Polyalcohols as ancillary ligands in manganese-oxime chemistry: Syntheses, structures and magnetic properties of a series of trinuclear complexes involving a linear MnII-MnIV-MnII core

Using di-2-pyridyl ketonoxime (Hdpko) as an oxime-based ligand in combination with several polyhydric alcohols, viz. ethanediol (H2ed), propanediol (H2pd) and pentaerythritol (H4per),wehave synthesized a series of trinuclear complexes involving a linear MnII-MnIV-MnII core, viz. [Mn3(dpko)4(ed)Cl2]-2CH3CN.H2O 1, [Mn3(dpko)4(pd)Cl2].CH3CN.H2O.0.5H2pd 2 and [Mn3(dpko)4(H2per)Cl2].4H2O 3, respectively. The trinuclear complexes contain mixed valent MnII-MnIV-MnII units in a linear topology in which MnII and MnIV spin carriers are ferromagnetically coupled. The temperature dependence of the magnetic susceptibility has been fitted with a liner spin trimer model based on the H = -2J{SMn1.SMn2 + SMn10.SMn2} Heisenberg Hamiltonian with J/kB = +1.4(1) K for 1; +4.9(1) K for 2 and +3.7(1) K for 3, leading for the three complexes to an ST = 13/2 ground state

Homo- and Heterometal Complexes of Oxido–Metal Ions with a Triangular [V(V)O–MO–V(V)O] [M = V(IV) and Re(V)] Core: Reporting Mixed-Oxidation Oxido–Vanadium(V/IV/V) Compounds with Valence Trapped Structures

A new family of trinuclear homo- and heterometal complexes with a triangular [V­(V)­O–MO–V­(V)­O] (M = V­(IV), <b>1</b> and <b>2</b>; Re­(V), <b>3</b>] all-oxido–metal core have been synthesized following a single-pot protocol using compartmental Schiff-base ligands, <i>N</i>,<i>N</i>′-bis­(3-hydroxysalicylidene)-diiminoalkanes/arene (H₄L¹–H₄L³). The upper compartment of these ligands with N₂O₂ donor combination (Salen-type) contains either a V­(IV) or a Re­(V) center, while the lower compartment with O₄ donor set accommodates two V­(V) centers, stabilized by a terminal and a couple of bridging methoxido ligands. The compounds have been characterized by single-crystal X-ray diffraction analyses, which reveal octahedral geometry for all three metal centers in <b>1</b>–<b>3</b>. Compound <b>1</b> crystallizes in a monoclinic space group <i>P</i>2₁/<i>c</i>, while both <b>2</b> and <b>3</b> have more symmetric structures with orthorhombic space group <i>Pnma</i> that renders the vanadium­(V) centers in these compounds exactly identical. In DMF solution, compound <b>1</b> displays an 8-line EPR at room temperature with ⟨<i>g</i>⟩ and ⟨<i>A</i>⟩ values of 1.972 and 86.61 × 10^–4 cm^–1, respectively. High-resolution X-ray photoelectron spectrum (XPS) of this compound shows a couple of bands at 515.14 and 522.14 eV due to vanadium 2p_3/2 and 2p_1/2 electrons in the oxidation states +5 and +4, respectively. All of these, together with bond valence sum (BVS) calculation, confirm the trapped-valence nature of mixed-oxidation in compounds <b>1</b> and <b>2</b>. Electrochemically, compound <b>1</b> undergoes two one-electron oxidations at <i>E</i> _1/2 = 0.52 and 0.83 V vs Ag/AgCl reference. While the former is due to a metal-based V­(IV/V) oxidation, the latter one at higher potential is most likely due to a ligand-based process involving one of the catecholate centers. A larger cavity size in the upper compartment of the ligand H₄L³ is spacious enough to accommodate Re­(V) with larger size to generate a rare type of all-oxido heterotrimetallic compound (<b>3</b>) as established by X-ray crystallography

Targeted syntheses of homo- and heterotrinuclear complexes involving MII-NiII-MII (M = Ni, Cu, and Pd) nonlinear core: Structure, spectroscopy, magnetic and redox studies

Homo- and heterotrinuclear complexes [LNi{M(Ln)}2](ClO4)2 H2O involving NiIIMII 2 nonlinear cores (M = Ni, Cu, and Pd) (1-6) have been synthesized by a single-pot reaction when the oximato metal complexes [MLn(H2O)]ClO4 (HLn are tridentate oxime ligands), prepared in situ in methanol are allowed to react with the precursor nickel(II) complex [LNi(H2O)2] (H2L = N,N0-dimethyl-N,N0-bis(2-hydroxy-3,5- dimethylbenzyl)ethylenediamine). Single crystal X-ray diffraction analysis, and ESI-MS spectroscopy have been used to establish their identities which involve an octahedral Ni(II) site flunked by two metal-oximate moieties, each in a square planar environment. The electronic and molecular structures of these compounds are interesting due to a synergistic bonding mechanism operative through the deprotonated oxime and the phenolate oxygen atoms via the metal centers.......

Heterobimetallic μ‑Oxido Complexes Containing Discrete V^V–O–M^III (M = Mn, Fe) Cores: Targeted Synthesis, Structural Characterization, and Redox Studies

Heterobimetallic compounds [L′OV^V(μ-O)­M^IIIL]_<i>n</i> (<i>n</i> = 1, M = Mn, <b>1</b>–<b>5</b>; <i>n</i> = 2, M = Fe, <b>6</b> and <b>7</b>) containing a discrete unsupported V^V–O–M^III bridge have been synthesized through a targeted synthesis route. In the V–O–Mn-type complexes, the vanadium­(V) centers have a square-pyramidal geometry, completed by a dithiocarbazate-based tridentate Schiff-base ligand (H₂L′), while the manganese­(III) centers have either a square-pyramidal (<b>1</b> and <b>3</b>) or an octahedral (<b>2</b> and <b>5</b>) geometry, made up of a Salen-type tetradentate ligand (H₂L) as established by X-ray diffraction analysis. The V–O–Mn bridge angle in these compounds varies systematically from 155.3° to 128.1° in going from <b>1</b> to <b>5</b> while the corresponding dihedral angle between the basal planes around the metal centers changes from 86.82° to 20.92°, respectively. The V–O–Fe-type complexes (<b>6</b> and <b>7</b>) are tetranuclear, in which the two dinuclear V­(μ-O)­Fe units are connected together by apical iron­(III)–aryl oxide interactions, forming a dimeric structure with a pair of Fe–O–Fe bridges. The X-ray data also confirm the VO → M canonical form to contribute predominantly on the overall V–O–M bridge structure. The molecules in solution also retain their heterobinuclear composition, as established by electrospray ionization mass spectrometry and ⁵¹V NMR spectroscopy. Electrochemically, these complexes are quite interesting; the manganese­(III) complexes (<b>1</b>–<b>5</b>) display three successive reductions (processes I–III), each with a monoelectron stoichiometry. Process I is due to a Mn^III/Mn^II reduction (<i>E</i>_1/2 ranges between −0.32 and −0.05 V), process II is a ligand-based reduction, and process III (<i>E</i>_1/2 = ∼1.80 V) owes its origin to a V^VO/V^IVO reduction; all potentials are versus Ag/AgCl. The iron­(III) compounds (<b>6</b> and <b>7</b>), on the other hand, show at least four irreversible processes, appearing at <i>E</i>_pc = −0.20, −1.0, −1.58, and −1.68 V in compound <b>6</b> (processes IV–VII), together with a reversible process (process VIII) at <i>E</i>_1/2 = −1.80 V (Δ<i>E</i>_p = 80 mV). While the first two of these are due to Fe^III/Fe^II reductions at the two iron­(III) centers of these tetranuclear cores, the reversible reduction at a more negative potential (ca. −1.80 V) is due to a V^VO/V^IVO-based electron transfer

Homo- and Heterometal Complexes of Oxido–Metal Ions with a Triangular [V(V)O–MO–V(V)O] [M = V(IV) and Re(V)] Core: Reporting Mixed-Oxidation Oxido–Vanadium(V/IV/V) Compounds with Valence Trapped Structures

A new family of trinuclear homo- and heterometal complexes with a triangular [V­(V)­O–MO–V­(V)­O] (M = V­(IV), <b>1</b> and <b>2</b>; Re­(V), <b>3</b>] all-oxido–metal core have been synthesized following a single-pot protocol using compartmental Schiff-base ligands, <i>N</i>,<i>N</i>′-bis­(3-hydroxysalicylidene)-diiminoalkanes/arene (H₄L¹–H₄L³). The upper compartment of these ligands with N₂O₂ donor combination (Salen-type) contains either a V­(IV) or a Re­(V) center, while the lower compartment with O₄ donor set accommodates two V­(V) centers, stabilized by a terminal and a couple of bridging methoxido ligands. The compounds have been characterized by single-crystal X-ray diffraction analyses, which reveal octahedral geometry for all three metal centers in <b>1</b>–<b>3</b>. Compound <b>1</b> crystallizes in a monoclinic space group <i>P</i>2₁/<i>c</i>, while both <b>2</b> and <b>3</b> have more symmetric structures with orthorhombic space group <i>Pnma</i> that renders the vanadium­(V) centers in these compounds exactly identical. In DMF solution, compound <b>1</b> displays an 8-line EPR at room temperature with ⟨<i>g</i>⟩ and ⟨<i>A</i>⟩ values of 1.972 and 86.61 × 10^–4 cm^–1, respectively. High-resolution X-ray photoelectron spectrum (XPS) of this compound shows a couple of bands at 515.14 and 522.14 eV due to vanadium 2p_3/2 and 2p_1/2 electrons in the oxidation states +5 and +4, respectively. All of these, together with bond valence sum (BVS) calculation, confirm the trapped-valence nature of mixed-oxidation in compounds <b>1</b> and <b>2</b>. Electrochemically, compound <b>1</b> undergoes two one-electron oxidations at <i>E</i> _1/2 = 0.52 and 0.83 V vs Ag/AgCl reference. While the former is due to a metal-based V­(IV/V) oxidation, the latter one at higher potential is most likely due to a ligand-based process involving one of the catecholate centers. A larger cavity size in the upper compartment of the ligand H₄L³ is spacious enough to accommodate Re­(V) with larger size to generate a rare type of all-oxido heterotrimetallic compound (<b>3</b>) as established by X-ray crystallography

Triple-Stranded Helicates of Zinc(II) and Cadmium(II) Involving a New Redox-Active Multiring Nitrogenous Heterocyclic Ligand: Synthesis, Structure, and Electrochemical and Photophysical Properties

The protonated form [H₂(L)]­(CF₃SO₃)₂ (<b>1</b>) of a new redox-active bis-bidentate nitrogenous heterocyclic ligand, viz., 3,3′-dipyridin-2-yl­[1,1′]­bi­[imidazo­[1,5-<i>a</i>]­pyridinyl] (L), and its zinc­(II) and cadmium­(II) complexes (<b>2</b> and <b>3</b>) have been synthesized and characterized by single-crystal X-ray diffraction analysis. In the solid state, both <b>2</b> and <b>3</b> have triple-stranded helical structures involving ligands that experience twisting and bending to the extent needed by the stereoelectronic demand of the central metal ion. The metal centers in the zinc­(II) complex [Zn₂(L)₃]­(ClO₄)₄ (<b>2</b>) are equivalent, each having a distorted octahedral geometry, flattened along the <i>C</i>₃ axis with a Zn1···Zn1# separation of 4.8655(13) Å. The cadmium complex [Cd₂(L)₃(H₂O)]­(ClO₄)₄ (<b>3</b>), on the other hand, has a rare type of helical structure, showing coordination asymmetry around the metal centers with a drastically reduced Cd1···Cd2 separation of 4.070 Å. The coordination environment around Cd1 is a distorted pentagonal bipyramid involving a N₆O donor set with the oxygen atom coming from a coordinated water, leaving the remaining metal center Cd2 with a distorted octahedral geometry. The structures of <b>2</b> and <b>3</b> also involve anion−π- and CH−π-type noncovalent interactions that play dominant roles in shaping the extended structures of these molecules in the solid state. In solution, these compounds exhibit strong fluxional behavior, making the individual ligand strands indistinguishable from one another, as revealed from their ¹H NMR spectra, which also provide indications about these molecules retaining their helical structures in solution. Electrochemically, these compounds are quite interesting, undergoing ligand-based oxidations in two successive one-electron steps at <i>E</i>_1/2 of ca. 0.65 and 0.90 V versus a Ag/AgCl (3 M NaCl) reference. These molecules are all efficient emitters in the red and blue regions because of ligand-based π*−π fluorescent emissions, tuned appropriately by the attached Lewis acid centers

Triple-Stranded Helicates of Zinc(II) and Cadmium(II) Involving a New Redox-Active Multiring Nitrogenous Heterocyclic Ligand: Synthesis, Structure, and Electrochemical and Photophysical Properties

The protonated form [H₂(L)]­(CF₃SO₃)₂ (<b>1</b>) of a new redox-active bis-bidentate nitrogenous heterocyclic ligand, viz., 3,3′-dipyridin-2-yl­[1,1′]­bi­[imidazo­[1,5-<i>a</i>]­pyridinyl] (L), and its zinc­(II) and cadmium­(II) complexes (<b>2</b> and <b>3</b>) have been synthesized and characterized by single-crystal X-ray diffraction analysis. In the solid state, both <b>2</b> and <b>3</b> have triple-stranded helical structures involving ligands that experience twisting and bending to the extent needed by the stereoelectronic demand of the central metal ion. The metal centers in the zinc­(II) complex [Zn₂(L)₃]­(ClO₄)₄ (<b>2</b>) are equivalent, each having a distorted octahedral geometry, flattened along the <i>C</i>₃ axis with a Zn1···Zn1# separation of 4.8655(13) Å. The cadmium complex [Cd₂(L)₃(H₂O)]­(ClO₄)₄ (<b>3</b>), on the other hand, has a rare type of helical structure, showing coordination asymmetry around the metal centers with a drastically reduced Cd1···Cd2 separation of 4.070 Å. The coordination environment around Cd1 is a distorted pentagonal bipyramid involving a N₆O donor set with the oxygen atom coming from a coordinated water, leaving the remaining metal center Cd2 with a distorted octahedral geometry. The structures of <b>2</b> and <b>3</b> also involve anion−π- and CH−π-type noncovalent interactions that play dominant roles in shaping the extended structures of these molecules in the solid state. In solution, these compounds exhibit strong fluxional behavior, making the individual ligand strands indistinguishable from one another, as revealed from their ¹H NMR spectra, which also provide indications about these molecules retaining their helical structures in solution. Electrochemically, these compounds are quite interesting, undergoing ligand-based oxidations in two successive one-electron steps at <i>E</i>_1/2 of ca. 0.65 and 0.90 V versus a Ag/AgCl (3 M NaCl) reference. These molecules are all efficient emitters in the red and blue regions because of ligand-based π*−π fluorescent emissions, tuned appropriately by the attached Lewis acid centers

Tetranuclear Hetero-Metal [Co^II₂Ln^III₂] (Ln = Gd, Tb, Dy, Ho, La) Complexes Involving Carboxylato Bridges in a Rare μ₄–η²:η² Mode: Synthesis, Crystal Structures, and Magnetic Properties

A new family of 3d–4f heterometal 2 × 2 complexes [Co^II₂(L)₂(PhCOO)₂Ln^III₂(hfac)₄] (<b>1</b>–<b>5</b>) (Ln = Gd (compound <b>1</b>), Tb (compound <b>2</b>), Dy (compound <b>3</b>), Ho (compound <b>4</b>), and La (compound <b>5</b>)) have been synthesized in moderate yields (48–63%) following a single-pot protocol using stoichiometric amounts (1:1 mol ratio) of [Co^II(H₂L)­(PhCOO)₂] (H₂L = <i>N</i>,<i>N</i>′-dimethyl-<i>N</i>,<i>N</i>′-bis­(2-hydroxy-3,5-dimethylbenzyl)­ethylenediamine) as a metalloligand and [Ln^III(hfac)₃(H₂O)₂] (Hhfac = hexafluoroacetylacetone) as a lanthanide precursor compound. Also reported with this series is the Zn–Dy analog [Zn^II₂(L)₂(PhCOO)₂Dy^III₂(hfac)₄] <b>6</b> to help us in understanding the magnetic properties of these compounds. The compounds <b>1</b>–<b>6</b> are isostructural. Both hexafluoroacetylacetonate and benzoate play crucial roles in these structures as coligands in generating a tetranuclear core of high thermodynamic stability through a self-assembly process. The metal centers are arranged alternately at the four corners of this rhombic core, and the carboxylato oxygen atoms of each benzoate moiety bind all of the four metal centers of this core in a rare μ₄–η²:η² bridging mode as confirmed by X-ray crystallography. The magnetic susceptibility and magnetization data confirm a paramagnetic behavior, and no remnant magnetization exists in any of these compounds at vanishing magnetic field. The metal centers are coupled in an antiferromagnetic manner in these compounds. The [Co^II₂Dy^III₂] compound exhibits a slow magnetic relaxation below 6 K, as proven by the AC susceptibility measurements; the activation energy reads <i>U</i>/<i>k</i>_B = 8.8 K (τ₀ = 2.0 × 10^–7 s) at <b>B</b>_DC = 0, and <i>U</i>/<i>k</i>_B = 7.8 K (τ₀ = 3.9 × 10^–7 s) at <b>B</b>_DC = 0.1 T. The [Zn^II₂Dy^III₂] compound also behaves as a single-molecule magnet with <i>U</i>/<i>k</i>_B = 47.9 K and τ₀ = 2.75 × 10^–7 s