Molecular squares, coordination polymers and mononuclear complexes supported by 2,4-dipyrazolyl-6H-1,3,5-triazine and 4,6-dipyrazolylpyrimidine ligands

Abstract

The Fe[BF₄]₂ complex of 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine (L¹) is a high-spin molecular square, [{Fe(L¹)}₄(μ-L¹)₄][BF₄]₈, whose crystals also contain the unusual HPzBF₃ (HPz = pyrazole) adduct. Three other 2,4-di(pyrazol-1-yl)-6H-1,3,5-triazine derivatives with different pyrazole substituents (L²–L⁴) are unstable in the presence of first row transition ions, but form mononuclear, polymeric or molecular square complexes with silver(I). Most of these compounds involve bis-bidentate di(pyrazolyl)triazine coordination, which is unusual for that class of ligand, and the molecular squares encapsulate one or two BF₄⁻, ClO₄⁻ or SbF₆⁻ ions through combinations of anion⋯π, Ag⋯X and/or C–H⋯X (X = O or F) interactions. Treatment of Fe[NCS]₂ or Fe[NCSe]₂ with 4,6-di(pyrazol-1-yl)-2H-pyrimidine (L⁵) or its 2-methyl and 2-amino derivatives (L⁶ and L⁷) yields mononuclear [Fe(NCE)₂L₂] and/or the 1D coordination polymers catena-[Fe(NCE)₂(μ-L)] (E = S or Se, L = L⁵–L⁷). Alcohol solvates of isomorphous [Fe(NCS)₂L₂] and [Fe(NCSe)₂L₂] compounds show different patterns of intermolecular hydrogen bonding, reflecting the acceptor properties of the anion ligands. These iron compounds are all high-spin, although annealing solvated crystals of [Fe(NCSe)₂(L⁵)₂] affords a new phase exhibiting an abrupt, low-temperature spin transition. Catena-[Fe(H₂O)₂(μ-L⁵)][ClO₄]₂ is a coordination polymer of alternating cis and trans iron centres.