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Synthesis, structure and electrochemical behaviour of manganese(II) complexes with 2,6-bis(benzimidazol-2′-yl)pyridine
Po/y/ze&on Vol. II, No. IS, pp. 1909-1915, Printed in Great Britain
1992 0
0277-5387/92 $5.00 + .a, 1992 Pergamon Press Ltd
SYNTHESIS, STRUCTURE AND ELECTROCHEMICAL BEHAVIOUR OF MANGANESE(H) COMPLEXES WITH 2,6-BIS(BENZIMIDAZOL-2’-YL)PYRIDINE WANG SI-IUANGXI, ZHU YING, ZHANG FANGJIE, and WANG LIUFANGT
WANG QIUYING
Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R.C. (Received 6 February 1992 ; accepted 24 March 1992)
Abstract-The complexes of manganese(I1) with 2,6-bis(benzimidazole-2’-yl)pyridine were synthesized and characterized by elemental analysis, electrical conductance, IR and electronic spectra and thermal analysis. The electrochemical behaviour of the complexes was described and the X-ray crystal structure of MnLCl, - DMF was determined. The complex crystallizes in the monoclinic system, space group P2,,, with 2 = 4, a = 14.56(2), b = 7.937, c = 19.862(4) A, j? = 102.31[2]“. The geometry about manganese is a distorted square pyramid.
Benzimidazole derivatives and their metal complexes have been extensively investigated. This has been mainly due to the following facts : (1) these compounds possess a broad spectrum of biological activities ;lm4 (2) the antiviral activity of some 2substituted benzimidazoles has been considered to be related to their ability to chelate with trace metal ions in biological system;3,5 and (3) it has been recognized that many of these complexes may serve as simple models which mimic both the structure and reactivity of metal ion sites in complex biological systems. k9 Studies on 2,6-bis(benzimidazol-2’-yl)pyridine (BBP), as a benzimidazole derivative, and its complexes with some divalent metals have been reported. ‘&I5 However, no paper concerning the study of manganese(I1) complex with BBP has been seen. Also, in our previous work’ 6we have reported the synthesis and structure of a manganese(B) complex with a hydrazone ligand derived from pyruvic acid and 4-pyridine carboxylic acid hydrazine. Therefore, in this paper, we wish to report the syntheses, characterization and structure of BBP complexes with different manganese(I1) salts and discuss their electrochemical properties.
EXPERIMENTAL Reagents
The ligand 2,6-bis(benzimidazole-2’-yl)pyridine was prepared by the literature method.” The hydrated manganese(I1) salts and organic solvents were of reagent grade. Preparation
of complexes
To a solution of BBP (10 mmol) in Me&O (20 cm3) a solution of the appropriate manganese(I1) salts (MnC12 * 4H20, Mn(Ac), *4H20, MnSO,. 7H20 and Mn(N03)2-6H20) (5 mmol) in Me, CO (10 cm’) was added dropwise with stirring at room temperature. A yellow colour appeared and a precipitate was formed in a few minutes. After stirring for several hours, the product was collected by filtration, washed with CH,OH, Me,CO and Et,O, and dried in a vacuum desiccator over P40, o. The complex MnL2(C10& * 3H20 was prepared in a similar manner to the above method except that the molar ratio of metal-ligand used was 1 : 3. A white precipitate was obtained. Measurements
t Author to whom correspondence should be addressed.
Carbon, nitrogen and hydrogen were determined by a Carlo-Erba 1106 elemental analyser. The IR
1909
1910
WANG
SHUANGXI
spectra were recorded on a Nicolet-170X FT-IR spectrophotometer in CsI discs in the range 400& 200 cm- i. UV spectra were measured with a Shimadzu W-240 spectrophotometer in the range 19& 900 nm using a solution in DMF. Electrolytic conductance measurements were made with a DDSIIA molar conductometer with DMF as the solvent at 25°C. TGA analyses were carried out with a Du Pont 1090 thermal analyser in a nitrogen atmosphere. Cyclic voltammograms were performed on a U.S. EG&E PARC electrochemical analyser at a complex concentration of 1.Ox lo- 3 M in DMF with 0.1 M (Et,N)ClO, as the supporting electrolyte. A glass-carbon working electrode, a platinum wire auxiliary electrode and a saturated calomel reference electrode were employed. X-ray structure determination
of MnLCl, * DMF
Single crystals were obtained by slow evaporation of a DMF solution of MnLCl,. A transparent light yellow crystal (0.15 x 0.22 x 0.37 mm) was mounted on an Enraf-Nonius CAD-4 diffractometer. The unit cell was measured by centring 25 reflections (10 < 0 < IS’) and refined by least-squares methods. Graphite-monochromated MO-K, radiation was used. Intensities were measured with an ~~-28 scan technique, scan width (0.52 + 0.34 tan 0) and 0 range 1 <0<24” (h= -16-16; k=O-9; I= O-23). 3939 independent reflections were collected, of which 2683 were considered as observed [I > 30(Z)]. Intensities were corrected for Lorentzpolarization and I,$empirical absorption corrections (transmission factor range from 77.72 to 99.8%). The manganese atom was located from a Patterson synthesis and the remaining non-hydrogen atoms from Fourier syntheses. The structure was refined isotropically and anisotropically by a leastsquares refinement. The function minimized was C w(]FOl- jFJ)2, where w = 1. All hydrogen atoms were located from a difference synthesis and refined with an overall isotropic thermal parameter. The final R factor was 0.062, (A/a)m,, = 0.23, and the final difference-Fourier map showed peaks being less than 0.45 e A- I. Atomic scattering factors were taken from ref. 17. All calculations were carried out on a PDP 11/44 computer using the SDP package. Supplementary data, including final atomic coordinates, thermal parameters, bond lengths and angles, and structure factors, have been deposited with the Editor and with the Cambridge Crystallographic Data Centre. Crystallographic
data
Crystal data. Monoclinic P2,/n, a = 14.561(2), c = 19.862(4) A, jI = 102.31(2)“,
b = 7.937(l),
et al.
V = 2242.6
A3, M, = 510.29,
~(Mo-K,) = 8.32
cm- ‘,
Z = 4, D, = 1.512 R = 0.062,
cm- ‘,
R, = 0.059. RESULTS AND DISCUSSION
Reactions of manganese(H) salts [MnSO, - 7Hz0, Mn(N03)2 * 6H20 and Mn(ClO,), * 6H2O] with BBP in Me,CO yield 1 : 2 (metal: ligand) complexes, while MnC12 * 4H,O and Mn(Ac), * 4H20 yield only 1: 1 (metal : ligand) complexes in spite of using a 1 : 2 or 1 : 3 molar ratio of metal : ligand (Table 1). The complexes are air-stable at room temperature, soluble in Me&JO, CH30H, DMF and DMSO and insoluble in water and nonpolar organic solvents. In Table 1 the TGA data of all complexes having water show that the water molecules are present as lattice water. IR spectra
The important IR data of the complexes are listed in Table 2. A broad band at 3185 cm- ’ in the free ligand assigned to the N-H group of the benzimidazole ring is shifted to lower frequencies by N 110 cm-’ in all complexes. This may be due to the existence of a hydrogen bond between the hydrogen of the N-H group of the bcnzimidazole ring and counter-anions in these complexes. The new bands in the 389-352 cm- ’ region in the spectra of all complexes are tentatively attributed to v(Mn-N). I ’ The IR spectrum of the acetate complex exhibits two bands at 1681 and 1363 err-’ assigned to v(C=O) and v(C-O), respectively, which indicates that the acetate groups are coordinated to the manganese(I1) centre as unidentate ligands. ” This is further supported by the fact that the complex behaves as a non-electrolyte and exhibits a medium new band at 531 cm-’ due to v(Mn-0). The IR spectrum of the sulphate complex shows splitting of v3(S04) (1098 and 1060 cm- ‘) and v4(S04) (602 and 633 cm- ‘) bands, suggesting unidentate behaviour for the sulphate group. This is in agreement with the non-electrolytic behaviour of the complex. So, the sulphate complex could be formulated as [MnL,(SO,)] * 4H20. It is possible that one of the two BBP ligands in the complex is tridentate and the other bidentate, and as observed in the copper complex, ” the manganese(I1) is sixcoordinated. In the IR spectrum of the nitrate complex, a strong absorption band at 1389 cm- ’ occurs which is typical of the uncoordinated nitrate group. Although the spectrum of the perchlorate complex exhibits splitting of the v3(C104) (1128 and
78 62
Pale yellow
Light yellow
White
[MnLzSOJa4Hz0
[MnLJ(NG&S3H@
[MnL j(ClO&*
3059brm 3078brm
3368sh 3480brw
a nm, in DMF. ‘a-’ cm2 mol-‘, in DMF. s : strong ; m : medium ; w : weak ; br : broad ; sh : shoulder.
172.0 101.0
312,333 313,330
[MnL21CNGJ2*3H~G [MnLJ(ClO& - 3H20
3061brm 3051brm
-
7.2 1.8
316,330 310,334
[MnL(AC)d [MnL,SO.,]*4H,O 3465sh
5.1
3185brm 3065brm
-
-
v(N-H)
v(GH)
Amb
311 314,322
UV” x + Jr*
Ligand [MnLCl,]
Complex
359
360
389
345
377
385
Decomposition point (“C)
r
52.7 (52.2) 51.4 (51.8) 56.7 (57.0) 54.4 (54.0) 53.6 (53.3) 48.8 (49.0)
C 16.3 (16.0) 16.2 (16.5) 14.4 (14.5) 16.2 (16.6) 19.3 (19.6) 14.7 (15.1)
N
3.5 (3.4)
(:f)
(Z)
(:I)
(Z) 3.9 (3.9)
H
\
(Z)
(E)
(&
-
-
r Weight loss%
I
1681s 1098s 633m 1389s 1128s
v(NG;)
1041s
1363m 1060s
-
v(SD;)
IR A
-
621s
531m 522~
-
-
602m
v(Mn-0)
352~ 380~
357w 389~
382~
-
v(Mn-N)
72-l 18
76-105
62-80
-
-
-
269~ 251~
v(Mn-Cl)
3H20
3H20
4Hz0
-
-
-
Assignment
TGA analysis , Temperature range (“C)
v(AC-)
\
Table 2. Important IR and electronic spectral data and molar conductances for the ligand and its complexes
‘Required values are given in parentheses.
47
56
Light yellow
[MnL(AC)J
3H20
49
Yellow
[MnLCl,] - DMF
61
Yellow
Colour
[MnLCl,]
Complex
Yield (%)
Analysis (%) L
Table 1. Analytical and physical data of the complexes
,
5,
g z
3 ; 4 $$
i 8’ p
5E 8 El a b ! % .ll 5” z x
1912
WANG SHUANGXI et al.
Fig. I. Geometry of [MnLCI,] - DMF with the atomic numbering scheme.
1041 cm- ‘) band, it is unlikely that the perchlorate anions are coordinated directly to the manganese(I1) centre since there is no indication of splitting of vq(C104). The splitting of v3(C104) in the complex is probably due to the formation of a hydrogen bond between an oxygen atom of the perchlorate anion and the N-H group of the benzimidazole ring. The spectrum of the chloride complex shows weak bands at 269 and 251 cm-‘, respectively, which are not seen in the other complexes and suggest they should be assigned to the v(Mn-Cl) modes. ”
manganese atom can be regarded as a distorted square pyramid. The basal positions are occupied by the three nitrogen atoms of the tridentate ligand, N(l), N(3) and N(5), and the chloride atom Cl(l). The apical position is occupied by the other chloride
Electronic spectra The UV spectra of the complexes (Table 2) are similar, but different from that of the ligand. The band at 311 nm assigned to R + 71transitions in the ligand is split into two bands (- 330 nm, 7~~+ w*, and - 313 nm, nb + na*) in these complexes. This indicates the coordination of the ligand in DMF. ’ 3 Description of the crystal structure of MnLCl,. DMF Figure 1 shows the geometry of the molecule with the atomic numbering scheme, Fig. 2 the unit-cell contents and Table 3 selected bond distances and angles. The coordination polyhedron about the
Fig. 2. The unit-cell packing diagram DMF.
of [MnLCl,]*
Mn” complexes of 2,6-bis(benzimidazol-2’-yl)pyridine
1913
Table 3. Selected bond distances (A) and angles (“) in MnLCl, * DMF Distance/angle
Distance/angle Mn coordination Mn-Cl( 1) Mn-Cl(2) Mn-N( 1)
Mn-N( Mn-N(
2.340(l) 2.385(2) 2.276(3) 112.92(5) 141.1(2) 101.44(9) 100.07(8) 105.9(l)
Cl(l)-Mn-Cl(2) Cl( l)-Mn-N( 1) Cl(l)-Mn-N(3) Cl(I)---Mn-N(5) C1(2)-Mn-N( 1)
sphere 3) 5)
2.229(3) 2.258(3) 99.9( 1) 101.5(2) 71.3(l) 71.3(l) 140.7(l)
C1(2)-Mn-N(3) C1(2)--Mn-N(5) N( 1)-Mn-N(3) N( 1)--Mn-N(5) N(3)-Mn-N(5)
Hydrogen bonding A-H . . . B N(2)-H(N2). N(4)-H(N4).
..0 . . Cl(2)
A...B 2.702 3.111
Symmetry code: a: 1/2-x,
A-H 1.115 1.004
1/2+y, l/2-2;
Cl(2). Compared with the idealized square pyramid (BP),” the valency angles at the manganese atom for the complex show significant distortions. The three apical to basal angles [C1(2)-Mn-N(1) : 1059(l)” ; C1(2)-Mn-N(3) : 99.9( 1)” ; C1(2)-Mn-N(5) : 101.5(2)“] slightly deviate from the value of 104.1” in ISP, while the Cl(l)-Mn-Cl(2) angle [112.92(5)“] is larger than 104. lo owing to the Cl( 1) * * * Cl(2) repulsion. Two of the four angles subtended at manganese by adjacent basal atoms [N(3)-Mn-N(1) and N(S)--Mn-N( 1) : 71.3(l)“] are smaller than the value of 86.6” in ISP ; the other two [Cl(l)Mn-N(3) : 101.44(g)” ; Cl(l)-Mn-N(5) : 100.07 (S)‘] are larger than 86.6”. These are mainly due to the steric requirements of the ligand. The N( l)-Mn-CI( 1) and N(3)-Mn-N(5) angles are 141.1(2)” and 140.7(l)“, respectively, also smaller than the value of 151.91” in ISP. atom
H...B 1.597 2.123 b: 2-q
-y,
a b
A-H . . . B 170.0 167.6
1 -z.
The Mn-N( 1) (pyridine nitrogen atom) distance (2.276(3) A) is longer than Mn-N(3) and -N(5) (benzimidazole nitrogen atoms) distances [2.229(3) and 2.258(3) 8, respectively] ; the Mn-Cl(l) basal distance [2.340( 1) A], as expected, is shorter than the Mn-Cl(2) apical distance (2.385 A). The basal atoms N(3), N(5), N(1) and Cl(l) are in a nearly planar arrangement with a maximum deviation of 0.192(5) 8, from the best plane (Table 4). The manganese(I1) atom is 0.618 A out of the plane towards the coordinated chloride atom [C1(2)], which is significantly larger than the value of 0.48 8, calculated for Zemann’s model.20 In the ligand the pyridine and the two benzimidazole rings are co-planar (Table 4) and therefore constitute a greater conjugated system. The molecular packing is mainly determined by van der Waals forces. The uncoordinated solvent (DMF) molecule and the MnLC12 unit are linked
Table 4. Planar fragments of the complex Plane 1 Atom A (A) Plane 2
(0.2978)x+O.8367y+(-0.4596)2-0.5068 N(1) 0.192
N(3) -0.149
= 0
(0.0849)x+O.8283y+(-0.5537)z+2.6537
Atom C(1) A (A) 0.062 Atom C(9) A (A) 0.007 Atom C(17) A (A) - 0.027 Dihedral angle : 13.38”
C(2) 0.015 C(l0) - 0.008 C(18) 0.092
C(3) - 0.053 CU 1) 0.028 C(l9) -0.051
Cl(l)
N(5) -0.148
C(4) - 0.053 C(12) -0.052 N(l) -0.111
Mn -0.618
0.105
= 0 C(5) 0.013 W3) - 0.054 N(2) -0.009
C(6) 0.064 C(14) 0.064 N(3) -0.060
C(7) 0.076 C(15) 0.142 N(4) 0.067
C(8) 0.055 W6) 0.094 N(5) -0.117
1914
WANG
SHUANGXI
et al.
Table 5. Cyclic voltammographic Complex
-% (v)
Epa (V)
[MnLCl,]
0.03 -0.60
b 6
[MnL2(S04)]*4H20 ]MnL(AC)J
-1.44 -0.34 -1.51 -0.47 -1.34
[MnLd(NO,),.3H,O
-0.97 -0.21 -1.44 -0.41 -1.27
data” AEr (mV) -
42
09
-
670 130 70 60 70
- 1.21 -0.28 -1.48 -0.44 -1.31
“Scan rate: 0.5 V s-‘. ’ No peak.
by a hydrogen
bond between the N-H group the benzimidazole ring and the oxygen atom
of of
the DMF molecule. Detailed data on the hydrogen bond are summarized in Table 3. Electrochemistry The cyclic voltammetric data for the complexes are presented in Table 5. The complex of [MnLCl,]
(Fig. 3) gives only the two reduction peaks, and no reverse oxidation peaks corresponding to the reduction peaks were observed. So the reductions are irreversible, probably involving the decomposition of the complex. The [MnL,(SO,)] *4H20 complex exhibits one irreversible reduction couple (AE, = 670 mV). The cyclic voltammogram of [MnL(AC)J shows two reduction couples: one seems to be quasi-reversible, the other reversible. Figure 4 shows a cyclic voltammogram of [MnL,](NO,), - 3H20. The complex shows two one-electron reduction processes and no oxidation processes were observed until + 1.8 V. Thus, the reduction processes were tentatively assigned to V) and Mn’/Mn’ Mn”/Mn’ (Ellz = -0.44 (El,* = - 1.31 V), respectively.” Acknowledgement-We acknowledge support from the National Foundation of China, Gansu.
05
IO
0
-0
5
-1.0
-I 5
REFERENCES
E(V)
Fig. 3. Cyclic voltammogram of NnLCld in DMF solution (10m3) with 0.1 M (Et,N)CIO, as a supporting electrolyte (scan rate 0.5 V s- ‘).
4.
5. 6. 7. I
I
I
I
I5
IO
0.5
0
I -0
5
I -10
I -I 5
I -2.0
8.
E(V)
Fig. 4. Cyclic voltammogram of [MnL,](NO,), - 3H20 in DMF solution (10m3 M) with 0.1 M (Et,N)ClO, as a supporting electrolyte (scan rate 0.5 V s- ‘).
9.
D. G. O’Sullivan and A. K. Wallis, J. Med. Chem. 1972, 15, 103. W. R. Roderick, C. W. Nordeen, A. M. Von Esch and R. N. Appell, J. Med. Chem. 1972,15,655. S. S. Kukalenko, B. A. Bovykin, S. I. Shestakova and A. M. Omelchenko, Russ. Chem. Rev. 1985,54, 676 and refs therein. S. Mylonas, A. Valavanidis, K. Dimitropoulos, M. Polissiou, A. S. Tsiftsoglou and I. S. Viziranakis, J. Znorg. Biochem. 1988,34,265. D. G. O’Sullivan and P. W. Sadler, Nature (London) 1961,192,341. R. J. Sundherg and R. B. Martin, Chem. Rev. 1974, 74,471. L. Alagna, S. S. Hassnain, B. Piggott and D. J. Williams, Biochem. J. 1984, 59, 220. H. M. J. Hendriks, P. J. M. W. L. Birker, G. C. Verschoor and J. Reedijk, J. Chem. Sot., Dalton Trans. 1982, 623. J. V. Rijn, J. Reedijk, M. Dartmann and B. Krebs, J. Chem. Sot., Dalton Trans 1987,2579.
Mn” complexes of 2,6-bis(benzimidazol-2’-yl)pyridine 10. ‘A. W. Addison and P. J. Burke, J. Heterocycl. Chem. 1981, 18, 803. 11. S. M. Nelson, F. S. Esho and M. G. B. Drew, J. Chem. Sot., Dalton Trans. 1982, 407. 12. S. B. Sanni, H. J. Behm, P. T. Beurskens, G. A. van Albada, J. Reedijk, A. T. H. Lenstra, A. W. Addison and M. J. Palaniandavar, J. Chem. Sot., Dalton Trans. 1988, 1429. 13. C. Piguet, B. Bocquet, E. Muler and A. F. Williams, Helv. Chim. Acta 1989, 72, 323. 14. A. W. Addison, S. Burn-ran, C. B. Wahlgren, 0. A. Rajan, T. M. Rowe and E. Sinn, J. Chem. Sot., Dalton Trans. 1987, 2621. 15. N. Shashikala, V. Gayathri, N. M. N. Gowda and
1915
G. K. N. Reddy, J. Znd. Chem. Sot. 1989,66,537. 16. W. Liufang, Z. Yin, Y. Zhengyin and W. Jigui, Polyhedron 1991, 10,2477. 17. International Tables for X-ray Crystallography, Vol. IV. Kynoch Press, Birmingham (1974). 18. K. Nakamoto, Znfrared and Raman Spectra of Znorganic and Coordination Compounds, 3th edn. John Wiley, New York (1978). 19. F. A, Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 4th edn. John Wiley, New York (1980). 20. J. Zemann, Z. Anorg. Allg. Chem. 1963,324,241. 21. M. C. Hughes, D. J. Macero and J. M. Rao, Znorg. Chim. Acta 1981,49, 241.
1992 0
0277-5387/92 $5.00 + .a, 1992 Pergamon Press Ltd
SYNTHESIS, STRUCTURE AND ELECTROCHEMICAL BEHAVIOUR OF MANGANESE(H) COMPLEXES WITH 2,6-BIS(BENZIMIDAZOL-2’-YL)PYRIDINE WANG SI-IUANGXI, ZHU YING, ZHANG FANGJIE, and WANG LIUFANGT
WANG QIUYING
Department of Chemistry, Lanzhou University, Lanzhou 730000, P.R.C. (Received 6 February 1992 ; accepted 24 March 1992)
Abstract-The complexes of manganese(I1) with 2,6-bis(benzimidazole-2’-yl)pyridine were synthesized and characterized by elemental analysis, electrical conductance, IR and electronic spectra and thermal analysis. The electrochemical behaviour of the complexes was described and the X-ray crystal structure of MnLCl, - DMF was determined. The complex crystallizes in the monoclinic system, space group P2,,, with 2 = 4, a = 14.56(2), b = 7.937, c = 19.862(4) A, j? = 102.31[2]“. The geometry about manganese is a distorted square pyramid.
Benzimidazole derivatives and their metal complexes have been extensively investigated. This has been mainly due to the following facts : (1) these compounds possess a broad spectrum of biological activities ;lm4 (2) the antiviral activity of some 2substituted benzimidazoles has been considered to be related to their ability to chelate with trace metal ions in biological system;3,5 and (3) it has been recognized that many of these complexes may serve as simple models which mimic both the structure and reactivity of metal ion sites in complex biological systems. k9 Studies on 2,6-bis(benzimidazol-2’-yl)pyridine (BBP), as a benzimidazole derivative, and its complexes with some divalent metals have been reported. ‘&I5 However, no paper concerning the study of manganese(I1) complex with BBP has been seen. Also, in our previous work’ 6we have reported the synthesis and structure of a manganese(B) complex with a hydrazone ligand derived from pyruvic acid and 4-pyridine carboxylic acid hydrazine. Therefore, in this paper, we wish to report the syntheses, characterization and structure of BBP complexes with different manganese(I1) salts and discuss their electrochemical properties.
EXPERIMENTAL Reagents
The ligand 2,6-bis(benzimidazole-2’-yl)pyridine was prepared by the literature method.” The hydrated manganese(I1) salts and organic solvents were of reagent grade. Preparation
of complexes
To a solution of BBP (10 mmol) in Me&O (20 cm3) a solution of the appropriate manganese(I1) salts (MnC12 * 4H20, Mn(Ac), *4H20, MnSO,. 7H20 and Mn(N03)2-6H20) (5 mmol) in Me, CO (10 cm’) was added dropwise with stirring at room temperature. A yellow colour appeared and a precipitate was formed in a few minutes. After stirring for several hours, the product was collected by filtration, washed with CH,OH, Me,CO and Et,O, and dried in a vacuum desiccator over P40, o. The complex MnL2(C10& * 3H20 was prepared in a similar manner to the above method except that the molar ratio of metal-ligand used was 1 : 3. A white precipitate was obtained. Measurements
t Author to whom correspondence should be addressed.
Carbon, nitrogen and hydrogen were determined by a Carlo-Erba 1106 elemental analyser. The IR
1909
1910
WANG
SHUANGXI
spectra were recorded on a Nicolet-170X FT-IR spectrophotometer in CsI discs in the range 400& 200 cm- i. UV spectra were measured with a Shimadzu W-240 spectrophotometer in the range 19& 900 nm using a solution in DMF. Electrolytic conductance measurements were made with a DDSIIA molar conductometer with DMF as the solvent at 25°C. TGA analyses were carried out with a Du Pont 1090 thermal analyser in a nitrogen atmosphere. Cyclic voltammograms were performed on a U.S. EG&E PARC electrochemical analyser at a complex concentration of 1.Ox lo- 3 M in DMF with 0.1 M (Et,N)ClO, as the supporting electrolyte. A glass-carbon working electrode, a platinum wire auxiliary electrode and a saturated calomel reference electrode were employed. X-ray structure determination
of MnLCl, * DMF
Single crystals were obtained by slow evaporation of a DMF solution of MnLCl,. A transparent light yellow crystal (0.15 x 0.22 x 0.37 mm) was mounted on an Enraf-Nonius CAD-4 diffractometer. The unit cell was measured by centring 25 reflections (10 < 0 < IS’) and refined by least-squares methods. Graphite-monochromated MO-K, radiation was used. Intensities were measured with an ~~-28 scan technique, scan width (0.52 + 0.34 tan 0) and 0 range 1 <0<24” (h= -16-16; k=O-9; I= O-23). 3939 independent reflections were collected, of which 2683 were considered as observed [I > 30(Z)]. Intensities were corrected for Lorentzpolarization and I,$empirical absorption corrections (transmission factor range from 77.72 to 99.8%). The manganese atom was located from a Patterson synthesis and the remaining non-hydrogen atoms from Fourier syntheses. The structure was refined isotropically and anisotropically by a leastsquares refinement. The function minimized was C w(]FOl- jFJ)2, where w = 1. All hydrogen atoms were located from a difference synthesis and refined with an overall isotropic thermal parameter. The final R factor was 0.062, (A/a)m,, = 0.23, and the final difference-Fourier map showed peaks being less than 0.45 e A- I. Atomic scattering factors were taken from ref. 17. All calculations were carried out on a PDP 11/44 computer using the SDP package. Supplementary data, including final atomic coordinates, thermal parameters, bond lengths and angles, and structure factors, have been deposited with the Editor and with the Cambridge Crystallographic Data Centre. Crystallographic
data
Crystal data. Monoclinic P2,/n, a = 14.561(2), c = 19.862(4) A, jI = 102.31(2)“,
b = 7.937(l),
et al.
V = 2242.6
A3, M, = 510.29,
~(Mo-K,) = 8.32
cm- ‘,
Z = 4, D, = 1.512 R = 0.062,
cm- ‘,
R, = 0.059. RESULTS AND DISCUSSION
Reactions of manganese(H) salts [MnSO, - 7Hz0, Mn(N03)2 * 6H20 and Mn(ClO,), * 6H2O] with BBP in Me,CO yield 1 : 2 (metal: ligand) complexes, while MnC12 * 4H,O and Mn(Ac), * 4H20 yield only 1: 1 (metal : ligand) complexes in spite of using a 1 : 2 or 1 : 3 molar ratio of metal : ligand (Table 1). The complexes are air-stable at room temperature, soluble in Me&JO, CH30H, DMF and DMSO and insoluble in water and nonpolar organic solvents. In Table 1 the TGA data of all complexes having water show that the water molecules are present as lattice water. IR spectra
The important IR data of the complexes are listed in Table 2. A broad band at 3185 cm- ’ in the free ligand assigned to the N-H group of the benzimidazole ring is shifted to lower frequencies by N 110 cm-’ in all complexes. This may be due to the existence of a hydrogen bond between the hydrogen of the N-H group of the bcnzimidazole ring and counter-anions in these complexes. The new bands in the 389-352 cm- ’ region in the spectra of all complexes are tentatively attributed to v(Mn-N). I ’ The IR spectrum of the acetate complex exhibits two bands at 1681 and 1363 err-’ assigned to v(C=O) and v(C-O), respectively, which indicates that the acetate groups are coordinated to the manganese(I1) centre as unidentate ligands. ” This is further supported by the fact that the complex behaves as a non-electrolyte and exhibits a medium new band at 531 cm-’ due to v(Mn-0). The IR spectrum of the sulphate complex shows splitting of v3(S04) (1098 and 1060 cm- ‘) and v4(S04) (602 and 633 cm- ‘) bands, suggesting unidentate behaviour for the sulphate group. This is in agreement with the non-electrolytic behaviour of the complex. So, the sulphate complex could be formulated as [MnL,(SO,)] * 4H20. It is possible that one of the two BBP ligands in the complex is tridentate and the other bidentate, and as observed in the copper complex, ” the manganese(I1) is sixcoordinated. In the IR spectrum of the nitrate complex, a strong absorption band at 1389 cm- ’ occurs which is typical of the uncoordinated nitrate group. Although the spectrum of the perchlorate complex exhibits splitting of the v3(C104) (1128 and
78 62
Pale yellow
Light yellow
White
[MnLzSOJa4Hz0
[MnLJ(NG&S3H@
[MnL j(ClO&*
3059brm 3078brm
3368sh 3480brw
a nm, in DMF. ‘a-’ cm2 mol-‘, in DMF. s : strong ; m : medium ; w : weak ; br : broad ; sh : shoulder.
172.0 101.0
312,333 313,330
[MnL21CNGJ2*3H~G [MnLJ(ClO& - 3H20
3061brm 3051brm
-
7.2 1.8
316,330 310,334
[MnL(AC)d [MnL,SO.,]*4H,O 3465sh
5.1
3185brm 3065brm
-
-
v(N-H)
v(GH)
Amb
311 314,322
UV” x + Jr*
Ligand [MnLCl,]
Complex
359
360
389
345
377
385
Decomposition point (“C)
r
52.7 (52.2) 51.4 (51.8) 56.7 (57.0) 54.4 (54.0) 53.6 (53.3) 48.8 (49.0)
C 16.3 (16.0) 16.2 (16.5) 14.4 (14.5) 16.2 (16.6) 19.3 (19.6) 14.7 (15.1)
N
3.5 (3.4)
(:f)
(Z)
(:I)
(Z) 3.9 (3.9)
H
\
(Z)
(E)
(&
-
-
r Weight loss%
I
1681s 1098s 633m 1389s 1128s
v(NG;)
1041s
1363m 1060s
-
v(SD;)
IR A
-
621s
531m 522~
-
-
602m
v(Mn-0)
352~ 380~
357w 389~
382~
-
v(Mn-N)
72-l 18
76-105
62-80
-
-
-
269~ 251~
v(Mn-Cl)
3H20
3H20
4Hz0
-
-
-
Assignment
TGA analysis , Temperature range (“C)
v(AC-)
\
Table 2. Important IR and electronic spectral data and molar conductances for the ligand and its complexes
‘Required values are given in parentheses.
47
56
Light yellow
[MnL(AC)J
3H20
49
Yellow
[MnLCl,] - DMF
61
Yellow
Colour
[MnLCl,]
Complex
Yield (%)
Analysis (%) L
Table 1. Analytical and physical data of the complexes
,
5,
g z
3 ; 4 $$
i 8’ p
5E 8 El a b ! % .ll 5” z x
1912
WANG SHUANGXI et al.
Fig. I. Geometry of [MnLCI,] - DMF with the atomic numbering scheme.
1041 cm- ‘) band, it is unlikely that the perchlorate anions are coordinated directly to the manganese(I1) centre since there is no indication of splitting of vq(C104). The splitting of v3(C104) in the complex is probably due to the formation of a hydrogen bond between an oxygen atom of the perchlorate anion and the N-H group of the benzimidazole ring. The spectrum of the chloride complex shows weak bands at 269 and 251 cm-‘, respectively, which are not seen in the other complexes and suggest they should be assigned to the v(Mn-Cl) modes. ”
manganese atom can be regarded as a distorted square pyramid. The basal positions are occupied by the three nitrogen atoms of the tridentate ligand, N(l), N(3) and N(5), and the chloride atom Cl(l). The apical position is occupied by the other chloride
Electronic spectra The UV spectra of the complexes (Table 2) are similar, but different from that of the ligand. The band at 311 nm assigned to R + 71transitions in the ligand is split into two bands (- 330 nm, 7~~+ w*, and - 313 nm, nb + na*) in these complexes. This indicates the coordination of the ligand in DMF. ’ 3 Description of the crystal structure of MnLCl,. DMF Figure 1 shows the geometry of the molecule with the atomic numbering scheme, Fig. 2 the unit-cell contents and Table 3 selected bond distances and angles. The coordination polyhedron about the
Fig. 2. The unit-cell packing diagram DMF.
of [MnLCl,]*
Mn” complexes of 2,6-bis(benzimidazol-2’-yl)pyridine
1913
Table 3. Selected bond distances (A) and angles (“) in MnLCl, * DMF Distance/angle
Distance/angle Mn coordination Mn-Cl( 1) Mn-Cl(2) Mn-N( 1)
Mn-N( Mn-N(
2.340(l) 2.385(2) 2.276(3) 112.92(5) 141.1(2) 101.44(9) 100.07(8) 105.9(l)
Cl(l)-Mn-Cl(2) Cl( l)-Mn-N( 1) Cl(l)-Mn-N(3) Cl(I)---Mn-N(5) C1(2)-Mn-N( 1)
sphere 3) 5)
2.229(3) 2.258(3) 99.9( 1) 101.5(2) 71.3(l) 71.3(l) 140.7(l)
C1(2)-Mn-N(3) C1(2)--Mn-N(5) N( 1)-Mn-N(3) N( 1)--Mn-N(5) N(3)-Mn-N(5)
Hydrogen bonding A-H . . . B N(2)-H(N2). N(4)-H(N4).
..0 . . Cl(2)
A...B 2.702 3.111
Symmetry code: a: 1/2-x,
A-H 1.115 1.004
1/2+y, l/2-2;
Cl(2). Compared with the idealized square pyramid (BP),” the valency angles at the manganese atom for the complex show significant distortions. The three apical to basal angles [C1(2)-Mn-N(1) : 1059(l)” ; C1(2)-Mn-N(3) : 99.9( 1)” ; C1(2)-Mn-N(5) : 101.5(2)“] slightly deviate from the value of 104.1” in ISP, while the Cl(l)-Mn-Cl(2) angle [112.92(5)“] is larger than 104. lo owing to the Cl( 1) * * * Cl(2) repulsion. Two of the four angles subtended at manganese by adjacent basal atoms [N(3)-Mn-N(1) and N(S)--Mn-N( 1) : 71.3(l)“] are smaller than the value of 86.6” in ISP ; the other two [Cl(l)Mn-N(3) : 101.44(g)” ; Cl(l)-Mn-N(5) : 100.07 (S)‘] are larger than 86.6”. These are mainly due to the steric requirements of the ligand. The N( l)-Mn-CI( 1) and N(3)-Mn-N(5) angles are 141.1(2)” and 140.7(l)“, respectively, also smaller than the value of 151.91” in ISP. atom
H...B 1.597 2.123 b: 2-q
-y,
a b
A-H . . . B 170.0 167.6
1 -z.
The Mn-N( 1) (pyridine nitrogen atom) distance (2.276(3) A) is longer than Mn-N(3) and -N(5) (benzimidazole nitrogen atoms) distances [2.229(3) and 2.258(3) 8, respectively] ; the Mn-Cl(l) basal distance [2.340( 1) A], as expected, is shorter than the Mn-Cl(2) apical distance (2.385 A). The basal atoms N(3), N(5), N(1) and Cl(l) are in a nearly planar arrangement with a maximum deviation of 0.192(5) 8, from the best plane (Table 4). The manganese(I1) atom is 0.618 A out of the plane towards the coordinated chloride atom [C1(2)], which is significantly larger than the value of 0.48 8, calculated for Zemann’s model.20 In the ligand the pyridine and the two benzimidazole rings are co-planar (Table 4) and therefore constitute a greater conjugated system. The molecular packing is mainly determined by van der Waals forces. The uncoordinated solvent (DMF) molecule and the MnLC12 unit are linked
Table 4. Planar fragments of the complex Plane 1 Atom A (A) Plane 2
(0.2978)x+O.8367y+(-0.4596)2-0.5068 N(1) 0.192
N(3) -0.149
= 0
(0.0849)x+O.8283y+(-0.5537)z+2.6537
Atom C(1) A (A) 0.062 Atom C(9) A (A) 0.007 Atom C(17) A (A) - 0.027 Dihedral angle : 13.38”
C(2) 0.015 C(l0) - 0.008 C(18) 0.092
C(3) - 0.053 CU 1) 0.028 C(l9) -0.051
Cl(l)
N(5) -0.148
C(4) - 0.053 C(12) -0.052 N(l) -0.111
Mn -0.618
0.105
= 0 C(5) 0.013 W3) - 0.054 N(2) -0.009
C(6) 0.064 C(14) 0.064 N(3) -0.060
C(7) 0.076 C(15) 0.142 N(4) 0.067
C(8) 0.055 W6) 0.094 N(5) -0.117
1914
WANG
SHUANGXI
et al.
Table 5. Cyclic voltammographic Complex
-% (v)
Epa (V)
[MnLCl,]
0.03 -0.60
b 6
[MnL2(S04)]*4H20 ]MnL(AC)J
-1.44 -0.34 -1.51 -0.47 -1.34
[MnLd(NO,),.3H,O
-0.97 -0.21 -1.44 -0.41 -1.27
data” AEr (mV) -
42
09
-
670 130 70 60 70
- 1.21 -0.28 -1.48 -0.44 -1.31
“Scan rate: 0.5 V s-‘. ’ No peak.
by a hydrogen
bond between the N-H group the benzimidazole ring and the oxygen atom
of of
the DMF molecule. Detailed data on the hydrogen bond are summarized in Table 3. Electrochemistry The cyclic voltammetric data for the complexes are presented in Table 5. The complex of [MnLCl,]
(Fig. 3) gives only the two reduction peaks, and no reverse oxidation peaks corresponding to the reduction peaks were observed. So the reductions are irreversible, probably involving the decomposition of the complex. The [MnL,(SO,)] *4H20 complex exhibits one irreversible reduction couple (AE, = 670 mV). The cyclic voltammogram of [MnL(AC)J shows two reduction couples: one seems to be quasi-reversible, the other reversible. Figure 4 shows a cyclic voltammogram of [MnL,](NO,), - 3H20. The complex shows two one-electron reduction processes and no oxidation processes were observed until + 1.8 V. Thus, the reduction processes were tentatively assigned to V) and Mn’/Mn’ Mn”/Mn’ (Ellz = -0.44 (El,* = - 1.31 V), respectively.” Acknowledgement-We acknowledge support from the National Foundation of China, Gansu.
05
IO
0
-0
5
-1.0
-I 5
REFERENCES
E(V)
Fig. 3. Cyclic voltammogram of NnLCld in DMF solution (10m3) with 0.1 M (Et,N)CIO, as a supporting electrolyte (scan rate 0.5 V s- ‘).
4.
5. 6. 7. I
I
I
I
I5
IO
0.5
0
I -0
5
I -10
I -I 5
I -2.0
8.
E(V)
Fig. 4. Cyclic voltammogram of [MnL,](NO,), - 3H20 in DMF solution (10m3 M) with 0.1 M (Et,N)ClO, as a supporting electrolyte (scan rate 0.5 V s- ‘).
9.
D. G. O’Sullivan and A. K. Wallis, J. Med. Chem. 1972, 15, 103. W. R. Roderick, C. W. Nordeen, A. M. Von Esch and R. N. Appell, J. Med. Chem. 1972,15,655. S. S. Kukalenko, B. A. Bovykin, S. I. Shestakova and A. M. Omelchenko, Russ. Chem. Rev. 1985,54, 676 and refs therein. S. Mylonas, A. Valavanidis, K. Dimitropoulos, M. Polissiou, A. S. Tsiftsoglou and I. S. Viziranakis, J. Znorg. Biochem. 1988,34,265. D. G. O’Sullivan and P. W. Sadler, Nature (London) 1961,192,341. R. J. Sundherg and R. B. Martin, Chem. Rev. 1974, 74,471. L. Alagna, S. S. Hassnain, B. Piggott and D. J. Williams, Biochem. J. 1984, 59, 220. H. M. J. Hendriks, P. J. M. W. L. Birker, G. C. Verschoor and J. Reedijk, J. Chem. Sot., Dalton Trans. 1982, 623. J. V. Rijn, J. Reedijk, M. Dartmann and B. Krebs, J. Chem. Sot., Dalton Trans 1987,2579.
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1915
G. K. N. Reddy, J. Znd. Chem. Sot. 1989,66,537. 16. W. Liufang, Z. Yin, Y. Zhengyin and W. Jigui, Polyhedron 1991, 10,2477. 17. International Tables for X-ray Crystallography, Vol. IV. Kynoch Press, Birmingham (1974). 18. K. Nakamoto, Znfrared and Raman Spectra of Znorganic and Coordination Compounds, 3th edn. John Wiley, New York (1978). 19. F. A, Cotton and G. Wilkinson, Advanced Inorganic Chemistry, 4th edn. John Wiley, New York (1980). 20. J. Zemann, Z. Anorg. Allg. Chem. 1963,324,241. 21. M. C. Hughes, D. J. Macero and J. M. Rao, Znorg. Chim. Acta 1981,49, 241.