Optimised hydrothermal synthesis of multi-dimensional hybrid coordination polymers containing flexible organic ligands

In this paper, we summarise our recent research interest in the hydrothermal synthesis and structural characterisation of multi-dimensional coordination polymers. The use of N-(phosphonomethyl)iminodiacetic acid (also referred to as H(4)pmida) in the literature as a versatile chelating organic ligand is briefly reviewed. This molecule plays an important role in the formation of centrosymmetric dimeric [V2O2(pmida)(2)](4-) anionic units, which were first used by us as building blocks to construct novel coordination polymers. Starting with [V2O2(pmida)(2)](4-) in solution, we have isolated [M2V2O2(pmida)(2) (H2O)(10)] species (where M2+ = Mn2+, Co2+ or Cd2+) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4'-bpy)(H2O)(2)]center dot(4,4'-bPY)(0.5)center dot(H2O), [CoVO(pmida)(4,4'-bpy)(H2O)(2)]center dot(4,4'-bpy)(0.5), [Co(H2O)(6)]CoV2O2(pmida)(2)(pyr)(H2O)(2)]center dot 2(H2O) and [Cd2V2O2(pmida)(2)(pyr)(2)(H2O)(4)]center dot 4(H2O) by the inclusion of bridging organic ligands in the reactive mixtures, such as pyrazine (pyr) and 4,4'-bipyridine (4,4'-bpy). These materials can contain channel systems, and exhibit magnetic behaviour, not only due to the V4+ centres but also to the transition metal centres which establish the links between neighbouring dimeric [V2O2(pmida)(2)](4-) anionic units. A closely related anionic moiety, [Ge-2(pmida)(2)(OH)(2)](2-), was engineered to allow the study of such crystalline hybrid materials using one- and two-dimensional high-resolution solid-state NMR. (C) 2005 Elsevier Ltd. All rights reserved.