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Favipiravir is an important selective antiviral against RNA-based viruses, and currently, it is being repurposed as a potential drug for the treatment of COVID-19. This type of chemical system presents different carboxamide-rotameric and hydroxyl-tautomeric states, which could be essential for interpreting its selective antiviral activity. Herein, the tautomeric 3-hydroxypyrazine/3-pyrazinone pair of favipiravir and its 6-substituted analogues, 6-Cl, 6-Br, 6-I, and 6-H, were fully investigated in solution and in the solid state through ultraviolet–visible, 1H nuclear magnetic resonance, infrared spectroscopy, and X-ray diffraction techniques. Also, a study of the gas phase was performed using density functional theory calculations. In general, the keto–enol balance in these 3-hydroxy-2-pyrazinecarboxamides is finely modulated by external and internal electrical variations via changes in solvent polarity or by replacement of substituents at position 6. The enol tautomer was prevalent in an apolar environment, whereas an increase in the level of the keto tautomer was favored by an increase in solvent polarity and, even moreso, with a strong hydrogen-donor solvent. Keto tautomerization was favored either in solution or in the solid state with a decrease in 6-substituent electronegativity as follows: H ≫ I ≈ Br > Cl ≥ F. Specific rotameric states based on carboxamide, “cisoide” and “transoide”, were identified for the enol and keto tautomer, respectively; their rotamerism is dependent on the tautomerism and not the aggregation state.

Background: Magnesium is an essential element related with biochemistry of the brain and different types of depression have been associated with its deficiency. Methods: The structure of a novel magnesium bis(DL-pyroglutamate) (Mg(DL-pGlu)2) was elucidated by X-ray crystallography. Wistar rats were used in the in vivoexperiments. The antidepressant-Iike effect was assessed by the forced swim test (FST) and the antinociceptive activity was evaluated using hot plate test. In both, non-specific effects were evaluated by the open field test. Anti-thyroid activity was examined using Lang’s method. Albumin binding behavior was evaluated by 3D fluorescence spectroscopy. Results: For the Mg(DL-pGlu)2complex (30 mg/kg), the FST test on Wistar rats revealed a decrease of 22% in the immobility time and an increment of 106% in the swimming time. The compound alters neither the locomotor activity nor the body weight after chronic administration. At the same dose, it showed antinociceptive activity, increasing the response latency. It blocks iodination reactions generating a charge transfer complex with iodine hence indicating anti-thyroid activity (Kc= 45366.5 ±29 M 1). Albumin 3D fluorescence spectroscopy experiments showed intensity increase of peak A and decrease of peak B. Conclusions: The results showed that the new compound produced a lowering of the immobility time and an increment of the swimming ability of the rats. The compound is able to increase the response latency in 70.0%, to capture iodine (anti-thyroid activity) and to interact with albumin through covalent type of interaction of the free NH groups.

Osteosarcoma cancers are becoming more common in children and young adults, and existing treatments have low efficacy and a very high mortality rate, making it pressing to search for new chemotherapies with high efficacy and high selectivity index. Copper complexes have shown promise in the treatment of osteosarcoma. Here, we report the synthesis, characterization, and anticancer activity of [Cu(N–N–Fur)(NO3)(H2O)] complex where N–N–Fur is (E)-N′-(2-hydroxy-3-methoxybenzylidene)furan-2-carbohydrazide. The [Cu(N–N–Fur)(NO3)(H2O)] complex was characterized via X-ray diffraction and electron spin resonance (ESR), displaying a copper center in a nearly squared pyramid environment with the nitrate ligand acting as a fifth ligand in the coordination sphere. We observed that [Cu(N–N–Fur)(NO3)(H2O)] binds to DNA in an intercalative manner. Anticancer activity on the MG-63 cell line was evaluated in osteosarcoma monolayer (IC502D: 1.1 ± 0.1 μM) and spheroids (IC503D: 16.3 ± 3.1 μM). Selectivity assays using nontumoral fibroblast (L929 cell line) showed that [Cu(N–N–Fur)(NO3)(H2O)] has selectivity index value of 2.3 compared to cis-diamminedichloroplatinum(II) (CDDP) (SI = 0.3). Additionally, flow cytometry studies demonstrated that [Cu(N–N–Fur)(NO3)(H2O)] inhibits cell proliferation and conveys cells to apoptosis. Cell viability studies of MG-63 spheroids (IC50= 16.3 ± 3.1 μM) showed that its IC50value is 4 times lower than for CDDP (IC50= 65 ± 6 μM). Besides, we found that cell death events mainly occurred in the center region of the spheroids, indicating efficient transport to the microtumor. Lastly, the complex showed dose-dependent reductions in spheroid cell migration from 7.5 to 20 μM, indicating both anticancer and antimetastatic effects.

The strange tautomeric equilibrium behavior exhibited by a new o-hydroxyphenyl diazepine derivative when the compound is analyzed both in solution and solid state opens the structural study of the enol-imino–keto-enamine forms and the influence of the intermolecular interactions in their equilibrium. The expected enol-imino form, in which the enol is part of a phenyl system and a strong O–H···N intramolecular hydrogen bond is established, results the most stable tautomer in gas phase (theoretical calculations) and was detected by NMR spectroscopy when the compound was dissolved in aprotic solvents. Nevertheless, the keto-enamine form ,in which the keto group integrates a cyclohexadienone moiety and the aromaticity of the phenol is lost, was the only tautomer in the crystal lattice according to single-crystal X-ray diffraction, vibrational spectroscopy, and diffuse reflectance results. The last form was also found as the main tautomer in UV–vis and NMR spectroscopy when a protic solvent was employed.

Isatin in a solution of dry N,N-dimethylformamide/NaClO4is electroreduced in the presence of CH3I. N-methylisatin (NMI) is obtained in quantitative molar yield and high current efficiency by controlled potential electrolysis (CPE). NMI and N-methylisatoic anhydride are the reaction products when CPE is performed in the absence of CH3I, but adding it once the CPE was completed. The water effect on the identity and yield of the reaction product(s) is investigated. Reaction pathways are proposed.

The crystal structure of pyridinium 6-methyl-1,2,3,-oxathiazine-4(3H)-one-2,2-dioxide [(C5NH6)(C4H4NO4S)], for short, pyH(ace), was determined by X-ray diffraction methods. It crystallizes as a twin in the monoclinic space group P21/cwith a=6.9878(9), b=7.2211(7), c=21.740(2) Å, β=91.67(1)° and Z=4 molecules per unit cell. The structure was determined employing 1599 reflections with I>2σ(I) from one of the twin domains and refined employing 2092 reflections from both crystal domains to an agreement R1 factor of 0.0466. Besides electrostatic attractions, intermolecular pyH···O=C(ace) hydrogen bonds stabilize the acesulfamate anion and the pyridinium cation into planar discrete units parallel to the (100) crystal plane. The units form stacks of alternating ace−and pyH+ions along the aaxis that favors inter-ring π–π interactions. The Fourier transform-infrared (FT-IR) spectrum of the compound was recorded and is briefly discussed. Some comparisons with related pyridinium saccharinate salts are also made.

Cadmium and lead(II) acesulfamate, Cd(C4H4NO4S)2·2H2O and Pb(C4H4NO4S)2, were prepared by the reaction of acesulfamic acid and the respective metal carbonates in aqueous solution, and characterized by elemental analysis. Their crystal structures were determined by single crystal X-ray diffraction methods. The Cd(II) compound crystallizes in the monoclinic space group P21/cwith Z=4 and the corresponding Pb(II) salt in the triclinic space group P1̅ with Z=2. In both salts, acesulfamate acts both as a bi-dentate ligand through its nitrogen and carbonyl oxygen atoms and also as a mono-dentate ligand through this same oxygen atom, giving rise to polymeric structures; in the Pb(II) salt the ligand also binds the cation through its sulfoxido oxygen atoms. The FTIR spectra of the compounds were recorded and are briefly discussed. Some comparisons with other related acesulfamate and saccharinate complexes are made.

Magnesium acesulfamate, Mg(C4H4NO4S)2·6H2O, was prepared by the reaction of acesulfamic acid and magnesium carbonate in aqueous solution, and characterized by elemental analysis. Its crystal structure was determined by single crystal X-ray diffraction methods. The substance crystallizes in the triclinic space group P1̅ with one molecule per unit cell. The FTIR spectrum of the compound was also recorded and is briefly discussed. Some comparisons with other simple acesulfamate and saccharinate salts are also made.

Three new acesulfamate salts, NaC4H4NO4S, RbC4H4NO4S and CsC4H4NO4S, were prepared by reactions in aqueous solutions and thoroughly characterized. Their crystal and molecular structures were determined by single crystal X-ray diffraction methods. They crystallize in the monoclinic space group P21/awith a= 7.2518(2), b= 8.9414(4), c= 10.5929(4) Å, β= 99.951(3)°, V= 676.52(4) Å3for the Na salt; a= 7.4663(3), b= 9.6962(4), c= 10.4391(4) Å, β= 95.150(3)°, V= 752.68(5) Å3for the Rb salt and a= 7.5995(4), b= 9.9439(4), c= 10.8814(6) Å, β= 91.298(5)°, V= 822.08(7) Å3for the Cs salt, and Z= 4 molecules per unit cell. The three compounds are isotypic to each other and to the previously reported potassium salt. The metal ions are in irregular polyhedral coordination with six neighboring acesulfamate anions through their nitrogen and carbonyl and sulfoxide oxygen atoms. The FTIR spectra of the compounds were also recorded and are briefly discussed.

The title compound was prepared by reaction, in aqueous solution, of Tl2CO3and H2C2O4·2H2O in a molar ratio of 1:2. Its crystal structure was solved by X-ray diffraction methods. It crystallizes in the monoclinic space group P21/a with Z = 2 molecules per unit cell. The oxalic acid molecule and the oxalate anion are planar, residing on crystallographic inversion centers, and linked to each other by strong O–H···O hydrogen bonds giving rise to a polymeric structure. The Tl(I) ion is in a distorted polyhedral coordination with nine neighboring O atoms, five of oxalate anions and four others of oxalic acid molecules. The FTIR and FT-Raman spectra of the compound were also recorded and are briefly discussed.

Ammonium acesulfamate, (NH4)C4H4NO4S, was prepared by the reaction of acesulfamic acid and ammonium carbonate in aqueous solution, and characterized by elemental analysis and 1H and 13C NMR spectroscopy. Its crystal and molecular structure was determined by single-crystal X-ray diffraction methods. The substance crystallizes in the orthorhombic space group Pnma with Z = 4 molecules per unit cell. The NH4+ion generates medium to strong hydrogen bonds with the carbonylic oxygen, the iminic nitrogen and the sulfonyl oxygen atoms of the acesulfamate anion. The FTIR spectrum of the compound was also recorded and is briefly discussed.

The synthesis of a Zn(II) complex of bispicen, the tetradentate ligand N,N′-bis(2-pyridylmethyl)- ethylenediamine, of composition [Zn(bispicen)Cl(H2O)]2[ZnCl4] is reported. Its crystal and molecular structure was determined by single-crystal X-ray diffraction methods. It crystallizes in the monoclinic space group C2=c with Z =4 molecules per unit cell. The Zn(II) cation in the [Zn(bispicen)Cl(H2O)]+complex is in a distorted octahedral environment, coordinated to a neutral bispicen molecule acting as a tetradentate ligand through its two amine nitrogen atoms, at cis positions, and its two pyridyl N atoms, at trans positions. The six-fold coordination is completed by a chloride ion and a water molecule. The tetrahedral [ZnCl4]2-counter-ion lies on a crystallographic twofold axis. The complex was further characterized by FTIR spectroscopy, and its vibrational behavior compared with that of the dihydrated tetrahydrochloride of free bispicen

The crystal structures of heptamethylenediammonium bis(saccharinate) monohydrate, [H3N - (CH2)7 -NH3](sac)2·H2O (1) and octamethylenediammonium bis(saccharinate) hemihydrate, [H3N- (CH2)8-NH3](sac)2·0.5H2O (2), were determined by single-crystal X-ray diffraction methods. Compound 1 crystallizes in the triclinic space group P1¯ with 2 molecules per unit cell, and 2 in the monoclinic space group P21/a with Z = 4. The saccharinate moiety is planar in both compounds presenting bonding characteristics comparable to those found in other saccharinate salts. The ionic crystals are further stabilized by an extensive H-bonding network, which links the anions and cations into an infinite three-dimensional supramolecular assembly. The FTIR spectra of the adducts are briefly discussed in comparison with those of the constituent molecules.

A series of palladium(II) thiosaccharinates with triphenylphosphane (PPh3), bis(diphenylphosphanyl)methane (dppm), and bis(diphenylphosphanyl)ethane (dppe) have been prepared and characterized. From mixtures of thiosaccharin, Htsac, and palladium(II) acetylacetonate, Pd(acac)2, the palladium(II) thiosaccharinate, Pd(tsac)2(tsac: thiosaccharinate anion) (1) was prepared. The reaction of 1with PPh3, dppm, and dppe leads to the mononuclear species Pd(tsac)2(PPh3)2·MeCN (2), [Pd(tsac)2(dppm)] (3), Pd(tsac)2(dppm)2(4), and [Pd(tsac)2(dppe)]·MeCN (5). Compounds 2, 4, and 5have been prepared also by the reaction of Pd(acac)2with the corresponding phosphane and Htsac. All the new complexes have been characterized by chemical analysis, UV/Vis, IR, and Raman spectroscopy. Some of them have been also characterized by NMR spectroscopy. The crystalline structures of complexes 3, and 5have been studied by X‐ray diffraction techniques. Complex 3crystallizes in the monoclinic space group P21/nwith a= 16.3537(2), b= 13.3981(3), c= 35.2277(7) Å, β= 91.284(1)°, and Z= 8 molecules per unit cell, and complex 5in P21/nwith a= 10.6445(8), b= 26.412(3), c= 15.781(2) Å, β= 107.996(7)°, and Z= 4. In compounds 3and 5, the palladium ions are in a distorted square planar environment. They are closely related, having two sulfur atoms of two thiosaccharinate anions, and two phosphorus atoms of one molecule of dppm or dppe, respectively, bonded to the PdIIatom. The molecular structure of complex 3is the first reported for a mononuclear PdII‐dppm‐thionate system.

The crystal structure of hexamethylenediammonium bis(thiosaccharinate) dihydrate, [H3N-(CH2)6-NH3](tsac)2· 2H2O (tsac=C7H4NO2S2, the anion of thiosaccharin), was determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P21/a with Z = 4. The thiosaccharinate moiety is planar and shows small but significant modifications in the bonding of the thioamide functional group as compared with the protonated neutral molecule. The ionic crystal is further stabilized by an extensive H-bonding network, which links the anions and cations into an infinite three-dimensional supramolecular assembly. The FTIR spectrum of the compound is briefly discussed in comparison with those of the neutral constituent molecules.

In the search for new therapeutic tools against American Trypanosomiasis palladium complexes with bioactive nitrofuran-containing thiosemicarbazones as ligands were obtained. Sixteen novel palladium (II) complexes with the formulas [PdCl2(HL)] and [Pd(L)2] were synthesized, and the crystal structure of [Pd(5-nitrofuryl-3-acroleine thiosemicarbazone)2]·3DMSO was solved by X-ray diffraction methods. Most complexes showed higher in vitro growth inhibition activity against Trypanosoma cruzi than the standard drug Nifurtimox. In most cases, the activity of the ligand was maintained or even increased as a result of palladium complexation. In addition, the complexes' mode of antitrypanosomal action was investigated. Although the complexes showed strong DNA binding, all data strongly suggest that the main trypanocidal mechanism of action is the production of oxidative stress as a result of their bioreduction and extensive redox cycling. Moreover, the complexes were found to be irreversible inhibitors of trypanothione reductase.

Two new saccharinate/NH3complexes of composition [Ni(sac)2(NH3)4] and [Zn(sac)2(NH3)2] were obtained and their crystal structures determined by single crystal X‐ray diffractometry. The elongated octahedral NiIIcomplex crystallizes in the monoclinic P21/c space group with Z = 2 whereas the tetrahedral ZnIIcomplex is triclinic (space group ${\rm P}{\bar 1}$and Z = 2). For [Ni(sac)2(NH3)4] the magnetic moment and electron absorption spectrum were obtained and discussed. The infrared spectra of both complexes were also recorded and briefly commented.

The crystal structure of NH4[tsac]·H2O (tsac = anion of the thiosaccharin molecule) has been determined by single crystal X‐ray diffractometry. It crystallizes in the orthorhombic space group Pbca with Z = 8. The infrared spectrum of the compound was also recorded and its most important features discussed on the basis of its structural peculiarities.

The reaction of the CuIIand NiIIcomplexes of saccharin with dicyandiamide (cyanoguanidine, cnge) in methanol produces the addition of methanol to the nitrile moiety of this molecule. Furthermore, the product of the reaction coordinates the metal centers generating two new complexes containing saccharinate as the counter anion. The crystal structures of [Cu(cnge‐OCH3)2](sac)2and of [Ni(cnge‐OCH3)2](sac)2·2H2O (cnge‐OCH3= 1‐amidino‐O‐methylurea) were solved by single crystal X‐ray diffractometry. Both complexes crystallize in the triclinic space group ${\rm P}{\bar 1}$and the metallic cations present a quite similar centrosymmetric planar conformation. The complexes were characterized by means of electronic and infrared spectroscopy and also their magnetic and thermal behavior was investigated.

The reactions of several derivatives of 1,2,5‐thiadiazole 1,1‐dioxide [3,4‐diphenyl‐(1a), 3,4‐bis(p‐methoxyphenyl)‐(1b), phenanthro[9,10‐c]‐(1c) and acenaphtho[1,2‐c]‐1,2,5‐thiadiazole 1,1‐dioxide (1d), 3,4‐diphenyl‐1,2,5‐thiadiazoline 1,1‐dioxide (2a) and 4‐ethoxy‐5‐methyl‐3,4‐diphenyl‐1,2,5‐thiadiazoline 1,1‐dioxide (2b)], with reagents possessing two nucleophilic nitrogen atoms (urea, N,N′‐dimethylurea, thiourea, N‐methylthiourea, N‐ethylthiourea, N‐allylthiourea, N,N′‐diethylthiourea, N,N′‐diphenylthiourea, dithioxamide and sulfamide), were followed by cyclic voltammetry (CV) and UV–visible spectrophotometry in aprotic solvent solution. The products were isolated, characterized by IR, 1H NMR and 13C NMR methods and their structure was confirmed by single‐crystal x‐ray diffraction. Several substrate–nucleophile combinations (1a–dand 2awith some ureas and thioureas) reacted to give good yields of new compounds formed by the addition reaction of the two nitrogen atoms of the nucleophile to the two >CN— double bonds of the 1,2,5‐thiadiazole 1,1‐dioxide ring. Some systems (1a–dithioxamide and 2b–thiourea) did not react, whereas in others (e.g. 1a–sulfamide) a monoaddition equilibrium reaction was observed. Copyright © 2004 John Wiley & Sons, Ltd.

The crystal structure of the complexes [Zn(sac)2(im)2] (1) and [Zn(sac)2(bzim)2]2⋅2Et-OH⋅H2O (2) (sac = saccharinate anion; im = imidazole; bzim = benzimidazole; EtOH = ethanol) was determined by single crystal X-ray diffractometry. Complex 1crystallizes in the monoclinic P21/nspace group with a= 9.1585(5), b= 16.4409(6), c= 15.0249(5) Å, β = 94.079(1)°, and Z= 4, whereas complex 2belongs to the triclinic space group P1with a= 10.8500(2), b= 12.4860(2), c= 13.5640(3) Å, α = 115,696(1), β = 100.086(1), γ = 102.169(1)°, and Z= 1. In both complexes, the Zn(II) cations are in a slightly distorted tetrahedral ZnN4environment, coordinated to two saccharinate anions and to two imidazole (1) and to two benzimidazole (2) molecules. The complexes were also characterized by means of infrared spectroscopy and their thermal behavior investigated by means of thermogravimetric and differential thermal analytical techniques.

Distribution data for alkali metal picrates in the water–chloroform solvent system in the absence and in the presence of acetonitrile were used to determine the partition constants of the dissociated electrolytes in the mutually saturated solvents and the ion-pair formation constants in the water saturated organic phase. These data were compared with those previously reported in water–benzonitrile and water–dichloromethane solvent systems. The same experiments carried out in the presence of ethyl p-tert-butylcalix4arene tetraethanoate, EtCalix4, led to the calculation of distribution and extraction constants in these solvent systems. The presence of acetonitrile in the organic phase enhances significantly the extraction constant to an extent that these are the highest values so far obtained in the solvent systems investigated. This enhancement in extraction is attributed to metal complex stabilization promoted by the presence of acetonitrile in the hydrophobic cavity of the ligand. The X-ray structures of two sodium complexes picrate as the counter-ion, isolated from water saturated chloroform with and without acetonitrile are reported for the first time. In the first complex, the macro-cycle is sited on a crystallographic four-fold axis and hosts an acetonitrile solvent molecule in its calix and a sodium ion in its hydrophilic cavity. The metal is in a eight-fold Archimedean square anti-prism environment, coordinated to the phenol oxygen atom and to the carbonyl oxygen atom of the four rotationally symmetry related pendant arms. The macro-cycle of the other complex adopts a slightly distorted cone conformation and its hydrophilic cavity also hosts a sodium ion. But now the metal is in a seven-fold environment, coordinated to the four phenol oxygen atoms and to the carbonyl oxygen atoms of three pendant arms acting as bidentate ligands. The fourth, mono-dentate, pendant arm points away from the hydrophilic cavity and its terminal –CH2-CH3group interacts hydrophobically with the calix of a neighboring complex giving rise to a supra-molecular polymeric structure in the lattice.

Distribution data for alkali metal picrates in the water–chloroform solvent system in the absence and in the presence of acetonitrile were used to determine the partition constants of the dissociated electrolytes in the mutually saturated solvents and the ion-pair formation constants in the water saturated organic phase. These data were compared with those previously reported in water–benzonitrile and water–dichloromethane solvent systems. The same experiments carried out in the presence of ethyl p-tert-butylcalix(4)arene tetraethanoate, EtCalix(4), led to the calculation of distribution and extraction constants in these solvent systems. The presence of acetonitrile in the organic phase enhances significantly the extraction constant to an extent that these are the highest values so far obtained in the solvent systems investigated. This enhancement in extraction is attributed to metal complex stabilization promoted by the presence of acetonitrile in the hydrophobic cavity of the ligand. The X-ray structures of two sodium complexes (picrate as the counter-ion), isolated from water saturated chloroform with and without acetonitrile are reported for the first time. In the first complex, the macro-cycle is sited on a crystallographic four-fold axis and hosts an acetonitrile solvent molecule in its calix and a sodium ion in its hydrophilic cavity. The metal is in a eight-fold Archimedean square anti-prism environment, coordinated to the phenol oxygen atom and to the carbonyl oxygen atom of the four rotationally symmetry related pendant arms. The macro-cycle of the other complex adopts a slightly distorted cone conformation and its hydrophilic cavity also hosts a sodium ion. But now the metal is in a seven-fold environment, coordinated to the four phenol oxygen atoms and to the carbonyl oxygen atoms of three pendant arms acting as bidentate ligands. The fourth, mono-dentate, pendant arm points away from the hydrophilic cavity and its terminal –CH₂-CH₃ group interacts hydrophobically with the calix of a neighboring complex giving rise to a supra-molecular polymeric structure in the lattice.

The crystal structures of [Tl(tsac)] (1) and [Tl(tsac)(ophen)] (2) (tsac = anion of thiosaccharin; ophen = 1, 10 phenanthroline) have been determined at 116 K by single crystal X‐ray diffractometry. Complex 1crystallizes in the monoclinic space group P21/a with Z = 4 and complex 2in the monoclinic space group C2/c with Z = 8.In both complexes TIis coordinated to a thiosaccharinate anion through its sulphur and nitrogen atoms. A distorted eight fold coordination sphere around the cation in complex 1is completed with two other longer Tl‐S bonds and four Tl···O contacts with five symmetry related neighbouring thiosaccharinate anions. A phenanthroline molecule acting as a bidentate ligand through its nitrogen atoms completes a four‐fold coordination around the metal atom in complex 2. The infrared spectra of both complexes were also recorded and their most important features discussed on the basis of its structural peculiarities.

We report the molecular structure and a single crystal EPR study at 9.8 and 33.9 GHz of a new copper(II) compound with the amino acid L-Glutamine, Cu[NH2CO2CH(CH2)2CONH2]2. The Cu^II ion is in an elongated octahedral environment equatorially trans-coordinated by two glutamine molecules acting as bidentate ligands through the nitrogen atom and one oxygen atom of each amino acid group, and axially by two carboxylate oxygen atoms of two neighboring glutamine molecules. Copper ions are arranged in layers connected by syn-anti carboxylate bridges that provide equatorial and apical ligands to the copper ions. Neighboring layers are connected by long chemical paths, which include two amino acid side chains connected by H bonds. Single crystal EPR spectra show a single exchange-collapsed resonance at both microwave frequencies for any magnetic field orientation. The evaluation of the molecular g-tensor from the angular variation of the EPR line position yielded g⊥ = 2.051 and g|| = 2.248, which indicates a dx²−y² ground orbital for the Cu ions. The angular variation of the EPR line width displays a contribution that is typical of a 2-D magnetic system, and another contribution depending on the microwave frequency, which is attributed to the incomplete collapse of the resonances corresponding to magnetically nonequivalent copper ions. A quantitative analysis of the line width data allowed us to estimate a mean exchange coupling constant |J/k| = 0.42(2) K, which is assigned to the syn-anti carboxylate chemical path that connects neighboring copper ions within a layer. The results are discussed and compared with those observed in similar systems. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

The molecular structure of diosgenone, a natural steroidal sapogenin, closely related to diosgenin and isolated from Solanum nudum, was solved by single crystal X-ray diffractometry at 120 K and refined by full-matrix least-squares to an agreement factor, R1 = 0.054. It crystallizes in the monoclinic space group P21, with a = 15.1870(4) Å , b = 7.2710(2) Å , c = 21.2840(6) Å , ß= 99.251(1) °, and four molecules in the unit cell (Z = 4). The results constitute the first structural report on a steroidal sapogenin from the diosgenin group.

In an attempt to obtain new square grid polymers we could prepare the copper(II) complex [Cu(4, 4'‐bipy)2(H2O)2](sac)2· DMF (4, 4'‐bipy = 4, 4'‐bipyridine; sac = anion of saccharin; DMF = dimethylformamide). Its structure was determined by single crystal X‐ray diffraction methods. It crystallizes in the orthorhombic space group Pcnb(a= 14.4994(2), b= 15.8128(3), c= 16.6850(2) Å, Z = 4) and is a square grid polymer with the saccharinate anions sandwiched between the complex layers and the DMF molecules filling the square holes. UV‐vis, diffuse reflectance and IR spectra, room temperature magnetic susceptibility and the thermal behaviour were also investigated.

The oxidation of thiosalicylic acid in methanol into 2‐sulfonatobenzoic acid was successfully achieved by the reaction with pyridine‐N‐oxide in aerobic media containing a copper(II) catalysts. The 100 K structure of the tetraphenylphosphonium 2‐sulfonatobenzoic acid [P(C6H5)4]C6H4SO3COOH (I) has been determined by X ray diffraction methods. The anion shows a novel conformation with a strong intramolecular COOH · · · OSO2bond. The oxidation reaction also produces [P(C6H5)4]2[Cu2Cl6] (II), as assessed by single crystal X‐ray measurements. When water is added to the reaction medium, the compound Iis reformed. Nevertheless, instead of compound II, chloro tetrapyridine‐N‐oxide copper(II) chloride monohydrate [Cu(C5H5NO)4Cl]Cl · H2O (III) is obtained. The crystal structure of this new copper complex has been determined and is also reported here. The copper ion is in a CuO4Cl pyramidal coordination with the oxygen atoms of four C5H5NO ligands at the square basis (average Cu—O distance of 1.98(1) Å) and a chlorine ion (d(Cu—Cl) = 2.4585(4) Å) at the pyramid apex. Vibrational studies of the three compounds have been performed. Compound IIIhas also been characterized by diffuse reflectance and UV‐vis spectroscopy and by its thermal and magnetic behavior.

The crystal structure of the title complex, [Cd(tsac)2(py)3], has been determined by single crystal X‐ray diffractometry. It crystallizes in the monoclinic space group C2/c with Z = 8.The Cd 2+cation is at the center of a square‐ bipyramidal environment, equatorially coordinated to two thiosaccharinate anions through their sulfur atoms and the nitrogen atom of one of them acting as a bidentate ligand. Nitrogen atoms of pyridine molecules occupy the fourth equatorial position and the two axial ones. The infrared and electronic spectra of the complex were briefly discussed. Its thermal stability was investigated by thermogravimetric and differential thermal analysis.

The crystal structures of two salts of bis­(thio­urea)­gold(I) complexes, namely bis­(thio­urea‐κS)­gold(I) chloride, [Au(CH4N2S)2]Cl, (I), and bis­[bis­(thio­urea‐κS)­gold(I)] sulfate, [Au(CH4N2S)2]2SO4, (II), have been determined. The chloride salt, (I), is isomorphous with the corresponding bromide salt, although there are differences in the bonding. The AuIion is located on an inversion centre and coordinated by two symmetry‐related thio­urea ligands through the lone pairs on their S atoms [Au—S 2.278 (2) Å and Au—S—C 105.3 (2)°]. The sulfate salt, (II), crystallizes with four independent [Au(CH4N2S)2]+cations per asymmetric unit, all with nearly linear S—Au—S bonding. The cations in (II) have similar conformations to that found for (I). The Au—S distances range from 2.276 (3) to 2.287 (3) Å and the Au—S—C angles from 173.5 (1) to 177.7 (1)°. These data are relevant in interpreting different electrochemical processes where gold–thio­urea species are formed.

Saccharinate complexes of the fourteen trivalent lanthanide cations and YIIIwere prepared by reaction between the respective lanthanide carbonates and saccharin in aqueous solution. Their crystal structures were determined by single crystal X‐ray diffractometry. They represent three different structural types. The first family, of composition [Ln(sac)(H2O)8](sac)2�H2O (sac = anion of saccharin; Ln = La, Ce, Pr, Nd.Sm, Eu), belongs to the monoclinic space group P21/c with Z = 4 and the LnIIIcation is in a tricapped trigonal prismatic environment with nine‐fold oxygen coordination. The second group of composition [Ln(sac)2(H2O)6]‐(sac)(Hsac)�4H2O with Ln = Gd, Dy, Ho, Er, Yb, Lu, and Y, pertains to the triclinic P1¯‐ space group, with Z = 2 and constitutes a new example of complexes containing simultaneously saccharin and its anion in the lattice. The TmIIIand TbIIIcompounds, which are also triclinic (space group P1¯‐ and Z = 2) present two closely related structures conformed by three and two [Ln(sac)(H2O)7]2+crystallographically independent complexes, respectively, with the [Tm(sac)(H2O)7]3(sac)6�9H2O and [Tb(sac)(H2O)7]2(sac)4�6H2O composition. For all the heavier lanthanides (Gd‐Lu) and yttrium the cation presents eight‐fold oxygen coordination, with the ligands at the corners of a slightly distorted square Archimedean antiprism.

Several new 1,2,5-oxadiazole N -oxide derivatives and some deoxygenated analogues were synthesized to be tested as potential selective hypoxic cell cytotoxins. Compounds prepared were designed in order to gain insight into the mechanism of action of this kind of cytotoxin. Compounds were tested in oxia and hypoxia and they proved to be non-selective. 3-Cyano- N 2 -oxide-4-phenyl-1,2,5-oxadiazole showed the best cytotoxic activity in oxia. The cytotoxicity observed for these derivatives could be explained in terms of the electronic characteristics of the 1,2,5-oxadiazole substituents. Electrochemical and ESR studies were performed on the more cytotoxic derivative.

A modified method for the synthesis of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra(benzoyl)methoxycalix(4)arene (1) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra(acetoyl)methoxycalix(4)arene (2) using 18-crown-6 as phase transfer catalyst is reported. Ligand 1 was structurally (1H NMR and X-ray crystallography) and thermodynamically characterised. An account of the steps required for the formulation of an equation representative of the complexation process involving metal cations and macrocycles is given using as an illustrative example the interaction of 1 with the Na(I) cation. Thus, detailed thermodynamics of this system are first reported taking into account the solution properties of the reactants and the product in various solvents with the aim of assessing quantitatively the medium effect on the complexation process. The sodium:monoacetonitrile:1 complex was isolated and its molecular structure was determinated from X-ray diffraction data. The calix now adopts a more symmetric cone conformation than the free ligand and its hydrophobic cavity is filled with an acetonitrile solvent molecule. The hydrophilic pocket hosts the sodium cation which is in an eight-fold coordination with the four ethereal oxygen atoms [average d(Na–O) = 2.45(4) Å] and the four carbonyl oxygen atoms [average d(Na–O) = 2.51(4) Å] forming the corners of a distorted Archimedean square antiprism. The key structural features relevant to the complexation process are discussed. 1H NMR and conductance measurements have been used to assess the interaction of 1 and 2 with alkali metal cations. Final conclusions are given. Attention is drawn about the relevance of detailed thermodynamic studies on cation complexation processes involving calixarene derivatives. This is discussed within the context of selectivity and the factors controlling it in solution processes.

Summary.:  The crystal structure of the title complex, [Cd(tsac)2(H2O)], has been determined by single crystal X-ray diffraction methods. It crystallizes in the monoclinic space group C2/c (a = 12.236(3), b = 8.919(3), c = 16.655(3) �, β = 96.18(2)�, Z = 4). The molecular structure was solved from 1705 independent reflections with I > σ(I) and refined to R 1 = 0.0489. Infrared and Raman spectra of the complex were recorded and are briefly discussed. Its thermal behaviour was investigated by thermogravimetry and differential thermal analysis.

The interaction of 2-pyridinecarboxaldehyde with N-tosyl-1,2-diaminobenzene leads to the isolation of two different products, {3-[ethoxy(2-pyridyl)methyl]-1-[(4-methylphenyl)sulfonyl]-2-(2-pyridyl)-2,3-dihydro-1H-benzo[d]imidazole}, L¹, and {1-[(4-methylphenyl)sulfonyl]-2-(2-pyridyl)-2,3-dihydro-1H-benzo[d]imidazole}, L², but not to the expected Schiff base 1-[(4-methylphenyl)sulfonamido]-2-[(2-pyridylmethylene) amino]benzene, HL³. Two kinds of complexes, containing the potentially tridentate and monoanionic [L³]^- as a ligand, were obtained by different routes. ML³(p-Tos)(H₂O)_n complexes (p-TosH=p-toluenesulfonic acid; M=Co, Cu, Zn; n=1–3) have been isolated by electrolysis of a solution phase composed of L¹ and p-toluenesulfonic acid, using metal plates as the anode. Metal complexes of composition ML³₂(H₂O)_n (M=Mn, Co, Cu, Zn; n=0–2) were obtained by template synthesis from M(acac)₂, 2-pyridinecarboxaldehyde and N-tosyl-1,2-diaminobenzene. All these compounds have been characterised by elemental analyses, magnetic measurements, IR, mass spectrometry and, in the case of M=Zn, by ¹H NMR spectroscopy. CuL³(p-Tos)(H₂O), 1, ZnL³(p-Tos)(H₂O), 2, CoL³₂, 3, CuL³₂, 4 and ZnL³₂·2CH₃CN, 5, were also crystallographically characterised.

The crystal structure of tetrabutylammonium nitroprusside dihydrate (TBANPDH, [(C4H9)4N]2[Fe(CN)5NO]·2H2O) was determined by single crystal X-ray diffraction (XRD) and the compound was also studied, as well as the anhydrous salt (TBANP), by room and low temperature Fourier Transform Infra-Red (FTIR) and room temperature Fourier Transform Near Infra-Red Raman (FTNIRR) spectroscopies. In addition to the ground states (GS), the metastable excited states (MSI and MSII) generated by laser excitation (488 nm) at low temperature were IR studied, both of the dihydrate and the anhydrate. TBANPDH crystallizes in the trigonal space group P3221, D63, with a= b= 13.777(2), c= 22.039(2) Å, and Z= 3. The structure was solved employing 1273 independent XR reflections, with I> 2σ(I), by Patterson and Fourier methods and refined by full-matrix least-squares to R1 = 0.054.

Two new Cu(II) complexes of stoichiometry [Cu(L-dipept)], containing as ligands the dipeptides L-alanine-L-valine and L-alanine-L-phenylalanine were prepared. They were characterized by single crystal X-ray diffractometry, and infrared and electronic spectroscopy. Both crystallize in the orthorhombic space group P212121with Z = 4. The Cu(II) ion has essentially the same elongated pyramidal coordination, being equatorially cis coordinated by a N2O2arrangement of ligand atoms and axially by a carbonyl oxygen atom. The compounds show rather similar polymeric structures that differ from each other basically in the dihedral angle between adjacent N2O2planes. The infrared and electronic spectra are briefly discussed on the basis of the structural characteristics of the complexes. Superoxide dismutase-like activity was tested for both compounds.