三环己基锡吡啶酸甲酯的合成、结构、热稳定性及其量子化学计算研究

邝代治 蒋伍玖 冯泳兰 张复兴 王剑秋 庾江喜

(功能金属有机材料湖南省普通高等学校重点实验室，衡阳师范学院化学与材料科学系，衡阳 421008)

0 Introduction

In recent years, organotin carboxylate have attracted interest due to their applications such as biological properties, coatings, catalysis and as additives to polymers[1-6]. A number of organotin carboxylates with anticancer activity and novel structure were synthesized by reaction of nitrogen heterocyclic with organotin[7-12]. In the past few years,we have successively reported some research on reaction of organotin with such nitrogen heterocyclic ring carboxylic acid ligands as pyridine-2-formic acid[13],pyridine-4-formic acid[13-14], indole-3-acetic acid[15],quinoline-2-formic acid[16-19]and so on.Research showed that the properties of organotin carboxylate are affected by the alkyl structure and ligand. Especially,some novel structure of organotin compounds could been synthesized by reaction of sterically hindered organotin[14,20-21]with ligand.In order to further investigate the relationship between sterically hindered alkyl and organotin carboxylate properties, a one-dimensional chain [(C5H4N)COOSnCy3]nhas been synthesized and characterized by IR,1H NMR spectra,elemental analysis and single crystal X-ray diffraction.

1 Experimental

1.1 Reagents and instruments

All the chemicals and solvents for the synthesis of compounds were of AR grade and used without further purification. Elemental analyses for C, H, and N were determined on a PE-2400 (Ⅱ) analyzer. IR spectrum was obtained for KBr pellets on Shimadzu FTIR-8700 spectrophotometer in the 4 000～400 cm-1.1H NMR analysis was performed on a Bruker INOVA-400 NMR spectrometer (TMS internal standardization,CDCl3solvent). Crystal structure was determined on a CCD area detector X-ray diffractometer. The TG studies were performed on a TA instruments TGA Q50 thermal analyzer under flowing nitrogen from 40 to 890 ℃at a heating rate of 20 ℃·min-1. Melting point measurement was executed on an XT-4 binocular micromelting point apparatus with the temperature unadjusted.

1.2 Complex synthesis

A mixture of Cy3SnOH 0.385 g (1 mmol) and nicotinic acid 0.123 g (1 mmol) was heated under reflux in methanol for 8 h. The solution obtained by filtration, the filtrate was removed by evaporation in vacuo. The crude adduct was recrystallized from methanol to give colorless crystals 0.43 g, Yield： 83%,m.p. 139～140 ℃. Anal. Calcd. for C24H37NO2Sn(%)： C,58.80; H, 7.61; N, 2.86. Found(%)： C, 58.61; H, 7.88;N, 2.87.1H NMR (400 MHz, CDCl3, ppm) δ： 1.35～2.04 (m, 33H, Cp-H), 7.34(s, 1H, 5-Pyridine-H), 8.31(s, 1H, 4-Pyridine-H), 8.71(s, 1H, 6-Pyridine-H), 9.25(s,1H,2-Pyridine-H).IR(KBr)：2 920.0,2846.7(s,νC-H),1 647.1 (vs, νasCOO-), 1 352.0 (m, νsCOO-), 754.1,704.0 (m, νAr-H), 567.0 (w, νSn-O), 491.8(w, νSn-N), 418.5(w, νSn-C).

1.3 Crystal structure determination

Table 1 Crystallographic data

Single crystal of suitable size of the complex was mounted on Bruker SMART APEX (Ⅱ)CCD diffractometer. Intensity data were collected with a graphitemonochromated Mo Kα radiation (λ=0.071 073 nm) at 296 (2)K.The structure was solved by directed method and the positions of the rest non-hydrogen atoms were determined from successive fourier syntheses. The hydrogen atoms were placed in the geometrically calculated positions and allowed to ride on their respective parent atoms. The position and anisotropic parameters of all non-hydrogen atoms were refined on F2by full-matrix least-squares method using the SHELXL-97[22]program package. Crystal data and structure refinement parameters of the complex are summarized in Table 1. Selected bond lengths and bond angles are shown in Table 2.

Table 2 Selected of bond lengths (nm) and bond angles (°)

CCDC： 817178.

2 Results and discussion

2.1 Spectrum characteristics

In the1H NMR of the complex, the pyridine ring of four protons formed respective single peak, which were at 7.34 ppm (5-pyridine-H), 8.31 ppm (4-pyridine-H), 8.71 ppm (6-pyridine-H), 9.25 ppm (2-pyridine-H), and proton in the cyclohexyl formed multiplet between 1.35～2.04 ppm.

In the infrared spectrum of the complex, the asymmetrical and symmetrical stretching vibration frequencies of carbonyl are 1 647.1 and 1 352.0 cm-1respectively, and their difference is Δν(CO2)=295.1 cm-1, which reveals that νas(COO) does not shift towards lower frequency and νs(COO) does not move to the higher frequency obviously. So conclusion could be drawn that carboxyl coordinates to Sn atom via a mono-oxygen mode[18]. Besides, weak peaks at 567.0,491.8 and 418.5 cm-1indicate the presence of O→Sn,N→Sn and Sn-C dative bond[14]. All the above IR attribution is consistent with the structural determination.

2.2 Crystal structure

The structural motif and the one-dimensional chain polymer of the complex are illustrated in Fig.1 and Fig.2 respectively.

Fig.1 Structural motif of the complex showing 5%probability displacement ellipsoids

Fig.2 One-dimensional chain polymer of the complex

As shown by Fig.1, Fig.2 and Table 2, a onedimensional linear polymer is formed through an interaction between the N atoms of nicotinic acid and tin atoms of an adjacent tricyclohexyltin nicotinate molecule, but this structure differs from the Cy3SnOOCC3H7[23], Cy3Sn(OOC)2C6H4[24]. The coordination geometry about Sn is a distorted trigonal bipyramid in which three carbon atoms of cyclohexyl groups form the equatorial plane, while one nitrogen atom and one oxygen atom occupy the apical positions. There was coordination between the ligand and Sn for forming the different bond parameters. The sum of the angles of C19-Sn1-C13 (112.18(8)°), C19-Sn1-C7 (117.11(12)°) and C13-Sn1-C7 (127.23(9)°) is 356.52° which deviates from 360° only 3.48°. The angle O1-Sn1-N1iof is 174.36(7)°, which deviate from 180° only 5.64°. The bond lengths of Sn1-O1 and Sn1-N1iare 0.213 7(2)and 0.281 1(2)nm respectively,which are very similar to those of Ph3SnOOC5H4N[25].The Sn1-O2 distance of 0.320 0 nm is greater than the sum of the covalent radius of Sn and O of 0.214 nm. It is shown that the O2 atom does not make any significant contacts with the Sn1 atom.

Fig.3 3D supramolecular framework of complex connected by C-H…O hydrogen bonding interactions

It is also noted that some intermolecular weak CH…O hydrogen bonding interactions extensively exist(H5…O2i0.250 1 nm,C5…O2i0.328 5 nm,∠C5-H5…O2i141.98°). The repeating one-dimensional chain units are linked by intermolecular C-H…O bonds thus giving a 3D supramolecular framework(Fig.3).

2.3 Energy and molecular orbital composition

Based on the crystal data, single point calculation was carried out with Gaussian03W[26]program at the B3lyp/lanl2dz level. 65atoms, 325 basis functions and 835 primitive gaussians were involved in calculation.104 occupied orbitals could be seen in the results. All calculations were performed on a P4 computer.

The total energy of the title complex is-1 144.663 872 98 a.u., the energy of HOMO is-0.232 87 a.u. and that of LUMO is -0.043 92 a.u.The LUMO-HOMO gap is 0.188 95 a.u. From the viewpoint of oxidation/reduction or charge transfer,these energy values indicate that the title complex is stability at the ground state and difficult to lose electron, in agreement with the experimental result.

In order to disclose the bonding character of the title complex, the molecular orbital was investigated systematically. The contribution of one atom to the molecular orbital is denoted as the sum of square of orbital coefficient and normalization. The compound is divided into five parts： (a) C atom, (b) H atom, (c) O atom, (d) N atom, (e) Sn atom.

Fig.4 Molecular orbitals composition of complex at the Lanl2dz level

Fig.4 and Fig.5 reveal the contribution of each atomic orbital to the molecular orbitals. Almost no change could be seen at deep empty molecular orbitals, but obvious change occurs around the frontier orbitals, which are therefore only focused on in this paper. In detail, the largest contribution of HOMO by C atom is 81.24%, and then follows the Sn atom is 10.83%, H atom is 6.21%, O atom is 1.35%, N atom is 0.36%. In the LUMO, C atom displays the largest contribution to the molecular orbitals of 79.68%, and then follows the O atom is 11.02%, N atom is 6.72%,Sn atom is 2.01%, H atom is 0.57%.

Fig.5 Schematic diagram of the frontier MO for the complex

From the orbital composition analysis of HOMO and LUMO, we can deduce that when electron transfer occurs from ground state to excited state,electrons mainly transfer from C atoms of cyclohexyl to orbital of pyridine ring and carboxyl to generate a charge-transfer excited complex.

2.4 Thermal analysis

Thermal stability studies were conducted for the complex. The thermal decomposition process can be divided into three stages. The initial stage starts from 42 to 273 ℃, hardly any weight loss can be observed.The next stage occurs in the range of 273 to 496 ℃,in which the complex displays an obvious weight loss with a total weight loss of 68.6%, corresponding to the loss of the three cyclohexyl groups and a nicotinic acid anion. When the temperature is above 496 ℃, no weight loss occurs. With the observed residual weight of 30.8%, the residue can be assumed as SnO2, in agreement with the calculated value of 30.7%.

Fig.6 TG curve of the title complex

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