Physical and spectroscopic studies on novel vanadyl complexes of some substituted thiosemicarbazides

Spectrochimica Acta Part A 61 (2005) 1113–1119

Physical and spectroscopic studies on novel vanadyl complexes of some substituted thiosemicarbazides N.M. El-Metwally, R.M. El-Shazly, I.M. Gabr, A.A. El-Asmy∗ Chemistry Department, Faculty of Science, Mansoura University, Egypt Received 8 April 2004; accepted 7 June 2004

Abstract Complexes of V(IV)O with N(4) ethyl and/or phenyl thiosemicarbazides have been prepared to study the role of substituents, on the two sides of thiosemicarbazide moiety, on the behavior of the complex formation. The study of ligands in solution reflected the dependence of their ionization values on the nature of the function groups neighboring the active sites. Two main (octahedral and square-pyramid) structures have been characterized for the solid complexes by the well known methods. There is some similarity between the structure and the color of the obtained complexes. Three modes of chelation were suggested for the investigated complexes. Complete disappearance of the nitrile group during the complex formation with cyano ligands is attributed to the promotion of water molecules to the cyano group. The intensity and position of the V O band in the IR spectra reflect not only the nature of the ligand but also the geometry of the complex formed. Some complexes were isolated as binuclear and confirmed by ESR spectra. The end product on thermal degradation of most complexes was VO2 . © 2004 Elsevier B.V. All rights reserved. Keywords: Thiosemicarbazide; Vanadyl ion; ESR; IR; UV–vis; Thermal analysis

1. Introduction Over the last three decades, there has been considerable interest in the chemistry of metal complexes of compounds containing NS and or NOS donors. Thiosemicarbazides have attracted a special attention due to their carcinostatic properties against a spectrum of transplaced neoplasm [1] and to their activity against certain types of tumors [2]. Transition metal complexes of these compounds have assumed an importance due to antituberclostatic activity [3] and medicinal properties [4]. Also, the importance is due to their use as analytical reagents in microdetermination of some metal ions [5], separation of some pollutants [6] and precious ions [7], preconcentration and speciation. Many complexes of thiosemicarbazones [8], diamines, pyrazolones, acetophenones [9], quinoloxine [10], carbohydrazone [11] and aldooxine [12] have been prepared with VO(II) ions. Complexes of the potentially tetradentate ligand, isonitrozo-acetylacetone ∗

Corresponding author. Tel.: +22 50 2261734; fax: +22 50 2246781. E-mail address: [email protected] (A.A. El-Asmy).

1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2004.06.027

dithiosemicarbazone, were prepared with different metal ions belonging VO(II) ion. The thiocarbonyl sulfur and imino nitrogen were the coordination sites inside a tetragonally or distorted octahedral structure [13]. In this work, a new series of vanadyl complexes with different thiosemicarbazide derivatives (Table 1) have been described. The general formula and the atom numbering of these ligands are presented in Scheme 1. 2. Experimental All reactants and solvents were pure compounds of analytical grade. 4-Methylthiosemicarbazide was purchased, from Merck and used without further treatment. 2.1. Preparation of ligands Two series of thiosemicarbazide derivatives were prepared comprising 4-ethyl- and 4-phenylthiosemicarbazides and their N(1) derivatives (phenyl-, cyanoacetyl- and trimethylammoniumchloride-acetyl). These compounds were synthesized as previously described [5] by reacting

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Scheme 1.

equimolar amounts of ethyl- or phenylisothiocyanate with hydrazine or its derivatives. The reactants were heated under reflux for a time depending on the type of hydrazine derivative. On cooling, white crystals were separated. The isolated ligands were characterized by spectra (IR and 1 H NMR) and elemental analysis. The name and abbreviation of the ligands are listed in Table 1. 2.2. Preparation of complexes The solid complexes were prepared by reacting the calculated amounts for 1:1 ratio of the ligands and vanadyl sulfate in aqueous–ethanol solution. The reaction pH was adjusted to ≈8 using sodium acetate and the mixture was heated under reflux for 4 h. The colored precipitate thus formed is removed by filtration, washed several times with bidistilled water, absolute ethanol and finally with diethylether. 2.3. Equipment and analysis Carbon and hydrogen content of the ligands and their complexes was determined at the microanalytical unit of Cairo University, Egypt. The vanadium content was determined complexometrically [14]. Thermogravimetric analysis was measured between 20 and 1000 ◦ C on a Shimadzu Thermogravimetric Analyzer (TGA-50). The nitrogen flow and heating rate were 20 ml min−1 and 10 ◦ C min−1 , respectively. The pH measurements were performed using a Metrohm E536 potentiograph equipped with a 665 Dosimat. The IR spectra were recorded as KBr disc on a Mattson 5000 FTIR Spectrophotometer. The 1 H NMR spectra in d6 DMSO for HPETS, H2 GTPTS and H2 CETS were recorded on a Varian Gemini Spectrophotometer (200 MHz). The UV–vis spectra of

the complexes were recorded on UV2 Unicam Spectrophotometer. The magnetic measurements were carried out on a Johnson–Matthey magnetic balance, UK. The ESR spectra of some complexes (DMF solution and powder) at 300 K were recorded on a Bruker EMX Spectrometer working in the Xband (9.78 MHz) with 100 KHz modulation frequency. The microwave power was set at 1 mw and the modulation amplitude at 4 G.

3. Results and discussion New series of VO(II) complexes have been synthesized upon reaction of VOSO4 with HMTS, HETS, HPTS, HPETS, HDPTS, H2 GT ETS, H2 GT PTS, H2 CETS and H2 CPTS. Some of the complexes were precipitated after the addition of sodium acetate. All are stable in air and have high melting points (>300 ◦ C). They are completely insoluble in common organic solvents and partially soluble in DMF and DMSO. The elemental analyses (Table 2) gave a suitable view about their formulae. 3.1. Infrared, electronic and magnetic measurements An insight about the mode of chelation for each ligand is gathered by comparing the IR spectra of the ligand with its complex and by considering the previous work on similar compounds. Studying the IR spectral data of the complexes (Table 3) one can predict three modes of chelation. The first mode is monodentate suggested for [VO (HPTS)2 (C2 H5 O)2 (C2 H5 OH)], [VO(HDPTS)(OH)2 (H2 O) (C2 H5 OH)] and [VO(MTS)(OH)(H2 O)2 ]. In [VO(HPTS)2 (C2 H5 O)2 (C2 H5 OH)], HPTS coordinates through the NH2 group (Fig. 1) based on the great lower shifts (91 cm−1 ) of the ν(NH2 ) and δ(NH2 ) in the complex spectrum. The ν(C S) and ν(N4 H) bands remain unaffected while the bands at 3407 and 1320 cm−1 are assigned to the ν(OH) and δ(OH) of ethanol molecule. The appearance of

Table 1 Name and abbreviation of RNHCSNHNHR R

R

Abbreviation

Name

CH3 C2 H5 C 6 H5 C2 H5 C6 H5

H H H C6 H5 C6 H5

HMTS HETS HPTS HPETS HDPTS

4-Methylthiosemicarbazide. 4-Ethylthiosemicarbazide. 4-Phenylthiosemicarbazide. 1-Ethyl-4-phenylthiosemicarbazide. 1,4-Diphenylthiosemicarbazide.

C2 H5

H2 GT ETS

1-(Trimethylammoniumchlorideacetyl)-4-ethylthiosemicarbazide.

C6 H5

H2 GT PTS

1-(Trimethylammoniumchlorideacetyl)-4-phenylthiosemicarbazide.

C2 H5

H2 CETS

1-Cynoacetyl-4-ethylthiosemi-carbazide.

C6 H4

H2 CPTS

1-Cynoacetyl-4-phenylthiosemi-carbazide.

N.M. El-Metwally et al. / Spectrochimica Acta Part A 61 (2005) 1113–1119

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Fig. 1. Infrared spectra of: (a) HPTS, (b) [VO(HPTS)2 (C2 H5 O)2 (C2 H5 OH)].

ν(V O) band at 1189 cm−1 offers the existence of vanadyl ion as V O [15]; its value is depicted when the vanadium atom is surrounded octahedrally. The new band at 400 cm−1 is assigned to ν(V N) while that appeared at 490 cm−1 is due to ν(V O) [16] of ethanol or ethanolate. In [VO(HDPTS)(OH)2 (C2 H5 OH)(H2 O)], the ligand binds through the N2 H group indicated by its shift (31 cm−1 ) to lower wavenumber and by the appearance of new bands at 3464 and 1380 cm−1 assigned to the ν(OH) and δ(OH) vibrations, respectively (the broadness of 3464 cm−1 band may be due to the overlapping with the ν(OH) of ethanol). The new bands at 390, 470 and 500 cm−1 attributed to ν(V N), ν(V O) and ν(V OH2 ) support the coordination centers. The complex [VO(MTS)(OH)(H2 O)2 ] is produced on adding sodium acetate during the complex formation. The mononegative monodentate behavior of HMTS is established by the disappearance of ν(C S), the appearance of ν(C N) at 1633 cm−1 (overlapped with the δ(NH2 ) band) and the 606 cm−1 band assigned to ν(C S) vibration [17]. The new band at 1380 cm−1 characteristic for δ(OH), and finally the observation of ν(V S), ν(V O) and ν(V O). The band position (970 cm−1 ) of ν(V O) agrees with the square-pyramid structure [18]. The electronic spectra of [VO(HPTS)2 (C2 H5 O) and [VO(HDPTS)(OH)2 (C2 H5 OH)H2 O] 2 (C2 H5 OH)] in DMF and Nujol mull show three bands (Table 4) assigned to the 2 B2 → 2 E (ν1 ), 2 B2 → 2 B1 (ν2 ) and 2 B2 → 2 A1 (ν3 ) transitions in an octahedral geometry [19]. The spectra do not altered in the two media. However, the spectrum of [VO(MTS)(OH)(H2 O)2 ] in DMF shows only one band assigned to the dxz –dxy transition in a square-pyramidal structure [20]. The magnetic moment values (Table 4) of [VO(HPTS)2 (C2 H5 O)2 (C2 H5 OH)] and [VO(MTS)(OH)(H2 O)2 ] fall within the range reported for

mononuclear complexes. However, the value (1.43 B.M) measured for [VO(HDPTS)(OH)2 (H2 O)(C2 H5 OH)] is lower than that reported (1.74–2.10 B.M) and may refer to the interaction of VO(II) with neighboring central ions [21]. The second mode of chelation (mononegative bidentat) is depicted for [VO(ETS)(OH)(H2 O)2 ] and [VO(PETS)2 (H2 O)]. This conclusion is supported by the disappearance of ν(N2 H) and ν(C S) vibrations coherently with the appearance of bands at 616 and 1605 cm−1 assigned to ν(C S) and ν(C N), respectively. The observable lower shift of the NH2 bands in the spectrum of [VO(ETS)(OH)(H2 O)2 ] and ν(N1 H) in the spectrum of [VO(PETS)2 (H2 O)] reveals their participation in coordination [22]. The appearance of new bands at 350, 410 and 1030 cm−1 attributed to ν(V S), ν(V N) and ν(V OH) vibrations, respectively. Such observations reveal that the main coordination site is the thiol sulfur while the second coordination site is the NH2 or the N1 H group. The electronic spectra of the two complexes in DMF show three bands similar to those reported for octahedral geometry [19]. Moreover, the spectra in Nujol are more or less the same as those recorded in DMF. The magnetic moments show normal value for [VO(PETS)2 H2 O] and subnormal for [VO(ETS)(OH)(H2 O)2 ]. The third mode of chelation is evaluated for [(VO)2 (H2 GT ETS)(C2 H5 OH)(SO4 )2 ] and [(VO)2 (HGT PTS)(OH) −(C2 H5 OH)SO4 ]. H2 GT ETS coordinates as a neutral tridentate molecule, while H2 GT PTS reacted in a mononegative tetradentate. The IR spectrum of [(VO)2 (H2 GT ETS)(C2 H5 OH)(SO4 )2 ] shows: (i) a lower shift (63 cm−1 ) of ν(C S) with no shift for ν(C O), (ii) a shift of thioamide(II) band by 44 cm−1 reveals the participation of N2 H in coordination, (iii) the appearance of new

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band at 1020 cm−1 due to the sulfate ions in a bidentate nature [23], (iv) the appearance of the stretching and bending (OH) vibrations of ethanol and (v) the observation of the ν(V S), ν(V N) and ν(V O) bands. The IR spectrum of [(VO)2 (HGTPTS)(OH)(C2 H5 OH)SO4 ] is characterized by: (i) the lower shift of ν(C S) and ν(N2 H) bands, (ii) the disappearance of ν(N1 H) and ν(C O) bands with the appearance of ν(C N) [24] and ν(C O) [25,26], (iv) the appearance of ν(OH) and δ(OH) bands, (v) the two new bands at 1185 and 1060 cm−1 assigned to ν(SO4 ) reveal its bidentate nature [27] as well as the appearance of ν(V O) at 976 cm−1 , which differ from that of mononuclear complex [28] and (vi) the appearance of the bands assigned to ν(V N), ν(V O) and ν(V OH) vibrations. These observations introduce H2 GT PTS as a chelating agent forming binuclear complex with VO(II). The electronic spectra of the two complexes recorded in Nujol and DMF show two distinguished bands (Table 3) assigned to the transitions in a square-pyramid [21,23] (structure 1). Their magnetic moments are low which refer to magnetic exchange interaction between the metal ions.

respectively. On the other hand, H2 CPTS changed to H3 CPTS (4-phenyl-1-carboxyacetylthiosemicarbazide) and formed [(VO)2 (HCPTS)(H2 O)4 (SO4 )]H2 O. The new ligand behaves as a binegative tetradentate which supported by the disappearance of amide band at 1697 cm−1 with the appearance of bands at 1130, 1634, 410, and 595 cm−1 attributed to ν(C O), ν(C N), ν(V N) and ν(V O), respectively. The appearance of a broad band centered at 3400 cm−1 prevents the NH’s characterization. The electronic spectra of the formed complexes in DMF show the bands (Table 3) characteristic for octahedral geometry around the vanadyl ion. The magnetic moment value of [VO(HCETS)(H2 O)3 ]H2 O (structure 2) is normal for one unpaired electron [20] where the value (1.3 BM) of [(VO)2 (HCPTS)(H2 O)4 (SO4 )]H2 O is low in agreement with the binuclear complexes having magnetic exchange interaction [20].

3.2. ESR spectra

Finally, it is interesting to discuss the complexes isolated with the ligands containing cyano group in more detail. The wonderful point is the complete disappearance of the nitrile group attributing to its complete hydrolysis [29] by promotion of water molecules. The condition of hydrolysis is suitable during the reaction of ligands with VOSO4 The medium becomes acidic where VO(II) ion may give the catalytic activity. The main feature is the disappearance of ν(CN) band with simultaneous appearance of new band due to ν(C O) of the carboxylic group produced from complete hydrolysis of CN group. The ν(OH) band of the carboxylic group is absent proving its deprotonation during the complexation. H2 CETS changes to H3 CETS (4-ethyl-1-carboxyacetylthiosemicarbazide) and gave [VO(HCETS)(H2 O)3 ]H2 O. H3 CETS coordinates as a binegative bidentate molecule through the deprotonated carboxylic OH group and the enolic oxygen atom. This conclusion is supported by the disappearance of the amide band at 1695 cm−1 , the appearance of bands at, 1123, 1630, 480, and 1040 cm−1 assigned to ν(C O), ν(C N), ν(M O) and ν(M OH) vibrations,

The room temperature (300 K) ESR spectra of [VO(MTS)(OH)(H2 O)2 ] (1) and [VO(HDPTS)(OH)2 (C2 H5 OH)(H2 O)] (2) in DMF solution give a typical eight-line pattern (Fig. 2a and b) similar to those reported for mononuclear vanadium molecule. In the powdered samples, the spectra showed the parallel and the perpendicular features which indicate axially symmetric anisotropy with well resolved sixteen-lines hyperfine splitting characteristic for the interaction between the electron and the vanadium nuclear spin (I = 7/2). The spin Hamiltonian parameters are calculated and given in Table 5. The calculated ESR parameters indicate that the unpaired electron (d1 ) of complex 1 is present in the dxy -orbital with square-pyramidal geometry [30]. The values obtained for complex (2) agree well with those reported for octahedral configuration around the VO(II) ion [31]. The ESR spectrum of [(VO)2 (HGT PTS)(OH)(C2 H5 OH)(SO4 )] consists of a single asymmetric line centered around g = 1.96 without resolved hyperfine structure (Fig. 2c). Generally, the mononuclear VO(II) ion (S = 1/2, I = 7/2) has a characteristic octet ESR spectrum showing the hyperfine coupling to the 51 V nuclear magnetic moment. Upon the existence of two vanadyl ions, the two electron spins may combine to a non-magnetic spin singlet

N.M. El-Metwally et al. / Spectrochimica Acta Part A 61 (2005) 1113–1119

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[23] A = −PK + 47 β2 P − (ge − g )P − 37 (ge − g⊥ )P A⊥ = −PK − 27 β2 P − ge − g =

11 14 (ge

− g⊥ )P

8α2 β2 γ E

where P = 136 G, λ = 170 cm−1 and E is the electronic transition energy of 2 B2 → 2 E. The calculated in-plane ␲-bonding (β2 ) values do not deviate much from unity. For most of the vanadyl complexes, β2 remains constant and spans in the 0.93–1.00 region. The results are consistent with Kiverlson’s conclusion [32] which suggests that the dxy orbital is essentially non-bonding while β2 remains constant. The lower values of α2 compared to β2 indicate that the in-plane ␴-bonding is more covalent. 3.3. Thermal studies

Fig. 2. ESR spectra of: (a) [VO(HDPTS)(OH)2 (C2 H5 OH)(H2 O)], (b). VO(MTS)(OH)(H2 O)2 ] and (c) [(VO)2 (H2 GT PTS)(OH)(C2 H5 OH)(SO4 )].

(S = 0) or a paramagnetic spin triplet state (S = 1); only the latter is ESR detectable. The superexchange interaction between the two vanadium ions lead to a configuration in which the two electron spins have an antiferromagnetic character, i.e. the singlet state is energetically favored. Therefore, the ESR spectrum of strongly coupled pairs has the form of a single broad line with inhomogeneous broadening. The data agree well with the subnormal magnetic moment values for those two complexes (Table 4) and confirm that the complexes contain the binuclear atoms. The molecular orbital coefficients α2 and β2 for (1) and (2) complexes were calculated using the following equations

The TGA thermogram of [VO(HPTS)2 (C2 H5 O)2 (C2 H5 OH)] shows a thermal stability till 178 ◦ C. A sudden decomposition stage with weight loss of 25.4 (Calcd. 25.6%) is attributed to the removal of C2 H5 OH and 2C2 H5 O. In the thermal curve of [VO(MTS)(OH)(H2 O)2 ] the first step (21.8% weight loss) is corresponding to the removal of the two coordinating water and the NH2 in the ligand at 334–409 ◦ C. The second step (42.8% weight loss) is referring to expel CH3 NHCSNH—as a second fragment at 409–491 ◦ C. VO2 is the residual part leaving 36% weight loss. The TGA curve of [VO)2 (H2 GTETS)(C2 H5 OH)(SO4 )2 ] shows a stability till 22 ◦ C and a gradual weight loss (29.1%) due to the loss of coordinating ethanol molecule with the fragment [(CH3 )3 N+ Cl− CH2 + C2 H5 ]. The stage ended at 70 ◦ C (18.6% weight loss) is due to the removal of HNCSNHNHCO. The remaining part is 2VOSO4 by 52.3%. [VO(HCETS)(H2 O)3 ]H2 O shows a decomposition stage (69–164 ◦ C) corresponding to removal of the hydrated water molecule by 5.3% weight loss. The stage ended at 423 ◦ C (43%) is correlated to the removal of three coordinating

Table 2 Elemental analysis of VO(II) complexes Compound

(C1) (C2) (C3) (C4) (C5) (C6) (C7) (C8) (C9)

Yield (%)

[VO(MTS)(OH)(H2 O)2 ] [VO(ETS)(OH)(H2 O)2 ] [VO(HPTS)2 (C2 H5 O)2 (C2 H5 OH)] [VO(PETS)2 (H2 O)] [VO(HDPTS)(OH)2 (C2 H5 OH)(H2 O)] [(VO)2 (H2 GT ETS)(C2 H5 OH)(SO4 )2 ] [(VO)2 (HGT PTS)(OH)(C2 H5 OH)SO4 ] [VO(HCETS)(H2 O)3 ]H2 O [(VO)2 (HCPTS)(H2 O)4 (SO4 )]H2 O

67 70 81 81 80 70 70 65 60

Analysis, found (Calcd.) C%

H%

V%

10.5 (10.7) 14.9 (15.1) 44.3 (44.7) 46.0 (45.7) 44.4 (44.1) 19.0 (19.1) 28.2 (28.2) 20.8 (21.1) 21.3 (21.1)

4.8 (4.9) 5.2 (5.5) 6.6 (6.4) 5.2 (5.5) 5.6 (5.7) 3.8 (4.0) 3.9 (4.2) 4.5 (4.6) 2.2 (2.4)

22.8 (22.7) 21.1 (21.4) 10.0 (9.5) 11.0 (10.7) 13.0 (12.5) 16.5 (16.2) 17.3 (17.1) 16.0 (15.7) 17.7 (17.9)

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Table 3 Infrared spectral bands of ligands and their VO(II) complexes Assignment L1

C1

L2

C2

L3

C3

L4

C4

L5

C5

L6

C6

L7

C7

ν(OH) ν(NH2 ) ν(N4 H) ν(N2 H) ν(N1 H) δ(NH2 ) ν(C N) ν(V O) ν(C S) ν(C S) δ(OH) ν(C O) ν(C O) ν(M O) ν(M N) ν(M S)

3433 3330 3185 – – 1633 1633 970 – 606 1380 – – 510 430 –

– 3345 3283 3193 – 1640 – – 780 – – – – – – –

3422 3282 3246 – – 1572 1605 1057 – 616 – – 1116 – 410 350

– 3301 3163 3109 – 1635 – – 780 – – – – – – –

3407 3210 3183 3113 – 1546 – 1189 780 – 1320 – – 490 400 –

– – 3336 3274 3166 – – – 776 – – – – – – –

3419 – 3331 – – – 1609 942 – 616 – – – – 420 375

– – 3279 3240 3188 – – – 776 – – – – – – –

3464 – 3282 3209 3171 – – 980 776 – 1380 – – 500 470 390

– – 3218 3134 3011 – – – 770 – – 1705 – – – –

3478

– – 3241 3193 3150 – – – 800 – – 1704 – – – –

3443 – 3229 3153 – – 1627 976 789 – 1380 – 1050 440 410 385

– 3331 3187 3143 – 1640 – – 810 – – – – – – –

3233 3100 3028 – – 978 707 – 1380 1708 480 420 380

L8

C8

L9

C9

–

–

–

3322 3267 3159 – –

3311 3234 – – 1630 975 795

3339 3282 3222 – –

800 – – 1695 – – –

– – 1123 480 – –

800 – – 1697 – – –

3427

– 1634 972 805 – – – 1130 595 410 –

Table 4 Magnetic moments an electronic spectral data of VO(II) complexes Compound

Color

µeff (BM)

State

d–d transtion bands (cm−1 )

Charge transfer (cm−1 )

Supposed structure

[VO(HPTS)2 (C2 H5 O)2 (C2 H5 OH)]

Blue

2.10

DMF Nujol

12195(␯1 ); 16,260(␯2 ) 12,315 (␯1 ); 18,150(␯2 )

27,470(␯3 ) 24,040(␯3 )

Octahedral

[VO(HDPTS)(OH)2 (C2 H5 OH)(H2 O)]

Green

1.43

DMF Nujol

14,280; 17,820 12,750; 17,390

25,320 20,080

Octahedral

[VO(MTS)(OH)(H2 O)2 ]

Dark green

1.66

DMF

11,100

[VO(ETS)(OH)(H2 O)2 ]

Faint green

0.95

DMF Nujol

16,665; 20,830 14,410; 22,220

32,895 27,775

Octahedral

[VO(PETS)2 (H2 O)]

Green

2.20

DMF Nujol

12,515; 17,920 12,360; 17,700

28,655

Octahedral

[(VO)2 (HGTETS) (C2 H5 OH)(SO4 )2 ]

Dark green

0.81

DMF Nujol

11,110(␯1 ) 11,110

27,930(␯3 ) 26,950

Square-pyramid

[(VO)2 (H2 GT PTS)(OH)(C2 H5 OH)(SO4 )]

Dark green

0.70

DMF Nujol

11,110(␯1 ) 11,110

28,170 26,315

Square-pyramid

[VO(HCETS)(H2 O)3 ]H2 O

Blue

1.94

DMF

12,500; 16,800

27,240

Octahedral

[(VO)2 (HCPTS)(H2 O)4 (SO4 )]H2 O

Blue

1.30

DMF

12,250; 18,590

27,550

Octahedral

Square-pyramid

water and C2 H5 NHCSNH as a terminal part in the ligand. The final stage ended at 643 ◦ C (24.7%) is due to the loss of NCOCH2 OC leaving VO2 as end product with 26.8%. Finally, the TGA curve of [(VO)2 (HCPTS)(H2 O)2 (SO4 )2 ] H2 O shows a step ended at 307 ◦ C by 20.4 (20.7%) weight loss due to the removal of the hydrated and coordinated water molecules as well as the phenyl group in the ligand. The final residue after 600 ◦ C is the thermally stable six-membered ring [(VO)2 (C3 H2 O3 )] by 35.0 (33.2%).

equations [33]. Plotting n´ A against the pH gives the protonligand formation curve. The ionization constants of each ligand (log K1 and or log K2 ) are calculated at n´ A values of 0.5 and or 1.5. The calculated values are given in Table 6. In H2 CPTS, the value of n´ A at 0.5 is not detected, so the pK1 value is evaluated by the mid-point method [30] using the following equation:

3.4. pH-metric studies

It is interesting to note that the ionization values of HMTS, HETS and HPTS have approximately the same. H2 GT PTS and H2 CPTS are distinguished by low values which may be attributed to the stronger electron withdrawing groups neighboring the ionization center. The ethyl derivatives have pK values higher than that of phenyl analogue.

The pH-metric measurements were carried out to calculate the protonation constants of the ligand and the stability constants of their complexes. The n´ A , n´ and pL values were calculated at different pH values using the Iriving–Rossotti

log K1 K2 = 2pH(at nA = 1)

N.M. El-Metwally et al. / Spectrochimica Acta Part A 61 (2005) 1113–1119 Table 5 The ESR parameters of VO(II) complexes at room temperature

References

Complex

g

g⊥

A × 10−4

A⊥ × 10−4

α2

β2

(1) (2)

1.94 1.93

1.98 1.97

180 173

78 70

0.54 0.68

0.93 0.99

Table 6 The deprotonation constants of the ligands and the formation constants of their VO(II) complexes Compound

H+ pK1

HMTS HETS HPTS HPETS HDPTS H2 GT ETS H2 GT PTS H2 CETS H2 CPTS a

10.56 10.70 10.33 8.20 7.70 6.35 5.25 10.85 10.80

VO(II) pK2

5.30 4.95 5.20 5.60

pK1

pK2

pK3

βa

8.80 9.30

7.20 8.10 8.40 3.30 6.90 8.85 5.30 5.40 4.90

4.20

20.2 17.40 15.20 9.60 14.25 26.85 16.40 16.00 9.40

6.30 7.35 9.85 6.10 5.85

6.80

8.15 5.00 4.75 4.50

1119

β is the overall stability constant.

The metal-ligand stability constants were obtained from the curves drawn between n− and pL using half method at n− values of 0.5, 1.5 and 2.5 for 1:1, 1:2 and 1:3 complexes, respectively. The obtained values clearly show that the values of β1 are found higher than that of β2 and β3 for the same complex. This fact is explained by the available sites for binding the first ligand molecule are freely than that used for binding the second or the third ligand. The variation in the stability may be due to the ability for ionization process of such ligands.

4. Conclusion The investigated thiosemicarbazides introduced new vanadyl complexes having octahedral and square-pyramidal structures. The colour and ν(V O) vibration gave more distinction between the two structures. The ν(V O) appeared at ∼1190 cm−1 in the octahedral complexes and at ∼980 cm−1 in the square–pyramidal complexes. The magnetic moment and the ESR data agree well with the binuclear complexes. The cyano group changed to carboxylic one upon its complete hydrolysis by promotion of water molecules. The calculated stability constants of the complexes in solution proved the ability of such ligands to the ionization process and showed the effect of substituents on the complex formation.

[1] B.L. Feedlander, A. Froust, J. Am. Chem. Soc. 18 (1952) 638. [2] H.G. Petering, H.H. Buskik, G.E. Underwood, Cancer Res. 64 (1964) 367. [3] J.P. Scovill, D.L. Kalyman, C.E. Franchino, J. Med. Chem. 25 (1982) 1261. [4] A.A. El-Asmy, A.S. Babaqi, A.A. Al-Hubishi, Transition Met. Chem. 12 (1987) 248. [5] S.E. Ghazy, M.A. Kabil, A.A. El-Asmy, Y.E. Sherif, Afinidad 456 (1995) 128. [6] M.A. Kabil, S.E. Ghazy, A.A. El-Asmy, Y.E. Sherif, Anal. Sci. 12 (1996) 431. [7] M.A. Kabil, S.E. Ghazy, A.A. El-Asmy, Y.E. Sherif, Fresenius, J. Anal. Chem. 357 (1997) 401. [8] A.F. Petrovic, V.M. Leovac, B. Ribar, Transition Met. Chem. 11 (1986) 207. [9] P.R. Athappan, G. Rajagopal, Ind. J. Chem. 36A (1997) 317. [10] D.S. Rani, P.V. Ananthalakshmi, V. Jayatyagaraju, Ind. J. Chem. 38A (1999) 843. [11] D.U. Warad, C.D. Statish, V.H. Kulkarni, C.S. Bajgur, Ind. J. Chem. 39A (2000) 415. [12] M.F. Hassan, A.M. Seyam, H.A. Hodali, Synth. React. Inorg. Met. Org. Chem. 26 (1996) 181. [13] S.N. Shetti, A.S. Murty, Transition Met. Chem. 23 (1998) 467. [14] T.S. West, Complexometry with EDTA and Related Reagents, third ed., 1969 (pp. 213–214). [15] I. Aiello, M. Ghedini, C. Zanchini, Inorg. Chim. Acta 255 (1997) 133. [16] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, Wiley, New York, 1970. [17] D.X. West, A.K. El-Sawaf, G.A. Bain, Transition Met. Chem. 23 (1) (1998). [18] P.R. Athappan, G. Rajogopal, Ind. J. Chem. 36 A (1997). [19] S. Bhattacharya, T. Ghosh, Ind. J. Chem. 38 A (1999) 601. [20] S.K. Sengupta, O.P. Pandey, G.K. Pandey, Ind. J. Chem. 37 A (1998) 644. [21] B.T. Thaker, J. Lekhadia, A. Potel, P. Thaker, Transition Met. Chem. 19 (1994) 623. [22] H. Keypour, H. Khanmohammadi, K.P. Wainwright, M.R. Taylor, Inorg. Chim. Acta 357 (2004) 1283. [23] D.U. Warad, C.D. Statish, V.H. Kulkarni, C.S. Bajgur, Ind. J. Chem. 39 A (2000) 415. [24] Y. Zhang, W. Ruan, X. Zhao, H. Wang, Z. Zhu, Polyhedron 22 (2003) 1535. [25] R. Karvembu, S. Hemalatha, R. Prabhakaran, K. Natarajan, Inorg. Chem. Commun. 6 (2003) 486. [26] R. Karmakar, C.R. Choudhury, G. Bravic, J. Sutter, S. Mitra, Polyhedron 23 (2004) 949. [27] H.S. Yadav, Polyhedron 12 (1993) 313. [28] M.M. Mostafa, A.M. Shallaby, A.A. El-Asmy, J. Inorg. Nucl. Chem. 43 (1981) 2992. [29] A.M. Mostafa, M.Sc. Thesis, Mansoura University, Egypt, 1992. [30] N. Raman, A. Kulandalsamy, C. Thangaraja, Transition Met. Chem. 28 (2003) 29. [31] R. Poonguzhali, R. Venkatesan, T.M. Rajendiram, P.S. Rao, R.V.S.S.N. Ravikumar, Y.P. Reddy, Cryst. Res. Technol. 35 (2000) 1203. [32] D. Kiverlson, S.K. Lee, J. Chem. Phys. 41 (1964) 1896. [33] H.M. Irving, H.S. Rossotti, J. Chem. Soc. (1954).