Synthesis and Characterization of Metal (II) Phthalocyanine Containing N, N-Dimethyl Phenyl Moieties

Introduction

Phthalocyanines are heteroaromatic macrocyclic compounds.  It is accidental investigated in 1928, the blue and green colour pigments¹. Phthaloyanines are more versatility and highly stable complexes due to more than seventy (70) transitional non-metallic and metallic ions substituted in the ring cavity².  Phthalocyanines applications such as dyes and pigments³, in photovoltaic cells^4-5, photodynamic therapy⁶, semiconductor materials⁷, as liquid crystals^8-9, LED¹⁰, optical storage devices ¹¹, moletronics¹², non-linear optical¹³, gas sensors¹⁴, and for electrochromic displays¹⁵. The reduction-oxidation properties of pthalocyanines are use as industrial applications like dyes and pigments¹⁶. To modify these macrocyclic compounds have been performed advanced materials for numerous properties and applications.

Phthalocyanines are partially soluble in organic solvents like CCl₄, acetone or in H₂O.  These insolubility due to peripheral substitution with long alkyl, alkylthio chain, alkoxy, and bulky groups lead to macrocyclic products. Phthalocyanines are soluble in a polar solvent. 

In this work, we attempt has been made to synthesize and characterization of a non-peripherally metal (II) phthalocyanine presence of tetra substituents of  (N,N-dimethyl phenyl) methan-imine molecule. The amino pthalocyaines complexes react with substituted aldehydes compounds to form imine group. Even though, literature papers revealed the reports on the synthesis and characterization of substituted metal (II) tetra-amino phthalocyanines, no documentary pieces of evidence were available on the newly synthesis and characterization of substituted metal- tetra-4-(N,N-dimethyl phenyl) methan-imine phthalocyanine pigments. 

This paper concerns suitable synthetic route available in the literature and modified the procedure the synthesis of metal (II)-tetra-4-(N,N-dimethyl phenyl) methan-imine phthalocyanines  in scheme-1. 

Scheme 1: Synthetic route of metal (II) tetra-4-(N,N-dimethyl phenyl) methane-imine phthalocyanine pigments. Click here to View Scheme

Scheme.1:  Synthetic route of metal (II) tetra-4-(N,N-dimethyl phenyl) methane-imine phthalocyanine pigments. a. 4-nitro-phthalic acid, b. MTNPc  c. MTAPc d. MTDMPhImPc

Materials and Methods

The carbon, hydrogen and nitrogen analysis carried out by the Sophisticated Test and Instrumentation Centre at Cochin University, Kochi, India.The FTIR spectra were recorded on a Nicolet MX-FTIR spectrometer using KBr pellets. Magnetic susceptibility studies by using a Gouy balance and at room temperature (301^oK). Diamagnetic corrections is calculate were used Pascal’s constants ^18-19. A calibrant used as a mercury tetra thiocyanato cobalt (II) complex and doubly distilled H₂O was used in the experiments. Electronic spectra on a UV–vis Shimadzu 3600 UV spectrophotometers. Rigaku Miniflex 600 XRD diffractometer was used to measure the diffraction pattern. Thermogravimetric and DTA analysis is carried out by using Perkin- Elmer Thermal analyzer at the rate of 10 ⁰C/minute in air and nitrogen atmosphere.

Experimental

4-nitrophthalic acid was prepared as per literature¹⁹ and other solvents and reagents used were analytical grade. The substituted metal (II) tetra-nitro phthalocynanines and metal (II) tetra-aminophthalocyanines were prepared by the reported procedure¹⁹. These complexes converted into imino substituted complexes  by condensation reaction²⁰. Finally we prepared metal (II)-4-(N,N-dimethyl phenyl) methan-imine phthalocyanines complexes and synthesized compound analytical data were summarized in the table.

Preparation of Cobalt (II)- tetra-4- (N, N-dimethyl phenyl) methan-imine phthalocyanine complex.

Cobalt (II) tetra-aminophthalocyanine (6.31g, /0.1mole) were 15 M H₂SO₄ added successively, 4-dimethylamino benzaldehyde (14.9g, / 0.1mole) was dissolved in ethanol and a small amount of concentrated H₂SO₄ was added, and refluxed 5hrs with constant stirring ²⁰. The blue-colored condensed tetra-4-(N,N-dimethyl phenyl) methan-imine phthalocyanine derivative and washed with ethanol until its free from substituted aldehyde and collect pure product. Finally, washed with dis. H₂O and product was dried vacuum desiccator over anhydrous O₁₀P₄.

The above same procedure adopted the preparation of Cu, Ni, and Zn -tetra-4-(N,N-dimethyl phenyl) methan-imine phthalocyanines  

Results and Discussion

All the substituted metal (II) phthalocyanines are bluish color. The metal phthalocyanine complexes are soluble in concentrated sulfuric acid and sparingly soluble in dimethyl sulfoxide, and Dimethylformamide  and pyridine. The solubility increasing order like sulfuric acid> dimethyl sulfoxide> Dimethylformamide > pyridine. The elementary analysis C, H, and N result summarized in table.1 and calculated values with consistent by the suggested structure(Figure-1).

Table 1: Magnetic susceptibility and elemental analysis data of metal (II)- tetra-4-(N,N-dimethyl phenyl) methanimine phthalocyanine.

Name of the Complex ( % Yield) [Colour ]	Molecular formulae. (Molecular weight)	Field KGauss	Magnetic susceptibility cm X(10-6 )	Magnetic moments meff [BM]	Elemental analysis [%] [found (calcd)]
CoTDMPhImPc       (75%) [Dark Blue]	C68H56N16Co    (1156.20)	2.21 2.63 3.10 3.57 4.02	+2611.13 +2434.05 +2114.43 +1929.02 +1808.03	2.64 2.46 2.28 2.17 2.13	C, 70.58; (70.45) H, 4.84; (4.79) N, 19.37; (19.27) Co, 5.09; (5.05)
CuTDMPhImPc        (74%) [Dark Blue]	C68H56N16Cu    (1160.81)	2.21 2.63 3.10 3.57 4.02	+2621.08 +2465.17 +2128.43 +1947.55 +1825.54	2.58 2.46 2.28 2.18 2.13	C, 70.34; (70.33) H, 4.82; (4.77) N, 19.31; (19.23) Cu, 5.47; (5.45)
NiTDMPhImPc       (70%)     [Dark Blue]	C68H56N16Ni     (1155.96)	2.63	-773.81	—	C, 70.59; (70.56) H, 4.84; (4.79) N, 19.37; (19.33) Ni, 5.07; (5.02)
ZnTDMPhImPc         (70%)     [Dark Blue]	C68H56N16Zn    (1162.65)	2.63	-1239.03	—	C, 70.18; (70.14) H, 4.81; (4.78) N, 19.26; (19.23) Zn, 5.62; (5.59)

Figure 1: Proposed structure of metal (II) – tetra-4-(N,N-dimethyl phenyl) methanimine phthalocyanines, where (M= Cu, Co, Ni, Zn) Click here to View figure

Electronic spectra (UV-visible)

The metal (II) -tetra-4-(N, N-dimethyl phenyl) methan-imine phthalocyanine complex (M-TDMPhImPc) were performed concentration range 1-1.5 X 10^-4 M in dimethyl sulfoxide  and the data are presented in Table -2. The peaks were shown in the range of 774-784 for all the complexes due to a_2u  → e_g and  a_2u  →   e_g transition ²⁰. The Q-band M-TDMPhImPc’s was found compared to higher corresponding parent substituted metal (II) phthalocyanines. The lower energy redshift band is due to extension in the p-p* transition electron of peripheral substitution of aromatic component imino group. CoTDMPhImPc, CuTDMPhImPc, NiTDMPhImPc and ZnTDMPhImPc absorption peak were shown in the range of  686 – 691 nm which indicate for attributed to the phthalocyanine complexes ²¹. B-band and L- band was observed in the range of 242- 249 nm and 206- 217 nm for all the complexes.

Table 2: UV-Visible, Infra-red and X-ray diffraction spectral data of metal(II)-tetra-4-(N,N-dimethyl phenyl) methan-imine phthalocyanine complexes.

Name of the Complex	UV-vis absorption l nm [logÎ]	IR spectral data [cm-1]	Powder XRD  2q (o)  (d Å)	Relative Intensity (%)
CoTDMPhImPc	206 (3.42) 242 (3.59) 481 (3.24) 691 (4.32) 784 (3.82)	741, 1040, 1175, 1386, 1633, 1708, 2364, 3450.	27.87, (3.49) 28.73, (3.08) 24.47, (3.42) 31.23, (2.83)	100.00 79.34 49.16 31.54
CuTDMPhImPc	209 (3.33). 257 (4.19) 478 (3.87) 688 (4.15) 776 (3.17)	773,1091, 1387, 1632, 1712, 2363, 3442.	45.54, (2.82) 31.72, (2.80) 43.73, (2.74) 25.93, (3.42)	100.00 80.23 50.47 33.35
NiTDMPhImPc	212 (3.49) 257 (4.15) 479 (3.41) 686 (4.54) 774 (3.64)	756, 1113, 1366, 1404, 1624, 2223, 2361, 3423.	27.81, (3.74) 28.83, (3.08) 23.24, (3.43) 42.77, (2.80)	100.00 79.78 44.15 28.58
ZnTDMPhImPc	217 (3.59) 259 (4.47) 471 (3.59) 689 (4.24) 779 (4.57)	771, 1121, 1387, 1633,2324, 2363, 3445.	27.93, (3.57) 28.87, (3.06) 42.93, (2.81) 20.52, (4.30)	100.00 80.87 50.15 35.93

Infra-red

The Infra-red spectral data of the metal (II)-tetra-4-(N,N-dimethyl phenyl) methanimine phthalocyanines   are presented in table 2 (Figure 2). A peak is assigned in the range of 3422-3442 cm^-1 in all the complexes due to H-bonding between the hydrogen atom of moisture observed on the KBr pellets and the nitrogen atom of the phthalocyanine skeleton ²². A sharp is observed in the range of 1624- 1633 cm^-1 are assigned to C=N bond of the imine group. The peaks in the range of 1367-1386 cm^-1 are attributed to C-N bond aromatic   stretching ¹⁸. A week peak at 2359-2367 cm^-1 are assigned to C-H stretching vibration due to phthalocyanine moiety.  All the peaks at 1040-1121 and 745- 776 cm^-1 can be attributed to the various characteristic phthalocyanine ring stretching skeletons ²².

Figure 2: Infrared absorption spectra of (1) CuTDMPHImPc (2) CoTDMPhlmPc (3) NiTDMPhlmPc (4) ZnTDMPhlmPc. Click here to View figure

Magnetic Susceptibility Measurement

The synthesized M-TDMPhImPc’s complexes are measure the magnetic susceptibility were solid state and summarized the results in Table.1. The measurement of applied magnetic field in the range of 2.21 to 4.02 kG and independent determination by average of three values.

While copper and CoTDMPhImPc are paramagnetic behavior and NiTDMPhImPc, ZnTDMPhImPc complexes are diamagnetic nature. The magnetic moments of CuTDMPhImPc and CoTDMPhImPc are higher values than the spin-spin only value corresponding to the one unpaired electron 1.73BM, due to the blending of higher energy state (b_2g)₂, (e_g)₃, (a_1g)₂ orbital with ground state (b_2g)₂,(e_g)₄ , (a_1g)₁ orbitals degenerate states and inter-molecular cooperative effect ²³. As per the literature the magnetic field is higher than the higher magnetic moment values at lower field strength due to magnetic anisotropy of phthalocyanine coupled with intermolecular magnetic interaction ^17-20.

Powder X-ray Diffraction

The powder XRD pattern of MTDMPhImPc’s are taken in the range of 2θ angle 06-70^o  and it was observed that all the peaks are identical data is reported in the Table. 2. In the spectra one of the sharp peak is observed maximum intensity with lower angle. The following values of interplanar spacing with angle. Co-TDMPhImPc 3.54, 27.87 Å ; Cu-TDMPhImPc 2.78, 45.62 Å; Ni-TDMPhImPc 3.64, 27.92 Å and Zn-TDMPhImPc 3.55, 27.91 Å, It is clearly indicating these complexes are crystalline nature. A similar pattern is observed in un-substituted parent phthalocyanine complexes. The broadening of the peaks in the MTDMPhImPc’s due to the attributed of the substituents group and play an important role in stacking the substituted metal (II) phthalocyanine complexes²⁴.

Thermogravimatric studies

Thermogravimetric analytical data of metal (II)- tetra-4-(N,N-dimethyl phenyl) methanimine phthalocyanine pigment reported in Table 3 and 4. In these complexes the decomposition take place in 2 steps. Initially weight loss of complexes 2-3% due to moisture.

Table 3: Thermogravimetric analysis data of metal(II)-tetra-4-(N,N-dimethyl phenyl) methanimine phthalocyanine

Complex	Decomposition Temperature (oC)	Weight  Loss (%)found      (%)calcd		Probable fragmentation loss
CuTDMPhImPc	240-350	28.74	29.03	4-subtituted imino groups
	351-620	64.56	64.92	Pc- moiety
CoTDMPhImPc	240-350	29.92	30.14	4-subtituted imino groups
	35I-620	65.86	65.03	Pc -moiety
NiTDMPhImPc	240-350	28.78	29.17	4-subtituted imino groups
	351-620	64.16	64.78	Pc- moiety
ZnTDMPhImPc	240-350	29.65	30.12	4-subtituted imino groups
	351-620	65.53	65.13	Pc -moiety

Table 4: Thermodynamic and kinetic parameters of tetra-4-(N,N-dimethyl phenyl) methan-imine phthalocyanines complexes in air and nitrogen.

Complex		Activation energy EO kJ/(mol)	Frequency factor. (lnA)	ΔH kJ/(mol)	ΔS J/K	ΔGkJ/(mol)
CuTDMPhImPc	I	5.86 (0.72)	6.17 (2.02)	2.73 (-1.28)	-165.05 (-160.02)	62.41 (61.53)
	II	3.73 (1.52)	5.37 (5.45)	-0.74 (-2.42)	-152.26 (-149.74)	81.64 (79.53)
CoTDMPhImPc	I	0.87 (0.65)	6.38 (3.37)	-1.27 (-1.13)	-175.07 (-173.12)	73.94 (73.76)
	II	4.67 (1.15)	7.40 (4.55)	2.86 (-1.22)	-143.93 (-140.98)	79.55 (76.23)
NiTDMPhImPc	I	1.46 (0.72)	5.23 (2.17)	-1.23 (-0.75)	-158.56 (-156.57)	72.85 (71.57)
	II	5.86 (1.55)	4.46 (4.80)	-0.84  (-0.81)	-148.78 (-142.64)	81.74 (79.98)
NiTDMPhImPc	I	1.74 (0.69)	3.47 (2.35)	-0.94 (-1.43)	-174.86 (-172.36)	74.23 (73.97)
	II	8.53 (5.52)	7.86 (6.35)	2.85 (-1.54)	-141.73 (-139.92)	81.47 (79.94)

The values I and II stage represent the degradation in nitrogen atmosphere.

1^st step of degradation the temperature ranges from 240-350^oC, in air, the loss of all the four substituted imino groups. In second step the temperature ranges 351 – 620^oC maximum weight loss is identified in all the phthalocyanines complexes due to the oxidative degradation in the phthalocyanine moiety. Destruction of phthalocyanine complexes only in the second step. Finally, the remaining residue corresponds to metal oxide ²³.

The metal (II) – tetra-4-(N,N-dimethyl phenyl) methan-imine  phthalocyanine complexes are thermally decomposition take place very slow in nitrogen atmosphere. For CoTDMPhImPc  was decomposed 68% at temperature 620 ^oC. For CuTDMPhImPc, 55%, NiTDMPhImPc,  53%  and ZnTDMPhImPc complexes  44% loss of weight at temperature 620 ^oC. From the result it is conclude that the thermal stabilities of these MTDMPhImPc in the order. CoTDMPhImPc >CuTDMPhImPc > NiTDMPhImPc > ZnTDMPhImPc. Thermodynamic and kinetic studies of the metal (II) – tetra-4-(N,N-dimethyl phenyl) methan-imine phthalocyanine complexes were evaluated by Boride’s method ²⁵. (Figure-3).

Figure 3: Thermal degradation ln(ln 1/y) v/s 1/T.CuTDMPhImPc, CoTDMPhImPc, NiTDMPhImPc and ZnTDMPhImPc in atm.air. Click here to View figure

Plot of graph ln(1/y) v/s 1/T. The activation energies (Eo), for the loss of periphery imino substituent groups in all the complexes lies in the range of 0.69 – 5.86 kJ/ ( mol) due to the periphery substituents groups are removed, and the disrupt of the phthalocyanines complex ring. It is exothermic reaction the negative entropies and the degradations are completed. The changes in entropies ∆S varies from –158.56 to -174.86 kJ due to this result it is indicated that all functional groups are associated with negative entropies. The enthalpy, entropy and free energy have been calculated by using standard equations and results are summarized in Table 4.

Conclusion

The synthesized  of metal (II)- tetra-4-(N,N-dimethyl phenyl) methanimine phthalocyanine substituted different transitional metal like (Cu, Co, Ni and Zn) by simple method and characterized. All the complexes the solubility increased in organic solvents  due to introduce of (N,N-dimethyl phenyl  group into periphery positions of metal phthalocyanine. Macrocyclic  compounds solubility increases the research community are potential applications in different field like sensor, catalysts, electrode coating and pharmaceutical industries. The magnetic susceptibility studies confirm that CuTDMPhImPc and CoTDMPhImPc are paramagnetic nature. XRD studies revealed that crystalline nature of the complex. The thermal stability of the metal (II) TDMPhImPc’s in air, the following order CuTDMPhImPc > CoTDMPhImPc > NiTDMPhImPc  > ZnTDMPhImPc.  

Acknowledgment

The authors are thankful to the Chairman, Department of Chemistry Manipal Institute of Technology, Manipal Academy of Higher Education, Manipal for providing the basic laboratory facilities.

Conflicts of Interest

All author declare that there is no conflict of interest.

Funding Sources

There are no funding sources.

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