Influence of ionic liquids on the syntheses and structures of Mn(ii) coordination polymers based on multidentate N-heterocyclic aromatic ligands and bridging carboxylate ligands

Abstract

Seven Mn(II) coordination polymers, namely {[Mn₂(ptptp)Cl₂(H₂O)₃]·H₂O}_n (1), {[Mn(μ-ptptp)₃]₂[Mn₃(μ₃-Cl)]₂}·2Cl·16H₂O (2), {[Mn₂(ptptp)(ip)₂(H₂O)₃]·H₂O}_n (3), {[Mn₂(ptptp)(5-CH₃-ip)₂(H₂O)₃]·H₂O}_n (4), {[Mn₄(ptptp)(5-Br-ip)₃(H₂O)₃]·4H₂O}_n (5), {[Mn₂(ptptp)(Hbtc)(H₂O)₂]·2H₂O}_n (6) and {[Mn₂(ptptp)(tdc)(H₂O)₂]·1.5H₂O}_n (7), have been prepared based on multidentate N-heterocyclic aromatic ligands and bridging carboxylate ligands (H₂ptptp = 2-(5-{6-[5-(pyrazin-2-yl)-1H-1,2,4-triazol-3-yl]pyridin-2-yl}-1H-1,2,4-triazol-3-yl)pyrazine; R-isophthalic acids, H₂ip-R: R = –H (3), –CH₃ (4), –Br (5); H₃btc = trimesic acid (6); H₂tdc = thiophene-2,5-dicarboxylic acid (7)), in order to further probe the multiple roles of [RMI]Br ionic liquids in the hydro/solvothermal synthesis (RMI = 1-alkyl-3-methylimidazolium, R = ethyl, or propyl, or butyl). The successful syntheses of complexes 2–6 suggest that in hydro/solvothermal synthesis the addition of a small amount of [RMI]Br plays a crucial role. Complex 1 exhibits single right-handed helices constructed by ptptp ligands and Mn(II) ions. Complex 2 possesses octanuclear helicate structures in which two propeller-shaped [Mn(μ-ptptp)₃]⁴⁻ units embrace two [Mn₃(μ₃-Cl)]⁵⁺ cluster cores inside. Complexes 3 and 4 are isostructural and display a 1D double chain formed by two kinds of pseudo meso-helices: (Mn-ptptp)_n and (Mn-5-R-ip)_n. Complex 5 has a 2D structure containing 1D Mn(II) ion chains formed through carboxylates and [ptptp]²⁻-N,N bridges. Complex 6 shows a 2D structure formed by a meso-helix (Mn-ptptp)_n and the partly deprotonated Hbtc ligands. Complex 7 features a heterochiral [2 + 2] coaxially nested double-helical column formed by using the outer double-helices (Mn-ptptp)_n as a template to encapsulate the inner double-helices (Mn-tdc)_n with opposite orientation. All complexes were characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, single-crystal X-ray crystallography and powder X-ray diffraction. The magnetic properties of 1–7 were also investigated.