International Journal of Inorganic ChemistryVolume 2013 (2013), Article ID 153023, 4 pageshttp://dx.doi.org/10.1155/2013/153023

Research Article

Synthesis and Crystal Structure of

Thampidas V. S, Aisha Basheer, and Saliny Shyla

Department of Chemistry, Sree Narayana College, Varkala, Kerala 695 145, India

Received 29 August 2012; Accepted 12 November 2012

Academic Editor: W.T. Wong

Copyright © 2013 Thampidas V. S et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

The title compound was synthesized by the reaction between a manganese(II) carboxylate and the tetradentate Schiff base ligand, 5-Br-salpnH₂ [N,N′-bis(5-Br-salicylidene)-1,3-diaminopropane] produced in situ. The complex crystallizes in the P2₁/c space group with unit cell dimensions (10), (10), (3), , (10), and . The manganese(III) ion is in a distorted octahedral environment with longer axial bonds.

1. Introduction

Recent advances in the coordination chemistry of manganese has been intimately connected to diverse fields such as, asymmetric catalysis [1, 2], molecular magnetism [3–5], and bioinorganic modeling [6–8]. With its accessible oxidation states of (II), (III), (IV), and (V), manganese plays several important roles in biological systems like the oxygen-evolving complex (OEC) of photosystem II [9, 10] and enzymes like superoxide dismutase, catalase, and arginase [11, 12]. Active sites of most of these systems contain manganese ligated mainly by N and O-donor atoms from the amino acid residues of the metalloproteins. Inorganic model complexes have made significant contributions to the progress in delineating the structural and functional aspects of the active sites of these systems [13–16]. Ligands such as aliphatic, cyclic Schiff bases, polypyridyl systems, and carboxylic acids can stabilize manganese in its various oxidation states [17, 18]. Schiff base ligands with nitrogen and oxygen donor atoms may provide a chemical environment which can mimic the coordination spheres of manganese in biological systems better than any other ligand type. A whole host of manganese Schiff base complexes have been reported in this context during the last few decades [19–27]. Among these, there is a sizeable number of complexes of the salpn [salpnH₂ = -bis (salicylidene)-1, 3-diaminopropane] and substituted salpn ligands [19–22]. We have been interested in the coordination chemistry of higher oxidation states of manganese for some time, and herein, we report the isolation of a new manganese(III) complex, [(5-Br-salpn)(DMF)₂][B(C₆H₅)₄].

2. Experimental

2.1. Materials and Physical Measurements

All chemicals were purchased from E-Merck and used without further purification. IR spectrum was recorded on a Nicolet 6700 spectrophotometer (KBr pellets, 4000–400 cm⁻¹) while UV-Vis spectrum was taken on a Cary 100 Bio UV-Vis spectrophotometer. Elemental analyses were performed using a Perkin-Elmer 2400 CHNS analyzer.

2.2. Synthesis of [MnIII(5-Br-salpn)(DMF)₂][B(C₆H₅)₄]

The starting material, [Mn₂(Hsal)₄(H₂O)₄], was prepared as reported earlier or alternatively by mixing hot aqueous solutions of sodium saliyclate and manganese(II)chloride (2 : 1 molar ratio), which gave pale pink crystals of the compound in yields greater than 80% in a day’s time [28]. To a solution of [Mn₂(Hsal)₄(H₂O)₄] (1.00 g, 2.19 mmol), 5-bromosalicylaldehyde (0.88 g, 4.38 mmol) and sodium tetraphenylborate (0.75 g, 2.19 mmol) in methanol/DMF mixture (20 mL, 1 : 1 v/v), 1,3-diaminopropane (0.16 g, 2.19 mmol) was added. The solution was stirred for a few minutes, filtered, and left to be evaporated in an open conical flask. Dark green crystals were deposited in 4-5 days. These were collected by filtration, washed with diethylether, and dried in air. Anal. calc. for C₄₇H₄₈BBr₂MnN₄O₄: C, 58.84; H, 5.00; N, 5.84; Mn, 5.73. Found: C, 58.12.; H, 4.94; N, 5.29; Mn, 5.38%. IR (KBr pellet): /cm⁻¹ = 3122 w, 3031 w, 1623 s, 1579 s, 1345 m, 1295 w, 1278 w, 1261 m, 1152 w, 999 w, 964 m, 798 s, 452 m. UV-Vis (methanol): λ/nm = 232 ( = 10136 mol⁻¹ dm³ cm⁻¹), 474 ( = 341 mol⁻¹ dm³ cm⁻¹).

2.3. X-Ray Crystallography

Data were collected on a Bruker APEX II diffractometer, equipped with a CCD area detector (Cu-Kα radiation, graphite monochromator, λ = 1.54178 Å, at 100(2) K). The crystal structure was solved by direct methods and refined by full-matrix least-squares methods based on values against all reflections including anisotropic displacement parameters for all non-H atoms, using SHELXS97 and SHELXL97 [29]. All the nonhydrogen atoms were located from a Fourier map and refined anisotropically. Hydrogen site locations were inferred from neighbouring sites and were treated by a mixture of independent and constrained refinement. The molecular graphics were done with MERCURY 2.0 [30]. Crystal data and parameters for data collection are listed in Table 1.

Table 1: Crystal data and parameters for data collection for [MnIII(5-Br-salpn)(DMF)₂][B(C₆H₅)₄].

Empirical formula
C₄₇H₄₈BBr₂MnN₄O₄

Formula weight
958.46

Temperature
100(2) K

Wavelength
1.54178 

Crystal system
monoclinic

Space group
P2₁/c

Unit cell dimensions
a = 12.3798(1) Å    α = 90°

b = 12.6099(1) Å     = 102.013(1)°

= 28.9438(3) Å     = 90°

Volume
4419.41(7) Å³

Z
4

Density (calculated)
1.441 mg/m³

Absorption coefficient
4.924 mm⁻¹

F(000)
1960

Crystal size
0.48 × 0.22 × 0.08 mm

range for data collection
3.12–67.31°

Limiting indices
−14 < h < 14, –15 < k < 15, −34 < l < 33

Reflections collected
36039

Independent reflections
7606

Absorption correction
SADABS

Refinement method
full-matrix least-squares on

Data/restraints/parameters
7606/0/537

Goodness-of-fit on
1.096

Final indices [σ(I)]
= 0.0610, = 0.0240

indices (all data)
= 0.0615, = 0.0248

, where .

3. Results

3.1. Crystal Structure of [MnIII(5-Br-salpn)(DMF)₂][B(C₆H₅)₄]

The complex crystallizes in the monoclinic space group, /c. Molecular structure of [Mn(5-Br-salpn)(DMF)₂]BPh₄ is depicted in Figure 1. The cation, [Mn(5-Br-salpn)(DMF)₂]⁺, is monomeric and octahedral. The 5-Br-salpn ligand, with its N₂O₂ donor set, holds the manganese(III) ion in an approximate square plane.

Figure 1: Molecular structure of [(5-Br-salpn)(DMF)₂][B(C₆H₅)₄]. Thermal ellipsoids are drawn at 50% probability level. Hydrogen atoms are omitted for clarity.

The Mn–Ophenol bonds [Mn–O2B = 1.8852(12) Å and Mn–O3B = 1.8955(12) Å] are slightly stronger than the Mn–Nimine bonds [Mn–N1 = 2.0259(14) Å and Mn–N4 = 2.0459(14) Å]. Oxygen atoms of the DMF solvent molecules coordinate with the manganese(III) ion and occupy the trans coordination positions of the complex. Jahn-Teller distortion causes an elongation of these axial bonds [Mn–O2 = 2.2119(12) Å, Mn–O1 = 2.2282(13) Å]. Selected bond angles and bond lengths of [Mn(5-Br-salpn)(DMF)₂]⁺ are given in Table 2. The counter ions form helical chains about a screw axisand extend parallel to the (010) plane (Figures 2 and 3).

Table 2: Selected bond distances (Å) and bond angles (°) of [MnIII(5-Br-salpn)(DMF)₂]⁺.

Mn–O2B
1.8852(12)
Mn–N4
2.0459(14)

Mn–O3B
1.8955(12)
Mn–O2
2.2119(12)

Mn–N1
2.0259(14)
Mn–O1
2.2282(13)

O2B–Mn–O3B
84.32(5)
N1–Mn–O2
86.02(5)

O2B–Mn–N1
90.08(5)
N4–Mn–O2
83.99(5)

O3B–Mn–N1
174.39(5)
O2B–Mn–O1
94.76(5)

O2B–Mn–N4
174.61(5)
O3B–Mn–O1
92.88(5)

O3B–Mn–N4
90.62(5)
N1–Mn–O1
87.72(5)

N1–Mn–N4
94.97(5)
N4–Mn–O1
87.34(5)

O2B–Mn–O2
94.50(5)
O2–Mn–O1
168.83(5)

O3B–Mn–O2
94.25(5)

Symmetry transformations: .

Figure 2: Crystal structure of [(5-Br-salpn)(DMF)₂][B(C₆H₅)₄] showing the close packing of the cationic Mn(III) complex and the counter ions.

Figure 3: Section of the crystal structure of [(5-Br-salpn)(DMF)₂][B(C₆H₅)₄] showing the helical array of [B(C₆H₅)₄]⁻ ions about a screw axis parallel to the (010) plane.

4. Conclusions

The present work investigated a single-step reaction for the synthesis of a Schiff base complex of manganese(III) from a manganese(II) carboxylate. X-ray diffraction analysis of the complex has shown that the high spin manganese(III) ion is in octahedral environment and displays an elongation along the axial bonds on account of Jahn-Teller effect. Other structural features are similar to that of the reported structures of complexes with symmetrical N₂O₂ donor set ligands. See Supplementary Material available online at doi: 10.1155/2013/153023.

Acknowledgments

The authors are grateful to Prof. R. Lalancette, Rutgers University, Newark, NJ, USA, for X-ray diffraction analysis.

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