A new tetrakis-substituted pyrazine carboxylic acid, 3,3′,3′′,3′′′-{[pyrazine-2,3,5,6-tetrayltetrakis(methylene)]tetrakis(sulfanediyl)}tetrapropionic acid: crystal structures of two triclinic polymorphs and of two potassium–organic frameworks

Two polymorphs of the title tetrakis-substituted pyrazine carboxylic acid, 3,3′,3′′,3′′′-{[pyrazine-2,3,5,6-tetrayltetrakis(methylene))tetrakis(sulfanediyl]}tetrapropionic acid, C20H28N2O8S4, (H4L1), have been obtained, H4L1_A and H4L1_B. Each structure crystallized with half a molecule in the asymmetric unit of a triclinic P\overline{1} unit cell. The whole molecules are generated by inversion symmetry, with the pyrazine rings being located about inversion centers. The crystals of H4L1_B were of poor quality, but the X-ray diffraction analysis does show the change in conformation of the –CH2—S—CH2—CH2– side chains compared to those in polymorph H4L1_A. In the crystal of H4L1_A, molecules are linked by two pairs of O—H...O hydrogen bonds, enclosing R 2 2(8) ring motifs forming layers parallel to plane (100), which are linked by C—H...O hydrogen bonds to form a supramolecular framework. In the crystal of H4L1_B, molecules are also linked by two pairs of O—H...O hydrogen bonds enclosing R 2 2(8) ring motifs, however here, chains are formed propagating in the [001] direction and stacking up the a-axis. Reaction of H4L1 with Hg(NO3)2 in the presence of a potassium acetate buffer did not produce the expected binuclear complex, instead crystals of a potassium–organic framework were obtained, poly[(μ-3-{[(3,5,6-tris{[(2-carboxyethyl)sulfanyl]methyl}pyrazin-2-yl)methyl]sulfanyl}propanoato)potassium], [K(C20H27N2O8S4)] n (KH3L1). The organic mono-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. A carboxy H atom is disordered by symmetry and the charge is compensated for by a potassium ion. A similar reaction with Zn(NO3)2 resulted in the formation of crystals of a dipotassium-organic framework, poly[(μ-3,3′-{[(3,6-bis{[(2-carboxyethyl)sulfanyl]methyl}pyrazine-2,5-diyl)bis(methylene)]bis(sulfanediyl)}dipropionato)dipotassium], [K2(C20H26N2O8S4)] n (K2H2L1). Here, the organic di-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. Two symmetry-related acid groups are deprotonated and the charges are compensated for by two potassium ions.

Water-soluble Sulfonated Phosphorus(v) Corrolazines and Porphyrazines: Effect of Macrocycle Contraction and Pyrazine Ring Fusion on Spectral, Acid-base and Photophysical Properties

Novel water-soluble dihydroxophosphorus(V) complexes of sulphophenyl substituted porphyrazine (6), corrolazine (7) and its pyrazine fused derivative (8) have been prepared and their spectral, acid-base and photophysical properties in aqueous solutions...

Crystal structures of [(μ2-L1)dibromidodicopper(II)] dibromide and poly[[(μ2-L1)diiodidodicopper(I)]-di-μ-iodido-dicopper(I)], where L1 is 2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane

The reaction of the hexathiapyrazinophane ligand, 2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane (L1), with copper(II) dibromide led to the formation of a binuclear complex, [μ2-2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane]bis[bromidocopper(II)] dibromide, [Cu2Br2(C16H24N2S6)]Br2, (I). The complex possesses inversion symmetry with the pyrazine ring being situated about a center of symmetry. The ligand coordinates to the copper(II) atom in a bis-tetradentate manner and the copper atom has a fivefold NS3Br coordination environment with a distorted shape. The reaction of ligand L1 with copper(I) iodide also gave a binuclear complex, which is bridged by a Cu2I2 unit to form a two-dimensional coordination polymer, poly[[μ2-2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane]tetra-μ-iodido-tetracopper(I)], [Cu4I4(C16H24N2S6)] n , (II). The binuclear unit possesses inversion symmetry with the pyrazine ring being located about a center of symmetry. The Cu2I2 unit is also located about an inversion center. The two independent copper(I) atoms are both fourfold coordinate. That coordinating to the ligand L1 in a bis-tridentate manner has an NS2I coordination environment and an irregular shape, while the second copper(I) atom, where L1 coordinates in a bis-monodentate manner, has an SI3 coordination environment with an almost perfect tetrahedral geometry. In the crystal of I, the cations and Br− anions are linked by a number of C—H...S and C—H...Br hydrogen bonds, forming a supramolecular network. In the crystal of II, the two-dimensional coordination polymers lie parallel to the ab plane and there are no significant inter-layer contacts present.

The crystal structures, Hirshfeld surface analyses and energy frameworks of two hexathiapyrazinophane regioisomers; 2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane and 2,5,8,11,14,17-hexathia-[9.9](2,5,3,6)-pyrazinophane

The title thiapyrazinophanes, 2,5,8,11,14,17-hexathia-[9.9](2,6,3,5)-pyrazinophane, C16H24N2S6, (I), and 2,5,8,11,14,17-hexathia-[9.9](2,5,3,6)-pyrazinophane, C16H24N2S6, (II), are regioisomers; m-bis L1 and p-bis L1, respectively. Both compounds have a central tetra-2,3,5,6-methylenepyrazine unit with two –S—CH2—CH2—S—CH2—CH2—S– chains, linking the methylene C atoms at positions 2 and 6 and 3 and 5 on the pyrazine ring of I, but linking the methylene C atoms at positions 2 and 5 and 3 and 6 on the pyrazine ring of II. Both compounds crystallize with half a molecule in the asymmetric unit. The whole molecule of I is generated by inversion symmetry, with the pyrazine ring being located about a center of symmetry. The whole molecule of II is generated by twofold rotation symmetry, with the pyrazine N atoms being located on the twofold rotation axis. In compound I, there are pairs of intramolecular C—H...S contacts present, but none in compound II. In the crystal of I, there are no significant intermolecular interactions present, while in the crystal of II, molecules are linked by pairs of C—H...S hydrogen bonds, forming corrugated layers lying parallel the ac plane. The Hirshfeld surfaces and the energy frameworks of the two regioisomers indicate little difference in the interatomic contacts, which are dominated by dispersion forces.

The Tyranny of Arm-Wrestling Methyls on Iron(II) Spin State in Pseudo-Octahedral [Fe(didentate)3] Complexes

The connection of a sterically constrained 3-methyl-pyrazine ring to a N-methyl-benzimidazole unit to give the unsymmetrical α,α’-diimine ligand L5 has been programmed for the design of pseudo-octahedral spin-crossover [Fe(L5)3]2+ units, the transition temperature (T1/2) of which occurs in between those reported for related facial tris-didentate iron chromophores fitted with 3-methyl-pyridine-benzimidazole in a LaFe helicate (T1/2 ~ 50 K) and with 5-methyl-pyrazine-benzimidazole L2 ligands (T1/2 ~350 K). A thorough crystallographic analysis of [Fe(L5)3](ClO4)2 (I), [Ni(L5)3](ClO4)2 (II), [Ni(L5)3](BF4)2∙H2O (III), [Zn(L5)3](ClO4)2 (IV), [Ni(L5)3](BF4)2∙1.75CH3CN (V), and [Zn(L5)3](BF4)2∙1.5CH3CN (VI) shows the selective formation of pure facial [M(L5)3]2+ cations in the solvated crystals of the tetrafluoroborate salts and alternative meridional isomers in the perchlorate salts. Except for a slightly larger intra-strand interannular twist between the aromatic heterocycles in L5, the metric parameters measured in [Zn(L5)3]2+ are comparable to those reported for [Zn(L2)3]2+, where L2 is the related unconstrained ligand. This similitude is reinforced by comparable ligand-field strengths (∆oct) and nephelauxetic effects (as measured by the Racah parameters B and C) extracted from the electronic absorption spectra recorded for [Ni(L5)3]2+ and [Ni(L2)3]2+. In this context, the strictly high-spin behavior observed for [Fe(L5)3]2+ within the 5–300 K range contrasts with the close to room-temperature spin-crossover behavior of [Fe(L2)3]2+ (T1/2 = 349(5) K in acetonitrile). This can be unambiguously assigned to an intraligand arm wrestling match operating in bound L5, which prevents the contraction of the coordination sphere required for accommodating low-spin FeII. Since the analogous 3-methyl-pyridine ring in [Fe(L3)3]2+ derivatives are sometimes compatible with spin-crossover properties, the consequences of repulsive intra-strand methyl–methyl interactions are found to be amplified in [Fe(L5)3]2+ because of the much lower basicity of the 3-methyl-pyrazine ring and the resulting weaker thermodynamic compensation. The decrease of the stability constants by five orders of magnitude observed in going from [M(L2)3]2+ to [M(L5)3]2+ (M = NiII and ZnII) is diagnostic for the operation of this effect, which had been not foreseen by the authors.

Poly[(μ4-5,7-dihydro-1H,3H-dithieno[3,4-b:3′,4′-e]pyrazine-κ4 N:N′:S:S′)tetra-μ3-iodido-tetracopper]: a three-dimensional copper(I) coordination polymer

The reaction of ligand 5,7-dihydro-1H,3H-dithieno[3,4-b:3′,4′-e]pyrazine (L) with CuI lead to the formation of a three-dimensional coordination polymer, incorporating the well known [Cu x I x ] n staircase motif (x = 4). These polymer [Cu4I4] n chains are linked via the N and S atoms of the ligand to form the three-dimensional coordination polymer poly[(μ4-5,7-dihydro-1H,3H-dithieno[3,4-b:3′,4′-e]pyrazine-κ4 N:N′:S:S′)tetra-μ3-iodido-tetracopper], [Cu4I4(C8H8N2S2)] n (I). The asymmetric unit is composed of half a ligand molecule, with the pyrazine ring located about a center of symmetry, and two independent copper(I) atoms and two independent I− ions forming the staircase motif via centers of inversion symmetry. The framework is consolidated by C—H...I hydrogen bonds.

Identification, synthesis and biological evaluation of pyrazine ring compounds from Talaromyces minioluteus (Penicillium minioluteum)

Three new pyrazine derivatives, named talaropyrazines A–C (1–3), were isolated from the chemical investigation of the fungus Talaromyces minioluteus.

Effect of alkyl distribution in pyrazine on pyrazine flavor release in bovine serum albumin solution

The methyl groups on the pyrazine ring affect the interaction of pyrazines with BSA. The non-covalent interaction between alkyl-pyrazines and BSA was confirmed. Alkyl-pyrazines could induce the polarity and conformation change of BSA.

Rational magnetic modification of N,N-dioxidized pyrazine ring expanded adenine and thymine: a diradical character induced by base pairing and double protonation

A magnetic modification strategy and possible magnetic modulation methods for the adenine/thymine-based magnets are reported.