Chemistry of the Polynuclear Metal Halides
Inorganic Chemistry, Vol. 17, No. 7 , 1978 1867 Contribution from Ames Laboratory-USDOE and the Department of Chemistry, Iowa State University, Ames, Iowa 5001 1
Chemistry of the Polynuclear Metal Halides. 13. Mixed-Metal M6X12n+Species Containing Both Tantalum and Molybdenum J. L. MEYER and R. E. McCARLEY* Received January 20, 1978 A new series of mixed-metal cluster compounds containing tantalum and molybdenum was prepared. The new compounds, which may be considered as metal-substituted derivatives of the (Ta6ClI2)"+clusters, were [(C2H5)4N]3[(Ta5MOCllZ)C16], [(C4H9),N],[(Ta5MoCIl2)Cl6], and [(C2H5)4N]2[(Ta4M02Cllz)c16]. In all cases the mixed-metal basic cluster units (Ta5MoCllz)3f and (Ta4MozC11z)4+were obtained by reduction of TaC15-MoCI, mixtures with aluminum in fused NaA1C14-A1C13 at 325 "C. Subsequent ion-exchange and solvent extraction procedures for separation of the individual species from the salt mixture and related clusters of the same structure and net ionic charge were moderately successful. Spectroscopic and magnetic data for the compounds, taking into account possible impurities, indicate that [( T ~ S M I J C ~ ~ ~ ) C ~ ~ ] ~ and [(Ta4M02CllZ)C16]zare analogues of [(Ta6C11z)C16]ehaving 16 metal-metal bonding electrons, and [(Ta5MOCll~)Cl6]~is the analogue of [(Ta6Cl12)C16]3-with 15 bonding electrons. for 3 days at 320 OC. The tube was then opened in air, and its contents Introduction were crushed with a mortar and pestle. Structural studies of the hexanuclear metal halide cluster The crushed product was added bit by bit to 600-800 mL of water species of niobium, tantalum, molybdenum, and tungsten have and stirred for 4 h in order to dissolve the NaAlCl,, AlCI,, and Ta6ClI4. shown the basic units'-9 are M6X12n+(with M = Nb or Ta, The resulting mixture was centrifuged; the collected solids were X = F, C1, Br, I) and usually MsX 2. With x = 3 one separation of impurities may be very difficult because of solid might expect (Ta3M03C112)5+, but an alternate possibility solution formation. Because the preparative procedures do would be for conversion to the more stable M6X8"+cluster lead to formation of mixtures of the cluster species and the arrangement, as typified by derivatives of ( M O ~ C ~ ~with )~', subsequent separations are difficult at best, the low moments 24 electrons in metal-metal bonding orbitals. Hence, for x found in these two cases are reasonably attributed to such > 2, completion of the series might result in the species impurities. Thus we believe the two mixed-metal ions (Mo3Ta3C18)+,( M ~ ~ T a ~ c land ~ ) ~( M + ,O ~ T ~ C ~In~ )the ~+, [ (Ta5MOCl12)C16]3- and [(Ta4M02Cl12)C16]2-are diamagnetic, present study no evidence was found for any mixed-metal and we assigned spin-singlet ground states like the isoelectronic species with x > 2, even though reaction mixtures with Mo/Ta [(Ta6Cl12)C16]4-.'8 = 1 were investigated. This result may not be surprising in The compound [(C4H9)4N]2[(Ta5MoCl12)C16] is paraview of the apparent hindered formation of the M6Xg4+clusters magnetic with 106xMvalues (temperature, K) of 2900 (77), (M = Mo or W; X = C1 or Br) in the same fused salt melts 979 (170), 966 (180), 749 (199), and 350 (296). From the at temperatures below 400 OC, as established in this laboslope of a Curie plot the magnetic moment of 1.47 pB is r a t ~ r y .Further ~~ work to extend the Ta-Mo mixed-metal calculated. Also, from the EPR spectrum of the powder, the clusters to species with x > 2 and to prepare clusters with other average g factor of 1.958 was obtained for this compound. combinations of metal atoms presently is in progress. With p(pB) = g[S(S + l)]ll2, and assuming S = lI2, the Registry No. [(C2H5)4N]2[(Ta4M~2C112)C16], 66523-92-0; [(ncalculated magnetic moment is 1.69 pB. In this case diaC4H9)4N]Z[ (Ta5MoClI2)Cl6],66523-93- 1; [ (C2H5)4N]3[(Ta5Momagnetic impurities, such as [(Ta6C112)C16]2- l 8 or Cll2)cl6],66523-91 -9; [(Ta6Cllz)C16]4-,66402-50-4; Cs2[Ta6C118], [(Ta4M02C112)C16]2-,apparently are present and cause the 66357-73-1; Csz[Ta5MoCll8],66357-74-2; MoC15, 10241-05-1;TaC15, observed moment to be less than the value calculated from the 7721-01-9. measured g factor. However, it seems clear that the ion References and Notes [(Ta~MOC112)C16]~contains one unpaired electron and thus (1) H. Schafer and H. G. Schnering, Angew. Chem., 76, 833 (1964). may be considered as isoelectronic with [ (Ta6C112)C16]3- or (2) J. Lewis, J . Pure Appl. Chem., 10, 11 (1965). [(Nb6cll2)cl61 (3) F. A. Cotton, Q. Reu., Chem. Soc., 20, 389 (1966). Infrared Spectra. In the region 30-400 cm-' the infrared (4) R. V. Parrish, Adu. Inorg. Chem. Radiochem., 9, 315 (1966). (5) D. L. Kepert and K. Vrieze in "Halogen Chemistry", Vol. 3, V. Gutmann, spectra arise from the vibrational modes of the cluster species. Ed., Academic Press, New York, N.Y., 1967, p 10; F. Fairbrother, ibid., As in the case of the electronic spectra it is apparent that p 123; J. E. Fergusson, ibid., p 227. substitution of Mo atoms into the Ta6Cl12cluster unit causes (6) F. A. Cotton, Rev. Pure Appl. Chem., 17, 25 (1967). little perturbation of the infrared-active vibrational modes. The (7) B. J. Bulkin and C. A. Rundell, Coord. Chem. Reu., 2, 37 (1967).
Table 11. Far-Infrared Soectra (cm-'Y' Et,N' Cs+ n-Bu,N+ CS' Ta,Mo- Ta,Mo- Ta,Mo,Ta ci,:f b ~1,:ci,,zci18*348sh 350sh 348vs,vb 332 vs (F) 335 vs 336 vs 290s(F) 296m 300s 303 s 282w 286w 253vs(F) 254vs 261 vs 260vs 200w 202m 202s 1 8 7 m 187s 185w 165 m (F) 171 vw 153 w 162w 163w 141 s(F) 142m 138m 144m 1 1 8 m ( F ) 1 2 2 m 122w 1 2 4 m 53 m 55 m 70 m
'-.
'-.
1872 Inorganic Chemistry, Vol. 17, No. 7, 1978
Lars Ivar Elding and Osten Groning
(8) B. R. Penfold, Perspect. Struct. Chem., 2, 71 (1968). (9) F. A. Cotton, Ace. Chem. Res., 2, 240 (1969). (10) R. Siepman, H. G. Schnering, and H. Schafer, Angew Chem., Int. Ed. Engl., 6, 637 (1967). ( 1 1 ) D. Bauer, H. G. Schnering, and H. Schafer, J . Less-Common Met., 8, 388 (1965). (12) A. Simon, H. G. Schnering, H. G.Wohrle, and H. Schafer, 2. Anorg. Allg. Chem., 339, 155 (1965);A. Simon, H. G.Schnering,and H. Schafer, ibid., 355, 295 (1967). (13) L. R. Bateman, J. F. Blount, and L. F. Dahl, J . A m . Chem. Soc., 88, 1082 (1966). (14) M . A. Kust, J. D. Corbett, and R. M. Friedman, Inorg. Chem., 7,2081 (1968).
(1 5) D. L. Kepert, R. E. Marshall,and D. Taylor, J. Chem. Soc., Dalton Trans.,
506 (1974).
(16) H. Schafer and B. Spreckelmeyer, J . Less-Common Met., 11,73 (1966). (17) H. Schafer and K. Dohman, 2. Anorg. Allg. Chem., 300, 1 (1959). (18) J. G. Converse and R. E. McCarley, Inorg. Chem., 9, 1361 (1970). (19) P. B. Fleming and R. E. McCarley, Inorg. Chem., 9, 1347 (1970). (20) F. A. Cotton and T. E. Haas, Inorg. Chem., 3, 10 (1964). (21) R. A. Mackay and R. F. Schneider, Inorg. Chem., 6, 549 (1967). (22) D. J. Robbins and A. J. Thomson, J . Chem. Soc., Dalton Trans., 2350 11972) \ - -
-1.
(23) P. B. Fleming, J. L. Meyer, W. K. Grindstaff, and R. E. McCarley, Inorg. Chem., 9, 1769 (1970). (24) W. C. Dorman and R. E. McCarley, Inorg. Chem., 13, 491 (1974).
Contribution from the Division of Physical Chemistry 1, Chemical Center, University of Lund, Lund 7, Sweden
Kinetics and Mechanism for Ligand Substitution Reactions of Square-Planar (Dimethyl sulfoxide)platinum( 11) Complexes. Stability and Reactivity Correlations LARS IVAR ELDING* and OSTEh' GRONING Received September 8, 1977 The 14 rate constants in the system (aqua ligands excluded) DMSO
n = f l = n DMSO
DMSO
CI
CI
DMSO
1'
c1
=
DMSO
CI
I'
21
II =DrsOmc' ci
c1
CI
have been determined at 25.0 "C and in 1.00 M perchloric acid medium using both stopped-flow and conventional spectrophotometry. The equilibrium constants have been obtained from the rate constants, and three of them, also from independent spectrophotometric equilibrium measurements. The overall stability constants for the complexes Pt(DMSO)CI,(H,O),#,j = 1, 2, 3, are PI = (1.20 f 0.12) X lo6 M-I, p2 = (3.2 h 1.1) X 1O'O M-2, and p3 = (5.8 & 2.9) X 10l2 M-3. Comparisons of thermodynamic and kinetic parameters for the reactions in this system with corresponding reactions of similar complexes have been used to distinguish between the cis and trans influence and the cis and trans effect for DMSO compared to other ligands. The cis and trans influences, obtained from comparisons of equilibrium constants, are related to energy differences between complexes in their ground states, while the cis and trans effects, obtained from comparisons of rate constants, are related to energy differences between transition states and ground states. A quantitative evaluation of these contributions to the reactivity gave the trans influence order H 2 0 = C1- =Br- < C2H4 = DMSO < N H 3 (1:1:1:3:4:10) and the cis influence order DMSO '= C2H4< Br- = C1- = H 2 0 < N H 3 (0.1:-0.3:1:1:1:1-2). Thus, DMSO destabilizes trans chlorides by a factor of about 4 and stabilizes cis chlorides by a factor of about 10 compared to water. These thermodynamic influences are small compared to the (kinetic) trans effects, which are in the order H 2 0 < NH3 < C1- < Br- < DMSO < C2H4(1:200:330:3000:2X 1O6:-1O"). The (kinetic) cis effects are generally much smaller than the trans effects and are approximately C2H4 < Br- = C1- < NH3 = H20 < DMSO (0.05:0.3:0.4:1:1:5). Thus, DMSO has an intermediate trans effect and a relatively large cis effect compared to other ligands. Activation parameters for some reactions have been determined. The variation of activation entropies indicates that the ionic charge of the substrate complex is also an important factor for the rates of halide anation reactions. It appears that both the stability and reactivity of simple square-planar complexes can be described by empirical relationships with a small number of parameters. The stability constant for Pt(DMSO)(H20)32' is at least lo7 M-'.
Introduction In aqueous solution, dimethyl sulfoxide (DMSO) reacts with tetrachloroplatinate(I1) forming a strong, sulfur-bonded 1: 1 complex which can be prepared in the solid state as the potassium salt KPt(DMSO)Cl,.' Isotopic exchange studies have indicated that the exchange of the trans chloride in Pt(DMSO)C13- is "instantaneous" whereas the cis chlorides are exchanged slowly.2 Hydrolysis products of the aqua complexes P t ( D M S O ) (H20)C12, c i s - P t ( D M S 0 ) (H20)2C1+, and Pt( D M S O ) ( H 2 0 ) 3 2 t have been prepared by equilibration of aqueous solutions of Pt(DMSO)Cl,- in the presence of excess silver(1) Kukushkid has reviewed these investigations. W e here report a complete kinetic and equilibrium study of the platinum(I1)-DMSO-chloro-aqua system. Comparisons of thermodynamic and kinetic parameters for the reactions in this system with corresponding reactions in the platinum(I1)-chloro-aqua system studied previously7 and with reactions of other similar complexes, such as Pt(C2H4)C13-, can be used to distinguish between the trans and cis influence and the trans and cis effect for D M S O compared to other 0020-1669/78/1317-1872$01.00/0
ligands. It also enables a quantitative evaluation of these contributions to the reactivity of the complexes.
Reaction Model and Rate Expressions The kinetic scheme in Figure 1 (eq 1-7) is applicable. Rate constants for chloride anations are denoted
D~2~~~~Z!
ks k-6
k, k-4
k, and for acid
t DMS0m k, 0H2
CI
DMSOOOHZ CI
CI
k-7
-
CI
5 t DMSOmCI
OH2
k-5
CI
OH2
Figure 1. Reaction model. Rate constants for chloride anations are denoted k, and for acid hydrolyses k,, n = 1, 2, ..., 7 . Vertical arrows
denote very fast substitutions of ligands trans to DMSO and horizontal arrows comparatively slow reactions.
0 1978 American Chemical Society
