• ‘Ionic crystals’ consisting of trinuclear macrocations and polyoxometalate anions exhibiting single crystal to single crystal transformation: breathing of crystals

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    • Keywords

       

      Iron and chromium basic carboxylates; silicotungstate Keggin cluster anion; ion pairing into ionic crystals; single crystal to single crystal transformations; dehydration; rehydration.

    • Abstract

       

      Ion pairing of trinuclear macrocation cluster (known as basic carboxylate), [M ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ¹⁺ and a Keggin type polyoxometalate cluster anion [SiW ₁₂O₄₀] ⁴⁻ is stabilized with a number of crystal water molecules in composite type compounds [M ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄[SiW ₁₂O₄₀] ·xH ₂O · 2ClCH ₂COOH [M = Fe ³⁺, x = 18(1); M = Cr ³⁺x = 14(2)]. When the crystals of 1 are heated at 85◦C and 135◦C for 3.5 hours in an open atmospheric condition, it goes to [Fe ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] ·10H ₂O ·2ClCH ₂COOH (dehydrated 1-85o ≡ 1'), and [Fe ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] · 8H ₂O · 2ClCH ₂COOH (dehydrated 1-135o ≡ 1'') respectively with the loss of considerable amount of lattice water molecules retaining their single crystallinity. On the other hand, the single crystals of compound 2, upon heating at 85◦C or 135◦C for 3.5 hours, undergo ‘crystal-to-crystal transformation’ to the single crystals of [Cr ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW₁₂O₄₀]·8H₂O·2ClCH ₂COOH (dehydrated 2 ≡ 2'). Crystal structure analyses show that the parent compounds 1 and 2 undergo molecular rearrangement (molecular motion in the solid state) in respective dehydrated compounds. Remarkably, these dehydrated crystals (1', 1'' and 2'), upon exposure to water vapor at an ambient condition, regenerate the crystals of parent compounds 1 and 2, respectively

    • Author Affiliations

       

      T ARUMUGANATHAN1 ASHA SIDDIKHA2 SAMAR K DAS2

      1. Department of Chemistry, Thiagarajar College, Madurai 625 009, Tamilnadu, India
      2. School of Chemistry, University of Hyderabad, Hyderabad, Telangana 500 046, India
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