Structural variety of 5-fluoroarene-2-aminopyrimidine in comparison to 2-aminopyrimidine silver(i) coordination polymers: progress report and overview

Abstract

A variety of fluoroarene-2-aminopyrimidine (FAP) silver(I) coordination polymers (CPs) has been synthesized based on newly synthesized FAP derivatives, namely 5-(p-methoxytetrafluorophenyl)-2-aminopyrimidine (OFAP) and 5-(p-dimethylaminotetrafluorophenyl)-2-aminopyrimidine (NFAP), and different counterions (OTf⁻, TFA⁻, ClO₄⁻, NO₃⁻). Their solid-state assembly as well as optical properties in terms of luminescence and infrared (IR) spectroscopy were investigated. Out of the several structures described herein, we obtained isomorphic CPs to previous studies (5, 9), a CP architecture with a short Ag–Ag distance (8, 3.049 Å), but also polymorphic crystals of [Ag(nfap)NO₃]_n (11a, 11b) and the latter showed differences in color and luminescence emission. Polymorphism gives an unparalleled possibility to investigate the origin of such phenomena since luminescence emission is quite often observed for these silver-hybrid solid-state materials and in several cases Ag⋯Ag interactions are attributed for this phenomenon. We show that this explanation does not necessarily have to be the only one. Therefore we focus also on structural relationships and differences in a comprehensive comparison of our own and other known systems to start a more systematic description of the rich coordination capabilities of FAP and congeneric 2-aminopyrimidine (2-AP) based silver(I) coordination polymers and networks. Density functional theory (DFT) calculations with periodic boundary conditions based on a plane wave basis are used to better understand the electronic structure of these crystalline materials. To complete the picture, steady-state spectroscopy studies (UV-Vis, fluorescence, IR) on all ligands and 2-AP itself were conducted as well as re-examination of the first reported CP of 2-AP and Ag^I under the above aspects.