Crystal structures of 5-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II) and Zn(II)

Crystal structures of 5-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II) and Zn(II)

K. Stêpniak^I; W. Ferenc^I,*; B. Cristóvão^I; T. Lis ^II

^IFaculty of Chemistry, Maria Curie-Sklodowska University, 20-031 Lublin, Poland

^IIFaculty of Chemistry, Wroclaw University, 50-383 Wroclaw, Poland

ABSTRACT

The crystal and molecular structures of [bis(5-chloro-2-methoxybenzoate)tetraaquamanganese(II)], [pentaaqua(5-chloro-2-methoxybenzoato)cobalt(II)] (5-chloro-2-methoxybenzoate), [pentaaqua(5-chloro-2-methoxybenzoato)nickel(II)] (5-chloro-2-methoxybenzoate) and [aquabis(5-chloro-2-methoxybenzoate)zinc(II)] monohydrate were determined by a single-crystal X-ray analysis. Mn(H2O)4L2 (where L = C8H6ClO3) crystallizes in the monoclinic system, space group P21/c. [Co(H2O)5L]L and [Ni(H2O)5L]L both are isostructural, space group P212121. The crystals of [Zn(H2O)L2] H2O are monoclinic, space group Pc. Mn(II) ion is positioned at the crystallographic symmetry center. Mn(II) and Co(II) ions adopt the distorted octahedral coordination but Zn(II) tetrahedral one.The carboxylate groups in the complexes with M(II) cations function as monodentate, bidentate and/or free COO-groups. The ligands exist in the crystals as aquaanions. The complexes of 5-chloro-2-methoxybenzoates with Mn(II), Co(II) and Zn(II) form bilayer structure.

Keywords: crystal structure; 5-chloro-2-methoxybenzoates; magnetic moment;

Introduction

5-Chloro-2-methoxybenzoic acid having formula C₈H₇ClO₃ is a white crystalline solid sparingly soluble in cold water, that is stable up to 199ºC after which it decomposes with the melting point temperature [1].

The complexes of 5-chloro-2-methoxybenzoic acid with Mn(II), Co(II), Ni(II) and Zn(II) were obtained and some of their physico-chemical properties such as: thermal stability in air and nitrogen atmospheres and magnetic properties in the range of 80–300 K were studied. The results of elemental and thermal analyses suggest that these complexes are di-, tetra- and pentahydrates, and the water molecules are released only in one step with the rise of temperature. The FTIR and FIR spectra analysis reveals the carboxylate group to be monodentate and bidentate ligands. The magnetic measurement results suggest, that the Mn(II), Co(II) and Ni(II) are high-spin complexes. The ligands form the weak electrostatic field in the coordination sphere of the central ions. The Zn(II) complex is diamagnetic as may be expected from Zn(II) closed shell electronic configuration and the absence of unpaired electrons [2-5].

In order to explain the physico-chemical properties of the complexes, to elucidate the ways of coordinations of Mn(II), Co(II), Ni(II) and Zn(II) ions with 5-chloro-2-methoxybenzoate ligand and to determine the positions of water molecules in the crystal lattice their structures were determined by single-crystal X-ray analysis.

Experimental details

Preparation of complexes

The 5-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II), and Zn(II) were prepared by the addition of equivalent quantities of 0.1M ammonium 5-chloro-2-methoxybenzoate (pH~5) to a hot solution containing the nitrates(V) of those elements and crystallizing at 293K. The solids were filtered off, washed with hot water and methanol to remove ammonium ions and dried at 303K to a constant mass. Suitable crystals of the title compounds for X-ray diffraction were grown by the recrystallization process evaporating an aqueous solution of the salts at 293 K. The contents of carbon and hydrogen in complexes were determined by elemental analysis using a CHN 2400 Perkin Elmer analyser and the content of chlorine by Schöniger method. The contents of M²⁺ metals were established by ASA method and TG curves. Anal. Calcd. for C₁₆H₂₀Cl₂O₁₀ Mn (M_r = 498): C, 38.56; H, 4.02; Cl, 14.06; Mn 11.03%; found: C, 38.85; H, 3.96; Cl, 14.61; Mn 10.95%. Calcd. for C₁₆H₂₂Cl₂O₁₁ Co (M_r = 519.9): C, 36.93; H, 4.23; Cl, 13.46; Co 11.33%; found: C, 37.25; H, 4.13; Cl, 13.71; Co 11.43%. Calcd. for C₁₆H₂₂Cl₂O₁₁ Ni (M_r = 519.7): C, 36.95; H, 4.23; Cl, 13.66; Ni, 11.29%; found: C, 37.03; H, 4.09; Cl, 13.30; Ni, 11.40%. Calcd. for C₁₆H₁₆Cl₂O₈ Zn (M_r = 472): C, 40.64; H, 3.39; Cl, 14.82; Zn 13.84%; found: C, 40.67; H, 3.32; Cl, 14.12; Zn 13.86%.

X-ray structure determination

X-ray diffraction data for title compounds were measured at 100 K on a KM4 CCD diffractometer with MoKa radiation (l = 0.710073Å). The data were corrected for empirical absorption. The crystal and experimental data are collected in Table 1.

The atomic coordinates of non-hydrogen atoms with their isotropic temperature factors after the final refinement are given in Table 2.

Crystal structure was solved by direct method, using the SHELXS-97 program [6] and refined by full matrix least-squares method on F² using the SHELXL-97 program [7]. The non-hydrogen atoms were refined with anisotropic displacement parameters. Positions of ligand H-atoms were calculated from the geometry assuming the trigonal or tetragonal configuration of respective non-H atoms, while that of water molecules were located in difference maps. H-atoms were given isotropic factors of 1.2U_eq and their positions are refined.

Magnetism

The magnetic susceptibilities of samples of 5-chloro-2-methoxybenzoates of Mn(II), Co(II) and Ni(II) at 4.4–294 K were measured using an AC Lake Shore 7225 magnetometer. The magnetic susceptibilities of these complexes were also determined by Gouy method using a sensitive Cahn RM-2 balance. The measurements were made at a magnetic field strength of 9.9 kQe. The calibrant employed was Hg[Co(SCN)₄] for which the magnetic susceptibility of 1.644×10^-5 cm³g ^-1 was taken and then the effective magnetic moment values were calculated for 5-chloro-2-methoxybenzoates of Mn(II), Co(II) and Ni(II). Correction for diamagnetism of the constituent atoms was calculated by the use of Pascal¢s constants [8].

Results and Discussions

The complexes of 5-chloro-2-methoxybenzoates of Mn(II), Co(II), Ni(II) and Zn(II) were obtained as crystalline products with a metal to ligand ratio of 1:2 and a general formula M(C₈H₆ClO₃)₂ ·nH₂O, where M = Mn, Co, Ni, Zn and n=4 for Mn(II), n=5 for Co(II), Ni(II), and n=2 for Zn(II). The colour of the complexes is typical of the particular divalent ion salts, i.e., is slightly pink in the case of Mn(II), pink for Co(II), green for Ni(II), and white for Zn(II) and originates from d®d electronic transitions of the central ions.

Molecular and crystal structure

Structure of 5-chloro-2-methoxybenzoate aquaanion

5-Chloro-2-methoxybenzoate ligands exist as aquaanions in the complexes with Mn(II), Co(II), Ni(II) and Zn(II). The scheme of aquaanion with atom numberings is shown in Figure 1.

As it is seen, the water molecule as proton donor interact with O2 and O3 oxygen atoms of the ligands as proton acceptors through three-centered intermolecular hydrogen bonds and forms (6) motives.

The phenyl rings of all ligands are planar within the experimental error. The C7-O1 and C7-O2 bond values in the carboxylate group lie in the range 1.255(5) - 1.269(2) Å in the Mn(II) and Co(II) complexes, and 1.248(4) - 1.287(4) Å in the Zn(II) complex, and are typical for the delocalized bonds. The COO^- groups are approximately coplanar with the benzene ring plane. Torsion angles C2-C1-C7-O2 change from -0.4(6) in Mn(H₂O)₄L₂ to -1.7(3)º (A ligand) and 8.7(3)º(B ligand) of the [Co(H₂O)₅L]L complexes. However, in the Zn(II) complex it rotates around C1–C7 bond, and the values of C2–C1–C7–O2 torsion angles are -43.4(3) and -24.7(5)º in the A and B ligands, respectively.

The methoxy groups in all complexes are approximately coplanar with benzene ring planes.

Structure of Mn(H₂O)₄L₂

The perspective view of the Mn(H₂O)₄L₂ complex is shown in Figure 2a.

The values of Mn-O bond lengths and O-Mn-O angles in the cation coordination spheres are given in Table 3.

The Mn(II) ion is positioned on the symmetry center and bonded to four oxygen atoms of water molecules and two of monodentate carboxylate groups (Figure 2a). Two independent Mn-O_w (O_w - oxygen atom of water molecule) bond lengths are almost equal (Table 3) and longer than Mn-O_c(O_c - oxygen atom of carboxylate group). The coordination geometry would be the best described by the distorted octahedral whose base contains water molecules and the vertices are occupied by symmetrically equivalent oxygen atoms of monodentate carboxylate groups. The MnO₆ spheres are linked through O1w-H1w1···O2wⁱ (ⁱ -x, y - 0.5, -z + 0.5) intermolecular hydrogen bonds and build two-dimensional hydrophilic cation-layers parallel to (100) lattice plane. Also, there are three types of intermolecular hydrogen bonds within cation-layers in which water molecule acts as the proton donor and the uncoordinating O2 carboxyl oxygen atom and O3 ortho-methoxy oxygen atom are proton acceptors. Mn(II)···Mn(II) separations within cation-layers are 5.887 Å (Table 4).

The methyl group of the monodentate ligands forms C8-H8···Cl^iv (^iv x, y-1, z) hydrogen bonds with neighbouring anions and build ribbons parallel to a axis. Moreover, p···p stacking was found to exist among the 5-chloro-2-methoxybenzoate aquaanions, the distances between the centroid of the benzene ring planes are 3.34 Å.

Structure of [Co(H₂O)₅L]L

The Co(II) complex consists of two discrete units: [Co(H₂O)₅L]⁺ cations and free ligands L^- as anions (Figure 2b).

The Co(II) cation occurs in distorted octahedral coordination (Table 3). The coordination sphere of Co(II) ion contains one oxygen atom of monodentate carboxylate group of A ligand and five water molecules completing octahedral coordination. In this complex there are intramolecular O_w-H...O_c (i.e., O5w-H1w5...O2A) and C-H...O_m (O_m - oxygen atom of methoxy group; i.e., C8A-H8A3...O3B) hydrogen bonds, and moreover intramolecular C7B...O3A electrostatic interaction (Table IV). The benzene ring plane of the coordinating (A) and uncoordinating (B) ligands are not entirely parallel, the values of the bond angles are 7.4(1)º. The first coordination spheres of the cations are connected through O_w-H...O_w (i.e., O1w-H1w4...O2w^vii and O2w-H1w2...O5wⁱⁱⁱ) hydrogen bonds and build cation-layer parallel to (001) lattice plane with Co...Co distances 5.92 and 5.94Å. Free anions are connected via C8B-H8B...Cl1B^xi weak hydrogen bonds along a axis.

Structure of {[Zn(H₂O)L₂]·H₂ O}_n

The Zn(II) cations function in distorted tetrahedral ZnO₄ coordination (Figure 2c).

Their coordination spheres contain one oxygen atom of monodentate carboxylate group of B ligand, two oxygen atoms of bidentate-bridging carboxylate group of A ligand and one water molecule. Coordination spheres are connected by bridging carboxylate groups forming the {[Zn(H₂O)L₂]·H₂ O}_n polymeric chains along the [100] direction.

The magnetic susceptibility of 5-chloro-2-methoxybenzoates of Mn(II), Co(II) and Ni(II) was determined in 4.4–294 K. All complexes show paramagnetic properties and they obey the Curie-Weiss law. The effective magnetic moment values experimentally determined for 5-chloro-2-methoxybenzoates of Mn(II) and Ni(II) change from 5.28 m_B (at 4.5 K) to 6.13 m_B (at 291 K) and from 2.80 m_B (at 4.3 K) to 3.04 m_B (at 293 K) for those of two appropriate complexes, respectively. The experimental data reveal that the magnetic moments of Mn²⁺ and Ni²⁺ ions in the complexes are connected with spin-only moments. Their theoretical values at room temperature are equal to 5.92 m_B for the Mn²⁺ and 2.83 m_B for the Ni²⁺, respectively. These spin – only values of magnetic moments of Mn(II) and Ni(II) indicate that they are high-spin d⁵ and d⁸ ions, respectively. In the case of 5-chloro-2-methoxybenzoate of Co(II) the effective magnetic moments of cobalt ion determined in 4.6–294 K are in the range of 4.08 – 4.64 m_B. The magnetic moment measured at room temperature for the Co²⁺ ion is equal to 4.64 m_B. This value differs from that of the spin-only moment which amounts to 3.88 m_B. The relatively large difference between measured and calculated values results from a spin-orbital coupling. The obtained values indicate that the studied compounds are high-spin complexes with octahedral coordination and the ligands form the weak electrostatic field in the coordination sphere of the central ions. The Zn(II) complex is diamagnetic as may be expected from its closed shell electronic configuration and the absence of unpaired electrons [2, 4, 8-14].

Supplementary data

The lists of the atomic coordinates, displacement parameters and complete geometry have been deposited with the Cambridge Crystallographic Data Centre as supplementary material No. CCDC 610630-610632. Copies of the data can be obtained free of charge on application to the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: [phone]; or e-mail: [e-mail]). The list of F_o/F_c-data is available from the author.

Conclusions

The complexes of Mn(II), Co(II), Ni(II), and Zn(II) with 5-chloro-2-methoxybenzoic acid anion were synthesized as hydrated salts. They form tetra-, penta-, and dihydrates, respectively. Their crystal structures were determined. The crystals of Zn(II) complex are monoclinic. Mn(II) and Co(II) ions adopt the distorted octahedral coordination but Zn(II) the tetrahedral one. Complexes of Co(II) and Ni(II) are isostructural. The carboxylate anion in the analysed complexes function as monodentate, bidentate and/or free COO^- groups. The Mn(II), Co(II), and Ni(II) compounds are high-spin complexes with octahedral coordination and the ligands form the weak electrostatic field in the coordination sphere of the central ions.

Received 16 April 2007

Accepted 17 May 2007

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Publication Dates

• Publication in this collection
  01 Oct 2007
• Date of issue
  2007

History

• Accepted
  17 May 2007
• Received
  16 Apr 2007