Spectroscopic and electrochemical studies on the chromotropism of
ternary copper(II) complexes
A. Taha¤
Department of Chemistry, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt
Received (in Montpellier, France) 7th February 2001, Accepted 22nd March 2001
First published as an Advance Article on the web 2nd May 2001
Ternary complexes of copper(II) with b-ketoesters [b-keto \ ethyl acetoacetate (HETAA) and ethyl benzoylacetate
(HETBA)] and diamines [diam \ N,N,N@,N@-tetramethylethylenediamine (Me en), N,N,N@-trimethylethylene-
4
diamine (Me en), N,N,N@-triethylethylenediamine (Et en) and N-methyl-1,4-diazacycloheptane (medach)] of general
3
3
formula Cu(b-keto)(diam)X, where X~ \ ClO , BPh , NO , Cl or Br, have been prepared. Their structure and
4
4
3
chromotropicity have been characterized using spectral analyses, electrochemical and magnetic susceptibility
measurements. Complexes having perchlorate, tetraphenylborate and nitrate as anions show a remarkable change
from reddish violet to green in di†erent solvents and anions with increasing donor strength of the solvent or anion.
Complexes having chloride and bromide as anions are highly inÑuenced by the acceptor property rather than the
donor property of the solvent. The spectral studies revealed the possibility of using these complexes as Lewis
acidÈbase color indicators for both solvent and anion donor strength. Cyclic voltammetric measurements on the
complexes in di†erent solvents showed that the reduction process is mainly di†usion controlled and
quasi-reversible or irreversible. Such behavior has been explained according to the ECE mechanism
(E \ electrochemical step, C \ chemical step). The solvent e†ect has been rationalized in terms of the thermo-
dynamics and kinetics of the redox processes. A correlation has been found between the copper(II) reduction
potential and the spectral data in di†erent solvents.
without further puriÐcation. The solvents, 1,2-dichloroethane
Introduction
(DCE), nitromethane (MeNO ), acetonitrile (MeCN), acetone
2
The ternary complexes of copper(II) with b-diketones and
methylated diamines have attracted great interest as color
indicators for solvent and anion donor strength.1h10 However,
b-ketoesters have not attracted the same attention as b-
diketones in this Ðeld. In our previous work spectral and
molecular orbital calculations on copper(II) complexes with
thenoyltriÑuoroacetone and diamine derivatives were re-
ported.11 As expected from the behaviors of the analogous
copper(II)Èb-diketone complexes, the ternary complexes of
copper(II) with the b-ketoesters ethyl acetoacetate (HETAA)
and ethyl benzoylacetate (HETBA) would be expected to be
strongly solvato- and anionochromic.
(Me CO), methanol (MeOH), formamide (FA), dimethyl-
2
formamide (DMF), dimethyl sulfoxide (DMSO) and hexa-
methylphosphotriamide (HMPA), were puriÐed using
standard methods.12,13 The e†ect of anions was studied using
their tetrabutylammonium salts (Bu NX) where X~ \ ClO ,
4
4
CF SO , I, SCN, Br, N or Cl, which were prepared as
3
3
3
described earlier,11,14 except for the CH CO ~ and CO 2~
3
2
3
anions which were ammonium salts.
The visible absorption spectra for Cu(b-keto)(diam)X
(5 ] 10~3 mol dm~3) solutions in various organic solvents,
and anions in nitromethane, and for solid complexes in Nujol
mulls were recorded with a Hitachi U-2000 spectrophotom-
eter using 10 mm quartz cells at 25 ¡C. The infrared spectra in
KBr (400È4000 cm~1) were recorded using a Shimadzu FTIR
8101 spectrometer. Magnetic moments were calculated from
the molar susceptibility values measured using the Gouy
method and a Johnson Matthey Alfa Products magnetic
balance MSB-MK I. Cyclic voltammetric measurements were
performed using a standard polarographic and potentiostatÈ
galvanostat system (Princeton Applied Research, Texas) based
on a three electrode system as described elsewhere.15 Cyclic
voltammograms were recorded at a potential scan rate of 100
mV s~1 for solutions of 0.1 mol dm~3 tetrabutylammonium
perchlorate as supporting electrolyte. Then 1 ] 10~3 mol
dm~3 of the investigated complex and the internal reference
were added, respectively. In the current study, two internal
references, ferroceneÈferrocenium (FcÈFc`) and bis(bi-
phenyl)chromium(I)/(0)16 have been employed due to the
restrictions on the solubility of both in the solvents used.
All potentials were then re-scaled to bis(biphenyl)chrom-
ium(I)/(0)17,18 due to its higher solubility in most solvents
used.
Based on the above, the present work reports the synthesis
of seven new ternary complexes: Cu(b-keto)(diam)X (b-
keto \ ETAA or ETBA; diam \ diamine \ N,N,N@,N@-tetra-
methylethylenediamine (Me en), N,N,N@-trimethylethylenedi-
4
amine (Me en), N,N,N@-triethylethylenediamine (Et en) and
3
3
N-methyl-1,4-diazacycloheptane
(medach);
X~ \ ClO ,
4
BPh , NO , Cl or Br). The e†ects of anions, solvents and
4
3
substituents on both b-ketoester and diamine ligands on the
structure have been investigated. These e†ects are correlated
with the spectral and electrochemical data of these complexes.
Experimental
Materials and methods
All the reagents and solvents used were from either Merck
or Aldrich. b-Ketoester and diamine ligands were used
¤ Present address: UAE University, Faculty of Science, Chemistry
Department, Al-Ain, P.O. Box 17551, United Arab Emirates. E-mail:
A.Taha=uaeu.ac.ae.
DOI: 10.1039/b101292b
New J. Chem., 2001, 25, 853È858
853
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2001