A Ferromagnetic Methoxido-Bridged Mn(III) Dimer and a Spin-Canted Metamagnetic μ1,3-Azido-Bridged Chain

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.

Metamagnetism and canted antiferromagnetic ordering in two monomeric CoII complexes with 1-(2-pyrimidyl)piperazine. Hirshfeld surface analysis and theoretical studies

Here we present the magnetic properties of two cobalt complexes formulated as: [Co(SCN)2(L)2] (1) and (H2L)2[Co(SCN)4]·H2O (2) (L = 1-(2-pyrimidyl)piperazine). The two compounds contain isolated tetrahedral CoII complexes with important intermolecular interactions that lead to the presence of a canted antiferromagnetic order below 11.5 and 10.0 K, with coercive fields at 2 K of 38 and 68 mT, respectively. Theoretical calculations have been used to explain this behaviour. Hirshfeld surface analysis shows the presence of strong intermolecular interactions in both compounds. The crystal geometries were used for geometry optimization using the DFT method. From the topological properties, electrostatic potential maps and molecular orbital analysis, information about the noncovalent interaction and chemical reactivity was obtained.

Selective Metal-Ligand Bond-Breaking Driven by Weak Intermolecular Interactions: From Metamagnetic Mn(III)-Monomer to Hexacyanoferrate(II)-Bridged Metamagnetic Mn2Fe Trimer

Metal-ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare example where metal-ligand bonds dissociate in an irreversible way, helped by a large number of weak intermolecular interactions that surpass the energy of the metal-ligand bond. Thus, we describe the design and synthesis of trinuclear Mn₂Fe complex {[Mn(L)(H₂O)]₂Fe(CN)₆},^2- starting from a mononuclear Mn(III)-Schiff base complex: [Mn(L)(H₂O)Cl] (1) and [Fe(CN)₆]^4- anions. This reaction implies the dissociation of Mn(III)-Cl coordination bonds and the formation of Mn(III)-NC bonds with the help of several intermolecular interactions. Here, we present the synthesis, crystal structure, and magnetic characterization of the monomeric Mn(III) complex [Mn(L)(H₂O)Cl] (1) and of compound (H₃O)[Mn(L)(H₂O)₂]{[Mn(L)(H₂O)]₂Fe(CN)₆}·4H₂O (2) (H₂L = 2,2'-((1E,1'E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(4-methoxyphenol)). Complex 1 is a monomer where the Schiff base ligand (L) is coordinated to the four equatorial positions of the Mn(III) center with a H₂O molecule and a Cl^- ion at the axial sites and the monomeric units are assembled by π-π and hydrogen-bonding interactions to build supramolecular dimers. The combination of [Fe(CN)₆]^4- with complex 1 leads to the formation of linear Mn-NC-Fe-CN-Mn trimers where two trans cyano groups of the [Fe(CN)₆]^4- anion replace the labile chloride from the coordination sphere of two [Mn(L)(H₂O)Cl] complexes, giving rise to the linear anionic {[Mn(L)(H₂O)]₂Fe(CN)₆}^2- trimer. This Mn₂Fe trimer crystallizes with an oxonium cation and a mononuclear [Mn(L)(H₂O)₂]⁺ cation, closely related to the precursor neutral complex [Mn(L)(H₂O)Cl]. In compound 2, the Mn₂Fe trimers are assembled by several hydrogen-bonding and π-π interactions to frame an extended structure similar to that of complex 1. Density functional theoretical (DFT) calculations at the PBE1PBE-D3/def2-TZVP level show that the bond dissociation energy (-29.3 kcal/mol) for the Mn(III)-Cl bond is smaller than the summation of all the weak intermolecular interactions (-30.1 kcal/mol). Variable-temperature magnetic studies imply the existence of weak intermolecular antiferromagnetic couplings in both compounds, which can be can cancelled with a critical field of ca. 2.0 and 2.5 T at 2 K for compounds 1 and 2, respectively. The magnetic properties of compound 1 have been fit with a simple S = 2 monomer with g = 1.959, a weak zero-field splitting (|D| = 1.23 cm^-1), and a very weak intermolecular interaction (zJ = -0.03 cm^-1). For compound 2, we have used a model with an S = 2 monomer with ZFS plus an S = 2 antiferromagnetically coupled dimer with g = 2.009, |D| = 1.21 cm^-1, and J = -0.42 cm^-1. The metamagnetic behavior of both compounds is attributed to the weak intermolecular π-π and hydrogen-bonding interactions.

A 3D Cu(ii) tetrazolate coordination polymer based on pentanuclear units with a large coercive field

A 3D Cu(ii) coordination polymer with the ligand 1,2-bis(tetrazol-5-yl) exhibits spin-canting magnetic behavior with a large coercive field of 2.3 kOe.

A New Mixed-Valence Mn(II)Mn(III) Compound With Catalase and Superoxide Dismutase Activities

The synthesis, X-ray molecular structure, physico-chemical characterization and dual antioxidant activity (catalase and superoxide dismutase) of a new polymeric mixed valence Mn(III)Mn(II) complex, containing the ligand H₂BPClNOL (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)] propylamine) is described. The monomeric unit is composed of a dinuclear Mn(II)Mn(III) moiety, [Mn(III)(μ-HBPClNOL)(μ-BPClNOL)Mn(II)(Cl)](ClO₄)·2H₂O, 1, in which the Mn ions are connected by two different bridging groups provided by two molecules of the ligand H₂BPClNOL, a phenoxide and an alkoxide group. In the solid state, this mixed valence dinuclear unit is connected to its neighbors through chloro bridges. Magnetic measurements indicated the presence of ferromagnetic [J = +0.076(13) cm⁻¹] and antiferromagnetic [J = −5.224(13) cm⁻¹] interactions. The compound promotes O2•- dismutation in aqueous solution (IC₅₀ = 0.370 μmol dm⁻³, k_cat = 3.6x10⁶ M⁻¹ s⁻¹). EPR studies revealed that a high-valent Mn(III)-O-Mn(IV) species is involved in the superoxide dismutation catalytic cycle. Complex 1 shows catalase activity only in the presence of a base, e.g., piperazine or triethylamine. Kinetic studies were carried out in the presence of piperazine and employing two different methods, resulting in k_cat values of 0.58 ± 0.03 s⁻¹ (detection of O₂ production employing a Clark electrode) and 2.59 ± 0.12 s⁻¹ (H₂O₂ consuption recorded via UV-Vis). EPR and ESI-(+)-MS studies indicate that piperazine induces the oxidation of 1, resulting in the formation of the catalytically active Mn(III)-O-Mn(IV) species.

Rare azido and hydroxido bridged tetranuclear Co(ii) complexes of a polynucleating Mannich base ligand with a defect dicubane core: structures, magnetism and phenoxazinone synthase like activity

Triply azido/hydroxido bridged defect dicubane tetranuclear Co(ii) complexes of a Mannich base ligand show ferromagnetic/antiferromagnetic coupling and phenoxazinone synthase like activity.

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.

New Twists and Turns for Actinide Chemistry: Organometallic Infinite Coordination Polymers of Thorium Diazide

Two organometallic 1D infinite coordination polymers and two organometallic monometallic complexes of thorium diazide have been synthesized and characterized. Steric control of these self-assembled arrays, which are dense in thorium and nitrogen, has also been demonstrated: infinite chains can be circumvented by using steric bulk either at the metallocene or with a donor ligand in the wedge.

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.

Comparative structure activity relationship for heterogeneous phosphatase-like catalytic activities of one-dimensional Cu(ii) coordination polymers

A structure activity relationship for heterogeneous phosphatase-like activities of one-dimensional Cu(ii) coordination polymers, has been studied. Complex 1 exhibits maximum activity due to coordinated water molecules, shorter metal–metal distance and exposed metal centers.

LnIII ion dependent magnetism in heterometallic Cu–Ln complexes based on an azido group and 1,2,3-triazole-4,5-dicarboxylate as co-ligands

Four Cu–Ln coordination polymers [Cu₂Ln(tda)₂N₃(H₂O)₄·2H₂O] (Ln = Gd (1), Tb (2), Dy (3), Sm (4), tda = 1,2,3-triazole-4,5-dicarboxylate) have been synthesized by employing H₃tda and azido as co-ligands.

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, Structure, and Catalytic Epoxidation Property of a New Phenolato and μ1,1,3-Azido Co-Bridged Polynuclear Manganese(III) Complex Derived from N,N′-Bis(5-methylsalicylidene)ethane-1,2-diamine

A new phenolato and μ1,1,3-azido co-bridged polynuclear manganese(iii) complex has been synthesised and characterised. The structure of the complex has been confirmed by single crystal X-ray diffraction analyses. The ability of the complex to catalyse the epoxidation of styrene using PhIO or NaOCl as oxidant has been studied. Results show the catalysis to occur efficiently in the presence of PhIO and NaOCl.

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.

Syntheses, crystal structures and thermal properties of six coordination polymers based on 2-(p-methylphenyl)-imidazole dicarboxylate

Through solvothermal reactions of 2-(p-methylphenyl)-1H-imidazole-4,5-dicarboxylic acid (p-MePhH3IDC) with transition-metal ions, six coordination polymers [Pb2(p-MePhHIDC)(p-MePhH2IDC)2(phen)2]n (phen = 1,10-phenanthroline) (), [Pb(p-MePhH2IDC)2]n (), [Cd3(p-MePhHIDC)2(p-MePhH2IDC)2(H2O)2]n (), {[Cd(p-MePhHIDC)(H2O)]4·H2O}n (), {[Cd2(p-MePhHIDC)2(4,4'-bipy)]·4H2O}n (4,4'-bipy = 4,4'-bipyridine) () and [Mn3(p-MePhHIDC)2(p-MePhH2IDC)2(4,4'-bipy)]n () have been synthesized successfully. X-ray single-crystal analyses show that polymers have rich structural chemistry ranging from one-dimensional (), two-dimensional () to three-dimensional polymers (, , and ). In these polymers, the p-MePhH3IDC ligand shows flexible coordination modes tuned by different synthetical conditions, including the addition of coligands, temperature, pH value and so on. Furthermore, the polymers have been investigated by solid-state ultraviolet spectra and thermogravimetric analyses.