Main group element nets to a T.

T-shaped nets (three-coordinated nets with an angular metric, bond angles near 90 degrees, 90 degrees, 180 degrees) are found in a number of extended structures. We explore in this paper the geometrical and electronic consequences of a stricter T-shape metric, where the distances between the vertices of the net are approximately equal and in the range of a chemical bond. Every atom in such a net has a T-shaped environment. One can think of these nets as extensions of BrF(3) or of substructures of various extended tellurium compounds. Several construction principles are found which allow an enumeration of a variety of one-, two-, and three-dimensional T-shape nets; not every three-coordinated net lends itself to the stricter geometrical and distance metric. Not everything is possible; there are no zero-dimensional T-nets, and none made entirely of three atom segments. Previous ideas on electron-rich multicenter bonding lead to a simple way of calculating the magic electron counts for each net; these lie in the range of 6 to 6.67.