Dimitris Mentzafos

Metal complexes of the anti-inflammatory drug sodium [2-[(2,6-dichlorophenyl)amino]phenyl]acetate (diclofenac sodium). Molecular and crystal structure of cadmium diclofenac

Abstract The reactions of ZnCl2, CdCl2 and Hg(NO3)2 · H2O with deprotonated diclofenac (L) were studied in aqueous solutions. Complexes of the formulae [Zn(L)2(H2O)], [Cd(L)2(H2O)], [HgL2] and (Cd2(H2O)(C2H5OH)2(L)4]n were isolated and characterized as solid products by elemental analyses and spectral (IR, 1H NMR) and thermal studies. The crystal structure of the complex [Cd2(H2O)(C2H5OH)2L4]n was also solved. The central feature of the macromolecule is a dinuclear moiety. Distorted octahedral coordination at Cd(1) is completed by oxygen atoms from one molecule of water, two molecules of C2H5OH, two oxygen atoms from one chelating ligand with a monoatomic bridging oxygen that bridges the atoms Cd(2)Cd(I) = 4.490(1) A and one oxygen from a bidentate bridging carboxylato group that bridges the atoms Cd(1)Cd(2) = 4.300(1) A. The geometry at Cd(2) is that of a distorted square pyramid with oxygen atoms from one chelating and one monodentate carboxylato group and the monoatomic bridging oxygen atom occupying equatorial positions. The apical site of the square pyramid is occupied by the oxygen atom of the bidentate briding carboxylato group. The crystal structure of the diclofenac acid is also reported.

The crystal structure of the 1:1 complex of β-cyclodextrin with trans-cinnamic acid

The crystal structure of the 1:1 complex of beta-cyclodextrin (cyclomaltoheptaose) with trans-cinnamic acid was studied by X-ray diffraction. Two beta-cyclodextrin molecules related by a twofold crystal axis form dimers in the hydrophobic cavity of which, two guest molecules are entirely buried. The complex crystallizes in the monoclinic C2 space group with channel-type molecular packing. The oxygen atoms of the carboxylate group of the trans-cinnamic acid molecule form strong hydrogen bonds with two water molecules lying in the interdimeric space of the hydrophobic channel.

The crystal structure of 6I-(6-aminohexyl)amino-6I-deoxycyclomaltoheptaose.

The monosubstituted cyclomaltoheptaose derivative, 6I-(6-aminohexyl)amino-6I-deoxycyclomaltoheptaose, crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 32.513(2), b = 15.3871(9), c = 15.2645(9) A, V = 7636.6(8) A3 and Z = 4. The macrocycles are spirally aligned along the twofold screw axis parallel to the c crystal axis forming polymeric-like columns. The 6-aminohexyl chain enters the cavity of an adjacent cyclomaltoheptaose moiety in the column from the secondary side and its extremity protrudes from the primary side of the latter. All the atoms of the chain exhibit high thermal motion.

Coordination chemistry of corrosion inhibitors of the benzotriazole type: Preparation and characterization of cobalt(II) complexes with 1-methylbenzotriazole (Mebta) and the crystal structures of [CoCl2(Mebta)2], trans-[Co(NCS)2 (Mebta)4], trans-[Co(NCS)2(MeOH)2(Mebta)2] and cis-[Co(NO3)2(Mebta)2]

Abstract An inorganic model approach to the corrosion inhibition of metals by benzotriazoles has been initiated. The preparation and characterization of monomeric cobalt(II) complexes of the types [CoX2(Mebta)2](X = Cl, Br, NCS, NO 3), (MebtaH)[CoCl3(Mebta)], (MebtaH)2[CoCl4], [Co(NCS)2(Mebta)4], [Co(NCS)2 (MeOH)2(Mebta)2] and [Co(NO3)2 L2(Mebta)2] (L = H2O, MeOH), where Mebta = 1-methylbenzotriazole, are described. Four representative complexes have been structurally characterized by single-crystal X-ray diffraction studies; [CoCl2(Mebta)2] (1), trans- [Co(NCS)2(Mebta)4] (5), trans-[Co(NCS)2 (MeOH)2(Mebta)2] (6) and cis-[Co(NO3)2(Mebta)2] (8). Mebta acts as a monodentateligand binding through N(3). The geometry about cobalt in 1 is tetrahedral, while complexes 5, 6 and 8 have octahedral stereochemistries. The new complexes were also characterized by elemental and thermogravimetric analyses, conductivity measurements, variable-temperature magnetochemistry and spectroscopic (IR, ligand field, low-temperature ESR) methods. The data are discussed in terms of the nature of bonding and known structures.

Structural study of the inclusion compounds of thymol, carvacrol and eugenol in β-cyclodextrin by X-ray crystallography

The crystal structures of the inclusion compounds of thymol, carvacrol and eugenol, (components of essential oils of vegetable origin) in β-cyclodextrin have been determined. Thymol/β-CD crystallizes in the space group P1 containing two host molecules in its asymmetric unit whereas both carvacrol/β-CD and eugenol/β-CD complexes crystallize in the space group C2. In all three complexes two host molecules form head-to-head dimers their guest/host stoichiometry being: 1/2 (carvacrol/β-CD), 2/2 (thymol/β-CD) and 3/2 (eugenol/β-CD). In the cases of the thymol/β-CD and the carvacrol/β-CD complexes the β-CD dimers are arranged according to the channel packing mode. The accommodation of the geometrical isomer guests is performed solely by their hydrophobic groups revealing the leading role of the hydrophobic driving forces in the complexation process whereas the position of their hydroxyl group affects the stoichiometry of the formed dimeric complexes. In the case of the eugenol/β-CD dimeric complex one guest molecule is found lying between the β-CD groups in a sandwich fashion whereas the other two symmetry related guests protrude outwards the narrower rim of the hosts with only their hydrophobic allyl-chain located inside the hosts’ cavities. This arrangement prohibits the formation of a channel and the observed crystal packing is that of a Tetrad mode.

Structure of the complex of β-cyclodextrin with β-naphthyloxyacetic acid in the solid state and in aqueous solution

Abstract The structure of the complex of β-cyclodextrin (cyclomaltoheptaose) with β-naphthyloxyacetic acid was studied in solid state by X-ray diffraction and in aqueous solution by 1 H NMR spectroscopy. The complex crystallizes in the channel mode, space group C 2, with a stoichiometry of 2:1; two β-cyclodextrin molecules related by a twofold crystal axis form dimers, in the cavity of which one guest molecule is found on average. The above stoichiometry indicates one guest per β-CD dimer statistically oriented over two positions or two guest molecules in π–π interactions in half of the β-CD dimers and the rest of the β-CD dimers empty. In addition, occupancy of 0.5 for the guest per every β-CD dimer is in accord with the occupancy of the two disordered primary hydroxyls. These two hydroxyl groups, to which the carboxylic oxygen atoms of the guest are hydrogen bonded, point towards the interior of the β-CD cavity. In aqueous solution, the 1 H NMR spectroscopic study indicated that there is a mixture of complexes with host–guest stoichiometries both 1:1 and 2:1.

Structure of the complex of heptakis(2,6-di-O-methyl)-β-cyclodextrin with (2,4-dichlorophenoxy)acetic acid ☆

The structure of the complex formed by heptakis(2,6-di-O-methyl)-beta-cyclodextrin and (2,4-dichlorophenoxy)acetic acid was studied by X-ray diffraction. The dichlorophenyl moiety of the guest molecule was found outside the host hydrophobic cavity in the primary methoxy groups region whereas the oxyacetic acid chain penetrates the cavity from the primary face. The host molecules stacks along the a crystal axis forming a column. In the space between three successive hosts of the column, a guest molecule is accommodated.

Synthesis, structural and physical studies of tin(IV) complexes with 2-(2-pyridyl)benzimidazole

The tin(IV) complexes [SnX4L][L = 2-(2-pyridyl)benzimidazole; X = Cl, Br or I] and [SnMe2Cl2L] were prepared by a dehydration reaction of N-(2-aminophenyl)pyridine-2-carboxamide L′ with either SnX4(X = Cl, Br or I) or SnMe2Cl2 in chloroform solution. The X-ray crystal structures of [SnMe2Cl2L] and [SnBr4L]·0.5MeNO2 show a distorted octahedral geometry around the tin(IV) atom in both molecules. The ligand L acts as a bidentate chelate with ligated atoms being the pyridine-type nitrogens of the heterocyclic rings. The chlorine atoms in [SnMe2Cl2L] are cis while the methyl groups are trans to each other, Infrared and Mossbauer spectra and a correlation of X-ray structural and anti-tumour (P388 lymphocytic leukaemia) data for the octahedral tin(IV) complexes are also reported. The X-ray structures are the first such reported for metal complexes containing 2-(2-pyridyl)benzimidazole.

New developments of the TWIN algorithm for phase extension and refinement in disordered supramolecular structures.

A new development of the TWIN algorithm is described and used for phase extension/refinement in supramolecular complexes. A small number of phased reflections at low resolution are sufficient for the quasi-automated determination of all atomic coordinates, including disordered atoms.

Structure of the 1 : 1 Complex of Hexakis(2,3,6-tri- O-methyl) α-Cyclodextrin with ( R)-(-)-1,7-Dioxaspiro[5.5]undecane

The crystal structure of the 1 : 1 inclusion complex of hexakis(2,3,6-tri-O-methyl)- α-cyclodextrin (TM αCD) with 1,7-dioxaspiro[5.5]undecane (spiroacetal) is orthorhombic, space group C2221, with a = 24.002(2), b = 14.812(1), c = 21.792(2) Å V = 7747.3(11) Å3 and Z = 8. The molecular six-fold axis of TM αCD coincides with the a two-fold crystallographic axis and the guest is located at the secondary methoxy group side, disordered over two positions related by that axis. The guest model used during the refinement is that of the (R)-enantiomer alone because trials to either refine a 1 : 1 mixture of (R)- and (S)-enantiomers or the (S)-enantiomer alone failed. The crystallographic evidence of enantioselectivity towards the (R)-enantiomer of spiroacetal was confirmed by independent experiments and may be attributed to numerous non bonding interactions between host and guest involving non conventional H-bonds.