(Ferrocenylmethyl)trialkyl ammoniums as template cations in optically active two-dimensional oxalate bridged [Cr–Mn] and [Cr–Ni] molecule-based magnets: synthesis and magnetic properties

A series of (ferrocenylmethyl)trialkyl ammoniums: FcCH2NR3+ with R=CH3 (1), C2H5 (2), n-C3H7 (3), n-C4H9 (4) (X-ray structure provided), n-C5H11 (5) and the planar chiral 1,2-disubstituted Fc(CH3)CH2NBu3+ (6) have been tentatively used as template cation in order to synthesise bidimensional (2D) oxalate bridged molecule-based magnets of general formula {[CrIIIMII(ox)3][FcCH2NR3]}n and{[CrIIIMII(ox)3][Fc(CH3)CH2NBu3]}n (M=Mn2+, Ni2+, ox=C2O42−). These polymeric compounds were obtained only for reactions performed with 2, 3, 4 and 6. Starting from resolved Cr(ox)32−, the networks were prepared in their two enantiomeric forms in the case of {[CrIIINiII(ox)3][FcCH2NBu3]}n ([CrΔ–NiΛ]-4 and [CrΛ–NiΔ]-4) or {[CrIIIMnII(ox)3][FcCH2NBu3]}n ([CrΔ–MnΛ]-4 and [CrΛ–MnΔ]-4)) and characterised by circular dichroism measurements. All these compounds are ferromagnets with a Curie temperature close to 6 K when M=Mn and to 17 K for Ni. While the manganese [Cr–Mn] containing compounds are soft magnets, the [Cr–Ni] networks show coercive force up to 2200 Oe far above those previously reported for these networks.