Mn(ii) complexes of different nuclearity: synthesis, characterization and catecholase-like activityElectronic supplementary information (ESI) available. CCDC 1425706-1425708. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5dt03659c

Two "end-off" compartmental ligands, 2-formyl-4-chloro-6- N -ethylmorpholine-iminomethyl-phenol (HL1) and 2-formyl-4-methyl-6- N -ethylpyrrolidine-iminomethyl-phenol (HL2) have been designed and three complexes of Mn( ii ), one mono-, one di- and a polynuclear, namely Mn(L1)(SCN) 2 (H 2 O)] ( 1 ), [Mn 2 (L1)(OAc) 2 ](BPh 4 )] ( 2 ), and [Mn 2 (L2)(OAc) 2 (dca)] n ( 3 ) have been synthesized and structurally characterized. Variable temperature magnetic studies of 2 and 3 have been performed and data analyses reveal that Mn centers are antiferromagnetic coupled with J = −9.15 cm −1 and J = −46.89, respectively. Catecholase activity of all the complexes has been investigated using 3,5-di- tert -butyl catechol (3,5-DTBC). All are highly active and the activity order on the basis of the k cat value is 2 > 1 > 3 . In order to unveil whether the metal centered redox participation or the radical pathway is responsible for the catecholase-like activity of the complexes, detailed EPR and cyclic voltammetric (CV) studies have been performed. In addition to the six-line EPR spectrum characteristic to Mn( ii ), an additional peak at g ∼ 2 is observed when the EPR study is done with the mixture of 3,5-DTBC and the catalyst, suggesting the formation of an organic radical, most likely ligand centered. The CV experiment with the mixture of 3,5-DTBC and the catalyst reveals ligand centered reduction rather than reduction of Mn( ii ) to Mn( i ). It is thus inferred that complexes 1-3 show catecholase-like activity due to radical generation. The origin of catecholase-like activity of Mn( ii )-Schiff-base complexes has been explored by studying structurally characterized mono-, di- and polynuclear Mn( ii ) complexes of two "end-off" compartmental Schiff-base ligands.