Hong C S, Koo J E, Son S K, Lee Y S, Kim Y S, Do Y
Department of Chemistry, School of Molecular Science and Center for Molecular Design and Synthesis, Korea Advanced Institute of Science and Technology, Daejeon.
Chemistry. 2001 Oct 1;7(19):4243-52. doi: 10.1002/1521-3765(20011001)7:19<4243::aid-chem4243>3.0.co;2-u.
Two new one-dimensional single azide-bridged metal(II) compounds [M(5-methylpyrazole)4(N3)]nn(H2O)n [M = Co (1a), Ni (2a)] were prepared by treating an M(II) ion with stoichiometric amount of sodium azide in the presence of four equivalents of the 3(5)-methylpyrazole ligand. The isostructural compounds 1a and 2a crystallize in the monoclinic space group P2(1)/n. The azide bridging ligands have a unique end-to-end coordination mode that brings two neighboring metal centers into a cis-position with respect to the azide unit to form single end-to-end azide-bridged cobalt(II) and nickel(II) chains. The two neighboring metal atoms at inversion centers adopt octahedral environments with four equatorial 3(5)-methylpyrazole ligands and two axial azide bridges. Two adjacent equatorial least-squares planes form dihedral angles of 60.5 degrees and 60.6 degrees for Co and Ni, respectively. In addition, the metal-azide-metal units form large M-N3-M torsion angles, which are magnetically important geometrical parameters, of 71.6 degrees for M=Co and 75.7 degrees for M=Ni. It should also be noted that the M-N-N angles associated with end-to-end azide group, another magnetically important structural parameter, fall into the experimentally observed range of 120-140 degrees as 128.3(3) and 147.8(3) degrees for cobalt species and 128.4(2) and 146.1(3) degrees for nickel species; these values deviate from the theoretical value of around 164 degrees at which the incidental orthogonality is achieved under the torsion angle of 0 degrees. The compounds 1a and 2a have unique magnetic properties of ferromagnetism, zero-field splitting, and spin canting. The MO calculations indicate that the quasiorthogonality between the magnetic orbitals of metal ions and the p atomic orbitals of the bridging azide is possible in the observed structures and leads to the ferromagnetism. The spin canting related to the perturbation of ferromagnetism arises from the magnetic anisotropy and antisymmetric interactions judged by the structural parameters of the zero-field splitting and the tilted MN4 planes in a chain. The enhancement of magnetic interactions was accomplished by dehydrating the chain compounds to afford two soft magnets with critical temperature T(C) and coercive field of 2 K and 35 G for 1b and 2.3 K and 20 G for 2b, respectively.
通过在四当量的3(5)-甲基吡唑配体存在下，用化学计量的叠氮化钠处理M(II)离子，制备了两种新型的一维单叠氮桥联金属(II)化合物[M(5-甲基吡唑)4(N3)]nn(H2O)n [M = Co (1a)，Ni (2a)]。同构化合物1a和2a结晶于单斜空间群P2(1)/n。叠氮桥联配体具有独特的端对端配位模式，使两个相邻的金属中心相对于叠氮单元处于顺式位置，形成单端对端叠氮桥联的钴(II)和镍(II)链。位于反演中心的两个相邻金属原子采用八面体环境，有四个赤道面的3(5)-甲基吡唑配体和两个轴向叠氮桥。对于Co和Ni，两个相邻的赤道面最小二乘平面分别形成60.5度和60.6度的二面角。此外，金属-叠氮-金属单元形成大的M-N3-M扭转角，这是磁学上重要的几何参数，对于M = Co为71.6度，对于M = Ni为75.7度。还应注意的是，与端对端叠氮基团相关的M-N-N角，这是另一个磁学上重要的结构参数，钴物种的角度为128.3(3)和147.8(3)度，镍物种的角度为128.4(2)和146.1(3)度，落入实验观察到的120 - 140度范围；这些值偏离理论值约164度，在扭转角为0度时可实现偶然正交。化合物1a和2a具有铁磁性、零场分裂和自旋倾斜的独特磁性。MO计算表明，在观察到的结构中，金属离子磁轨道与桥联叠氮的p原子轨道之间可能存在准正交，从而导致铁磁性。与铁磁性扰动相关的自旋倾斜源于零场分裂的结构参数和链中倾斜的MN4平面所判断的磁各向异性和反对称相互作用。通过使链状化合物脱水，实现了磁相互作用的增强，得到了两种软磁体，1b的临界温度T(C)和矫顽场分别为2 K和35 G，2b的临界温度T(C)和矫顽场分别为2.3 K和20 G。
