多核配合物高自旋基态分子的设计--一个理论和实践的总结

多核配合物高自旋基态分子的设计和合成是分子磁学的一项重要研究内容.作者结合本课题组的工作,总结了合成高自旋基态分子的几种重要模型,包括磁轨道正交、自旋极化、非正规自旋态及自旋失措模型.简要介绍了它们的基本原理和应用这些模型取得成功的一些实例,为分子磁工程的实现提供了一些可行的策略和方法.     

三核自旋偶合体系的磁化率公式

对多核自旋偶合体系的研究是设计分子基铁磁体的基础犤１犦。在多核自旋偶合体系中，磁交换参数Jij值的评估对研究多核间的磁交换机理和研究多核自旋偶合体系的磁－构相关性是至关重要的。多核间的磁交换参数Jij值不能从实验直接得到，理论计算又有很大的困难和不准确性。目前，Jij值主要是通过多核自旋偶合体系的变温磁化率公式拟合实验数据来评估。因此，磁化率公式在磁化学研究中具有重要的理论和实际意义。通常，磁化率公式是通过求解多核自旋偶合体系的自旋交换Hamiltonian算符的本征方程，求出体系的能量本征值，然后用Boltzmann分…     

零维到三维结构中三核铜自旋阻挫簇单元的磁构关系和反对称交换

量子自旋液体是最近几年刚被人们证实除铁磁体、反铁磁体之外的第三种磁性类型,因其有望解释高温超导的运行机制、改变计算机硬盘信息存储方式而在物理、材料等领域备受关注。自旋阻挫作为量子自旋液体的最小单元可能是解开量子自旋液体诸多问题的钥匙,所以在磁学、电学研究领域再一次成为人们研究的热点。基于文献报道的三核铜配合物[Cu3(μ3-OH)(μ-OPz)3(NO3)2(H2O)2]·CH3OH(1),我们合成了三维金属有机框架配合物{[Ag(HOPz)Cu3(μ3-OH)(NO3)3(OPz)2Ag(NO3)]·6H2O}n(2)(HOPz=甲基(2-吡嗪基)酮肟),并从自旋阻挫的角度对二者磁性质进行对比和详细分析。磁化率数据表明自旋间有很强的反铁磁相互作用和反对称交换。通过包含各向同性和反对称交换的哈密顿算符对两者磁学数据进行拟合并研究其磁构关系,所获最佳拟合参数为:配合物1:Jav=-426 cm^-1,g⊥=1.83,g∥=2.00;配合物2:Jav=-401 cm^-1,g⊥=1.85,g∥=2.00。     

多金属偶合体系的量子化学计算及其应用

多核配合物内顺磁离子间磁相互作用的量子化学计算配合物化学和量子化学的一个具有挑战性的课题，本文综述了近年多金属偶合体系的量子化学计算及其应用。     

密度泛函理论在分子磁学中的应用2.混合桥联三核镍配合物自旋交换作用

用密度泛函理论结合对称性破损方法(DFF-BS)研究了混合桥联三核镍配合物的磁交换耦合作用．这类化合物是由三唑和异硫氰酸根桥联形成的混合桥配合物．计算表明，在标题化合物中，三唑桥传递反铁磁耦合作用，而异硫氰酸根桥传递铁磁耦合作用；并且，随着异硫氰酸根取代三唑桥的数目增加，配合物的铁磁作用增强，在一定意义上说明了混合桥磁耦合作用的加合性．Mulliken自旋布居分析表明，无论是三唑桥还是异硫氰酸根桥，它们的磁交换作用机理都是磁中心的自旋离域．分子磁轨道分析显示，对于三唑桥，在局域磁轨道之间存在着强的轨道作用，导致了反铁磁耦合；对于异硫氰酸根桥，局域磁轨道之间弱的相互作用，表现了铁磁耦合作用．对标题化合物的研究说明了DFF-BS方法可用于三核体系磁交换作用的研究．     

基于顺磁稀土离子的磁性分子材料

构建含镧系稀土金属离子的分子基磁性材料是当前分子磁学研究的重要领域之一．本文按照单稀土离子,稀土离子-稀土离子（4f-4f）相互作用体系,稀土离子．过渡金属离子（4f-3d）相互作用体系,稀土离子．自由基（4f-p）相互作用体系的顺序,介绍了含镧系稀土金属离子的单离子磁体,基于稀土金属离子,过渡金属离子和自由基多核簇的单分子磁体、单链磁体和磁有序体系的磁学性质．根据磁性分子材料中自旋载体和磁耦合性质的不同,分别用实例介绍了磁耦合、磁有序和磁驰豫性质的特点和来源．首先,本文综述了孤立的单稀土离子配合物体系的结构和磁学性质．由于稀土金属离子的4f电子具有强的旋轨耦合作用和较大的磁各向异性,所以有些单稀土离子配合物如双酞菁铽、镝等体系具有慢的磁驰豫行为,其低温下的磁滞回线呈现台阶状,被称为单离子磁体．该类分子基磁性配合物慢磁驰豫性质的来源可以用镧系稀土离子的电子自旋磁矩、轨道磁矩、核自旋磁矩之间的相互作用解释．具有场诱导缓慢磁驰豫行为的单稀土离子配合物是另一类引起关注的磁性分子材料．该类配合物在零场下交流磁化率的虚部没有峰值,而在一定的外磁场下,其交流磁化率的虚部出现峰值并具有频率依赖性．这种现象可能可以归因为体系的Kramer简并基态在外场下消除了快的磁驰豫过程,使慢的磁驰豫过程,如Orbach过程成为主导．其次,本文综述了稀土离子的4f电子之间的磁耦合作用和磁学性质．一方面,对于具有4f^7电子构型的含Gd（III）离子配合物,f电子之间的磁耦合作用主要是各向同性磁交换作用．由于4f电子能量很低,同其他稀土离子f电子之间的耦合作用被外层轨道屏蔽,所以磁耦合常数很小,无法形成磁有序的结构;另一方面,对于有强旋轨耦合作用的非4f^7电子构型的稀土离子配合物,由于理论计算和拟合上的困难,其4f电子之间的磁耦合作用的机理研究还很少．值得关注的是,有报道发现Dy3簇合物具有单分子磁体的性质,并且基态几乎是非磁的,其磁性来源主要是丰富的低激发态能谱,也就是说,一般认为的单分子磁体必须具有大的自旋基态并不是发生缓慢磁驰豫行为的必要条件．再次,本文综述了稀土金属离子一过渡金属离子簇合物的磁学性质．由于4f-3d之间的磁耦合作用要远大于4f-4f电子之间的磁耦合作用,所以此类配合物磁学性质和磁构关系的研究相对较多,其磁学性质也相对丰富．由于Gd离子和Cu离子的旋轨耦合作用较小,理论计算和磁性数据的拟合相对简单,所以对于磁构关系和磁耦合性质的研究主要集中在Gd—Cu体系．对于存在强旋轨耦合作用的其他镧系稀土离子,可能出现磁有序,慢的磁驰豫等其他磁学现象．实验上也合成了一些基于4f-3d作用的单分子磁体和单链磁体．此外,本文还综述了稀土金属离子．自由基体系的磁学性质．对于自由基与稀土金属离子之间的耦合,由于不需要通过抗磁性的其他原子,所以可能产生比4f-4f,4f-3d体系更强的磁耦合作用．实验上,也的确发现了一些具有磁有序行为的4f-自由基分子磁性材料,但磁有序主要发生在低温区．最后,对稀土分子基磁性材料研究中需要解决的问题和未来发展前景进行了展望．     

单核Cu（H）配合物C18H12CuN402的密度泛函研究

用量子化学从头算方法，在R0B3LYP／LANL2MB水平上，对单核配合物C18H12CuN402进行了理论计算，优化得到了该配合物的平衡几何构型，并计算了它的谐振动频率．结果表明：该配合物分于是可以稳定存在的，电子自旋布居主要集中在Cu原于及配体原于上，Cu原于和配体原于的自旋布居符号相同，说明体系中存在较强的自旋离城效应．体系的前沿轨道主要由cu原于的d轨道和配体原于的p轨道组成，这种组成有利于配体与磁中心之间的电子转移．计算结果与实验符合得较好。     

一维链状锰配位聚合物[Mn（C10H9O3）2（4，4＇-bipy）（H2O）2】n的合成、晶体结构及荧光性质分析

锰元素不仅在生物化学的酶催化过程中扮演重要的角色．而且在合成分子磁体、开展多核间磁交换作用的研究方面也受到人们的关注．锰配合物的的研究已引起人们的极大兴趣。近年来．我们合成了一些锰配合物．并对其性能进行了初步测定和分析。我们合成的锰配合物．主要集中在芳香羧酸配体体系：为了较系统地研究这类配合物的功能和配体结构的关系．     

氮杂环卡宾配位的两配位二价钴亚胺基配合物:合成、结构与反应性质

<正>Angew.Chem.Int.Ed.2015,54,12640~12644低配位过渡金属配合物因其在小分子活化和单分子磁性方面的潜在价值而获得研究者的广泛关注.已知金属配合物的最低配位数是两配位,其中金属-配体多为σ-单键.最近,中国科学院上海有机化学研究所邓亮课题组采用大位阻的氮杂环卡宾和大位阻芳基亚胺基为配体实现了两配位钴-亚胺基配合物的合成.该配合物是首例含钴-主族元素多重键的两配位配合物.单晶X射线衍射、核磁氢谱、溶液相磁矩、理论计算等表明化合物自旋基态S=3/2.这一高自旋低配位钴亚胺基配合物可与一氧化碳作用发生乃春转移反应生成异氰酸酯,与乙烯反应生成乙醛亚胺,与     

羧酸桥对反铁磁性EO叠氮铜双核配合物磁性影响的理论研究

基于密度泛函理论结合对称性破损态(DFT-BS)方法,运用不同的密度泛函和基组对反铁磁性EO叠氮铜双核配合物[Cu2(dmpe)2(μ1,1-N3)2(CH3COO)]+的磁性质进行研究.结果显示,杂化泛函计算的结果与实验数据非常吻合,能够准确描述反铁磁性EO叠氮铜双核配合物的磁性质.磁轨道分析表明,配合物中存在3个磁通道(2个叠氮桥、1个羧酸桥),磁通道中N原子、O原子与顺磁中心二价铜离子间都存在p d轨道重叠,对体系反铁磁性耦合相互作用都有贡献.从自旋布居分布角度来看,该配合物中顺磁中心间主要是自旋离域作用.配合物中羧酸桥传递强反铁磁性相互作用,使得顺磁中心间磁轨道的重叠增加,体系的反铁磁性相互作用增强.     

Spin Frustration and Competing Magnetic Exchange Interactions in Polynuclear Complexes of 3d Metals

Published examples of the use of the term "spin frustration" (SF) to describe the magnetochemical behavior of polynuclear complexes are examined critically. The difference between topological and real SF is demonstrated. A precise definition of SF in which SF only arises with degeneracy of the ground state of the complex with the presence of topological SF as an essential condition is proposed. The change of the energy levels forming the ground state of tri- and tetranuclear complexes of transition metals was analyzed in relation to the values of the exchange parameters. It was shown that not every degenerate ground state corresponds to spin frustration.     

Ligand-induced distortion of a tetranuclear manganese butterfly complex

The reaction of the pentadentate Schiff-base ligand 1,3-bis(salicylideneamino)-2-propanol (salproH3) with [Mn3O(O2CR)6(py)3] (R = Me, Et, But) gives the corresponding tetranuclear manganese product [Mn4O2O2CR)5(salpro)] (4Mn(III)). The syntheses, structure and magnetochemical characterization of these complexes are reported. The structure of the [Mn4(mu3-O)2]8+ is butterfly-like much more closed than in previous complexes with this core as a result of the alkoxide oxygen of the salpro ligand bridging the two wingtip Mn atoms. Variable-temperature, solid-state magnetic susceptibility studies reveal that these complexes possess S = 0 ground state spins. Fitting of the magnetic susceptibility data to the theoretical chiMT vs. T expression derived for a C2v symmetry complex, assuming an isotropic Heisenberg spin-Hamiltonian and using the Van Vleck equation, revealed that the various exchange parameters are all antiferromagnetic, and the core thus experiences spin frustration effects.     

Role of the spin magnitude of the magnetic ion in determining the frustration and low-temperature properties of kagome lattices

In view of the variety of low-temperature magnetic properties reported recently for kagome lattices with transition-metal ions in different oxidation states, we have investigated the low-energy spectrum and low-temperature thermodynamic properties of antiferromagnetic kagome lattices with varying magnitudes of site spins, employing quantum many-body Heisenberg models. The ground state and the low-lying excitation spectrum are found to depend strongly on the nature of the spin magnitude of the magnetic ions. The system remains highly frustrated if spins are half-odd-integer in magnitude, while the frustration is very weak or almost absent for integer spins or mixed-spin systems. In fact, for a mixed-spin kagome system with a certain magnitude, the whole system behaves as a classical magnet with a ferrimagnetic ground state without any frustration. These theoretical findings are consistent with a few experimental observations recently reported in the literature and would be of value in designing new kagome systems with unusual and interesting low-temperature magnetic properties.     

Spin maximization: switching of the usual S = 11 state of Mn(II)4Mn(III)3 disklike complexes to the maximum S = 16

The S = 11 ground states of the Mn 7 family of mixed-valence complexes with a metal-centered hexagonal topology have been found by density functional theory calculations to arise by spin frustration involving small differences in the magnitudes of the two weakest interactions controlling the alignment of the central spin. Targeted structural perturbation has allowed a complex with the central spin flipped to be discovered, which thus possesses the maximum S = 16 ground state.     

Spin dimer analysis of the spin exchange interactions in paramelaconite Cu(4)O(3) and its analogue Ag(2)Cu(2)O(3) and the spin ordering of the Cu(2)O(3) spin lattice leading to their magnetic phase transitions

The magnetic structures of the Cu(2)O(3) spin lattices present in Cu(4)O(3) and Ag(2)Cu(2)O(3) were analyzed by studying their spin exchange interactions on the basis of spin dimer analysis. Calculations of spin exchange parameters were calibrated by studying LiCuVO(4) whose intrachain and interchain antiferromagnetic spin exchange parameters are known experimentally. The magnetic phase transition of Cu(4)O(3) at 42.3 K doubles the unit cell along each crystallographic direction. The spin arrangements of the Cu(2)O(3) lattice consistent with this experimental observation are different from conventional antiferromagnetic ordering. Our analysis indicates that spin fluctuation should occur in Cu(4)O(3), low-dimensional magnetism should be more important than magnetic frustration in Cu(4)O(3), and Ag(2)Cu(2)O(3) and Cu(4)O(3) should have similar structural and magnetic properties.     

On the high magnetic-ordering temperature of the 5d magnetic oxide Ca3LiOsO6 crystallizing in a trigonal crystal structure: density functional analysis

The 5d magnetic oxide Ca(3)LiOsO(6) has a trigonal arrangement of its LiOsO(6) chains parallel to the c-direction and hence has triangular arrangements of high-spin Os(5+) (d(3)) ions but exhibits no spin frustration and undergoes a long-range antiferromagnetic ordering at a high temperature. The origin of this apparently puzzling observation was examined by evaluating the nearest-neighbor Os-O···O-Os spin exchange interactions of Ca(3)LiOsO(6) on the basis of density functional calculations. Our study shows that, of the two nearest-neighbor interchain spin exchanges, one dominates over the other and that the intrachain spin exchange and the dominating interchain spin exchange are strong and form a three-dimensional antiferromagnetic spin lattice with no spin frustration, which is responsible for the long-range antiferromagnetic ordering of Ca(3)LiOsO(6) at high temperature. In determining the strengths of the Os-O···O-Os exchange interactions of Ca(3)LiOsO(6), the Li(+) and Ca(2+) ions of the O···Li(+)···O and O···Ca(2+)···O linkages are found to play only a minor role.     

甲酸根桥联双核铜配合物磁学性质理论研究

基于DFT-BS方法,选择不同的泛函方法和基组,研究anti,anti甲酸桥联双核铜配合物的磁学性质.结果表明,在B3P86/TZV水平计算得到顺磁中心Cu(Ⅱ)离子间磁耦合常数为-55.63 cm^-1,与实验值-55.60 cm^-1最接近,可准确描述甲酸桥联双核铜配合物的磁学性质.顺磁中心Cu(Ⅱ)与甲酸根桥联配体间有较强的轨道作用,其磁轨道主要来源于Cu(Ⅱ)离子的3dyz轨道、桥联配体甲酸根离子的离域π键,顺磁中心Cu(Ⅱ)离子为自旋离域机理.在不同桥联模式的甲酸桥联双核铜配合物中,随顺磁中心Cu(1)自旋密度增加,Cu(Ⅱ)离子间的反铁磁性贡献逐渐增加,其磁耦合常数J值逐渐减小.     

Importance of the O-M-O bridges (M = V5+, Mo6+) for the spin-exchange interactions in the magnetic oxides of Cu2+ ions bridged by MO4 tetrahedra: spin-lattice models of Rb2Cu2(MoO4)3, BaCu2V2O8, and KBa3Ca4Cu3V7O28

The spin-lattice models relevant for the magnetic oxides Rb2Cu2(MoO4)3, BaCu2V2O8, and KBa3Ca4Cu3V7O28 were determined by evaluating the relative strengths of the spin-exchange interactions between their Cu2+ ions on the basis of spin dimer analysis. Our study shows that the O-M-O bridges (M = V5+, Mo6+) between the magnetic ions Cu2+, provided by the MO4 tetrahedra, are crucial for the spin-exchange interactions and hence for deducing the spin-lattice models needed to interpret the magnetic properties of these oxides. The spin-lattice model of Rb2Cu2(MoO4)3 is not a uniform chain but two interpenetrating spin ladders that interact weakly with geometric spin frustration. The spin-lattice model of BaCu2V2O8 is an alternating chain as expected, but the spin-exchange paths responsible for it differ from those expected. With respect to the strongest spin exchange of BaCu2V2O8, the spin exchange of KBa3Ca4Cu3V7O28 is only slightly weaker, but the strongest spin exchange of Rb2Cu2(MoO4)3 is much weaker. This difference in the spin-exchange strengths is caused by the difference in the bridging modes of the MO4 tetrahedra leading to these spin-exchange interactions.     

Density functional perturbational orbital theory of spin polarization in electronic systems. II. Transition metal dimer complexes

We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.