(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: FcCH(2)NR(3)(+) with R = CH3 (1), C2H5 (2), n-C3H7 (3), n-C4H9 (4) (X-ray structure provided), n-C5H 11 (5) and the planar chiral 1,2-disubstituted Fc(CH3)CH2NBu3+ (6) have bee n tentatively used as template cation in order to synthesise bidimensional (2D) oxalate bridged molecule-based magnets of general formula {[(CrMII)-M- III(ox)(3)][FcCH(2)NR(3)]}(n) and {[(CrMII)-M-III(ox)(3)][Fc(CH3)CH2NBu3]}( n) (M = Mn2+, Ni2+, ox = C2O42-). These polymeric compounds were obtained o nly for reactions performed with 2, 3, 4 and 6. Starting from resolved Cr(o x)'-, the networks were prepared in their two enantiomeric forms in the cas e of ([(CrNiII)-Ni-III(ox)(3)][FcCH(2)NBu(3)])(n) ([Cr-Delta-Ni-Lambda]-4 a nd [Cr-Lambda-Ni-Delta]-4) or {[(CrMnII)-Mn-III(ox)(3)][FcCH(2)NBu(3)]}(n) ([Cr-Lambda-Mn-Delta]-4 and [Cr-Lambda-Mn-Delta]-4)) and characterised by c ircular 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 m anganese [Cr-Mn] containing compounds are soft magnets, the [Cr-Ni] network s show coercive force up to 2200 Oe far above those previously reported for these networks. (C) 2001 Elsevier Science B.V. All rights reserved.