双自由基间苯体系铁磁分子设计

采用量子化学从头算UHF方法对不同组成的双自由基及其异构体进行了系统比较,进而对系列双自由基体系的基态自旋耦合规律进行了研究,并讨论了具有空间位阻的顺反异构现象对双自由基自旋耦合的影响。对以双自由基为基础的有机铁磁体的合成具有指导意义。     

邻、间、对-二甲氧基亚甲基苯及衍生物双自由基体系的自旋耦 合规律

采用量子化学abinitio法对具有甲氧基的碳、氧双自由基邻、间、对二甲氧基亚甲基苯及衍生物体系基态自旋耦合规律进行研究,得到非平面共轭体系中自由基之间磁性耦合的拓朴规则:共轭体系中,两个自由基之间以偶数个碳原子耦合,则有效交换积分J~i~j<0,体系具有低自旋基态;两个自由基之间以奇数个碳原子耦合,则J~i~j>0,体系具有高自旋基态。自由基性质对自旋耦合的影响较大,正离子自由基间磁性耦合能力较强,这些结论为有机磁性材料的分子设计与实验合成提供了理论依据。     

咪唑氧自由基分子NLO性质的密度泛函理论研究

采用密度泛函理论(DFT) UB3LYP方法, 在6-31g(d)水平上对2,2’-(1,2-乙炔基-4,1-亚苯基)双[4,4’,5,5’-四氢]咪唑氧自由基分子及其异构体的自旋耦合性质进行分析, 并结合有限场(FF)方法计算它们的非线性光学(NLO)系数, 以探讨咪唑氧环在共轭链不同位置时体系的自旋耦合规律和NLO系数. 结果表明, 所有体系基态自旋符合自旋极化规则, 它们的极化率随自旋多重度的增加而减小; 一阶超极化率因受分子对称性影响, 对称性不同其一阶超极化率的变化也不同; 二阶超极化率呈现随着自旋多重度的增加而增加的趋势. 从理论上探讨这些自由基分子自旋耦合规律与NLO活性的关系, 为有机自由基NLO材料的分子设计与实验研究提供一定的理论依据.     

以喹啉为耦合单元双自由基体系的理论研究

设计用4种自由基自旋中心连接在耦合单元喹啉的不同位置上的双自由基体系,用AM1-CI方法计算的结果表明:双自由基连接的位置不同对体系耦合作用的影响符合双自由基之间磁性耦合的拓扑规则,即共轭体系中,两个自由基之间以偶数个C(或N)原子耦合,体系具有低自旋基态,表现反铁磁耦合;两个自由基之间以奇数个C(或N)原子耦合,体系具有高自旋基态,表现铁磁耦合.当双自由基连接在喹啉的相邻奇数个C或N原子位置时,体系具有高自旋基态,表现铁磁耦合.     

构象对同位乙烯双自由基体系基态自旋多重度及其稳定性影响的理论研究

用DFT,CASSCF和QCISD(T)方法6-31G^*基组计算了构象对同位二取代乙烯双自由基体系基态自旋多重度及其稳定性的影响.结果表明,用DFT或CASSCF方法计算的单、三重态的能量差随自由基与乙烯间的二面角增加成不规则变化;用QCISD(T)方法计算的单、三重态的能量差随二面角的增加而逐渐降低,并呈规律性变化,说明QCISD(T)方法用于计算分子的磁性是可信的.对于同位二取代乙烯双自由基体系,无论双自由基旋转,还是单自由基旋转,高自旋基态稳定性随自由基与乙烯间二面角的增加而降低,只是降低的幅度不同,当二面角接近90°时,同位乙烯由具有平面或近似平面构象时强的铁磁耦合单元变成接近垂直平面构象时弱的反铁磁耦合单元或弱的铁磁耦合单元.     

含杂环并具有高自旋基态的双自由基体系的理论设计

以—·N—O—为自旋中心(SC),间苯为铁磁耦合单元(FC),苯、吡啶、哒嗪、嘧啶、吡嗪、三嗪为端基(EG),设计一系列新型稳定高自旋分子.另外以—·N—O—为SC,苯、吡啶、哒嗪、嘧啶、吡嗪、三嗪为FC,苯为EG,又设计另一系列新型稳定高自旋分子,并通过AM1—CI方法计算,研究了不同杂环作为端基或耦合单元对高自旋分子自旋多重度稳定性的影响.     

构型与构象对苯双自由基体系基态自旋多重度及其稳定性的影响

利用AM1-CI方法计算了构象对邻、间、对二取代苯双自由基体系基态自旋多重度及其稳定性的影响. 结果表明单 - 三重态能量差(△ES－T)和部分占据分子轨道的能量劈裂(△EPOMO)随自由基与苯环间的二面角而变化. 当二面角接近90°时, 分子具有平面或近平面构象时强的铁磁或反铁磁耦合单元, 由于具有近简并的高自旋和低自旋基态, 而变成弱的反铁磁或铁磁耦合单元. 由此提出为获得具有稳定高自旋基态的高自旋分子, 实验上应尽量避免选用强烈扭曲的邻、对苯分子构象.     

TTF+1-π共轭桥-6-氧四联氮阳离子双自由基NLO性质的理论研究

采用量子化学UPBE1PBE结合有限场(FF)方法,对系列TTF+?-π共轭桥-6-氧四联氮阳离子双自由基体系的稳定性,极化率αs和第一超极化率βtot进行研究.结果表明,TTF+?-6-氧四联氮阳离子双自由基引入共轭桥后,随体系共轭性增强,αs和βtot值均增大(体系2S的βtot值除外).自旋多重度和构象对双自由基体系的极化率和第一超极化率都有影响,双自由基体系由单重态转变为三重态时,极化率减小,而第一超极化率明显增大.以体系2为例,在单重态时αs和βtot值随构象变化较小,而三重态时αs和βtot值随二面角θ1和θ2的增加而减小.     

DFT calculations of 31P spin-spin coupling constants and chemical shift in dioxaphosphorinanes

One-bond heteronuclear spin-spin coupling constants (1)J(PX) (X=H, O, S, Se, C and N) between the phosphorus atom and axial and equatorial substituents in dioxaphosphorinanes are computed using density functional theory (DFT). The experimental values of these coupling constants for a variety of substituents can be applied to identify different diastereoisomers. The DFT calculations confirm the systematic trend observed in experiment, and indicate that the computed (1)J(PX) coupling constants are related to the length of the axial and equatorial bonds. A similar relation between the phosphorus chemical shift and the R(PX) bond length appears to be valid, with the exception of selenium substituents.     

NMR spin–spin coupling constants in hydrogen‐bonded glycine clusters

The influence of the hydrogen bond formation on the NMR spin–spin coupling constants (SSCC), including the Fermi contact (FC), the diamagnetic spin‐orbit, the paramagnetic spin‐orbit, and the spin dipole term, has been investigated systematically for the homogeneous glycine cluster, in gas phase, containing up to three monomers. The one‐bond and two‐bond SSCCs for several intramolecular (through covalent bond) and intermolecular (across the hydrogen‐bond) atomic pairs are calculated employing the density functional theory with B3LYP and KT3 functionals and different types of extended basis sets. The ab initio SOPPA(CCSD) is used as benchmark for the SSCCs of the glycine monomer. The hydrogen bonding is found to cause significant variations in the one‐bond SSCCs, mostly due to contribution from electronic interactions. However, the nature of variation depends on the type of oxygen atom (proton‐acceptor or proton‐donor) present in the interaction. Two‐bond intermolecular coupling constants vary more than the corresponding one‐bond constants when the size of the cluster increases. Among the four Ramsey terms that constitute the total SSCC, the FC term is the most dominant contributor followed by the paramagnetic spin‐orbit term in all one‐bond interaction.     

Spin–orbit corrections to the indirect nuclear spin–spin coupling constants in XH4 (X=C, Si, Ge, and Sn)

Summary.  Using the quadratic response function at the ab initio SCF level of approximation we have calculated the relativistic corrections from the spin–orbit Hamiltonian, H ^SO, to the indirect nuclear spin–spin coupling constants of XH₄ (X=C, Si, Ge, and Sn). We find that the spin–orbit contributions to J _X–H are small, amounting only to about 1% for J _Sn–H. For the geminal H–H coupling constants the relativistic corrections are numerically smaller than for J _X–H, but in some cases relatively larger compared to the actual magnitude of J _H–H. We also investigate the use of an effective one-electron spin–orbit Hamiltonian rather than the full H ^SO in the calculation of these corrections. Received July 12, 1996 / Final revision received September 12, 1996 / Accepted September 17, 1996     

Determination of heisenberg exchange coupling constants in clusters with magnetic sites: A local spin approach

This work studies the ability of the two‐center local spin quantities, provided by the partitioning of the expectation value of the spin‐squared operator corresponding to N‐electron systems, for determining spin‐exchange coupling constants within the Heisenberg spin Hamiltonian model. The spin‐exchange parameters, which characterize this Hamiltonian for a determined system, have been evaluated in the HeH₂ aggregate and in several clusters (n = 2, 3, 4) with different geometrical arrangements, using internuclear distances larger than the equilibrium ones (beyond the bonding regions). The results found have been analyzed and compared with those arising from other approaches, showing the feasibility of our methodology. © 2014 Wiley Periodicals, Inc.     

Density functional theory studies on structures and absorption spectra of [Au(tpy)Cl]2+ and its derivatives: Role of basis set,functional, solvent effect,and spin orbit effect

The geometries of [Au(tpy)Cl]²⁺ (tpy = 2,2′:6′,2″‐terpyridine) and its derivatives ( 1 – 4 ) were optimized using relativistic density functional theory (DFT) at both scalar and two‐component spin orbit coupling (SOC) level of theory via zero order regular approximation (ZORA). The combination of OPTX exchange, PW91c correlation functional (denoted as OP91), all‐electron ZORA TZ2P basis set was found to be the optimal combination for geometry. The results reveal that both SOC and substituents have little effect on the geometry of complexes 1 – 4 . Then, their absorption spectra were investigated by scalar relativistic time dependent DFT (TDDFT)/SAOP/TZ2P in vacuum, in CH₂Cl₂, CH₃CN solvents by means of conductor like screening model. The calculations indicate that the nature of the low‐lying spin‐allowed excited states is gold‐perturbed intraligand transition, namely charge reorganization. This fact also demonstrates that the influence of the polarity of solvent on absorption spectra of 1 – 4 is negligible. The spin orbit TDDFT was also performed to get further insight into the effect of SOC on the absorption spectra. It is found that the SOC has little influence on the simulation of electronic spectrum of complexes 1 – 4 due to no significant involvement of d‐orbitals during electronic transition. Our conclusions are reliable and are in good agreement with the previous experimental results and theoretical investigations. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Indirect relativistic bridge and substituent effects from the ‘heavy’ environment on the one‐bond and two‐bond 13C1H spin–spin coupling constants

Indirect relativistic bridge effect (IRBE) and indirect relativistic substituent effect (IRSE) induced by the ‘heavy’ environment of the IV‐th, V‐th and VI‐th main group elements on the one‐bond and geminal ¹³C? ¹H spin–spin coupling constants are observed, and spin‐orbit parts of these two effects were interpreted in terms of the third‐order Rayleigh–Schrödinger perturbation theory. Both effects, IRBE and IRSE, rapidly increase with the total atomic charge of the substituents at the coupled carbon. The accumulation of IRSE for geminal coupling constants is not linear with respect to the number of substituents in contrast to the one‐bond couplings where IRSE is an essentially additive quantity. Copyright © 2015 John Wiley & Sons, Ltd.     

Benzylic coupling constants in toluene derivatives by J doubling in the frequency domain and DFT calculations

The recently modified J doubling in the frequency domain method (MJDFDM) allowed the determination of ^{4, 5, 6}J in toluene, a series of 4‐mono‐ and 3,5‐disubstituted toluene derivatives, as well as in 4‐picoline. The methyl and aromatic signals were subjected to successive deconvolution processes, which at the end led to singlet signals and afforded the corresponding coupling constant values with a high degree of accuracy. Density functional theory calculation of benzylic coupling constants by addition of the Fermi contact, the spin‐dipole, the diamagnetic spin‐orbit, and the paramagnetic spin‐orbit terms revealed good agreement between predicted and measured values when the B3LYP/aug‐cc‐pVTZ level of theory was used. Evaluation of the substituent effect over the coupling constant was made for all studied compounds and some limitations of the methodology were evidenced. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of spin-orbit coupling contributions in the framework of density functional theory

We present a noniterative method to calculate spin-orbit coupling by means of a theoretical approach that provides the use of the full Breit-Pauli operator. This method was applied to compute one and two-electron spin-orbit coupling contributions between singlet and triplet, and doublet and doublet states, respectively. These states have been represented by monodeterminantal wave functions and optimized using the PW91 gradient-corrected exchange-correlation functional and the hybrid B3LYP one. They have been supplied by the conventional density functional theory packages, and thus coupled by our spin-orbit coupling code. Different size basis sets have been employed and the obtained results have been compared with the corresponding ones provided by some of the already existing methods and with the experimental data. They have been found to be in good quantitative agreement.