Mixed Ca/Sr salt forms of salicylic acid, tuning structure and aqueous solubility

Ten isostructural single-crystal diffraction studies of mixed cation Ca/Sr salt forms of the salicylate anion are presented, [Ca(1 − x)Srx(C7H5O3)2(OH2)2], where x = 0, 0.041, 0.083, 0.165, 0.306, 0.529, 0.632, 0.789, 0.835 and 1. The structure of an isostructural Sr/Ba species [Sr0.729Ba0.271(C7H5O3)2(OH2)2], is also described. The Ca/Sr structures form a series where, with increasing Sr content, the unit cell expands in both the crystallographic a and c directions (by 1.80 and 3.18% respectively), but contracts slightly in the b direction (−0.31%). The largest percentage structural expansion lies parallel to the direction of propagation of the one-dimensional coordination polymer that is the primary structural feature. This structural expansion is thus associated with increased M—O distances. Aqueous solubility measurements show that solubility generally increases with increasing Sr content·Thus tuning the composition of these mixed counterion salt forms leads to sytematic structural changes and allows solubility to be tuned to values between those for the pure Ca and Sr species

A predicted dimer-based polymorph of 10,11-dihydrocarbamazepine (Form IV)

A novel polymorph of 10,11-dihydrocarbamazepine (form IV), which had been predicted to be thermodynamically feasible, was obtained from the vapour phase and displays an R22(8) hydrogen bonded dimer motif in contrast to the catemeric motifs in forms I–III

3-Amino­carbonyl­pyridinium difluoro­acetate at 123 K

In the crystal of the title compound, C6H7N2O+·C2HF2O2 −, the cation adopts a catemeric N—H⋯O hydrogen-bonded chain motif involving the carboxamide group, with two further N—H⋯O hydrogen bonds connecting the cations to adjacent difluoro­acetate anions via the carboxamide and pyridinium N atoms. The carboxamide group of the nicotinamidium ion is twisted by 32.3 (6)° from the pyridine ring plane. A number of C—H⋯O and C—H⋯F interactions consolidate the packing

Solid-State Forms of β-Resorcylic Acid: How Exhaustive Should a Polymorph Screen Be?

An extensive experimental screen, coupled with a computational study, revealed seven new solid-state forms of β-resorcylic acid. The known, stable polymorph II° shows a reversible phase transformation to the new, kinetically stable, probably disordered high temperature form I. The study provides a consistent picture of the solid-state of β-resorcylic acid

Structure and stability of two polymorphs of creatine and its monohydrate

An experimental search for crystalline forms of creatine including a variable temperature X-ray powder diffraction study has produced three polymorphs and a formic acid solvate. The crystal structures of creatine forms I and II were determined from X-ray powder diffraction data plus the creatine formic acid (1 : 1) solvate structure was obtained by single crystal X-ray diffraction methods. Evidence of a third polymorphic form of creatine obtained by rapid desolvation of creatine monohydrate is also presented. The results highlight the role of automated parallel crystallisation, slurry experiments and VT-XRPD as powerful techniques for effective physical form screening. They also highlight the importance of various complementary analytical techniques in structural characterisation and in achieving better understanding of the relationship between various solid-state forms. The structural relationships between various solid-state forms of creatine using the XPac method provided a rationale for the different relative stabilities of forms I and II of creatine with respect to the monohydrate form

Unraveling unprecedented charge carrier mobility through structure property relationship of four isomers of didodecyl[1]benzothieno[3,2-b][1]benzothiophene

Since the dawn of organic electronics in the 1970’s, academic and industrial research efforts have led to dramatic improvements of the solubility, stability, and electronic properties of organic semiconductors (OSCs).[1, 2] The common benchmark to characterize the electrical performances of OSCs is their charge carrier mobility μ (cm2 V–1 s–1), defined as the drift velocity of the charge carrier (cm s–1) per unit of applied electric field (V cm–1). Reaching high mobilities in OSCs is highly desirable as it allows faster operation of transistors and energy savings by reduced calculation times.[2, 3] However, OSCs performances (conventional values usually range from 1 to 10 cm2 V–1 s–1, with highest values obtained with single-crystal devices mostly exempt of structural defects) are still not comparable to that of state-of-the-art inorganic semiconductors (e.g. metal oxides with µ = 20-50 cm2 V–1 s–1 and polycrystalline silicon with µ > 100 cm2 V–1 s–1) thereby hampering important potential technological applications such as flexible organic light-emitting diode (OLED) displays and wearable electronics.[3, 4

A structural database for salts selection

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Alkaline earth metal salts of 1-naphthoic acid

The structures of the Mg, Ca, Sr and Ba salts of 1-naphthoic acid are examined and compared with analogous structures of salts of benzoate derivatives. It is shown that catena-poly[[[diaquabis(1-naphthoato-kappa O)magnesium(II)]-mu-aqua]dihydrate], {[Mg(C11H7O2)(2)(H2O)(3)]center dot 2H(2)O}(n), exists as a one-dimensional coordination polymer that propagates only through Mg-OH2-Mg interactions along the crystallographic b direction. In contrast with related benzoate salts, the naphthalene systems are large enough to prevent inorganic chain-to-chain interactions, and thus species with inorganic channels rather than layers are formed. The Ca, Sr and Ba salts all have metal centres that lie on a twofold axis (Z'=1/2) and all have the common name catena-poly[[diaquametal(II)]-bis(mu-1-naphthoato)-kappa O-3,O':O;kappa O-3:O,O '], [M(C-11-H7O2)(2)(H2O)(2)](n), where M = Ca, Sr or Ba. The Ca and Sr salts are essentially isostructural, and all three species form one-dimensional coordination polymers through a carboxylate group that forms three M-O bonds. The polymeric chains propagate via c-glide planes and through MOMO four-membered rings. Again, inorganic channel structures are formed rather than layered structures, and the three structures are similar to those found for Ca and Sr salicylates and other substituted benzoates

Lithium aspirinate hemihydrate

The title compound {systematic name: catena-poly[ lithium(I)-mu(3)-acetylsalicylato-hemi-mu(2)-aqua]}, {[Li(C9H7O4)]center dot 0.5H(2)O}(n), is the hemihydrate of the lithium salt of aspirin. The carboxylate groups and water molecules bridge between Li atoms to form a one-dimensional coordination chain composed of two distinct ring types. The water O atom lies on a twofold axis. Hydrogen bonding between water donors and carbonyl acceptors further links the coordination chains to form a sheet structure

Close encounters of the 3D kind – exploiting high dimensionality in molecular semiconductors

In this Research News article we discuss the significance of dimensionality on the charge-transport properties of organic semiconductors. Dimensionality is defined in two ways: as a function of (i) the -conjugated framework within the molecular structure, and (ii) the degree and direction of intermolecular close-contacts between molecules in the bulk. In terms of dimensionality, silicon is a good role model for organic semiconductors, since it demonstrates 3D architecture in the bulk through covalent bonding. Achieving this for organics is challenging and requires not only a 3D molecular structure, but also a network of intermolecular short contacts in three dimensions. This review identifies the limitations of low dimensional materials and summarizes the challenges faced in progressing towards fully 3D organic semiconductors