New Route to Local Order Models for Disordered Crystalline Materials: Diffuse Scattering and Computational Modeling of Phloroglucinol Dihydrate

A new, readily tractable route to determining short-range order models for materials exhibiting occupational disorder and diffuse scattering using first-principles solid-state quantum mechanical calculations is presented and illustrated with application to the disordered, layered molecular material phloroglucinol dihydrate

Hydroxido-Supported and Carboxylato Bridge-Driven Aggregation for Discrete [Ni₄] and Interconnected [Ni₂]_<i>n</i> Complexes

Four different carboxylato bridges have been efficiently utilized for growth of three tetranuclear nickel­(II) complexes [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-CH3CO2)2]­(ClO4)2 (1), [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-C2H5CO2)2]­(ClO4)2·1/2H2O (2), and [Ni4(μ3-H2L)2(μ3-OH)2(μ1,3-O2C-C6H4-pNO2)2]­(ClO4)­(p-NO2-C6H4-CO2)·DMF·5H2O (3) and one dinuclear nickel­(II)-based chain complex {[Ni2(μ-H2L)­(μ1,3-O2CCH2Ph)2(H2O)]­(ClO4)·1/2­(CH3OH)}n (4). These were obtained via the reaction of Ni­(ClO4)2·6H2O with H3L [2,6-bis­((2-(2-hydroxyethylamino)­ethylimino)­methyl)-4-methylphenol] and RCO2Na (R = CH3,C2H5, p-NO2C6H4, and PhCH2). This family of complexes is developed from {Ni2(μ-H2L)}3+ fragments following self-aggregation. The complexes were characterized by X-ray crystallography and magnetic measurements. The changes from acetate, propionate, and p-nitrobenzoate to phenylacetate groups resulted in two different types of coordination aggregation. These compounds are new examples of [Ni4] and [Ni2]n complexes where organization of the building motifs are guided by the type of the carboxylate groups responsible for in-situ generation and utilization of HO– bridges with alteration in the aggregation process within the same ligand environment. Studies on the magnetic behavior of the compounds reveal that the exchange coupling within 1–4 is predominantly antiferromagnetic in nature

New Route to Local Order Models for Disordered Crystalline Materials: Diffuse Scattering and Computational Modeling of Phloroglucinol Dihydrate

A new, readily tractable route to determining short-range order models for materials exhibiting occupational disorder and diffuse scattering using first-principles solid-state quantum mechanical calculations is presented and illustrated with application to the disordered, layered molecular material phloroglucinol dihydrate

Hydroxido-Supported and Carboxylato Bridge-Driven Aggregation for Discrete [Ni₄] and Interconnected [Ni₂]_<i>n</i> Complexes

Four different carboxylato bridges have been efficiently utilized for growth of three tetranuclear nickel­(II) complexes [Ni₄(μ₃-H₂L)₂(μ₃-OH)₂(μ_1,3-CH₃CO₂)₂]­(ClO₄)₂ (<b>1</b>), [Ni₄(μ₃-H₂L)₂(μ₃-OH)₂(μ_1,3-C₂H₅CO₂)₂]­(ClO₄)₂·1/2H₂O (<b>2</b>), and [Ni₄(μ₃-H₂L)₂(μ₃-OH)₂(μ_1,3-O₂C-C₆H₄-<i>p</i>NO₂)₂]­(ClO₄)­(<i>p</i>-NO₂-C₆H₄-CO₂)·DMF·5H₂O (<b>3</b>) and one dinuclear nickel­(II)-based chain complex {[Ni₂(μ-H₂L)­(μ_1,3-O₂CCH₂Ph)₂(H₂O)]­(ClO₄)·1/2­(CH₃OH)}_<i>n</i> (<b>4</b>). These were obtained via the reaction of Ni­(ClO₄)₂·6H₂O with H₃L [2,6-bis­((2-(2-hydroxyethylamino)­ethylimino)­methyl)-4-methylphenol] and RCO₂Na (R = CH₃,C₂H₅, <i>p</i>-NO₂C₆H₄, and PhCH₂). This family of complexes is developed from {Ni₂(μ-H₂L)}³⁺ fragments following self-aggregation. The complexes were characterized by X-ray crystallography and magnetic measurements. The changes from acetate, propionate, and <i>p</i>-nitrobenzoate to phenylacetate groups resulted in two different types of coordination aggregation. These compounds are new examples of [Ni₄] and [Ni₂]_<i>n</i> complexes where organization of the building motifs are guided by the type of the carboxylate groups responsible for in-situ generation and utilization of HO^– bridges with alteration in the aggregation process within the same ligand environment. Studies on the magnetic behavior of the compounds reveal that the exchange coupling within <b>1</b>–<b>4</b> is predominantly antiferromagnetic in nature

Three-Way Crystal-to-Crystal Reversible Transformation and Controlled Spin Switching by a Nonporous Molecular Material

Porous materials capable of hosting external molecules are paramount in basic and applied research. Nonporous materials able to incorporate molecules via internal lattice reorganization are however extremely rare since their structural integrity usually does not resist the guest exchange processes. The novel heteroleptic low-spin Fe­(II) complex [Fe­(bpp)­(H2L)]­(ClO4)2·1.5C3H6O (1; bpp = 2,6-bis­(pyrazol-3-yl)­pyridine, H2L = 2,6-bis­(5-(2-methoxyphenyl)­pyrazol-3-yl)­pyridine) crystallizes as a compact discrete, nonporous material hosting solvate molecules of acetone. The system is able to extrude one-third of these molecules to lead to [Fe­(bpp)­(H2L)]­(ClO4)2·C3H6O (2), switching to the high-spin state while experiencing a profound crystallographic change. Compound 2 can be reversed to the original material upon reabsorption of acetone. Single crystal X-ray diffraction experiments on the latter system (1′) and on 2 show that these are reversible single-crystal-to-single-crystal (SCSC) transformations. Likewise, complex 2 can replace acetone by MeOH and H2O to form [Fe­(bpp)­(H2L)]­(ClO4)2·1.25MeOH·0.5H2O (3) through a SCSC process that also implies a switch to the spin state. The 3→1 transformation through acetone reabsorption is also demonstrated. Besides the spin switching at room temperature, this series of SCSC transformations causes macroscopic changes in color that can be followed by the naked eye. The reversible exchanges of chemicals are therefore easily sensed at the temperature at which these occur, contrary to what is the case for most of the few existing nonporous spin-based sensors, which feature a large temperature gap between the process monitored and the mechanism of detection

Three-Way Crystal-to-Crystal Reversible Transformation and Controlled Spin Switching by a Nonporous Molecular Material

Porous materials capable of hosting external molecules are paramount in basic and applied research. Nonporous materials able to incorporate molecules via internal lattice reorganization are however extremely rare since their structural integrity usually does not resist the guest exchange processes. The novel heteroleptic low-spin Fe­(II) complex [Fe­(bpp)­(H2L)]­(ClO4)2·1.5C3H6O (1; bpp = 2,6-bis­(pyrazol-3-yl)­pyridine, H2L = 2,6-bis­(5-(2-methoxyphenyl)­pyrazol-3-yl)­pyridine) crystallizes as a compact discrete, nonporous material hosting solvate molecules of acetone. The system is able to extrude one-third of these molecules to lead to [Fe­(bpp)­(H2L)]­(ClO4)2·C3H6O (2), switching to the high-spin state while experiencing a profound crystallographic change. Compound 2 can be reversed to the original material upon reabsorption of acetone. Single crystal X-ray diffraction experiments on the latter system (1′) and on 2 show that these are reversible single-crystal-to-single-crystal (SCSC) transformations. Likewise, complex 2 can replace acetone by MeOH and H2O to form [Fe­(bpp)­(H2L)]­(ClO4)2·1.25MeOH·0.5H2O (3) through a SCSC process that also implies a switch to the spin state. The 3→1 transformation through acetone reabsorption is also demonstrated. Besides the spin switching at room temperature, this series of SCSC transformations causes macroscopic changes in color that can be followed by the naked eye. The reversible exchanges of chemicals are therefore easily sensed at the temperature at which these occur, contrary to what is the case for most of the few existing nonporous spin-based sensors, which feature a large temperature gap between the process monitored and the mechanism of detection

Multimetastability in a Spin-Crossover Compound Leading to Different High-Spin-to-Low-Spin Relaxation Dynamics

The relaxation kinetics of both the thermally trapped and photoinduced high-spin (HS) states of the spin-crossover compound [Fe­(H4L)2]­(ClO4)2·H2O·2­(CH3)2CO (1) were measured and found to differ significantly. Calorimetry measurements then demonstrated that relaxation of the thermally trapped phase was concurrent with two separate processes, not previously detected as such. Determination of the photogenerated HS structure revealed a new metastable HS state of the system, much closer structurally to the low-spin phase than the thermally trapped one. This difference is proposed as the root of the disparate kinetic behavior, which is proposed to require two processes in the case of the structurally more complex thermally trapped state. Therefore, light irradiation is shown as a mechanism to decouple effectively the structural and magnetic phase transitions that occur in 1 during the course of its spin crossover

Three-Way Crystal-to-Crystal Reversible Transformation and Controlled Spin Switching by a Nonporous Molecular Material

Porous materials capable of hosting external molecules are paramount in basic and applied research. Nonporous materials able to incorporate molecules via internal lattice reorganization are however extremely rare since their structural integrity usually does not resist the guest exchange processes. The novel heteroleptic low-spin Fe­(II) complex [Fe­(bpp)­(H2L)]­(ClO4)2·1.5C3H6O (1; bpp = 2,6-bis­(pyrazol-3-yl)­pyridine, H2L = 2,6-bis­(5-(2-methoxyphenyl)­pyrazol-3-yl)­pyridine) crystallizes as a compact discrete, nonporous material hosting solvate molecules of acetone. The system is able to extrude one-third of these molecules to lead to [Fe­(bpp)­(H2L)]­(ClO4)2·C3H6O (2), switching to the high-spin state while experiencing a profound crystallographic change. Compound 2 can be reversed to the original material upon reabsorption of acetone. Single crystal X-ray diffraction experiments on the latter system (1′) and on 2 show that these are reversible single-crystal-to-single-crystal (SCSC) transformations. Likewise, complex 2 can replace acetone by MeOH and H2O to form [Fe­(bpp)­(H2L)]­(ClO4)2·1.25MeOH·0.5H2O (3) through a SCSC process that also implies a switch to the spin state. The 3→1 transformation through acetone reabsorption is also demonstrated. Besides the spin switching at room temperature, this series of SCSC transformations causes macroscopic changes in color that can be followed by the naked eye. The reversible exchanges of chemicals are therefore easily sensed at the temperature at which these occur, contrary to what is the case for most of the few existing nonporous spin-based sensors, which feature a large temperature gap between the process monitored and the mechanism of detection

Multimetastability in a Spin-Crossover Compound Leading to Different High-Spin-to-Low-Spin Relaxation Dynamics

The relaxation kinetics of both the thermally trapped and photoinduced high-spin (HS) states of the spin-crossover compound [Fe­(H₄L)₂]­(ClO₄)₂·H₂O·2­(CH₃)₂CO (<b>1</b>) were measured and found to differ significantly. Calorimetry measurements then demonstrated that relaxation of the thermally trapped phase was concurrent with two separate processes, not previously detected as such. Determination of the photogenerated HS structure revealed a new metastable HS state of the system, much closer <i>structurally</i> to the low-spin phase than the thermally trapped one. This difference is proposed as the root of the disparate kinetic behavior, which is proposed to require two processes in the case of the structurally more complex thermally trapped state. Therefore, light irradiation is shown as a mechanism to decouple effectively the structural and magnetic phase transitions that occur in <b>1</b> during the course of its spin crossover

Statistical Distribution of Binary Ligands within Rhodium–Organic Octahedra Tunes Microporosity in Their Assemblies

Structure–porosity relationships for metal–organic polyhedra (MOPs) are hardly investigated because they tend to be amorphized after activation, which inhibits crystallographic characterization. Here, we show a mixed-ligand strategy to statistically distribute two distinct carbazole-type ligands within rhodium-based octahedral MOPs, leading to systematic tuning of the microporosity in the resulting amorphous solids