Self-assembled Transition Metal Coordination Frameworks of ...

C 0pper( ll ) complexes
bis[(1E)-1-(2-pyridyl)ethylidene] ethanedihydrazide having two N,N,O coordination
pockets on reaction with Fe(ClO4)3- 61-I20 have been reported to undergone an
oxidative degradation of the side chain (-CO-CO-) and a reduction of Fem to Fen to
form a complex, with crystallographic evidence [49].
The transition metal complexes may be very stable, or very reactive; and the
stabiljties of transition metal complexes may be thermodynamic or kinetic in origin.
As the metal compounds are frequently colored and the color of a particular metal ion
will depend upon its oxidation state and environment, the color change can be
indicative of chemical changes. The changes on coordination environment or even a
change in oxidation state may be behind the color loss. The follow up of UV spectra
of 13 in methanol solution at different intervals were carried out and found useful to
identify this change. It was seen that the absorption at 22030 cm", attributed to
O—>Cu(II) charge transfer transition, gradually losses its intensity. However the band
at 28250 cm“ assigned to Cl—>Cu(H) charge transfer transition retains its identity.
Therefore it is attributed to the degradation of -CO— group of complex 13 in methanol
2.5 — . . .
,|n|t|a|
solution on exposure to air. The UV spectra follow up is given in Fig. 4.54.
' , after 2h
2°‘ ' ~i / afler4h
“” afler24h
- “I “ afler48h
1 , , / r /" -" ...-’ 1‘ I
. - / v
_/ '/ / /" /Iv.
0.0- e-1' ~
/ - _, /‘
/ ~’-__
.
' . * /" / after 60h
1 /I _./J /J //I _-‘fl
Iaflgf 96h
0.5 - * /’/
Q ,1 I ,3 V V. ./ . "
1 ' | ' | ' I ' | ' | ' I ' I I | ' |
1oo zoo aoo 400 soo eoo woo aoo eoo 1ooo
Wavelength (nm)
Fig. 4.54. The Electronic spectra follow up of complex 13in 104 M methanol.
181