Insight into self-assembly of malonate-based copper(II) phenanthroline complexes: Syntheses, crystal structures and properties

Abstract

One-pot reactions of Cu(ClO4)2·6H2O, phenanthroline (phen), malonic acid (H2mal) and NaOH in molar ratio 1:1:1:2 (mmol) in 40mL H2O/MeOH afforded two novel complexes [Cu2(phen)2(H2O)3(mal)(ClO4)](ClO4) ([4]ClO4) and [Cu6(phen)6(H2O)2(mal)4(ClO4)2](ClO4)2 ([5](ClO4)2) besides three known complexes [Cu(phen)2(H2O)](ClO4)2 ([1](ClO4)2), [Cu(phen)(H2O)(mal)]·1.5H2O ([2]·1.5H2O) and [Cu3(phen)3(H2O)2(mal)3]·11H2O ([3]·11H2O). Complexes [2]·1.5H2O, [3]·11H2O, [4]ClO4 and [5](ClO4)2 commonly have a basic building motif of a general formulation [Cu(phen)(mal)X]n with the Cu square-pyramidally coordinated by phen molecule, (mal−) anion and an apical X group (X=H2O, ClO4−, [Cu(phen)(H2O)(mal)], n=0, +1). [3]·11H2O is built up of the hydrogen-bonded [Cu3(phen)3(H2O)2(mal)3] trimers and (H2O)11 clusters, while [4]ClO4 and [5](ClO4)2 feature 1D 1∞ {[Cu2(phen)2(H2O)3(mal)](ClO4)2/2}+ chain and hexanuclear [Cu6(phen)6(H2O)2(mal)4(ClO4)2]2+ complex cations, respectively. Self-assembly routes to the malonate-based Cu(II) phenanthroline complexes were well established on the basis of the [Cu(phen)(H2O)(mal)] complex molecule. Both acentric polar complexes [3]·11H2O and [4]ClO4 represent the first two examples of metal malonato complexes with ferroelectric property with a remnant polarization (Pr) of ca. 0.045 and 0.2002μCcm−2, coercive field (Ec) of ca. 0.70 and 1.79kVcm−1, and saturation of the spontaneous polarization (Ps) at ca. 0.39 and 0.248μCcm−2, respectively. The magnetic properties of [4]ClO4 and [5](ClO4)2 follow Curie–Weiss law χm=C/(T−Θ) with the Curie constant C=0.480(2), 0.587(7)cm3mol−1K and Weiss constant Θ=0.32(1), 0.61(2)K, respectively. The weak ferromagnetic behaviors can be well analyzed using dinuclear Cu2 and V-shaped trinuclear Cu3 models, respectively, and best-fittings gives J=6.2(6)cm1 for equatorial–equatorial syn–anti μ-COO groups.