Antonio R. Tapia-Benavides

Crystal structure, ferromagnetostructural behavior and evidence of cooperative Jahn–Teller interactions of the complex [CuL]Cl·H2O (L=N-glycyl-2(aminomethyl)benzimidazol), synthesized by a novel simple method of peptide bond formation.

Abstract [CuL]Cl·H2O 1 (L=N-glycyl-2(aminomethyl)benzimidazol) compound crystallizes in the orthorhombic space group Pna21 with unit cell parameters a=7.140(5) A , b=17.621(5) A , c=9.941(5) A . Its structure shows that the copper(II) ion is tetra coordinated with a square planar geometry. The ligand acts as a tridentate and the chloride ion is the fourth ligand. Symmetry related units stack into helicoidal columns along the ā direction producing weakly bonded strips with dihedral angles of 2.6° between two consecutive molecular planes. UV/VIS spectrum of 1 shows one broad and weak band at 622xa0nm, characteristic of d–d transitions, indicative of low local Cu(II) symmetry. X band ESR spectra of 1 at 300 and 77xa0K are axial exchange narrow lines with g∥=2.135 and g⊥=2.028. However, the axial spectrum at 6.4xa0K shows an increment Δg∥=0.076(6) and Δg⊥=0.028(4) which suggests a cooperative Jahn–Teller interactions between complexes via the hydrogen-bonding network. Magnetic susceptibility data at 18–300xa0K and fitted to the modified Bleany–Bowers equation indicate a weak ferromagnetic coupling with 2J≅+17 cm −1 , which is compatible with the helium temperature ESR results and with the helicoidal stacking into columns of the molecules along the a-axis with 78.9° Cu′–Cl′–Cu and 81.2° Cu′–N(1)–Cu bonds angles. The synthesis is a novel, simple and efficient method: in aqueous conditions and heterogeneous phase with basic copper(II) carbonate, which carries out the formation of the stable peptide bond.

SYNTHESES OF N-SUBSTITUTED 2,5-PIPERAZINDIONES

The synthesis of 2,5-piperazindiones, 1,6-dimethoxycarbonylmethyl-2,5- piperazindione (la), 1,6-di-a-methylbenzylcarboxamidomethyl-2,5-piperazindione (I b), 1,6-dibenzhydrylcarboxamidomethyl-2,5-piperazindione (lc) and 1,6-di-2-(1- phenylbenzimidazo1yl)methyl-2,5-pipe~.azindione (Id), is reported. The cyclic dipeptide (la) was obtained from the auto-condensation of the dimethyliminodiacetate promoted by triethylborane or triphenylsilane. Compounds (lb-ld) were prepared by refluxing iminodiacetic acid and the corresponding amine. The X-Ray diffraction structure of (la) reveals boat conformation for its 2,5-piperazindione ring.

Do spiroarsoranes exhibit polytopal equilibrium in solution

The spiroarsoranes 5-phenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (6), (3R,8R)-3,8-dimethyl-5-phenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (7), (2S,7S)-2,7-dimethyl-5-phenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (8), and (3S,8S)-3,8-dimethyl-(2R,7R)-2,5,7-triphenyl-1,6-dioxa-4,9-diaza-5lambda(5)-arsaspiro[4.4]nonane (9) were prepared by reaction of phenylarsonic acid and the correspondig amino alcohol. The presence of polytopal Delta left arrow over right arrow Lambda equilibrium in 6-9 was demonstrated by HPLC and NMR studies. NBO computations at the MP2/6-31+G(2d,2p) level indicate that methyl substitution in C2 or C3 of the oxazarsolane ring determines the predominance of Delta or Lambda stereoisomers. GIAO B3LYP/6-311++G(2d,2p) computations were used to assign experimental (1)H and (13)C NMR spectra.

Syntheses and structural studies of hexa- and pentacoordinated Zn complexes derived from 2-(aminomethyl)benzimidazole and water

AbstractThe complexes trans-bis[2-(aminomethyl)-1H-benzimidazole-κ2N′,N″]diaquazinc(II) dichloride dihydrate 1 and trans-bis[2-(aminomethyl)-1H-benzimidazole-κ2N′,N″]aquazinc(II) dichloride dihydrate 2 were synthesized selectively by the promotion of O–H···Cl hydrogen bond interactions. The hexacoordinated complex 1 was synthesized at pH 4.5. The dilution of 1 in deionized water produced the pentacoordinated complex 2. NMR and vibrational spectroscopies corroborated the presence of these compounds. Moreover, mass spectrometry and thermogravimetric (TGA) studies demonstrated that chloride ions and crystallization water molecules are essential for the stabilization of 1 but not for complex 2. X-ray diffraction crystallography studies indicated that the presence of two water molecules bonded to the Zn atom elongated all of the coordination bonds. The incidence of a network of hydrogen bond interactions compensates for the unstable hexacoordination. Natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM) studies of the crystal structures of 1 and 2 were used to explain the nature of the coordination bonds and the complexes’ stabilityn.

Synthesis and structure of Zn(II) and Cu(II) complexes derived from 2-(aminomethyl)benzimidazole and glycine.

Reactions of 2-(aminomethyl)benzimidazole di-hydrochloride (1·2HCl) and glycine with 3Zn(OH)2·2ZnCO3 or Cu(OAc)2·H2O led to the synthesis of the quaternary coordination complexes 2 and 3. X-ray diffraction showed that these complexes are composed of 2a = [Zn(L)Cl(L′)] and 2b = [Zn(L)(H2O)2(L′)], and of 3a = [Cu(L)(H2O)0.25Cl(L′)] and 3b = [Cu(L)(H2O)1.5(L′)], respectively, where Lu2009=u20092-(aminomethyl)benzimidazole and L′u2009=u2009glycinate. Zn(II) in 2a has an intermediate geometry between a square-pyramid and a trigonal bipyramid structure. However, the geometry about the metal ion of units 2b, 3a, and 3b is distorted octahedral. Moreover, the supramolecular structures for 2 and 3 were assembled through N–H⋯O and O–H⋯Cl hydrogen bonds. In these complexes, H2O and N–H groups serve as proton donors, whereas chloride and C=O groups serve as proton acceptors. Also π–π stacking interactions between aromatic rings contribute to the stabilization of the supramolecular structure of 2 and 3. The Zn and Cu complexes were studied by infrared and Raman spectroscopy, which indicated that 2 and 3 have similar molecular structures in the solid state. Ultrasound activation at the end of the reaction was necessary to yield 2. Graphical Abstract

2-(4-Acetamido-phen-oxy)-2-methyl-propanoic acid.

In the title compound, C12H15NO4, the dihedral angle between the acetamide group and the ring is 29.6u2005(2)(su?)°. In the crystal molecules are linked through N—H⋯O and O—H⋯O hydrogen bonds, thereby forming corrugated sheets propagating in the ac plane. These sheets are composed of R 4 4(28) graph-set motifs.

trans-Bis[2-(aminomethyl)-1H-benzimidazole-κ2N2,N3]aquacopper(II) dichloride dihydrate

In the title compound, [Cu(C8H9N3)2(H2O)]Cl2·2H2O, the CuII ion is coordinated in a square-pyramidal geometry, with four N atoms as basal ligands and one water O atom as an apical ligand. The complex molxadecule is situated on a crystallographic twofold rotation axis. The molxadecules are bonded to their neighbours by N—H⋯O, O—H⋯Cl and N—H⋯Cl hydogen bonds. The packing is further stabilized by π–π interxadactions between the substituted imidazole molxadecules.