基于吡啶-4-甲酸构筑的二维Cu(Ⅱ)配位聚合物及其密度泛函研究

采用上下层扩散法合成了一种新型配合物[Cu(IN)2(CH3OH)2](1)(HIN=吡啶-4-甲酸),通过X射线单晶衍射测定了晶体结构,并用元素分析、红外光谱、热分析、磁学性质等技术对其进行了表征.配合物1属单斜晶系,空间群C2;晶胞参数为:a=0.947(3)nm,b=1.333(3)nm,c=0.746(18)nm,β=128.25(5)°,Z=2,V=0.740(3)nm3,Mr=371.83,Dc=1.669Mg?m-3,μ=1.510mm-1,F(000)=382,最终偏离因子R1=0.0751,wR2=0.1468.配合物1的中心原子Cu(II)与4个吡啶-4-甲酸根及2个甲醇分子配位,形成具有畸变八面体的几何构型;吡啶-4-甲酸配体采用桥联模式连接Cu(II)原子形成二维(4,4)层状结构;进而籍层间C—H…O氢键作用拓展为具有二重穿插的α-Po拓扑网络的三维超分子结构.此外,利用B3LYP方法,在6-31G(d)基组水平上对化合物1进行几何构型优化,在此基础上,采用对称性破损(BS)方法研究了配合物的磁性,计算结果表明配合物1具有弱的反铁磁相互作用.     

4-羟甲基吡啶的热力学性质

用精密自动绝热量热计测定了4-羟甲基吡啶在79～380 K温区的摩尔热容. 实验结果表明, 该化合物在79～301 K温区无相变和热异常现象发生, 在301～331 K, 发生固-液相变, 其熔化温度、摩尔熔化焓及摩尔熔化熵分别确定为：325.12 K, 11.78 kJ•mol^-1 和36.23 J•K^-1•mol^-1. 根据热力学函数关系式, 从热容值计算了4-羟甲基吡啶在80～380 K温区以标准状态（298.15 K）为基准的热力学函数值. 用热重法(TG)对该化合物的热稳定性作进一步考察, 从TG曲线上观察到该化合物在490 K有最大的蒸发失重速率.     

6-甲基-4-羟基嘧啶单体及二聚体质子转移过程的理论研究

应用密度泛函理论的B3LYP/6-311+G(d)方法研究了6-甲基-4-羟基嘧啶单体及二聚体质子转移的异构化反应.对反应势能面的研究发现,该化含物可能存在9种单体异构体,对其最稳定的单体构型进行分析.各单体间异构化反应的过渡态共有9种,反应的活化能最小为22.06 kJ/mol,最大为356.55 kJ/mol,最可能的反应路径在室温下即可进行. 研究了2种二聚体及其异构化反应的过渡态,发现二聚体均比其对应的单体稳定,而且质子转移所需要的活化能仅为20.13 kJ/mol,比单体低很多. 氢键在这种变化中起了主要作用,由单体和二聚体的总能量计算了氢键的键能.     

低阶煤中氢键作用的色散校正密度泛函理论研究

本研究以苯酚…苯酚、苯酚…苯、苯酚…二苯醚、苯酚…喹啉和苯甲酸…苯甲酸为对象，采用色散校正的密度泛函理论分别研究褐煤中自缔合OH、OH-π、OH-醚O、OH-N和COOH-COOH之间形成的氢键。此外，还研究了氢键供体中取代基(CH₃-、CH₃O-、OH-、NH₂-、COOH-和NO₂-)对氢键的影响。对上述复合物进行了几何优化，并计算了能量、Mulliken电荷分布及振动频率。从优化的结构中可以看出上述复合物之间都存在氢键，所有复合物中O-H键键长都比苯酚中自由羟基的长，这表明这些复合物之间存在相互作用。其中，羧酸…羧酸复合物中O-H键的键长最长。此外，通过Mulliken电荷分布可看出上述复合物之间存在电荷转移。基于振动频率分析，所有的O-H键伸缩振动都发生了红移，尤其是羧酸…羧酸和苯酚…喹啉复合物，这可为煤中羟基振动的红外光谱分析提供依据。根据键能不同氢键强度按以下顺序依次递减：COOH-COOH>OH-N > 自缔合OH≈OH-醚O > OH-π，这与振动频率的分析结果一致。此外，不同取代基对氢键作用的影响不同。     

1,2,4-三氮杂苯-(H2O)n复合物氢键相互作用的密度泛函理论研究

用密度泛函理论方法在B3LYP/6-31++G**水平上对1,2,4-三氮杂苯-(H₂O)_n (n＝1, 2, 3)氢键复合物的基态进行了结构优化和能量计算, 结果表明复合物之间存在较强的氢键作用, 所有稳定复合物结构中形成一个N…H—O氢键并终止于弱O…H—C氢键的氢键水链的构型最稳定. 同时, 用含时密度泛函理论方法(TD-DFT)在TD-B3LYP/6-31++G**水平上计算了1,2,4-三氮杂苯单体及其氢键复合物的单重态第一¹(n, π^*)垂直激发能.     

7-羟基喹啉-(H2O)n(n=1,2)复合物氢键相互作用的密度泛函理论研究

许多生理过程都通过分子间相互作用来实现。氢键则是最基本的化学作用力之一。具有碱性和酸性双官能团的芳香族化合物能与水作用形成氢键网络,对于实现生物体系的物质转移（质子转移、离子转移）起着十分重要的作用。在非水溶剂中,通过氢键发生质子转移反应动力学实验特征也己进行了广泛的研究。本文用密度泛函B3LYP方法在6-311G^＊基组水平上对7-羟基喹啉-水复合物相互作用进行了研究,从成键特征及氢键复合物的稳定关系方面进行了理论计算。     

3-氨甲基-4-三氟甲基吡啶的合成研究

以4,4,4-三氟乙酰乙酸乙酯与氰基乙酰胺为起始原料, 经环合、氯化、催化氢解和还原四步反应高纯度、高收率地得到了3-氨甲基-4-三氟甲基吡啶. 改进后的合成方法具有低成本、分离纯化容易、设备要求低等优点, 适合工业化生产.     

1,2,4-三氮杂苯-(H2O)n复合物氢键相互作用的密度泛函理论研究

用密度泛函理论方法在B3LYP／6—31 G**水平上对1，2，4-三氮杂苯-(H2O)n(n=1，2，3)氢键复合物的基态进行了结构优化和能量计算，结果表明复合物之间存在较强的氢键作用，所有稳定复合物结构中形成一个N…H--O氢键并终止于弱O…H—C氢键的氢键水链的构型最稳定．同时，用含时密度泛函理论方法(TD—DPT)在TD—B3LYP／6—31 G**水平上计算了1,2，4-三氮杂苯单体及其氢键复合物的单重态第-1(n，π*)垂直激发能．     

2-羟基吡啶与水氢键作用的理论研究

本文采用量子化学的Hatree-Fock方法和密度泛函理论(DFT)的B3LYP方法,在6-31G(d)水平上,研究了2-羟基吡啶分子(Hy)及其酮式互变异构体2(1H)-吡啶酮(Py)与水的相互作用。考察它们之间在形成Hy…H2O,Py…H2O,Hy…Hy,Py…Py和Hy…Py等复合物前后的能量变化和分子结构参数变化特点。计算结果表明,在这些复合物中都形成了较强的氢键作用,在水合物中,Py与水形成复合物时能量降低较多,与实验结果一致。经过零点振动能(ZPVE)和基组叠加误差(BSSE)校正后的复合物离解能分别为38.3,40.8,73.0,82.7和71.1 kJ/mol(B3LYP/6-31G(d)),水合物的离解能远小于二聚体复合物,而酮式结构的二聚体的离解能最大。     

Density Functional Theory Study of Hydrogen Bonding Dimers with 4-Pyridinecarboxylic Acid Hydrazine

The H‐bonding dimers of 4‐pyridinecarboxylic acid hydrazine were studied using density functional theory (DFT) at B3LYP/6‐311++G** level. The results showed that the most stable dimer D1 had two same linear N H···O hydrogen bonds, and the interaction energy between them was 51.038 kJ·mol⁻¹ which was corrected by the basis set superposition error and zero‐point. The stretching vibration frequency of N H bond had a red shift because of the hydrogen bonds. The natural bond orbital analysis showed that each N H···O hydrogen bond in D1 had the biggest interaction stabilization energy of 69.078 kJ·mol⁻¹. Thermodynamic analysis indicated that the formation process of D1 was exothermic and spontaneous at low and room temperatures.     

Density Functional Theory Study of Hydrogen Bonds of Bipyridine with 1,3,5-Benzenetricarboxylic Acid

The hydrogen‐bonded dimer and trimer formed between 1,3,5‐benzenetricarboxylic acid and bipyridine have been investigated using a density functional theory (DFT) method and 6‐31++G** basis set. The interaction energies are ?45.783 and ?89.998 kJ·mol^?1 for the most stable dimer and trimer, respectively, after the basis set superposition error and zero‐point corrections. The formation of O–H...N hydrogen bonds makes O–H symmetric stretching modes in the dimer and trimer red‐shifted relative to those of the 1,3,5‐benzenetricarboxylic acid monomer. The natural bond orbit analysis shows that the inter‐molecular charge transfers are 0.60475e and 1.20225e for the dimer and trimer, respectively. Thermodynamic analysis indicates that the formation of trimer is an exothermic and spontaneous process at low and room temperature. A supramolecule can be constructed through the strong N···H–O intermolecular hydrogen bonds between bipyridine and 1,3,5‐benzenetricarboxylic acid, which is in good agreement with the experimental results.     

Density Functional Theory Study on Hydrogen Bonding Interaction of Catechin-(H2O)n

Density functional theory B3LYP method with 6‐31G* basis set has been used to optimize the geometries of the catechin, water and catechin‐(H₂O)_n complexes. The vibrational frequencies have been studied at the same level to analyze these complexes. Six and eleven stable structures for the catechin‐H₂O and catechin‐(H₂O)₂ have been found, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) have been utilized to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are from ?13.27 to ?83.56 kJ/mol. All calculations also indicate that there are strong hydrogen‐bonding interactions in catechin‐water complexes. The strong hydrogen‐bonding contributes to the interaction energies dominantly. The O–H stretching motions in all the complexes are red‐shifted relative to that of the monomer.     

Performance of Density Functional Theory for Transition Metal Oxygen Bonds

The accuracy of density functional theory (DFT) limits predictions in theoretical catalysis, and strong chemical bonds between transition metals and oxygen pose a particular challenge. We benchmarked 30 diverse density functionals against the bond dissociation enthalpies (BDE) of the 30 MO and 30 MO⁺ diatomic systems of all the 3d, 4d, and 5d metals, to test universality across the d-block as required in comparative studies. Seven functionals, B98, B97-1, B3P86, B2PLYP, TPSSh, B3LYP, and B97-2, display mean absolute errors (MAE) <30 kJ/mol. In contrast, many commonly used functionals such as PBE and RPBE overestimate M−O bonding by +30 kJ/mol and display MAEs from 48–76 kJ/mol. RPBE and OPBE reduce the over-binding of PBE but remain very inaccurate. We identify a linear relationship (p-value 7.6 ⋅ 10⁻⁵) between the precision and accuracy of DFT, i. e. inaccurate functionals tend to produce larger, unpredictable random errors. Some functionals commonly deviate from this relationship: Thus, M06-2X is very precise but not very accurate, whereas B3LYP* and MN15-L are more accurate but less precise than M06-2X. The best-performing hybrids have 10–30 % HF exchange, but this can be relieved by double hybrids (B2PLYP). Most functionals describe trends well, but errors comparing 5d to 4d/3d are ∼10 kJ/mol larger than group-wise errors, due to uncertainties in the spin-orbit coupling corrections for effective core potentials, affecting e. g. Pt/Pd or Au/Ag comparisons.     

Hydrogen bonding in 4‐nitrobenzene‐1,2‐diamine and two hydrohalide salts

The structures of 4‐nitrobenzene‐1,2‐diamine [C₆H₇N₃O₂, (I)], 2‐amino‐5‐nitroanilinium chloride [C₆H₈N₃O₂⁺·Cl⁻, (II)] and 2‐amino‐5‐nitroanilinium bromide monohydrate [C₆H₈N₃O₂⁺·Br⁻·H₂O, (III)] are reported and their hydrogen‐bonded structures described. The amine group para to the nitro group in (I) adopts an approximately planar geometry, whereas the meta amine group is decidedly pyramidal. In the hydrogen halide salts (II) and (III), the amine group meta to the nitro group is protonated. Compound (I) displays a pleated‐sheet hydrogen‐bonded two‐dimensional structure with R₂²(14) and R₄⁴(20) rings. The sheets are joined by additional hydrogen bonds, resulting in a three‐dimensional extended structure. Hydrohalide salt (II) has two formula units in the asymmetric unit that are related by a pseudo‐inversion center. The dominant hydrogen‐bonding interactions involve the chloride ion and result in R₄²(8) rings linked to form a ladder‐chain structure. The chains are joined by N—H...Cl and N—H...O hydrogen bonds to form sheets parallel to (010). In hydrated hydrohalide salt (III), bromide ions are hydrogen bonded to amine and ammonium groups to form R₄²(8) rings. The water behaves as a double donor/single acceptor and, along with the bromide anions, forms hydrogen bonds involving the nitro, amine, and ammonium groups. The result is sheets parallel to (001) composed of alternating R₅⁵(15) and R₆⁴(24) rings. Ammonium N—H...Br interactions join the sheets to form a three‐dimensional extended structure. Energy‐minimized structures obtained using DFT and MP2 calculations are consistent with the solid‐state structures. Consistent with (II) and (III), calculations show that protonation of the amine group meta to the nitro group results in a structure that is about 1.5 kJ mol⁻¹ more stable than that obtained by protonation of the para‐amine group. DFT calculations on single molecules and hydrogen‐bonded pairs of molecules based on structural results obtained for (I) and for 3‐nitrobenzene‐1,2‐diamine, (IV) [Betz & Gerber (2011). Acta Cryst. E 67 , o1359] were used to estimate the strength of the N—H...O(nitro) interactions for three observed motifs. The hydrogen‐bonding interaction between the pairs of molecules examined was found to correspond to 20–30 kJ mol⁻¹.     

Density Functional Theory Studies on Intermolecular Interactions of 4‐Amino‐3,5‐dinitropyrazole with NH3 and H2O

Density functional theory (DFT) method with 6‐311++G** basis set was applied to study intermolecular interactions of 4‐amino‐3,5‐dinitropyrazole (LLM‐116)/NH₃ and LLM‐116/H₂O supermolecules. Four optimized stable supermolecules were found on the potential energy surface. The intermolecular interaction energy was calculated with basis set superposition error (BSSE) correction and zero point energy (ZPE) correction. The greatest corrected intermolecular interaction energies of LLM‐116/NH₃ and LLM‐116/H₂O supermolecules are –42.75 and –19.09 kJ×mol^‐1 respectively, indicating that the intensity of interaction between LLM‐116 and NH₃ is stronger than that of LLM‐116/H₂O. The intermolecular interaction is an exothermic process accompanied by a decrease in the probability of supermolecules formation, and the interactions become weak as temperature increase. Natural bond orbital (NBO) analysis was performed to reveal the origin of interaction. The IR spectra were obtained and assigned by vibrational analysis. Based on vibrational analysis, the changes of thermodynamic properties from LLM‐116 to supermolecules with temperature ranging from 200.0 to 400.0 K were obtained using statistical thermodynamic method.     

Density Functional Theory Study of the Interaction between Thymine and Luteolin

The density function B3LYP method has been used to optimize the geometries of the luteolin, thymine and luteolin‐thymine complexes at 6‐31+G?? basis. The vibrational frequencies have been studied at the same level to analyze these seventeen complexes, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) have been utilized to investigate the hydrogen bonds involved in all the systems. The interaction energies of the complexes corrected by basis set superposition error are between ?93.00–?76.69 kJ/mol. The calculating results indicate that strong hydrogen bonding interactions have been found in the luteolin‐thymine complexes.     

Anti‐Electrostatic Hydrogen Bonds

Ab initio and hybrid density functional techniques were employed to characterize a surprising new class of H‐bonded complexes between ions of like charge. Representative H‐bonded complexes of both anion–anion and cation–cation type exhibit appreciable kinetic stability and the characteristic theoretical, structural, and spectroscopic signatures of hydrogen bonding, despite the powerful opposition of Coulomb electrostatic forces. All such “anti‐electrostatic” H‐bond (AEHB) species confirm the dominance of resonance‐type covalency (“charge transfer”) interactions over the inessential (secondary or opposing) “ionic” or “dipole–dipole” forces that are often presumed to be essential for numerical modeling or conceptual explanation of the H‐bonding phenomenon.