Polymorphism and photoluminescence in a naphthalene-based ligand, and its supramolecular structures through second-sphere coordination with the [CoCl4]2− anion

Abstract

A naphthalene-based ligand, N,N,N′,N′-tetrabenzyl-naphthalene-1,5-diamine (L1) has been synthesized and crystallized as two polymorphs, α and β. There are no strong hydrogen bonding donors, instead C–H⋯π interactions play critical roles in the stabilization of the structures of the two polymorphs with different packing motifs. The ligand L1 can be doubly protonated and coordinate with the “second-sphere” of [CoCl₄]²⁻ using N–H hydrogen bond donors to form two neutral supramolecular complexes [H₂L1]²⁺[CoCl₄]²⁻ (1) and EtOH ⊂ [H₂L1]²⁺[CoCl₄]²⁻ (2). L1 in 1 and 2 adopts the arrangement manner of stable polymorph α. The [CoCl₄]²⁻ anions are connected with L1 through N–H⋯Cl interactions, meanwhile, the anion [CoCl₄]²⁻ acting as an “off–on” switching template controls the photoluminescence.