Directed Synthesis of {Mn 18 Cu 6 } Heterometallic Complexes
Directed Synthesis of {Mn 18 Cu 6 } Heterometallic Complexes
复制标题
{Mn 18 Cu 6 }异金属配合物的定向合成
DOI：
10.1002/ange.201208781
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发表时间：
2013
影响因子：
--
通讯作者：
Milway V
中科院分区：
文献类型：
--
作者：
Milway V
The development of new synthetic strategies to assemble high-nuclearity transition metal complexes is a key target in modern coordination chemistry.[1] One of the driving forces for this is their fascinating magnetic properties for example, single-molecule magnets [2] or magnetic refrigerants [3] and molecules with large spin ground states [4] or large anisotropy barriers.[5] The use of two, or more, different metal ions to assemble these clusters is an attractive synthetic target and controlling the bottom-up assembly of large heterometallic molecules is a considerable challenge.[6, 7] However, the potential rewards are significant, as there is a real possibility of control/design over the individual magnetic parameters that contribute to the overall molecular properties.[8] Furthermore, new functionality can be added, such as the combination of magnetic and optical properties,[9] or the production of catalysts or catalyst precursors with high activity and/or selectivity.[10] Previously, polydentate ligands with specific binding sites/donor atoms,[11] linear linkers such as cyanide [12] or rigid structure-directing ligands [13] have been used to prepare heterometallic complexes. Herein, we describe a new stepby-step approach to synthesize large 3d–3d’heterometallic oxo-bridged clusters. Firstly, we use a preformed CuII complex, which contains multiple, latent hydroxy binding sites, to target the trapping and encapsulation of an inner metal-oxo core. Secondly, the choice of CuII as the central ion increases the flexibility further, due to its range of typical coordination environments from [4] to [4+ 2]. We report two compounds that contain a striking “core-shell”{Mn18Cu6} complex as either a hexa-or dication, where the CuII precursors encapsulate a hexacapped cuboctahedral manganese oxide {MnIII 12MnII 6O14} nanocluster. The CuII center is enclosed using the bis-tris propane ligand {2, 2’-(propane-1, 3-diyldiimino) bis [2-(hydroxymethyl)-propane-1, 3-diol](H6L, Scheme1) forming the precursor complex [Cu (H6L) Cl] Cl· 1.25 H2O (1· 1.25 H2O)(see Supporting Information, Figure S1) in almost quantitative yield (see Experimental). This is then redissolved and utilized in a second reaction to generate the heterometallic complexes: addition of base to a solution of 1, followed by addition of MnCl2· 4 H2O leads to the formation of [Mn18Cu6O14-(H2L) 6Cl2 (H2O) 6] Cl6· H2O (2· H2O) using NMe4OH/EtOH or [Mn18Cu6O14 (H2L) 6Cl6] Cl2· 10 H2O· 6 CH3OH (3· 10 H2O· 6 CH3OH) using NEt3/MeOH. Both compounds can be prepared reproducibly, albeit in low yields, which is not uncommon in the area of high-nuclearity complexes.[14] We have been unable to obtain these complexes using a range of one-pot reactions and preformation of the CuII complex appears to be essential.The structure of the cationic cluster in 2 is based upon a {MnIII 12MnII 6O14} 20+ core, encapsulated by six {Cu (H2L)} 2À groups. Oxidation states have been confirmed by bondvalence sum (BVS) calculations and by consideration of charge balance/coordination environments. The twelve MnIII and fourteen O2À anions, form a hollow cube (ca. 3.8 OÀO edge)(Figure 1a). The MnIII cations describe a cuboctahedron, capped on each square face by a MnII, forming a giant octahedron (Figure 1 b). Six faces of this giant octahedron are capped by a CuII center, which resides off-center, above one of the smaller constituent {MnIIMnIII 2} triangular faces (Figure 1c). The CuII ions describe a further octahedron, twisted with respect to the {MnII 6} octahedron, giving a remarkable level of self-assembly: polyhedral shells of expanding size describing archimedian {MnIII 12}< platonic {MnII 6}< platonic {CuII
The development of new synthetic strategies to assemble high-nuclearity transition metal complexes is a key target in modern coordination chemistry.[1] One of the driving forces for this is their fascinating magnetic properties for example, single-molecule magnets [2] or magnetic refrigerants [3] and molecules with large spin ground states [4] or large anisotropy barriers.[5] The use of two, or more, different metal ions to assemble these clusters is an attractive synthetic target and controlling the bottom-up assembly of large heterometallic molecules is a considerable challenge.[6, 7] However, the potential rewards are significant, as there is a real possibility of control/design over the individual magnetic parameters that contribute to the overall molecular properties.[8] Furthermore, new functionality can be added, such as the combination of magnetic and optical properties,[9] or the production of catalysts or catalyst precursors with high activity and/or selectivity.[10] Previously, polydentate ligands with specific binding sites/donor atoms,[11] linear linkers such as cyanide [12] or rigid structure-directing ligands [13] have been used to prepare heterometallic complexes. Herein, we describe a new stepby-step approach to synthesize large 3d–3d’heterometallic oxo-bridged clusters. Firstly, we use a preformed CuII complex, which contains multiple, latent hydroxy binding sites, to target the trapping and encapsulation of an inner metal-oxo core. Secondly, the choice of CuII as the central ion increases the flexibility further, due to its range of typical coordination environments from [4] to [4+ 2]. We report two compounds that contain a striking “core-shell”{Mn18Cu6} complex as either a hexa-or dication, where the CuII precursors encapsulate a hexacapped cuboctahedral manganese oxide {MnIII 12MnII 6O14} nanocluster. The CuII center is enclosed using the bis-tris propane ligand {2, 2’-(propane-1, 3-diyldiimino) bis [2-(hydroxymethyl)-propane-1, 3-diol](H6L, Scheme1) forming the precursor complex [Cu (H6L) Cl] Cl· 1.25 H2O (1· 1.25 H2O)(see Supporting Information, Figure S1) in almost quantitative yield (see Experimental). This is then redissolved and utilized in a second reaction to generate the heterometallic complexes: addition of base to a solution of 1, followed by addition of MnCl2· 4 H2O leads to the formation of [Mn18Cu6O14-(H2L) 6Cl2 (H2O) 6] Cl6· H2O (2· H2O) using NMe4OH/EtOH or [Mn18Cu6O14 (H2L) 6Cl6] Cl2· 10 H2O· 6 CH3OH (3· 10 H2O· 6 CH3OH) using NEt3/MeOH. Both compounds can be prepared reproducibly, albeit in low yields, which is not uncommon in the area of high-nuclearity complexes.[14] We have been unable to obtain these complexes using a range of one-pot reactions and preformation of the CuII complex appears to be essential.The structure of the cationic cluster in 2 is based upon a {MnIII 12MnII 6O14} 20+ core, encapsulated by six {Cu (H2L)} 2À groups. Oxidation states have been confirmed by bondvalence sum (BVS) calculations and by consideration of charge balance/coordination environments. The twelve MnIII and fourteen O2À anions, form a hollow cube (ca. 3.8 OÀO edge)(Figure 1a). The MnIII cations describe a cuboctahedron, capped on each square face by a MnII, forming a giant octahedron (Figure 1 b). Six faces of this giant octahedron are capped by a CuII center, which resides off-center, above one of the smaller constituent {MnIIMnIII 2} triangular faces (Figure 1c). The CuII ions describe a further octahedron, twisted with respect to the {MnII 6} octahedron, giving a remarkable level of self-assembly: polyhedral shells of expanding size describing archimedian {MnIII 12}< platonic {MnII 6}< platonic {CuII