a complex network is formed with coordination
number 4 for the Be atom (see Figure 3-7). BeC12 tends to dimerize to a 3-coordinate
structure in the vapor phase, but the linear monomer is also known at high
temperatures. The monomeric structure is unstable; in the dimer and polymer, the halogen
atoms share lone pairs with the Be atom and bring it closer to the octet structure.
The monomer is still frequently drawn as a singly bonded structure with only four electrons
around the beiyllium and the ability to accept more from lone pairs of other molecules
(Lewis acid behavior, discussed in Chapter 6).