L. Alte da Veiga

Pyrrolidine-based amino alcohols: novel ligands for the enantioselective alkylation of benzaldehyde

A series of easily obtained pyrrolidine-based -amino alcohols derived from tartaric acid and primary amines was synthesized and used as chiral ligands in the enantioselective alkylation of benzaldehyde. Using diethylzinc, 1-phenyl-1-propanol was obtained with enantiomeric excesses of up to 80% when (3S,4S)-N-(1-naphthylmethyl)-3,4-dihydroxypyrrolidine was used. The nature of the N-substituent on the ligand, as well as the reaction temperature proved to significantly influence reaction product distribution as well as the enantiomeric excess of the chiral alcohol.

Crystal structure of tetrakis (μ-betaine-O,O′) dichloro-dicopper(II) dichloride tetrahydrated

Abstract[Cu2(bet)4Cl2]Cl2·4H2O (bet = betaine: IUPAC name: trimethylammonioacetate) is monoclinic, space group P21/c, a = 11.0510(10) Å, b = 14.7140(4) Å, c = 11.1620(15) Å, β = 107.40(2)°. The dinuclear copper(II) cation [Cu2(bet)4Cl2]2+ is counterbalanced by two naked Cl− ions. The copper(II) ions have a square bipyramidal environment with oxygen atoms from the acetato groups in the basal planes and a chlorine and a copper atom occupying the apical positions. The metal atoms are μ2-bridged by four acetato groups and the molecular symmetry is close to C2h. The two symmetry-independent chelating betaine molecules are present in their zwitterionic, neutral form.

2,4-Dibromo-5-hydroxybenzaldehyde

The title compound, C 7 H 4 Br 2 O 2 , crystallizes as cen trosymmetric dimers in which two molecules are linked by two hydrogen bonds between the hydroxyl and carbonyl groups, with an O. . .O distance of 2.839(5)A Other intermolecular interactions are weak. There are no unusual intramolecular bond distances or angles. The atoms of the aldehyde group and the Br atoms, however are found to deviate significantly from the plane of the benzene ring.

An oxo-centred trinuclear FeIII complex: tri­aqua­hexakis(μ2-betaine-O:O′)-μ3-oxo-triiron(III) bis­(tetra­chloro­manganate) trichloride ­hexahydrate

The title compound, [Fe(3)(C(5)H(11)NO(2))(6)O(H(2)O)(3)](MnCl(4))(2)Cl(3).6H(2)O, contains a triiron core linked by a mu(3)-bridging oxide ion. Each of the iron(III) ions has a distorted octahedral environment, being coordinated, in addition to the oxide ion, by four neutral betaine molecules and one water molecule. The N-alkylated alpha-amino acid betaine is present in the dipolar zwitterionic form and chelates pairs of Fe atoms at the vertices of the triangular [Fe(3)O](7+) ionic core. The Fe complex has a crystallographically imposed D3 symmetry. The water molecules fully exhaust their potential as hydrogen donors, forming a two-dimensional hydrogen-bond network in planes parallel to (001).

Crystal structure of the nonlinear optical compound L-arginine fluoride

L-arginine fluoride is a promising compound that exhibits nonlinear optical properties. It efficiently converts two single photons of the same polarization and frequency ω to one photon of frequency 2ω (type I phase matching). C6H15N4O2+F− is monoclinic, space group P21, a = 5.4475(4) Å, b = 8.5133(6) Å, c = 10.2195(7) Å, β = 93.475(6)°. The cation has a zwitterionic form, protonated at both the guanidyl and amino groups. The arginine Cγ atom is in a trans position to the carboxyl group. A complex three-dimensional hydrogen bond network links the anions and cations together.

Very short F—H⋯F hydrogen bond in l-argininium fluoride hydrogen fluoride

There are two symmetry-independent formula units of the title compound, C6H15N4O2+·F−·HF, per cell. Both cations have a zwitterionic form, protonated at both the guanidyl and amino groups. The two symmetry-independent cations differ in their conformation. In one of them the Cγ atom is in a gauche position to both the amino and carboxyl groups, while in the other this atom is trans to the amino group. The two anions have very similar geometry. The F− ions are strongly hydrogen bonded to an HF molecule [F—H⋯F 2.233 (2) and 2.248 (3) A], thereby forming an asymmetric non-linear bifluoride anion. These F⋯F distances are the shortest reported for an asymmetric HF2− anion.

A new orthorhombic phase of N,N'-diphenylguanidine

A new orthorhombic phase of the title compound, C 13 H 13 N 3 , is reported. There are two symmetry-independent molecules in the unit cell, as in the monoclinic phase, both having a syn-anti conformation of the phenyl rings with respect to the unsubstituted N atom. This orthorhombic phase differs from the monoclinic one in the hydrogen-bonding scheme and molecular packing. Bond lengths and angles within the guanidine moiety are close to those expected for a central Csp 2 atom with one C=N and two C-N bonds. The anti ring binds to the guanidine moiety as C aryl -NH-C and the syn ring as C aryl -N=C.

N,N'-Diphenylguanidinium Nitrate

The cation of the title salt, C 13 H 14 N + 3 .NO - 3 , is found to have a conformation with both phenyl rings lying in syn positions with respect to the unsubstituted N atom. The geometry of the guanidinium group is close to that expected for a central C sp . atom. The structure is stabilized by a two-dimensional network of hydrogen bonds in the (100) plane, where the O atoms of the anion are acceptors from the N-H guanidinium groups.

A New Allotropic Form of trans‐Dichlorobis(creatinine)platinum(II) Dihydrate

The synthesis and crystal structure of a new allotropic form (violet crystals) of trans-bis(2-amino-1-methyl-1,5-dihydro-4H-imidazol-4-one-N 1 )dichloroplatinum(II), [PtCl 2 (C 4 H 7 N 3 O) 2 ].2H 2 O, are reported. This form differs from the two crystal forms (yellow and green crystals) studied previously in its intermolecular hydrogen-bonding scheme. The crystal structure of the new form is isomorphous with that reported for the corresponding palladium complex, trans-[PdCl 2 (C 4 H 7 N 3 O) 2 ].2H 2 O.

On the prediction of order in the σ phases on the basis of a sphere-packing model

A theory for the order in tr phases based on the sphere-packing model of Wilson & Spooner [Acta Cryst. (1973), A29, 342-352] has been examined using a mathematical analysis. The analysis suggests that the prediction of order in these phases based on latticeconstant variations associated with variations in atomic diameter should be treated with caution, particularly where the results are at variance with experimentally determined results.