Framework-structured weak ferromagnets are new rising stars in molecule-based magnetic materials. The framework structures are powerful carriers for long-range ordering of spins. And weak ferromagnetism due to spin canting is an effective approach for magnets because of its frequent occurrence and desired spontaneous magnetization as long as the canting angle γ is large enough. In this critical review, we provide an overview of the various framework-structured weak ferromagnets based on different grades of ligands (from mono-atom to three-atom-like ligands). Particular emphasis is given to the relationships between structural features and the properties, rational employment of the ligands, and weak ferromagnetic strategies for molecule-based magnets with exciting properties and applications (273 references).

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Two novel lanthanide-organic frameworks (LnOFs) with (4(10),6(5))(4(9),6(6)) topology, [Ln(Hbptc)(H(2)O)](n) (Ln = Eu(1), Gd(2); H(4)bptc = 3,3',4,4'-biphenyltetracarboxylic acid) were synthesized via the hydrothermal in situ reaction between lanthanide salts and 3,3',4,4'-biphenyltetracarboxylic dianhydride (bpta) under low pH conditions. In complexes 1 and 2, homohelix bundles with opposite chirality are assembled alternately and result in pillar-like 3D extended networks incorporated with coordinated water molecules, which show high thermal stability. The luminescence properties are illustrated by the Eu(III) complex (1) and its Gd-doped compound, which are intensive red emitters. The magnetic properties of complexes 1 and 2 are also investigated.

The synthesis and crystal structures of three new lanthanide–organic frameworks [Ln(pza)(OH)(H2O)]n (Ln = Y(1), Er(2), Yb(3); H2pza = 2,3‐pyrazinedicarboxylic acid) with helical chains and novel 2D (43)2(46,66,83) topology are reported. The topology is obtained by simplifying the dinuclear metal core as a six‐connected node and the ligand as a three‐connected linker. The upconversion property measurement gives green and red emissions coming from two‐photon excitation of Y: Er, Yb codoped coordination polymer and arising from ErIII transitions of 4S3/2/2H11/2→4I15/2 and 4F9/2→4I15/2. The magnetic properties of complexes 2 and 3 are also studied.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)