On the Nature of Bonding in Synthetic Charged MolecularAlloy P7ZnP74– Cluster andIts Relevant P73– Zintl Ion

摘要

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 C2 [P7ZnP7]^4– cluster and its relevant Zintl ion C3v [P7]^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 C3v [P7]^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. C2 [P7ZnP7]^4– cluster is formulated as [P7]^2–[Zn]⁰[P7]^2–, in which [P7]^2– ligands maintain the structural and bonding integrity of [P7]^3– Zintl ion despite their difference in charge state. Two [P7]^2– ligands collectively bind with Zn center via four bridging P sites, resulting in a quasi-tetrahedral ZnP4 core with the eight-electron counting. This bondingpicture can alternatively be rationalized using the superatom concept.The Zn–P bonds are weak with a bond order of around 0.5, becausethe P centers have partial nonbonding 3p character, akin to 3p² lone-pairs albeit with a lower occupation number.