Abstract
Charged molecular alloys and Zintl ions are of interest in synthetic chemistry. However, their chemical bonding has seldom been elucidated using modern quantum chemistry tools. Herein, we report on in-depth chemical bonding analyses for a charged molecular alloy C (2) [P(7)ZnP(7)](4-) cluster and its relevant Zintl ion C (3v) [P(7)](3-) ligand, making use of electronic structure calculations at PBE0/def2-TZVP level, natural bond orbital and orbital composition analyses, canonical molecular orbitals, and adaptive natural density partitioning (AdNDP). The computational data show that C (3v) [P(7)](3-) Zintl ion has three isolated, negatively charged, bridging P sites. Such charges are largely P 3p lone-pairs in nature, but they also participate in secondary P-P bonding along the bridging sites. C (2) [P(7)ZnP(7)](4-) cluster is formulated as [P(7)](2-)[Zn](0)[P(7)](2-), in which [P(7)](2-) ligands maintain the structural and bonding integrity of [P(7)](3-) Zintl ion despite their difference in charge state. Two [P(7)](2-) ligands collectively bind with Zn center via four bridging P sites, resulting in a quasi-tetrahedral ZnP(4) core with the eight-electron counting. This bonding picture can alternatively be rationalized using the superatom concept. The Zn-P bonds are weak with a bond order of around 0.5, because the P centers have partial nonbonding 3p character, akin to 3p(2) lone-pairs albeit with a lower occupation number.