Synthesis and characterisation of thermally stable ka[cu2(p-oc6h4coo)a(ch3(ch2)ncoo)4-a] and [cu2(p-h3nc6h4coo)a(ch3(ch2)ncoo)4-a]xa and their reactions with selected ketones / Zaimatul ‘Azian Kamarazaman
This research focussed on the development of the synthetic methods and characterisation (structural, thermal, magnetic and redox properties) of two types of ionic copper(II) mixed-carboxylates: (a) Ka[Cu2(p-OC6H4COO)a(CH3(CH2)nCOO)4-a], and (b) [Cu2(p-H3NC6H4COO)a(CH3(CH2)14COO)4-a]Xa, where a =...
| Summary: | This research focussed on the development of the synthetic methods and
characterisation (structural, thermal, magnetic and redox properties) of two types of
ionic copper(II) mixed-carboxylates: (a) Ka[Cu2(p-OC6H4COO)a(CH3(CH2)nCOO)4-a],
and (b) [Cu2(p-H3NC6H4COO)a(CH3(CH2)14COO)4-a]Xa, where a = 1, 2; n = 14, 10, 8,
and 6; X = Cl, CH3COO and CF3SO3. These complexes were designed to be thermally
stable and magnetic metallomesogens and/or metal-containing ionic liquids.
The synthetic methods used to prepare these complexes were one-pot reaction,
ligand-exchange reaction, and acid-carbonate-base reaction. A total of twelve (12)
complexes were successfully prepared and fully characterised (Table 1).
Table 1 The structural formulas of the complexes
Complex Structural formula
1 K2[Cu2(p-OC6H4COO)2(CH3(CH2)14COO)2(p-HOC6H4COOH)2].2H2O
2 [Cu2(p-HOC6H4COO)2(CH3(CH2)14COO)2(CH3(CH2)14COOH)(H2O)].
CH3CH2OH
3 [Cu2(p-H2NC6H4COO)2(CH3(CH2)14COO)2].2H2O
4 K[Cu2(p-OC6H4COO)(CH3(CH2)14COO)3]
5 [Cu2(p-HOC6H4COO)(CH3(CH2)14COO)3(CH3CH2OH)2]
6 [Cu2(p-HOC6H4COO)(CH3(CH2)10COO)3].H2O
7 [Cu2(p-HOC6H4COO)(CH3(CH2)8COO)3].CH3CH2OH
8 [Cu2(p-HOC6H4COO)(CH3(CH2)6COO)3(CH3(CH2)6COOH)
(CH3CH2OH)].H2O
9 [Cu2(CH3(CH2)14COO)2(OH)2(H2O)4].2C2H5OH
10 K2[Cu2(CH3(CH2)10COO)2(OH)4]
11 K2[Cu2(CH3(CH2)8COO)2(OH)4]
12 K2[Cu2(CH3(CH2)6COO)2(OH)4]
iv
The structural formulas of these complexes were deduced from elemental
analyses, FTIR and UV-vis spectroscopies. The thermal properties were determined by
TGA and DSC, while the mesomorphic properties were determined by OPM. The
magnetic properties were determined by Gouy method using a magnetic susceptibility
balance, and the redox properties by cyclic voltammetry. Additionally, GCMS was
used to analyze the products formed from the carbon-carbon bond-forming reaction of
methyl carbonyl (3,3-dimethyl-2-butanone).
The structure of most of the complexes were dimeric paddle-wheel with either
square planar or square pyramidal geometry at copper(II) centres.
Complex 1 had the highest thermal stability (Tdec = 424oC) compared to the other
complexes (Tdec = 200oC – 250oC). Additionally, the complexes with a higher ratio of
the alkylcarboxylate ligands (aromatic: aliphatic = 1:3) were more thermally stable; the
stability increases with increasing alkyl chain length. However, the opposite trend was
noted for the melting temperatures: complexes with a higher ratio of the
alkylcarboxylate ligands had a lower melting point.
Six of the complexes (Complex 2, Complexes 5 - 9) exhibited metallomesogenic
properties. However, the type of mesophase cannot be deduced with certainty from
OPM.
All complexes were magnetic at room-temperature. Except for Complex 1 which
showed a weak ferromagnetic interaction (μeff = 3.12 B.M.; 2J = 60 cm-1), the other
complexes had magnetism (μeff = 1.87 B.M. - 2.62 B.M.) which were lower than the
spin-only value for two unpaired electrons (μeff = 2.83 B.M.), with variable strength of
antiferromagnetic interaction (2J = -78 cm-1 to -346 cm-1). The complexes with a higher
ratio of the alkylcarboxylate ligands have a stronger antiferromagnetic interaction.
However, the difference in the chain length did not have much effect on the magnetic
interaction.
v
All of the complexes were redox-active and showed step-wise quasi-reversible
electrochemical reaction. The initial reduction potentials were in the range of
0.07-0.30 V.
Both Complex 1 and Complex 4 ‘catalysed’ the carbon-carbon bond-forming
reaction of 3,3-dimethyl-2-butanone. Complex 4 seemed to be a better ‘catalyst’ as the
products formed were in higher purity and amount.
The findings of this research were published in one (1) ISI journal and presented
either orally or as poster at three (3) national and four (4) international conferences and
seminars (Appendix 1). |
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