Crystal packing in tetraphenylphosphonium salts of trithiocyanuric acid and its methanol solvate

Abstract

Trithiocyanuric acid (1,3,5-triazine-2,4,6(1H,3H,5H)-trithione, commonly known as 2,4,6-trimercaptotriazine TMTH₃) is a weakly acidic planar molecule with threefold symmetry, and, at the N and S atoms, it contains three hydrogen bond donors and three acceptors, respectively. For this reason it has been used previously for the formation of crystals containing 1- or 2-D hydrogen bonded nets. In this paper we describe and discuss aspects of the crystal packing of Ph₄P⁺ salts of TMTH₂⁻ and TMTH²⁻ (capable of forming coordination complexes). The crystals reported are (Ph₄P⁺)₂TMTH²⁻(H₂O)₃ 1, Ph₄P⁺TMTH₂⁻H₂O 2, and Ph₄P⁺TMTH₂⁻ 3, together with TMTH₃CH₃OH 4. Standard multiple phenyl embrace motifs between Ph₄P⁺ occur in 1 and 3 as zig-zag chains of sixfold edge-to-face interactions (EF)₆, resulting in channels containing 1-D tapes of fully hydrogen bonded TMTH₂⁻ molecules in 3, while in 1 the fewer TMTH²⁻ ions in the channels are separated by hydrogen bonded water molecules. In 2 there are corrugated sheets of TMTH₂⁻ which hydrogen bond in pairs linked by hydrogen bonded water molecules, without standard multiple phenyl embraces between Ph₄P⁺. Unsolvated crystals of TMTH₃ are not known, but the methanol solvate 4 contains a completely hydrogen bonded net in which 1-D tapes of TMTH₃ are linked by chains of CH₃OH.