Speeding-Up the Preparation of Coordination Compounds in Undergraduate Laboratory Classes When designing a laboratory course in coordination chemistry a t the second and third year undergraduate levels, difficulty often occurs in finding suitable preparative experiments when only one, weekly, three or four hour session is available. It is our belief, however, that many so-called "standard" preparative methods for coordination complexes, which apparently require inordinate amounts of laboratory time, could well be modified in order to be completed within 3-4 hr. This is certainly the ease for various cobalt(II1) complexes, where we have found ways of markedly speeding up their preparation. Of particular interest will he the preparation of transdichlorobis(ethylenedimine)c~balt(IIIchloride, t-[Co(en)~Clz]Cl, a very popular second year experiment. Traditionally a stream of air is passed through a solution of a cobalt(I1) salt and the required amount of ethylenediamine for many hours in order to oxidize the cohalt(I1) and produce the required cobalt(II1) can,of course, be completed in minutes complex. This tedious oxidation procedure (still suggested in many leading texts (1-4)) by using a few ml of "100 vol." hydrogen peroxide (5, 6). Evaporation to incipient crystallization of the resulting cobalt(II1) complex solution is then rapidly achieved by using a rotary evaporator, and the need for prolonged heating over a steam bath is thus avoided. So far as we are aware, this has not been previously suggested. Typically, in preparing i-[Co(en)&]CI, the initial volume of the cobalt(II1) solution is about 180 ml, and this must be reduced to about 75 ml before crystallization of the complex can occur ( 5 ) . The rotary evaporator (using maximum water-pump vacuum and a boiling water bath) can achieve this in about 15 min. The concentrated solution when allowed t o cool in an ice-bath for 30 minutes, produces an excellent crop of well-formed crystals (leaving t o crystallize overnight is unnecessary). Using this modified method we have even found an improvement in both yield and purity over standard method results. Hence an average-good student can complete the preparation of t-[Co(en)nCh]Cl in about 1% hr. Using a similarly modified procedure the racemate tris(ethylenediamine)cobdt(III)chloride, [Co(en)8]Cls,can be prepared in ahout 1hr. The preparation of both the above cobalt(II1) complexes can therefore be completed in the one 3-hr laboratory session. We have also used the technique to drastically reduce the preparation time of ehloropentaamine cobalt(II1) chloride and transdichloratetra~minecobalt(II1)chloride. Details may he obtained from the authors. Literature Cited (11 Cotton. F. A.. and Wilkinson, G.."Advaneed Jnorganie Chaiatry: 3rd ad., lntarseianca, Nev Yark. 1972. p. 883. (21 Para, G., and Suteliffe, H.."Practical Inorganic Chemistm? 2nd ed., Chapman and Hsll. London, 1974,~. 104. (3) Braver, G. IEdiforI, '"HandboakofPrsparative lnorgsnicchemiatry: 2nd nl.,AcedemiePress, New York, 1965,Vol. 2, pp. 15361538. I41 Adams, D.M., and bynor, J. B.. ''Advanced Practicd Inorganic Chemistry? John Wilay & Sons. Ine.. London, 1967,pp. 67,141. ( 5 ) Hofacker, U.A., 'Themiesl Experimentation? Freeman, San Francisco. 1972,p 6. (61 Angdiei, R. J., "Synthesis and Teehni~uein Inorganic Chemistry: Saunders, Philadelphia, 1969,~. 16 (but also seep. 711.
N.S.W. Institute of Technology Sydney, Australia
440 / Journal of ChemicalEducation
Peter Leverett Mervyn J. Oliver
