научная статья по теме SYNTHESIS, STRUCTURE, AND ELECTROCHEMICAL PROPERTIES OF [M(N-MEIM)6]2+ (M = NI, CO, CU) ASSOCIATED WITH [HGCL4]2 Химия

КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 3, с. 138-142

УДК 541.49

SYNTHESIS, STRUCTURE, AND ELECTROCHEMICAL PROPERTIES OF [M(N-MeIm)6]2+ (M = Ni, Co, Cu) ASSOCIATED WITH [HgCl4]2-

© 2014 L. Gao

College of Chemistry and Pharmaceutical Sciences, Qingdao Agriculture University, Qingdao, 266109 P.R. China

E-mail: lbgao@126.com Received February 21, 2012

Reaction of Hg(NO3)2 with 4 equivalent KI in water afford K2[HgI4]. By using K2[HgI4] as the precursor, three new heterobimetallic compounds [Ni(N-MeIm)6][HgI4] (I), [Co(N-MeIm)6][HgI4] (II), and [Cu(N-MeIm)6][HgI4] (III) have been characterized by elemental analysis, IR spectra, and the single-crystal X-ray crystallorgraphy analysis. Three complexes are isomorphous and crystallized in monoclinic symmetry space group P2i/c. The coordination around each center metal(II) atom is octahedral with six nitrogen atoms of N-MeIm ligand. Each structure contains one tetrahedral [HgI4]2- as an anion to balance the charge of the molecular. Thermogravimetry analysis indicates these complexes have the similar departure process and cyclic voltammogram exhibits a significant pair of redox peaks.

DOI: 10.7868/S0132344X14020030

INTRODUCTION

Small molecules with metal center have been widely studied as model complexes in the more complex biological systems of metalloproteins [1], because the structural geometries of the model complexes are often quite comparable to those in the proteins [2]. Imidazole and its derivatives, such as histamine, histidine, pilocarpine, and allantoin occurring in living organisms have been well studied to elucidate the interaction of the proteins with the metal ions or to model the biological systems including imidazole type bonding [3—6]. Many proteins and enzymes are known to contain active sites with multiple histidine residues bound to a metal center. The catalytic activity of enzymatic reactions involving Co2+, Ni2+, Fe2+, Cu2+, and Zn2+ ions has been found to depend on its tendency towards coordination and on the structure of the compounds [7]. Therefore, it is much more important to study the structure and physicochemical properties of metal complexes with ligands incorporating the imidazole ring [8].

N-Methylimidazole (N-MeIm), as a derivative of the imidazole, has been used as ligand in biological systems, e.g., one or more N-MeIm units bound to metal ions in copper- and ruthenium-containing complexes have been attracting considerable attention for their antitumor activity and ability to ligate radiosensitizing agents to DNA [9—11]. Such compounds are also increasingly being studied in coordination chemistry because of N-methylimidazole as a stronge donor ligand in transition metal compounds. N-MeIm also has been proved to be a useful displacing ligand other than halides from trivalent lanthanide metal centers [12]. However, these systems involve an anionic metal-ha-

lide component for charge balance has comparatively been neglected. Mercury(II) typically regarded, as a Lewis acid, readily forms [HgI4]2- by accepting halide ions (I-) from multiple donor sources [13]. In the recent paper, the [HgI4]2- function as a halide ion donor with the lanthanide and transitional metals has been reported [14]. In this paper, we describe the syntheses, characterization, redox properties of a new series of [M(N-MeIm)6]2+ (M = Cu (I), Co (II), Ni (III)) associated with [HgI4]2-.

EXPERIMENTAL

Measurements. Elemental analyses for carbon, hydrogen and nitrogen were performed using a Perkin-Elmer 240C elemental instrument. Thermal analysis was recorded on Shimadzu TGA-50 thermogravimet-ric analyzer. Cyclic voltammetric analysis was carried out on an Autolab/PGSTAT30 potentiostat. A glass carbon (2 mm diameter) working electrode, a platinum sheet counter electrode and a saturated calomel electrode reference were employed. FT-IR and electronic spectra were recorded on a PerkinElmer 2000 FT-IR and Shimadzu 3100 Uvi-Vis-NIR spectrometer, respectively.

All manipulations were carried out in air. All chemicals were of analytical reagent grade and used directly without further purification.

Synthesis of the precursor K2[HgI4]. (Hg(NO3)2 (0.324 g, 1 mmol) was dissolved in 10 mL water, and to this solution was added a solution of KI (0.332 g, 2 mmol) in 10 mL water. An orange precipitate was obtained, to this suspended solution was added KI

(0.332 g, 2 mmol) in 10 mL of water, causing dissolution to a pale yellow solution.

Synthesis of [Ni(N-MeIm)][HgI4] (I). To 10 mL of water were added NiCl2 (0.129 g, 1 mmol), and N-MeIm (0.5 g, 6.1 mmol). This mixed solution was stired at room temperature for 1 h. To this solution was added K2[HgI4] slowly with strring, producing a precipitate. The precipate was filtered, washed twice with water and dried in vacuo. A crystal suitable for X-ray diffraction was formed after dissolution in DMF at 36°C for 2 days. The yield was 91%.

For C24H36N12l4HgNi

anal. calcd., %: C, 22.89; H, 2.88; N, 13.34. Found, %: C, 22.57; H, 2.64; N, 14.54.

IR spectrum (KBr; v, cm-1): 3431 m, 3116 s, 2924 w, 1654 v.s, 1531 s, 1517 sh, 1400 s,1371 sh, 1280 m, 1230 s, 1103 v.s, 1082 s, 1028 sh, 938 m, 828 m, 740 m, 664 s, 618 m, and 471 m.

Synthesis of [Co(N-MeIm)][HgI4] (II) was carried out the same as that of I except for the use of CoCl2 • 6H2O instead of NiCl2. The yield was 86%.

For C24H36N12I4HgCo

anal. calcd., %: C, 22.88; H, 2.88; N, 13.34. Found, %: C, 22.35; H, 2.53; N, 14.26.

IR spectrum (KBr; v, cm-1): 3416 m, 3115 s, 2324 w, 1653 v.s, 1531 s, 1400 s, 1229 m, 1103 s, 1081 sh, 1027 sh, 937 m, 829 m, 742 m, 663 s, 618 m, and 476 m.

Synthesis of Cu(N-MeIm)][HgI4] (III) was carried out the same as that of I except for the use of CuCl2 instead of NiCl2. The yield was 82%.

For C24H36N12I4HgCu

anal. calcd., %: C, 22.80; H, 2.87; N, 13.29. Found, %: C, 21.95; H, 2.45; N, 14.05.

IR spectrum (KBr; v, cm-1): 3426 w, 3116 s, 2927 sh, 1653 v.s, 1531 s, 1415 s, 1373 sh, 1229 m, 1103 v.s, 1082 sh, 1027 sh, 938 m, 828 m, 740 m, 664 s, 618 m, and 476 w.

X-ray structure determination. The selected crystal was mounted on Enraf-Nonius CAD4/Mach3 dif-fractometer. Reection data were measured at 20°C using graphite monochromated Mo^a (X = 0.71073 A) radiation. The collected data were reduced by using the program SAINT. The structure was solved by direct methods and rened by full-matrix least-squares method on Fobs2 by using the SHELXTL software package [15]. All non-H atoms were anisotropically rened. The hydrogen atom positions were fixed geometrically at calculated distances and allowed to ride on the parent carbon atoms. The summary of the key crystallographic information of compounds I—III are

given in Table 1. Supplementary material has been deposited with the Cambridge Crystallographic Data Centre (nos. 894450 (II) and 894451 (III); deposit@ccdc. cam.ac.uk or http://www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

Three novel heterobimetallic species [M(N-meth-ylimidazole)6]2+ (M = Ni (I), Co (II), Cu (III)) associated with [HgI4]2- as anion have been synthesized by reaction of metal salts MCl2 • xH2O with N-MeIm ligand and K2[HgI4] under analogous conditions. Hg(NO3)2 was treated with KI in water to afford a yellow solution ofK2[HgI4] as a precursor. Free ligand N-MeIm and metal salts was stirred at room temperature for 1 h, then K2[HgI4] solution was added slowly to afford a precipitate. After work up, three compounds was obtained in good yield. Complexes I—III are stable toward air and moisture, soluble in DMF, and insoluble in diethyl ether, hydrocarbon solvents and water.

The IR spectra of I—III are quite similar, which provides support to the characterization of the product by identifying the vibration of the ligands surrounding the central transition metal. The absorption frequencies of the aromatic hydrogen atoms C—H of 1-MeIm are located in the 3132—2937 cm-1 in all IR spectra. Vibrations corresponding to v(C=N) of the coordinated imidazole ring appeared at ~1653 cm-1 suggesting the coordination of the ligand N-MeIm through imidazole nitrogen [16].

The structures of I—III were determined by single-crystal X-ray diffraction. Selected bond distances and angles for compound III are summarized in Table 2. The molecular structure of III is listed in Fig. 1, as well as a perspective view of the crystal packing in the unit cells is showed in Fig. 2. The crystal structure of the compounds I and II are similar to that of III with the M2+ (Ni, Co and Cu) atoms coordinated by six 1-me-thylimidazolium groups. Every single-crystal structure contains a [HgI4]2- anion.

For complex III, the Cu atom is in an distorted octahedral environment formed by six N atoms of1-me-thylimidazolium moieties. The bond distances involved in this octahedral geometry (Cu(1)—N(2), Cu(1)—N(4), and Cu(1)—N(6)) are the most close to the regular octahedron [17]. The Cu—N bond distances fall in the range of 2.118(10)-2.152(11) A. These values are comparable to those reported elsewhere [18]. The Hg—I lengths are in the range from 2.776(4) to 2.797(4) A and the IHgI angles vary within the range from 105.45(16)° to 110.58(12)°. As indicated in

packing diagram in Fig. 2, the tetrahedral HgI4 was linked not only by the electrostatic forces but also by the C—H---I hydrogen bonds. One [HgI4]2- anion connects with one neighboring CH3 of the [M(N-MeIm)]2+

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Table 1. Crystallographic data and experimental details for complexs II and III

Parameter Value

II III

Formula weight 1259.77 1264.38

Color Pink Blue

Space group P2i/c P2l/c

Crystal system Monoclinic Monoclinic

a, A 9.5000(19) 9.5445(19)

b, A 19.964(4) 20.153(4)

c, A 20.379(4) 20.244(4)

P, deg 99.91(3) 99.80(3)

V, A3 3807.4(13) 3837.1(13)

Z 4 4

Pcalcd g cm—3 2.198 2.189

p., mm—1 7.739 7.801

F(000) 2332 2340

9 Range, deg 2.03-25.00 1.44-25.00

Reflection collected 7131 15475

Independent reflections (Rint) 6702 (Rint = 0.0623) 6723 (Rint = 0.0821)

Reflections with I > 2a(I) 3120 5109

Number of paramete

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