To improve these rules, experiments have begun to identify the metals that can be adjacent to an electride electron. So far, only Ca , Sr , Ba , Y , Hf , and Gd have been incorporated next to the electride site (Figure ), while Sc and several of the lanthanide series have been identified as candidates computationally . This delicate balance between electron counting and electronegativity was recently explored in the case of Ca5Pb3 (not an electride) and Ca3Hf2Pb3 (an electride), as replacing calcium for hafnium makes the compound electron rich . Despite these findings, the limit of cation electronegativity in the formation of electrides is not yet known. Therefore, to develop improved design rules for electrides and for their structure-property relationships, we explore the trivalent metal carbides with a layered structure. This family is informative because Y2C is a known electride , Sc2C has been predicted , and Al2C is unknown, and further, these metals vary systematically in electronegativity (Figure ).