Structurally diverse manganese(III) complexes of tetradentate N₂O₂ Schiff-base ligands with ancillary carboxylate donors 

Abstract

A number of manganese(III) complexes of tetradentate N₂O₂ Schiff-base ligands have been prepared with various additional carboxylate anions. Five of these compounds have been crystallographically characterised revealing that a remarkable array of structural chemistry is available. A polymeric species is observed for [{Mn(saltn)(O₂CEt)}_n] 1, whereas a monomeric species is found in [Mn(saltn)(O₂CBu^t)] 2 [H₂saltn = N,N′-bis (salicylidene)trimethylenediamine]. The anti-anti bridging of the manganese centres in 1 is in contrast to that in [{Mn(bsaltn)(O₂CCH₂Ph)}_2n ] 3 (H₂bsaltn = 5-bromo derivative of H₂saltn), which exhibits rare syn-anti bridging; 3 also contains a dimeric repeat unit due to an alternate 180° twist in the polymeric chain necessitated by steric constraints. In contrast, the complexes containing the dianion of N,N′-bis(3-methoxysalicylidene)ethane-1,2- diamine (H₂msalen) appear to be isostructural, [{Mn(msalen)(O₂CEt)}₂]·EtOH 4 and [{Mn(msalen)(O₂CBuⁿ)}₂] 5 being structurally characterised as essentially identical phenoxy-bridged dimers. An insoluble material of stoichiometry Mn₄(O₂CR)₃(saltn)₃(H₂ O)_n (n = 0–3) was isolated from all reactions involving the saltn ligand; attempts to characterise these compounds by X-ray diffraction have been unsuccessful. However, the previously characterised manganese(IV) dimer [{Mn(saltn)O}₂]·2dmf 6 (dmf = dimethylformamide) and the monomeric species [Mn(saltn)(O₂CEt)] 7 were isolated in attempts to crystallise these materials.

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