Guanidinium sulfates as directors of noncentrosymmetric structures

Abstract

The structures of seven compounds based on guanidinium cations, isolated sulfate anions, and additional organic cations and solvent molecules are reported. All seven compounds, (C(NH₂)₃)₂(SO₄) (1), (C(NH₂)₃)₃(C₅H₆N)(SO₄)₂ (2), (C(NH₂)₃)₃(C₅H₆N)(SO₄)₂·H₂O (3), (C(NH₂)₃)₃(C₅H₆N)(SO₄)₂·CH₃OH (4), (C(NH₂)₃)₁₁(C₅H₆N)(SO₄)₆·2.5C₂H₅OH (5), (C(NH₂)₃)₃(C₆H₁₆N)(SO₄)₂ (6), and (C(NH₂)₃)₂(C₂₀H₂₆N₂O₂)(SO₄)₂ (7) crystallize without a center of symmetry, and are built of related motifs of six-membered rings via hydrogen bonding of three guanidinium cations and three sulfate anions. These six-membered rings form extended sheets and frameworks through additional hydrogen bonding interactions. The presence of additional cations and solvent molecules in varying ratios add structural diversity by modifying the guanidinium sulfate frameworks, but retaining the acentricity of the structures. The study reveals a remarkable tendency for these guanidinium sulfate frameworks to crystallize without a center of symmetry, and furthermore, in polar or chiral space groups. This provides a potential pathway for the use of hydrogen bonding interactions to design structures having interesting physical or nonlinear optical properties.