Designing Optical Anisotropy: Silver-Aminoalkylpyridine Nitrate Complexes with Tunable Structures

Abstract

To introduce a design strategy for improving optical properties, two silver-amino alkylpyridine nitrate complexes, AgC 6 H 8 N 3 O 3 and Ag 2 C 14 H 20 N 6 O 6 , were successfully synthesized using a recrystallization method. By employing polarizable π-conjugated [NO 3 − ] ions, two types of pyridine ligands, and silver cations with a high affinity for pyridine, we obtained a one-dimensional chain structure with 4-aminomethylpyridine (AgC 6 H 8 N 3 O 3 ) and a zero-dimensional molecular compound by introducing a relatively flexible aliphatic chain with 4-(2aminoethyl)pyridine (Ag 2 C 14 H 20 N 6 O 6 ). The compounds crystallize in the triclinic crystal system with the centrosymmetric P-1 space group, exhibiting a change in orientation between the π-conjugated system and the silver ion. Despite similar optical band gaps (3.69 eV for AgC 6 H 8 N 3 O 3 and 3.73 eV for Ag 2 C 14 H 20 N 6 O 6 ), AgC 6 H 8 N 3 O 3 shows higher absorption in the 350−600 nm range. Electronic structure calculations support the ultraviolet absorption findings, suggesting that charge transfer with π-conjugated systems influences birefringence. Ag 2 C 14 H 20 N 6 O 6 exhibits experimental birefringence (0.261@ 546.1 nm) surpassing that of AgC 6 H 8 N 3 O 3 (0.212@546.1 nm), placing it among the highest recorded values within metal-pyridine incorporating nitrate complexes. The nonconventional orientation of π-conjugated [NO 3 − ] ions contributes to this phenomenon, enhancing the action of free π-conjugated orbitals. This design strategy for micromodulating the alignment of the π-conjugated system promises to be an effective approach for enhancing optical properties, such as birefringence.