Polymorphism in 4-Methoxy-3-nitrobenzaldehyde

Two of the three earlier reported polymorphic forms of 4-methoxy-3-nitrobenzaldehyde have been reinvestigated and fully characterized by a variety of methods including variable temperature powder X-ray diffraction, vibrational spectroscopy (infrared and Raman), calorimetry (differential scanning calorimetry, DSC), and optical microscopy. Differences of DSC thermograms, which were carried out with different cooling rates, suggest a thermodynamic/kinetic competition in the crystallization from the melt. The crystal structures of these two forms have been solved, one by single-crystal methods and the second from synchrotron powder diffraction

Polymorphism in 4-Methoxy-3-nitrobenzaldehyde

Two of the three earlier reported polymorphic forms of 4-methoxy-3-nitrobenzaldehyde have been reinvestigated and fully characterized by a variety of methods including variable temperature powder X-ray diffraction, vibrational spectroscopy (infrared and Raman), calorimetry (differential scanning calorimetry, DSC), and optical microscopy. Differences of DSC thermograms, which were carried out with different cooling rates, suggest a thermodynamic/kinetic competition in the crystallization from the melt. The crystal structures of these two forms have been solved, one by single-crystal methods and the second from synchrotron powder diffraction

Polymorphism in 4-Methoxy-3-nitrobenzaldehyde

Two of the three earlier reported polymorphic forms of 4-methoxy-3-nitrobenzaldehyde have been reinvestigated and fully characterized by a variety of methods including variable temperature powder X-ray diffraction, vibrational spectroscopy (infrared and Raman), calorimetry (differential scanning calorimetry, DSC), and optical microscopy. Differences of DSC thermograms, which were carried out with different cooling rates, suggest a thermodynamic/kinetic competition in the crystallization from the melt. The crystal structures of these two forms have been solved, one by single-crystal methods and the second from synchrotron powder diffraction

Diruthenium Tetracarbonate Trianion, [Ru^II/III₂(O₂CO)₄]³⁻, Based Molecule-Based Magnets: Three-Dimensional Network Structure and Two-Dimensional Magnetic Ordering

HxK1−xMII[Ru2(CO3)4](H2O)y(MeOH)z (M = Mn, Fe, Co, Ni, Mg) were synthesized from the reaction of MII and K3[Ru2(CO3)4] in water and are isomorphous with an orthorhombic three-dimensional network structures based on μ3-CO32− linkages to Ru2 moieties forming layers and also to trans-MII(OH2)4 sites forming linked chains that connect the layers. They, as well as non-isomorphous M = Cu, magnetically order as canted ferrimagnets with Tc = 4.4 ± 1.0 K. The presence of S = 0 MII = Mg(II) has essentially no effect on Tc suggesting that the main magnetic pathway does not occur the through MII-based chains, but only via Ru2···Ru2 linkages that reside in layers. This is a rare example of a magnet based upon a second row transition metal

Enforced Stacking in Crowded Arenes

Enforced Stacking in Crowded Arene

Structures and Magnetostructural Correlation of Two Desolvated Polymorphs of Ferrimagnetic <i>meso</i>-Tetrakis(4-chlorophenyl)porphinatomanganese(III) Tetracyanoethenide, [MnTClPP]⁺[TCNE]^•−

The structures of two polymorphs of [MnTClPP][TCNE] have been determined by Rietveld refinement of the X-ray powder diffraction method. Samples were prepared by thermolysis of the toluene and CH2Cl2 solvates, [MnTClPP][TCNE]·2Sol (Sol = PhMe, CH2Cl2). The desolvated structures are similar to their solvates, consisting of alternating stacks of the molecular donor and acceptor. Among the four structures, the largest changes are observed for the dihedral angle between the mean Mn(N4)TPP and [TCNE]•− planes, and the Mn−(N−C)TCNE angle. A magnetostructural correlation between the intrachain coupling and both the dihedral angle between the mean Mn(N4)TPP and [TCNE]•− planes and Mn−(N−C)TCNE angles is observed. This is in accord with the intrachain coupling arising from the overlap of MnIII dz2-like singly occupied molecular orbital (SOMO) and the z component of the [TCNE]•− π* (πz*) SOMO, which increases with decreasing dihedral angle between the mean Mn(N4)TPP and [TCNE]•− planes and Mn−(N−C)TCNE angle

Diruthenium Tetracarbonate Trianion, [Ru^II/III₂(O₂CO)₄]³⁻, Based Molecule-Based Magnets: Three-Dimensional Network Structure and Two-Dimensional Magnetic Ordering

HxK1−xMII[Ru2(CO3)4](H2O)y(MeOH)z (M = Mn, Fe, Co, Ni, Mg) were synthesized from the reaction of MII and K3[Ru2(CO3)4] in water and are isomorphous with an orthorhombic three-dimensional network structures based on μ3-CO32− linkages to Ru2 moieties forming layers and also to trans-MII(OH2)4 sites forming linked chains that connect the layers. They, as well as non-isomorphous M = Cu, magnetically order as canted ferrimagnets with Tc = 4.4 ± 1.0 K. The presence of S = 0 MII = Mg(II) has essentially no effect on Tc suggesting that the main magnetic pathway does not occur the through MII-based chains, but only via Ru2···Ru2 linkages that reside in layers. This is a rare example of a magnet based upon a second row transition metal

Layered Structure and Swelling Behavior of a Multiple Hydrate-Forming Pharmaceutical Compound

Investigation of one anhydrous and four hydrated forms of a pharmaceutical compound (1) using both single-crystal and high-resolution powder X-ray diffraction methods revealed a two-dimensional framework which, upon exposure to moisture, absorbed water between the layers, causing the lattice to expand by as much as 20% of the axial length along a. The single-crystal structure was solved and refined for the pentahydrate form in space group C2 with unit cell parameters a = 36.961(5) Å, b = 7.458(2) Å, c = 20.691(4) Å, β = 99.461(1)°, and V = 5626(4) Å3. In the single-crystal structure the water layers were parallel to the bc plane and sandwiched by the crystalline compound 1 framework. Upon a change of relative humidity, water goes in and out of the interlayer space with the retention of the layer structure of the development compound. Starting from the anhydrous form, each additional water of hydration increased the interlayer spacing of the pharmaceutical solid by ∼1.3 Å, half the size of a water molecule. In an exploratory formulation, this expansion of interlayer spacing caused tablets to crack upon storage at high relative humidity

The Tetracyanopyrazinide Dimer Dianion, [TCNP]₂²⁻. 2-Electron 8-Center Bonding

The reaction of Cr(C6H6)2 and 1,2,4,5-tetracyanopyrazine (TCNP) forms [Cr(C6H6)2][TCNP], and TCNP is reduced and forms the eclipsed π-[TCNP]22− dimer. Diamagnetic [TCNP]22− has an intradimer separation of 3.14(2) Å. The intradimer C···C and N···N separations are 3.29(2) and 3.42(2) Å, respectively, and increase with the distance from the center of the molecule, due to nitriles bending away from the plane of the molecule by 5 ± 1°. [TCNP]22− is best described by an atoms-in-molecules analysis as having a 2e−/8c C−C bond involving the four C atoms from each six-member ring. The results of B3LYP/6-31+G(d)-computed interactions indicate that the [TCNP]•−···[TCNP]•− interactions in an isolated [TCNP]22− are repulsive by 58.9 kcal/mol, and that the stability of [TCNP]22− primarily originates from [TCNP]•−···cation+ electrostatic interactions, whose sum (−209.8 kcal/mol) exceeds the sum of the repulsive [TCNP]•−···[TCNP]•− and cation+···cation+ interactions (140.3 kcal/mol)

Structures and Magnetostructural Correlation of Two Desolvated Polymorphs of Ferrimagnetic <i>meso</i>-Tetrakis(4-chlorophenyl)porphinatomanganese(III) Tetracyanoethenide, [MnTClPP]⁺[TCNE]^•−

The structures of two polymorphs of [MnTClPP][TCNE] have been determined by Rietveld refinement of the X-ray powder diffraction method. Samples were prepared by thermolysis of the toluene and CH2Cl2 solvates, [MnTClPP][TCNE]·2Sol (Sol = PhMe, CH2Cl2). The desolvated structures are similar to their solvates, consisting of alternating stacks of the molecular donor and acceptor. Among the four structures, the largest changes are observed for the dihedral angle between the mean Mn(N4)TPP and [TCNE]•− planes, and the Mn−(N−C)TCNE angle. A magnetostructural correlation between the intrachain coupling and both the dihedral angle between the mean Mn(N4)TPP and [TCNE]•− planes and Mn−(N−C)TCNE angles is observed. This is in accord with the intrachain coupling arising from the overlap of MnIII dz2-like singly occupied molecular orbital (SOMO) and the z component of the [TCNE]•− π* (πz*) SOMO, which increases with decreasing dihedral angle between the mean Mn(N4)TPP and [TCNE]•− planes and Mn−(N−C)TCNE angle