Spin-Canted Antiferromagnetic Phase Transitions in Alternating Phenoxo- and Carboxylato-Bridged MnIII-Salen Complexes

The crucial role of hydrogen bonding in shaping the structures of zinc-based coordination polymers using tridentate N, N, O donor reduced Schiff base ligands and bridging acetates

In this manuscript we report the synthesis and characterization of two new polynuclear zinc(ii) complexes, [Zn2L1(μ-OAc)3]n·H2O (1) and [Zn2L2(μ-OAc)3]n (2) using two tridentate ligands, HL1 {4-chloro-2-(((2-(methylamino)ethyl)amino)methyl)phenol} and HL2 {2,4-dibromo-6-(((3-(methylamino)propyl)amino)methyl)phenol}. The structures were confirmed by single-crystal X-ray diffraction analysis. Both complexes form 1D chains. The energy of H-bonding interaction in the solid state structures of the complexes has been estimated by DFT calculation and the crucial role of hydrogen bonding in shaping their structures has been highlighted.

Synthesis, Molecular, and Supramolecular Structures of Two Azide-Bridged Cd(II) and Cu(II) Coordination Polymers

Two 1D coordination polymers were synthesized by reaction of two ligands, 2-amino-4-picoline (2A4Pic) and quinoline-6-carboxylic acid (Qu-6-COOH) with two metal (II) nitrate (M = Cd and Cu) in the presence of azide as a linker. The synthesized metal complexes [Cd(2A4Pic)2(N3)2]n; (1) and [Cu(Qu-6-COO)(N3)(H2O)]n; (2) were isolated in single crystals and their X-ray structures revealed a 1D polymeric structure. Due to symmetry considerations, the asymmetric formula is half a [Cd(2A4Pic)2(N3)2] unit for 1 and one [Cu(Qu-6-COO)(N3)(H2O)] unit for 2. In complex 1, the Cd(II) is hexa-coordinated with two 2A4Pic molecules and four μ(1,1) azide units. Hence, the CdN6 coordination environment has a slightly distorted octahedral geometry. In 2, the Cu(II) is hexa-coordinated with three different ligands (Qu-6-COO¯, H2O and μ(1,1) N3¯) where all are connectors between the crystallographically related Cu(II) sites. Additionally, complex 2 distorted CuN2O4 octahedral geometry. In both complexes, the polymer arrays are connected by N…H hydrogen bonds and π–π stacking interactions. Based on Hirshfeld analysis, the percentages of N…H contacts are 43.1 and 27.4% for 1 and 2, respectively, while %C...C are 5.6 and 9.3%, respectively. Analysis of Cu-N, Cu-O, and Cd-N bonds using DFT calculations showed predominantly closed-shell coordination interactions with little covalent characters. Additionally, the negatively charged ligand groups were found to compensate the positive charge of the central metal ion to a larger extent than the electrically neutral ligands.

Pentanuclear MII–MnII (M = Ni and Cu) complexes of N2O2 donor ligands with a variation of carboxylate anions: syntheses, structures, magnetic properties and catecholase-like activities

One NiII2MnII3 and two CuII2MnII3 complexes have been synthesized using N2O2 donor ligands. The former complex exhibits spin crossover at 2 K temperature. All the complexes exhibit catecholase-like activities.

Crystal structures and magnetic properties of one-dimensional compounds constructed from Mn2(salen)2 building blocks and organic selenite acid ligands

Two new compounds composed of MnIII salen building blocks and organic selenite acid with ClO4− counter anions, namely [Mn2(salen)2(C6H5SeO2)](ClO4)(1) and [Mn2(salen)2(C6H4FSeO2)](ClO4)(2) [salen = N,N′-bis(salicylidene)-ethylenediamine], were synthesized through a one-pot reaction and characterized structurally and magnetically.

Canting angle dependence of single-chain magnet behaviour in chirality-introduced antiferromagnetic chains of acetate-bridged manganese(III) salen-type complexes

Canted antiferromagnetism (AFM) is considered an effective tool for designing single-chain magnets (SCMs) in homometallic chain systems. The family of manganese(iii) (MnIII) salen-type Schiff-base complexes is an outstanding building-unit candidate for designing SCMs because such complexes possess relatively large uniaxial magnetic anisotropy in the out-of-plane direction. However, SCM behaviour in simple alternating chains based on monomeric MnIII salen-type complexes has not been studied extensively. Herein, we report the SCM behaviour of canted AFM in an alternating chain of an acetate-bridged MnIII salen-type complex.

The catalytic activities and magnetic behaviours of rare μ3-chlorido and μ1,1,1-azido bridged defective dicubane tetranuclear Mn(ii) complexes

A μ₃-chlorido and a μ_1,1,1-azido bridged defective dicubane tetranuclear Mn(ii) complexes of polynucleating Mannich base ligand show significant catalytic oxidase activities and are antiferromagnetically coupled which is rationalized by DFT calculations.

Synthesis, structure and phenoxazinone synthase-like activity of three unprecedented alternating CoII–CoIII 1D chains

Three new one-dimensional Co^II/Co^III chains have been synthesized using N-salicylidene-l-alanine/N-salicylidene-l-phenylalanine and 2,2′-bipyridine/1,10-phenanthroline. All three complexes exhibit phenoxazinone synthase-like activity.

A 2D rhomboidal system of manganese(ii) [Mn(3-MeC6H4COO)2(H2O)2]n with spin canting: rationalization of the magnetic exchange

The crystal structure of Mn(ii) carboxylate with 3-methylbenzoate as a bridging ligand [Mn(3-MeC₆H₄COO)₂(H₂O)₂]_n shows a rhomboidal layer, where each pair of neighbor Mn(ii) ions are bridged through only one carboxylate group with a syn-anti conformation. The magnetic exchange between neighbor ions is weakly antiferromagnetic (J = -0.52 cm^-1, g = 2.04), and at low temperature the system shows spin canting with T_B = 3.8 K. Computational studies, based on periodic calculations of the energies of the significant spin states on the magnetic cell and some higher supercells, corroborate the weak AF interaction between the adjacent Mn(ii) ions and preclude the negligible effect of frustration caused by very weak interactions between the non-adjacent ions in the magnetic response of the system. The results provide compelling evidence that the observed spin canting is due to the local coordination geometry of the manganese ions leading to two antiferromagnetically coupled subnets with different axial vectors.

The first alternating MnII–MnIII 1D chain: structure, magnetic properties and catalytic oxidase activities

A one-dimensional mixed-valence Mn^II/Mn^III chain has been synthesized using N-salicylidene-l-alanine and 2,2′-bipyridine. The complex shows moderate catecholase and phenoxazinone synthase-like activity.

Importance of C–H⋯π interactions in stabilizing the syn/anti arrangement of pendant alkoxy side arms in two manganese(iv) Schiff base complexes: exploration of catechol oxidase and phenoxazinone synthase like activities

Two manganese(iv) complexes have been prepared and characterized. Both complexes exhibit catechol oxidase and phenoxazinone synthase like activities.

Slow relaxation of the magnetization observed in an antiferromagnetically ordered phase for SCM-based two-dimensional layered compounds

We showed 2D-layered compounds exhibiting SCM-like behavior in an AF ordered phase. By introducing counteranions with a different size, Néel temperature and spin-flip inversion field could be tuned.

Synthesis of mixed-valence hexanuclear Mn(II/III) clusters from its Mn(II) precursor: variations of catecholase-like activity and magnetic coupling

One Mn(II) coordination polymer, [Mn(o-(NO2)C6H4COO)2(pyz)(H2O)]n (1), has been synthesized and oxidized with n-Bu4NMnO4 in non-aqueous media to two mixed-valence hexanuclear Mn(II/III) complexes [MnIII2MnII4O2(pyz)0.61/(MeOH)0.39(o-(NO2)C6H4COO)10·(H2O)·{(CH3)2CO}2]·(CH3)2CO (2) and [MnIII2MnII4O2(pyz)0.28/(MeCN)3.72(o-(NO2)C6H4COO)10·(H2O)] (3) (where pyz = pyrazine). All three complexes were characterized by elemental analyses, IR spectroscopy, single-crystal X-ray diffraction analyses, and variable-temperature magnetic measurements. The structural analyses reveal that complex 1 is comprised of linear chains of pyz bridged Mn(II), which are further linked to one another by syn–anti carboxylate bridges, giving rise to a two-dimensional (2D) net. Complexes 2 and 3 feature mixed valence [MnIII2MnII4] units in which each of the six manganese centres reside in an octahedral environment. Apart from the variations in terminal ligands (acetone for 2 and acetonitrile for 3), the complexes are very similar. Using 3,5-di-tert-butyl catechol (3,5-DTBC) as the substrate, the catecholase-like activity of the complexes has been studied and it is found that the mixed valent Mn6 complexes (2 and 3) are much more active towards aerial oxidation of catechol compared to the Mn(II) complex (1). Variable-temperature (1.8–300 K) magnetic susceptibility measurements showed the presence of antiferromagnetic coupling in all three complexes. The magnetic data have been fitted with a 2D quadratic model derived by Lines, giving the exchange constant J/kB = −0.0788(5) K for 1. For 2 and 3, antiferromagnetic interactions within the Mn6 cluster have been fitted with models containing three exchange constants: JA/kB = −70 K, JB/kB = −0.5 K, JC/kB = −2.9 K for 2 and JA/kB = −60 K, JB/kB = −0.3 K, JC/kB = −2.8 K for 3.

The first photochromic bimetallic assemblies based on Mn(iii) and Mn(ii) Schiff-base (salpn, dapsc) complexes and pentacyanonitrosylferrate

The bimetallic cyano-bridged complexes demonstrating photochromism and magnetism were obtained and studied.

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 of salen type Schiff base ligands have been synthesized in order to correlate their magnetic properties with structural parameters, theoretically and experimentally.

Synthesis and characterization of monomeric Mn (IV) and pseudo-tetrameric Mn (III) complexes: magnetic properties of Mn (III) complex

Two novel monomer Mn (IV) [Mn(3,5-ClL1)2]⋅(CH3OH), (1), [3,5-ClL1H2=N-(2-hydroxyethyl)-3,5-dichlorosalicylaldimine] (1) and hydrogen-bonded pseudo-tetramer Mn (III) [Mn(5-BrL2)(H2O)2]2⋅[Mn(5-BrL2)(H2O)]2⋅2⋅(ClO4), (2), [5-BrL2H2=N,N'-bis(5-bromosalicylidenato)-1,2-diamino-2-methylpropane)] (2) Schiff base complexes have been synthesized and their crystal structures have been determined by single crystal X-ray diffraction analysis. A variable temperature magnetic susceptibility measurement study has been performed for complex (2) and the result indicates there is a very weak antiferromagnetic interaction (J=-0.40±0.016cm(-1)) between the two manganese (III) centers.

Synthesis, crystal structure and magnetic properties of two alternating double μ1,1 and μ1,3 azido bridged Cu(ii) and Ni(ii) chains

Two new alternating double μ_1,1 and μ_1,3 azido bridged 1D Cu(ii) and Ni(ii) complexes have been synthesized and their magnetic data were fitted to an alternating ferro/antiferromagnetic chain model.

Role of dicarboxylate linkers in Mn(III)-salicylaldoximate based extended structures: synthesis, structures, and magnetic behavior

Four new oxo-centered Mn(III)-salicylaldoximate triangle-based extended complexes [Mn(III)6O2(salox)6(EtOH)4(phda)]n·(saloxH2)n·(2H2O)n (1), [Mn(III)6O2(salox)6(MeOH)5(5-I-isoph)]n·(3MeOH)n (2), [Mn(III)6O2(salox)6(MeOH)4(H2O) (5-N3-isoph)]n·(4MeOH)n (3) and [Mn(III)3NaO(salox)3(MeOH)4(5-NO2-isoph)]n·(MeOH)n (H2O)n (4) [salox=salicylaldoximate, phda=1,3-phenylenediacetate, isoph=isophthalate] have been synthesized under similar reaction conditions. Single crystal X-ray structures show that in 1, only one type of Mn6 cluster is arranged in 1D, whereas in 2 and 3 there are two types of clusters, differing in the way the triangle units are joined and assembled. In complex 4, however, the basic building structure is heteronuclear and based on Mn3 units extended in 2D. Susceptibility measurements (dc and ac) over a wide range of temperatures and fields show that the complexes 1, 2, and 3 behave as single molecule magnets (SMMs) with S=4 ground state, while 4 is dominantly antiferromagnetic with a ground spin state S=2. Density functional theory calculations have been performed on model complexes to provide a qualitative theoretical interpretation for their overall magnetic behavior.

Two novel heterometallic chains featuring Mn(II) and Na(I) ions in trigonal-prismatic geometries alternately linked to octahedral Mn(IV) ions: synthesis, structures, and magnetic behavior

Two new one-dimensional heterometallic complexes, [Mn(3)Na(L)(4)(CH(3)CO(2))(MeOH)(2)](ClO(4))(2)·3H(2)O (1), [Mn(3)Na(L)(4)(CH(3)CH(2)CO(2))(MeOH)(2)](ClO(4))(2)·2MeOH·H(2)O (2) [LH(2) = 2-methyl-2-(2-pyridyl)propane-1,3-diol], have been synthesized and characterized by X-ray crystallography. Both complexes feature Mn(II) and Na(I) ions in trigonal-prismatic geometries that are linked to octahedral Mn(IV) ions by alkoxy bridges. Variable-temperature direct- and alternating-current magnetic susceptibility data indicated a spin ground state of S = 11/2 for both complexes. Density functional theory calculations performed on 1 supported this conclusion.