Interpenetrating Diamond-Like Nets

By far the largest class of interpenetrating structures involves diamond-related nets. 2-Fold interpenetration in the case of Zn(CN)2 has already been considered and many examples varying in the degree of interpenetration from 2-fold to 9-fold are referred to in the comprehensive review [1]. The mode of 9-fold interpe- 

---

Figure 26. Representation of the structure of [Ag(4,4 -biphenyldicarbonitrile)2](PF6) consisting of nine interpenetrating diamond-like nets. Circles represent Ag. The dinitrile ligand links Ag to Ag.

FIG. 3.40. (a) Single diamond net. (b) System of three interpenetrating diamond-like nets. 

Some general points about interpenetrating networks can be illustrated by the example of Zn(CN)2, which was structurally characterized over half a century ago [3]. It consists of two independent diamond-like nets with the 66-a topology, in which zinc provides the tetrahedral nodes and cyanide provides linear connections between nodes. These two equivalent but independent nets interpenetrate as shown in Figure 4, such that the nodes of one net are located at the centers of the... 

Another interesting case in crystal engineering is the one of interpenetrated cyano-bridged diamondoid networks. Zinc(II) easily adopts a tetrahedral geometry, so the solid-state structure of Zn(CN)2 is quite predictable tetrahedral zinc ions are connected by cyano groups generating a diamond-like net, with double interpenetration (Schemel). The cadmium derivative. 

Cd(CN)2, is isomorphous. To prevent the interpenetration, relatively large species must be hosted into the diamondoid network. Indeed, the mixed metal complex NMe4[Cu Zn CN)4] shows no interpenetration because the tetra-methylammonium cations, whose size fits to that of the adamantane-like cavity, occupy half of these cavities (both Cu and Zn ions are tetracoordinated). The interpenetration of neutral M(CN)2 nets (M = Zn, Cd) can be hindered by hosting neutral molecules, structurally similar to NMe4. The solution of this problem is obvious and elegant The crystallization of Cd(CN)2 in the presence of Me4C leads to a single diamond-like net. ... 

Figure 37. Schematic representation of the interpenetration of one NbO-like Bi604 net ( open connections) and two independent diamond-like (Ga Sh /s Og nets (one heavy die other fine ) in the structure of BisGaSbOn. Smaller circles represent the centers of (Ga b Oe clusters, larger circles represent the centers of Bi404 cube-like clusters.

---