Hydrazine Complexes of Lanthanides with 3-Acetoxy-and 4-Acetoxybenzoic Acids : Spectroscopic , Thermal , and XRD Studies

New bis-hydrazine lanthanide complexes with 3-acetoxybenzoic acid (3-abH) of formula, [Ln(3-ab)3(N2H4)2]⋅xH2O where Ln = La, Ce, Pr and Gd and xx x 0; Ln =Nd and Sm and xx x 1, and monohydrazine complexes of some trivalent lanthanides with 4-acetoxybenzoic acid (4-abH) of formula, [Ln(4-ab)3(N2H4)]⋅H2O where Ln = La, Ce, Pr, Nd, Sm and Gd have been prepared in ethanolic medium and characterized by spectroscopic techniques (IR and �V re�ectance), microelemental analysis, thermoanalytical technique, powder XRD, SEM-EDS studies, and magnetic susceptibility measurements. e IR spectra of both series show bidental coordination of carboxylate ion with the metal by displaying, ννCxO (asym) in the range of 1587–1602 cm −1 and the ννCxO (sym) in the range of 1433–1410 cm , with a separation of around 200 cm. e ester C =O remains unaltered indicating the noninvolvement in coordination. All the complexes show ννN−N absorption in the range of 929–962 cm −1 indicating the presence of hydrazine in a bridged bidentate fashion.e thermal data reveals that the hydrated compounds show endothermic dehydration followed by exothermic decomposition to leave their metal oxide as end products, and the anhydrous compounds undergo exothermic decomposition to form the respective metal oxide residues.


Introduction
Salicylic acid plays vital role in coordination chemistry due to its capacity for chelation.One of its acetyl derivatives, aspirin, has also been used in the preparation of complexes due to its therapeutic applications [1][2][3].It has been used as an axial ligand for the preparation of tin porphyrin complexes [4].e other two isomers of aspirin, namely, 3-acetoxybenzoic acid (3-abH) and 4-acetoxybenzoic acid (4-abH) have not been used for synthesis of complexes yet.In our laboratory, we have been synthesising metal carboxylate complexes using hydrazine as coligand [5][6][7].When hydrazine is used as a coligand, it generally leads to the formation of polymeric complexes owing to its action as bridging ligand [8][9][10][11].With the idea of preparing new hydrazine complexes, we selected the 3 and 4-acetoxybenzoic acids.In this paper, we have presented the preparation and the characterization of 3-and 4-acetoxybenzoic acid complexes of some lighter lanthanides with hydrazine as coligand by IR, uv-visible spectroscopic studies, thermoanalytical, XRD, SEM-EDX, and magnetic susceptibility measurement studies.

Experimental
e solvents were distilled prior to use, and double distilled water was used for the preparation and chemical analyses.e chemicals used were of AR grade.In all the reactions, 99.99% pure hydrazine hydrate was used as received.(3-ab) 3 (N 2 H 4 ) 2 ]⋅xH 2 O Where Ln = La, Ce, Pr, and Gd and   ; Ln = Nd and Sm and   1. Lanthanum oxide (0.325 g, 1 mmol) was dissolved in a minimum quantity of 1 : 1 HNO 3 , evaporated to eliminate excess of acid, and dissolved in 20 mL of ethanol.is was added slowly to a freshly prepared ethanolic solution (40 mL) of the ligand containing 3-abH (1.081 g, 6 mmol) and hydrazine hydrate (0.40 g, 8 mmol), stirring the reaction mixture at pH 3. en the reaction mixture was kept over hot water bath for 1 h 30 min.A dull white, crystalline product obtained was washed with alcohol, ether, and air dried.A similar procedure was adopted for obtaining the other lanthanides with the molar ratio Metal : Acid : Base = 1 : 6 : 8.

Preparation of [Ln
Where Ln = La, Ce, Pr, Nd, Sm and Gd.ese complexes were prepared using 4-abH, hydrazine hydrate and their respective lanthanum nitrates in alcohol medium at pH 3.5 by adopting similar procedure as mentioned above.e products obtained were washed with alcohol, ether and dried in air.All these complexes were prepared by using the molar ratio Metal : Acid : Base = 1 : 6 : 8.

Physico chemical Methods
. e hydrazine content in all complexes was determined volumetrically using 0.025 M potassium iodate solution under Andrews' conditions [12].e metal content was determined by EDTA complexometric titration [12] aer decomposing a known weight of the sample with 1 : 1 HNO 3 .Magnetic measurements were carried out by the Gouy method using Hg[Co(NCS) 4 ] as calibrant.e electronic spectra for solid-state complexes were obtained using a Varian, Cary 5000 recording spectrophotometer.Infrared spectra were recorded using KBR disc (4000-400 cm −1 ) on a Shimadzu FTIR-8201 (PC) S spectrophotometer.e simultaneous TG-DTA studies were done on a Perkin Elmer Diamond TG/DTA analyzer, and the curves were obtained in static air using 5-10 mg of the samples at the heating rate of 10 ∘ C/min.e XRD patterns were recorded on a Bruker AXS D8 advance diffractometer with an X-ray source Cu, wavelength 1.5406 Å using a Si (Li) PSD detector.e elemental analysis was carried out using a CHNS Elementar Vario EL III Elemental Analyzer.e SEM with EDX analysis was obtained using JEOL model JSM-6390 LV and JEOL model JED-2300 instrument.

Results and Discussion
All the complexes obtained were polycrystalline powders that are stable in air and insensitive to light.Lanthanum complex is sparingly soluble in water but other complexes were insoluble.ey were also insoluble in organic solvents such as ethanol, ether, and benzene, but soluble in DMSO.
e analytical data of the complexes is given in Table 1 and the values were consistent with the proposed formulae for them.
3.1.Electronic Spectra and Magnetic Susceptibility Measurements.e compounds were insoluble in water and organic solvents, and hence their electronic spectra were recorded for solid samples.e electronic spectral data and the assignments were summarized in

IR Spectra of Complexes
. e IR data of the complexes and that of the respective acids are given in Table 3. e spectrum of 3-abH acid shows absorptions at 1091 cm −1 , 1207 cm −1 , 1276 cm −1 due to  C-O ester , 1761 cm −1 due to  C=O ester , and 1676 cm −1 due to  C=O acid .Spectra of the complexes show broad spectrum 1246-1315 cm −1 and centered at 1315 cm −1 (La), 1277 cm −1 (Ce), 1300 cm −1 (Pr), 1303 cm −1 (Nd), 1300 cm −1 (Sm), and 1300 cm −1 (Gd) due to  C-O ester .A medium sharp band observed at 1091 cm −1 for the acid is found at 1112 cm −1 for the complexes.ese absorptions are found to shi in the same direction for all the complexes due to coordination [16].
In addition, the hydrated complexes show broadbands observed in the range of 3400 cm −1 corresponding to OH stretching and 862 cm −1 corresponding to OH bending of water molecules present in the lattice.is broadband extends up to 3030 cm −1 may be because of the merging of N-H stretching of hydrazine molecule with  O-H of water.4. e sequence of reactions proposed for the decompositions is:

ermal Analysis of
where Ln = Sm and Nd where Ln = Ln, Pr and Gd (3) where Ln = Ln, Pr and Gd T 5: X-ray diffraction data of lanthanide complexes of 3-abH and 4-abH (D spacing in Å units and intensity in parentheses).

ermal Analysis of
where Ln: La, Ce, Pr and Gd and  = 0; Ln: Nd, and Sm,  = 1 and 3-abH: where Ln = La, Ce, Pr, Nd, Sm and Gd where Ln = La, Pr, Nd and Sm where Ln = La and Pr where Ln = Nd and Sm 3.4.X-Ray Diffraction Analysis.e powder XRD patterns along with their d spacings are given in Table 5. e comparison of XRD patterns of the lanthanide complexes is shown in Figures 5 and 6. e XRD patterns of lanthanides of 4-abH and 3-abH reveal that each set of complexes has similarity in their structures implying similar compositions.A comparable XRD data of complexes imply that they have similar type of structures.However, single crystal XRD can only con�rm their structures.In our case since the complexes are insoluble in any solvent due to their polymeric nature, single crystals could not be prepared.SEM-EDX analysis indicated the oxides formation in microsize.

3. 5 .
SEM-EDX Studies.e complexes were calcined in muffle furnace at their decomposition temperature, heating subsequently at the same temperature, and analyzed for their morphology and particle size.e SEM-EDX images of residues obtained from [Gd(3-ab) 3 (N 2 H 4 ) 2 ] and [Nd(4ab) 3 (N 2 H 4 )]⋅H 2 O are shown in Figures7, 8, 9, and 10.From the images, it is understood that the residues are microsized metal oxides with irregular shapes.

4 .
Conclusione isomeric acetoxybenzoic acids and hydrazine hydrate yield the complexes of formulae, [Ln(3-ab)  3 (N 2 H 4 ) 2 ]⋅H 2 Owhere Ln = La, Ce, Pr and Gd and   0; Ln = Nd and Sm and   1 and [Ln(4-ab) 3 (N 2 H 4 )]⋅H 2 O where Ln = La, Ce, Pr, Nd, Sm and Gd resulting from their reaction with the respective metal nitrates.e compositions of the complexes were con�rmed by elemental data.e presence of hydrazine in bidental bridging mode is inferred from their N-N stretching frequencies.e complexes of 3-abH release hydrazine exothermally in the temperature range 166-178 ∘ C whereas 4-abH complexes undergo exothermic dehydrazination at higher temperature range 180-197 ∘ C indicating that the two molecules of hydrazine are tightly held between the metal atoms in four directions.All the complexes of 3-abH undergo oxidative decomposition in the range of 437-477 ∘ C excepting for lanthanum, and the complexes of 4-abH in the range of 490-550 ∘ C. e lowertemperature decomposition of 3-abH complexes may be due to fuelling effect of two hydrazine molecules.e magnetic and electronic data indicate the presence of metal in the complexes.
[21]66-175 ∘ C and oxidative decomposition showing many exotherms in the range of 213-550 ∘ C to metal oxide residue.La and Pr complexes show the formation of metal carbonate intermediate[21]before �nal decomposition to metal oxide, whereas the other two do not.Ce and Gd complexes, though found to follow similar type of decomposition to form metal oxide residue, the TG traces are not clear to identify dehydrazination and the intermediate formation.e thermal degradation patterns are indicated by the following reactions: