J . Phys. Chem. 1990, 94, 2150-2154
2150
present in glasses with less than 15 atom % phosphorus, the data in Figure 8 suggest that partial phosphorus segregation persists even at lower P contents. This may be understood in terms of a larger-than-statistical probability of P-S-P linkages. Furthermore, the spin-echo N M R data confirm that P-P bonds are essentially absent in P-S glasses. I n summary, the present study illustrates that modern solid-state N M R techniques can provide valuable information concerning the chemical segregation processes and the structural units present in non-oxide chalcogenide glasses. It is instructive to compare the present results on the P-S system with those recently obtained on the homologous system phosphor~s-selenium.~~ Both systems have in common that P-P bonds are absent in the compositional region considered (0-25 atom % P); however, the fraction of tetrahedral groups is markedly reduced in the P-Se system, reflecting a more efficient competition of homoatomic (Se-Se) with heteroatomic (P=Se) bond formation. In agreement with this finding, molecular clusters analogous to P4S9and P4Sl0are absent in the system phosphorus-selenium. On the other hand, MAS-
NMR data indicate that P-Se glasses with 50 atom % P or more contain significant amounts of molecular P4Se3units.51 It seems, therefore, that molecular clusters are a common characteristic feature in phosphorus chalcogenide glasses. However, the NMR studies show, that these molecules, which have stoichiometries corresponding to the stable bordering crystalline phases, only occur in the vicinity of the glass-forming boundaries.
Acknowledgment. We are grateful for financial support by the UCSB Academic Senate. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for financial support of this research. Partial funding was also provided by a grant from the U S . Department of Energy (Contract No. DE AS03-76SF00034) to Professor R. G. Pearson (UCSB). We are indebted to Professor Pearson for his support. We also thank Cheryl Liang for a sample of P4Ss. Registry No. P. 7723-14-0; S, 7704-34-9. (51) Lathrop, D.; Eckert, H. J . Pfiys. Cfiem. 1989, in press
Anion Dependence of the Complexation of Na' with the Macrocycle 18C6 in Propylene Carbonate Licesio Rodriguez,+Edward M. Eyring,f and Sergio Petrucci*v' Weber Research Institute, Long Island Center, Polytechnic University, Farmingdale, New York 11735, and Department of Chemistry, University of Utah, Salt Lake City, Utah 841 12 (Received: March 7 , 1989; In Final Form: July 13, 1989)
-
Ultrasonic relaxation spectra in the frequency range 1-500 MHz for NaB9, (9 = C6HS),NaCIO,, and NaSCN in the concentration range 0.1-0.5 M and in the solvent propylene carbonate (PC) at 25 'C are reported. This solvent has been selected because, despite its high dielectric permittivity, its donor number is relatively low. Thus in the competition for sites in the first coordination sphere of metal cations, macrocycles and anions will be favored over solvent molecules. Previous kinetic studies of decomplexation of electrolytes in PC and other solvents of low donor numbers (such as acetonitrile and nitromethane) by NMR techniques have indicated a bimolecular mechanism involving excess cation: MC+ + *M+ s *MC+ + M+, where M+ denotes a metal cation and C denotes a macrocycle. The present work shows a dependence of the amplitude of the ultrasonic absorption spectra on the nature of the electrolyte (anion) for the same cation. This raises the question of whether the bimolecular mechanism is simply a reflection of anion vs macrocycle competition for the first-coordination sphere of the cation, namely MC+ + X- s MX + C, where X- denotes the anion. Indeed in solvents of much lower permittivity such as ethers, the attack of the crown ether C on the substrate, consisting of an ion pair MX (according to the reverse of the above scheme) has already been established. The present study provides experimental evidence that the bimolecular mechanism of metal-ion complexation by macrocycles touted by NMR spectroscopistscould have its origins in the availability of a high concentration of anions.
Introduction Investigations of the rates of complexation of alkali-metal cation by crown ether macrocycles with an ultrasonic relaxation technique' have established the general application of the EigenWinkler mechanism of stepwise solvent substitution2 MS+
ko +ce M+SC k,
ki
k-I
k
MC+ 2(MC)+ k-2
(1)
where MS+ is the solvated cation, C the macrocycle, M'SC a solvent-separated species, MC+ the contact or exclusive species, and (MC)+ the inclusive species with the metal imbedded in the cavity of the ligand. If the overall complexation (formation) constant K2 is high in scheme 1, at the concentrations attainable by ultrasonic techniques, the above reaction scheme reduces, for all practical purposes, to' k
k
M'SC
k-I
MC+
k-2
(MC)+
(2)
Polytechnic University. !University of Utah.
0022-3654/90/2094-2150$02.50/C
In solvents of very low permittivity such as ethers, the electrolyte is heavily associated to form ion pairs MX and at times to dimers or quadrupoles (MX),. The overall reaction scheme then becomes3 (MX), G 2MX MX
+ C F! M C + + X-
(3)
where the first equilibrium establishes a competition for MX (either to dimerize or to be attacked by C). In aprotic solvents of intermediate permittivity but low donor number such as propylene carbonate (€25 = 64.4; DN = 15.1), acetonitrile (e25 = 35.95; D N = 14.1), and nitromethane (e25 = 35.94; DN = 2.7), recent work by N M R techniques4 has found ( 1 ) Chen, C.; Wallace, W.; Eyring, E. M.; Petrucci, S. J . Pfiys. Cfiem. 1984, 88, 2541; 1985,89, 1357. Wallace, W.; Eyring, E. M.; Petrucci, S. J . Pfiys. Cfiem. 1984, 88, 6353.
(2) Eigen, M.; Winkler, R. M. In Neurosciences: Second Study Program; Schmidt, F. O., Ed.; Rockefeller University Press: New York, 1970; p 685. (3) Farber, H.; Petrucci, S . J. Pfiys. Cfiem. 1981,85, 1396. Richman, H.; Harada, Y . ; Eyring, E. M.; Petrucci, S. J . Pfiys. Cfiem. 1985, 89, 2373.
0 1990 American Chemical Society
Complexation of Na+ with the Macrocycle 18C6 in PC
The Journal of Physical Chemistry, Vol. 94, No. 5, 1990 2151 Background sound absorwion B = ( ~ l f , ) ~ , , ~as ~ a function of electrolyte concentration in propylene carbonate, t=25OC
t "n
100
J
.'E,
0
v
50
: * 20
v
/
-"
Na6~40.4M+18C6 0.4M in
A
m
NaSCN NaC!04 NaB+,
0
a
'L
f , =80MHz
u = 1.473 B = 88x10-17~m-1s2
2
5
10
-
l l ! : r
I . I
1
20
50
f(MHz) 80 1 0 0 200 100
200
500
500
f(MHz)-
Figure 1. Representative ultrasonic absorption spectrum for the system NaB0, + 18C6 in PC at 25 "C in the form of excess sound absorption per wavelength p vs frequencyf. The inset reports the data for a / f vs f a t the tail of the relaxation process.
l
l
l
l
l
l
l
l
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
l
l
l
0.8 0.9
1.0
CN,,(M)-
Figure 2. Background sound absorption over the square of the frequency B = (a/f)fi,r vs total concentration of electrolyte for NaBa., + 18C6, NaC104 -+ 18C6, and NaSCN + 18C6 in PC at 25 OC.
I 8ooL
pmws. CC ,,
for N a X t l 8 C 6 in propylene carbonate, t =25'C
evidence of the existence of two paths for dissociation of the (MC)+ complexes, one monomolecular and one bimolecular. The monomolecular mechanism proposed is4 (MC)+
+ sS MS+ + c k'l
(4) Legend
that is clearly just the reverse of scheme 1 above. The bimolecular path identified by N M R spectroscopists4 is a cation (in excess) assisted process *M+ + (MC)'
k L2
(*MC)+
+ M+
0NaB+4
(5)
With an excess of electrolyte *M+ (and necessarily X-), path 5 becomes predominant. In scheme 5, the dissociation reaction is thought to be promoted by the attacking metal cation (rather than by the solvent as in scheme 4). Because of the importance of this issue, some of the above sample systems have now been examined by ultrasonic relaxation techniques. Ancillary infrared spectra have also been produced to reinforce the deductions from the ultrasonic spectra.
Experimental Section The equipment and procedures for the ~ltrasonicI*~ and infrared work6 have been reported elsewhere. NaB@4(@ = C6H5;Aldrich) was dried in vacuo at 40 OC; NaCIO, and NaSCN where dried in vacuo at 70 OC. Propylene carbonate was distilled twice under reduced pressure over P205in an all-Pyrex column without grease on the joints. The original solvent was a Gold Label Aldrich product. 18C6 (Aldrich) was purified and dried as reported previously.' Solutions were prepared in volumetric flasks with the solute added by weight to freshly distilled solvent. Contact with the atmosphere was limited to 30-60 s overall during the time of sample preparation and cell (ultrasonic or infrared) filling. Results and Calculations ( a ) Electrolytes 18C6. Figure 1 reports the ultrasonic absorption of a representative concentration of N a B a 4 + 18C6 in propylene carbonate at 25 OC in the form of the excess sound absorption per wavelength p = (cy - Bf)urlvs frequencyf. Here,
+
(4) Shamsipur, M.; Popov, A. I. J . Phys. Chem. 1988, 92, 147, and previous literature quoted therein. ( 5 ) Echegoyen, L.; Gokel, G. W.; Kim, M. S.; Eyring, E. M.; Petrucci, S. J . Phys. Chem. 1987, 91, 3854. (6) Saar, D.; Petrucci, S. J . Phys. Chem. 1986, 90, 3326. (7) Maynard, K. J.; Irish, D. E.; Eyring, E. M.; Petrucci, S. J . Phys. Chem. 1984, 88, 729.
I
1
01
02
A
-18C6 R=l NaB+4 0.5M-18C6 0 1M R=5 NaCiO, 05M*18C6 0 1M R=5
A
Nac/04
-1BC6
R=I
0 NaSCN
-18C6
R=l0
I
1
03
04
05
1' 8C6(M)-
Figure 3. Maximum excess sound absorption per wavelength ,I vs total concentration of macrocycle for NaBQ, + 18C6, NaCIO, + 18C6, and NaSCN 18C6 at the various molar ratios R investigated in PC at 25 OC.
+
a is the attenuation constant (cm-I); u the sound velocity (cm SI); and B the background value, B = (cy/f),,,,,, at the frequencies far above the relaxation frequencyf,. An inset in Figure 1 shows the form of cy/f VSJ the data leading to B. The solid line in Figure 1 has been calculated by fitting the data to a single Debye relaxation process according to the alternate functional form*
Table I reports the calculated parameters pm,f,,and B and the sound velocities u for all the concentrations of NaB@4 18C6 investigated. One notices that the results for pm do not seem to change drastically with the molar ratio R = [NaBa4]/[ 18C61. However, the background absorption B changes with the concentration of the electrolyte (Figure 2). Indeed, it appears to be a function of [NaB@4] as evidenced by the fact that for [NaB@,,] = 0.5 M without 18C6 the value of B agrees well with those for the NaBa4 + 18C6 systems. Evidently, the electrolyte
+
(8) Farber, H.; Petrucci, S. In Chemical Physics of Solvation; Dogonadze, R., et al., Eds.; Elsevier: Amsterdam, 1986; Vol. B.
2152
The Journal of Physical Chemistry, Vol. 94, No. 5, 1990
TABLE I: Ultrasonic Parameters f, PC at 25 OC electrolyte NaBa, NaB3, NaB3, NaB3, NaB9, NaB3, 0.20 M NaBa4 0.2 M NaCIO, NaCIO, NaC104 NaCIO, NaCIO, NaCIO4 NaCIO, NaC104 NaSCN" NaSCN'
cm,and B , and Sound Velocity,
macrocycle 18C6 18C6 18C6 18C6 18C6
+
Csalt, M 0.40 0.30 0.20 0.10 0.50 0.50 0.40
.
u, for Sodium Salts
0.40 0.30 0.20 0.10 0.10 0.40
0.50 0.40 0.35 0.27 0.10 0.50
0.50 0.40 0.35 0.27 0.10 0.10
18C6 18C6
0.45 0.25
0.45 0.25
1 .o
+ 18C6 at the Various Concentrations Investigated in
L, MHz
C18C63
18C6 18C6 18C6 18C6 18C6 18C6
Rodriguez et al.
1 0 5 ~ ~
80 70 80 70 70
850 580 400 215 240
80
700
80 70 70 80 80 70
850 620 600 500 190 175
70 90
800 450
1017~, cm-' s2 88 66 55 50 100 102 67
1o-su, cm s-I 1.473 1.467 1.462 1.462 1.502 1.487 1.470
69 67 62 58 50 67 1026 68 52
1.468 1.441 1.446 1.460 1.435 1.462 1.468 1.457 1.459
"Sodium thiocyanate as an electrolyte is written NaSCN, whereas as an ion pair it is written NaNCS in order to emphasize that the nitrogen atom is the binding post." = A B.
+
NaSCN 0.45M-18CG 0 45M in PC, t = 2 5 % pm=
2ono
800x10-5
f,
= 70MHz
u
= I 457x105cm s-'
B = 68x10
17cpn-'s'
t
lO0OC
-
1
2
in
5
20
so
1
100
I
200
500
I
5
2
in
20
50
inn
200
500
f(MHz)-
f(MHzJ--
Figure 4. Representative ultrasonic absorption spectrum ( p vs for NaC104 + 18C6 in PC at 25 OC. The inset reports the (a/f2)vsfdata at the tail of the relaxation process.
Figure 5. Representative ultrasonic absorption spectrum ( p vs for NaSCN + 18C6 in PC at 25 "C. The inset reports the (a/f2)vsfdata at the tail of the relaxation process.
influences the shear viscosity 7, and bulk viscosity ov of the solvent according to the Stokes-Navier equation9 a 272 - = y ( ? 3 0 s + 7,) (7)
spectrum for NaSCN + 18C6 in PC. The calculated parameters and B are reported in Table I. Whereas it appears that thef, values are comparable for the three electrolytes 18C6, the same is not true for the values of B and of pm. Figure 2 shows the individual behavior of N a B a 4 vs NaC104 or NaSCN, the latter two showing the same trend in B within experimental error (about f l X lo-'' cm-' s2). Further, Figure 3 shows a definite difference in pm vs f for NaBa4 18C6 with repsect to the two other electrolytes. Evidently, the anion Ba4-has a different influence than C104- and NCS- with respect to B and the relaxation parameter pm. It is on this lastfinding that we focus attention. Differencs in pm with the identity of the anion point out differences in the equilibrium concentrations of Na+ (available to react with 18C6) to form one of the various forms of the complexes Na+SC, NaC+, or (NaC)'. For a simple process*A G B, with A = Na+SC and B = NaC+, for instance
f2
PU
No relaxation process appears for [NaBa4] = 0.5 M up to -500 MHz with the value of a/f = B being a constant independent of the sound frequency f. Figure 3 reports the values of pm vs concentration for 18C6. A straight line passing through the origin can account for the data. This and constancy, within experimental error, in the values of f, with increasing concentration confirms the first-order or psuedo-first-order character of the observed process, which can be interpreted as one of the two steps of scheme 2 above. The reasons for the observability of only one relaxation process could reside in the concentration distribution of the species M%C, MC+, and (MC)+, in the close coupling of the two steps or in the fact that the last relaxation step leading to (MC)' has anf, much below 1 MHz. Figure 4 reports a representative ultrasonic absorption spectrum (p v s n for NaC104 + 18C6 in PC at 25 OC. Figure 5 is a similar (9) Litovitz, T. A. In Physical Acoustics; Mason, W., Ed.; Academic Press: New York. 1964; Vol. 11, Part B.
pm,fr,
+
+
where CAand CBare the equilibrium concentrations entering the observed process. Note that AV, = V,(B) - Vs(A) with Vs(B) and Vs(A) the isoentropic or adiabatic molar volumes of the species
Complexation of Na' with the Macrocycle 18C6 in PC
1
The Journal of Physical Chemistry, Vol. 94, No. 5, 1990 2153 Digtized hlrared Abiorballce w wave number of the G4 envelope of NICQ 1.OM In Propykna Carbonate Lcell=O.OSmm
I
N ~ C / 0 4 0 . 1 Min PC. 1=25OC
Parameters:
Yj2 = 634 em-' NaB$40.5M in PC. t = 2 5 " C
;1 2 0 100
I
F
Figure 7. Infrared spectrum (absorbance A vs wavenumber J ) for 1 M NaC104in PC for the v4 vibrational mode region of CIO, ion. The solid line corresponds to the sum of three Gaussian-Lorentzian product functions. The band at 8 = 624.5 cm-I, representative of the spectroscopic free CIO,, is inadequate to describe the spectral envelope. In this experiment, the cell length was 1 = 0.005 cm. The parameter used were AIo = 1.05, pol = 624.5 cm-I, (AvJIl2 = 11 cm-I; Azo= 0.27, 802 = 634 cm-I, ( A J ~ ) = ~ ,11 ~ cm-I; A30 = 0.10, Jo3 = 645 cm-', (AP3)1/2 = 11 cm-I.
6ol 10
20
50
--
100 f(MHrl-
200
0
500
Figure 6. Ultrasonic absorption spectrum in the form of a/f vsffor 1 M NaC104 (A) and 0.5 M NaBa4 (B) in PC at 25 OC.
involved. AVs = AVT - (O/pCp)AH,with AVT the isothermal volume change, AH the enthalpy change due to the process, and 0, p , and C the expansivity (e In V/87'), density, and specific heat, respectivery. The point we make is that if C, is different from the stoichiometric value (because part of it is bound to the anion), pm will be smaller as observed for NaC10, and NaSCN in Figure 3. ( 6 ) Collateral Evidence of Association of NaCIO, and of NaSCN in Propylene Carbonate. Figure 6A shows the ultrasonic absorption spectrum of 1 M NaC10, in the form of a/f vs f in propylene carbonate at 25 OC. A relaxation process is present. Since the background absorption (surely different from the solvent value) is unknown, the data cannot be fitted quantitatively but the relaxation process is clearly present. Figure 6B shows that for 0.5 M NaBa4 even though the value of a/f is much larger than the value for the pure solvent (Bo = SO x 1O-I' cm-I s2), no relaxation process is present. Figure 7 shows the infrared spectrum of 1 M NaC104, corresponding to the I, mode of the C10, in the wavenumber region 600-660 cm-I. A single Gaussian-Lorentzian product functionlo
with J = 1,2,3 and (rJ = (A15)1,2/1.46, is completely inadequate to describe the spectrum profile. The spectrum can be interpreted by the sum of three Gaussian-Lorentzian product functions as and interpreted was done for LiC104 in 2-methyltetrahydrof~ran'~ as due to possible coexistence of C104- (or Li+S, ClO,-), contact species LiCIO,, and dimers (LiC10,)2. Whatever the nature of the species in the present case, for NaCIO, in propylene carbonate, the IR spectrum reinforces the ultrasonic absorption spectrum by indicating NaC10, to be associated to a sizeable extent in PC. This in turn explains the differences in F,,, vs total, shown in Figure 3. Past work" on alkali thiocyanate in PC showed that free SCNhas a -C=N stretching band at 2059 cm-l. The ion pair LiNCS has a new band at 2074.5 cm-I. For the ion pair NaNCS, the corresponding band is at 2065 cm-I. The differences 16 and
-
(IO) Maaser, H.; Xu,M.; Hemmes, P.; Petrucci, S . J . Phys. Chem. 1987, 91, 3047. ( 1 1) Paoli, D.; Lucon, M.; Chabanel, M. Spectrochim. Acra, Part A 1978, 34, 1087. Menard, C. Doctoral Thesis, University of Nantes, France, 1973.
50-
"!
NaBq4 0 20M + N a c ( q 0 2OM + lBCB 0 .OM in PC. 1.259:
1
5
lb
i0
1bO 2bO
f(MHr) -*
5;O
20 "1
2
5
10
20
50
100 200
500
l[MHz)-
Figure 8. Ultrasonic absorption spectrum for the systems 0.20 M NaBa4 + 0.20 M NaC104 + 0.40 M 18C6 (a) and 0.40 M NaC10, + 0.40 M 18C6 (b) in PC at 25 OC in the form of ~1 vsf. The insets report the data for a/f v s f a t the tail of the relaxation process.
6 cm-' are typical for free vs associated NCS- ions with Li+ and Na+, respectively, as also in other solvents such as dimethylacetamide.l'J2 Hence, anions such as C104- and SCN- (nitrogen bonding to alkali-metal ions) are associated partially in PC to Na+ and even to the heavily solvated Li+. (K+, Rb+, and Cs' are generally more associated than Na+ and Li+ with a given anion.)
Conclusion The results of the present ultrasonic and infrared investigation of the reaction of Na+ with the macrocycle 18C6 in the solvent PC at 25 "C underline the importance of the nature of the anion as a competitor for the first-coordination sphere around the cation. The N M R results often indicate a bimolecular dissociative process in excess electrolyte. One may wonder whether this is due to the excess anion necessarily introduced in the system. If the results of the present investigation are found to have a general validity in future work, a unified picture of the mechanism of decomplexation of macrocycle-cation complexes may eventually emerge. The decomplexation is solvent-assisted (or pseudofirst-order in an excess of solvent) in solvents where the cation is completely ionized. This is most probably the case at molar ratio R N 1. The decomplexation may be anion-assisted in solvents where the metal cation is mainly a complexed MX species. In intermediate cases, both reaction paths XS + M+ e MS,+ + C and X- + MC+ s MX + C will be operative, the bimolecular (12) Irish, D. E.; Tang, S.-Y.;Talts, H.; Petrucci, S . J . Phys. Chem. 1979, 83,3268.
J. Phys. Chem. 1990, 94, 2154-2159
2154 Maximum sound absorption per
Appendix
wavelength vs. anion mole fraction
One reviewer of the present paper contended that “the anion dependence of p, is evident, but it depends mainly on the ligand concentration and is independent of the salt/ligand ratio. Therefore it seems to be doubtful to explain the NMR observations of bimolecular dissociative processes by an excess of electrolyte.” The reported experiments (Figure 3, Table I) at varying molar ratio R show an apparent independence of pm with R within the combined experimental errors of the pm values. It is unfortunate that larger total concentrations and/or molar ratios for NaC104 are not feasible because of the obscuring effect of the ultrasonic relaxation caused by the electrolyte itself, as reported in Figure 6. The above reviewer’s comment did, however, suggest some further experiments that show that the value of pm depends on the nature of the anion and not simply on the anion concentration. A fixed concentration of total cation [Na+Io= 0.40 M and total macrocycle concentration [ 18C6l0 = 0.40 M while varying the anion mole fraction Xclo4-= [NaCI04]/{[NaC104]+ [NaB@.,]J , - 0.5 and XC,Q was used to prepare sample solutions having X C l ~ = = 1. The resulting absorption ultrasonic spectra in PC at 25 O C are shown in Figure 8A,B. The spectrum for Xclo4-= 0 is depicted in Figure 1. The ultrasonic parameters for the spectra are reported in Table I. Figure 9 reports the values of pm vs XClo,-for the above mixtures and shows unambiguously a trend much larger than the average error associated with the pm values (f5%).
%tofor Nax 0.40M
+
18C6 0.4M
in propylene carbonate at t=ZbC.
+
1-
[NaCb XC‘@=[NaC&,]+[iaB’$4]
800 ~
700
600
c
500h
I 0.5
%to,
I
-
1.0
Figure 9. Plot of the maximum sound absorption per wavelength vs anion mole fraction Xclo,- for 0.40 M NaX + 0.40 M 18C6 in propylene carbonate at 25 “C.
mechanism becoming predominant in the presence of an excess of anions.
Acknowledgment. We thank the National Science Foundation (Grant No. CHE85-13266 and CHE88-22333) for generous support of this work.
Registry No. Na, 7440-23-5; 18-crown-6, 17455-13-9;Ba4-,435826-3; CIOL, 14797-73-0;SCN-, 302-04-5.
Piezochromism: sressure-Induced Isomerizations in the Tetrachlorocuprate Anion in the Solid State w th Various Cations Kevin L. Bray and Harry G . Drickamer* School of Chemical Sciences, Department of Physics, and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (Received: June 30, 1989; In Final Form: September 11, 1989)
The effects of high pressure on Cs2CuC14,bis(trimethylbenzy1ammonium) tetrachlorocuprate, (N-phenylpiperazinium) tetrachlorocuprate, bis(N-benzylpiperazinium) tetrachlorocuprate bis(hydrochloride), and bis(N-methylphenethylammonium) tetrachlorocuprate are reported. Electronic spectroscopy indicates molecular rearrangements in the tetrachlorocuprate ions with increasing pressure. The changes in geometry and nature of the rearrangements are discussed. The general result is that at high pressure there is a considerably smaller range of dihedral angles for the five complexes. The results are considered in the context of stereochemical structural pathways for copper(I1) systems.
Introduction
A variety of stereochemistries is known for the tetrachlorocuprate ( C U C I ~ ~ion - ) in the solid state.’ Square p l a ~ ~ aand r~,~ nearly tetrahedra14*5geometries have been observed as have a number of intermediate distorted The most (1) Smith, D. W. Coord. Chem. Rev. 1976, 21, 93. (2) Battaglia, L. P.; Bonamartini Corradi, A.; Marcotrigiano, G.; Menabue, L.; Pellacani, G. C. Inorg. Chem. 1982, 21, 3919. (3) Udupa, M. R.; Krebs, B. Inorg. Chim. Acta 1979, 33, 241. (4) Lamotte-Brasseur, P. J. Acra Crysrallogr. 1974, A30, 487. ( 5 ) Willett, R. D.; Liles, 0. L.; Michelson, C. Inorg. Chem. 1967, 6, 1885. (6) Bloomquist, D. R.; Willett, R. D.; Dcdgen, H. W. J . Am. Chem. SOC. 1981, 103, 2610. (7) Fernandez, V.; Moran, M.; Gutierrez-Rios, M. T.; Foces-Foces, C.; Cano. F. H . Inorg. Chim. Acta 1987, 128, 239.
0022-3654/90/2094-2154$02.50/0
common configuration is the slightly compressed tetrahedron. The solid-state geometry of the tetrachlorocuprate ion reflects a balance of two opposing effect^.^ Crystal field theory predicts that a square planar geometry is preferred for a free copper(I1) ion. Chloride-chloride repulsions, however, are minimized in a tetrahedral geometry. The geometry observed, therefore, in a given tetrachlorocuprate complex represents a compromise between the two effects. Consequently solid-state interactions, primarily lattice packing forces1° and anion-cation hydrogen bonding,ll are ulti(8) Harlow. R. L.; Wells. W. J.; Watt, G. W.: Simonsen, S. H. In0r.c. Chem. 1975, 14, 1768. (9) Demuvnck. J.; Veillard, A.: Wahlgren, U. J . Am. Chem. SOC.1973, 95, 5563. (10) Nelson, H. C.; Simonsen, S. H.; Watt, G.W. J . Chem. SOC.,Chem. Commun. 1979. 632.
0 1990 American Chemical Society
