Targeted Synthesis of Heterobimetallic Compounds Containing a Discrete Vanadium(V)−μ-Oxygen–Iron(III) Core

Heterobimetallic compounds [L¹OV^VO→Fe­(metsalophen)­(H₂O)] (<b>1</b>) and [L²OV^VO→Fe­(metsalophen)­(H₂O)]­CH₃CN (<b>2</b>), where H₂L¹ and H₂L² are tridentate dithiocarbazate-based Schiff base ligands, containing a discrete V^V–μ-O–Fe^III angular core have been synthesized for the first time through a targeted synthesis route: confirmation in favor of such a heterobimetallic core structure has come from single-crystal X-ray diffraction analysis and electrospray ionization mass spectrometry

Targeted Synthesis of Heterobimetallic Compounds Containing a Discrete Vanadium(V)−μ-Oxygen–Iron(III) Core

Heterobimetallic compounds [L¹OV^VO→Fe­(metsalophen)­(H₂O)] (<b>1</b>) and [L²OV^VO→Fe­(metsalophen)­(H₂O)]­CH₃CN (<b>2</b>), where H₂L¹ and H₂L² are tridentate dithiocarbazate-based Schiff base ligands, containing a discrete V^V–μ-O–Fe^III angular core have been synthesized for the first time through a targeted synthesis route: confirmation in favor of such a heterobimetallic core structure has come from single-crystal X-ray diffraction analysis and electrospray ionization mass spectrometry

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

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

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

Pentanuclear 3d–4f Heterometal Complexes of M^II₃Ln^III₂ (M = Ni, Cu, Zn and Ln = Nd, Gd, Tb) Combinations: Syntheses, Structures, Magnetism, and Photoluminescence Properties

A new family of pentanuclear 3d–4f heterometal complexes of general composition [Ln^III₂(M^IIL)₃(μ₃-O)₃H]­(ClO₄)·<i>x</i>H₂O (<b>1</b>–<b>5</b>) [Ln = Nd, M = Zn, <b>1</b>; Nd, Ni, <b>2</b>; Nd, Cu, <b>3</b>; Gd, Cu, <b>4</b>; Tb, Cu, <b>5</b>] have been synthesized in moderate yields (50–60%) following a self-assembly reaction involving the hexadentate phenol-based ligand, viz., <i>N</i>,<i>N</i>-bis­(2-hydroxy-3-methoxy-5-methylbenzyl)-<i>N</i>^′,<i>N</i>^′-diethylethylenediamine (H₂L). Single-crystal X-ray diffraction analyses have been used to characterize these complexes. The compounds are all isostructural, having a 3-fold axis of symmetry that passes through the 4f metal centers. The [M^IIL] units in these complexes are acting as bis-bidentate metalloligands and, together with μ₃-oxido bridging ligands, complete the slightly distorted monocapped square antiprismatic nine-coordination environment around the 4f metal centers. The cationic complexes also contain a H⁺ ion that occupies the central position at the 3-fold axis. Magnetic properties of the copper­(II) complexes (<b>3</b>–<b>5</b>) show a changeover from antiferromagnetic in <b>3</b> to ferromagnetic 3d–4f interactions in <b>4</b> and <b>5</b>. For the isotropic Cu^II–Gd^III compound <b>4</b>, the simulation of magnetic data provides very weak Cu–Gd (<i>J</i>₁ = 0.57 cm^–1) and Gd–Gd exchange constants (<i>J</i>₂ = 0.14 cm^–1). Compound <b>4</b> is the only member of this triad, showing a tail of an out-of-phase signal in the ac susceptibility measurement. A large-spin ground state (<i>S</i> = 17/2) and a negative value of <i>D</i> (−0.12 cm^–1) result in a very small barrier (8 cm^–1) for this compound. Among the three Nd^III₂M^II₃ (M = Zn^II, Ni^II, and Cu^II) complexes, only the Zn^II analogue (<b>1</b>) displays an NIR luminescence due to the ⁴F_3/2 → ⁴I_11/2 transition in Nd^III when excited at 290 nm. The rest of the compounds do not show such Nd^III/Tb^III-based emission. The paramagnetic Cu^II and Ni^II ions quench the fluorescence in <b>2</b>–<b>5</b> and thereby lower the population of the triplet state