These species wind in a helix around E·M·A·Cs, which are some of the simplest molecular wires. Instances of these species like BDC and imidazolates serve as “linkers” between secondary building units in a class of polymers exemplified by HKUST-1. Based on whether they donate 0, 1, or 2 electrons, these species are classified as L, Z, or X-type, (15[1])which determines their contribution to the 18-electron rule. Inner-sphere electron transfer requires a ■END■