Supramolecular assemblies of dimetal complexes with polydentate N-donor ligands: From a discrete pyramid to a 3D channel network

Reactions of a dinuclear metal complex in the form of dirhodium(II) tetra(trifluoroacetate), [Rh-2(O2CCF3)(4)] (1), with a number of strong N-donor ligands having functional groups rigidly oriented at different directing angles have been found to yield supramolecular architectures of differing complexity. All structures have been established by X-ray crystallography. From reaction of 1 with neutral tris(4'-pyridyl)methylsilane ligand, CH3Si(C5H4N)(3) (L1), a discrete pyramid-shaped hexanuclear complex {[Rh-2(O2CCF3)(4)](3)CH3Si(C5H4N)(3)(eta(1)-C6H6)(3)}.C6H6 (2.C6H6) has been isolated from benzene. In 2 three molecules of 1 are strongly coordinated to one L1 ligand at only one axial position of each dirhodium unit at the Rh-N distances of 2.152(6) Angstrom. The second rhodium atom of each dimetal complex in 2 weakly coordinates a benzene molecule with an Rh-C distance of 2.69(2) Angstrom. A supramolecular complex of the composition {[Rh-2(O2CCF3)(4)](2)(C6H5)(2)Si(C5H4N)(2)} (3) has been prepared by reacting the dinuclear units 1 with a potentially bidentate ligand, bis(4'-pyridyl)diphenylsilane, (C6H5)(2)Si(C5H4N)(2) (L2), having two pyridyl groups rigidly oriented at 109degrees. In 3, one L2 ligand coordinates two dirhodium molecules 1 through their axial positions with the Rh-N distance of 2.150(5) Angstrom. An interesting extended 2D layered motif is formed by additional contacts of open axial positions of dirhodium units with phenyl groups of the neighboring ligands at Rh-C distances which average to 2.88(1) Angstrom. A supramolecular compound of the composition {[Rh-2(O2CCF3)(4)](3)(HO)C(C5H4N)(3)(eta(1)-C6H6)}.(1)/2C6H6 (4.(1)/2C6H6) has been formed when linear dirhodium units 1 were reacted with tris(4'-pyridyl) methanol (L3) having tetrahedral directing angles that average to 110degrees. A building block in the solid structure of 4 is a hexanuclear molecule in which one L3 ligand binds three dimetal units of 1 through N atoms of pyridyl groups at the average Rh-N distance of 2.143(7) Angstrom. A unique extended pseudo-3D structure in 4 is created by additional Rh-O coordination bonds as well as by weak metal-arene interactions.