Hydrothermal synthesis of divalent metal pyromellitate/dipyridylamine complexes: From an unprecedented supramolecular three-dimensional topology to an anionic coordination polymer framework with large incipient cation-bearing voids

Abstract

Hydrothermal synthesis has afforded two divalent metal coordination complexes incorporating both fully deprotonated pyromellitate (pyro) anions and the kinked dipodal organodiimine 4,4′-dipyridylamine (dpa), {[Co(H₂O)₄(Hdpa)₂][pyro]} (1) and {[H₂dpa][Zn(pyro)]·2H₂O} (2). Both new complexes were characterized by single crystal X-ray diffraction and spectral and thermogravimetric analyses. Complex 1 possesses discrete [Co(H₂O)₄(Hdpa)₂]⁴⁺ cations linked into supramolecular 2-D (4,4) rhomboid grid layer motifs by hydrogen bonding between the unligated pyro anions and the aquo ligands. The pendant, monodentate Hdpa⁺ cations also engage in charge-separated hydrogen bonding to pyro anions in neighboring layers, resulting in a supramolecular 3-D structure with an unprecedented 6-connected 4⁴6¹⁰8 topology. In contrast, 2 is a true coordination polymer, with divalent Zn atoms linked by ligated pyro anions into a binodal 4-connected PtS-type anionic network (4²8⁴ topology), which encapsulates H₂dpa²⁺ cations and unligated water molecules within large incipient pores coursing through the structure. Irradiation of a solid sample of 2 with ultraviolet light resulted in blue-light emission, likely indicative of π–π* transitions within the orbital manifolds of both the pyro anions and unligated H₂dpa²⁺ cations.