Synthesis of Structurally Diverse Ferrimagnetically and Antiferromagnetically Coupled M^II–Mn^II (M = Cu, Ni) Heterometallic Schiff Base Compounds with a Dicyanamide Spacer and Study of Biomimetic Catalytic Activity

Abstract

The two heterometallic Schiff base compounds {[(CuL)­Mn­(N­(CN)2)2]·CH3CN}∞ (1) and [(NiL)4Mn2(N­(CN)2)2]­(ClO4)2 (2) have been synthesized using the N2O2 donor ligand 2,2′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)­bis­(azanylylidene))­bis­(methanylylidene))­diphenol (H2L) and a dicyanamide spacer. Single-crystal X-ray structural analyses reveal that compounds 1 and 2 have a one-dimensional zigzag polymeric structure and a discrete hexanuclear structure, respectively. Magnetic studies of 1 reveal the presence of intrachain ferrimagnetic coupling between Cu­(II) and Mn­(II) spins. Alternating interactions in an F–AF–F sequence (F, ferromagnetic; AF, antiferromagnetic) of 1 impose the ideal situation of noncompensation in spin moments considering intrachain magnetic interactions. On the other hand, an antiferromagnetic interaction between neighboring Mn­(II) ions is observed for 2. ESI-MS and EPR studies help to predict the solution-phase structures of the two compounds. Between them, 1 dissociates to form Cu­(II)–Mn­(III) species with three N­(CN)2 – and one CH3OH, making it catalytically active in mimicking the two well-known proteins phenoxazinone synthase and phosphatase. The calculated turnover numbers (k cat) for the aerial oxidation of o-aminophenol and hydrolysis of 4-nitrophenylphosphate (4-NPP) are 5129 h–1 and 25.052 s–1, respectively. However, in the solution state 2 behaves as a discrete structure, which causes its inability to catalyze reactions. A probable mechanistic pathway has been studied by using experimental tools such as ESI-mass spectra, cyclic voltammetry, and EPR measurements, suggesting the formation of an imine radical during the catalytic reaction of phenoxazinone synthase like activity.

Modulation of Nuclearity in CuII−MnII Complexes of a N2O2 Donor Ligand Depending upon Carboxylate Anions: Structures, Magnetic Properties and Catalytic Oxidase Activities

“…The other two complexes contain the usual linear tri‐nuclear [(CuL) 2 Mn] 2+ unit where the acetate (for 2 )/phenyl acetate (for 3 ) ligands occupy mutually trans orientation. The Cu II −O/Cu II −N/Mn II −O bond distances are in well agreement with those of previously reported Cu II −Mn II complexes of salicylaldimine ligand [3a,b,11a,c,14e,15b,23] …”

“…A CSD search reveals that quite a few hetero‐metallic Cu II −Mn II complexes have been synthesized by “metalloligand” synthetic strategy where the “metalloligand” [CuL] is prepared from N 2 O 2 donor symmetrically and asymmetrically di‐condensed tetradendate Schiff base ligands [3b,11a,c,14e,15b,23] . However, in all of them, the carbonyl group in the Schiff base ligand is salicyldehyde or its derivatives.…”

“…Excepting few di‐nuclear [(CuL)Mn] 2+ , [23a] and tetra‐nuclear [(CuL) 3 Mn] 2+[23b] species,most of these reported complexes are discrete tri‐nuclear [(CuL) 2 Mn] 2+ [3b,11c,15b,23a] . Besides, some complexes having repetitive [(CuL)Mn] 2+ /[(CuL) 2 Mn] 2+ units are also documented [3b,11a] . The geometry of the tri‐nuclear units are linear or angular depending upon the choice of anionic co‐ligands.…”

Syntheses, Characterization, and X-Ray Crystal Structure of a Co-Crystal Containing One Neutral Mononuclear Copper (II) Unit and One Cationic Dinuclear Copper (II) Unit Assembled with Schiff Base and Perchlorate Copper(II) Salt

“…Due to the bridging capacity of the phenoxo group, these ligands always show coordination capacity with both transition metal ions and lanthanide ions [17][18][19][20][21]. They can make it possible to obtain mononuclear which can be used as bricks to build other molecular buildings blocks [22][23][24]. Therefore, ligands with salicylaldimine moieties are effective for the construction of hetero-metallic complexes with d-block and f-block elements [25][26][27].…”

“…These ligands have also made it possible to prepare molecular species containing both s-block and d-or f-block elements [28][29][30]. Several compounds with magnetic [23,24], catalytic [31,32], and bioactivity [22] properties are listed in the literature. Our research group have already used salicylaldimine derivatives to prepare metalloligands and use them to prepare multinuclear complexes [29,30].…”