КООРДИНАЦИОННАЯ ХИМИЯ, 2007, том 33, № 12, с. 943-946
УДК 541.49
COORDINATION PATTERNS: SPECTROSCOPIC AND ELECTROCHEMICAL INVESTIGATION ON MANGANESE (II) WITH MACROCYCLIC LIGANDS DERIVED FROM TWO DIFFERENT
ORGANIC SKELETONS
© 2007 R. Kumar* and S. Singh**
* Department of Chemistry, University of Delhi, New Delhi 110007, India ** Indian Institute of Management, Kolkata, India Received August 8, 2006
Two novel macrocyclic ligands and their complexes Mn(Lx and L2)]X2 (L1 and L2 = 1,10-diaza-5,6,15,17-tet-raoxa (tetrathia)-2,3:8,9:12,13,18:19-tetrabenzocyclododeca-10,20-diene; X = Cl, NO3, NCS, SO4) were primed and their capacity to sustain the Mn2+ ion in solid, as well as in aqueous solution, was resoluted from an assortment of physicochemical measurements, viz., elemental analyses, molar conductance measurements, magnetic susceptibility measurements, mass, IR, 1H NMR electronic, ESR spectral studies, and cyclic voltam-metric (CV) measurements.
INTRODUCTION
Our interests are primarily inattentive on synthetic and structural aspects of coordination chemistry with particular stress on the use of geometric factors to control metal-ligands interactions and other properties in ring systems [1-2]. As it was earlier observed, manganese plays an essential responsibility in the metabolism of dioxygen and its condensed forms [3]. Previous efforts make accessible a better understanding of the structure, spectral features, and reactivity patterns of small molecules that can act as models for each of these categories of enzymatic reactions in biological systems have been represented [4-7]. This letter is geared up in such a way in which new manganese(II) complexes with macrocyclic ligands containing different donor atoms. Ligands L1 (1,10-diaza-5,6,15,17-tetraoxa-2,3:8,9:12,13,18:19-tetrabenzocyclododeca-10,20-diene [N2O4]) and L2 (1,10-diaza-5,6,15,17-tetrathia-2,3:8,9:12,13,18:19-tetrabenzocyclododeca-10,20-diene [N2S4]) have been developed.
EXPERIMENTAL
All used solvents were purified before use according to standard procedures. 1,2-Di(c-nitrophenoxy)ethane has been prepared and reduced to 1,2-di(c-aminophe-noxy)ethane. By analogy, 1,2-di(c-nitrothiol)ethane has been prepared and reduced to 1,2 di(c-aminophe-noxy)ethane. Both used diamines have been prepared as it was reported earlier [1].
Elemental analysis (C, H, N) of complexes was carried out on a Carlo-Erba 1106 elemental analyzer. Molar conductance was measured on an ELICO conductivity bridge (Type CM82T). Magnetic susceptibility measurements were made on a Gouy Balance at room temperature using CuSO4 • 5H2O as calibrant. The molecular
weight of the complexes was determined in benzene (freezing point). IR spectra were recorded on a Perkin Elmer 137 instrument as Nujol mulls/KBr pellets. Electronic spectra were recorded in a DMSO solution on a Shimadzu UV 1240-mini spectrophotometer. XH NMR spectra of the macrocyclic ligands were recorded on Bruker Avance 300 spectrophotometer at 100 kHz modulation and higher frequency. Electron impact mass spectra were recorded on Jeol, JMX, and DX-303 mass spectrometers. ESR spectra of the complexes were recorded as powdered samples at room temperature on an E-4 ESR spectrometer using diphenylpicrylhydrazyl (DPPH) as the g-marker and in a DMSO solution, as well as in different solution. Their electrochemical behavior was examined by cyclic voltammetry using a platinum wire as auxiliary and Ag/AgCl as reference electrodes.
Synthesis of ligands L1 and L2. A hot (~500°C) solution (1 mmol, 20 ml) of corresponding diamines in 80% ethanol (20 ml) was added to an ethanolic solution (20 ml) of dialdehyde (1 mmol) in the presence of 1 ml of HCl (conc.), and the mixture was stirred in a 100 ml round bottle flask. The mixture was refluxed for several hours at a temperature of ~70-80°C, and the progress of the reaction was ascertained by noted the liberated water azeotropical-ly. The reaction mixture was cooled to ~5°C, and the precipitate was filtered off and washed with 50% ethanol and dried over P4O10 in a vacuum desiccator.
Spectral data for macrocyclic ligands. The IR spectra of both ligands show the absence of a band in the region ~3400 cm-1 corresponding to free primary diamine and suggests that complete condensation takes place between free amino groups with carbonyl groups which confirms the complete condensation of the precursor molecule, but new stretching vibration band for azomethine
Table 1. Elemental analysis data for the synthesized macrocyclic manganese(II) complexes
Complex (empirical formula) Color Content (found/calcd), %
Mn C H N
[Mn(L1)]Cl2(MnC3oH26N2O4Cl2) Light yellow 9.00/9.09 59.21/59.62 3.90/3.99 8.32/8.52
[Mn(L1)](NO3)2(MnC3oH26N4O1o) Yellow 8.21/8.36 54.65/54.80 4.20/4.26 11.00/11.11
[Mn(L1)](NCS)2(MnC32H26N4O4S2) Light yellow 8.32/8.46 59.43/59.16 3.90/4.03 8.12/8.62
[Mn(L1)]SO4(MnC3oH26N2O8S) Yellow 8.50/8.73 57.01/57.24 3.91/4.16 4.21/4.45
[Mn(L2)]Cl2(MnC3oH26N2S4Cl2) Light yellow 7.91/8.01 53.32/53.89 3.34/3.60 10.21/10.7
[Mn(L2)](NO3)2(MnC3oH26N4S4O6) Light yellow 8.10/8.22 60.00/60.42 3.67/3.92 4.10/4.19
[Mn(L2)](NCS)2(MnC32H26N4S6) Light yellow 7.10/7.70 53.43/53.84 3.69/3.82 7.12/7.85
[Mn(L2)]SO4(MnC3oH26N2S5O4) Light yellow 7.25/7.92 51.23/51.93 3.53/3.78 4.21/4.04
>C=N groups appears at 1608 and 1510 cm1 [2, 3] providing strong evidence for the presence of a cyclic product. The absorption in IR spectra of the ligands in the ranges of 777-778 and 1420-1110 cm-1 is due to the presence of phenyl group [4].
The XH NMR spectrum of all the ligands in CDCl3 does not give any signal corresponding to primary amine. These data support the macrocyclic nature of the product. For L1 1H NMR (5, ppm): 8.9 (s., 2H); 7.3 (m., 4H); 7.1 (m., 8H); 6.9 (m., 2H); 6.8 (m., 2H); 4.4 (s., 8H) and for L2 1H NMR (5, ppm): 8.8 (s., 2H); 7.4 (m., 4H); 7.2 (m., 8H); 6.9 (m., 2H); 6.8 (m., 2H); 4.2 (s., 8H).
The electron impact mass spectra of metal free ligands confirm the proposed formula by showing a peak corresponding to the macrocyclic moiety. The series of peaks can be assigned to various fragments. Their intensity gives an idea of stability of the fragments. The proposed structures of the macrocyclic ligands are given below:
L1 (Y = O); L2 (Y = S)
Synthesis of complexes. A hot (~65°C) ethanolic solution (20 ml) of the ligands (0.02 mol) and a hot (~55°C) ethanolic solution (20 ml) of the manganese(II) salt (2 mmol) were mixed together with constant stirring. The mixture was refluxed for 5-6 h at 85-90°C. On cooling the content to ~5°C, the colored complexes were precipitated out. They were filtered off, washed with cold EtOH, and dried under vacuum over P4O10. The re-
actions (1) and (2) are quite facile and can be completed in 5-6 h of refluxing
L1 + MnX2 • nH2O Mn(L1 )X2 + nH2O, (1)
L2 + MnX2 • nH2O—- Mn(L2)X2 + nH2O, (2) where X = Cl-, SO-, NO3, and NCS-.
RESULTS AND DISCUSSION
On the basis of the elemental analyses (Table 1), the compositions of all the complexes is [ML]X2 (L = L1 or L2). The molar conductance of all the complexes was measured in DMSO and the observed values correspond to the 1 : 2 electrolytic nature. All the studied manga-nese(II) complexes show a magnetic moment in the range of ^eff = 5.85-6.00 corresponding to five unpaired electrons at room temperature.
The presence of the main IR bands corresponding to various fragments of the both ligands confirms complex-ation and formations of cyclic system after condensation. In IR spectra of complexes, all peaks are shifting to lower frequency as compared to the macrocyclic ligands that demonstrates the coordination linkage (Table 2).
Nitrate ion presence is confirmed in the complexes of both ligands by displaying a sharp band at 1385 and 1384 cm-1 which represents the free ion nature [8-9]. Spectral studies of sulfato complexes of both ligands show sharp bands in the range of 1101-1115 cm-1 which confirm ionic behavior of the sulfato group [10].
The electronic spectra of the manganese(II) complexes (Table 3) exhibit four weak-intensity absorption bands in the ranges 17421-18911, 23255-25630, 28653-29001, and 34482-34401 cm-1 , which can be assigned to the transitions: %g — %g(4G), 6Alg — %, 4Alg(4G) (10B + 5C), 6A1g —- %(4D) (17 B + 5C) and 6A1g — — 4T1g(4P) (7B + 7C), respectively [11-13].
All the ligand field parameters are calculated to demonstrate the stereochemistry of the complexes. First, we tried to detect the value of parameters B and C, which were calculated from the second and third transitions. The
SPECTROSCOPIC AND ELECTROCHEMICAL INVESTIGATION ON MANGANESE(II) 945
Table. 2. IR spectral data (cm x) of the manganese(II) complexes
Complex v(C=N) v(Mn-N) v(Mn-O) v(NO3) v(NCS) v(SO4)
[Mn(L1)]Cl2 1601 601 500, 511
[Mn(L1)](NO3)2 1601 601 500 1385
[Mn(L1)](NCS)2 1601 601 500 2050
[Mn(L1)]SO4 1602 604 500 1184, 1042
[Mn(L2)]Cl2 1601 617
[Mn(L2)](NO3)2 1601 607 1384
[Mn(L2)](NCS)2 1607 606 2050
[Mn(L2)]SO4 1603 605 1184, 1042
reason to take them and use mathematically is because these transitions are free from the crystal field splitting. Their values are represented in Table 4. These parameters are linear combinations of certain Coulomb and exchange integral, which are generally treated empirical parameters obtained from the spectra of the free ions. Orgel [14] calculated the values of Dq with the help of the curve of transition energies versus Dq, as given by using of the energy due to the transition 6A1g —► 4T1g (4G). F2 and F4 are known as Slater-Condon shortly repulsion parameters, which are calculated and relate to Racah parameters B and C as: B = F2-5F4 and C = 35F4. From the observed data it is clear that the electron-electron repulsion in the complexes is observed more than in the free ion, resulting in an increased distance between electrons. Thus, it affects the size of the orbital. On increasing delocalization, the value of P decreases to less than one in the complexe
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