научная статья по теме SYNTHESIS, CRYSTAL STRUCTURE, AND THERMAL STABILITY OF [ ] · (C8H9N2)2 · 2H2O Химия

КООРДИНАЦИОННАЯ ХИМИЯ, 2014, том 40, № 1, с. 55-60

УДК 541.49

SYNTHESIS, CRYSTAL STRUCTURE, AND THERMAL STABILITY OF [Mo2O4(^2-O)(C6H4O2)2(H2O)] • (C8H9N2)2 • 2H2O

© 2014 X. J. Xu

College of Chemistry and Materials, Yulin Normal University, Yulin, 537000 P.R. China E-mail: xxjhb2011@hotmail.com Received September 22, 2011

From hydrothermal treatment of benzene-1,2-diamine, pyrocatechol, and MoO3 in acetic acid solution, a new compound, [Mo2(p.2-O)2(C6H4O2)2(H2O)] ■ (C8H9N2)2 ■ 2H2O (I), constructed from pyrocatechol chelated dinuclear molybdenum units and 2-methylbenzimidazole has been synthesized. Single-crystal structure analysis reveals that the compound crystallizes in the monoclinic space group P2i/c with a = 23.365(2), b = 7.2214(5), c = 19.3021(16) Á, в = 97.929(4), V = 3225.6(5) Á3, Z = 4, M = 808.46, pc = 1.665 g/cm3, ^(Mo!a) = 0.84 mm-1, Д000) = 1608, the final R = 0.0622 and wR = 0.1484 for 7385 independent reflections with Rint = 0.0393. Interestingly, an in situ condensation between acetic acid and benzene-1,2-diamine has occurred, and the unexpected 2-methyl-1-H-benzo[d] imidazoles serve as counterions and N-H donors to form stable hydrogen-bond network in the crystal. Furthermore, intermolecular hydrogen bonds are found among the cations, anions and crystalline water molecules. The double nuclear molybdenum units are connected by O-H-O hydrogen bonds with the crystalline water molecules to form one-dimensional chains, and the chains are further joined together by N-H-O to form a quasi-two dimensional structure.

DOI: 10.7868/S0132344X14010095

INTRODUCTION

In the past few years, the research on hybrid molecular materials has grown into an attractive subject in inorganic chemistry for their structural diversity, fascinating properties and potential applications [1—4]. In this research field, catecholate-coordinated molybdenum compounds, a class of molecular materials, have aroused much interests for their structure similarity to the oxo-transfer enzymes and potential applications in catalysis, DNA cleavage and so on [4—8].

As far as the molecular structure of catecholate is concerned, it has several favorable factors in the preparation of hybrid molecular materials. Firstly, the ster-ic geometry and activity of the center metals can be modulated by two hydroxyl groups at the ortho position via chelated coordination [9]. Secondly, the catecholate molecules can effectively control the self-condensation of the anions which are tend to form complex structures, such as atomic clusters [7, 10]. Thirdly, the lone pair electrons in the oxygen atoms of the hydroxyl groups make it possible to form large amounts of hydrogen bonds which are favorable for selective catalysis and separation. Besides, the aromatic rings can serve as antenna for photon receiving and emission in the hybrid molecular materials with fascinating optical property.

Here MoO3, catecholate, and o-phenylenediamine were selected as reaction substrates for the preparation of new molybdenum base hybrid molecular materials

in a hydrothermal process. In the reaction system, acetic acid was used to modulate the pH values, while o-phenylenediamine was designed to be used as structure directing reagents and counter ions. Interestingly, 2-methylbenzimidazoles, unexpected species coming from in situ condensation of o-phenylenediamine with acetic acid were found in the crystal structure. Furthermore, the pyrocatechol controlled the self-condensation of MoO4 into clusters and resulted in the formation of di-nuclear molybdenum subunits. Thirdly, there are two kinds of hydrogen bonds as O-H-O and N-H-O make the subunits orderly organized into a quasi-2-dimensional structure.

EXPERIMENTAL

Materials and instruments. All starting materials were purchased commercially and used as received without further purification. IR spectrum (KBr pellets) was recorded on a Magna 750 FT-IR spectrometer in the range of 400—4000 cm-1. Elemental analysis was carried out on an Elementar Vario EL III elemental analyzer. Thermogravimetric analysis (TGA) was performed on a NETSCHZ STA-449C thermoana-lyzer from 30 to 1200°C with a heating rate of 10°C/min in flowing air.

Synthesis of [Mo2O4(^2-O)(C6H4O2)2(H2O)] • • (C8H9N2)2 • 2H2O (I). In a typical synthesis, MoO3 (0.1 g), benzene-1,2-diamine (0.1 g), pyrocatechol

Table 1. Crystallographic data and experimental details for complex I

Parameter Value

Crystal system Monoclinic

Space group P21/c

a, A 23.365(2)

b, A 7.2214(5)

c, A 19.3021(16)

a, deg 90.00

P, deg 97.929(4)

Y, deg 90.00

V, A3 3225.6(5)

Z 4

P calcd g cm-3 1.665

Crystal size, mm 0.32 x 0.29 x 0.06

F(000) 1632

^(Moia), mm-1 0.84

9 Range for data collection, deg 3.02 to 27.48

Index range h, k, l -30 < h < 23, -9 < k < 9, -25 < l < 25

Type of scan ro scans

Reflections collected 24100

Independent reflections (Rint) 7385 (0.0393)

Reflections with I > 2ct(I) 6419

Number of parameters 415

Goodness-of-fit on F 2 1.081

Final R1, wR2 (I> 2ct(I))* R1 = 0.0622, wR2 = 0.1484

R1, wR2 (all data)** R1 = 0.0745, wR2 = 0.1575

APmax and Apmjn e AT3 0.889 and -0.658

* R = E(F0 - Fc)/S(Fo), ** wR2 = {EMF2 - Fc2)2]/I(F2)2}12.

(0.1 g), and H2O (13 mL) were mixed in a 23 mL Teflon-lined stainless steel autoclave. After stirring for a few minutes, the pH value was modulated to 4.3 with acetic acid, and then the autoclave was sealed, heated to 180°C, and maintained at the temperature for 5 days. After the reactor was cooled down to room temperature at a rate of 5°C/h, red-brown crystals suitable for X-ray structure analysis were separated by filtration and dried naturally (86% yield based on molybdenum).

For C28H32N4Oi2Mo2 (I)

anal. calcd., %: C, 41.25; H, 4.02; N, 6.77. Found, %: C, 41.66; H, 3.97; N, 6.94.

IR (v, cm-1): 3426 m, 3060 w, 1629 m, 1575 m, 1477 s, 1257 s, 1104 w, 1020 w, 905 s, 814 s, 738 s, 624 s.

X-ray structure determination. A red brown single crystal with dimensions of0.32 x 0.29 x 0.06 mm was selected and mounted on a glass fiber for structure determination. X-ray diffraction data were collected on a Bruker Smart CCD diffractometer equipped with graphite-monochromated MoAa radiation (X = 0.71073 A) in the range of 3.02° < 9 < 27.48° at 293 K. An empirical absorption correction was applied using the SADABS program [11]. The crystal structure was solved by direct methods with SHELXS-97 program [12], and refined by full-matrix least-squares techniques on F 2 with SHELXL-97 software package [13]. All non-hydrogen atoms were rened anisotropically. The position of the hydrogen atoms were generated geometrically, rened with isotropic thermal parameters, and allowed to ride on their parent atoms before the final cycle of refinement.

For I, the final R = 0.0622, wR = 0.1484 (w = 1/[a2(Fo2) +

+ (0.0697P)2 + 7.0167P], where P = (Fo2 + 2Fc2)/3) based on 6419 reflections with I > 2a(I), S = 1.081 and (A/a)max = 0.001.

A summary of the crystallographic data and structure refinement is shown in Table 1, the selected bond distances and bond angles are listed in Table 2, and the hydrogen bond lengths and bond angles are given in Table 3.

Supplementary material for structure I has been deposited with the Cambridge Crystallographic Data Centre (no. 819677; deposit@ccdc.cam.ac.uk or http: //www.ccdc.cam.ac.uk).

RESULTS AND DISCUSSION

The crystal structure of I is built up of pyrocatechol coordinated di-nuclear molybdenum anions, proto-nated 2-methylbenzimidazole cations, and lattice water molecules (Fig. 1). In terms of the anions, both of the metal atoms are in octahedral geometry. The Mo(1) atom is coordinated by six oxygen atoms, including two terminal oxygen atoms (O(4), O(5)), O(8) and O(9) atoms provided by a pyrocatechol, O(7)

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Table 2. Selected bond lengths (A) and bond angles (deg) for complex I

Bond d, A Bond d, A Bond d, A

Mo(1)—O(4) 1.694(4) Mo(1)-O(8) 2.140(3) Mo(2)-O(3) 1.930(3)

Mo(1)-O(5) 1.728(4) Mo(1)-O(7) 2.329(3) Mo(2)-O(6) 1.961(4)

Mo(1)-O(3) 1.948(3) Mo(2)-O(2) 1.705(4) Mo(2)-O(7) 2.116(3)

Mo(1)-O(9)) 1.975(4) Mo(2)-O(1) 1.714(4) Mo(2)-O(10) 2.506(4)

Angle ю, deg Angle ю, deg Angle ю, deg

O(4)Mo(1)O(5) 102.11(18) O(4)Mo(1)O(7) 166.16(16) O(3)Mo(2) O(6) 148.03(15)

O(4) Mo(1)O(3) 97.61(17) O(5)Mo(1)O(7) 86.47(15) O(2)Mo(2)O(7) 101.69(17)

O(5) Mo(1)O(3) 102.78(17) O(3)Mo(1)O(7) 69.67(12) O(1)Mo(2)O(7) 153.97(18)

O(4) Mo(1)O(9) 102.53(18) O(9)Mo(1)O(7) 87.74(14) O(3)Mo(2)O(7) 74.83(13)

O(5)Mo(1)O(9) 92.51(17) O(8)Mo(1)O(7) 79.27(13) O(6)Mo(2)O(7) 76.07(14)

O(3)Mo(1)O(9) 151.53(15) O(2)Mo(2)O(1) 104.3(2) O(2)Mo(2)O(10) 175.15(17)

O(4)Mo(1)O(8) 94.11(17) O(2)Mo(2)O(3) 98.60(18) O(1)Mo(2)O(10) 80.51(17)

O(5)Mo(1)O(8) 161.86(16) O(1)Mo(2)O(3) 102.65(17) O(3)Mo(2)O(10) 79.50(13)

O(3)Mo(1)O(8) 82.81(14) O(2)Mo(2)O(6) 99.99(18) O(6)Mo(2)O(10) 79.82(13)

O(9)Mo(1)O(8) 75.92(15) O(1)Mo(2)O(6) 97.67(18) O(7)Mo(2)O(10) 73.53(13)

atom from another pyrocatechol, and O(3) sharing with the Mo(2) atom. The Mo(2) atom is also coordinated by six oxygen atoms, including O(1) and O(2) as terminal atoms, O(6) and O(7) from the pyrocatechol, O(3) sharing with the Mo(1) atom, and an oxygen O(IO) provided by the coordinated water. The two MoO6 octahedrons are sharing a common edge constructed by O(7) from a pyrocatechol and ^2-O(3).

Apart from static electronic interactions among the anions and cations, abundant hydrogen bonds are found to link the subunits from different directions. As listed in Table 2, there are two kinds of hydrogen bonds as O—H—O and N—H—O that make the subunits orderly organized. Typical O—H—O hydrogen bonds are shown in Fig. 2 and the H atoms are omitted for clarity. Firstly, the lattice water molecules marked as O(2w) are serving as double hydrogen donors to form hydrogen bonds with terminal oxygen atoms O(5) and O(8) from neighboring anions. Secondly, another kind of lattice water molecules marked as O(1w) are also serving as double hydrogen donors to form hydrogen b

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