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(1,3)-Calix[5]arene-crown-3 derivatives 1a and 1b, bearing either three n-butylureido or 1-naphthylureido moieties at the lower rim, respectively, have been synthesised. Their cationic and anionic binding domains have been investigated by a combination of 1D- and 2D-NMR, UV/vis absorption and fluorescence and ESIMS techniques. Complexation data show that the attachment of 1-naphthyl groups at the lower rim of calix[5]crown-3 1b dramatically increases its anion-binding ability over the n-butyl-bearing derivative 1a. Overall, both 1a and 1b act as highly efficient heteroditopic receptors for n-butylammonium halides and in so doing bind these salt species—as spatially-separated ions—much more effectively than the single ionic components. The X-ray crystal structure of the pivotal tris-[2-(2-chloroethoxy)ethoxy]-calixcrown precursor 2 is also reported.

In recent years, X-ray structural determinations of cobalamins (Cbl) have become very accurate thanks to the use of new detectors and synchrotron radiation. This has allowed in depth study of the geometrical features of cobalamins, regarding the large equatorial ligand and, more importantly, their axial fragment, which is involved in the binding of Cbl to proteins and in the catalytic mechanisms of Vitamin B12 based enzymes. These structural aspects, together with their particular crystal packing, are the focus of this review. Several chemical properties, derived from their structural chemistry and not reported in other reviews, are underlined. A comparison to the well-known simple Cbl model, the cobaloximes is also presented and discussed, as this furnishes useful insights into cobalamin chemistry.

SummaryA simple model for evaluation of diffusion times of small molecule into protein crystals has been developed, which takes into account the physical and chemical properties both of protein crystal and the diffusing molecules. The model also includes consideration of binding and the binding affinity of a ligand to the protein. The model has been validated by simulation of experimental set-ups of several examples found in the literature. These experiments cover a wide range of situations: from small to relatively large diffusing molecules, crystals having low, medium, or high protein density, and different size. The reproduced experiments include ligand exchange in protein crystals by soaking techniques. Despite the simplifying assumptions of the model, theoretical and experimental data are in agreement with available data, with experimental diffusion times ranging from a few seconds to several hours. The method has been used successfully for planning intermediate cryotrapping experiments in maltodextrin phosphorylase crystals.

The monocarbonyl Ru(II)–dmso precursor cis,cis,trans-RuCl2(dmso-S)2(dmso-O)(CO) (1) equilibrates slowly in light protected chloroform solution with two new geometrical isomers of formula cis,cis,cis-RuCl2(dmso-S)2(dmso-O)(CO) (2) and cis,mer-RuCl2(dmso-S)3(CO) (3). The three isomers have similar stabilities in solution. In 2 and 3 the three sulfoxides are in a meridional geometry, with the CO ligand coordinated trans to one of the cis chlorides. The new complexes 2 and 3 differ only in the coordination mode of one of the two trans sulfoxides: they are both S-bonded in 3, while one is S-bonded and the other O-bonded in 2. Thus 2 and 3 are linkage isomers of each other. The three isomers 1–3 are also obtained as a mixture by treatment of cis-RuCl2(dmso)4 with CO. The spectroscopic characterization of the new compounds 2 and 3 is reported, together with the X-ray structure of 2. Isomer 2 is the first example of a Ru(II)–CO complex in which coordination through the oxygen atom is found for a dmso that is not trans to CO; isomer 3 is the first example of a Ru(II)–dmso complex featuring three S-bonded dmso ligands with a meridional geometry. Considerations relating the stability of the three isomers to their geometry and to the binding mode of the dmso ligands are reported.

Compounds with hydroxyl ammonium cations, [RR′NHOH][ fac -RuCl 3 (dmso–S) 3 ], with R=R′=H ( 1 ), R=Me, R′=H ( 2 ) and R=R′=Et ( 3 ), have been prepared and structurally characterized by X-ray analyses. The three compounds display chain-like structures, formed by hydrogen bonding between the hydroxyl ammonium cations and the chlorine and oxygen atoms of the ruthenium anion. H-bonding involving the dmso oxygen atoms causes a lengthening of the S–O bonds. The comparison of the solid state structures with results of Molecular Mechanics calculations show that the arrangement of the fac -dmso–S ligands is not determined by H-bonding or packing effects, but from intramolecular steric and electrostatic interactions. These give rise to hindered rotation about the Ru–S bonds.

A method is described for the chiral synthesis of (3 R ,4 S )-3-methyl-3-hydroxy-4-phenyl-β-lactam, a useful precursor for the semi-synthesis of 2′-methyl-taxoids. This protocol follows Seebach's synthetic principle of `self-regeneration of stereocenters' (SRS) and has been applied to addition reactions of the (2 S )-chiral enolates of dioxolan-4-ones, derived from the acetalization of ( S )-α-lactic acid and tert -butylaldehyde or pinacolone, to N- trimethylsilylphenyl aldimine.

A number of trans-3-acetyl-4-alkylpyrrolidin-2-ones 8a–d and 11a,b were prepared and reduction of the keto group, carried out with KBH4 in CH3OH, led mainly to 3-hydroxyethylpyrrolidin-2-ones 13a–d and 19a,b with high stereoselection. Configuration of the newly formed stereogenic centre on the hydroxyethyl chain was assigned by 1H NMR data supported by molecular mechanic calculations and eventually confirmed by X-ray diffraction analysis of p-iodobenzoate derivative 15.

The absolute stereochemistry of a series of (3R)-3-hydroxy-3-alkyl-β-lactams has been determined by circular dichroism and NMR spectroscopies. The sign of the circular dichroism band between 250 and 220 nm was related to the stereochemistry by applying the β-lactam sector rule. The NMR analysis unambiguously determines the relative configuration at C3 and C4 of the β-lactam ring. The reliability of the method has been proved by X-ray analysis of two of the examined compounds. The obtained results are in agreement with the mechanism proposed for the employed synthetic route.

A series of neutral and anionic Rh(III)-chloride compounds bearing ammonia or imidazole (Im) ligands, and isostructural to Ru(III) complexes endowed with antineoplastic activity, were synthesized and characterized spectroscopically. The X-ray crystal structure of [ImH][ trans -RhCl 4 (Im) 2 ] was determined. Crystal data: monoclinic, space group C 2/ c , Z =4, a =13.133(3), b =7.977(1), c =16.683(4) A, β =113.84(2)°. The solution behaviour and some biological parameters of the new rhodium compounds, including cytotoxicity, in vitro interactions with DNA and in vivo antitumour activity against a tumour model, were investigated and compared with those of the corresponding ruthenium analogues.

A series of organometallic complexes derived by organocobaloximes and organorhodoximes in which either one or both the hydrogen bridges have been replaced by BPh 2 groups, RM(DH)(DBPh 2 ) N -MeIm and RM((DBPh 2 ) 2 N -MeIm, respectively, have been synthesised and characterised, both in solution and in solid state. 1 H NMR spectra show that they assume different interconverting conformations in solution. With increasing steric bulk of R, the axial phenyls of the BPh 2 group tend to face N -MeIm, forcing the latter in an orientation which is quite unusual in organocobaloximes and causing a lengthening of the Co-N bond. Some possible implications on the strength of the trans Co-C bond are discussed.

Preparations of [Rh(Hdmg) 2 (H 2 O) 2 ]ClO 4 ( 1 ) (Hdmg=dimethylgyoximate) from [Rh(H 2 O) 6 ](ClO 4 ) 3 and dimethylglyoxime and of [Rh(Hdmg) 2 (PPh 3 ) 2 ]ClO 4 ( 2 ) from 1 and PPh 3 are described. 1 crystallizes in the space group with a =14.910(3), b =6.058(1), c =18.617(4), A, β =107.649(8)°, Z =4. The structure was refined up to R =0.021 for 1849 reflections. The IR and NMR spectra and electrochemical behavior of 1 and 2 are discussed and compared with other rhodoximes. Three polarographic and CV processed can be detected for 2 , the first two, respectively to Rh(II) and Rh(I), being followed by fast reactions.

The title compounds, mer-trichloro-cis-bis(1-methylimidazole)dimethyl sulfoxideruthenium(III) (1) and 4-ethylpyridinium trans-(4-ethylpyridine) (dimethyl sulfoxide)tetrachlororuthenate(III) (2) have been synthesized and structurally characterized. Crystals of 1 [RuCl3(C4H6N2)2(C2H6OS)]·0.5(C3H6O) are monoclinic, space group P2/c with a = 16.836(9), b = 8.646(3), c = 14.017(7) A , β = 110.19(2)°, Z = 4 . Crystals of 2 [RuCl4(C7H9N)(C2H6OS)][C7H10N] are monoclinic, space group P21/n with a = 7.996(1), b = 11.670(1), c = 23.979(3) A , β = 98.39(1)°, Z = 4 . The sulfoxide ligands are S-bonded and trans to the N-planar ligands in both Ru(III) complexes. The two 1Me-Im ligands in 1 are cis to each other and the arrangement is such that its B/B′ interbase dihedral angle is 65.6°. B/RuL4 and B′/RuL4 Dihedral angles are 26.8 and 66.8°, respectively. The 4Et-Py plane in 2 bisects the ClRuCl bond angles. The conformation of the planar N-ligand observed in the X-ray structures is discussed in terms of an interaction between the ligands.

The reaction between methylrhodoxine, CH 3 Rh(DH 2 ) 2 L (L = N-Melm or Py ), and diphenylborinic anhydride affords derivatives containing either one or two diphenylboryl bridges, depending on the ratio complex:diphenylborinic anhydride. Kinetic studies show that the insertion of the diphenylboryl bridges is a two-step process involving the formation of a relatively stable intermediate. The X-ray structure of CH 3 Rh(DH)(DBPh 2 )NMelm shows that the axial phenyl faces the NMeIm, whereas the main conformation in solution, as inferred from 1 H NMR spectra, has the axial phenyl facing the methyl. The bis(diphenylborylated) derivatives are less stable than those of the corresponding cobaloximes, and adopt a conformation with trans axial phenyls.

The effects on the local environment of metal centres in Ti- and Fe-silicalites, induced by a vacuum treatment and by subsequent NH3 dosage, has been studied by means of XANES and UV-vis spectroscopies. The Ti(IV) environment is mainly tetrahedral in vacuo and becomes octahedral after interaction with NH3. Fe(III) is in tetrahedral coordination in presence of adsorbates, while in vacuo it is in a distorted tetrahedral symmetry. These conclusions are qualitatively supported by IR and Raman data.

The reduction of CrCl3 by zinc dust in THF solution followed by slow addition to an ethanolic solution K(acacen) gave a brown powder, which when reacted with pyridine produced an intractable brown tar. Careful recrystallization of the tat from methanol gave a small quantity of crystalline [Cr(acacen)py2][ZnCl3py]. The structure consists of a set of two crystallographically independent complex cations and anions of the above formula. Crystal data: monoclinic space group P21, a=12.667(4), b=16.146(4), c=16.262(5) A, β=108.57(1)°, V=3153(2) A3, Z=4. A total of 7657 reflections was collected with graphite monochromated Mo Kα radiation (to 20=54°), of which 4536 were used in subsequent structure solution and refinement (I ⩾ 3σ(I)). The structure was solved by direct methods, and least-squares refinement converged at R=0.037.

The first crystal structure of a copper(II) complex containing a disulfoxide is reported. The 1,3-bis(n-propylsulfinyl)propane ligand acts as a bis(monodentate) ligand bridging the metal ions through its oxygen atoms to form layers of distorted square planar CuO4 groups (Cu–O, 1.942(3) A) connected by nPrS(CH2)3SnPr bridges (S–O, 1.533(5) A), with homochiral sulfur atoms. Each copper atom achieves a square pyramidal coordination, interacting with the oxygen atom of one perchlorate ion (Cu–O, 2.36(2) A). Crystals consist of a racemic mixture of layers of opposite chirality, held together essentially by van der Waals forces.

The determination of the X-ray structure and formation constant of a Rh III organometallic complex containing bis(salicyl-aldehyde)ethylendiiminate [(pyridine)Rh(salen)(adamantyl)], revealed a cis -influence on the axial metal-nitrogen bond significantly greater than that found in the analogous dimethylglyoximate. Comparison of the formation constants suggests that the stability of the hexacoordinate species with respect to the pentacoordinate species in Rh complexes is greater than that for Co complexes.

Some diastereoisomeric pentacoordinate complexes of the type [Ir(COD)-(NNR ★ )I] (COD = cis , cis -1,5-cyclooctadiene; NNR ★ = 2-pyridinal-1-phenylethylimine (PPEI) (I), 2-acetylpyridine-1-phenylethylimine (APPEI) (II)) have been synthesized. The complexes are active and selective catalysts for asymmetric hydrogen transfer from propan-2-ol to prochiral ketones. Optical yields of up to 84% have been obtained in the reduction of t-butyl phenyl ketone. The structure and absolute configuration of complexes I and II were determined by X-ray diffraction.