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Science Foundation, We are most grateful to Dr. Gordon Rodley for synthesizing single crystals suitable for X-ray analysis. Supplementary Material Available. A listing of structure factor amplitudes will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the supplementary
material from this paper only or microfiche (105 x 148 mm, 2 4 x reduction, negatives) containing all of the supplementary material for the papers in this issue may be obtained from the Journals Department, American Chemical Society, 1155 16th St., N.W., Washington, D. c. 20036. Remit check or money order for $3.00 for photocopy or $2.00 for microfiche, referring to code number JACS-
74-4428.
Kinetics and Thermodynamics of Rapid Structural Interconversions of Dichloro-1, 1,7,7-tetraethyldiethylenetriamineni~kel(11) in Acetonitrile Hideo Hirohara, Kenneth J. Ivin, John J. McGarvey," and John Wilson Contribution f r o m the Department of Chemistrj>,The Queen's Unicersity of Belfast, Belfast, BT9 5AG, Northern Ireland. Received January 3, 1974
Abstract: Spectrophotometric and conductometric studies in acetonitrile solutions of dichloro-1,1,7,7-tetraethyldiethylenetriaminenickel(I1) (NiLCI2where L is the tridentate ligand 1,1,7,7-tetraethyldiethylenetriamine)are interpreted in terms of the following equilibria, where NiLCl+lIC1- represents an outer-sphere complex : NiLCL e NiLCl+IICl- e NiLClf 4C1- (eq 2). The equilibrium constants have the following values a t 20": Ki = kll/k?i = 0.95; K, = kZ3/k3* = 8 X 10P mol dm-3; Kd = K,Ks/(l + Ki) = 3.9 x 10-5 mol dm-3. Values of AH" and A S o were also determined. Kinetic data for this system were obtained by relaxation methods, in which the equilibria were suddenly perturbed by an electric field jump or by means of a pulse of radiation from a Q-switched neodymium laser. The results were interpreted in terms of the above mechanism; values for the rate constants k?l and k32 were estimated to be 7 X lo5sec-l and 2 x 109 M-1 sec-l, respectively, at 20".
A
lthough five-coordination is somewhat unusual1 for nickel(I1) compounds, a considerable number of complexes of this type have now been prepared and characterized. The complexes frequently contain bulky, polydentate ligands so that the tendency to attain six-coordination is suppressed by crowding around the central metal ion. As well as being of stereochemical interest, five-coordinate species have frequently been proposed as intermediates in substitution reactions3 and structural inter conversion^^,^ of transition metal complexes. One example of a nickel(l1) compound which can exist in a stable five-coordinate form is dichloro-1,1,7,7tetraethyldiethylenetriaminenickel(II), written as NiLC&, where L is the tridentate ligand Et2N(CH& NH(CH&NEt2. On the basis of spectral, magnetic, and conductometric evidence, Dori and Gray6 showed that in acetonitrile and other polar organic solvents this compound was capable of existing in at least two stereochemical modifications present in equilibrium : a five-coordinate, paramagnetic, un-ionized species NiLCI, (absorption maximum 450 nm) and a four-coordinate, square-planar, diamagnetic, ionized species NiLCI+ (absorption maximum 530 nm). In describing ( I ) P. Orioli, Coord. Chem. Rec., 6,285 (1971). (2) B. F. Hoskins and F. D. Williams, Coord. Chem. Rec., 9, 365 (1973). (3) E g . , M. L. Tobe, "Inorganic Reaction Mechanisms," Nelson, London, 1972. (4) R . D. Farina and J. H. Swinehart, J . Amer. Chem. Soc., 91, 568 (1969). ( 5 ) I0.4Z at the fastest oscilloscope sweep rates used (50 nsec cm-9. The electric field-jump apparatus was based on the designs of Eyring, el u / . , ~and of Staples, Turner, and Atkinson.'a High voltage pulses were generated by means of the coaxial delay-line technique." The coaxial cable (loo0 m of Uniradio Type 67) was charged through a limiting resistance from a high voltage supply (Hursant Ltd. Model 308) and discharged into a termination matched to the characteristic impedance (50 n) of the cable. The pulses had a rise time of less than 0.2 psec, a duration of 9.2 psec, and a fall time of about 2 psec. Figure 1 shows the sample and reference cells. The electrodes, 2.5 cm diameter and 1 mm thick, were constructed from platinum. In the sample cell, they were fused into the ends of soft glasslpyrex graded seals, the interelectrode distance being fixed a1 2.5 mm. In the reference cell the interelectrode distance was variable (2-10mm), and in this case the electrodes were pressed tightly (without an adhesive) into the ends of Teflon tubes. Before assembling the cells, the electrodes were polished to remove all scratches and sharp edges. Both cells were immersed in a bath of silicone oil, the temperature of which was held constant t o better than 0.1". The rapid changes in conductance following perturbation of the weak electrolyte equilibrium were followed by means of the rapid changes in voltage across an asymmetric Wheatstone bridge. The sample and reference cells formed two arms of the bridge, (3.58.6) X IO'n, the other two arms being low resistance terminations, 20-50 n. The voltage changes across the bridge were recorded on a Hewlett-Packard 181A oscilloscope, fitted with a differential amplifier (type 1803A). The asymmetry of the bridge ensured that the output signals from the bridge t o the differential amplifier remained below 50 V, thereby eliminating the need for high voltage attenuators at the oscilloscope inputs and making it easier t o balance the bridge.' In order to compensate for the small increase in conductance in the sample cell resulting from the first Wien effect," it was balanced against a reference cell containing a solution of a ( 8 ) R. Jamison, Ph.D. Thesis, The Queen's University of Belfast. 1972. (9) D. T.Rnmplon. L. P. Holmcs, D. L. Cole. R.P. Jensen. and E. M. Eyring. Reu. Sci. Imfrum.,38, 1637 (1967). (101 B. R. Stapler, D. J. Turner, and G. Atkinson. Chem. lnsfnrm., 2,127(1969]. (11) M. Eigcn and L. DeMaeycr in "Techniques of Organic Chcmiotry." Vol. 8, Part 11, 2nd ed, S. L. Fries, E. S. Lewis. and A. Weissberger, Ed.. Interscience, New York, N. Y.,1963,p 988 if. (12) M. Wien, An,r.Phj)s. (Leiprig),83, 327(1927).
strong electrolyte (approximately IO-' M NaBPh,) in the same sdvent.13 At the start of the experiment the interelectrode distance in the reference cell was set a1 2.5 mm and the concentration of the strong electrolyte was adjusted until the conductance of the reference cell (measured with a 1000-Hz impedance bridge, Wayne Kerr Model B221A) matched that of the sample cell. Small adjustments were then made in the concentration of strong electrolyte and the interelectrode spacing until both conductance and capacitance matched as closely as possible. Considerable efforts were made t o keep the capacitance mismatch as small as possible ( 2 0 0 0 d j f (-40") NIN variation of solvent viscosity, 77 exp(B/RT). N S
[ Ni( Meetren)(CH3CN)I2+
jNi?+/
