Dec 1, 1993 - Polyhedron Vol. ... Department of Chemistry, Faculty of Science, El-Menoufia University, Shebin El-Kom, ... Abstract-The reactions of ruthenium(II1) chloride (1 mol) with ..... J. Lewis and R. G. Wilkins, Modern Coordination.
Polyhedron
Pergamon 0277-5387(93)30083-C
Vol. 13, No. 11, pp. 1781-1786, 1994 Copyright 0 1994 Ekvier Science Ltd Printed in Great Britain. All rights reserved 0277-5387/M S7.OO+O.M)
SYNTHESIS, CHARACTERIZATION AND ELECTROCHEMICAL PROPERTIES OF /I-DIKETONE COMPLEXES OF RUTHENIUM(II1) FATHY A. EL-SAIED, RAMADAN M. EL-BAI-INASAWY, MAGDI ABDEL AZZEM* and AYMAN K. EL-SAWAF Department
of Chemistry, Faculty of Science, El-Menoufia University, Shebin El-Kom, Egypt (Received 1 December 1993; accepted 9 December 1993)
Abstract-The reactions of ruthenium(II1) chloride (1 mol) with acetylacetonylidene-4aminoantipyrine (HL’), monobenzoylacetylacetonylidene-4-aminoantipyrine (HL2), dibenzoylmethanylidene-4-aminoantipyrine (HL3) and antipyrine-4-azo-fi-ethylacetoacetate (HL4) (1 mol) produce complexes of the general formula RuHLC13. The ligand antipyrine4-azo-/I-acetylacetone (HL’) (1 mol) reacts with RuC13*3H20 to produce RuLS C1,(H20).H20. The ligands HL*-HL3 react as neutral bidentates in the ketoenamine form, whereas HL4 reacts as a neutral bidentate in the hydrazo form. HL5 reacts as a monobasic tridentate in the azo form. The complexes were characterized using a variety of analytical, spectral, magnetic and thermal measurements. The electrochemical redox properties of complexes I-V have been studied by cyclic voltammetry in acetonitrile. The chloro-bridged dimer complexes I-IV showed two reversible diffusion-controlled oxidation peaks. The first was attributed to the oxidation of the ruthenium(II1) to the corresponding mixed-valence complex and the second to the ruthenium(IV) complex. The redox properties of complexes I-IV are dependent on the nature of ligand. The monomeric complex V has quite different properties.
Coordination complexes of Schiff base ligands derived from 4-aminoantipyrine such as salicylidene-4_aminoantipyrine, 5-chlorosalicylidene4_aminoantipyrine, 2,4-dihydroxybenzylidene-4aminoantipyrine, 2-hydroxy-1-naphthylidene-4aminoantipyrine and 2-hydroxyacetophenonylidene-4-aminoantipyrine have been studied.‘” Metal complexes of some azo dyes derived from 4aminoantipyrine have also been studied.‘,’ The high alhnity of bivalent ruthenium for the azo function -N=Nis well documented.%” The cyclic voltammetry was used to test the influence of ligand variation on the potentials of Ru”‘/Ru” and RuV/Ru”’ couples. I6 The present work is a continuation of our previous studies on the synthesis and characterization
*Author to whom correspondence should be addressed.
of metal complexes of ligands derived from 4aminoantipyrine. In this paper ruthenium(II1) complexes of the ligands acetylacetonylidene4-aminoantipyrine (HL’), monobenzoylacetonylidene-4-aminoantipyrine (HL’), dibenzoylmethanylidene-4-aminoantipyrine antipy(HL3), rine-4-azo+ethylacetoacetate (HL4) and antipyrine-4-azo+acetylacetone (HL’) have been prepared and characterized using a variety of spectral, analytical, magnetic and thermal methods. The effect of different ligands on the redox properties of ruthenium(II1) complexes has also been studied. EXPERIMENTAL Materials
Reagent-grade chemicals were used without further purification.
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EL-SAIED et al.
Preparation of the ligands
The ligands HL’-HL3 were prepared by condensing equimolar amounts of 4-aminoantipyrine with acetylacetone (HL’), monobenzoylacetone (HL*) and dibenzoylmethane (HL3) in ethanol.2 The ligands HL4 and HL’ were prepared by coupling the diazonium salt of 4-aminoantipyrine with ethylacetoacetate and acetylacetone in sodium acetate solution.” The products were recrystallized several times from ethanol. Preparation of the complexes
All the complexes were prepared by mixing the ligand (1 mol) in ethanol with ruthenium(I11) chloride trihydrate (1 mol) in ethanol. The reaction mixture was stirred magnetically at 60°C for ca 3 h. The precipitated products were filtered off, washed several times with EtOH and dried over P205 in vacua. Measurements
Elemental analyses (C,H,Cl) were performed at the microanalytical unit of the University of Cairo. IR spectra were measured as KBr discs using a Perkin-Elmer 1430 spectrophotometer. The molar conductivity measurements were made in N,Ndimethylformamide (DMF) solutions ( 10e3 M)
Table 1. Analytical
using a Tacussel conductimeter type CD 6N. Magnetic susceptibilities were measured at 27°C by the modified Gouy method using a Johnson-Matthey magnetic susceptibility balance. Diamagnetic corrections were made using Pascal’s constants.18 The magnetic moments were calculated from the equation ~~,=2.84 (xz’?r’) ‘/’ . Crystalline ESR spectra were recorded on a ESR spectrometer E-line century series E-109 ESR system. DTA was performed in air using a Schimadzu DT-30 thermal analyser with a heating rate of 15°C min-’ and a sample weight of 10 mg. TGA was performed under a nitrogen atmosphere using a Shimadzu DT-40 thermal analyser. Cyclic voltammetric measurements were performed using an EG and GPAR computer measuring system for the electrochemical analysis model 250. Current-voltage curves were recorded on a Hewlett-Packard model 7440 A X, Y-recorder. Analytical cell model C-1H and a platinum working electrode (Bioanalytical systems) were used together with a platinum counter electrode and an Ag/AgCl reference electrode. Acetonitrile was used as a solvent and lithium perchlorate as a supporting electrolyte for all electrochemical measurements.
RESULTS AND DISCUSSION The analytical data for ligands HL’-HL’ and their ruthenium(II1) complexes are listed in Table 1.
data for ligands HL’-HL’
AM No. Compound
I
HL’
Pale yellow
RuHL’C13*3H20
Brown
HL*
II RuHL2C13*3H20 HL” III
RuHL3C13*2H20 HL4
IV RuHL4C13
V
Colour
(a-’
cm* mol-‘)
22.5
Yellow Brown
34.6
Yellow Brown
39.5
Orange Brown
HL’
Yellow
RuL’ClZ(H20).H20
Brown
19.3
31.0
and their complexes
Found C
(Calc.) H
66.8 (67.4) 34.7 (35.1) 72.7 (72.6) 40.8 (41.4) 76.4 (76.3) 47.4 (47.8) 59.1 (59.3) 37.3 (37.0) 61.0 (61.2) 37.4 (36.9)
6.5
% Cl
DTA peaks (“C) Endo. Exo.
280
-
(6.7) (Z) (Z) 4.5 (4.4)
19.5 (19.5)
17.9 (17.5)
80
280
-
-
80
320 -
(G) (X) 5.6 (5.8) 3.8 (3.6) 6.0
16.7 (16.3) -
-
19.5 (19.3)
80
14.0 (13.6)
75
(5.7) (Z)
180
fi-Diketone complexes of ruthenium(II1)
These show that the 1:1 molar ratio reactions of ruthenium(II1) chloride with HL’-HL’ produce 1: 1 metal complexes. These air-stable complexes are partially soluble in most organic solvents but soluble in DMF, dimethylsulphoxide and acetonitrile giving stable solutions. The conductance data (Table 1) show that all complexes are non-electrolytes,19*20 suggesting the coordination of the chloride ions. Table 2 shows the most characteristic IR spectral bands of the ligands and their complexes. The IR spectra of the Schiff bases HL’-HL3 show broad absorption bands near 3 170 cm-‘, assigned to intramolecular hydrogen bonding (N-H...O). The appearance of this band indicates ketoimine-ketoenamine tautomerism. 21,22The IR spectra of HL’HL3 also show three bands at 1680-1665, 16251615 and 1593-1570 cm-‘, assigned to v&&O) of the side chain, v(CA0) of the pyrazolone ring and v(C=N), respectively. The IR spectra of ruthenium(II1) complexes of HL’-HL3 show a negative shift in v(N-H) and v(C=O) of the side chain, compared with those of the ligands indicating that the N-H and the sidechain carbonyl oxygen are involved in coordination. On the other hand, the v(C=N) disappears upon metal complexation which favours the ketoenamine tautomer formation. The band corresponding to v(C=O) of the pyrazolone ring does not change upon complexation. The above arguments indicate that the ligands (HL’-HL3) react with ruthenium(II1) as neutral bidentate ligands in the ketoenamine form as shown in Scheme 1. This mode of bonding has been reported for the palladium(I1) complex of (HL1).4 The IR spectra of the ligands HL4 and HL5 show three bands at 1665-1655, 1650-1645 and 1520 cm-’ , assigned to v(C=O) (ketonic), v(O) (pyrazolone ring) and v(N=N), respectively. The spectrum of HL4 shows a strong band at 1705 cm-‘, assigned to v(C=O) (ester). The spectrum of RuHL4C13 shows two new bands at 3230 and 1620 cm-‘, assigned to coordinated N-Hs6 and uncoordinated C&N, respectively; this indicates that the ligand reacts in its hydrazo form. The spectrum also shows that the two bands corresponding to v(C=O) (ketonic) and v(C=O) (pyrazolone ring) do not change upon complexation. On the other hand, the band characteristic of the ester group is split and shifted to a higher frequency compared with that of the ligand, indicating that it is coordinated. These arguments indicate that HL4 reacts as a neutral bidentate ligand as shown in Scheme 1. The IR spectrum of RuL5CI,(H,0)*H20 shows three bands at 1630, 1556 and 1550 cm-‘, assigned
F.A. EL-SAIEDet al.
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to v(C=O) ketonic, v(C=O) (pyrazolone ring) and v(N=N), respectively. The former two bands are at lower frequencies compared with those of the ligand and the latter one is at a higher frequency compared with that of the ligand indicating that one of the ketonic carbonyls, c---O (pyrazolone)3*4 and N=N groups are involved in coordination. The spectrum also shows a strong band at 1660 cm-’ assigned to uncoordinated C=O (ketonic). These arguments indicate that the ligand reacts as a monobasic tridentate ligand in its azo form. The IR spectra of all complexes exhibit new bands at 525-505 and 460-440 cm-‘, assigned to v(Ru-N)‘~ and v(Ru-O),*~.*~ respectively, and also strong bands and shoulders at 3 18-305 and 315-305 cm-‘, assigned to v(R~-cl).~’ The splitting of this band indicates the cis-configuration.27 The spectra of the complexes except HLS show weak bands at 29&280 cm-‘, assigned to bridging v(Ru-Cl). The appearance of the latter band suggests a dimeric structure for all complexes, except that of HL’ which is a monomer as shown in Scheme 1. The spectra of the hydrated complexes
show broad bands at 3520-3440 cm-‘, assigned to v(O-H) of water molecules. The room-temperature magnetic moments per ruthenium atom (0.93, 0.95, 0.89 and 1.45 B.M.) for complexes I-IV, respectively, are less than the lowspin d5 configurations, indicating magnetic exchange interactions between ruthenium(II1) ions. This could be explained by a dimer formation through chloride bridges as shown in Scheme 1. RuL5C12(H20)*H20 shows a magnetic moment value (1.76 B.M.) corresponding to a low-spin dS configuration. The ESR spectra of the polycrystalline complexes III-V were recorded at room temperature. The spectra of III and IV are quite similar. The spectra of III and IV are characteristic of low-spin dS configurations, six lines were observed from the interaction of the unpaired electron spin with 99Ru and “‘Ru (1=5/2; 12.8 and 17% abundant, respectively). The line widths are anisotropic. The spectra exhibit two features assigned as g,=2.5 and g1=2.1 (A,,=125 G), which are characteristic of species with octahedral symmetry.** These parameters show a relation such that gll>gl, which refers to the unpaired electron
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