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), [Rh2(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 {[Rh2(O2CCF3)4]3CH3Si(C5H4N)3(η1-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) Å. The second rhodium atom of each dimetal
complex in 2 weakly coordinates a benzene molecule with an Rh−C distance of 2.69(2) Å. A supramolecular
complex of the composition {[Rh2(O2CCF3)4]2(C6H5)2Si(C5H4N)2} (3) has been prepared by reacting the dinuclear
units 1 with a potentially bidentate ligand, bis(4‘-pyridyl)diphenylsilane, (C6H5)2Si(C5H4N)2 (L2), having two pyridyl
groups rigidly oriented at 109°. In 3, one L2 ligand coordinates two dirhodium molecules 1 through their axial
positions with the Rh−N distance of 2.150(5) Å. 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) Å. A supramolecular compound of the composition {[Rh2(O2CCF3)4]3(HO)C(C5H4N)3(η1-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 110°. 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) Å. A unique extended pseudo-3D structure in 4 is created by additional
Rh−O coordination bonds as well as by weak metal−arene interactions.