Controlling the structure of manganese(II) phosphates by the choice and ratio of organophosphate and auxiliary ligands

Abstract

Tetranuclear manganese(II) phosphates [Mn(dipp)(bpy)]₄·4H₂O (1) and [Mn₄(dmpp)₂(dmppH)₄(bpy)₄(H₂O)₂]·H₂O (2) have been prepared from Mn(OAc)₂·4H₂O and 2,6-diisopropylphenyl phosphate (dippH₂) or 2,6-dimethylphenyl phosphate (dmppH₂) in the presence of 2,2'-bipyridine (bpy). In contrast, the reaction between [Mn(bpy)₂(OAc)(ClO₄)]·H₂O and dippH₂ affords [Mn(bpy)₂(dippH)]₂·2ClO₄·2CH₃OH (3). The reactions of Mn(OAc)₂·4H₂O, dippH₂, and pyridine (py) or 3,5-dimethylpyrazole (dmpz) in CH₃CN under reflux afford hexanuclear complexes [Mn₆(dipp)₆(py)₈]·2CH₃CN (4) and [Mn₆(dipp)₆(dmpz)₆(AcOH)₂]·2H₂O (5), respectively. Although compounds 1 and 2 are tetrameric, the former is a closed cubane-like structure resembling the D4R secondary building unit of zeolites, whereas the latter exists in a staircase structure with fused Mn₂O₄P₂ rings. The core structure of 3 contains a Mn₂O₄P₂ eight-membered ring that resembles the S4R building block of zeolites. Single-crystal X-ray diffraction studies reveal that compounds 4 and 5 have a similar core structure and differ from each other by the neutral ligands coordinated to manganese ions. All six phosphate ligands exist in a doubly deprotonated [(RO)PO₃^2-] form and exhibit two types of binding modes [5.222] and [3.111]. An interesting feature of compounds 1-5 is that although they are oligonuclear complexes, there is an absence of oxido bridges. The magnetic properties of compounds 1-5 have been investigated in the temperature range 5-298 K, and it was found that all the compounds obey the Curie law.