Anion encapsulation promoted by anion⋯π interactions in rationally designed hexanuclear antiferromagnetic wheels: synthesis, structure and magnetic properties
Anion encapsulation promoted by anion⋯π interactions in rationally designed hexanuclear antiferromagnetic wheels: synthesis, structure and magnetic properties
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DOI：
10.1039/b906382j
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发表时间：
2009-09
期刊：
影响因子：
3.1
通讯作者：
E. Colacio;Hakima Aouryaghal;A. Mota;J. Cano;R. Sillanpää;A. Rodrı́guez-Diéguez
中科院分区：
文献类型：
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作者：
E. Colacio;Hakima Aouryaghal;A. Mota;J. Cano;R. Sillanpää;A. Rodrı́guez-Diéguez
Kpymca （pymca =嘧啶-2-羧基阴离子）与MX2·6H2O和tmda （N，N,N ',N ' -四亚甲基乙二胺）以1:3:3的摩尔比，以甲醇/水（3:1）为溶剂，反应得到六核配合物[M6（µ-pymca）6(tmda)6]X6·4H2O （M = NiII, X = ClO4−1,BF4−2;M = CoII, X = ClO4−3）。pymca与Cu(ClO4)2·6H2O或Cu(BF4)2·6H2O反应均无确定产物。然而，在强配位氯阴离子存在下，可以得到线性四核配合物[Cu4（µ-pymca）3Cl(H2O)](ClO4)4·4.5H2O 4。1-3的结构非常相似，由轮形六核[M6（µ-pymca）6(tmda)6]6+阳离子组成，具有伪d3d对称性，配体以螯合/桥接模式起作用。配体的嘧啶环交替地在轮盘平面的上下向轮盘平面的法线方向收敛，形成一个碗状的胶囊，由一个ClO4−（1和3）或BF4−(2)阴离子占据。ClO4−/BF4−与配体嘧啶环的π电子密度之间存在紧密的接触。4的四核阳离子呈锯齿形线性构象，其中铜离子由三个双（螯合）/桥接pymca配体桥接。变温磁化率研究表明，配合物1和4通过pymca配体在金属离子之间表现出适度的反铁磁偶联，其中1的J =−26.3 cm−1,4的J1 =−16.3 cm−1和J2 =−43.78 cm−1。四核配合物4具有两种不同的磁耦合常数，分别用于外中心（J1）和中心-中心（J2）铜相互作用。根据影响磁路的几何因素，讨论了4的J1和J2值的大小。此外，已经进行了DFT计算来支持4中J参数的相对大小。采用自旋-轨道耦合（λ）、轨道约简因子（Ak）、轴向零场分裂（Δ）和磁交换耦合(J)模型对3号卫星的磁数据进行了分析。经过对角化处理后，这些参数的值分别为：Ak = 1.15, λ = - 122 cm−1，Δ = 650 cm−1,J = - 5.2 cm−1。
The reaction of Kpymca (pymca = pyrimidine-2-carboxylato anion) with MX2·6H2O and tmda (N,N,N′,N′-tetramethylethylenediamine) in 1 : 3 : 3 molar ratio, using a MeOH/water mixture (3 : 1) as solvent, afforded the hexanuclear complexes [M6(µ-pymca)6(tmda)6]X6·4H2O (M = NiII, X = ClO4−1, BF4−2; M = CoII, X = ClO4−3). The reaction of pymca with either Cu(ClO4)2·6H2O or Cu(BF4)2·6H2O did not lead to any definite product. However, in the presence of strong coordinating chloride anions the linear tetranuclear complex [Cu4(µ-pymca)3Cl(H2O)](ClO4)4·4.5H2O 4 could be obtained. The structures of 1–3 are very similar and consist of wheel-shaped hexanuclear [M6(µ-pymca)6(tmda)6]6+ cations, with pseudo-D3d symmetry in which the ligand acts in a bis(chelating)/bridging mode. The pyrimidine rings of the ligands converge alternatively above and below the plane of the wheel toward the normal to this plane, leading to the formation of a bowl-shaped capsule, which is occupied by one ClO4− (1 and 3) or BF4− (2) anion. There exist tight contacts between ClO4−/BF4− and the π-electron density of the pyrimidine rings of the ligands. The tetranuclear cations of 4 exhibit a zig-zag linear conformation, in which copper ions are bridged by three bis(chelating)/bridging pymca ligands. Variable-temperature magnetic susceptibility studies reveal that complexes 1 and 4 show moderate antiferromagnetic coupling between the metal ions through the pymca ligands with J = −26.3 cm−1 for 1, and J1 = −16.3 cm−1 and J2 = −43.78 cm−1 for 4. The tetranuclear complex 4 has two different magnetic coupling constants accounting for the external–central (J1) and central–central (J2) copper interactions. The magnitude of the J1 and J2 values for 4 has been discussed on the basis of the geometrical factors affecting the magnetic pathways. Moreover, DFT calculations have been performed to support the relative magnitude of the J parameters in 4. A model accounting for spin–orbit coupling (λ), orbital reduction factors (Ak), axial zero-field splitting (Δ) and magnetic exchange coupling (J) was used to analyse the magnetic data of 3. The values of these parameters after the diagonalisation process were: Ak = 1.15, λ = −122 cm−1, Δ = 650 cm−1 and J = −5.2 cm−1.