Electronic spectra and structure of methyl derivatives of 4-nitropyridine N-oxide

The UV spectra of seven methyl derivatives of 4-nitropyridine N-oxide in ethanol have been examined. The electronic spectra were calculated by a modified INDO method. Transition energies, intensities and assignments were compared with UV spectra. Spectroscopic manifestations of intramolecular interaction indicate that methyl groups modify the electronic interaction between the N-oxide and NO₂ groups mainly through a steric strain.Department of Organic Chemistry, University of Economics, Pl-53342 Wroclaw, Poland. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 786–793, June, 2000.     

Electron correlation in weakly coupled transition metal dimers: Bimetallocenylenes and bimetallocenes

The Hartree-Fock (HF) instabilities in a series of bimetallocenes (1) and bimetallocenylenes (2) with Fe, Co, Ni and Cr as 3d centers have been investigated by means of a semiempirical INDO Hamiltonian. The HF picture is only valid in the case of the iron dimers. Strong correlation effects are encountered in the Co, Ni and Cr complexes. The necessary conditions for singlet, non-singlet (triplet) and non-real variations of the HF orbitals are discussed in detail. Singlet fluctuations are the result of intraatomic angular correlation (short-range) at each 3d center. The violation of the spin symmetry corresponds to a long-range interaction between the transition metal centers. Only for MOs with large 3d _xz amplitudes there exists a channel for the interatomic spin decoupling. Consequences for polymetallocenes are shortly discussed.     

Analysis of the effect of the electronic structure of the Cl atom in complexes of chlorides of group IV elements on Cl NQR frequency and asymmetry parameter

Analysis of changes in ³⁵Cl NQR frequency of complexes MCl₄.L and MCl₄.2L for M = Si, Ge, Sn and Ti was performed. The population of the atomic orbitals was calculated by the quantum chemistry methods PM3 and INDO. The results provided an explanation of the changes in ³⁵Cl NQR frequency and the asymmetry parameter upon complex formation. In the complexes of non-transition elements, a decrease in ³⁵C1 NQR frequency is first of all related to increasing population of p_z orbitals on Cl atoms. In the complexes of Ti, the increase in ³⁵Cl NQR frequency depends on a decrease in the p_π to d_π electron density transfer.     

二—(2,2''—联吡啶)—三—(硝酸)合镧(Ⅲ)La(C10H8N2)2(NO3)3的电子结构和化学键

希土化合物由于涉及f轨道,用分子轨道方法有一定困难,前人曾采用过多种处理方法。     

［Ln（HCOO）_3·phen·C_2H_5OH］［Ln＝Pr、Gd］的电子

［Ｌｎ（ＨＣＯＯ）＿３·ｐｈｅｎ·Ｃ＿２Ｈ＿５ＯＨ］［Ｌｎ＝Ｐｒ、Ｇｄ］的电子结构和化学键董南，朱龙观，蔡国强，吴念慈（杭州大学化学系杭州３１００２８）关键词：化学键，电子结构，ＩＮＤＯ，配合物［Ｌｎ（ＣＣｌ＿３ＣＯＯ）＿３·ｐｈｅｎ·Ｃ＿２Ｈ＿５Ｏ...     

Synthesis and characterization of β-fused porphyrin-BODIPY dyads

Novel dyads in which a porphyrin ring is directly fused through two β-pyrrolic carbons to a BODIPY^® moiety have been prepared using a stepwise approach starting from the copper(II) complex of pyrrolo[2,3-c]-5,10,15,20-tetraphenylporphyrin. Formylation and reaction with 3,5-dimethylpyrrole afforded 8; subsequent BF₂ complexation gave the TPP-BODIPY^® dyad in reasonable yields. Demetalation in TFA/H₂SO₄ led to the corresponding free base 12, opening the way to the subsequent preparation of the Zn complex 13. Both 12 and 13 exhibited complex optical spectra with an intensely red-shifted Q-band. Luminescence spectra displayed a very intense band around 700 nm making these species suitable as near-IR dyes and sensors in biological media. Optical analyses of 12, using the INDO/SCI technique, were performed to obtain information to establish the origin of the novel optical properties. These studies showed that the optical properties of 12 cannot be attributed to deformation of the molecular skeleton, but derive from the increased extension of the conjugation between the TPP and BODIPY^® π-systems.     

C76及Cn76离子的电子结构和单态的电子光谱

KxC76不同于K3C60的半导体行为[1]引起了我们对Cn-76的研究兴趣. 自Ettl[2]分离表征C76以来, 相应的实验及理论研究已经开始[3,4], 但对C-76以外其它离子的电子结构和光谱的理论研究尚未见报道. 本文用INDO系列方法对Cn76进行系统研究, 考察其是否发生Jahn-Teller畸变, 首次计算了Cn76单态离子的电子光谱, 对电子跃迁进行理论指认, 讨论了Cn76光谱的特征吸收与C76相比发生红移的原因.     

硝基取代亚酞菁衍生物的电子光谱和非线性光学性质的理论研究

在AM₁方法优化的几何结构基础上,用INDO/CI-SOS方法深入探讨亚酞菁(C₂₄H₁₂B₁Cl₁N₆)的硝基取代对体系的电子光谱和二阶非线性光学性质的影响.结果表明,吸电子取代基和取代基的共轭链的增长对亚酞菁的分子结构和电子光谱的最大吸收峰影响很小,但对非线性光学性质都有较大影响,随着共轭链的增长,二阶非线性光学系数大幅度增强.未被取代的亚酞菁的β₀计算值与实验值十分相符,分别为-0.73×10^-28和-0.70×10^-28esu,共轭链最长的硝基取代化合物β₀值增大到-1.47×10^-28esu,增加约近1倍.     

富勒醇C-60(H)8的结构和UV谱的理论研究

用INDO系列方法研究C60（OH）88种异构体的结构和光谱，探讨羟基不同加成位置对异构体稳定性的影响，表明8个羟基以1，2－加成方式加在C60的五元环与六元环相邻棱上所得的异构体最稳定， 生成热比次稳定异构体低25eV，故实验室合成的C60（OH）8主要以这种构型存在。以优化构型为基础，计算了8种异构体的UV谱，对电子跃迁进行理论指认，讨论产物UV谱带红移的原因，对反应机理进行探讨，并对C60R8（R＝F，OH，Cl）的某些性质进行了对比。     

Electron paramagnetic resonance of NH 3 + radical in potassium sulphate

Room temperature EPR spectra of (NH₄)₂SO₄ doped K₂SO₄ monocrystals irradiated with x-rays show the presence of NH₃ ⁺ radicals. The EPR parameters areg ‖=2.0037 andg ⊥ = 2.0068;¹⁴NA _XX=13.75;A _YY=24.5;A _ZZ=25.5 gauss;¹HA _XX=A _YY=22 andA _ZZ=25 gauss. From the¹⁴N and¹H coupling constants it has been inferred that at room temperature the planar NH₃ ⁺ radical undergoes rotation about theC ₃ axis which corroborates with the equivalence of the protons, but the radical itself is in an asymmetric crystal field environment. The 77K spectra indicate a considerable reduction in the motion of the radical with the free motion almost completely stopped. Part of Ph.D. work of the second author