Meridial arrangements

Figure 2.8 Geometrical isomers. A) Meridial arrangement (Drew-Pfitzner structure). B) Facial arrangement (Pfeiffer-Schetty structure).

The complex [ReX (PEt2Ph] ] and [ReNX (PEt Ph) ] must have the same cis-meridial arrangement of phosphine molecules. The alternative cis-facial arrangement would demand much higher dipole moments. Comparing these two series of complexes it is evident that replacement of chlorine by nitrogen, with appropriate change in oxidation number of the rhenium has little effect on the dipole moment. It appears, therefore, that the Re(V N and Re(III)-Cl bond moments are about equal. 

Macrocyclic ligands, mac, are usually coordinated into the equatorial plane of the metal ions, the axial positions being occupied by weakly bonded ligands, which can be replaced by the cyano bridges. The self-assembly process involving ro 5-[M (wac)(H20)2] and [M(CN)6] ions yields 2D [M 3M2] networks. Within a layer, each mac)f moiety is linked to two [M (CN)6] ions in trans positions, and each [M(CN)6] ion is surrounded by three [M(wac)f units. If the three M. mac) units adopt a facial configuration around the M ion, then layers with a stair-shaped honeycomb architecture are formed mac stands for cyclam, 1,4,8,11-tetraazacyclotetradecane) (Fig. 36). A meridial arrangement of the three M mac)f moieties leads to flat brick-wall-like layers mac = 3,10-diethyl-l,3,5,8,10,12-hexaazacyclotetradecane (Fig. 37). ... 

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