Synthesis and Spectral Studies of Cobalt (II) and Nickel (II) Complexes with 18-membered Macrocyclic Ligand Derived from Malonodihydrazide

Introduction

 Worldwide attentions have been given to studies on macrocyclic complexes with tetraaza   system^1-4 Consequently, we in the present communication, in continuation of our earlier interest^5-6, are reporting a series of cobalt(II) and nickel(II) macrocyclic complexes obtained by macrocyclization  between bis-(malonodihydrazide)metal(II) precursors with diketones such as 1-phenyl propane-1,2, dione: butane-2, 3-dione: pentane-2, 3-dione: and octane 2, 3-dione. Stoichiometry of the complexes have been found to be of the type [M(H₂Cy^1-4)]; where M = Co(II) and Ni(II); H₄Cy¹ = 8, 18-dimethyl-9, 17-diphenyl- 3, 5, 12, 14-tetraoxa, 1, 2, 6, 7, 10, 11, 15, 16-octaaza cyclooctadeca (18), 7, 9, 16-tetraene, H₄Cy²= 8, 9,17, 18,-tetramethyl- 3, 5, 12, 14-tetraoxa, 1, 2, 6, 7, 10, 11, 15, 16-octaaza cyclooctadeca (18), 7, 9, 16-tetraene; H₄Cy³ = 8, 18-dimethyl-9, 17- diethyl-3, 5, 12, 14-tetraoxa, 1, 2, 6, 7, 10, 11, 15, 16-octaaza cyclooctadeca (18), 7,9, 16-tetraene; H₄Cy⁴ = 8, 18-dimethyl-9, 17-dipentyl-3, 5, 12, 14-tetraoxa, 1, 2, 6, 7, 10, 11, 15, 16-octaaza cyclooctadeca¹ (18), 7, 9, 16-tetraene.

Figure 1: R=CH3; R’ = CH3, C2H5, C5H11, C6H5 Click here to View table

 

Experimental

 

All solvents and chemicals were of reagent grade. Solvents were dried over 4Å molecular sieves and degassed with dry nitrogen before use. Synthesis and manipulation were carried out under nitrogen atmosphere.

Nickel(II) acetate tetrahydrate was prepared by dissolving the carbonate in acetic acid of BDH quality followed by crystallization. Malonodihydrazide was prepared according to literature procedure⁷ and recrystallized several times before use.

Although the synthetic procedure of these compounds are reported in the literature we developed a new method. Preparation of one of the complex is described here.

[Ni(H₄Cy⁴)] 8, 18-dimethyl-9, 17-dipentyl- 3, 5, 12, 14-tetraoxa, 1, 2, 6, 7, 10, 11, 15, 16-octaaza cyclooctadeca¹ (18), 7, 9, 16-tetraene.

About 2.4g (0.02 mol) of malonodihydrazide was dissolved in 200 ml of hot water. A solution of metal(II) chloride hexahydrate (2.4g, 0.01 mol) in 100 ml of water was added to malonodihydrazide solution. A greenish blue solution was formed and it was refluxed for an hour. Octane-2, 3-dione (2.84 g, 0.02 mol) dissolved in a minimum amount of hot ethanol was added to the refluxing solution in small portions. The reflux was continued for a day. A mauve coloured solid was obtained. It was cooled, filtered and washed with warm water and hot ethanol and dried in vacuo. The dry solid was analysed. Analytical data, colour, magnetic moment and conductivity data have been shown in Table – 1.

Table 1: Analytical, colour, magnetic moment and molar conductivity data for nickel(II) and cobalt(II) macrocyclic complexes of the type [M(H₂Cy^1-4)] 

Compound (Colour)	% analysis found (calculated)				μeff	Ω-1cm2 mol-1
	M	C	N	H
Co(H2Cy1) (Brown)	14.63 (14.65)	41.64 (41.69)	27.70 (27.80)	4.95 (4.97)	2.2	8
Co(H2Cy2) (Chocolate)	10.76 (1.79)	52.13 (52.66)	20.41 (20.48)	4.37 (4.39)	2.3	7
Co(H2Cy3) (Red)	12.99 (13.09)	42.42 (42.58)	24.66 (24.88)	5.31 (5.33)	2.6	9
Co(H2Cy4) (Brown)	10.25 (10.27)	45.37 (45.92)	19.41 (19.18)	6.24 (6.27)	2.1	11
Ni(H2Cy1) (Pink)	14.61 (14.65)	41.62 (41.69)	27.66 (27.80)	4.93 (4.97)	Diamagnetic	8
Ni(H2Cy2) (Violet)	10.72 (10.79)	52.14 (52.66)	20.43 (20.48)	4.34 (4.39)	Diam	9
Ni(H2Cy3) (Mauve)	12.96 (13.09)	42.44 (42.58)	24.68 (24.88)	5.29 (5.33)	Diam	10
Ni(H2Cy4) (Yellow)	10.22 (10.27)	45.43 (45.92)	19.16 (19.18)	6.19 (6.27)	Diam	12

 

Table 2 : Important i.r. spectral bands (cm^-1) of malonodithydrazide, precursors [M(dihydrazide)₂Cl₂] and macrocycles [M(H₂Cy^1-4)] 

Compound	VN-H	VS(NH2)	VS(NH2)	Amide I	Amide II	Amide III	VC-N	VM-X
Malonodihydrazide	3290	3150	3015	1690	1620	1285	1120
[Ni(dihyd)2Cl2]	3350	3155	3010	1630	1615	1260	1100	460
[Ni(H2Cy1)]	3380	3200		1650	1540	1200	1120	465
[Ni(H2Cy2)]	3385	3205		1645	1545	1220	1110	470
[Ni(H2Cy3)]	3375	3210		1640	1540	1215	1115	465
[Ni(H2Cy4)]	3360	3205		1655	1550	1210	1110	460
[Co(dihyd)2Cl2]	3320	3150	3005	1675	1620	1250	1120	470
[Co(H2Cy1)]	3340	3180		1640	1535	1210	1110	455
[Co(H2Cy2)]	3335	3185		1645	1530	1215	1105	450
[Co(H2Cy3)]	3340	3180		1650	1535	1220	1125	460
[Co(H2Cy4)]	3345	3190		1640	1540	1210	1110	465

 

Results and Dicussion

 Macrocyclic complexes (Fig.2) containing a pair of α –diimine groups were synthesized by metal ion assisted template condensation of bis-(malonodihydrazide) (II) complexes with vicinal diketones like 1- phenyl propane-1, 2, dione ; butane-2, 3-dione; pentane-2, 3-dione; and octane-2, 3-dione;

The cyclisation reactions with diketones takes place readily and was marked by rapid change of colour. Besides, these reagents being comparatively less soluble in alcohol, dropwise addition of the ketones was carried out at longer intervals to avoid their precipitation and the reaction was likewise followed by observing gradual change of intensity of colour as the reaction progressed.

Infrared Spectra

Spectra have been recorded in the range 4000-400 cm^-1 and important bands have been recorded in Table-2. The spectra are clearly marked by a strong band in the region 3350 to 3200 cm^-1 testifying the presence of NH groups of one kind belonging to the amide functions. The lack of multiplicity of N-H stretching vibrations in this region further illustrates that the terminal NH₂ groups of parent dihydrazide complexes have entered into condensation with α –diketones to yield the macrocyclic complexes.

In the fingerprint region, the macrocyclic complexes show differences in their spectral features from one another and from parent precursors. The profiles of the spectra are strikingly dependent on the substituents on the α –diimine moieties. Nevertheless the vibrational bands corresponding to amide I, amide II, amide III and C-N stretching bands are clearly displayed in the regions 1680-1630 cm^-1, 1570-1515 cm^-1, 1270 – 1220 cm^-1 respectively.

The vibrational spectra of complexes show a well-defined band near 1680 cm^-1 which posesses the attributes of  stretching vibrations. A large number of bands are observed in the range 1600-1400 cm^-1. The bands appear in close proximity and this is the region where we expect ring-breathing vibrations of phenyl groups. Although from intensity considerations, we have been able to identify  stretching vibrations near 1600 cm^-1, for the Me₂Ph₂O₄ [16] tetraenato –(2) N₄(N₄)- metal (II) complexes, this band is not, however, distinct. ­­­­

In the region 900-300 cm^-1 we observe additional bands due to out-of-plane deformations for phenyl groups of the macrocyclic complexes besides some of the bands observed for the dihydrazide moieties. The spectra clearly demonstrate template condensation of the bis-(malonodihydrazide) complexes with the α –diketones. The structural features of these complexes involve bonding of amide groups with the metal centres and the macrocyclic ligand exists in a dianionic form. The di-anionic from of the ligands for the group of macrocycles appears to be one of the important factors for electrostatic interaction of the metal ion with the macrocyclic ligands, enclosing the metal ion in the macrocyclic cavity forming 6-membered chelate rings with the amide moieties and 7-membered rings involving α –diimine groups. A strong band in the region 460-470 cm^-1 in the spectra of all the macrocyclic complexes has been assigned to M-N stretching vibration; on⁸.

Electronic spectra and magnetic properties

The nickel(II) macrocyclic complexes [Ni(H₂Cy^1-4)] are diamagnetic and their electronic spectra show two intense bands one in the region 19000 to 21000 and another near 27000 cm^-1. The transitions are assigned to ¹A_2g ™¹A_1g and  ¹B_1g ™¹A_1g under a square planar environment having NiN₄ chromophore. The higher energy band is, however, more intense and the intensity is believed to arise due to metal šligand π* charge transfer transitions⁹.

The cobalt (II) complexes are of low spin type and are found to possess magnetic moments in the range 2.2 to 2.7 B.M. Electronic spectra of the complexes are similar and most of them exhibit two transition near 20,000 and 25000 cm^-1 respectively. The lower energy band has been assigned to the transition ²A_1g ground term to one of the higher energy term , ²A_2g or ²E_g , the split components of the orbitally triplets ²T_1g term. The higher energy band is more intense and indicates its origin due to metal šligand (π*) charge transfer transition^10,11.

Molar conductivity measured in DMF solution lies in the range 7-12 Ω^-1 cm² mol^-1 and indicate the macrocyclic complexes to be non-electrolytic in nature.

Table  3: Electronic spectral bands (in cm^-1) of the macrocyclic nickel(II) and cobalt(II) complexes of the type [M(H₂Cy^1-4)] 

S.N.	Complexes	L.F. Bands	C.T. Band	μeff (in B.M.)
01	Ni(H2Cy1)	20,000  25,000	28,000	Diamagnetic
02	Ni(H2Cy2)	20,800  25,200	28,000	Diamagnetic
03	Ni(H2Cy3)	19,300  22,500	27,000	Diamagnetic
04	Ni(H2Cy4)	20,500  22,700	27,500	Diamagnetic
05	Co(H2Cy1)	19,000	25,000	2.19
16	Co(H2Cy2)	19,500	24,800	2.37
07	Co(H2Cy3)	19,600	25,600	2.65
08	Co(H2Cy4)	19,400	25,300	2.48

 

 

On the basis of information received from spectral, magnetic and conductivity studies, macrocycles have been assigned structure as shown in Fig. 2.

Figure 2: M = Ni(II) and Co(II); R = CH3; R’ = CH3, C2H5, C5H11, C6H5 Click here to View figure

 

References 

1. S. Chandra, L.K. Gupta and Sangeetika, Synth. React. Inorg. Metal. Org. Chem., 34, 1591 (2004).
2. S. Chandra and L.K. Gupta, Spectrochim. Acta, 60A, 1563 (2004).
3. S. Chandra and A. Gautam, J.  Ind. Chem. Soc., 85, 980 (2008).
4. R.R. Jha and N.Sahu, Asian J. Chem., 20, 6301 (2008).
5. H.C. Rai and B.K. Rai, Asian J.Phys. 12, 133 (2003).
6. H.C. Rai, J.Tiwary and Rekha Kumari, Ind. J. Chem 27A, 1054 (1988).
7. B.S. Furniss et al., Vogel’s Textbook of Practical Organic Chemistry, ELBS/Longman, England, 1125 (1978).
8. S.Surendra Babu, P.G. Krishna, K. Hussain Reddy and G.H. Philip, Indian J. Chem., 47A, 1663 (2008)
9. A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier Pub. Co., Amsterdam, 343 (1968)
10. M. Nicolini, C. Pecile and A. Turco, Coord. Chem. Rev., 1, 133 (1966)
11. A.B.P. Lever, J. Lewis and R.S. Nyholm, J. Chem. Soc., 2552 (1963).

---

This work is licensed under a Creative Commons Attribution 4.0 International License.