Trinuclear heterometallic CuII-MnII complexes of a salen type Schiff base ligand: anion dependent variation of phenoxido bridging angles and magnetic coupling

Five new trinuclear heterometallic CuII-MnII complexes [(CuL)2Mn(O2CPh)2] (1), [(CuL)2Mn(N3)2] (2), [(CuL)2Mn(NCO)2] (3), [(CuL)2Mn(NO3)2] (4) and [(CuL)2Mn(Sal)2]∙CH2Cl2 (5) have been synthesized with the di-Schiff base ligand H2L (where, H2L= N,N'-bis(salicylidene)-1,3-propanediamine and Sal= salicylate). These complexes with different anionic co-ligands have been synthesized to attain a large variation in phenoxido bridging angles and to investigate its consequence on magnetic properties. Single crystal X-ray diffraction analyses reveal that complexes 1, 2, 4 and 5 are linear, whereas 3 has an angular geometry. Variable temperature magnetic susceptibility measurements suggest that all five complexes possess an overall antiferromagnetic interaction between CuII and MnII ions, which results in a final ferrimagnetic ground state with spin 3/2 in the CuII-MnII-CuII trinuclear structure. The weakest antiferromagnetic interaction (JCu-Mn= -7.0 cm-1) is observed for 2 having the lowest value of the Cu-O-Mn angle (92.0°), while the strongest antiferromagnetic interaction (JCu-Mn= -26.5 cm-1) is observed for 3 having the largest Cu-O-Mn angle (101.4°). Complexes 1, 4 and 5 show an average Cu-O-Mn angles of 98.2°, 97.6° and 97.7°, respectively, that lead to intermediate antiferromagnetic interactions (JCu-Mn = -9.6, -9.7, -9.3 cm-1 respectively)

Ferro- to antiferromagnetic crossover angle in diphenoxido- and carboxylato-bridged trinuclear Ni(II)2-Mn(II) complexes: experimental observations and theoretical rationalization

Three new trinuclear heterometallic NiII-MnII complexes have been synthesized using [NiL] metalloligand where H2L = N,N′- bis(salicylidene)-1,3-propanediamine. The complexes [(NiL)4Mn2(OCn)4(CH3OH)4]·2CH3OH (1), [(NiL)4Mn2(OPh)4(CH3OH)2]·H2O (2) and [(NiL)4Mn(OSal)2(CH3OH)2] (3) (where OCn = cinnamate, OPh = phenylacetate, OSal= salicylate) have been structurally characterized. In all three complexes, in addition to the double phenoxido bridge, the two terminal NiII atoms are linked to the central MnII by means of syn-syn bridging carboxylate, giving rise to a linear structure. Complexes 1 and 2 with Ni-O-Mn angle of 97.24 and 96.43° respectively exhibit ferromagnetic interactions ( JNi-Mn = +1.38 and +0.50 cm-1 respectively) whereas 3 is antiferromagnetic (JNi-Mn= -0.24 cm-1) having Ni-O-Mn angle of 98.51°. DFT calculations indicate that there is a clear magneto-structural correlation between Ni-O-Mn angle and JNi-Mn values which is in agreement with the experimental results

Antiferro- to ferromagnetic crossover in diphenoxido bridged (Ni2MnII)-Mn-II complexes derived from N2O2 donor Schiff base ligands

Three new trinuclear Ni-II-Mn-II complexes have been synthesized using three different 'metalloligands' [NiL1], [NiL2] and [NiL3] derived from the Schiff bases H2L1 = N,N'-bis(salicylidene)-1,3-pentanediamine, H2L2 = N,N'-bis(salicylidene)-1,3-propanediamine and H2L3 = N,N'-bis(salicylidene)-1,3,-diaminopropan-2-ol), respectively. In all three complexes, [(NiL1)(2)Mn(OOCPh)(2)(H2O)(2)]center dot CH3OH (1), [(NiL2)(2)Mn(OOCPh)(2)(CH3OH)(2)]center dot CH3OH (2) and [(NiL3)(2)Mn(OOCPh)(2)(H2O)(2)]center dot CH3OH (3), in addition to the double phenoxido bridge, the two terminal Ni-II atoms are linked to the central Mn-II by means of a syn-syn bridging benzoate, giving rise to a linear structure. Complex 1 with Ni-O-Mn angle of 97.35 degrees exhibits antiferromagnetic interactions (J(Ni-Mn) = -0.60 cm(-1)) whereas ferromagnetic exchange is observed in 2 and 3 (J(Ni-Mn) = +2.00 and +1.10 cm(-1) respectively) having Ni-O-Mn angle 97.34 degrees (in 2), 97.27 degrees (in 3). Theoretical calculations have been performed in order to understand the effect of structural parameters that can tune the magnetic properties of this type of complexes such as small differences in the Ni-O-Mn angle and/or slight variations in intermolecular contacts within the crystal. (C) 2016 Elsevier Ltd. All rights reserved

Tuning of exchange coupling by the Mn–O distance and phenoxido bridging angle: an experimental and theoretical study of the family of Mn(iii) dimers with salen type ligands

Three new Mn(III) complexes [Mn₂L₂(ClO₄)₂] (1), [Mn₂L₂(NCS)₂] (2) and [Mn₂L₂N(CN)₂]ClO₄•CH₃CN (3) have been synthesized from the Schiff base ligand H₂L (where H₂L = N,N′-bis(2-hydroxypropiophenone)-1,2- ethanediamine) and various anionic coligands e.g. perchlorate, thiocyanate and dicyanamide. X-ray crystal structure analysis reveals that 1 and 2 are dinuclear complexes, joined together by Mn⋯O (phenoxido) interactions. Whereas 3 consists of an alternating phenoxido and μ_1,5 dicyanamido bridge, resulting in a 1D chain. In 1 and 2 ferromagnetic coupling exists between the Mn(III) centres within the dimer but 3 possesses antiferromagnetic interaction. This difference in magnetic exchange interactions has been rationalized on the basis of structural parameters like longer bridging Mn–O distance and Mn–O–Mn angle in these complexes with the help of DFT calculations

Functional model for catecholase-like activity: A mechanistic approach with manganese(III) complexes of salen type Schiff base ligands

Three new Mn(III) complexes [MnL1(OOCH)(OH2)] (1), [MnL2(OH2)(2)][Mn2L22(NO2)(3)] (2) and [Mn2L21(NO2)(2)] (3) (where H2L1 = H(2)Me(2)Salen = 2,7-bis(2-hydroxyphenyl)-2,6-diazaocta-2,6-diene and H2L2 = H(2)Salpn = 1,7-bis(2-hydroxyphenyl)-2,6-diazahepta-1,6-diene) have been synthesized. X-ray crystal structure analysis reveals that 1 is a mononuclear species whereas 2 contains a mononuclear cationic and a dinuclear nitrite bridged (mu-1 kappa O:2 kappa O') anionic unit. Complex 3 is a phenoxido bridged dimer containing terminally coordinated nitrite. Complexes 1-3 show excellent catecholase-like activity with 3,5-di-tert-butylcatechol (3,5-DTBC) as the substrate. Kinetic measurements suggest that the rate of catechol oxidation follows saturation kinetics with respect to the substrate and first order kinetics with respect to the catalyst. Formation of bis(mu-oxo)dimanganese(III,III) as an intermediate during the course of reaction is identified from ESI-MS spectra. The characteristic six line EPR spectra of complex 2 in the presence of 3,5-DTBC supports the formation of manganese(II)-semiquinonate as an intermediate species during the catalytic oxidation of 3,5-DTBC

Trinuclear heterometallic Cu^II–Mn^II complexes of a salen type Schiff base ligand: anion dependent variation of phenoxido bridging angles and magnetic coupling

Five new trinuclear heterometallic CuII–MnII complexes [(CuL) 2Mn(O2CPh)2] (1), [(CuL) 2Mn(N3)2] (2), [(CuL) 2Mn(NCO)2] (3), [(CuL) 2Mn(NO3)2] (4) and [(CuL) 2Mn(Sal) 2]•CH2Cl2 (5) have been synthesized with the di-Schiff base ligand H2L (where H2L = N,N′-bis(salicylidene)-1,3-propanediamine and Sal = salicylate). These complexes with different anionic co-ligands have been synthesized to attain a large variation in phenoxido bridging angles and to investigate its consequence on magnetic properties. Single crystal X-ray diffraction analyses reveal that complexes 1, 2, 4 and 5 are linear, whereas 3 has an angular geometry. Variable temperature magnetic susceptibility measurements suggest that all five complexes possess an overall antiferromagnetic interaction between CuII and MnII ions, which results in a final ferrimagnetic ground state with spin 3/2 in the CuII–MnII–CuII trinuclear structure. The weakest antiferromagnetic interaction (JCu–Mn = −7.0 cm−1) is observed for 2 having the lowest value of the Cu–O–Mn angle (92.0°), while the strongest antiferromagnetic interaction (JCu–Mn = −26.5 cm−1) is observed for 3 having the largest Cu–O–Mn angle (101.4°). Complexes 1, 4 and 5 show average Cu–O–Mn angles of 98.2°, 97.6° and 97.7°, respectively, that lead to intermediate antiferromagnetic interactions (JCu–Mn = −9.6, −9.7, −9.3 cm−1 respectively)

Analyses of supramolecular interactions present in a coordination polymer of Mn(II) with 2-picolinate and 4,4′-Azobis(pyridine)

A new 2D coordination polymer [Mn^II(pic)(4,4′ -azpy)(H₂O)]ClO₄•EtOH (pic = 2-picolinate) has been synthesized where each of the octahedral Mn(II) center is connected by trans coordinating 4,4′-azpy and syn-anti bridging picolinate, resulting in a sheet like structure. Density Functional Theory (DFT) calculations, at the BLYP-D3/def2-TZVPD level of theory, are performed to explore the interplay of various supramolecular interactions present within the coordination polymer

Solvent-templated supramolecular isomerism in 2D coordination polymer constructed by Ni^II₂Co^II nodes and dicyanamido spacers: drastic change in magnetic behaviours

Two heterometallic Coordination Polymers (CPs) have been prepared using [NiIIL]2CoII (where H2L = N,N′-bis(salicylidene)-1,3-propanediamine) as nodes and dicyanamido spacers by varying the solvent for synthesis. Structural characterizations revealed that methanol assisted the formation of a two-dimensional (4,4) connected rhombic grid network of [(NiL)2Co(NCNCN)2]∞ (1a) whereas relatively less polar acetonitrile afforded a different superstructure {[(NiL)2Co(NCNCN)2]•CH3CN}∞ (1b) with a two-dimensional (4,4) connected square grid network. The presence of acetonitrile molecules in the structure of 1b seems to change the spatial orientation of the terminal metalloligands [NiL] from pseudo-eclipsed in 1a to staggered-like in 1b around the central Co(II). These structural changes in the nodes together with the conformationally flexible dicyanamido spacers, which are cis coordinated to the Co(II) in both trinuclear units, led to the differences in the final 2D network. Variable-temperature magnetic susceptibility measurements revealed that this supramolecular isomerism led to a drastic transition from spin-frustrated antiferromagnetism for 1a to a dominant ferromagnetic behaviour for 1b. The geometrical differences in Ni2 Co Coordination Clusters (CCs) which are scalene triangular in 1a but nearly linear in 1b, are held responsible for the changes of the magnetic properties. The DFT calculations of exchange interactions between metal centres provide a clear evidence of the role played by the fundamental geometrical factors on the nature and magnitude of the magnetic coupling in these pseudo-polymorphic CPs

Analyses of supramolecular interactions present in a coordination polymer of Mn(II) with 2-picolinate and 4,4′-Azobis(pyridine)

[eng]A new 2D coordination polymer [MnII(pic)(4,4′ -azpy)(H2O)]ClO4·EtOH (pic = 2-picolinate) has been synthesized where each of the octahedral Mn(II) center is connected by trans coordinating 4,4′-azpy and syn-anti bridging picolinate, resulting in a sheet like structure. Density functional theory (DFT) calculations, at the BLYP-D3/def2-TZVPD level of theory, are performed to explore the interplay of various supramolecular interactions present within the coordination polymer

Analysis of the contribution of the p-acidity of the s-tetrazine ring in the crystal packing of coordination polymers

Reaction of manganese(II) with the electron-deficient ligand 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine (pbptz) leads to distinct coordination networks whose topologies are influenced by the nature of the anions used. As anticipated, the linear ditopic ligand pbptz is involved in various types of supramolecular-p interactions, i.e.p...p, lone pair...p and C–H...p interactions, which clearly play a role in the formation of the different solid-state architectures obtained, as shown by DFT calculations