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A family of heteroleptic spin crossover (SCO) [FeIII(qsal-5-I)(qsal-5-OMe)]A·sol (qsal-5-X = 5-X-2-[(8-quinolylimino)methyl]phenolate; A = NO3−1 sol = 2MeOH, NCS−2 sol = 0.75MeOH·1.3H2O, BF4−3 sol = MeOH, OTf−4, sol = MeOH) complexes have been synthesized. Most of the complexes exhibit gradual SCO, with the exception of NCS, which is principally high spin. In contrast, the OTf complex shows an abrupt hysteretic SCO (35 K) after solvent loss. The magnetic properties of this complex are significantly improved in comparison to the related homoleptics, [Fe(qsal-I)2]OTf 5 (hysteresis, 8 K) and [Fe(qsal-5-OMe)2]OTf·CH2Cl26 (gradual SCO). Structural studies reveal that slight changes in the crystal packing cause stronger interactions improving the cooperativity. These findings are supported by DFT calculations using the r2SCAN functional in which the calculated structures show that SCO from the LS to the HS state causes pronounced scissoring of the 1D π–π chains and substantial changes in their relative orientation following loss of MeOH. [ABSTRACT FROM AUTHOR]

A series of three solvates [Fe(naphPren)2]I·CH2Cl21, [Fe(naphPren)2]I·CHCl32 and [Fe(naphPren)2]I·acetone 3 with the novel ligand HnaphPren {2-([(2-(propylamino)ethyl]imino)methyl)naphthalen-2-ol} is reported. Magnetic studies of these complexes reveal that 1 exhibits an abrupt SCO at 162 K, whereas 2 possesses a more gradual SCO centred at 172 K. 3 is trapped in the HS state, but irradiation at 980 nm enables accessibility to a hidden LS state via reverse-LIESST. The structures of 1–3 reveal that 1 and 2 show reversible disorder in the propyl group that is coupled to SCO which is absent in the acetone solvate. This study demonstrates how solvent subtly alters the packing impacting the potential flexibility of the propyl chain and thereby switching SCO on or off. [ABSTRACT FROM AUTHOR]

Sildenafil is a specific inhibitor of the phosphodiesterase type 5 (PDE-5) enzyme that protects cyclic guanosine monophosphate from breakdown by PDE-5. It is a biopharmaceutical categorization system Class II medication with low bioavailability because it is almost insoluble in water. The objectives of this study were to prepare sildenafil cocrystals with co-former molecules including aspirin (acetylsalicylic acid [ASA]), fumaric acid (FMA), and benzoic acid (BZA) to improve the water solubility of sildenafil. The cocrystals were prepared by antisolvent addition (AA) and slow solvent evaporation (SE) methods. The stoichiometric ratios of sildenafil and co-former molecules were varied. The obtained crystals were characterized by stereomicroscope, Fourier transformed infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), and powder X-ray diffraction (PXRD). The water solubility of sildenafil cocrystals was compared with sildenafil base. In the AA method, the crystals only form in sildenafil-ASA reaction. These crystals were not cocrystals between sildenafil and ASA because they were formed to new substances that were confirmed by single-crystal X-ray diffraction. In the SE method, the cocrystals were successfully prepared in the reaction of sildenafil with ASA, FMA, and BZA which use acetone or ethyl acetate as a solvent. The obtained crystals are irregular shapes and their FT-IR, NMR, and PXRD results exhibited the characteristics of sildenafil and its co-former. The stoichiometric ratios of sildenafil and co-formers after cocrystallization were different from an initial of crystallization. The sildenafil cocrystals with ASA, FMA, and BZA by SE method had higher water solubility than sildenafil base. The sildenafil-FMA cocrystals had the highest water solubility and increased up to five times when compared with sildenafil base. [ABSTRACT FROM AUTHOR]

The influence of the halogen substituent on crystal packing and redox properties is investigated in a series of heteroleptic complexes [Fe(qsal-X)(dipic)]·MeOH (qsal-X = 4-halogen-2-[(8-quinolylimino)methyl]phenolate; dipic = 2,6-pyridinedicarboxylate; X = F 1, Cl 2, Br 3 and I 4). Compounds 1 and 2 exhibit triclinic symmetry (P1¯), whereas 3 and 4 crystallise in monoclinic P21/n. The crystal packing shows self-sorting of the ligands with π-π interactions between the qsal-X ligands and overlap of the dipic ligands to form a 1D chain, that is supported by C–H⋯O interactions. In 1 and 2, the cross-section of the 1D chain is square, while for 3 and 4, it is rectangular. In the former, the dipic ligands interact through C＝O⋯π interactions, while π–π interactions are found in 3 and 4. Neighbouring chains are connected via π–π interactions involving the quinoline rings, but their relative position is driven by the preference of 1 and 2, for C–H⋯X interactions, whereas 3 and 4 form O⋯X halogen bonds. The nature and topology of the electron density of these interactions have been investigated using molecular electrostatic potential (MEP) mapping, quantum theory of atoms in molecules (QTAIM) and 'non-covalent interactions' (NCI) analysis. UV-visible experiments show LMCT bands associated with the qsal-X ligands, confirming the structure is stable in solution. Electrochemical studies reveal slight tuning of the Fe3+/Fe2+ redox couple showing a linear relationship between E°′ and the Hammett parameter σp. [ABSTRACT FROM AUTHOR]