Coordination chemistry of tetradentate N-donor ligands containing two pyrazolyl-pyridine units separated by a 1,8-naphthyl spacer: Dodecanuclear and tetranuclear coordination cages and cyclic helicates
Coordination chemistry of tetradentate N-donor ligands containing two pyrazolyl-pyridine units separated by a 1,8-naphthyl spacer: Dodecanuclear and tetranuclear coordination cages and cyclic helicates
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DOI：
10.1021/ic060157d
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发表时间：
2006-05-15
影响因子：
4.6
通讯作者：
Ward, Michael D.
中科院分区：
文献类型：
--
作者：
Argent, Stephen P.;Adams, Harry;Ward, Michael D.
四齿配体L-naph含有两个N-供体双齿吡唑基-吡啶单元，通过亚甲基间隔基连接到1，8-萘基核; L-*45和L-*56是手性配体，其结构类似于Lnaph，但带有与末端吡啶环的C-4和C-5或C-5和C-6稠合的蒎烯基团。配合物[Cu（L-naph）]（OTf）和[Ag（L-naph）]（BF 4）具有不明显的单核结构，其中Cu-I为四配位，Ag-I为两配位，具有两个额外的弱相互作用（即，“2 + 2”坐标）。相比之下，[Cu-4（L-naph）（4）][BF 4]（4）是一种环状四核螺旋酸酯，在中心空腔中具有四氟硼酸根阴离子，通过阴离子模板效应形成;电喷雾质谱（ESMS）光谱显示溶液中存在其他环状低聚物。手性配体显示出相当的行为，[Cu（L-*45）]（BF 4）和[Ag（L-*45）]（ClO 4）具有相似的单核晶体结构，并且配体是四齿螯合物。相比之下，[Ag-4（L-*56）（4）]（BF 4）（4）是一种环状四核螺旋酸盐，其中络合物的两种非对映体都存在于晶体中;这两种非对映体具有相似的总体几何形状，但在细节上显著不同。尽管它们的晶体结构不同，但根据ESMS研究，[Ag（L-*45）]（ClO 4）和[Ag-4（L-*56）（4）]（BF 4）（4）在溶液中的行为相似，形成了一系列环状低聚物（高达Ag 9 L9）。L-naph与过渡金属配位离子Co-II、Cu-II和Cd-II形成一系列不寻常的十二核配位笼[M-12（L-naph）（18）]X-24（X- = ClO 4-或BF 4-），其中12个金属离子占据截顶四面体的顶点，18个边中的每一个边都有一个桥连配体。每个笼的中心空腔可以容纳四个抗衡离子，并且每个笼分子是手性的，所有12个金属三螯合物都是纯手性的;晶体是外消旋的。广泛的芳族堆积周围的笼周围的配体之间似乎是一个重要的因素，在他们的组装。手性类似物L*45形成了更简单的四核四面体配位笼[Zn-4（L-*45）（6）]（ClO 4）（8），在中心空腔中有一个阴离子;尽管可以通过ESMS在溶液中检测到痕量的[Zn-12（L-*45）（18）]（ClO 4）（24），但蒎烯手性助剂的空间体积阻止了十二核笼的形成。[Zn-4（L-*45）（6）]（ClO 4）（8）的形成是非对映选择性的，其中蒎烯基团的手性控制四核笼的手性。
The tetradentate ligand L-naph contains two N-donor bidentate pyrazolyl-pyridine units connected to a 1,8-naphthyl core via methylene spacers; L-*45 and L-*56 are chiral ligands with a structure similar to that of Lnaph but bearing pinene groups fused to either C-4 and C-5 or C-5 and C-6 of the terminal pyridyl rings. The complexes [Cu(L-naph)](OTf) and [Ag(L-naph)](BF4) have unremarkable mononuclear structures, with Cu-I being four-coordinate and Ag-I being two-coordinate with two additional weak interactions (i.e., "2 + 2" coordinate). In contrast, [Cu-4(L-naph)(4)][BF4](4) is a cyclic tetranuclear helicate with a tetrafluoroborate anion in the central cavity, formed by an anion-templating effect; electrospray mass spectrometry (ESMS) spectra show the presence of other cyclic oligomers in solution. The chiral ligands show comparable behavior, with [Cu(L-*45)](BF4) and [Ag(L-*45)](ClO4) having similar mononuclear crystal structures and with the ligands being tetradentate chelates. In contrast, [Ag-4(L-*56)(4)](BF4)(4) is a cyclic tetranuclear helicate in which both diastereomers of the complex are present in the crystal; the two diastereomers have similar gross geometries but are significantly different in detail. Despite their different crystal structures, [Ag(L-*45)](ClO4) and [Ag-4(L-*56)(4)](BF4)(4) behave similarly in solution according to ESMS studies, with a range of cyclic oligomers (up to Ag9L9) forming. With transition-metal dications Co-II, Cu-II, and Cd-II, L-naph generates a series of unusual dodecanuclear coordination cages [M-12(L-naph)(18)]X-24 (X- = ClO4- or BF4-) in which the 12 metal ions occupy the vertices of a truncated tetrahedron and a bridging ligand spans each of the 18 edges. The central cavity of each cage can accommodate four counterions, and each cage molecule is chiral, with all 12 metal trischelates being homochiral; the crystals are racemic. Extensive aromatic stacking between ligands around the periphery of the cages appears to be a significant factor in their assembly. The chiral analogue L*45 forms the simpler tetranuclear, tetrahedral coordination cage [Zn-4(L-*45)(6)](ClO4)(8), with one anion in the central cavity; the steric bulk of the pinene chiral auxiliaries prevents the formation of a dodecanuclear cage, although trace amounts of [Zn-12(L-*45)(18)](ClO4)(24) can be detected in solution by ESMS. Formation of [Zn-4(L-*45)(6)](ClO4)(8) is diastereoselective, with the chirality of the pinene groups controlling the chirality of the tetranuclear cage.