Attractive and repulsive forces in a crystal of [Rb(18-crown-6)][SbCl6] under high pressure.

The compression behavior of [Rb(18-crown-6)][SbCl6] crystal under pressure up to 2.16 (3) GPa was investigated in a diamond anvil cell (DAC) using a mixture of pentane-isopentane (1:4) as the pressure-transmitting fluid. The compound crystallizes in trigonal space group R3 and no phase transition was observed in the indicated pressure range. The low value of pressure bulk modulus [9.1 (5) GPa] found in this crystal is a characteristic of soft materials with predominant dispersive and electrostatic interaction forces. The nonlinear relationship between unit-cell parameters under high pressure is attributed to the influence of reduced intermolecular H...Cl contacts under pressure over 0.73 GPa. It also explains the high compression efficiency of [Rb(18-crown-6)][SbCl6] crystals at relatively low pressures, resulting in a significant shift of the Rb atom to the center of the crown ether cavity. At pressures above 0.9 GPa, steric repulsion forces begin to play a remarkable role, since an increasing number of interatomic H...Cl and H...H contacts become shorter than the sum of their van der Waals (vdW) radii. Below 0.9 GPa, both unit-cell parameter dependences (P-a and P-c) exhibit hysteresis upon pressure release, demonstrating their influence on the disordered model of Rb atoms. The void reduction under pressure also demonstrates two linear sections with the inflection point at 0.9 GPa. Compression of the crystal is accompanied by a significant decrease in the volume of the voids, leading to the rapid approach of Rb atoms to the center of the crown ether cavity. For the Rb atom to penetrate into the center of the crown ether cavity in [Rb(18-crown-6)][SbCl6], it is necessary to apply a pressure of about 2.5 GPa to disrupt the balance of atomic forces in the crystal. This sample serves as a compression model demonstrating the influence of both attractive and repulsive forces on the change in unit-cell parameters under pressure.

Novel O-acylated (E)-3-aryl-6,7-dihydrobenzisoxazol-4(5H)-one oximes targeting HSP90-HER2 axis in breast cancer cells.

Novel O-acylated (E)-3-aryl-6,7-dihydrobenzisoxazol-4(5H)-one oximes were designed as potential HSP90 inhibitors. A series of the compounds was synthesized by oximation of (E)-3-aryl-6,7-dihydrobenzisoxazol-4(5H)-ones followed by O-acylation with acylamidobenzoic acids. The obtained compounds showed an antiproliferative effect on three breast cancer cell lines (MCF7, MDA-MB-231 and HCC1954). Compound 16s exhibited high antiproliferative potency against HCC1954 breast cancer cells with the IC50 value of 6 µM was selected for in-depth evaluation. Compound 16s did not inhibit the growth of normal epithelial cells. We have demonstrated that the compound 16s can induce apoptosis in cancer cells via inhibition of HSP90 "client" proteins including a key oncogenic receptor, HER2/neu. Described here compounds can be considered for further basic and preclinical investigation as a part of HSP90/HER2-targeted therapies.

Synthesis and crystal structure of a solvated CoIII complex with 2-hy-droxy-3-meth-oxy-benzaldehyde thio-semicarbazone ligands.

The title CoIII complex, bis-[bis-(2-hy-droxy-3-meth-oxy-benzaldehyde thio-semi-carbazonato)cobalt(III)] di-thio-nate-dimethylformamide-methanol (1/4/3), [Co(C9H10N3O2S)2]2(S2O6)·4C3H7NO·3CH3OH, with monodeprotonated 2-hy-droxy-3-meth-oxy-benzaldehyde thio-semicarbazone as ligands crystallizes in the space group P . The asymmetric unit consists of two mononuclear [CoL 2]+ cations, one di-thio-nate anion (S2O6)2- as counter-anion and seven solvate mol-ecules (four di-methyl-methanamide and three methanol). Each CoIII ion has a moderately distorted octa-hedral S2N2O2 geometry. In the crystal, the components are linked by numerous N-H⋯O and O-H⋯O contacts.

A bis-chelate o-vanillin-2-ethano-lamine copper(II) complex bearing both imine and amine forms of the ligand.

The mol-ecular bis-chelate complex (2-{[(2-hy-droxy-ethyl-κO)amino-κN]meth-yl}-6-meth-oxy-phenolato-κO)(2-{[(2-hy-droxy-eth-yl)imino-κN]meth-yl}-6-meth-oxy-phenolato-κO)copper(II), [Cu(C10H14NO3)(C10H12NO3)] or [Cu(HL im)(HL am); HL im = C10H14NO3; HL am = C10H12NO3, represents the first compound containing a salicyl-idene-2-ethano-lamine type ligand in both imino HL im (Schiff base) and amino HL am (reduced Schiff base) forms that has been structurally characterized on the basis of X-ray data. Two mol-ecules of the monodeprotonated ligands coordinate the CuII ion in an (N,O phen)-bidentate and an (N,O phen,O alc)-tridentate fashion in the case of the imino and amino forms, respectively. The shape of the CuN2O3 coordination polyhedron is a distorted square-pyramid (geometry index τ5 = 0.26). Inter-molecular N-H⋯O and O-H⋯O hydrogen bonds, involving H atoms of the amino and hy-droxy-ethyl groups, create a two-dimensional supra-molecular array extending parallel to (010).

Crystal structure of bis(µ-{2-[(5-bromo-2-oxido-benzyl-idene)amino]-eth-yl}sulfanido-κ3 N,O,S){2,2'-[(3,4-di-thia-hexane-1,6-di-yl)bis-(nitrilo-methanylyl-idene)]bis-(4-bromo-phenolato)-κ4 O,N,N',O'}dicobalt(III) di-methyl-formamide monosolvate.

The title binuclear CoIII complex, [Co2(C9H8BrNOS)2(C18H16Br2N2O2S2)]·C3H7NO, with a Schiff base ligand formed in situ from cyste-amine (2-amino-ethane-thiol) and 5-bromo-salicyl-aldehyde crystallizes in the space group P21. It was found that during the synthesis the ligand undergoes spontaneous oxidation, forming the new ligand H2 L' having an S-S bond. Thus, the asymmetric unit consists of one Co2(L)2(L') mol-ecule and one DMF solvent mol-ecule. Each CoIII ion has a slightly distorted octa-hedral S2N2O2 coordination geometry. In the crystal, the components are linked into a three-dimensional network by several S⋯ Br, C⋯ Br, C-H⋯Br, short S⋯C (essentially shorter than the sum of the van der Waals radii for the atoms involved) contacts as well by weak C-H⋯O hydrogen bonds. The crystal studied was refined as an inversion twin.

Tris(µ2-2-meth-oxy-6-{[(2-sulfido-eth-yl)imino]meth-yl}phenolato)trinickel(II) di-methyl-formamide monosolvate: crystal structure, spectroscopic characterization and anti-bacterial activity.

The title trinuclear nickel(II) complex, [Ni3(C10H11NO2S)3]·C3H7NO, with a Schiff base ligand formed in situ from 2-amino-ethane-thiol and o-vanillin crystallizes in the ortho-rhom-bic space group Pbca. Its asymmetric unit consists of one neutral Ni3 L 3 mol-ecule and one DMF solvent mol-ecule. The solid-state organization of the complex can be described as an insertion of the solvent mol-ecules within the crystallographically independent trinuclear NiII species. Several C-H⋯π edge-to-face inter-actions and π-π stacking inter-actions link the components in the crystal. A first example of a short inter-molecular C-H⋯Ni contact is found. Anti-bacterial in vitro screening revealed that the title compound has anti-bacterial activity, the best effect being against Acinetobacter baumannii.

Bis{µ-2,2'-[(3,4-di-thia-hexane-1,6-di-yl)bis-(nitrilo-methanylyl-idene)]bis-(4-bromo-phenolato)-κ4O,N,N',O'}dicopper(II).

The crystal structure of the title compound, [Cu2(C18H12Br2N4O2S2)2], consists of binuclear complex units which lie across inversion centres and are connected by weak Cu-O coordination bonds forming chains along the b axis. The CuII ion is five-coordinated by two N atoms and two O atoms of the chelating ligand and one symmetry-related O atom forming a square-pyramidal coordination geometry. In the crystal, short S⋯Br contacts connect neighbouring chains into a two-dimensional network parallel to (101).

Crystal structure of bis(µ2-4-bromo-2-[({2-[({2-[(5-bromo-2-oxidobenzylidene)amino]ethyl}sulfanyl)sulfonyl]ethyl}imino)methyl]phenolato)dicopper(II) dimethylformamide disolvate.

The title dinuclear copper(II) complex [Cu2(C18H16Br2N2O4S2)2] was prepared by direct synthesis of a dianionic Schiff base derived from 5-bromo-salicyl-aldehyde and cyste-amine. The discrete mol-ecules lie across inversion centers and crystallize with two di-methyl-formamide (DMF) mol-ecules of crystallization. The unique CuII ion is four-coordinated by two tetra-dentate Schiff base ligands in a distorted square-planar N2O2 environment. In the crystal, short inter-molecular S⋯Br contacts, weak C-H⋯O hydrogen bonds and intra- and inter-molecular π-π stacking inter-actions between rings of the ligand link the components into a two-dimensional network parallel to (010).

Crystal structure of tetra-kis-[µ2-2-(di-methyl-amino)-ethano-lato-κ(3) N,O:O]di-µ3-hydroxido-di-thio-cyanato-κ(2) N-dichromium(III)dilead(II) di-thio-cyanate aceto-nitrile monosolvate.

The tetra-nuclear complex cation of the title compound, [Cr2Pb2(NCS)2(OH)2(C4H10NO)4](SCN)2·CH3CN, lies on an inversion centre. The main structural feature of the cation is a distorted seco-norcubane Pb2Cr2O6 cage with a central four-membered Cr2O2 ring. The Cr(III) ion is coordinated in a distorted octa-hedron, which involves two N atoms of one bidentate ligand and one thio-cyanate anion, two µ2-O atoms of 2-(di-methyl-amino)-ethano-late ligands and two µ3-O atoms of hydroxide ions. The coordination geometry of the Pb(II) ion is a distorted disphenoid, which involves one N atom, two µ2-O atoms and one µ3-O atom. In addition, weak Pb⋯S inter-actions involving the coordinating and non-coordinating thio-cyanate anions are observed. In the crystal, the complex cations are linked through the thio-cyanate anions via the Pb⋯S inter-actions and O-H⋯N hydrogen bonds into chains along the c axis. The chains are further linked together via S⋯S contacts. The contribution of the disordered solvent aceto-nitrile mol-ecule was removed with the SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] procedure in PLATON. The solvent is included in the reported mol-ecular formula, weight and density.

Unusual centrosymmetric structure of [M(18-crown-6)](+) (M = Rb, Cs and NH4) complexes stabilized in an environment of hexachloridoantimonate(V) anions.

In (1,4,7,10,13,16-hexaoxacyclooctadecane)rubidium hexachloridoantimonate(V), [Rb(C12H24O6)][SbCl6], (1), and its isomorphous caesium {(1,4,7,10,13,16-hexaoxacyclooctadecane)caesium hexachloridoantimonate(V), [Cs(C12H24O6)][SbCl6]}, (2), and ammonium {ammonium hexachloridoantimonate(V)-1,4,7,10,13,16-hexaoxacyclooctadecane (1/1), (NH4)[SbCl6]·C12H24O6}, (3), analogues, the hexachloridoantimonate(V) anions and 18-crown-6 molecules reside across -3 axes passing through the Sb atoms and the centroids of the 18-crown-6 groups, both of which coincide with centres of inversion. The Rb(+) [in (1)], Cs(+) [in (2)] and NH4(+) [in (3)] cations are situated inside the cavity of the 18-crown-6 ring; they are situated on -3 axes and are equally disordered about centres of inversion, deviating from the centroid of the 18-crown-6 molecule by 0.4808 (13), 0.9344 (7) and 0.515 (8) Å, respectively. Interaction of the ammonium cation and the 18-crown-6 group is supported by three equivalent hydrogen bonds [N...O = 2.928 (3) Šand N-H...O = 162°]. The centrosymmetric structure of [Cs(18-crown-6)](+), with the large Cs(+) cation approaching the centre of the ligand cavity, is unprecedented and accompanied by unusually short Cs-O bonds [2.939 (2) and 3.091 (2) Å]. For all three compounds, the [M(18-crown-6)](+) cations and [SbCl6](-) anions afford linear stacks along the c axis, with the cationic complexes embedded between pairs of inversion-related anions.

Crystal structure of aqua-1κO-{µ-2-[(2-hydroxy-ethyl)methylamino]ethanolato-2:1κ(4) O (1),N,O (2):O (1)}[µ-2,2'-(methylimino)diethanolato-1:2κ(4) O,N,O':O]dithiocyanato-1κN,2κN-chromium(III)copper(II).

The title compound, [CrCu(C5H11NO2)(C5H12NO2)(NCS)2(H2O)] or [Cr(µ-mdea)Cu(µ-Hmdea)(NCS)2H2O], (where mdeaH2 is N-methylethanolamine, C5H13NO2) is formed as a neutral heterometal Cu(II)/Cr(III) complex. The mol-ecular structure of the complex is based on a binuclear {CuCr(µ-O)2} core. The coordination environment of each metal atom involves the N,O,O atoms of the tridentate ligand, one bridging O atom of the ligand and the N atom of the thio-cyanato ligands. The Cu(II) ion adopts a distorted square-pyramidal coordination while the Cr(III) ion has a distorted octa-hedral coordination geometry completed by the aqua ligand. In the crystal, the binuclear complexes are linked via two pairs of O-H⋯O hydrogen bonds to form inversion dimers, which are arranged in columns parallel to the a axis. In the µ-mdea ligand two -CH2 groups and the methyl group were refined as disordered over two sets of sites with equal occupancies. The structure was refined as a two-component twin with a twin scale factor of 0.242 (1).

Crystal structure of {2-[({2-[(2-amino-eth-yl)amino]-eth-yl}imino)-meth-yl]pheno-lato}aqua-copper(II) bromide.

In the mononuclear copper(II) title complex, [Cu(C11H16N3O)(H2O)]Br, the Cu(II) atom is coordinated by one O and three N atoms of the Schiff base ligand that forms together with one water mol-ecule a slightly distorted [CuN3O2] square-pyramidal polyhedron. The deviation of the Cu(II) atom from the mean equatorial plane is 0.182 (2) Å. The equatorial plane is nearly coplanar to the aromatic ring of the ligand [angle between planes = 10.4 (1)°], and the water molecule is situated in the apical site. All coordinating atoms (except the imine nitro-gen) and the bromide ion contribute to the formation of the N-H⋯Br, O-H⋯Br and O-H⋯O hydrogen bonds, which link mol-ecules into chains along [01-1].

Poly[[tri-µ-aqua-do-deca-aqua-tris-(µ3-1-hy-droxy-ethyl-idene-1,1-di-phospho-nato)tricalcium(II)tripalladium(II)] penta-hydrate].

The asymmetric unit of the title compound, {[CaPd{CH3OHC(PO3)2}(H2O)5]·5/3H2O} n , consists of one half of the complex [Pd{CH3OHC(PO3)2}](2-) anion (point group symmetry m..), one Ca(2+) cation [site symmetry (.2.)] that is surrounded by three water mol-ecules (one of which is on the same rotation axis) and by three disordered lattice water mol-ecules. The anions form a trinuclear metallocycle around a crystallographic threefold rotation axis. The cations are related by a twofold rotation axis to form a [Ca2(H2O)10](2+) dimer. The slightly distorted square-planar coordination environment of the Pd(II) atoms in the complex anions is formed by O atoms of the bidentate chelating phospho-nate groups of the 1-hy-droxy-ethyl-idene-1,1-di-phospho-nate ligands. In the crystal, cations are bound to anions through -Ca-O-P-O- bonds, as well as through O-H⋯O hydrogen bonds, resulting in a three-dimensional polymer. The structure is completed by five disordered solvent mol-ecules localized in cavities within the framework.

Chlorido-bis-(1,10-phenanthroline-κ(2) N,N')copper(II) chlorido-(1,10-phen-anthroline-κ(2) N,N')(pyridine-2,6-di-carboxyl-ato-κ(3) O (2),N,O (6))manganate(II) methanol monosolvate.

The title complex, [CuCl(C12H8N2)2][Mn(C7H3NO4)Cl(C12H8N2)]·CH3OH, consists of discrete [CuCl(phen)2](+) cations (phen is 1,10-phenanthroline), [MnCl(pydc)(phen)](-) anions (H2pydc is 2,6-pyridine-2,6-di-carb-oxy-lic acid) and one methanol solvent mol-ecule of crystallization per asymmetric unit. It should be noted, that a solvent-masking procedure as implemented in OLEX2 [Dolomanov et al. (2009). J. Appl. Cryst. 42, 339-341 ▶] was used to remove the electronic contribution from one disordered solvent molecule, presumably methanol. Only the atoms used in the refined model are reported in chemical formula and related values. The Cu(II) ion is five-coordinated by two phenanthroline ligands and one chloride ion in a distorted trigonal-bipyramidal geometry. The dihedral angle between the phen ligands is 65.21 (5)°. The Mn(II) ion is six-coordinated by one Cl atom, two N atoms from a phen ligand, as well one N atom and two O atoms from pydc in a distorted octa-hedral coordination geometry, with cis angles ranging from 72.00 (8) to 122.07 (8)° and trans angles ranging from 143.98 (8) to 163.15 (6)°. In the crystal, C-H⋯O, O-H⋯O and C-H⋯Cl hydrogen bonds, cation-anion π-π inter-actions between the phen ring systems with centroid-centroid distances in the range 3.881 (34)-4.123 (36) Å, as well as cation-cation, anion-anion π-π inter-actions between the phen rings with centroid-centroid distances in the range 3.763 (4)-3.99 (5) Šand pydc rings with centroid-centroid distances 3.52 (5) Šlink the various components.

trans-Chloridobis-(ethane-1,2-di-amine-κ(2) N,N')(thio-cyanato-κN)cobalt(III) diammine-tetra-kis-(thio-cyanato-κN)cromate(III).

The title ionic complex [CoCl(NCS)(C2H8N2)2][Cr(NCS)4(NH3)2], which crystallizes as a non-merohedral twin, is build up of a complex cation [CoCl(NCS)(en)2](+) (en is ethane-1,2-di-amine) and the Reinecke's salt anion [Cr(NCS)4(NH3)2](-) as complex counter-ion. A network of N-H⋯S and N-H⋯Cl hydrogen bonds, as well as short S⋯S contacts [3.538 (2) and 3.489 (3) Å], between the NCS groups of the complex anions link the mol-ecules into a three-dimentional supra-molecular network. Intensity statistic indicated twinning by non-mero-hedry with refined weighs of twin components are 0.5662:0.4338.

Bis[chloridobis(1,10-phenanthroline)copper(II)] penta-cyanido-nitro-soferrate(II) di-methyl-formamide monosolvate.

The title complex [CuCl(C12H8N2)2]2[Fe(CN)5(NO)]·C3H7NO, consists of discrete [Cu(phen)2Cl](+) cations (phen is 1,10-phenanthroline), [Fe(CN)5NO](2-) anions and one di-methyl-formamide (DMF) solvent mol-ecule of crystallization per asymmetric unit. The Cu(II) atom is coordinated by two phenanthroline ligands and one chloride ion in a distorted trigonal-bipyramidal geometry. The dihedral angle between the phen ligands is 77.92 (7)°. The cation charge is balanced by a disordered nitro-prusside counter-anion with the Fe(II) atom located on an inversion center with a slightly distorted octa-hedral coordination geometry. In the crystal, weak C-H⋯N and C-H⋯Cl hydrogen bonds connect anions and cations into a two-dimensional network parallel to (100). In addition, π-π stacking inter-actions are observed with centroid-centroid distances in the range 3.565 (2)-3.760 (3)Å. The di-methyl-formamide solvent mol-ecule was refined as disordered about an inversion center.

Tris(2,2'-bipyridine)-copper(II) penta-cyanido-nitro-soferrate(II) methanol disolvate monohydrate.

The title complex [Cu(C10H8N2)3][Fe(CN)5(NO)]·2CH3OH·H2O, consists of discrete [Cu(bpy)3](2+) cations (bpy is 2,2'-bipyridine), [Fe(CN)5NO](2-) anions and solvent mol-ecules of crystallization (two methanol mol-ecules and one water mol-ecules per asymmetric unit). The Cu(II) ion adopts a distorted octa-hedral environment, coordinated by six N atoms from three bpy ligands. The cation charge is balanced by a nitro-prusside counter-anion, which has a slightly distorted octa-hedral coordination geometry. In the crystal, anions and solvent mol-ecules are involved in O-H⋯N and O-H⋯O hydrogen bonds, which form chains along [100]. The cations are located between these chains.

Bis(2,9-dimethyl-1,10-phenanthroline)copper(I) penta-cyanido-nitro-soferrate(II).

The asymmetric unit of the title complex [Cu(C14H12N2)2]2[Fe(CN)5(NO)], consists of a [Cu(dmp)2](+) cation (dmp is 2,9-dimethyl-1,10-phenanthroline) and half an [Fe(CN)5(NO)](2-) anion. The anion is disordered across an inversion center with the Fe(II) ion slightly offset (ca 0.205Å) from the inversion center in the direction of the disordered trans-coordinating CN/NO ligands. The anion has a distorted octa-hedral coordination geometry. The Cu(I) ion is coordinated by two phenanthroline ligands in a distorted tetra-hedral geometry. The dihedral angle between the phenanthroline ligands is 77.16 (4) Å. In the crystal, the cations are connected to the anions by weak C-H⋯N hydrogen bonds. In addition, weak π-π stacking inter-actions are observed, with centroid-centroid distances in the range 3.512 (3)-3.859 (3) Å.

Cadmium(II) chloride, bromide and iodide complexes with 4,4'-bipyridazine: when are diazine and halide bridges (in)compatible?

In poly[di-µ-chlorido-µ-(4,4'-bipyridazine)-κ(2)N(1):N(1')-cadmium(II)], [CdCl(2)(C(8)H(6)N(4))](n), (I), and its isomorphous bromide analogue, [CdBr(2)(C(8)H(6)N(4))](n), (II), the halide atom lies on a mirror plane and the Cd(II) ion resides at the intersection of two perpendicular mirror planes with m2m site symmetry. The pyridazine rings of the ligand lie in a mirror plane and are related to each other by a second mirror plane perpendicular to the first. The compounds adopt the characteristic structure of the [M(II)X(2)(bipy)] type (bipy is bipyridine) based on crosslinking of [Cd(µ-X)(2)](n) chains [Cd-Cl = 2.5955 (9) and 2.6688 (9) Å; Cd-Br = 2.7089 (4) and 2.8041 (3) Å] by bitopic rod-like organic ligands [Cd-N = 2.368 (3)-2.380 (3) Å]. This feature is discussed in terms of supramolecular stabilization, implying that the periodicity of the inorganic chain [Cd···Cd = 3.7802 (4) Å in (I) and 3.9432 (3) Å in (II)] is favourable for extensive parallel π-π stacking of monodentate pyridazine rings, with centroid-centroid distances of 3.7751 (4) Å in (I) and 3.9359 (4) Å in (II). This is not the case for the longer iodide bridges, which cannot stabilize such a pattern. In poly[tetra-µ-iodido-µ(4)-(4,4'-bipyridazine)-κ(4)N(1):N(2):N(1'):N(2')-dicadmium(II)], [Cd(2)I(4)(C(8)H(6)N(4))](n), (III), the ligands are situated across a centre of inversion; they are tetradentate [Cd-N = 2.488 (2) and 2.516 (2) Å] and link successive [Cd(µ-I)(2)](n) chains [Cd-I = 2.8816 (3)-3.0069 (4) Å] into corrugated layers.

Tetra-kis(µ(2)-cyanido-κ(2)C:N)dicyanido-tetra-kis-[tris-(2-amino-eth-yl)amine-κ(3)N,N',N'',N''']tetra-copper(II)iron(II) bis[pentacyanidonitrosoferrate(II)] hexahydrate.

The asymmetric unit of the title complex, [Cu(4)Fe(CN)(6)(C(6)H(18)N(4))(4)][Fe(CN)(5)(NO)](2)·6H(2)O, comprises a complex [{Cu(tren)CN}(4)Fe(CN)(2)](4+) [tren is tris-(2-amino-eth-yl)amine] cation, which exhibits -1 symmetry with the terminal cyanide ligands oriented trans to each other, and two [Fe(CN)(5)(NO)](2-) nitroprussiate counter-anions. In the crystal, N-H⋯N hydrogen-bonding inter-actions are observed between H atoms on the primary amine groups of the tren ligand and the terminal cyanide groups of the nitro-prussiate counter-ions. The N atom in the terminal CN ligand of the cation is equally disordered over two positions. The structure also contains disordered lattice water mol-ecules. Their contribution was elimin-ated from the refinement using the procedure described by van der Sluis & Spek (1990 ▶).