lower cost per analysis, greater speed of analysis, and smaller bench space requirements for performing the analysis.
LITERATURE CITED (1) J. Korbland R. Pribil, Chem. lnd., London, 233 (1957). (2) J. Korbl and R. Pribil, Chem. Listy, 51 1061 (1957). (3) A. L. Lazrus, K. C. Hill and J. P. Lodge, Proceedings from the 1965 Technicon Symposium "Automation in Analytical Chemistry", Medicad Inc.. 1966, p 291.
(4) American Public Health Association, "Standard Methods for the Examination of Water and Wastewater", 13th ed., APHA. Washington, DC, 1971, p 330. (5) G. W. Snedecor and W. G. Cochran, "Statistical Methods", 6th ed., Iowa State University Press, 1967. p 139. (6) W. J. Youden, "Statistical Methods for Chemists", Chapman and Hall, London, 1951, p 16.
RECEIVEDfor review October 25, 1974. Accepted January 20, 1975.
Formation Constant and the Structure of a Bridged Adduct of Triethylenediamine and Bis(0,O'-diethyldithiophosphato)nickel(ll) Walter Rudzinski, Motoo Shiro, and Ouintus Fernando Department of Chemistry, University of Arizona, Tucson, AZ 8572 1
For a number of years, we have been concerned with the relationship between the structures of the adducts of extractable metal chelates and their thermodynamic properties (1-3). T h e planar metal chelates, bis(0,O'-diethyldithiophosphato)nickel(II), Ni[S2P(OC2H5)2]2, or bis(0,O'dimethyldithiophosphato)nickel(II), Ni[S2P(OCH3)2]2, served as model compounds in most of our studies because they formed adducts very readily with a wide variety of heterocyclic nitrogen bases. Recently, Diemert and Kuchen ( 4 ) reported t h a t pyrazine and 4,4'-bipyridyl reacted with the planar chelate, bis( diethyldithiophosphinato)nickel(II), Ni[S2P(CzHj)z]2, and formed 1:l adducts which were regarded as coordination polymers in which the nickel ions were six-coordinate. With 1,4-diazabicyclo[2.2.2]octane, however, a 2:l adduct was formed and the electronic spectrum of the compound indicated t h a t the nickel ions were most probably five-coordinate. This unexpected result prompted us to study the interaction of 1,4-diazabicyclo[2.2.2]octane, (Dabco) with the nickel chelate, Ni[SeP(OC2Hj)2]2,and t o determine the structure of the adduct t h a t was formed.
EXPERIMENTAL Synthesis and Purification of Compounds. The ammonium salt of diethyldithiophosphonic acid was synthesized from ethanol and phosphorus pentasulfide as described before (3). The nickel complex, bis(0,O'-diethyldithiophosphato)nickel(II), Ni(dtp)2, was precipitated by the addition of nickel sulfate to an aqueous solution of the ammonium salt and recrystallized from acetone. The molar absorptivity of the compound in ethanol at 524 nm was found to be 90 and was employed as a criterion of purity. Triethylenediamine, or 1,4-diazabicyclo[2.2.2]octane, or Dabco, was obtained from Houdry Process and Chemical Co., Philadelphia, PA. The compound was purified by sublimation under vacuum. The solid adduct was prepared by adding an excess of Dabco dissolved in ethanol to an ethanol solution of Ni(dtp)2. Red crystals were formed when the solution was allowed to stand for 24 hours. Spectrophotometric Measurements. The spectra of about forty different solutions containing varying concentrations of Ni(dtp):! and Dabco were recorded with a Cary 14 spectrophotometer. An isosbestic point was found at 505 nm, and the location of the band maximum of the 2:l adduct of Ni(dtp), and Dabco was at 468 nm. The molar absorptivities of Ni(dtp)g in ethanol at 468 nm, (cc4"), and at 524 nm, were calculated by recording the spectra of nine solutions varying in concentration from 2.20 X 10-3M to 6.16 X 10-3M. The average value of cc468was 50 and of ec524was 90. The molar absorptivities of the adduct at 468 nm, 1194
ANALYTICAL CHEMISTRY, VOL. 47, NO. 7, JUNE 1975
and at 524 nm were obtained by recording the absorption spectra of eight different solutions containing Ni(dtp)2 and Dabco; the Ni(dtp)z concentration varied from 2.94 X 10-4M to 4.93 X 10-3M and the concentration of Dabco in each of these solutions was at least 500 times the concentration of the Ni(dtp)2. was 950 and that of c~~~~ was 90. The average value of Determination of the Adduct Formation Constant. The reaction of the nickel(I1) chelate C, with the base, B, to form the adduct, A, is represented by: 2C
+
B S
A
and the formation constant, K , of the adduct is given by:
where the quantities in brackets represent equilibrium concentrations in mol/l. If the initial concentrations of the base, Dabco, and the nickel(I1) chelate, Ni(dtp12, are COB and C 0 c mol/l., respectively, c"B
=
LB1
+
CAI
(2 1
and CoC = [C] + 2[A] (3 ) At 468 nm and at 524 nm, the only absorbing species are the adduct A, and the nickel chelate, C. The values of the absorbance of a solution in a 1.00-cm cell containing Ni(dtp)Z, Dabco, and the adduct, at 468 nm and at 524 nm are given by the following equations which contain the experimentally determined molar absorptivities.
+
[A]
