Slow Magnetic Relaxation in a Hydrogen-Bonded 2D Array of Mononuclear Dysprosium(III) Oxamates

The reaction of <i>N</i>-(2,6-dimethylphenyl)­oxamic acid with dysprosium­(III) ions in a controlled basic media afforded the first example of a mononuclear lanthanide oxamate complex exhibiting a field-induced slow magnetic relaxation behavior typical of single-ion magnets (SIMs). The hydrogen-bond-mediated self-assembly of this new bifunctional dysprosium­(III) SIM in the solid state provides a unique example of 2D hydrogen-bonded polymer with a herringbone net topology

Slow Magnetic Relaxation in a Hydrogen-Bonded 2D Array of Mononuclear Dysprosium(III) Oxamates

The reaction of <i>N</i>-(2,6-dimethylphenyl)­oxamic acid with dysprosium­(III) ions in a controlled basic media afforded the first example of a mononuclear lanthanide oxamate complex exhibiting a field-induced slow magnetic relaxation behavior typical of single-ion magnets (SIMs). The hydrogen-bond-mediated self-assembly of this new bifunctional dysprosium­(III) SIM in the solid state provides a unique example of 2D hydrogen-bonded polymer with a herringbone net topology

Cytosine Nucleobase Ligand: A Suitable Choice for Modulating Magnetic Anisotropy in Tetrahedrally Coordinated Mononuclear Co^II Compounds

A family of tetrahedral mononuclear CoII complexes with the cytosine nucleobase ligand is used as the playground for an in-depth study of the effects that the nature of the ligand, as well as their noninnocent distortions on the Co­(II) environment, may have on the slow magnetic relaxation effects. Hence, those compounds with greater distortion from the ideal tetrahedral geometry showed a larger-magnitude axial magnetic anisotropy (D) together with a high rhombicity factor (E/D), and thus, slow magnetic relaxation effects also appear. In turn, the more symmetric compound possesses a much smaller value of the D parameter and, consequently, lacks single-ion magnet behavior

Theoretical Insights into the Ferromagnetic Coupling in Oxalato-Bridged Chromium(III)-Cobalt(II) and Chromium(III)-Manganese(II) Dinuclear Complexes with Aromatic Diimine Ligands

Two novel heterobimetallic complexes of formula [Cr­(bpy)­(ox)2Co­(Me2phen)­(H2O)2]­[Cr­(bpy)­(ox)2]·4H2O (1) and [Cr­(phen)­(ox)2Mn­(phen)­(H2O)2]­[Cr­(phen)­(ox)2]·H2O (2) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, and Me2phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the “complex-as-ligand/complex-as-metal” strategy by using Ph4P­[CrL­(ox)2]·H2O (L = bpy and phen) and [ML′(H2O)4]­(NO3)2 (M = Co and Mn; L′ = phen and Me2phen) as precursors. The X-ray crystal structures of 1 and 2 consist of bis­(oxalato)­chromate­(III) mononuclear anions, [CrIIIL­(ox)2]−, and oxalato-bridged chromium­(III)-cobalt­(II) and chromium­(III)-manganese­(II) dinuclear cations, [CrIIIL­(ox)­(μ-ox)­MIIL′(H2O)2]+ [M = Co, L = bpy, and L′ = Me2phen (1); M = Mn and L = L′ = phen (2)]. These oxalato-bridged CrIIIMII dinuclear cationic entities of 1 and 2 result from the coordination of a [CrIIIL­(ox)2]− unit through one of its two oxalato groups toward a [MIIL′(H2O)2]2+ moiety with either a trans- (M = Co) or a cis-diaqua (M = Mn) configuration. The two distinct CrIII ions in 1 and 2 adopt a similar trigonally compressed octahedral geometry, while the high-spin MII ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in 1 and 2, respectively. Variable temperature (2.0–300 K) magnetic susceptibility and variable-field (0–5.0 T) magnetization measurements for 1 and 2 reveal the presence of weak intramolecular ferromagnetic interactions between the CrIII (SCr = 3/2) ion and the high-spin CoII (SCo = 3/2) or MnII (SMn = 5/2) ions across the oxalato bridge within the CrIIIMII dinuclear cationic entities (M = Co and Mn) [J = +2.2 (1) and +1.2 cm–1 (2); H = –J SCr·SM]. Density functional electronic structure calculations for 1 and 2 support the occurrence of S = 3 CrIIICoII and S = 4 CrIIIMnII ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the dyz(Cr)/dxy(M), dxz(Cr)/dxy(M), dx2–y2(Cr)/dxy(M), dyz(Cr)/dxz(M), and dxz(Cr)/dyz(M) pairs of orthogonal magnetic orbitals and the dx2–y2(Cr)/dx2–y2(M), dxz(Cr)/dxz(M), and dyz(Cr)/dyz(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in 1 and 2

Two-Dimensional Coordination Polymers Constructed Using, Simultaneously, Linear and Angular Spacers and Cobalt(II) Nodes. New Examples of Networks of Single-Ion Magnets

Two novel bidimensional coordination polymers, [Co­(azbbpy)­(4,4′-bipy)_0.5(DMF)­(NCS)₂]·MeOH (<b>1</b>) and [Co­(azbbpy)­(bpe)_0.5(DMF)­(NCS)₂]·0.25H₂O (<b>2</b>), resulted from the assembling of cobalt­(II) ions by 1,3-bis­(4-pyridyl)­azulene, using either 4,4′-bipyridyl or 1,2-bis­(4-pyridyl)­ethylene as neutral spacers. The cobalt­(II) nodes in <b>1</b> and <b>2</b> act as single-ion magnets (SIMs)

Cytosine Nucleobase Ligand: A Suitable Choice for Modulating Magnetic Anisotropy in Tetrahedrally Coordinated Mononuclear Co^II Compounds

A family of tetrahedral mononuclear Co^II complexes with the cytosine nucleobase ligand is used as the playground for an in-depth study of the effects that the nature of the ligand, as well as their noninnocent distortions on the Co­(II) environment, may have on the slow magnetic relaxation effects. Hence, those compounds with greater distortion from the ideal tetrahedral geometry showed a larger-magnitude axial magnetic anisotropy (<i>D</i>) together with a high rhombicity factor (<i>E</i>/<i>D</i>), and thus, slow magnetic relaxation effects also appear. In turn, the more symmetric compound possesses a much smaller value of the <i>D</i> parameter and, consequently, lacks single-ion magnet behavior

Utilizing Raman Spectroscopy as a Tool for Solid- and Solution-Phase Analysis of Metalloorganic Cage Host–Guest Complexes

The host–guest chemistry of coordination cages continues to promote significant interest, not least because confinement effects can be exploited for a range of applications, such as drug delivery, sensing, and catalysis. Often a fundamental analysis of noncovalent encapsulation is required to provide the necessary insight into the design of better functional systems. In this paper, we demonstrate the use of various techniques to probe the host–guest chemistry of a novel Pd2L4 cage, which we show is preorganized to selectively bind dicyanoarene guests with high affinity through hydrogen-bonding and other weak interactions. In addition, we exemplify the use of Raman spectroscopy as a tool for analyzing coordination cages, exploiting alkyne and nitrile reporter functional groups that are contained within the host and guest, respectively

Theoretical Insights into the Ferromagnetic Coupling in Oxalato-Bridged Chromium(III)-Cobalt(II) and Chromium(III)-Manganese(II) Dinuclear Complexes with Aromatic Diimine Ligands

Two novel heterobimetallic complexes of formula [Cr­(bpy)­(ox)₂Co­(Me₂phen)­(H₂O)₂]­[Cr­(bpy)­(ox)₂]·4H₂O (<b>1</b>) and [Cr­(phen)­(ox)₂Mn­(phen)­(H₂O)₂]­[Cr­(phen)­(ox)₂]·H₂O (<b>2</b>) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, and Me₂phen = 2,9-dimethyl-1,10-phenanthroline) have been obtained through the “complex-as-ligand/complex-as-metal” strategy by using Ph₄P­[CrL­(ox)₂]·H₂O (L = bpy and phen) and [ML′(H₂O)₄]­(NO₃)₂ (M = Co and Mn; L′ = phen and Me₂phen) as precursors. The X-ray crystal structures of <b>1</b> and <b>2</b> consist of bis­(oxalato)­chromate­(III) mononuclear anions, [Cr^IIIL­(ox)₂]⁻, and oxalato-bridged chromium­(III)-cobalt­(II) and chromium­(III)-manganese­(II) dinuclear cations, [Cr^IIIL­(ox)­(μ-ox)­M^IIL′(H₂O)₂]⁺ [M = Co, L = bpy, and L′ = Me₂phen (<b>1</b>); M = Mn and L = L′ = phen (<b>2</b>)]. These oxalato-bridged Cr^IIIM^II dinuclear cationic entities of <b>1</b> and <b>2</b> result from the coordination of a [Cr^IIIL­(ox)₂]⁻ unit through one of its two oxalato groups toward a [M^IIL′(H₂O)₂]²⁺ moiety with either a <i>trans-</i> (M = Co) or a <i>cis</i>-diaqua (M = Mn) configuration. The two distinct Cr^III ions in <b>1</b> and <b>2</b> adopt a similar trigonally compressed octahedral geometry, while the high-spin M^II ions exhibit an axially (M = Co) or trigonally compressed (M = Mn) octahedral geometry in <b>1</b> and <b>2</b>, respectively. Variable temperature (2.0–300 K) magnetic susceptibility and variable-field (0–5.0 T) magnetization measurements for <b>1</b> and <b>2</b> reveal the presence of weak intramolecular ferromagnetic interactions between the Cr^III (<i>S</i>_Cr = 3/2) ion and the high-spin Co^II (<i>S</i>_Co = 3/2) or Mn^II (<i>S</i>_Mn = 5/2) ions across the oxalato bridge within the Cr^IIIM^II dinuclear cationic entities (M = Co and Mn) [<i>J</i> = +2.2 (<b>1</b>) and +1.2 cm^–1 (<b>2</b>); <b>H</b> = –<i>J</i> <b>S</b>_<b>Cr</b>·<b>S</b>_<b>M</b>]. Density functional electronic structure calculations for <b>1</b> and <b>2</b> support the occurrence of <i>S</i> = 3 Cr^IIICo^II and <i>S</i> = 4 Cr^IIIMn^II ground spin states, respectively. A simple molecular orbital analysis of the electron exchange mechanism suggests a subtle competition between individual ferro- and antiferromagnetic contributions through the σ- and/or π-type pathways of the oxalato bridge, mainly involving the d_<i>yz</i>(Cr)/d_<i>xy</i>(M), d_<i>xz</i>(Cr)/d_<i>xy</i>(M), d_{<i>x</i>²–<i>y</i>²}(Cr)/d_<i>xy</i>(M), d_<i>yz</i>(Cr)/d_<i>xz</i>(M), and d_<i>xz</i>(Cr)/d_<i>yz</i>(M) pairs of orthogonal magnetic orbitals and the d_{<i>x</i>²–<i>y</i>²}(Cr)/d_{<i>x</i>²–<i>y</i>²}(M), d_<i>xz</i>(Cr)/d_<i>xz</i>(M), and d_<i>yz</i>(Cr)/d_<i>yz</i>(M) pairs of nonorthogonal magnetic orbitals, which would be ultimately responsible for the relative magnitude of the overall ferromagnetic coupling in <b>1</b> and <b>2</b>

Field-Induced Slow Magnetic Relaxation in a Six-Coordinate Mononuclear Cobalt(II) Complex with a Positive Anisotropy

The novel mononuclear Co­(II) complex <i>cis</i>-[Co^II(dmphen)₂(NCS)₂]·0.25EtOH (<b>1</b>) (dmphen = 2,9-dimethyl-1,10-phenanthroline) features a highly rhombically distorted octahedral environment that is responsible for the strong positive axial and rhombic magnetic anisotropy of the high-spin Co^II ion (<i>D</i> = +98 cm^–1 and <i>E</i> = +8.4 cm^–1). Slow magnetic relaxation effects were observed for <b>1</b> in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co­(II) complex with a transverse anisotropy energy barrier

Field-Induced Slow Magnetic Relaxation in a Six-Coordinate Mononuclear Cobalt(II) Complex with a Positive Anisotropy

The novel mononuclear Co­(II) complex <i>cis</i>-[Co^II(dmphen)₂(NCS)₂]·0.25EtOH (<b>1</b>) (dmphen = 2,9-dimethyl-1,10-phenanthroline) features a highly rhombically distorted octahedral environment that is responsible for the strong positive axial and rhombic magnetic anisotropy of the high-spin Co^II ion (<i>D</i> = +98 cm^–1 and <i>E</i> = +8.4 cm^–1). Slow magnetic relaxation effects were observed for <b>1</b> in the presence of a dc magnetic field, constituting the first example of field-induced single-molecule magnet behavior in a mononuclear six-coordinate Co­(II) complex with a transverse anisotropy energy barrier