【作者】 马登学；

【导师】 张弛；

【作者基本信息】 南京理工大学 ， 材料科学与工程， 2011， 博士

【摘要】 运用量子化学密度泛函理论(DFT)方法,对多系列叠氮硼、叠氮铝簇合物的结构和性能进行了较为系统的计算,并注意关联BN和AlN材料的潜在的单一源前驱体的寻求。主要包括两部分内容：第一部分叠氮硼簇合物结构和性能的理论研究。采用DFT-B3LYP方法,在不同基组下求得多聚叠氮甲硼烷簇合物(BH2N3)2-4的全优化几何构型,它们均为包含Bn(Nα)n骨架结构的环状构型。三聚体(BH2N3)3拥有船式和椅式两种构象,其结合能相近。四聚体的四种构象的能量稍有差别。随簇合物聚合度(n)增大,Nα-NB和B-H键长增加,Nβ-Nγ键长减小,预示较易失去N2(Nβ-Nγ)和H2,从而利于生成BN材料。对计算所得气相IR谱进行归属,并讨论了聚合度对IR谱的影响。研究表明热力学函数(C°p,m、S°m及H°m)随聚合度和温度的增加而增大；构象异构体的热力学函数值彼此很接近。等压下三聚化和四聚化反应在298.2 K可自发进行,而二聚化反应则不能。通过分析比较6-311+G*和6-311++G**以及aug-cc-pVTZ三个基组下的计算结果,表明选用较经济的6-311+G*基组研究(BH2N3)1-4体系的结构和性能是比较合适的。以B3LYP/6-311+G*方法,分别计算研究了多聚叠氮二卤化硼簇合物(BN3X2)n (n=1-4; X=F,Cl, Br)的几何构型、电子结构、IR谱和聚合反应的热力学函数的变化,重点考察了尺寸效应。结果表明,Nα-Nβ、B-X键长和B-Nα-B、Nα-B-Nα键角随簇合物尺寸的增大而增大,而Nβ-Nγ键长则减小。二聚体中B-Nα键长较在三聚体和四聚体中大,可能归因于四元环张力较大。讨论了聚合反应中的电荷递变规律。计算所得振动频率与已有实验值相吻合,表明经校正的计算IR谱较为可信。IR谱有三个特征区：分别对应于N3的反对称和对称伸缩振动以及复杂的指纹区。在室温下,聚合反应的吉布斯自由能变化(AG)均为正值,表明等压下聚合反应不能自发进行。以DFT-B3LYP/6-311+G*方法对最简单有机多聚叠氮硼簇合物(BMe2N3)n(n=1-3)进行计算。探讨了B-Nα、Nα-Nβ、Nβ-Nγ和B-C键长随聚合度的变化规律,环状构型中B-Nα-B键角较Nα-B-Nα键角大。对所得优化构型进行振动频率计算,并对其IR谱进行归属。计算所得振动频率与已有实验值很接近。比较能量和热力学数据,表明三聚二甲基叠氮化硼的船式构象较椅式构象稳定。在298.2 K下,三聚化为放热反应,而二聚化则为吸热反应。随温度升高,聚合反应越来越不利。第二部分叠氮铝簇合物结构和性能的理论研究。以DFT-B3LYP/6-311+G*方法,计算研究了最简单叠氮二氟化铝簇合物(AlN3F2)n(n=1-4)的结构和性质。所得多聚体均为环状构型,取Al-Nα-Al连接方式。随聚合度(n)增大,Nα-Nβ和Al-F键长略微变长,而β键长则变短,表明利于形成AlN材料。随聚合度增大,原子上电荷变化明显。构象异构体的结合能稍有差别,零点能校正对结合能影响不大。热力学数据表明,温度升至800 K,等压下聚合反应仍可自发进行。基于方程ΔG=-RTInKp,求得298.2 K下最稳定二聚体、三聚体和四聚体的平衡常数均非常大,推测叠氮二氟化铝体系是二聚、三聚和四聚体的平衡共存体。经简谐振动分析,求得(AlN3F2)n(n=1-4)的IR谱,并对其进行了归属。随聚合度增加,N3反对称伸缩振动发生蓝移,而对称伸缩振动发生红移。基于DFT-B3LYP/6-311+G*类似研究,求得(AlN3X2)n(n=1-4, X=Cl, Br)的全优化几何构型。讨论了几何参数Al-Nα、Nα-Nβ、Nβ-Nγ和A1-X与聚合度的关系。环状构型中,Al-Nα-Al的键角总较Nα-Al-Nα大。未见三聚体和四聚体(AlN3X2)3-4(X=Cl,Br)的实验和理论相关报道。计算所得IR谱均具三个特征区：其中两个较强特征峰分别对应于N3的对称和反对称伸缩振动；在较小频率区还存在一个较为复杂的指纹区。随聚合度增加,N3反对称和对称伸缩振动频率分别发生蓝移和红移。计算所得振动频率与已有实验值很接近。所得热力学函数(C°p,m、S°m及H°m)均随聚合度和温度的增加而近似地呈线性递增；随温度升高,C°p,m与S°m增幅减小,而H°m则相反。多聚化反应在298.2K等压下可自发进行。综上所述,本文对系列叠氮化硼、叠氮化铝簇合物进行了分子设计,对其结构-性能关系进行了系统的量子化学DFT计算研究,解释了大量已有实验事实,预示了许多未知结果,提供了丰富信息和规律、利于对当前热门的BN和AlN材料前驱体的实验合成提供参考和指导。更多还原

【Abstract】 The structures and properties of several series of azide-clusters of boron and aluminum are systematically studied using density functional theory (DFT). The process of searching for single source precursors to BN and AlN materials has been completed. The whole work can be divided into two parts:The first part is concentrated on the theoretical studies on the structures and properties of boron azide clusters.The fully optimized structures of the clusters (BH2N3)n(n=1 to 4) are obtained using DFT theory at B3LYP level with different basis sets. All the cyclic structures (BH2N3)2-4 contain Bn(Nα)n skeleton structures. The boat-like and chair-like trimers are found to exhibit two minima with very similar binding energies. The tetramers have four structures that correspond to minima with slightly different binding energies. The Nα-Nβand B-H bond lengths increase with the increasing oligomerization degree n, however, the Nβ-Nγbond lengths decrease. Which shows it could easily eliminate N2 (Nβ-Nγ) and H2 groups to yield BN materials. The calculated IR spectra in the gas phase are assigned, and related with the oligomerization degree are discussed. The thermodynamic properties (C0p,m S0m and H0m) all increase with increasing temperature and oligomerization degree n. As for isomers, their thermodynamic functions are all close. The isobaric oligomerizations can occur spontaneously for n=3 and 4 at 298.2 K, but is unfavorable for the case of n=2. The results with the 6-311+G*,6-311++G** and aug-cc-pVTZ basis sets show it is suitable to choose the economic 6-311+G* basis set to study the clusters (BH2N3)n(n=1 to 4).The geometric configurations, electronic structures, IR and thermodynamic properties of the clusters (BN3X2)n(n=1 to 4; X=F, Cl, Br) have been studied at the B3LYP/6-311+G* level of DFT. The Nα-Nβ, B-X bond lengths and the B-Nα-B, Nα-B-Nαbond angles all increase with the size of the cluster growing, however, Np-Ny bond lengths decrease. Owing to the strain of the four-membered ring, the B-Nαbonds in the dimer are longer than those in trimers and tetramers. The charge transfer is discussed during oligomerization. The calculated IR spectra are reliable compared with the experimental results. They have three main characteristic regions:the N3 asymmetric stretching, the N3 symmetric stretching and the complicated fingerprint region. The Gibbs free energies (ΔG) of the oligomerizations at 298.2 K are positive, which indicates the isobaric oligomerizations can not occur spontaneously.The simplest models for the organoboron azide clusters (BMe2N3)n(n=1 to 3) have been studied similarly at the DFT-B3LYP/6-311+G* level. The trends in the B-Na, Nα-Nβ, Nβ-Nγ and B-C bond lengths with oligomerization degree n are discussed. The B-Nα-B angles in the cyclic oligomers are consistently larger than the Nα-B-Nαones. Frequency calculations have been carried out for each optimized structure, and their IR spectra are assigned. The calculated frequencies agree reasonably with experiment ones. Both the energies and thermodynamic properties demonstrate that twist-boat conformation is preferred over chair conformation in the gas phase for the (BMe2N3)3. Thermodynamic analysis of the gas-phase reaction shows that the trimerization is exothermic at 298.2 K, however, the dimerization is endothermic. With the increasing temperature, the oligomerization becomes less favorable.The second part focuses on the theoretical studies of the structures and properties for the aluminum azide clusters.DFT/B3LYP method with 6-311+G* basis set was used to calculate the clusters AlN3F2 consisting of up to four molecules, and it predicts that (AlN3F2)n(n=2 to 4) are cyclic-like clusters with Al-Nα-Al linkages. The Nα-Nβand Al-F bond lengths all increase slightly with the size of the cluster growing, however, Nβ-Nγbond lengths decrease, showing it could easily yield AlN materials. With the oligomerization degree n increasing, the charge transfers for the clusters are large. As for isomers, their binding energies are all close, respectively. The ZPE correction has little effect on the binding energy. Thermodynamic properties demonstrate that the isobaric formations of dimer, trimers and tetramers are favorable thermodynamically even up to 800 K. The calculated equilibrium constants for the formation more stable dimer, trimer and tetramer, based on the equation AG=-RTInKp, are large. It reveals that the AIN3F2 systems occur dimer-trimer—tetramer equilibriums. By the vibrational analysis, the simulated infrared (IR) spectra for the AIN3F2 monomer and its clusters are obtained and assigned. The N3 asymmetric stretching moves to higher frequency (hypsochromic phenomenon) as the cluster becomes larger, however, the N3 symmetric stretching moves to lower frequency (bathochromic phenomenon).The fully optimized structures for the (AIN3X2)n(n=1 to 4, X=Cl, Br) are obtained similarly at the DFT-B3LYP/6-311+G* level, respectively. The trends in the Al-Nα, Na-Np, Nβ-Nγand Al-X bond lengths with oligomerization degree n are discussed. Al-Nα-Al angles in the cyclic oligomers are consistently larger than the Nα-Al-Nαones. The trimers and tetramers (AlN3X2)3-4 (X=Cl, Br) have not been found experimentally and theoretically. The calculated IR spectra have three main characteristic regions:two of them are very strong. One corresponds to the N3 asymmetric stretching, and the other is associated with the N3 symmetric stretching. And the remaining one is in the lower frequency range and corresponds to the complicated fingerprint region. With the oligomerization degree n increasing, the N3 asymmetric and symmetric stretchings move to higher frequency (hypsochromic phenomenon) and lower frequency (bathochromic phenomenon), respectively. To testify the reliability of the theoretical IR, the experimental and calculated vibrational frequencies are compared. It is evident that the calculated frequencies agree reasonably with experiment ones. Thermodynamic properties all increase linearly with increasing temperature and oligomerization degree n. The gradients of C0p,m and S0m to the temperature decrease, but that of H0m increases. All the isobaric oligomerizations can occur spontaneously at 298.2 K.In a word, the systemic studies on the structures, properties and the molecular designs have been investigated for several series of azide-clusters of boron and aluminum using DFT method, which explains a great deal of the experimental facts and predicts many unknown results. The abundance of information and the rules provided are used to instruct the experimental synthesis for the precursors to the currently hot BN and AlN materials.更多还原