Cation structures hexanuclear complexes

Using tridentate ligands with various functionalities and coordinating abilities, a series of neutral and cationic tri-, tetra- and hexanuclear metalla-cycles have been synthesised [34]. Cyclic tetramers composed of Cp Ir, Cp Rh or (arene)Ru half-sandwich complexes and 6-purinethione derivatives have been isolated as triflate salts [351. The cationic complex (Cp Ir)4(Ll)4 (where L1 = 2-amino-6-purinethione), presented in Fig. 9a, forms in the solid state an infinite channel-like structure with, S symmetry. Replacing the 6-purinethione with pyridine-4-thiolato bridging ligands (L2), the trinuclear metalla-cycle [(Cp Ir)3(L2)3] was obtained (Fig. 9b) [36]. 

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

FIGURE 124 Clockwise from top left molecular structure of tpen, crystal structure of a dinuclear hydroxo complex [La(tpen)(/r-OH)]2(/r-V OTf) +, crystal structure of cationic hexanuclear cluster [La6(tpen)4(MeCN)2(H20)2(/r3-7j 7j 7j C03)4 (/t3-7] 7] 7] C03)2], and its core motif (redrawn after Natrajan et al., 2006). 

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