Synthesis and Spectral studies of Ru (II) complexes with Macrocyclic Ligands

Introduction

During past few decades the chemistry of macrocyclic of metal have been developed very extensively due to its applications in coordination chemistry^1,2 bioinorganic chemistry³ catalysis ^4-6 organometallic chemistry; ⁷ and biocoordination chemistry ⁸. Many macrocyclic ligands e-g. Robson type tetraiminodiphenol macrocyclic ligands ^9,10 N₄S₂ donor macrocyclic ligands ¹¹; crown ethers; porphyrins; saturated and unsaturated polyamine ^6-12; polyazamacrocycles ¹⁸; have been synthesised.

A number of schiff base macrocyclic ligands have been reported ¹⁴. In which many macrocyclic ligands have been synthesised by the template condensation reaction ¹⁵. Several transition metal ion complexes in living organisms work as enzymes or carriers in macrocyclic ligand environment ¹⁶ and used as modelling on the active sites of metalloenzymes ¹⁷.

Various macrocyclic metal complexes have been used as detecting tumor lesions¹⁸ ; as in labeling monoclonal antibodies with radioactive models ¹⁹ as in metal ion separation ²⁰; as anticancerous ²¹; as toxicity against bacterial fungal growth ²²; as photosenstizer ²³; in photosynthesis and dioxygen transport ²⁴ ; as catalyst ^25-27; as pharmalogical agent; ^28,29 cancer  diagonsis ^30-32; as therapeutic radiotherapeutic ³³; as antitumour ³⁴; as potential medical applications ³⁵; as environmental importance ³⁶; as RNA cleavage catalyst ³⁷; and as NMR shift and relaxation agents ³⁸.

Few comprehensive reviews on macrocyclic ligands, their metal complexes and applications have been also published in last few years ³⁹. Many ruthenium (II) & (III) Schiff base and macrocyclic Schiff base complexes have been extensively studied in last few years due to their importance as biochemical and analytical reagents ⁴⁰. But ruthenium (II) macrocyclic Schiff base complexes are less known e.g.

Spectroscopic data studies and structures of trans–Ru(II) and Ru(III) bis (cyanide) complexes sustained by tetradentate macrocyclic tertiary amine ligand ⁴¹; N- macrocyclic complexes of Ru (II) & Ru (III); tetraaza macrocyclic Ru(II) complexes: synthesis, spectral and catalytic studies ⁴²; the versatile Ru II / Ru III teraaza macrocyclic complexes and their nitrosyl derivative [43]; Ru(II) & (III) complexes with cyclam and related species ⁴⁴; Ru (II) / (III) and oxovanadiun (IV) complexes with macrocyclic schiff base complexes; Ru (II) complexes of a new tetrapyrazolic macrocyclic; some new polynucleating ligands containing Ru (II) complexes incorporating terpyridyl and macrocyclic aza-crown binding sites. Recently some reviews on macrocyclic ligands have been also published ⁴⁵.  

Shankar et al. ⁴⁶ have been synthesised various ruthenium (II) complexes with macrocyclic Schiff base ligands derived from orthophthaldehyde and different diamines. Characterised and used as catalysts for the reduction of pralidoxime to its amino derivatives. In this present communication, fifteen macrocyclic schiff base ligands will be synthesie by condensation reaction of 2,5-diformyl furan or furil or phenanthrene 9,10-dione with different aliphatic diamines NH₂(CH₂)_nNH₂ i.e. NH₂CH₂CH₂NH₂ or NH₂CH₂CH₂CH₂NH₂ or NH₂CH₂CH₂CH₂CH₂NH₂ or NH₂CH₂CH₂CH₂CH₂CH₂NH₂ or NH₂CH₂CH₂CH₂CH₂CH₂CH₂NH₂ and their ruthenium (II) metal complex through template synthesis in 2:2:1 molar ratio respectively.

Experimental

RuCl₃.3H₂O (Johnson Matthey & Co, Ltd; triphenylphosphine Merck, Mumbai); ethanol (Merck, Mumbai); dichloromethane (Aldrich) and acetone (Aldrich ) were AR Grade and used after purification and dried. Solvents were distilled from relevent drying agents immediately in advance of use. [RuCl₂ (PPh₃)₄] was prepared by published method.

Melting points were determined by using in sealed capillary tube on Melting point apparatus. The C and H were determined by CDRI, LUCKNOW, INDIA. Nitrogen and chlorine were determined by Kjeldahl’s and Volhard’s methos respectively. Molar conductivity was measured on Elico-CM 82 conductivity bridge in acetone at room temperature. IR spectra were recorded on Perkin-Elmer 1000 IR spectrometer using KBr/CsI pellets. Electronic spectral measurements were recorded on Elico SL159 spectrophotometer in the range 300-1000 nm. Magnetic measurements were carrid out a Cahn 2000 electo balance by Faraday Method using Hg[Co(SCN)₄] as calibrant. Pascal constants were used for diamagnetic corrections. Kratos analytical Axis Supra ESCA i.e. X-ray photoelectron spectroscopy i.e. XPS instrument equipped with monochromatised Alk_α (1486.6 eV) source is used. All the peaks were rectified for charging with reference to C1_S peak 284.8 eV and counterd with Shirley background and a union of Gavssian and Lorentzian line- shapes, using ESCApe software.

2,5- diformylfuran or furil or phenanthrene 9,10- dione was mixed in dry ethanolic solution of  NH₂(CH₂)_nNH₂ (2 mmol) (where (2 mmol) n=2 or 3 or 4 or 5 or 6). and refluxed for 2 hrs for preparation of ligands L₁ to L₁₅). In this resulting each solution poured [RuCl₂(PPh₃)₄ (1mmol ) i.e. 1:1 molar ratio and again refluxed for about 2 hrs. The resulting precipitate was filtered and recrystallised by benzene: pet-ether (9:1) ratio (Figs. 1-3).

Figure 1: Preparation of [RuCl2L1-5] complexes Click here to View figure

Figure 2: preparation of [RuCl2 (L6-10)] complexes. Click here to View figure

Figure 3: Preparation of [RuCl2(L11-15)] complexes Click here to View figure

Results and Discussion

Fifteen tetraaza macrocycliccomplexes containing Ru(II) were synthesised by interaction of [RuCl₂(PPh₃)₄] with fifteen macrocyclic Schiff base ligands (L¹ to L¹⁵). The complex were soluble in DMF, DMSO and chloroform. The elemental analysis (C, H, N and Cl) were consistent within ±0.5% with the suggested structure of the complexes. The molar conductance values were found to below (12.0-20.0 ohm^-1 cm² mol^-1) recommending the non electrolytic nature of the complexes ⁴⁷.

In these entire [RuCl₂L^1-15] complexes IR band due to ν_C=N was shifted towards lower side about 20-40 cm^-1 with respect to the ligand spectra and was obtained in the range of 1600- 1580 cm^-1. A low intensity band in the region of 520-500 cm^-1 were observed due to ν_Ru-N vibration confirm that ligands coordinate to Ru metal ion through nitrogen of C=N group in all these complexes ⁴⁸. Only one band was observed in the range of 320-300 cm^-1 in IR spectra of all these complexes indicating the presence of two chloride ions in trans position around ruthenium ion [49]. All the Characteristic IR bands were also observed due to aromatic rings in the expected region in all these [RuCl₂L^1-15] complexes ⁴⁹.

The ground state of Ru (II) t_2g⁶ electronic configuration is ¹A_1g. For octahedral Ru (II) complexes four electronic transition are possible i.e ¹A_1g→³T_1g; ¹A_1g→³T_2g; ¹A_1g→¹T_1g and ¹A_1g→¹T_2g. In each complexes of [RuCl₂ (L^1-15)] two electronic bands were observed in the region 200-530 nm. These electronic bands have been assigned to the spin allowed ¹A₁g-¹T₁g transition at lower wavelength (460-520 nm) based on molar extinction coefficient. The another high intensity band at 280-290 nm region has been assigned due to charge transfer transition originated from the excitation of an electron from the  metal t_2g level to the unfilled molecular orbital derived from the π* level of the ligands. All these [RuCl₂L^1-15] complexes have shown negative magnetic susceptibility and magnetic moment values below then 1.0 BM at room temperature corresponding to diamagnetic nature.

Table 1: Physical and Analytical data of [RuCl₂L^1-15)] Complexes

Sr. No	Complexes	% found (Calculated)				^M Ohm-1 cm2 mol-1
		C	H	N	Cl
1	[RuCl2.L1)]	41.4	3.2	11.6	15	10
		-41.5	-3.3	-11.8	-15
2	[RuCl2.L2)]	43.4	4	11	14.2	12
		-43.5	-4	-11.2	-14.3
3	[RuCl2.L3)]	42.6	4.4	10.6	13.4	18
		-42.7	-4.5	-10.6	-13.5
4	[RuCl2.L4)]	47.6	5	10	12.6	16
		-47.8	-5	-10.1	-12.8
5	[RuCl2.L5)]	50.4	5.4	9.4	12	10
		-50.5	-5.4	-9.4	-12
6	[RuCl2.L6)]	54.2	3.6	10.5	13.4	12
		-54.4	-3.7	-10.5	-13.4
7	[RuCl2.L7)]	56	4.2	10	12.6	14
		-56	-4.3	-10	-12.7
8	[RuCl2.L8)]	69	5.6	11.4	14.6	16
		-69.2	-5.7	-11.5	-14.6
9	[RuCl2.L9)]	30.6	4	7	9	12
		-30.7	-4.4	-7.1	-9
10	[RuCl2.L10)]	59.8	3.2	11.6	15	18
		-59.9	-3.3	-11.8	-15
11	[RuCl2.L11)]	68	4.8	7	9	20
		-68	-4.9	-7.1	-9
12	[RuCl2.L12)]	68.6	4.6	9.2	11.8	18
		-68.8	-4.7	-9.4	-11.9
13	[RuCl2.L13)]	69.4	5	9	11.2	16
		-69.5	-5.1	-9	-11.4
14	[RuCl2.L14)]	71.2	4	8.6	11	14
		-71.3	-4.4	-8.7	-11.1
15	[RuCl2.L15)]	75	4.2	8.6	11	12

Table 2: Infrared Spectral data of [RuCl₂(L^1-15)] Complexes

Sr. No	Complex	Selected IR bands (cm-1)
		VC=N	VRu-N	V Ru-Cl
1	[RuCl2.L1)]	1580	520	320
2	[RuCl2.L2)]	1570	515	310
3	[RuCl2.L3)]	1575	518	305
4	[RuCl2.L4)]	1580	515	316
5	[RuCl2.L5)]	1570	500	300
6	[RuCl2.L6)]	1580	510	315
7	[RuCl2.L7)]	1580	505	305
8	[RuCl2.L8)]	1580	500	320
9	[RuCl2.L9)]	1600	515	315
10	[RuCl2.L10)]	1600	518	320
11	[RuCl2.L11)]	1590	510	320
12	[RuCl2.L12)]	1580	508	315
13	[RuCl2.L13)]	1600	515	310
14	[RuCl2.L14)]	1580	520	305
15	[RuCl2.L15)]	1580	515	320

Table 3: Ru3p_{1/2, 3/2}; N1s and Cl2p binding energies (eV) in ligand; [RuCl₂(L^1-15)] complexes.

Sr. No	Ligand & Complexes	Ru3P1/2, 3/2		N1s	Cl2p
		Ru3P1/2	Ru3P3/2
1	L1	—	—	400.6	—
2	L2	—	—	400.6	—
3	L3	—	—	400.6	—
4	L4	—	—	400.6	—
5	L5	—	—	400.6	—
6	L6	—	—	400.6	—
7	L7	—	—	400.6	—
8	L8	—	—	400.6	—
9	L9	—	—	400.6	—
10	L11	—	—	400.6	—
11	L11	—	—	400.6	—
12	L12	—	—	400.6	—
13	L13	—	—	400.6	—
14	L14	—	—	400.6	—
15	L15	—	—	400.6	—
16	[RuCl2(PPh3)4]	482.8	460.8	—	201.6
17	[RuCl2.L1)]	482	460	402.8	202.8
18	[RuCl2.L2)]	482	460	402.8	202.8
19	[RuCl2.L3)]	482	460	402.8	202.8
20	[RuCl2.L4)]	482	460	402.8	202.8
21	[RuCl2.L5)]	482	460	402.8	202.8
22	[RuCl2.L6)]	482	460	402.8	202.8
23	[RuCl2.L7)]	482	460	402.8	202.8
24	[RuCl2.L8)]	482	460	402.8	202.8
25	[RuCl2.L9)]	482	460	402.8	202.8
26	[RuCl2.L10)]	482	460	402.8	202.8
27	[RuCl2.L11)]	482	460	402.8	202.8
28	[RuCl2.L12)]	482	460	402.8	202.8
29	[RuCl2.L13)]	482	460	402.8	202.8
30	[RuCl2.L14)]	482	460	402.8	202.8
31	[RuCl2.L15)]	482	460	402.8	202.8

 

The binding energies (eV) of prepared ligands i.e. L^1-15; [RuCl₂(PPh₃)₄] and [RuCl₂(L^1-15)] in Table­ I (Figs.4-6) for Ru3p_{1/2, 3/2}, N1s and Cl2p photoelectron peaks. It was observed that Ru3p_1/2, _3/2 binding energies in starting material [RuCl₂(PPh₃)₄] were higher (BE= ~ 482.8 eV and 460.8 eV for Ru3p_1/2 and Ru3p_3/2) than in prepared [RuCl₂L^1-15] complexes (Ru3p_1/2 BE= 482.0 eV and Ru₃P_3/2 BE 460.0 eV ); suggesting that electron density in ruthenium metal ion is more in prepared [RuCl₂L^1-15] complexes than in [RuCl₂(PPh₃)₄] due to coordination [50] (Figs.4-6).

Figure 4: Ru3p1/2 binding energies (eV) in [RuCl2(L1-15)] complexes Click here to View figure

Figure 5: Ru2p3/2 binding energies (eV) in [RuCl2(L1-16)] complexes prepared [RuCl2(L1-15)] metal complexes. Click here to View figure

Figure 6: N1s binding energies (eV) in Ligands and [RuCl2(L1-15)]  complexes prepared. Click here to View figure

The N 1s photoelectron spectra of all these [RuCl₂(L^1-15)] complexes have shown only one signal symmetrical photoelectron peak towards higher binding energies side ( BE= ~ 402.8 eV) than N_1S photoelectron peak of each ligand (~  BE = 400.6 eV) suggesting all four nitrogen atoms of each ligand is coordinated with ruthenium (II) metal ion ⁵⁰ (Fig.6) & Table.I) The Ru 3s photoelectron peak in all these prepared [RuCl₂(L^1-15] metal complexes. have shown symmetrical peak at 584.6 i.e. have not shown multiple splitting diamagnetic nature [50]. The Cl_2p photoelectron spectra of all these [RuL₂(L^1-15] complexes have shown one sharp peak at BE~ 202.4-202.0 eV; suggesting inner sphere chlorine atom in trans position ⁵⁰.

Conclusion

In the present paper, fiffteen Ru(II) complexes of the type [RuCl₂L^1-15] have been synthesized and characterized with fifteen tetraaza macrocyclic ligands. On account of analytical and spectralstatistics octahedral geometry were provisionallyproposed for all of these complexes.

Acknowledgement

The author AshishRajak is thankful to Chemistry Department, University of Allahabad, Prayagraj for affording financial assistance to the research work and instrumental facilities and Arpit Srivastava, Ramakant and SCS are gratified to UGC-CSIR, New Delhi, India for providing the financial support as UGC JRF (Ref. no- 191620091263), UGC-SRF (Ref. no- 354/CSIR-UGC NET DEC. 2017) and UGC-SRF (Ref. no- 19/06/2016(i)EU-V) respectively.

Conflicts of interest

The authors declareno conflict of interest in the present research work.

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