Polymer complexes. LVI. Supramolecular architectures consolidated by hydrogen bonding and π–π interaction

Spectrochimica Acta Part A 86 (2012) 547–553

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Polymer complexes. LVI. Supramolecular architectures consolidated by hydrogen bonding and ␲–␲ interaction A.A. El-Bindary, A.Z. El-Sonbati ∗ , M.A. Diab, M.E. Attallah Chemistry Department, Faculty of Science (Demiatta), Mansoura University, Demiatta, Egypt

a r t i c l e

i n f o

Article history: Received 3 September 2011 Received in revised form 25 October 2011 Accepted 9 November 2011 Keywords: Acryloyl hydrazine Supramolecular polymer complexes ESR and thermal analysis studies

a b s t r a c t The amidation of aliphatic amine with acryloyl chloride in dry benzene as a solvent has been performed. Moreover, the polymer complexes have been prepared and structurally characterized by analyses, molar conductance measurements, magnetic susceptibility measurements, spectral techniques like IR, UV, NMR, ESR and thermal methods. Acryloyl hydrazine (AH) has been shown to behave as a bidentate ligand via its nitrogen (NH2 of hydrazine group) and C–O/C O (acryloyl group) in polymer complexes, all of which exhibit supramolecular architectures assembled through weak interaction including hydrogen bonding and ␲–␲ stacking .The magnetic and spectral data indicate a square planar geometry for Cu2+ complexes and an octahedral geometry for Co(II) and UO2 (II). The ESR spectral data of the Cu(II) complexes showed that the metal–ligand bonds have considerable covalent character. The thermal stability was investigated using thermogravimetric analysis. The results showed that the polymer complexes are more stable than the homopolymer. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Recently, the polymeric metal complexes [1–4] with biocoordination ligands have attracted considerable interests, because they gather the advantage of inorganic metal ions and conjugation polymer and have many advantages compared with inorganic and organic/aliphatic small molecules complexes, such as good thermal stability, process ability and easy film-forming. The polymeric metal complexes play an important role in light-emitting materials [1,2,5], which have nice electronic transfer functions, caused by the intramolecular charge transfer transitions from ligand-toligand (LLCT), ligand-to-metal (LMCT), and have also good whole transfer functions from the conjugation bone. In the laboratories of Diab and El-Sonbati, the coordination behaviour, chemical equilibria, thermal analysis and electron paramagnetic resonance of novel supramolecular d-block polymer complexes have been investigated in depth [6–12]. Interest in coordination chemistry is increasing continuously with the preparation of organic/aliphatic ligands containing a variety of donor groups and it is multiplied manifold when the ligands have biological importance [7,6,8–10]. The number and diversity of nitrogen, oxygen and/or sulfur chelating agents used to prepare new coordination and organometallic compounds has increased rapidly during the past few years [10–13].

∗ Corresponding author. Tel.: +20 160081581; fax: +20 572403868. E-mail address: [email protected] (A.Z. El-Sonbati). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.11.009

The ligands that contain an amide bond are capable of keto and enol tautomerism and are coordinated to a metal ion in neutral and/or deprotonated form. However, the coordination behaviour of ligands depends on the metal ion, the pH of the medium and the reaction condition [10–13]. A literature survey has revealed that no work appears to have been reported on the synthesis and characterization of the metal derivatives of the homopolymers. In view of the above, we were, therefore, intrigued by this notion to synthesize and characterize the novel homopolymer and their metal derivatives. Due to the sensitivity of metal complexes towards physical, electrochemical and optical sensors, the integration of coordinative ligands into macromolecules has become an important approach for the preparation of novel functional polymers. Therefore, chelating compounds such as acryloyl hydrazine are being utilized as suitable ligands. They enable the formation of rigid coordination polymers. In order to obtain well-defined supramolecular polymer structures, maintained and controlled polymerization methods may be performed, using functionalized units as initiators [6–8]. 2. Experimental 2.1. Materials Hydrazine hydrate and acryloyl chloride (AC) (Aldrich chemical Co. Inc.) were used without further purification. 2,2 -Azobisisobutyronitrile (AIBN) (Aldrich chemical Co. Inc.) was purified by dissolving in hot ethanol and filtering [14]. The

A.A. El-Bindary et al. / Spectrochimica Acta Part A 86 (2012) 547–553

H2C

CH

H 2C

C

CH C

NH

O 8.56 10.21 13.23 14.31 18.20 9.56

Molar conductance (−1 mol−1 cm2 )

548

(AH)

N

HO

NH 2

NH 2

– 17.66 (17.96) – – – 42.93 (43.43) 14.50 (14.94) 12.65

H 2C

– 39.55 (40.12) – 29.68 (29.92) 39.85 and 29.69(35.21) – 57.52 (58.00) –

O H

enol

H 2C

CH C

O

NH

CH

H

C N

H H

N H

N H

Fig. 1. Synthesized monomer AH in tautomeric form.

solution was left to cool. The pure material then being collected by filtration and dried. MO*: Residual weight of the polymer complexes at 1000 ◦ C, dia: diamagnetic. a Microanalytical data as well as metal estimations are in good agreement with the stoichiometry of the proposed complexes. b The excellent agreement between calculated and found data supports the assignment suggested in the present work.

– 31.61 (31.82) 23.75 (22.97) 22.23 (22.52) 29.73 and 22.5(26.21) 22.40 (22.09) 44.80 (45.35) 42.50 (43.80) 32.56 (32.58) 13.93 (13.72) 10.47 (10.68) 21.14 (21.08) 14.21 and 21.16(18.22) 11.29 (1089) 11.16 (11.32) 10.00 (10.00) 6.98 (6.93) 2.98 (2.69) 4.40 (4.43) 5.29 (5.33) 3.55 and 5.29(4.65) 2.42 (2.21) 2.78 (2.69) 3.21 (3.28) PAH 1 AH–CuCl2 2 AH–Cu(OAc)2 3 AH–CoCl2 4 AH–NiCl2 5 AH–FeCl3 6 AH–CdCl2 7 AH–UO2 (OAc)2 8

41.86 (41.81) 17.91 (17.61) 31.40 (31.23) 27.18 (27.23) 18.26 and 27.21(23.74) 14.50 (14.27) 14.35 (14.31) 21.43 (21.30)

MO* M N H C

Analysis, % (Calc./Found) Polymer

Table 1 Elemental analysis,a residual weights and molar conductance of the PAH homopolymer and polymer complexes (for molecular structures see Fig. 2).b

Cl

keto

2.2. Preparation of acryloyl hydrazine (HL) monomer HL monomer was prepared by the reaction of equimolar amounts of AC and hydrazine hydrate in dry benzene until the evolution of hydrogen chloride ceased. Microanalysis for C3 H6 N2 O. Found C, 41.8; H, 6.9; N, 32.6%. Calc. C, 41.9; H, 6.9; N, 32.6%. 2.3. Preparation of poly (acryloyl hydrazine) (PHL) homopolymer PHL homopolymer was prepared by free radical initiation of HL using 0.1%, w/v AIBN as initiator and DMF as solvent for 6 h. The polymer product was precipitated by pouring in distilled water and dried in a vacuum oven for several days at 40 ◦ C. The PHL homopolymer has been characterized by IR, 1 H NMR. 2.4. Preparation of the polymer complexes Polymer complexes were prepared by refluxing anhydrous Cu(II), Ni(II), Co(II), Cd(II), UO2 (II) and Fe(III) salts (0.001 mole) with the corresponding ligand (0.001 and/or 0.002 mole) in 20 ml DMF as a solvent, and 0.1% (w/v) AIBN as initiator. The resulting mixture was heated at reflux for ∼8 h. The hot solution was precipitated by pouring in large excesses of distilled water containing dilute hydrochloric acid, to remove the metal salts that were incorporated into the polymer complexes. The polymer complexes (2–8, see Table 1) were filtered, washed with water, and dried in a vacuum oven at 40 ◦ C for several days. 2.5. Measurements C, H, and N microanalyses were carried out at the Cairo University Analytical Center, Egypt. The metal content of the HL ligand was determined by complexometric titration against EDTA after decomposition with concentrated nitric acid [9–13,15]. The 1 H NMR spectrum was obtained with a Jeol FX90 Fourier transform spectrometer with DMSO-d6 as the solvent and TMS as an internal reference. Infrared spectra were recorded using Perkin-Elmer 1340 spectrophotometer. Ultraviolet–Visible (UV–Vis) spectra of the

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549

H

H

C

CH 2

C

Cl

CH 2

n

C

n

C

O

N

M

NH 2

H 2O H 2N

N

Co

NH 2 OH 2

O

N

OH 2

O

C (

C

CH 2

M= Cu(II) and Cd(II)

)n

H structure II

structure I

H H CH2 CH2

C

n

C

X

O

NH

Cu

NH 2

C

n

C

NH

O

X H 2N

M

HN

O

NH2 X

C

X (

X= OAc

C

CH2

)n

H

structure III

X= OAc , M= UO 2 structure IV Cl

Cl O

Cl Fe

Fe N H2

Cl Cl

H2 N

O Cl

structure V Fig. 2. Proposed structure of polymer complexes.

polymer were recorded in nuzol solution using a Unicom SP 8800 spectrophotometer. The magnetic moment of the prepared solid complexes was determined at room temperature using the Gouy‘s method. Mercury(II) (tetrathiocyanato)cobalt(II), [Hg{Co(SCN)4 }], was used for the calibration of the Gouy tubes. Diamagnetic corrections were calculated from the values given by Selwood [16] and Pascal’s constants. Magnetic moments were calculated using the equation, eff = 2.84 [T M coor. ]1/2 . EPR measurements of powdered samples were recorded at room temperature (Tanta University, Egypt) using an X-band spectrometer utilizing a 100 kHz magnetic field modulation with diphenylpicrylhydrazyle (DPPH) as a reference material. TG measurements were made using a Du Pont 950 thermobalance. Ten milligram samples were heated at a rate of 10 ◦ C/min in a dynamic nitrogen atmosphere (70 ml/min); the sample holder was boat-shaped, 10 × 5 × 2.5 mm deep; the temperature measuring thermocouple was placed within 1 mm of the holder. The halogen content was determined by combustion of

the solid complex (30 mg) in an oxygen flask in the presence of a KOH–H2 O2 mixture. The halide content was then determined by titration with a standard Hg(NO3 )2 solution using diphenyl carbazone indicator.

3. Results and discussion 3.1. Structure of the ligand (HL) On the basis of IR and NMR spectral studies, an keto–enol tautomeric structure has been established for the ligand (HL) (Fig. 1). The IR spectrum of ligand does not show band around 3500 cm−1 corresponding to OH group. This indicates that the ligand exist in keto form in solid state. However the 1 H NMR spectrum of ligand shows a singlet at 10.2 ppm corresponding to OH group which suggest the existence of ligand in enolic form in solution (Fig. 1).

550

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3.2. Metal polymer complexes

3.5. Magnetic and electronic spectral studies

The results of the elemental analyses listed in Table 1 are in good agreement with those calculated for the suggested formulae of the polymer complexes. The formation of these polymer complexes may proceed according to the following equation:

3.5.1. Copper(II) polymer complexes The room temperature magnetic moments for copper(II) polymer complexes (Table 2) are 1.85 and 1.79 BM for polymer complexes, (2) (structure I, Fig. 2) and (3) (structure III, Fig. 2), respectively, characteristic of one unpaired electron. This indicates the presence of low-lying excited term, which mixes some of its orbital angular momentum with the spin angular momentum of the ground state via spin orbital coupling [19]. This mixing is quit common for copper(II) complexes with distorted ligand fields [19]. The electronic spectra of both polymer complexes are similar and display bands at 16,400, 15,300 cm−1 (2 B1g → 2 Eg ) for chloro complex (structure I, Fig. 2) and at 16,550, 15,050 cm−1 (2 B1g → 2 B2g ) transitions, for the acetate complex (structure III, Fig. 2) (Table 2), in D4h symmetry. These bands are due to d–d transitions and consistent with that reported for copper(II) ions in square planar ligand fields [20] with a bidentate and/tridentate ligands. In square planar field three possible transitions are expected. The third band due to 2 B1g → 2 A1g could not be identified but it may be responsible for the asymmetric nature of the lower energy band.

MCl2 + HL → [M(L)(Cl)(OH2 )] (M = Cu(II) or Cd(II)) (structure I, Fig.2)

CoCl2 + HL → [Co(L)(OH2 )2 ] (structure II, Fig.2) M(OAc)2 + HL → [M(HL)n (OAc)2 ] (M = Cu(II), n = nill; UO2 , n = 2 (structures III and IV, Fig.2) FeCl3 + HL → [Fe(HL)Cl3 ]2

(structure V, Fig.2)

Formation of the polymer complexes has been done on the basis of their elemental analytical data, molar conductance values and magnetic susceptibility data. All the complexes shoe 1:1/1:2 metal:ligand stoichiometry. They are non-hydroscopic, decompose and possess good keeping qualities. All the polymer complexes are insoluble in common organic solvents except DMF and DMSO. The value of magnetic moments calculated with the help of measured value of magnetic susceptibility indicates that the polymer complexes are paramagnetic in nature except Cd(II) and UO2 (II) polymer complexes. Analytical data of the ligand and their polymer complexes are given in Table 1 and are in well agreement with the expected values (see Fig. 2). 3.3. Molar conductance The molar conductance values in DMF as 25 ◦ C (Table 1) for the polymer complexes were found to be in the range 8.75–18.20 −1 mol−1 cm2 . The relatively low values indicate the non-electrolytic nature of these complexes [17]. This can be accounted for the satisfaction of the bi- or tri-valency of the metal by the chloride or acetate. This implies the coordination of the anions to the metal ion centers. 3.4.

1H

NMR spectra

The 1 H NMR spectrum of PAH homopolymer exhibit three broad signals centered at NH2 (5.3 ppm), OH (10.2 ppm) and imino protons (11.7 ppm) assigned for hydrogen bonded OH or NH protons (Fig. 1). These signals were disappeared in the presence of D2 O. The last two signals were disappeared in the spectrum of Cd(II) polymer complex. This was attributed to the ligand is capable of exhibiting keto–enol tautomerism and coordination of the enolization OH to the metal ion [8,9]. Also, the spectrum of complex showed abroad signal at ı 3.38 ppm which attributed to the presence of coordinated water molecule. The spectrum exhibit also a singlet at ı 2.2 and ı 1.9 ppm correspond to methylene and methane protons, respectively, are in agreement with the presence of AH in its enolic form in solution. The NMR spectrum of AH monomer showed the expected peaks and pattern of the vinyl group (CH2 CH), 6.25 ppm (dd, J = 17, 11 Hz) for the vinyl CH proton and proton ı 5.12 ppm (AM part of AMX system dd, J = 17, 1 Hz) for the vinyl CH2 protons, respectively. These peaks disappeared on polymerization while a triplet at ı 1.86 ppm (t, J = 7 Hz) and a doublet at 1.80 ppm (d, J = 7 Hz) appeared, indicating that the polymerization of AH monomer occurs on the vinyl group [6,18]. It is worth noting that the rest of the proton spectrum of the monomer and polymer remain almost without change.

3.5.2. ESR spectra The spectra of the copper(II) polymer complexes (2 and 3) show typical axial behaviour with slightly different g and g⊥ values. In these Cu(II) polymer complexes tensor values of g > g⊥ > ge (2.0023), are consistent with a dx2 −y2 ground state [13]. The geometric parameter G, which is a measure of the exchange interaction between the copper centers in the polycrystalline compound, is calculated using the equation reported by others [13]. If G > 4, exchange interaction is negligible (2 and 3), but if G < 4, considerable exchange interaction is indicated in the solid complex. The various Hamiltonian parameters have been calculated for polymer complexes [g = 2.321, g⊥ = 2.078, A = 145 for (2) and g = 2.330, g⊥ = 2.071, A = 145 for (3)]. It has been reported that g values of copper(II) complexes can be used as a measure of the covalent character of the metal–ligand bond. If the value is more than 2.3, the metal–ligand bond is essentially ionic and the value less than 2.3 is indicative of covalent character [13]. A part from this, the covalency parameter (˛2 ) has been calculated using the following equation [21]. ˛2 =

A 3 + (g − 2.0023) + (g⊥ − 2.0023) + 0.04 7 0.035

The covalency parameter [˛2 = 0.795 for (2) and 0.803 for (3)] indicates considerable covalent character for the metal–ligand bond [13]. Also, The trend g > g⊥ > ge observed for this complexes indicated that the unpaired electron is most likely in the dx2 −y2 orbital. The empirical ratio g /A is frequently used to evaluated distortions in tetra-coordinated copper(II) complexes [22]. The values of the g /A ratio for polymer complexes (2 and 3) (ca. 160) indicate nearly square planar, environments. Based on this observation, a square planar geometry is proposed for the polymer complexes. The ESR study of the copper(II) polymer complexes has provided supportive evidence to the conclusion obtained on the basis of electronic spectra and magnetic moment values. 3.5.3. Cobalt(II) polymer complexes Co(II) polymer complex (4) (structure II, Fig. 2) (Table 2) exhibits a typical spectrum for octahedral species in the solid state [20,23]. Two main bands (2 and 3 ) transitions are observed, the band 1 , due to transition 4 T1g (F) → 4 T2g (F) which is usually under 10,000 cm−1 , as ligand field parameters, 10Dq, B and ˇ were calculated using the following equations the following equations: 10Dq = (22 − 3 ) + 15B

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551

Table 2 Electronic spectral bands and magnetic moments of the polymer complexes (for molecular structures see Fig. 2). Spectral bands (cm−1 )

Assignments



2 3 4

16,400; 15,300 16,550; 15,050 13,550 18,365

1.85 1.79 5.23

5

17,100 27,700 22,720 15,680 19,980 16,000–21,000 ∼24,690

B1g → Eg B1g → 2 B2g [4 T1g (F) → 4 A2g (F) (2 )] [4 T1g (F) → 4 T1g (P) (3 )] 10Dq = 7261 cm−1 , B = 867 cm−1 , ␤ = 0.88 3 A1g → 3T2g (F) 3 A2g → 3 T1g (P) 3 A1g → 1 B2g 2 T2 → 4 A2 ␲–t2g L → M and CT 1 u  g → 3 ␲u

Compounda

6

8 a b

2

2

2

eff.b (BM)

1.89

2.10

dia.

See footnote Table 1. Measured at room temperature.

3.6. IR spectra B=

1 1/2 [7(3 − 22 ) ± 3{8132 − 162 (2 − 3 )} ] 510

10Dq = 2 − 1 340Dq2 = 18(2 + 3 )Dq + 2 3 = 0 B=

1 (3 + 2 − 30Dq) 15

ˇ=

B B◦

The calculated values of the ligand field parameters are in good agreement with the predicted values for octahedral polymer complexes of Co(II) [24]. The nephelauxetic ratio ˇ for the polymer complex (4) suggesting an ionic character of cobalt(II)–ligand bonds [25]. The room temperature magnetic moment value, 5.23 BM demonstrates that the Co(II) polymer complex is paramagnetic and has a high-spin octahedral configuration. 3.5.4. Nickel(II) polymer complex The electronic spectrum of AH–NiCL2 polymer complex (5) (Table 2) shows bands at 17,100 and 27,700 cm−1 characteristic of a distorted octahedral structure. They may be assigned to the 3 A → 3 T (F) and 3 A → 3 T 2g 2g 2g 1g (P) transition, respectively. There is also a band at 22,720 cm−1 similar to the one reported for square planar Ni(II) complexes and may be assigned to 3 A1g → 1 B2g transition [26]. Although such transition is expected to be forbidden according to the selection rules, some intensity comes to this band from the near stronger one [20]. The magnetic moment of the AH–NiCl2 polymer complex as represented in Table 2 was found to be 1.89 BM, suggesting that the complex forms a mixture of octahedral and square planar structures. 3.5.5. Iron(III) polymer complex The spectrum of AH–FeCl3 (6) (structure V, Fig. 2)) (Table 2) display bands at 15,680, 19,980 and 22,720 cm−1 . The room temperature magnetic moment of 2.2 BM indicates a low spin octahedral iron(III) complex [27]. In an octahedral ligand field around iron (III), the in the 16,000–21,000 cm−1 range are commonly due to L → M CT transition [20]. Also, in this iron polymer complex, the shoulder at 15,680 and the band at 19,980 cm−1 are due to 2 T → 4 A and ␲–t 2 2 2g transitions. The spectrum of the Cd(II) polymer complex (7) (structure 1, Fig. 2) exhibited bands assigned to ligand ␲–␲* and L → M charge transfer [20]. This polymer complex is diamagnetic as expected. The metal normally prefers tetrahedral coordination.

The IR spectrum of ligand exhibits bands at 3350 (w); 3280 (w); 1650 (s); 810 (s), 515 (m) and 495 (m) cm−1 [28], due to different modes of vibrations of NH2 group, namely , ı, , and  respectively. These bands are affected in position and shape on complexation with metal ions. So, the NH2 group (exocyclic NH2 nitrogen) is coordinated to the metal ion in polymer complexes [26]. The shift of band (NH2 ) at 672 cm−1 on complexation indicated that the NH2 is involved in chelation [29]. In the IR spectra of the polymer complexes (except 3, 6 and 8) the C O (1661 cm−1 ) stretching vibration corresponding to the free ligand are not observed. This fact, along with the presence of a medium intensity band in 1385–1395 cm−1 range, assignable to C–O, indicates that the deprotonated ligand is predominantly in the enolate in the polymer complexes (see Fig. 1). These observations support the formation of M–O bonds via deprotonation. So, the H-bond-OH group has been replaced by the metal ion. On complex formation, there is also a characteristic band at ∼1635 cm−1 due to C N group. The IR spectra of copper and uranyl acetate polymer complexes show downward shift in (C O) and (NH2 ) in comparison with the free ligand. This is indicating coordination through oxygen and nitrogen, respectively [28]. Hence, it may be concluded that in these polymer complexes, the ligand is behaving as neutral bidentate ON donor through the exocyclic oxygen and the terminal nitrogen of hydrazine. The bands corresponding to (M–N) and (M–O) are observed in the range 343–464 cm−1 and 450–550 cm−1 [30]. The dioxouranium(VI) compound (7) exhibits sym (O U O) and asym (O U O) at 794 and 916 cm−1 , respectively, the usual range for such complex [1,13] being asym 870–950 and sym 780–855 cm−1 . The force constant (FU–O ) value is 6.78 mdynes/Å, which agree well with the force constant values of similar dioxouranium(VI) complexes [10,13]. The U–O bond distance calculated ˚ well within from the equation, RU–O = 1.17 + 1.08f−1/3 is 1.73 A, ˚ observed for dioxouranium(VI) comthe usual range (1.60–1.9 A) plexes [1,13]. The dioxouranium complex exhibits a new band at 24,690–24,510 cm−1 , which is assigned to the 1 u g → 3 ␲u transition, typical of OUO for the symmetric stretching frequency for the first excited state. The elemental analysis, IR, and the electronic spectra data indicate that AH reacts with CuCl2 , Cu(OAc)2 , FeCl3 and CdCl2 in a 1:1 ratio (structures I, III and V, Fig. 2)) and with CoCl2 and UO2 (OAc)2 in 2:1 molar ratios (structures II and IV, Fig. 2). The AH–NiCl2 polymer complex is a mixture of both structures (I and II). 3.6.1. Vibration modes of the inorganic Co-ligand The acetate polymeric complexes display bands at 1642–1638 and 1355–1348 cm−1 due to the symmetric and asymmetric stretching vibrations of the acetate group [6] with  = 290 cm−1

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Table 3 Weight loss percentage for the homopolymer of PAH and AH–metal chloride polymer complexes. Polymer

Volatilization temperature (◦ C)

First stage ◦

Tmax , C PAH AH–CuCl2 AH–CoCl2 AH–NiCl2 AH–CdCl2

112 130 127 128 132

207 155 151 156 158

Second stage Wt. loss, % 47 11 14 12 9

characteristic for monodentate nature of this group [6]. The Fe(III) polymer complex show (Fe–Cl) frequencies that seem too low for terminal Fe–Cl bonds and corresponding to bridging chlorine (∼236 cm−1 ) groups. However, bands in the region 355–385 cm−1 may be attributed to terminal Fe–Cl groups, to which there are no corresponding ligand bands. These assignments are in good agreement with the assignment given by Woodward and Taylor [31] and El-Sonbati [32]. The chloro polymeric complexes exhibit new bands at 275–305 cm−1 characteristic of terminally coordinated chloride ions. The IR spectra of polymer complexes 2, 4 and 7 show broad troughs in the region 3650–3350 cm−1 indicative of (OH) of coordinated water [4,6,13] as confirmed by thermal analysis. The rocking mode of coordinated water is also observed in the range 985–905 cm−1 [4,6,13]. The non-ligand bands in the range of 520–280 cm−1 are due to (M–N), (M–O) and (M–Cl) vibrations [6,7,13]. We have recently reported seven polymer complexes of acryloylhydrazin (AH) generated with CuCl2 , Cu(OAc)2 , NiCl2 , CoCl2 , CdCl2 , FeCl3 and UO2 (OAc)2 , all of which exhibit an infinite chain structure with AH acting as the bridging ligand [6,30]. The supramolecular assembly in these polymer complexes via weak interactions such as hydrogen bonding and ␲–␲ stacking interaction is worthy of note. Fig. 2 shows the coordination environment of the metal centers in the polymer complexes. The metal atoms in structures (II, IV and V) both adopt octahedral coordination geometry; in II, it is coordinated to two pairs of trans-related ligands, namely aqua ligands, monodentate; in IV it is surrounded by a four pairs of chloro groups and two AH ligands in trans positions. The Cu(II) atom in III exhibits a square planar coordination geometry, binding to a two pairs of acetate groups and on AH ligand in cis-positions. In our previously reported metal polymer complexes of acryloyl hydrazin, the nitrogen atom (NH2 of the hydrazine group) and the carbonyl group (of the acryloyl group) in an individual ligand AH are consistently cis-related, while in polymer complexes (structures II, IV and V), they are trans-related as shown in Fig. 2. The IR spectra of these polymer complexes show significant differences in the vibrational modes of ligand AH.

◦

Wt., % remaining at 1000 ◦ C

Third stage ◦

Tmax , C

Wt. loss, %

Tmax , C

Wt. loss, %

233 253 248 250 258

45 30 32 32 24

– 363 359 360 371

– 26 29 28 21

8 33 25 28 46

Fig. 3. DTA traces of PAH homopolymer and AH–metal chloride polymer.

each polymer complex and the maximum rate of weight loss shown by the derivative equipment associated with the TG apparatus. The final weight of residues, which can be considered as metal oxide, are in good agreement with those calculated from the metal content using EDTA. The polymer complexes are more stable than PAH homopolymer. This is similar to the results obtained by Diab et al. [33,34] with polymer complexes derived from 5-vinylsalicylaldehyde and 5-vinylsalicylidene anthranilic acid with some transition metal salts. The stabilities of the polymer complexes of AH increase in the order AH–CdCl2 > AH–CuCl2 > AH–NiCl2 > AH–CoCl2 > PAHhomoploymer. The greater stabilities of the polymer complexes compared with PAH homopolymer may be due to the formation of 5-membered ring structures.

3.7. Thermal methods of analysis DTA traces of PAH homopolymer and AH with CuCl2 , CoCl2 , NiCl2 and CdCl2 polymer complexes are illustrated in Fig. 3. Two endothermic peaks are clearly visible. Their relative importance being dependent upon the type of polymer complexes. The Tmax for each peak is shown on the traces, which are comparable to those of the corresponding polymers. TG curves of PAH homopolymer and polymer complexes of AH with CuCl2 , CoCl2 , NiCl2 and CdCl2 are shown in Fig. 4. PAH homopolymer degrades in two stages. The first starts at ∼112 ◦ C with a weight loss of 47% and the second at ∼235 ◦ C with a weight loss of 45%. In the AH–CuCl2 , AH–CoCl2 , AH–NiCl2 and AH–CdCl2 polymer complexes, there are three degradation steps. The first stage at 130, 127, 128 and 132 ◦ C, respectively, due to coordinated water molecules. Table 3 lists the percentage of weight losses for

Fig. 4. TG curves of PAH homopolymer and AH–metal chloride polymer.

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The significant change in the PAH bands upon complexation is the decrease in (C N) group indicating the involvement of the adjacent oxygen in the coordination. The antisymmetric and symmetric (NH2 ) stretching frequencies appear in the region 3450–3100 cm−1 in the homopolymer. These frequencies have been considerably higher in the polymer complexes and this fact, along with changes in deformation, wagging and rocking (NH2 ) vibration suggest that the metals are coordinated through the nitrogen atom of amine group. The ESR study of the copper(II) polymer complexes has provided supportive evidence to the conclusion obtained on the basis of electronic spectra and magnetic moment values. The thermogravemetric analysis confirms the presence of coordinated water molecules in polymer complexes 2, 4 and 7. References

Fig. 5. Arrhenius plots for the degradation of PAH homopolymer and AH–metal chloride polymer complexes. Table 4 Activation energies of the thermal degradation of PAH homopolymer and AH–metal chloride polymer complexes. Polymer

Ea (KJ mol−1 )

PAH AH–CuCl2 AH–CoCl2 AH–NiCl2 AH–CdCl2

15.2 25.3 21.7 23.0 27.2

The effective activation energies for the thermal degradation of PAH and AH–metal salt polymer complexes were determined from the temperature dependence of the chain rupture rate. The rate constant of the thermal degradation was plotted according to Arrhenius relationship (Fig. 5). Table 4 lists the activation energy of PAH homopolymer and AH–metal salt polymer complexes. The activation energy of the homopolymer is smaller than that of the polymer complexes. Therefore PAH homopolymer will undergo decomposition more readily than the polymer complexes. 4. Conclusion Acryloyl hydrazine (AH) has been shown to behave as a monobasic/neutral bidentate ligand via its C–O/C O (of the acryloyl group) and N atom (NH2 of hydrazine group) in seven new metal(II)/(III) polymer complexes and also, the oxygen atoms of two water molecules and two chloro molecules with axial/bridge positions, respectively. UO2 (II), Co(II) and Fe(III) ions are six-coordinated in an elongated octahedral fashion. The center metal ion is coordinated equatorially by a nitrogen atom (of hydrazine group) and an oxygen atom (of acryloyl group) and oxygen atom of each acetato group, and also, the oxygen atoms of two water molecules and two chloro molecules with axial/bridge positions, respectively.

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