Zigzag chains linear chain compounds

The principal compounds in this category are the monochalacogenides, which are formed by all three metals. It is a notable indication of the stability of tetrahedral coordination for the elements of Group 12 that, of the 12 compounds of this type, only CdO, HgO and HgS adopt a structure other than wurtzite or zinc blende (both of which involve tetrahedral coordination of the cation — see below). CdO adopts the 6-coordinate rock-salt structure HgO features zigzag chains of almost linear O-Hg-0 units and HgS exists in both a zinc-blende form and in a rock-salt form. 

The presence and the number of double bonds. Crystallization of paraffinic compounds is difficult but occurs easiest if the chains can assume a linear zigzag conformation. A chain with a cis double bond cannot do this it tends to form a bend (see Figure 15.19b, SOS). This makes crystallization more difficult. The effect will be greater for more double bonds. Cf. the series SSS-OOO-LiLiLi-LnLnLn. 

From the reaction of Au with alkali metal polysulfide liquids, LiAuS and NaAuS were discovered. Both compounds contain infinite one-dimensional (AuS) chains, featuring alternating sulfide anions and linear coordinated Au centers. In LiAu8, the chains are zigzag and fully extended and they pack in mutually perpendicular sets. In NaAuS, the same chains coil in an unusual fashion so that they become interwoven to form layers reminiscent of chicken-wire (Figure 17). This novel coiling mode allows Au Au contacts to form, which help to stabilize the structure. 

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