Magnetic Properties of the Distorted Kagomé Lattice Mn3(1,2,4-(O2C)3C6H3)2.

Kagomé lattice types have been of intense interest as idealized examples of extended frustrated spin systems. Here we demonstrate how the use of neutron diffraction and inelastic neutron scattering coupled with spin wave theory calculations can be used to elucidate the complex magnetic interactions of extended spin networks. We show that the magnetic properties of the coordination polymer Mn3(1,2,4-(O2C)3C6H3)2, a highly distorted kagomé lattice, have been erroneously characterized as a canted antiferromagnet in previous works. Our results demonstrate that, although the magnetic structure is ferrimagnetic, with a net magnetic moment, frustration persists in the system. We conclude by showing that the conventions of the Goodenough-Kanamori rules, which are often applied to similar magnetic exchange interactions, are not relevant in this case.

Pyridine-2,4-dicarboxylate: a versatile building block for the preparation of functional coordination polymers.

The hydrothermal reaction of the pyridine-2,4-dicarboxylate (2,4-pdc) dianion with various 3d metal(II) cations resulted in the formation of a series of one-, two- and three-dimensional coordination polymers with varied network topologies. 2,4-pdc reacted directly with MnCI2 or FeCl2 in water at 200 degrees C under mild basic conditions to give a dense three-dimensional polymer, [M(2,4-pdc)] (M = Mn, 1a; M = Fe, 1b), which supports a highly-connected three-dimensional magnetic exchange lattice. Both 1a and 1b undergo antiferromagnetic ordering and the latter Fe(II)-containing material exhibited spin-canting behavior below 6.5 K. Reaction of 2,4-pdc with CoCl2 under identical conditions gave an unusual zigzag chain polymer, [Co4(2,4-pdc)4(OH2)10] (2), that has large amounts of coordinated H2O. The magnetism of 2 based on isolated Co(II) dimers was modeled using a modified van Vleck approach. Adjustment of the reaction pH resulted in the formation of additional Co(II)-containing materials with strongly contrasting structures: at lower pH in the presence of oxalic acid, the same reaction components gave a protonated molecular species, [Co(2,4-pdcH)2(OH2)2]. 2H2O (3); at higher pH in the presence of excess hydroxide, a highly porous, three-dimensional material was obtained, [Co3(micro3-OH)2(2,4-pdc)2] x 9H2O (4a). 4a contains cobalt hydroxide chains, whose magnetic behavior has been studied in detail by neutron diffraction. A Ni(II)-containing analogue was also prepared using NiCI2 (4b), which shows weak antiferromagnetic coupling. Attempts to obtain a Zn(II)-based analogue of the porous material 4 gave instead a unique coordination material, [Zn(micro2-OH)2(2,4-pdc)] (5), which contains uncommon zinc hydroxide bridging modes.