New organically templated thiocyanatocadmates and chlorocuprate(ii): synthesis and structural characterization

Abstract

With various organic base molecules as the countercations, five new thiocyanatocadmates [H₂(tmen)][Cd(SCN)₄] (tmen = N,N,N′,N′-tetramethylethylenediamine) 1, [H₂(tmba)][Cd₂(SCN)₆] (tmba = N,N,N′,N′-tetramethyl-1,4-butanediamine) 2, [H₂(teen)][Cd₂(SCN)₆] (teen = N,N,N′,N′-tetra-ethylethylenediamine) 3, [H(amp)][Cd(SCN)₂(CH₃COO)] (amp = 2-amino-6-methylpyridine) 4 and [H(abp)]₄[Cd(SCN)₄]SO₄·H₂O (abp = 2-amino-6-bromopyridine) 5, and one new chlorocuprate(II) [H₂(cha)][CuCl₄] (cha = 1,4-cyclohexanediamine) 6 were obtained from a series of simple room-temperature self-assemblies at pH = 2 or 6.5. X-ray single-crystal diffraction analysis reveals that (i) templated by [(CH₃)₂NH(CH₂)₂NH(CH₃)₂]²⁺ (H₂(tmen)²⁺), the anion [Cd(SCN)₄]²⁻ in 1 shows a 1-D linear single-chain structure, whereas templated by [(CH₃)₂NH(CH₂)₄NH(CH₃)₂]²⁺ (H₂(tmba)²⁺), the anion [Cd₂(SCN)₆]²⁻ in 2 shows a 1-D linear double-chain structure. The number of C atoms between the two N atoms in the templating agent controls the width of the anionic chain through the N_amino–H⋯N_SCN interactions; (ii) templated by [(C₂H₅)₂NH(CH₂)₂NH(C₂H₅)₂]²⁺ (H₂(teen)²⁺), the anion [Cd₂(SCN)₆]²⁻ in 3 exhibits a 3-D open-framework structure, which is based on zigzag anionic chains. A direct change of the substituent group from –CH₃ to –C₂H₅ alters indirectly the shape of the anionic chain from a linear shape to a zigzag shape; (iii) 4 shows a 3-D supramolecular network structure, which is built up from the 1-D zigzag anionic structures by the H(amp)⁺ molecules via N–H⋯O interactions. The formation of the zigzag chain derives from the chelation of the CH₃COO⁻ groups to the Cd²⁺ centers; (iv) 5 is indeed a double salt of [H(abp)]₂[Cd(SCN)₄] and [H(abp)]₂SO₄. SO₄²⁻ and H(abp)⁺ form a supramolecular aggregation. Surrounded by the aggregations, the anion [Cd(SCN)₄]²⁻ only shows a dinuclear structure; and (v) templated by H₂(cha)²⁺, the anion [CuCl₄]²⁻ in 6 displays a 2-D perovskite layer structure. The photoluminescence analysis indicates that upon excitation (λ_ex = 335 nm for 4, λ_ex = 395 nm for 5), 4 and 5 emit light (λ_em = 365 nm for 4, λ_em = 470 nm for 5), which can be seen clearly under the UV lamp.