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

Abstract

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 H4pmida) 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 M2þ ¼ Mn2þ, Co2þ or Cd2þ) via the hydrothermal synthetic approach, which were then employed for the construction of [CdVO(pmida)(4,4#-bpy)(H2O)2]$(4,4#-bpy)0.5$(H2O), [CoVO(pmida)(4,4#-bpy)(H2O)2]$(4,4#-bpy)0.5, [Co(H2O)6][CoV2O2(pmida)2(pyr)(H2O)2]$2(H2O) and [Cd2V2O2(pmida)2(pyr)2(H2O)4]$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 V4þ 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, [Ge2(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.