Isomer B is also a racemate. The first and most extensively studied series of synthetic tetraaza macrocycles were
initially prepared by Curtis, who reported that the reaction of
tris-(1,2-diaminoethane)nickel(II) perchlorate and acetone at room temperature produced a
yellow crystalline product. The compound was diamagnetic and very resistant to hydrolysis.
The original structure proposed was not a macrocycle but this was later corrected to fit
in with the chemical inertness, the infrared spectrum and its reaction with hydrogen to
give 1,2-diaminoethane and mesityl oxide. The product can occur in two noninterconvertible
forms, which Curtis originally designated as A and B. The A isomer occurring in two
interconvertible forms called Aa and Ab.
The three isomers are similar in appearance and physical properties although some
differences in their IR spectra have been noted. The first crystals of cyclic complex
which crystallise from the reaction medium are isometrically pure B(ClO4)2.
The Aa(ClO4)2 isomer usually begins to crystallise after about 25%
of the total product has separated. The separation occurs since the B form is less
soluble. The A-B isomerism comes from cis- trans arrangements of the imine linkages in the
macrocyclic ring, with A corresponding to the trans- form and B the cis-isomer.
Later studies have shown that Aa is the more stable form and that it corresponds to the
racemic mixture of isomers (the asymmetry exists at the tetrahedral nitrogen atoms in the
diene complex) and that Ab is the meso isomer.
70% aqueous 1,2-diaminoethane (ethylenediamine, 2.8 g, 3.1 cm3) is added to
a solution of nickel(II) chloride hexahydrate (2.4 g) in 10 -15 cm3 of water.
The resulting purple solution is filtered to remove any insoluble material and the
solution is then evaporated down to approximately 6 cm3 on a steam bath. Two
drops of 1,2 diaminoethane are then added and the solution is cooled in an ice-bath.
The orchid coloured crystals are collected on a sintered glass filter funnel and washed
twice with 3 cm3 portions of ethanol and finally air-dried. The mother liquor
should not be discarded since further product can be obtained by addition of ethanol and
further cooling.
Record the yield and show the product to a demonstrator.
The perchlorate salt is more soluble in acetone than the chloride and this is used for
the subsequent reaction. Tris-(1,2-diaminoethane)nickel(II) chloride (2 g) is dissolved in
hot ethanol and sodium perchlorate (2 g) is then added. The solution is cooled and the
complex precipitating out is collected by suction.
Record the yield and show the product to a demonstrator.
NB. Perchlorate salts have been known to detonate spontaneously and should be
treated as potentially hazardous.
Tris-(1,2-diaminoethane)nickel(II) perchlorate dihydrate (0.5 g) is dissolved in 7 cm3
of acetone and the purple solution is thoroughly shaken. The reaction mixture is left to
stand for a few hours (may be left overnight) after which yellow crystals are formed.
These are collected by suction and air-dried.
Record the yield and show the product to a demonstrator.
An IR spectrum is available, record the major peaks
and try to account for their position and intensity.
1. Outline a possible reaction scheme for the template synthesis of the Ni(II) complex.
2. What is The Macrocyclic Effect?
L.F. Lindoy, "The Chemistry of Macrocyclic Ligand Complexes", Cambridge
University Press, 1989, Chapter 2.
G.A. Melson, "Coordination Chemistry of Macrocyclic Compounds", Plenum Press,
New York, 1979. Chapter 2.
return to list of C31L experiments
Return to Chemistry, UWI-Mona, Home Page
Nov-96, rjl