Manganese- and Lanthanide-Based 1D Chiral Coordination Polymers as an Enantioselective Catalyst for Sulfoxidation

The chiral 1D-coordination polymers (CP) {[Ln₂­(MnLCl)₂­(NO₃)₂­(dmf)₆­(H₂O)₂]·<i>x</i>H₂O}_<i>n</i> [Ln = Pr (<b>1</b>), Nd (<b>2</b>), Sm (<b>3</b>), and Gd (<b>4</b>)] were synthesized by the reaction of <i>N,N</i>′-bis­(4-carboxy­salicylidene)­cyclo­hexane­di­amine (H₄L) with [MnCl₂·4­(H₂O)] and [Ln­(NO₃)₃·<i>x</i>(H₂O)] in the presence of dmf/pyridine at 90 °C. The polymers consist of manganese-salen-based moieties having carboxylate linkers connected to rare earth atoms in a 1D-chain structure. The polymers are very easily accessible. A one-step synthesis for the ligand and a second step for the preparation of the 1D coordination polymers starting from commercially available material are needed. The solid state structures of <b>1</b>–<b>4</b> were established by single-crystal X-ray diffraction. Compounds <b>1</b>–<b>4</b> were investigated as heterogeneous catalysts for the sulfoxidation reaction of various alkyl and aryl sulfides. The influence of various solvents and oxidizing agents on the catalytic reaction was examined. It was found that the catalysts were active for more than one reaction cycle without significant loss of activity. For phenylsulfide with 1 mol % of the catalyst <b>4</b>, a maximum conversion 100% and a chemoselectivity 88% were observed

Origin of Ferromagnetic Exchange Coupling in Donor–Acceptor Biradical Analogues of Charge-Separated Excited States

A new donor–acceptor biradical complex, TpCum,MeZn(SQ-VD) (TpCum,MeZn+ = zinc(II) hydro-tris(3-cumenyl-5-methylpyrazolyl)borate complex cation; SQ = orthosemiquinone; VD = oxoverdazyl), which is a ground-state analogue of a charge-separated excited state, has been synthesized and structurally characterized. The magnetic exchange interaction between the S = 1/2 SQ and the S = 1/2 VD within the SQ-VD biradical ligand is observed to be ferromagnetic, with JSQ‑VD = +77 cm–1 (H = −2JSQ‑VDŜSQ·ŜVD) determined from an analysis of the variable-temperature magnetic susceptibility data. The pairwise biradical exchange interaction in TpCum,MeZn(SQ-VD) can be compared with that of the related donor–acceptor biradical complex TpCum,MeZn(SQ-NN) (NN = nitronyl nitroxide, S = 1/2), where JSQ‑NN ≅ +550 cm–1. This represents a dramatic reduction in the biradical exchange by a factor of ∼7, despite the isolobal nature of the VD and NN acceptor radical SOMOs. Computations assessing the magnitude of the exchange were performed using a broken-symmetry density functional theory (DFT) approach. These computations are in good agreement with those computed at the CASSCF NEVPT2 level, which also reveals an S = 1 triplet ground state as observed in the magnetic susceptibility measurements. A combination of electronic absorption spectroscopy and CASSCF computations has been used to elucidate the electronic origin of the large difference in the magnitude of the biradical exchange coupling between TpCum,MeZn(SQ-VD) and TpCum,MeZn(SQ-NN). A Valence Bond Configuration Interaction (VBCI) model was previously employed to highlight the importance of mixing an SQSOMO → NNLUMO charge transfer configuration into the electronic ground state to facilitate the stabilization of the high-spin triplet (S = 1) ground state in TpCum,MeZn(SQ-NN). Here, CASSCF computations confirm the importance of mixing the pendant radical (e.g., VD, NN) LUMO (VDLUMO and NNLUMO) with the SOMO of the SQ radical (SQSOMO) for stabilizing the triplet, in addition to spin polarization and charge transfer contributions to the exchange. An important electronic structure difference between TpCum,MeZn(SQ-VD) and TpCum,MeZn(SQ-NN), which leads to their different exchange couplings, is the reduced admixture of excited states that promote ferromagnetic exchange into the TpCum,MeZn(SQ-VD) ground state, and the intrinsically weaker mixing between the VDLUMO and the SQSOMO compared to that observed for TpCum,MeZn(SQ-NN), where this orbital mixing is significant. The results of this comparative study contribute to a greater understanding of biradical exchange interactions, which are important to our understanding of excited-state singlet–triplet energy gaps, electron delocalization, and the generation of electron spin polarization in both the ground and excited states of (bpy)Pt(CAT-radical) complexes

Tetranuclear and Pentanuclear Compounds of the Rare-Earth Metals: Synthesis and Magnetism

The Schiff-base proligand 4-<i>tert</i>-butyl-2,6-bis-[(2-hydroxy-phenylimino)­methyl]­phenol (H₃L) was prepared in situ from 4-<i>tert</i>-butyl-2,6-diformylphenol and 2-aminophenol. The proligand (H₃L) was used with dibenzoylmethane (DBMH) or acetylacetone (acacH) with lanthanides giving compounds with varying arrangements of metal atoms and nuclearities. The tetranuclear compound {[Dy₄(L)₃(DBM)₄]­[Et₃NH]} (<b>1</b>) and pentanuclear compound {[Dy₅(μ₃-OH)₂(L)₃(DBM)₄(MeOH)₄]·4­(MeOH)} (<b>2</b>) were obtained from the ligand (L)^3– and dibenzoylmethane. The tetranuclear compounds {[Dy₄(μ₄-OH)­(L)₂(acac)₄(MeOH)₂(EtOH)­(H₂O)]·(NO₃)·2­(MeOH)·3­(EtOH)} (<b>3</b>) and {[Ln₄(μ₃-OH)₂(L)­(HL)­(acac)₅(H₂O)] (HNEt₃)­(NO₃)·2­(Et₂O)} (Ln = Tb (<b>4</b>), Dy (<b>5</b>), Ho (<b>6</b>), and Tm (<b>7</b>)) resulted when the ligand (L)^3– was used in the presence of acetylacetone. In the solid state structures, the tetranuclear compound <b>1</b> adopts a linear arrangement of metal atoms, while tetranuclear compound <b>3</b> has a square grid arrangement of metal atoms, and tetranuclear compounds <b>4</b>–<b>7</b> have a seesaw-shaped arrangement of metal atoms. The composition found from single-crystal X-ray analysis of compound <b>1</b> and <b>3</b>–<b>7</b> is supported by electrospray ionization mass spectrometry (ESI-MS). The magnetic studies on compounds <b>1</b> suggest the presence of weak ferromagnetic interactions, whereas compounds <b>2</b>–<b>6</b> exhibit weak antiferromagnetic interactions between neighboring metal centers. Compounds <b>1</b>,<b> 2</b>, and <b>3</b> also show single-molecule magnet behavior under an applied dc field

Tetranuclear and Pentanuclear Compounds of the Rare-Earth Metals: Synthesis and Magnetism

The Schiff-base proligand 4-<i>tert</i>-butyl-2,6-bis-[(2-hydroxy-phenylimino)­methyl]­phenol (H₃L) was prepared in situ from 4-<i>tert</i>-butyl-2,6-diformylphenol and 2-aminophenol. The proligand (H₃L) was used with dibenzoylmethane (DBMH) or acetylacetone (acacH) with lanthanides giving compounds with varying arrangements of metal atoms and nuclearities. The tetranuclear compound {[Dy₄(L)₃(DBM)₄]­[Et₃NH]} (<b>1</b>) and pentanuclear compound {[Dy₅(μ₃-OH)₂(L)₃(DBM)₄(MeOH)₄]·4­(MeOH)} (<b>2</b>) were obtained from the ligand (L)^3– and dibenzoylmethane. The tetranuclear compounds {[Dy₄(μ₄-OH)­(L)₂(acac)₄(MeOH)₂(EtOH)­(H₂O)]·(NO₃)·2­(MeOH)·3­(EtOH)} (<b>3</b>) and {[Ln₄(μ₃-OH)₂(L)­(HL)­(acac)₅(H₂O)] (HNEt₃)­(NO₃)·2­(Et₂O)} (Ln = Tb (<b>4</b>), Dy (<b>5</b>), Ho (<b>6</b>), and Tm (<b>7</b>)) resulted when the ligand (L)^3– was used in the presence of acetylacetone. In the solid state structures, the tetranuclear compound <b>1</b> adopts a linear arrangement of metal atoms, while tetranuclear compound <b>3</b> has a square grid arrangement of metal atoms, and tetranuclear compounds <b>4</b>–<b>7</b> have a seesaw-shaped arrangement of metal atoms. The composition found from single-crystal X-ray analysis of compound <b>1</b> and <b>3</b>–<b>7</b> is supported by electrospray ionization mass spectrometry (ESI-MS). The magnetic studies on compounds <b>1</b> suggest the presence of weak ferromagnetic interactions, whereas compounds <b>2</b>–<b>6</b> exhibit weak antiferromagnetic interactions between neighboring metal centers. Compounds <b>1</b>,<b> 2</b>, and <b>3</b> also show single-molecule magnet behavior under an applied dc field

Mononuclear and Tetranuclear Compounds of Yttrium and Dysprosium Ligated by a Salicylic Schiff-Base Derivative: Synthesis, Photoluminescence, and Magnetism

The Schiff-base (2-aminoethyl)­hydroxybenzoic acid (H₂L) as a proligand was prepared in situ from 3-formylsalicylic acid and ethanolamine (ETA). The mononuclear {[Y­(HL)₄]­[ETAH]·H₂O} (<b>1</b>) and {[Dy­(HL)₄] [ETAH]·3MeOH·H₂O} (<b>2</b>) and tetranuclear {[Y₄(HL)₂(L)₄(μ₃-OH)₂]·4MeOH·4H₂O} (<b>3</b>), {[Dy₄(HL)₂(L)₄(μ₃-OH)₂]·5­(MeOH)₂·7H₂O (<b>4</b>), and {[Dy₄(HL)₈(L)₂]·4MeOH·2H₂O}­(<b>5</b>) rare-earth metal complexes of this ligand could be obtained as single-crystalline materials by the treatment of H₂L in the presence of the metal salts [Ln­(NO₃)₃·(H₂O)_<i>m</i>] (Ln = Y, Dy). In the solid state, the tetranuclear compounds <b>3</b> and <b>4</b> exhibit butterfly structures, whereas <b>5</b> adopts a rectangular arrangement. Electrospray ionization mass spectrometry data of the ionic compounds <b>1</b> and <b>2</b> support single-crystal X-ray analysis. The yttrium compounds <b>1</b> and <b>3</b> show fluorescence with 11.5% and 13% quantum yield, respectively, whereas the quantum yield of the dysprosium complex <b>4</b> is low. Magnetic studies on the dysprosium compounds <b>4</b> and <b>5</b> suggest the presence of weak antiferromagnetic interactions between neighboring metal centers. Compound <b>4</b> shows single-molecule-magnet behavior with two relaxation processes, one with the effective energy barrier <i>U</i>_eff = 84 K and the preexponential factor τ₀ = 5.1 × 10^–9 s

Mononuclear and Tetranuclear Compounds of Yttrium and Dysprosium Ligated by a Salicylic Schiff-Base Derivative: Synthesis, Photoluminescence, and Magnetism

The Schiff-base (2-aminoethyl)­hydroxybenzoic acid (H₂L) as a proligand was prepared in situ from 3-formylsalicylic acid and ethanolamine (ETA). The mononuclear {[Y­(HL)₄]­[ETAH]·H₂O} (<b>1</b>) and {[Dy­(HL)₄] [ETAH]·3MeOH·H₂O} (<b>2</b>) and tetranuclear {[Y₄(HL)₂(L)₄(μ₃-OH)₂]·4MeOH·4H₂O} (<b>3</b>), {[Dy₄(HL)₂(L)₄(μ₃-OH)₂]·5­(MeOH)₂·7H₂O (<b>4</b>), and {[Dy₄(HL)₈(L)₂]·4MeOH·2H₂O}­(<b>5</b>) rare-earth metal complexes of this ligand could be obtained as single-crystalline materials by the treatment of H₂L in the presence of the metal salts [Ln­(NO₃)₃·(H₂O)_<i>m</i>] (Ln = Y, Dy). In the solid state, the tetranuclear compounds <b>3</b> and <b>4</b> exhibit butterfly structures, whereas <b>5</b> adopts a rectangular arrangement. Electrospray ionization mass spectrometry data of the ionic compounds <b>1</b> and <b>2</b> support single-crystal X-ray analysis. The yttrium compounds <b>1</b> and <b>3</b> show fluorescence with 11.5% and 13% quantum yield, respectively, whereas the quantum yield of the dysprosium complex <b>4</b> is low. Magnetic studies on the dysprosium compounds <b>4</b> and <b>5</b> suggest the presence of weak antiferromagnetic interactions between neighboring metal centers. Compound <b>4</b> shows single-molecule-magnet behavior with two relaxation processes, one with the effective energy barrier <i>U</i>_eff = 84 K and the preexponential factor τ₀ = 5.1 × 10^–9 s

Mononuclear and Tetranuclear Compounds of Yttrium and Dysprosium Ligated by a Salicylic Schiff-Base Derivative: Synthesis, Photoluminescence, and Magnetism

The Schiff-base (2-aminoethyl)­hydroxybenzoic acid (H₂L) as a proligand was prepared in situ from 3-formylsalicylic acid and ethanolamine (ETA). The mononuclear {[Y­(HL)₄]­[ETAH]·H₂O} (<b>1</b>) and {[Dy­(HL)₄] [ETAH]·3MeOH·H₂O} (<b>2</b>) and tetranuclear {[Y₄(HL)₂(L)₄(μ₃-OH)₂]·4MeOH·4H₂O} (<b>3</b>), {[Dy₄(HL)₂(L)₄(μ₃-OH)₂]·5­(MeOH)₂·7H₂O (<b>4</b>), and {[Dy₄(HL)₈(L)₂]·4MeOH·2H₂O}­(<b>5</b>) rare-earth metal complexes of this ligand could be obtained as single-crystalline materials by the treatment of H₂L in the presence of the metal salts [Ln­(NO₃)₃·(H₂O)_<i>m</i>] (Ln = Y, Dy). In the solid state, the tetranuclear compounds <b>3</b> and <b>4</b> exhibit butterfly structures, whereas <b>5</b> adopts a rectangular arrangement. Electrospray ionization mass spectrometry data of the ionic compounds <b>1</b> and <b>2</b> support single-crystal X-ray analysis. The yttrium compounds <b>1</b> and <b>3</b> show fluorescence with 11.5% and 13% quantum yield, respectively, whereas the quantum yield of the dysprosium complex <b>4</b> is low. Magnetic studies on the dysprosium compounds <b>4</b> and <b>5</b> suggest the presence of weak antiferromagnetic interactions between neighboring metal centers. Compound <b>4</b> shows single-molecule-magnet behavior with two relaxation processes, one with the effective energy barrier <i>U</i>_eff = 84 K and the preexponential factor τ₀ = 5.1 × 10^–9 s