Self-assembly of transition metal ion complexes of a hybrid pyrazine–terpyridine ligand
作者:Artur R. Stefankiewicz、Monika Wałęsa-Chorab、Jack Harrowfield、Maciej Kubicki、Zbigniew Hnatejko、Maria Korabik、Violetta Patroniak
DOI:10.1039/c2dt31982a
日期:——
A new hybrid pyrazineâterpyridine ligand L (C34H22N8) and its complexes with different transition metal ions, M (M = Mn(II) 1, Zn(II) 2, Fe(II) 3, Co(II) 4, Cu(II) 5 and Cd(II) 6), have been synthesised. In the presence of a nitrate counter-anion, both Cu(II) and Cd(II) give complexes in which the ratio Mâ:âL is 2â:â1, whereas with perchlorate, trifluoromethanesulfonate or tetrafluoroborate, the other metal ions provide solids in which this ratio is 1â:â1. From mass spectral measurements and a single crystal, X-ray structure determination for the Fe(II) complex 3, however, all the latter species are concluded to be 2â:â2 complexes. Both the Fe(II) complex 3 and the Co(II) complex 4, generated from tetrafluoroborate reactant salts, have the composition [M2L2F2(H2O)](BF4)2, the presence of fluoride ligands being presumed to reflect the abstraction of fluoride ions from tetrafluoroborate by the metal ions under the preparative conditions. The crystal structure of complex 3 shows the Fe(II) centres to be inequivalent, one being high-spin and heptacoordinate with a FeN4F2O coordination sphere, the other low-spin and octahedral with a FeN6 sphere. The two ligand molecules differ markedly, one being heptadentate, the other clearly âhypodentateâ, with only three N-donor atoms of a terpyridine-like arm coordinated, although their conformations are similar, showing significant differences from that of C2 symmetry found for the free ligand by a crystal structure determination. Mass spectra are consistent with the Cu(II) and Cd(II) complexes having the composition [M2L(H2O)n(NO3)4ân](NO3)4ân, and the weak antiferromagnetic coupling observed for the Cu(II) complex is consistent with a preliminary crystal structure determination which indicates that the two Cu(II) centres are not bridged by a pyrazine unit.
这项研究内容如下:
研究者合成了一种新的吡嗪-三联吡啶杂化配体L(C34H22N8)及其与不同过渡金属离子形成的配合物,金属离子包括Mn(II)、Zn(II)、Fe(II)、Co(II)、Cu(II)和Cd(II)。
主要发现:
1. 当对阴离子为硝酸根时,Cu(II)和Cd(II)形成的配合物中金属与配体比例为2:1。
2. 当对阴离子为高氯酸根、三氟甲磺酸根或四氟硼酸根时,其他金属离子形成的固体中金属与配体比例为1:1。但通过质谱测定和Fe(II)配合物的单晶X射线衍射分析表明,这些配合物实际都是2:2配合物。
3. Fe(II)配合物3和Co(II)配合物4的组成为[M2L2F2(H2O)](BF4)2。其中氟配体的存在可能是由于在制备条件下金属离子从四氟硼酸根中提取氟离子导致的。
4. Fe(II)配合物3的晶体结构显示两个Fe(II)中心不等价:
- 一个为高自旋,七配位,配位环境为FeN4F2O
- 另一个为低自旋,八面体构型,配位环境为FeN6
5. Cu(II)和Cd(II)配合物的组成为[M2L(H2O)n(NO3)4-n](NO3)4-n。Cu(II)配合物表现出弱反铁磁耦合,这与初步的晶体结构分析结果一致,表明两个Cu(II)中心没有通过吡嗪基团桥联。