Template Synthesis of Macrocyclic Complexes of Bivalent CoII, NiII, PdII,ZnII and CdII Ions with Cyclic Glyoxal Carbohydrazone (1,2,4,5,8,9,11,12-octaazacyclotetradeca-5,7,12,14-tetraene-3,10-dione)

Introduction

The concept of macrocyclic compound and their metal complex grew rapidly after synthesis of crown ether by Pederson in 1966¹. The growing application of macrocyclic complexes in transport of alkali metal nutrient to plant kingdom enhanced the interest of Chemist and Biologist to synthesize and characterize the metal complexes with macrocycliccrown ether^2-5. In present paper we describe the
preparation and characterization of complexes ofmacrocyclicligand bis(glyoxalcarbohydrazone) with bivalent metal ions.

Experiment

The metal salts, glyoxaldihydrate, hydrazine hydrate, diethylcarbonate and organic solvents were extra pure reagent of E.Merck and AnalR grade chemicals of BDH. Palladium (II) Chloride was obtained from JohnsonMetthey London.Carbohydrazide was prepared by refluxing diethylcarbonate {O=C(OC₂H₅)} with 98% hydrazine hydrate on steam bath as reported in literature⁶. The magnetic susceptibility of complexes were determined by Gouy method at room temperature using [Hg{Co(NCS)₄}]as standered(χ_g= 16.24×10^-6 CGS.unit at 20^oC). The metal content, halogens and sulphate were determined by standard process⁸. The results of C,H and N were obtained from BIT Mesra. Ranchi.The IR spectra were recorded as KBr disc in the range 450–4000cm^-1 onShemadzu Spectrophotometer and Electronic spectra on UV-Vis 2500PC series spectrophotometerat IIT Patna.

Preparation of complex salts: -M{bis (glyoxalcarbohydrazone)}X₂nH2O (M = Co^II, Ni^II, Pd^II, Zn^II and Cd^II, n = 0, 1 or 4, X =Cl‾ or 1/2 SO₄^-2). About 0.01 mol of carbohydrazide, 0.01molglyoxaldihydrate, and 0.005 mol metal chlorides were mixed in 100 ml water and 50 ml ethanol. The mixed reaction mixtures were refluxed on steam bath with constant stirring for 8–10 hours. The resulting solution was filtered and concentrated to 20-25 ml and pH was adjusted to 4-5 by adding a few drop of appropriate dilute acid. On cooling and standing the refluxateovernightin cold,microfine crystalline precipitate separated. The product were collected on Buckner funnel and washed with cold ethanol. The products were dried over CaCl₂desiccators and analyzed.The complexsulphates were obtained when metal salt was taken as sulphate. The analytical results and molar electrical conductance value of products are mention in Table-A and B.

Results and discussion

The analytical results of macrocyclic complexes formed on condensation of glyoxaland carbohydrazide with Co^II, Ni^II, Pd^II, Zn^IIand Cd^IIsalts corresponds to composition M(glyoxalcarbohydrazone)₂X₂nH₂O (M = Co^II, Ni^II, Pd^II, Zn^II and Cd^II, n = 0 forPd^II,Zn^IIand Cd^IIwhile  4 for Co^II orNi^IIand X = Cl^‾ or 1/2 SO₄^-2). The complex salts are soluble in hot water or hot aqueous ethanol. The neutral complexes M(glyoxalcarbohydrazone)₂X₂nH2O dissolved in DMF and pyridine base on warming. The complexes are stable in air and aqueous medium. The electrical conductance value of complex salts in DMF occur in the range Ʌ_∞ = 102–138 ohm^-1mol^-1cm² indicating ionic nature of complexes⁷. As expected Zn^II, Cd^II and Pd^II complexes are diamagnetic and Co^II orNi^II complexes are paramagnetic. The magnetic moment at room temperature of Co^II complexes were found 4.92 and 5.01 for Co(glyoxalhydrazone)₂X₂nH₂O (X = Cl^‾ and 1/2 SO₄^-2). Which is similar to most of the spin free octahedral Co^II complexes⁶­^–7. The magnetic moment value of Ni^II complexes (Table-B) occur in the range ofoctahedral environment of Ni^IIatom⁹.

The electronic absorption spectra of Ni^IIcomplexes displayed three distinct absorption band at 9680-9700, 16240-16360 and 24600-24840 cm^-1 assignable to ³A_2g →³T_2g,→³T_1g,→³T_1g(P) transitions. The electronic absorptionspectra of aqueous ethanolic solution of Co^IIcomplex salts displayed electronic transitions near 19250-19300 and 23400-23500 cm^-1 as weak and broad bands due to d-d transitions. The electronic bands are assigned as ⁴T_1g→⁴A_2g and ⁴T_1g→⁴T_1g(P) transition as observed for octahedral Co^IIatom^7-8. The Pd^II complexes displayed a medium band at 425nm (23570 cm^-1) attributed from ¹A_1g →¹A_2g transition in square planer field^8-9. (Table-A)

The spectral parameters 10Dq, B and β for Ni^IIcomplexsalts [Ni(glyoxalcarbohydrazone)₂(H₂O)₂]X₂nH₂O (X = Cl^‾ or 1/2 SO₄^-2 and n = 2)were calculated using diagonal sum rule¹²and found to be 10Dq = 9680 cm^-1, B =786 cm^-1 and β  = 0.75 forcomplex chlorides and 10Dq = 9700cm^-1, B = 806cm^-1 and β = 0.77forcomplexsulphates. The 20 – 25% reduction of β value indicated appreciable covalent character in complex^10,12 [Ni(glyoxalcarbohydrazone)₂(H₂O)₂]X₂nH₂O. The infrared spectra of complexes in KBr disc exhibit broad band at 3050-3400cm^-1 attributed from ν(N-H),ν(C-H) and hydrogen bonded H₂O and coordinated H₂O of complexes molecule. The complexes shows a broad strong band at 1665-1652 cm^-1 attributed from ν(C=O) of carbohydrazone (-NH-CO-NH-) group of cyclic ring ^13,14. The medium band at 1592 cm^-1 and 1540 cm^-1are assigned to ν(C=N) and δ(N-H) of cyclic ring. The IR bands at 1430, 1332, 1256 and 1105 cm^-1 are due to β(N-H), ν(C-C), ν(N-N) and ν(C-N) of cyclic ring system of the complex¹³. The complex sulphates display a strong a broad band at 1100-1120 cm^-1and second weak band of 618 cm^-1attributed from ionic sulphate group present in complex sulphates. A medium band at 836 and 735 cm^-1 and weak bands at 635 and 506 cm^-1areattributed to δ(N-H), δ(C-H) and deformation vibrations of ring system.A medium broad band located near 675-685 cm^-1 is attributed to rocking vibration of coordinated water molecule^13,14. Thus on the basis of above observationsmacrocycic structure is proposed to complex M(glyoxalcbhzH)₂X₂nH₂O. The complexes of Ni^II and Co^II possess octahedral structure with two coordinated H₂O molecule while Zn^II and Cd^II complexes are four coordinated tetrahedral but Pd^II complex [Pd(glyoxalcbhzH)₂]Cl₂ is squre planer.

Thermal stability: – The complexes are quite stable in air. The hydrated complexes [M(glyoxalcbhzH)₂(H₂O)₂]SO₄2H₂O gradually lose two water molecules on heating above 50^oC and Cd^II or Zn^II complexes become anhydrous below 90^oC while Ni^IIand Co^II complexes salts retain two H₂Oand these are lost on heating above 160^oC. The complexes decompose above 300^oC to 380^oCeither in metal oxide and complex sulphate. In case of sulphate salt the final residue of heated product was metal oxide obtained between 460^oC to 530^oC. The thermal stability was studied at heating rate 10^oC per minute in static air. The decomposition of complex sulphate can be shown as follow on the basis of TGA studies.

The probable structure on the basis of analytical results, electrical conductance data and their physical measurement are suggested for Co^II, Ni^II,Pd^II,Zn^II and Cd^II complexes as shown below.

Scheme 1 Click here to View scheme

 

[M = Co^II or Ni^II and X = Cl^‾ or 1/2 SO₄^-2]Tetrahedral for[M = Zn^II or Cd^II]

Planer for Pd^II and n = 0 or 1 and X = Cl^‾ or 1/2 SO₄^-2

Acknowledgement

One of the autherRakeshRoshan (UGC fellow) is thankful to the UGC, New Delhi for the financial assistance. We are also thankful to the authority of BIT Mesra, Ranchi, for recording TGA. IIT Patna for IR and UV-spectra.

 

Table 1: Analytical Table and physical data

Complex Compound	Elemental analysis found (calc)			Electronic UV datacm-1
	% of M	% of N	% of anion
[Co{bis(glyoxalcbhzH)} (H2O)2]Cl22H2O	13.3 (13.7)	26.5 (26.3)	16.4 (16.9)	19000, 23000 cm-1
[Ni{bis(glyoxalcbhzH)} (H2O)2]Cl22H2O	13.4 (13.7)	26.1 (26.3)	16.6 (16.9)	9680, 16200, 24600 cm-1, 10Dq = 9680 cm-1, B = 680 cm-1, β = 0.77
[Pd{bis(glyoxalcbhzH)}]Cl2	26.1 (26.5)	28.2 (27.9)		23570 cm-1
[Zn{bis(glyoxalcbhzH)}]Cl2	17.7 (18.1)	30.7 (31.1)	19.6 (19.9)	—–
[Cd{bis(glyoxalcbhzH)}]Cl2	27.3 (27.6)	27.2 (27.5)	17.1 (17.4)	—–
[Zn{bis(glyoxalcbhzH)}]SO4H2O	15.6 (16.0)	27.5 (27.8)	23.6 (23.8)	—–
[Cd{bis(glyoxalcbhzH)}]SO4H2O	25.2 (25.6)	24.6 (24.9)	20.8 (21.1)	—–
[Ni{bis(glyoxalcbhzH)}(H2O)2]SO42H2O	13.2 (12.9)	25.2 (24.8)	13.4 (13.1)	9700, 16360 &14840 cm-110Dq=9700, B=806 cm-1, β=0.77
[Co{bis(glyoxalcbhzH)}(H2O)2]SO42H2O	13.4 (12.9)	25.2 (24.9)	13.3 (13.1)	19250 & 23400 cm-1

Table 2

Complex Compound	Color	µeff in BM R.T.	λαmol-1ohm-1cm2
[Ni{bis(glyoxalcbhzH)}(H2O)2]Cl22H2O	Light green	2.92	128
[Co{bis(glyoxalcbhzH)}(H2O)2]Cl22H2O	Light pink	4.92	138
[Zn{bis(glyoxalcbhzH)}]Cl2	Cream	Dia.	122
[Cd{bis(glyoxalcbhzH)}]Cl2	Cream	Dia.	131
[Ni{bis(glyoxalcbhzH)}(H2O)2]SO42H2O	Bluish green	3.01	120
[Co{bis(glyoxalcbhzH)}(H2O)2]SO42H2O	Pinkish cream	5.01	123
[Zn{bis(glyoxalcbhzH)}]SO4H2O	Cream	Dia.	128
[Cd{bis(glyoxalcbhzH)}]SO4H2O	Cream	Dia.	126

bis(glyoxalcbhzH) =bis (glyoxalcabohydrazone)

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