
Table 5 63 Cu quadrupole coupling constants (e 2Qqyh) of copper (I) complexes from CuClO4 solutions in binary mixtures of AN with BN, PN, 3MPN and 3HPN at 298 K ANqBNa mol % BN (e 2Qqyh) (MHz) ANqPNa mol % PN (e 2Qqyh) (MHz) ANq3MPNb mol % 3MPN (e 2Qqyh) (MHz) ANq3HPNc mol % 3HPN (e 2Qqyh) (MHz)
0.0
5.4
18.0
33.9
54.5
82.2
5.26
5.27
5.56
5.99
6.08
6.93
0.0
12.98
27.16
42.71
59.86
78.56
5.26
5.77
5.95
6.30
6.48
6.96
0.0
2.96
6.05
16.18
36.68
5.26
5.47
5.48
5.57
0.0
2.6
13.42
5.26
5.71
6.31
94.3
97.4
6.98
7.38
63.47
83.91
91.67
96.45
5.79
6.07
6.26
6.35
6.47
27.93
43.66
60.79
71.80
79.49
91.56
6.63
7.18
7.57
7.44
7.38
7.24
Calculated from the linewidth data available in aRef. w9x; bRef. w11x; cRef. w10x
92
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
Fig. 4. Quadrupole coupling constants (e2Qqyh) for 63 Cu NMR from 0.064 M CuClO4 solution in ANqco-solvent mixtures vs. mol% co-solvent at 298 K ⽧ – ANqSN; j – ANqADN; D – ANqn-BTN; xANqiso-BTN; * – ANqBN; d – ANqPN; h – ANq3MPN; m – ANq3HPN.
Fig. 5. Chemical shift (d), plot (a); linewidth (D), plot (b) and relative intensity (I), plot (c) for solution vs. molar concentration (C) of CuClO4 in iso-BTN at 298 K.
65
Cu NMR signal from 0.064 M CuClO4
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
mixtures. The change of (e 2Qqyh) in various ANqcosolvent mixtures is in the order: ANqADN)ANq SN)ANq3HPN)ANqiso-BTN)ANqn-BTN) ANqPN)ANqBN)ANq3MPN. 3.2. Effect of CuClO4 concentration on the copper quadrupole coupling constant Many salts are strongly associated in pure and mixed organic solvents at high concentrations. They form ionpairs, which can be easily detected by conductance and NMR measurements. Since CuClO4 is highly soluble in iso-BTN, the effect of salt concentration on 63Cu NMR parameters was also investigated in ANqiso-BTN mixtures. The variation of d, D and relative intensity of the signal (I) as a function of CuClO4 concentration is presented in Fig. 5. With the increase of CuClO4 concentration, d decreases linearly while D increases non-linearly. The linear increase of I with salt concentration shows the absence of ion-pairing of CuClO4 in these solvent systems. The evaluation of the 65Cu quadrupole coupling constant at different CuClO4 concentrations in ANqiso-BTN mixtures gave a constant value (7.86"0.1 MHz) which indicates the absence of ion-pairing of CuClO4 even at relatively higher concentrations (Table 4). Conductance and transport number studies of some copper (I) salts in ANqco-solvent mixtures reported by Gill and co-workers w20,21x also confirm the absence of ion pairs. 4. Conclusions In all ANqnitrile mixtures, the (e 2Qqyh) values for copper (I) complexes increase significantly with increase of co-solvent composition and this increase continues upto a large range of solvent composition. The results show that all nitriles used as co-solvents have strong tendency to replace AN from the complex ion wCu(CH3CN)4xq forming the mixed complexes of the form wCu(CH3CN)4yx(S)x xq (xs1y4). These mixed complex ions remain stable even in the co-solvent rich region of the mixtures. Dinitriles have stronger effect on the solvation of Cuq than the mononitriles at the corresponding compositions. 65Cu and n-BTN form comparatively more symmetrical complexes indicated by their relatively low (e 2Qqyh) values. The (e 2Qqyh) value for 65Cu at different CuClO4 concentrations in iso-BTN remains practically constant (7.86"0.1 MHz)
93
indicating that there is no effect of salt concentration on (e 2Qqyh) values. Acknowledgments DSG is grateful to the Gledden Trust and the University of Western Australia for the award of Visiting Senior Gledden Fellowship. VP thanks the UGC, New Delhi for the award of Junior Research Fellowship. BKV thanks the UGC for the Teacher Fellowship and the DAV College, Chandigarh, for the grant of long study leave. References w1x A.J. Parker, Search 4 (1973) 425–432. w2x I.D. MacLeod, D.M. Muir, A.J. Parker, P. Singh, Aust. J. Chem. 30 (1977) 1423–1437. w3x D.S. Gill, R. Srivastava, J. Chem. Soc. Faraday T. I 78 (1982) 1533–1538. w4x D.S. Gill, R. Srivastava, Ind. J. Chem. 22A (1983) 140–142. w5x D.S. Gill, R. Srivastava, Ind. J. Chem. 22A (1983) 479–481. w6x D.S. Gill, R. Noerding, Z. Phys. Chem. (N.F.) 136 (1983) 117–122. w7x P. Kroneck, J. Kodweiss, O. Lutz, A. Nolle, D. Zepf, Z. Naturforsch. 37A (1982) 186–190. w8x D.S. Gill, L. Rodehueser, J.J. Delpuech, J. Chem. Soc. Faraday T. 86 (1990) 2847–2852. w9x D.S. Gill, L. Rodehueser, P. Rubini, J.J. Delpuech, J. Chem. Soc. Faraday T. 91 (1995) 2307–2312. w10x D.S. Gill, L. Byrne, T.I. Quickenden, Z. Naturforsch. 53a (1998) 1004–1008. w11x D.S. Gill, U. Kamp, A. Doelle, M.D. Zeidler, Ind. J. Chem. 40A (2001) 693–699. w12x W. Ochsenbein, C.W. Schlaepfer, Helv. Chim. Acta 63 (1980) 1926–1931. w13x P. Kroneck, O. Lutz, A. Nolle, H. Oehler, Z. Naturforsch. 35A (1980) 221–225. w14x O. Lutz, H. Oehler, P. Kroneck, Z. Naturforsch. 33a (1978) 1021–1024. w15x B.J. Hathaway, D.G. Holah, J.D. Postlethwaite, J. Chem. Soc. (1961) 3215–3218. w16x F.A. Bovey, L. Jelinski, P.A. Mirau, Nuclear Magnetic Resonance Spectroscopy, 2nd edn, Academic Press, New York, 1988, p. 16,28,264. w17x A. Gierer, K. Wirtz, Z. Naturforsch. 8a (1953) 532–538. w18x M.D. Zeidler, Ber. Bunseng. Phys. Chem. 69 (1965) 659–669. w19x R.P. Kluener, A. Doelle, J. Phys. Chem. A 101 (1997) 1657–1661. w20x D.S. Gill, R. Singh, V. Ali, J. Singh, S.K. Rehani, J. Chem. Soc. Faraday T. 90 (1994) 583–586. w21x D.S. Gill, P. Singh, J. Singh, P. Singh, G. Senanayake, G.T. Hefter, J. Chem. Soc. Faraday. T. 91 (1995) 2789–2795.
Copper quadrupole coupling constants in binary mixtures of acetonitrile with some other nitriles at 298 K Dip Singh Gilla,*, T.I. Quickendenb, L. Byrneb, Vivek Pathaniaa, B.K. Vermania b
a Department of Chemistry, Panjab University, Chandigarh-160 014, India School of Biomedical and Chemical Sciences, University of Western Australia, Crawley, Western Australia-6009, Australia
Received 7 April 2003; accepted 16 August 2003
Abstract 63 Cu and 65Cu nuclear magnetic resonance (NMR) and viscosity studies of 0.064 M CuClO4 have been made in binary mixtures of acetonitrile (AN) with succinonitrile (SN), adiponitrile (ADN), n-butyronitrile (n-BTN) and iso-butyronitrile (isoBTN) as co-solvents at 298 K using 500 MHz NMR spectrometer and an Ubbelohde viscometer, respectively. Chemical shift (d) and linewidth (D) for both 63Cu and 65Cu signals have been recorded relative to 0.064 M CuClO4 solution in pure anhydrous AN. Quadrupole relaxation rates (1yT2 )Q , reorientational correlation times (tR ) and copper quadrupole coupling constants (e 2Qqy h) have been calculated in all cases. The variation of these NMR parameters has been examined as a function of molecular percent co-solvent to compare the relative effects of these co-solvents on the solvation behaviour of Cuq and hence on the stabilization of copper (I) complexes formed. The (e 2 Qqyh) values in all ANqnitrile mixtures are larger than the values in pure AN and increase with the increase of molecular percent co-solvent. The strong increase of (e 2 Qqyh) values in all ANqnitrile mixtures with the increase of molecular percent co-solvent indicates the formation of mixed complexes of the form wCu(CH3CN)4yx(S)xxq (xs1y4) due to the replacement of AN molecules from the original complex wCu(CH3CN)4 xq formed in pure AN by the co-solvent molecules (S). The results also show that mixed copper (I) complexes in all cases remain stable even at high co-solvent compositions. The (e 2 Qqyh) values also indicate that the effect of dinitriles is relatively stronger than that of mononitriles, the effect of 63Cu isotope is relatively stronger than that of 65 Cu and the effect of iso-BTN is relatively stronger than that of n-BTN in the formation of mixed copper (I) complexes. 䊚 2003 Elsevier B.V. All rights reserved.
Keywords:
63
Cu;
65
Cu; NMR; Acetonitrile; Other nitriles
1. Introduction Stabilization of copper (I) salts in solution leads to applications in the hydrometallurgical purification of copper and silver w1–6x. Therefore, stabilization of concentrated copper (I) solutions is industrially a useful subject. Copper has two stable isotopes, 63Cu and 65Cu, which have high quadrupole moments and very favourable sensitivities w7x. Because of its large natural abundance (69.1%), 63Cu has been preferred for NMR studies w8–11x. Although, 63Cu NMR studies are very interesting but such studies are still meagre due to several difficulties. Firstly, Cu NMR studies can be made using only diamagnetic copper salts. For this purpose, copper (I) salts have to be used, the preparation *Corresponding author. Fax: q91-172-2545074. E-mail address: [email protected] (D.S. Gill).
of which, in the pure state, is difficult. Secondly, copper (I) solutions are stable only in a limited number of solvents, therefore, the choice of an appropriate solvent or solvent mixture is generally very laborious and difficult. Thirdly, 63Cu and 65Cu nuclei have large quadrupole moments (y0.211=10y28 m2 and y0.195=10y28 m2, respectively) due to which Cu NMR signals are usually very broad in pure solvents and become even broader in mixed solvents w8–12x because of the strong field gradient. Fourthly, the Cu NMR signal can be observed only in those cases where Cuq has tetrahedral symmetry at the copper nucleus. Tetrahedrally coordinated cuprous complexes such as Cu(CH3CN)4ClO4 or Cu(CH3CN)4BF4 which produce tetra-coordinated copper (I) complex ions in solution are shown to be very suitable salts for 63Cu NMR studies w8–10,12x. For bi-coordinated and tri-coordinat-
0167-7322/04/$ - see front matter 䊚 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.molliq.2003.08.022
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D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
ed copper (I) complexes in solution, the 63Cu NMR signal, however, cannot be observed w13,14x. The symmetry at the copper site is thus very important for Cu NMR measurements. 63Cu or 65Cu NMR chemical shifts (d) and linewidths (D) are very sensitive to the solvent medium. By measuring such parameters, significant information about the solvation behaviour of Cuq in mixed solvents can be obtained w8–10x. In this paper, we present some interesting Cu NMR results in binary mixtures of acetonitrile (AN) with some other nitriles (dinitriles and mononitriles) to throw light on the following three important aspects: (1) Which of the two isotopes 63Cu or 65Cu gives more symmetrical copper (I) complexes and hence better NMR signals? (2) Whether or not nitriles with two-C^ N groups in the same molecule are better solvents for the stabilization of copper (I) salts as compared to nitriles with a single–C^ N group? (3) Whether or not two isomers, e.g. n-butyronitrile (n-BTN) and iso-butyronitrile (isoBTN) have a similar effect on Cu NMR parameters? 2. Experimental Copper (I) perchlorate tetraacetonitrile Cu(CH3CN)4 ClO4 used for all NMR measurements was prepared by the method reported earlier w8,15x. The salt was stored in a dry box and was handled under anhydrous conditions. Water free AN (Unichrom, 99.7%), n-BTN (Fluka)99%), iso-BTN (Merck)98%) and adiponitrile (ADN) (Aldrich, 99%) were stored over well dried ˚ for several days before use. molecular sieves (4 A)
Succinonitrile (SN) (BDHLR)99%) was used as received. 63Cu and 65Cu NMR measurements were made ¨ at 298"1 K using 10 mm NMR tubes on a Bruker 500 MHz spectrometer using a broadband probe head at 132.612 MHz and 142.057 MHz frequencies. Copper (I) solutions were prepared by fixing the salt concentration as 0.064 M. All chemical shifts (d) and linewidths (D) were measured relative to 0.064 M CuClO4 in pure anhydrous AN, which was taken as a reference solution for all other measurements. For the reference solution, D for 63Cu and 65Cu was 482 Hz and 422 Hz, respectively, and d values in all cases were set as 0.0 ppm. The reference solution was measured from time to time to ensure consistency of all NMR results. The reproducibility d and D values was estimated as "2% and "3%, respectively. Densities and viscosities of all binary mixtures and 0.064 M CuClO4 solutions were measured at 298.15"0.01 K using Anton Paar Digital Densitimeter and Ubbelohde suspended level viscometer, respectively. The reproducibility of density measurements was within "2.0=10y3% and of viscosity measurements within "0.3%. 3. Results and discussion The linewidth of the 63Cu NMR signal at 482 Hz in the present measurement for 0.064 M CuClO4 solution in pure AN is in good agreement with the previous values between 480 to 550 Hz reported in the literature w7–10,12,13x. The linewidth of the 65Cu NMR signal 422 Hz, however, is smaller than that obtained for 63Cu.
Fig. 1. Chemical shift (d), plot (a) and linewidth (D), plot (b) for 63Cu NMR signal from 0.064 M CuClO4 solutions vs. mol % co-solvent in ANqco-solvent mixtures at 298 K ⽧ – ANqSN;j – ANqADN; D – ANqn-BTN; = – ANqiso-BTN.
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
87
Fig. 2. Chemical shift (d), plot (a) and linewidth (D), plot (b) for 65Cu NMR signal from 0.064 M CuClO4 solutions versus mol % co-solvent in ANqco-solvent mixtures at 298 K ⽧ – ANqSN;j – ANqADN; D – ANqn-BTN; = – ANqiso-BTN.
The linewidth found in both cases increased significantly with the water content of the AN. Trace amounts of copper (II) as impurity in CuClO4 also increased the linewidth of the copper signal considerably. It was, therefore ensured that AN used was completely water free and the trace amounts of copper (II) salt were absent. The linewidths of the 63Cu and 65Cu NMR signals in pure AN from various samples were reproducible within the experimental error. The chemical shift (d) and linewidth (D) have been measured for 63Cu and 65Cu NMR signals using 0.064 M CuClO4 solutions in binary mixtures of AN with SN, ADN, n-BTN and iso-BTN at different compositions of the mixtures (relative to 0.064 M CuClO4 solution in pure AN) and these NMR parameters as a function of molecular percent co-solvent for 63Cu and 65Cu are plotted in Figs. 1 and 2, respectively. It is observed from Figs. 1 and 2 that CuClO4 in binary mixtures of AN with other nitriles shows positive chemical shift and this shift becomes more positive with the increase of cosolvent composition in AN. In our previous 63Cu NMR studies also w7–11x, we observed that the chemical shift (d) in binary mixtures of AN with benzonitrile (BN), propionitrile (PN), 3-hydroxypropionitrile (3HPN) and 3-methoxypropionitrile (3MPN) were positive w9–11x and increased with the increase of molecular percent cosolvent. In each case, stable mixed complex ions of the form wCu(CH3CN)4yx(S)x xq (xs1y4) were formed due to the replacement of AN from the original complex
wCu(CH3CN)4xq formed in pure AN by the co-solvents. Negative d values for 63Cu NMR signals, however, were observed in binary mixtures of AN with many other organic solvents w7–11x. In such solvent systems, the mixed complexes wCu(CH3CN)4yx(S)x xq (xs1y4) were not very stable over the entire solvent composition range due to the fast replacement of AN by the cosolvent w7–11x. Even the complexes of the form wCu(P)4xq where P is co-solvent were not stable in all cases except for the cases where pyridine (Py) or triethylphosphite (C2H5O)3P were used as co-solvents w7,8x. A comparison of 63Cu and 65Cu NMR parameters (d and D) has been made by plotting these parameters against molecular percent co-solvent in all cases. d values in various solvent systems are almost identical for 63Cu and 65Cu but D values are relatively different. For illustration, the plot of these NMR parameters vs. molecular percent co-solvent in ANqn-BTN mixtures is shown in Fig. 3. The physical constants of all these binary mixtures used in the present work were not available in the literature, therefore an attempt was made to measure these parameters at different compositions of the mixtures. The measured dielectric constant (´0), density (r0) and viscosity (h0) of the binary mixtures of the solvent systems used at various compositions are presented in Table 1 and rs and hs parameters for 0.064 M copper (I) perchlorate solutions required for the calcu-
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
88
Fig. 3. Chemical shift (d), plot (a) and linewidth (D), plot (b) for BTN in ANqn-BTN mixtures at 298 K ⽧ – 63Cu;j – 65Cu
63
Cu and
65
Cu NMR signals from 0.064 M CuClO4 solutions vs. mol% n-
Table 1 Dielectric constant (´0), density (r0 in g cmy3) and viscosity (h0 in cP) for ANqco-solvent mixtures at 298.15 K
Table 2 Density (rs in g cmy3) and viscosity (hs in cP) for 0.064 M CuClO4 solutions in ANqco-solvent mixtures at 298.15 K
ANqSN
ANqSN
ANqn-BTN
ANqn-BTN
mol.% SN
´0
r0
h0
mol.% n-BTN
´0
r0
h0
mol.% SN
rs
hs
mol.% n-BTN
rs
hs
0.00 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
36.0 36.5 37.0 37.4 39.2 41.0 43.5 46.5 51.5 54.0
0.77685 0.78787 0.79689 0.80595 0.82401 0.85986 0.88738 0.90755 0.93813 0.97260
0.343 0.388 0.409 0.432 0.545 0.678 0.858 1.039 1.528 2.054
0.00 2.45 7.58 13.10 19.00 28.60 47.40 60.70 70.60 87.40 97.70 100.00
36.0 35.5 35.0 34.5 34.0 33.0 31.5 30.0 29.2 28.1 26.9 24.5
0.77685 0.77819 0.77884 0.77948 0.78013 0.78077 0.78228 0.78379 0.78463 0.78547 0.78605 0.78662
0.343 0.363 0.376 0.389 0.402 0.415 0.445 0.474 0.501 0.527 0.539 0.551
0.00 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
0.77783 0.79811 0.80692 0.81574 0.83436 0.87008 0.89687 0.91267 0.94848 0.98333
0.373 0.410 0.429 0.451 0.567 0.705 0.890 1.089 1.595 2.133
0.00 2.45 7.58 13.10 19.00 28.60 47.40 60.70 70.60 87.40 97.70 100.00
0.77783 0.78902 0.79007 0.79014 0.79037 0.79064 0.79153 0.79390 0.79453 0.79619 0.79626 0.79638
0.373 0.382 0.400 0.419 0.428 0.437 0.469 0.501 0.529 0.538 0.545 0.557
r0
h0
r0
h0
rs
hs
0.77685 0.79361 0.81858 0.84124 0.85446 0.86767 0.87308 0.87849 0.95850
0.343 0.411 0.506 0.634 0.724 0.800 0.901 0.983 5.99
0.77685 0.77641 0.77538 0.77498 0.77466 0.77349 0.77183 0.77016 0.76916 0.76815 0.76752 0.76688
0.343 0.373 0.379 0.387 0.394 0.401 0.418 0.436 0.457 0.478 0.483 0.487
0.77783 0.80574 0.82938 0.85109 0.85989 0.88443 0.90119 0.91796 0.97526
0.373 0.432 0.553 0.686 0.755 0.848 0.940 1.115 6.058
ANqADN mol% ´0 ADN 0.00 36.0 3.88 35.8 10.40 35.5 17.93 35.2 23.63 34.9 27.08 34.7 32.68 34.4 34.88 34.2 100.00 32.4
ANqiso-BTN ´0 mol% iso-BTN 0.00 36.0 2.40 35.2 7.44 34.4 12.85 33.6 18.65 32.8 28.22 31.5 46.93 29.3 60.25 27.4 70.22 26.3 87.15 25.2 97.69 24.6 100.00 23.8
ANqADN mol.% ADN 0.00 3.88 10.40 17.93 23.63 27.08 32.68 34.88 100.00
ANqiso-BTN rs mol.% BTN 0.00 0.77783 2.40 0.78870 7.44 0.78724 12.85 0.78638 18.65 0.78553 28.22 0.78514 46.93 0.78371 60.25 0.78199 70.22 0.78059 87.15 0.77973 97.69 0.76930 100.00 0.76866
hs 0.373 0.392 0.404 0.416 0.422 0.427 0.450 0.473 0.479 0.483 0.486 0.490
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
lation of quadrupole coupling constants and the molar volumes of the solvent systems used for the estimation of solvent radii (rs) are reported in Table 2. 3.1. Evaluation of quadrupole relaxation rates (1yT2)Q, reorientational correlation times (tR) and quadrupole coupling constants (e 2Qqyh) The spin lattice relaxation of copper nuclei is essentially governed by the quadrupole relaxation rate (1y T2)Q, which is extracted from the linewidth (D) and depends on the asymmetry factor of the solvation sphere (h) and the reorientational correlation time (tR) according to the relations w16x: B
C
1E F spD D T2 GQ
(1)
1E 3p2 Ž2Iq3. w h2 zw e2Qq z2 F s x1q |x | tR 2 D T2 GQ 10I Ž2Iy1. y 3 ~y h ~
(2)
B
C
where D represents the linewidth at half the height of the signal, I the is nuclear spin for the Cu nucleus and (e 2Qqyh) is the quadrupole coupling constant. Eq. (1) is applicable when NMR line shapes are Lorentzian. Eq. (2) is applicable for the limit of extreme narrowing when v2t2R<1. The h values for all these systems are not available, therefore, it was not possible to evaluate the factor (1qh2 y3) in Eq. (2). For the symmetrical complex wCu(CH3CN)4 xq formed in pure AN, where copper had tetrahedral symmetry at the Cu nucleus, the value of h is zero. In mixed solvents, the replacement of AN by any of the other analogous nitriles having identical shape and almost similar size and forming tetrahedral complexes of the type wCu(CH3CN)4yx(S)x xq (xs1y4), h can have a value which may not be zero but is too small to be significant. Setting Is3y2 for the 63Cu and 65Cu nuclei and (1q h2 y3)s1 as before w9,11x, Eq. (2) simplifies to Eq. (3) from which (e 2Qqyh) can be calculated. B
w 2 1E e Qq z2 F s3.9478x | tR D T2 GQ h ~ y
C
(3)
When the size of the solute molecule is much larger than that of the solvent molecule, the reorientational correlation time tR in Eq. (3) can be calculated by using the relation w16x: tRs
4pr3i hS 3kT
(4)
where ri is the radius of the spherical solvated ion or solute molecule and hS is the viscosity of the solution.
89
When the size of the solute and the solvent molecules, however, becomes comparable, Eq. (4) is no longer valid. Gierer and Wirtz w17x proposed a method of calculating tR values of the solute molecules when the solute molecules are of comparable size to the solvent molecules. This model takes into account the microviscosity factor, f GW, given by: w
fGWsx6 y
rS B 2rS Ey3zy1 F | qC1q ri D ri G ~
(5)
where ri is the radius of the solute or solvated ion and rS is the radius of the solvent molecule. In the macroscopic limit when ri4rS, this microviscosity factor becomes equal to unity but in case of neat liquids where ri;rS, its value lies between 0.06 and 0.17 w18x. For the ions and molecules of comparable size, the actual reorientational correlation time tR can be calculated by applying microviscosity correction to tR in Eq. (4). The following relation then becomes valid for the calculation of actual tR values w17,19x. tRs
4pri3hS w rS B 2r Ey3zy1 x6 qC1q S F | 3kT y ri D ri G ~
(6)
Using Eqs. (1), (3) and (6) and the solution viscosity (hS) for 0.064 M CuClO4 from Table 2, the copper quadrupole coupling constants (e 2Qqyh) in various solvent systems have been calculated. By taking solvated radii for Cuq (ri) from conductance data in pure solvents and the averaged ri values at various compositions in different solvent mixtures using these ri values, the tR values have been calculated using Eq. (6). These tR values are reported in Tables 3 and 4. The solvent radii (rs) were estimated by calculating the averaged molar volumes of the mixed solvents by using densities (r0) of the solvent mixtures from Table 1 and hs values from Table 2. The microviscosity factor f GW of Eq. (5) was found to lie between 0.24 and 0.29 in the present systems. The copper quadrupole coupling constants for 63 Cu and 65Cu complexes evaluated by this method are reported in Table 3. The quadrupole coupling constant usually increases with the formation of mixed complexes w10x. It can be seen from Table 3 that the quadrupole coupling constant values in all ANqnitrile mixtures are larger than the values in pure AN and increase with the increase of molecular percent co-solvent. The increase in these values with molecular percent co-solvent is larger in nitriles having double–C^ N groups as compared to nitriles having a single–C^ N group. The (e 2Qqyh) values at definite composition for 65Cu isotope are relatively smaller than the values for 63Cu at the corresponding compositions of the solvent mixtures. The (e 2Qqyh) values for copper (I) complexes in n-BTN
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
90
Table 3 Reorientational correlation times (tR ) and quadrupole coupling constants (e2 Qqyh) of 63 Cu and in AN q co-solvent mixtures at 298 K
65
Cu complexes from 0.064M CuClO4 solutions
ANqSN 63
65
Cu NMR
Cu NMR
mol.% SN
tR.10 (s)
e Qqyh(MHz)
mol.% SN
tR.1011(s)
e 2Qqyh(MHz)
0 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
1.39 1.40 1.47 1.53 1.91 2.15 2.78 3.00 3.46 4.33 ANqADN
5.26 5.48 5.44 5.86 5.62 6.86 7.29 7.92 9.09 10.67
0 1.81 2.5 6.8 13.2 24.1 32.2 39.8 54.3 69.4
1.39 1.40 1.47 1.53 1.91 2.15 2.48 3.00 3.94 4.33
4.92 5.08 5.06 5.41 5.18 6.31 7.09 7.22 7.70 9.65
e 2Qqyh(MHz) 5.26 5.92 6.31 7.00 7.49 7.81 8.44 8.73
mol.% ADN 0 3.88 10.4 17.93 23.63 27.08 32.68 34.88
65 Cu NMR tR.1011(s) 1.39 1.49 1.76 2.10 2.30 2.48 2.71 2.92
e 2Qqyh(MHz) 4.92 5.51 5.98 6.83 7.11 6.97 7.78 7.66
e 2Qqyh(MHz) 5.26 5.34 5.43 5.57 5.59 6.08 6.56 6.65 6.94 7.74 8.01
mol.% n-BTN 0 2.45 7.58 13.1 19 28.6 47.4 60.7 70.6 87.4 97.7
e 2Qqyh(MHz) 5.26 5.18 5.30 5.47 5.71 5.84 6.54 7.00 7.17 8.05 8.54
mol.% iso-BTN 0 2.4 7.44 12.85 18.65 28.22 46.93 60.25 70.22 87.15 97.69
mol.% ADN 0 3.88 10.4 17.93 23.63 27.08 32.68 34.88
11
63 Cu NMR tR.1011(s) 1.39 1.49 1.83 2.35 2.59 2.36 2.71 2.78 ANqn-BTN 63
mol.% n-BTN 0 2.45 7.58 13.1 19 28.6 47.4 60.7 70.6 87.4 97.7
65
Cu NMR
tR.1011(s) 1.39 1.42 1.46 1.52 1.66 1.67 1.87 2.11 2.19 2.17 2.33 ANqiso-BTN 63
mol.% iso-BTN 0 2.4 7.44 12.85 18.65 28.22 46.93 60.25 70.22 87.15 97.69
2
Cu NMR e 2Qqyh(MHz) 4.92 4.96 5.00 5.18 5.18 5.62 6.04 6.13 6.40 7.10 7.33
65
Cu NMR
tR.1011(s) 1.39 1.45 1.48 1.51 1.52 1.64 1.67 1.72 1.85 1.86 1.94
tR.1011(s) 1.39 1.42 1.46 1.52 1.66 1.67 1.87 2.11 2.19 2.17 2.33 Cu NMR
tR.1011(s) 1.39 1.45 1.48 1.51 1.52 1.64 1.67 1.72 1.85 1.82 1.94
e 2Qqyh(MHz) 4.92 4.86 4.94 5.11 5.36 5.47 6.11 6.56 6.74 7.57 7.88
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93 Table 4 Reorientational correlation times (tR) and 65Cu quadrupole coupling constants (e 2Qqyh) of copper (I) complexes from CuClO4 solutions in iso-BTN at different salt concentrations (C, in mol dmy3) at 298 K C
tR.1011(s)
e 2Qqyh(MHz)
0.032 0.064 0.128 0.256 0.411 0.512
1.88 1.93 2.23 2.54 2.68 2.78
7.90 7.89 7.89 7.87 7.81 7.81
are relatively smaller than those in iso-BTN at the same composition of the solvent mixtures. The result shows that in each case, stable mixed complexes of the form wCu(CH3CN)4yx(S)x xq (xs1y4) are formed due to the replacement of AN by co-solvents (S) from the original complex wCu(CH3CN)4 xq formed in pure AN. The mixed copper (I) complexes remain stable at all compositions of the solvent mixtures, if the co-solvents used are nitriles. The evidence for the stability of these complexes comes from the systematic increase of the (e 2Qqyh) values with the increase of co-solvent composition. If the co-solvents, however, are other organic solvents, the mixed complex ions do not remain stable beyond certain compositions of the co-solvents. A sudden jump of (e 2Qqyh) values after a certain co-solvent composition in these cases indicates the instability of the complexes w11x. The quadrupole coupling constant for 63Cu has a value of 5.26 MHz in pure AN which increases to 8.01 MHz at 97.7 mol.% n-BTN and 8.54 MHz at 97.69 mol.% iso-BTN. The (e 2Qqyh) for both
91
63
Cu and 65Cu nuclei at all compositions of AN with two isomeric nitriles n-BTN and iso-BTN differ slightly from each other. The value is relatively more in isoBTN than in n-BTN. The quadrupole coupling constant (e 2Qqyh) values in ANqSN mixture and ANqADN mixture increases largely by the increase of co-solvent composition. The value becomes 10.67 MHz at 69.4 mol.% SN and 8.39 MHz at 34.88 mol.% ADN. For 65 Cu also, the quadrupole coupling constant values increase largely by the increased composition of the cosolvent. The increase in the value of the quadrupole coupling constant is much stronger in case of SN and ADN, i.e. in nitriles having two –C^ N groups. Dinitriles are chelating ligands and form more asymmetric complexes as compared to those formed by mononitriles and thus, the larger (e 2Qqyh) values are obtained using dinitriles as co-solvents. The (e 2Qqyh) values for 65Cu in all ANqnitrile mixtures are relatively smaller in comparison to 63Cu values and the ratio of the (e 2Qqy h)2 values for 65Cu to 63Cu in all cases are in good agreement with the ratio of their corresponding linewidths (D). The linewidth data for CuClO4 in binary mixtures of AN with BN, PN, 3HPN and 3MPN were available from the previous work reported by Gill et al. w9–11x. Using these data, the copper quadrupole coupling constants (e 2Qqyh) for 63Cu complexes have been calculated and reported in Table 5 and for better comparison with the present values (from Table 3) have been plotted in Fig. 4. It is observed from this figure that the (e 2Qqyh) values in all cases increase with the increase of molecular percent co-solvent in ANqcosolvent mixtures. The increase is maximum in case of ANqADN mixtures and minimum for ANq3MPN
Table 5 63 Cu quadrupole coupling constants (e 2Qqyh) of copper (I) complexes from CuClO4 solutions in binary mixtures of AN with BN, PN, 3MPN and 3HPN at 298 K ANqBNa mol % BN (e 2Qqyh) (MHz) ANqPNa mol % PN (e 2Qqyh) (MHz) ANq3MPNb mol % 3MPN (e 2Qqyh) (MHz) ANq3HPNc mol % 3HPN (e 2Qqyh) (MHz)
0.0
5.4
18.0
33.9
54.5
82.2
5.26
5.27
5.56
5.99
6.08
6.93
0.0
12.98
27.16
42.71
59.86
78.56
5.26
5.77
5.95
6.30
6.48
6.96
0.0
2.96
6.05
16.18
36.68
5.26
5.47
5.48
5.57
0.0
2.6
13.42
5.26
5.71
6.31
94.3
97.4
6.98
7.38
63.47
83.91
91.67
96.45
5.79
6.07
6.26
6.35
6.47
27.93
43.66
60.79
71.80
79.49
91.56
6.63
7.18
7.57
7.44
7.38
7.24
Calculated from the linewidth data available in aRef. w9x; bRef. w11x; cRef. w10x
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D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
Fig. 4. Quadrupole coupling constants (e2Qqyh) for 63 Cu NMR from 0.064 M CuClO4 solution in ANqco-solvent mixtures vs. mol% co-solvent at 298 K ⽧ – ANqSN; j – ANqADN; D – ANqn-BTN; xANqiso-BTN; * – ANqBN; d – ANqPN; h – ANq3MPN; m – ANq3HPN.
Fig. 5. Chemical shift (d), plot (a); linewidth (D), plot (b) and relative intensity (I), plot (c) for solution vs. molar concentration (C) of CuClO4 in iso-BTN at 298 K.
65
Cu NMR signal from 0.064 M CuClO4
D.S. Gill et al. / Journal of Molecular Liquids 111 (2004) 85–93
mixtures. The change of (e 2Qqyh) in various ANqcosolvent mixtures is in the order: ANqADN)ANq SN)ANq3HPN)ANqiso-BTN)ANqn-BTN) ANqPN)ANqBN)ANq3MPN. 3.2. Effect of CuClO4 concentration on the copper quadrupole coupling constant Many salts are strongly associated in pure and mixed organic solvents at high concentrations. They form ionpairs, which can be easily detected by conductance and NMR measurements. Since CuClO4 is highly soluble in iso-BTN, the effect of salt concentration on 63Cu NMR parameters was also investigated in ANqiso-BTN mixtures. The variation of d, D and relative intensity of the signal (I) as a function of CuClO4 concentration is presented in Fig. 5. With the increase of CuClO4 concentration, d decreases linearly while D increases non-linearly. The linear increase of I with salt concentration shows the absence of ion-pairing of CuClO4 in these solvent systems. The evaluation of the 65Cu quadrupole coupling constant at different CuClO4 concentrations in ANqiso-BTN mixtures gave a constant value (7.86"0.1 MHz) which indicates the absence of ion-pairing of CuClO4 even at relatively higher concentrations (Table 4). Conductance and transport number studies of some copper (I) salts in ANqco-solvent mixtures reported by Gill and co-workers w20,21x also confirm the absence of ion pairs. 4. Conclusions In all ANqnitrile mixtures, the (e 2Qqyh) values for copper (I) complexes increase significantly with increase of co-solvent composition and this increase continues upto a large range of solvent composition. The results show that all nitriles used as co-solvents have strong tendency to replace AN from the complex ion wCu(CH3CN)4xq forming the mixed complexes of the form wCu(CH3CN)4yx(S)x xq (xs1y4). These mixed complex ions remain stable even in the co-solvent rich region of the mixtures. Dinitriles have stronger effect on the solvation of Cuq than the mononitriles at the corresponding compositions. 65Cu and n-BTN form comparatively more symmetrical complexes indicated by their relatively low (e 2Qqyh) values. The (e 2Qqyh) value for 65Cu at different CuClO4 concentrations in iso-BTN remains practically constant (7.86"0.1 MHz)
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indicating that there is no effect of salt concentration on (e 2Qqyh) values. Acknowledgments DSG is grateful to the Gledden Trust and the University of Western Australia for the award of Visiting Senior Gledden Fellowship. VP thanks the UGC, New Delhi for the award of Junior Research Fellowship. BKV thanks the UGC for the Teacher Fellowship and the DAV College, Chandigarh, for the grant of long study leave. References w1x A.J. Parker, Search 4 (1973) 425–432. w2x I.D. MacLeod, D.M. Muir, A.J. Parker, P. Singh, Aust. J. Chem. 30 (1977) 1423–1437. w3x D.S. Gill, R. Srivastava, J. Chem. Soc. Faraday T. I 78 (1982) 1533–1538. w4x D.S. Gill, R. Srivastava, Ind. J. Chem. 22A (1983) 140–142. w5x D.S. Gill, R. Srivastava, Ind. J. Chem. 22A (1983) 479–481. w6x D.S. Gill, R. Noerding, Z. Phys. Chem. (N.F.) 136 (1983) 117–122. w7x P. Kroneck, J. Kodweiss, O. Lutz, A. Nolle, D. Zepf, Z. Naturforsch. 37A (1982) 186–190. w8x D.S. Gill, L. Rodehueser, J.J. Delpuech, J. Chem. Soc. Faraday T. 86 (1990) 2847–2852. w9x D.S. Gill, L. Rodehueser, P. Rubini, J.J. Delpuech, J. Chem. Soc. Faraday T. 91 (1995) 2307–2312. w10x D.S. Gill, L. Byrne, T.I. Quickenden, Z. Naturforsch. 53a (1998) 1004–1008. w11x D.S. Gill, U. Kamp, A. Doelle, M.D. Zeidler, Ind. J. Chem. 40A (2001) 693–699. w12x W. Ochsenbein, C.W. Schlaepfer, Helv. Chim. Acta 63 (1980) 1926–1931. w13x P. Kroneck, O. Lutz, A. Nolle, H. Oehler, Z. Naturforsch. 35A (1980) 221–225. w14x O. Lutz, H. Oehler, P. Kroneck, Z. Naturforsch. 33a (1978) 1021–1024. w15x B.J. Hathaway, D.G. Holah, J.D. Postlethwaite, J. Chem. Soc. (1961) 3215–3218. w16x F.A. Bovey, L. Jelinski, P.A. Mirau, Nuclear Magnetic Resonance Spectroscopy, 2nd edn, Academic Press, New York, 1988, p. 16,28,264. w17x A. Gierer, K. Wirtz, Z. Naturforsch. 8a (1953) 532–538. w18x M.D. Zeidler, Ber. Bunseng. Phys. Chem. 69 (1965) 659–669. w19x R.P. Kluener, A. Doelle, J. Phys. Chem. A 101 (1997) 1657–1661. w20x D.S. Gill, R. Singh, V. Ali, J. Singh, S.K. Rehani, J. Chem. Soc. Faraday T. 90 (1994) 583–586. w21x D.S. Gill, P. Singh, J. Singh, P. Singh, G. Senanayake, G.T. Hefter, J. Chem. Soc. Faraday. T. 91 (1995) 2789–2795.