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, which determines their contribution to the 18-electron rule. Inner-sphere electron transfer requires a (*) "bridging" one of these species. Donation to the antibonding pi orbitals of these species contributes to the splitting energy of their strong-field examples at the end of the spectrochemical series. Multidentate examples of these species (10[3]-5[1])can act as chelating (10[1])agents for toxic metals. For 10 points, name these species that bond to the metal center in a coordination complex. ■END■ (10[1])