Coordination Polymers of N, N’-di-(8- Hydroxyquinolinolyl- 5-methyl)-N, N-diethyl-1, 3-propane diamine (QEPD)

Coordination polymers containing a novel bis(oxine) bidentate ligand, namely N,N’-di(8-hydroxyquinolinolyl-5-methyl)-N,N’-diethyl-1,3propane diamine (QEPD) have been prepared with the metal ions Zn(II), Cu(II), Ni(II), Co(II) and Mn(II). The novel bis-(bidentate) ligand was synthesized by condensation of 5-chloromethyl-8-hydroxyquinoline hydrochloride with N,N’-diethyl-1,2propane diamine in the presence of a base catalyses. All of these coordination polymers and the parent ligand were characterized by elemental analyses, IR spectral and diffuse reflectance spectral studies. The thermal stability and numberaverage molecular weights ( Mn ) of all of the coordination polymers were determined by thermogravimetric analyses and non-aqueous conductometric titrations, respectively. In addition, all of the coordination polymers have been characterized by their magnetic susceptibilities.


Preparation of coordination polymers
A solution of copper acetate (1.9 g, 0.001 mol) in aqueous formic acid (50 mL, 50%) was added drop wise to a solution of QEPD (3.30 g, 0.01 mol) in aqueous formic acid (240 mL, 20%) with stirring. The reaction mixture was heated on a water bath for 0.5 h. The reaction mixture was made alkaline by the addition of dilute aqueous ammonia until the precipitation was completed. The polymer separated out in the form of a suspension and was digested on boiling water bath. Finally, the resultant solid brownish yellow precipitates was collected by filtration and washed with hot water, dimethylformamide (DMF) and then acetone. The polymer (QEPD-Cu[II]) was air dried. A similar procedure was used to prepare the QEPD-Co[II], QEPD-Ni(II), QEPD-Mn(II) and QEPD-Zn(II). The yields of all coordination polymers were almost quantitative.

Measurements
In the co-ordination polymers, metals were analysis by using the EDTA titration and for this process decomposed co-ordination polymers used 13 . The percentage composition. (C, H and N) for the coordination polymers was determined by a C,H,N Elemental analyzer ( Table 1). The IR spectra of the bis-ligand QEPD and each of the coordination polymers samples were scanned as KBr pellets using a Perkin Elmer IR spectrophotometer. The solid diffusion, reflectance spectra of all the coordination polymers were recorded on Shimadzu spectrophotometer with a solid reflectance attachment MgO was employed as the reference compound.
The number average molecular weights ( Mn ) of all the coordination polymers were estimated by end-group analysis. End-group analysis of the hydroxyl group was carried out by non-aqueous conductometric titration using pyridine as solvent and sodium methoxide as titrant base 14,15 .
Magnetic susceptibility measurements of all the coordination polymers were carried out at room temperature by the Gouy method. Mercury [tetrathiocynatocobalt] was used for the instrument calibration 18 . Molar susceptibilities were corrected for diamagnetism of the component almost using Pascal's constant 18 . Thermogravimetry of all these coordination polymers was carried out using a Dupont thermogravimetric analyzer (TGA). The data are reported in Table 3.

Results and Discussion
The synthesis QEPD was performed by chloromethylation of the oxine followed by condensation with N,N'-diethyl-1,3-proapne diamine (Scheme 1).
Coordination polymers, QEPD-Mt, Where Mt= Cu, Ni,Co, Mn, Zn Scheme 1 The important IR spectral features are (i) a broad band from 3550 cm -1 to 3200 cm -1 that is attributed to the hydrogen-bonded OH group 17 . (ii) The weak bands near 1220 cm -1 and 1020 cm -1 that are due to asymmetric and symmetric stretching vibrations of methylene groups (CH 2 ) of the -CH 2 -NH-CH 2 -bridge. (iii) The weak band at 1110 cm -1 that confirms the presence of a dialkyl amine function. and (iv) the bands near 1610, 1508, 1470 and 1420 cm -1 that are the characteristic frequencies of the 8-hydroxyquinoline nucleus 12 . The weak band around 1085 and 1118 cm -1 may also be attributed to the amine group bridge. It was also observed that H 2 L has numerous IR spectral features in common with those of 5,5methylene bis(8-hydroxyquinoline) 1 . These features support the proposed structure of H 2 L. The coordination polymers derived from H 2 L are insoluble in common organic solvents. All these coordination polymers decomposed at approximately 250 o C. The molecular mass was estimated by evaluating the number of terminal OH groups using non-aqueous conductometric titration. Perusal of the literature revealed that there are few reports regarding the determination of the number average molecular weight ( Mn ) of coordination polymers. [18][19][20][21] However, efforts are made by the present authors to estimate ( Mn ) of the H 2 L coordination polymers by utilizing the non-aqueous conductometrie titration method under controlled experimental conditions 22 . For the sake of convenience, the required amount of coordination polymer was suspended in pyridine for 24 h. It was observed that the properties of polymers did not change in the presence of pyridine.
Assuming that the only end-groups in the polymers are OH, the titration was carried out by addition of controlled volume of NaOMe, since more volume of NaOMe may cause decoordination of polymers. A discernible break was observed in the titration curve and the molecular weights were calculated as shown in Table 1. Examination of the metal content in the polymers (Table 2)   Comparison of the IR spectrum of the ligand H 2 L and those of the coordination polymers reveal certain characteristic difference. Thus, the broad band in the region from 3550 to 3200 cm -1 for H 2 L is absent in the spectra of the polymers. This is consistent with the involvement of OH groups in a coordinate interacting with the polymers. However, the weak band near 3400 cm -1 for H 2 L-Mn 11 indicates that water molecules might be strongly absorbed by the polymer sample. The band in H 2 L due to C = N stretching at 1600 cm -1 is shifted towards lower frequency (ca 1558 cm -1 ) in the coordination polymers. The red shift suggests coordination of metal ion through the nitrogen of 8-hydroxyquinoline. In addition, a weak band at 1100 cm -1 is attributed to the C-O-M stretching frequency 16 . The band at 1430 cm -1 in QEPD is assigned to the in-plane OH deformation 16 . This band is shifted toward higher frequency (1468 cm -1 ) in the spectra of the polymers and supports the formation of a metal-oxygen bond.
The magnetic moments (µ eft ) of the polymeric chelates are given in Table 3. The diffuse electronic spectrum of QEPD-Cu(II) coordination polymer shows two broad bands near 15.625 cm-1 and 22.222 cm -1 . The first band may be due to 2T g → 2E g transition while the second may be due to charge transfer. The first band shows some structural characteristics that suggest a distorted octahedral geometry. The higher theoretical value of µ eff of the QEPD-Cu(II) polymer supports this view. The QEPD-Ni(II) and QEPD-Co(II) polymers exhibit two absorption bands at 16,000 and 23,809 cm -1 respectively. These bands are assigned to the 4 T 1g → 2 T 2g . 4 T 1g → 2 T 2g (P) transitions, respectively 22 both the absorption bands and the values of µ eff lower than required for a spin value only state.