Construction of supramolecular assembly frameworks based on salamo-type polynuclear Cu(II) polymer and dimer utilizing secondary bonds

Abstract

Using the advantages of the salamo structure, we successfully constructed a coordination polymer [Cu2(L)]n(ClO4)n (CP) and a coordination dimer [Cu4(L)2(EtOH)2](NO3)2 (CD). The CP has primary building unit [Cu2(L)], which contains a fully deprotonated part (L)3− and two Cu(II) ions. These units are infinitely connected by Cu-O coordination bonds to form a 1-D chain-like secondary building unit [Cu2(L)]n. The CD has primary building unit [Cu2(L)(EtOH)], which contains a fully deprotonated part (L)3−, two Cu(II) ions, and a coordinated ethanol molecule. Two primary building units are connected by Cu-O coordination bonds to form a dimer, which serves as the secondary building unit [Cu4(L)2(EtOH)2]. Both the CP and CD are stabilized through the formation of Cu-O coordination bonds and π···π interactions. Additionally, secondary bonds are used to form supramolecular assembly frameworks (SAFs). Reaction sites and secondary bonds were further analyzed and discussed through theoretical calculations including molecular orbitals (MO), molecular electrostatic potentials (MEPs), Hirshfeld surfaces (HS), Interaction Region Indicators (IRI), Localized Orbital Locator (LOL), and Electron Localization Function (ELF).