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The aim of this work was to search for new polymorphic forms of febantel, an anthelminthic drug of great present interest for the veterinary industry. Solvent-based recrystallization, thermal and mechanical treatments and spray drying were chosen to discover new solid forms. The solids obtained were physicochemically characterized by thermal techniques (DSC and TG), FTIR spectroscopy, laboratory and synchrotron X-ray powder diffraction and scanning electron microscopy. Our work leads to obtain a new solid form never described in the literature. In particular, the new polymorph was obtained by the anti-solvent method and the crystallization from isopropanol. The experimental conditions of crystallization favorable to the formation of the highest amount of the new solid phase were selected. The new phase shows a thermal, spectroscopic and diffractometric behavior unique. Furthermore, the preliminary structure investigation suggests two possible crystal systems: an orthorhombic or a monoclinic one, with really comparable lattice parameters and cell volume. Measurements put into evidence that the new phase is a metastable polymorph that is in monotropic relationship with the stable and known form.

An X-ray diffraction study has been carried out on single crystals of two symmetrical ureines (N,N′-diiopropylurea and the familiar N,N′-dicyclohexylurea) and one unsymmetrical ureine (N-tert.-butyl.N′-methylurea). The presence/absence of intermolecular H-bonds in the crystal state has been compared to the situation assessed in solution by 1H n.m.r. It was shown by i.r. absorption that soluble ureines may disrupt intermolecular (peptide)N—H- O=C(peptide) H-bonds in methylene chloride, a point of practical interest, particularly in solid-phase peptide synthesis.

The macrocyclic receptor 3, featuring two diaminomethylpyridine moieties as ligand subunits and two diphenylmethane lipophilic spacers was synthesized and the crystal structure of its dinuclear Cu(II) complex, 3.2Cu, defined by X-ray analysis. From a kinetic study of the catalytic activity of 3.2Cu in the hydrolysis of the p-nitrophenyl ester of beta-alanine (AlaPNP), a beta-amino acid, clear evidence of co-operativity of the two metal ions was obtained. Such an allosteric effect was not observed in the hydrolysis of the p-nitrophenyl ester of leucine (LeuPNP), an alpha-amino acid. The reactivity of 3 2Cu was compared with that of the mononuclear complex of the acyclic ligand 4 having a single diaminomethylpyridine subunit and to that of Cu(II) alone. At pH=6.3 in a 1:1 water/DMSO mixture, being [Cu(II)]=6x10(-4) M, a 80-fold acceleration was observed employing 3.2Cu compared with a 35-fold rate increase with Cu(II) alone and a 17-fold increase with 4.Cu. The crystal structure of the dinuclear Cu(II) complex gives a distance between the two Cu(II) centers of 9.9 Angstrom, suitable for the co-ordination of the beta-amino ester by both Cu(II) ions with the nitrogen of the amino group and the oxygen of the C=O. Although significant the rate accelerations observed employing 3.2Cu are rather modest and this is likely due to the orientation of the two pyridine moieties in the macrocycle which does not allow the most favorable inclusion mode of the substrate.

In studies on caregiving, high levels of perceived burden are commonly considered as synonymous with poor well-being. This study aimed at better disentangling the relationship between burden and well-being dimensions through their joint investigation. To this purpose, perceived well-being and social resources were evaluated among caregivers reporting different levels of burden. Participants were 91 caregivers (mean age=50.4; SD=9.6), parents of people diagnosed with severe neuromotor and cognitive disorders. Participants completed a semi-structured interview and a set of scaled questionnaires: Caregiver Burden Inventory (CBI), Satisfaction with Life Scale, Positive and Negative Affect Schedule, Depression Anxiety Stress Scale, Eudaimonic and Hedonic Happiness Investigation, Resilience Scale for Adults, and Multidimensional Scale of Perceived Social Support. Participants were divided into two groups according to their perceived burden level, assessed through CBI. In both groups, the subjective components of burden accounted for the major fraction of the total burden level. Participants perceiving high burden reported higher levels of depression related emotions, lower life satisfaction and lower resilience than participants perceiving low burden. No group difference emerged in perceived meaningfulness and social support. A regression analysis showed that the best predictor of perceived burden was life satisfaction, followed to a lesser extent by resilience, while depression related emotions did not provide significant contribution. Findings suggest that the joint assessment of burden and well-being dimensions, that are co-existing in caregivers' experience, allow for the identification of personal and relational resources that can be usefully included in interventions addressed to caregivers.

The heteronuclear complex CO 4 Mo μ- PMe 2 2 W CO 4 (1) has been prepared by thermal cyclization of the linear dimer [(CO)5MoPMe2PMe2W(CO)5]. An improved yield in 1, with respect to the literature, has been obtained with a different synthetic route to the linear complex and with a better separation, by flash chromatography, of 1 from its homonuclear Mo–Mo and W–W congeners. The conditions of thermal cyclization are rather critical and in one case the major product was the phosphine complex [M(μ-PMe2)(CO)3(PMe3)]2 (M=Mo and W in 1/4 ratio: monoclinic, space group P21/n, a=9.568(1), b=9.305(1), c=15.009(2) A, β=102.3(1)°, Z=2, R=0.035, Rw=0.036). Complex 1 is a convenient MOCVD precursor and sublimes at low temperatures, ⩽85 °C, to give thin films of mixed MoO3/WO3 oxides or Mo/W alloys, depending on the deposition conditions.

The crystal and molecular structure of sodium 5-sulfosalicylate dihydrate, Na[(H2Ssal)(H2O)2], (1) (H3Ssal=5-sulfosalicylic acid) has been determined through X-ray diffraction analysis. The 5-sulfosalicylate anion has lost the proton at the SO3H group but retains the usual intermolecular hydrogen bond between phenolic and carboxylic oxygen. The reaction in water of 1 with [Cu(II)(H2O)4]SO4·H2O, gives rise to the green sodium[triaqua(5-sulfosalicylato)copper(II)] 2 hemihydrate, Na[(H2O)3(Ssal)Cu(II)]·2×0.5H2O, (2). The 5-sulfosalicylate anion, (Ssal3−), coordinates rather unusually in the syn–syn coordination mode since it binds bidentately the Cu(II) ion through the carboxylic and the phenolic oxygens, with Cu(II)Ocarboxylic=1.909(4) A and Cu(II)Ophenolic=1.885(4) A distances. Copper(II) completes its square-planar coordination with two water molecules and in addition, perpendicularly to the square-planar coordination plane, another two water molecules with long bonds are present (Cu(II)O=2.518 and 2.912 A). The green complex 2 reacts easily with adenine in water at pH 7 giving rise to the violet tetraadeninato(diaqua)-bis(copper(II)) dihydrate, [Cu2(Ade)4(H2O)2])]·2H2O, (3) (Ade−=adeninato monoanion). This complex, that geometrically resembles copper(II) acetate monohydrate, was already described by Sletten. Finally, on the basis of the present results a possible mechanism for the anticancer activity of complex 2 and of other Cu(II)–salicylate complexes is proposed and discussed.

Complexes of L-methionyl-L-histidine (H2MetHis) with R2Sn(IV) ions (R = Me, nBu, Ph) have been synthesized. The crystal and molecular structures of Me2SnMetHis·0.5MeOH have been determined by X-ray diffraction. The title compound contains two crystallographically independent molecular units possessing the same trigonal-bipyramidal geometry at tin, each dimethyltin(IV) moiety being coordinated by the terminal amino nitrogen, deprotonated peptide nitrogen and terminal carboxylate group, neither the imidazole nor thioether groups being involved in bonding. IR spectroscopy was used to probe the structure of the complexes in the solid state, and the structure in solution (CD3OD) was assessed by 1H and 13C NMR. Me2Sn(IV)dipeptide complexes appear to be undissociated and to retain a pentacoordinated structure. Rotamer population of C-terminal histidine was determined by analysis of vicinal coupling constants and side-chain orientations have been interpreted with a view to potential applications of the compounds as recognition agents. Biological activity was tested on Ascidian embryos of Ciona intestinalis at different stages of development. Copyright © 2000 John Wiley & Sons, Ltd.

In this study are reported the syntheses of three bis(diarylhydrazonecarbonyl)methylene derivatives [{ArPhCNNHC(O)}2CH2] [Ar = 2C5H4N (5), C6H5 (6), and 2-C4H3S (7)], obtained by condensation of corresponding hydrazones with carbon suboxide, C3O2. The solid-state self-assembly of these carbonyl derivatives, giving rise to polymeric and dimeric networks, is described. In the formation of these structural features, in addition to N—H· · ·OC intermolecular hydrogen bonds, stabilizing intramolecular NH· · · π (systems) and intermolecular CO· · ·π (systems) interactions also seem to play an important role. Solution 1H-nmr data of compounds 5–7 indicate that the polymeric and dimeric structures are not maintained in solution and show the occurrence of keto-enolic equilibria. © 1999 John Wiley & Sons, Inc. Biopoly 49: 541–549, 1999

Oxidative homocoupling of R-(−)-carvone 4, R-(−)-hydrocarvone 21, 1R,5R-(+)-pinocarvone25 and other monoterpenic ketones leads to the respective C2-symmetric dimers 6, 20 and 26 in most cases as single diastereoisomers. Subsequent reactions of dimeric compounds were investigated in detail. Other monoterpenes (menthone, pulegone) undergo homocoupling in low yields and poor diastereoselectivity.

The interaction between Ag(O 3 SCF 3 ), trialkyl- or trialkyl-phosphineligands (PR 3 : R = phenyl, o - m - and p -tolyl, benzyl; PMePh 2 ), and the anionic N 3 -donor tris(3,5-diphenylpyrazol-1-yl)borate [Tp Ph2 ] in tetrahydrofuran or methanol gives new air-stable and highly soluble 1:1 [Tp Ph2 ]Ag{PR 3 } and [Tp Ph2 ]Ag{PMePh 2 } compounds. The tricyclohexylphosphine (PCy 3 ) is able to displace PPh 3 and PBz 3 from the coordination sphere of silver(1), yielding the derivative [Tp Ph2 ]Ag{PCy 3 }. In contrast, imidazole, 1-methylmercaptoimidazole, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline are not able to displace either phosphine or [Tp Ph2 ] from the coordination center. Reaction of Ag(O 3 SCF 3 ) with 1 equiv. of [Tp Ph2 ] and CNR (R = Cy or Bu 1 ) yields the air-stable neutral compounds [Tp Ph2 ]Ag(CNR). When the reaction between [Tp Ph2 ] and Ag(O 3 SCF 3 ) is carried out in tetrahydrofuran at −70°C in the absence of the phosphorus donor, breaking of the BN bond occurs in the anionic ligand and the ionic compound [(3,5-Ph 2 PzH) 3 Ag](O 3 SCF 3 )·(H 2 O) 2 was obtained from the reaction solution. All the derivatives were characterized through elemental analyses, spectral data (IR, 1 H, 31 P and 13 C NMR) and conductivity measurements. Comparison is made with the results previously obtained with other tris(pyrazol-1-yl)borates. The solid state structures of [Tp Ph2 ]Ag{PPh 3 } and [Tp Ph2 ]Ag{PBz 3 }·2/3CHCL 3 show that the silver atom adopts a distorted tetrahedral geometry with the donor [Tp Ph2 ] coordinating in tridentate fashion.

Reaction of Ag(NO3) with 1 equiv of K[HB(3,5-Me2pz)3] (pzH=pyrazole) and 1 equiv of PR3 (R OPh or C6F5) in methanol provides two new air stable derivatives {[HB(3,5-Me2pz)3]Ag(PR3)}. When the interaction between Ag(O3SCF3), CNR (R But or cyclohexyl), and K[HB(3,5-Me2pz)3] was carried out in CH2Cl2 at 0°C the air stable neutral compounds {[HB(3,5-Me2pz)3]Ag(CNR)} were obtained. The borderline monodentate imidazole (ImH) reacts with the dinuclear {[HB(3,5-Me2pz)3]Ag}2 yielding the mixed-ligand complex {[HB(3,5-Me2pz)3]Ag(ImH)}. On the other hand when the soft donor 1-methyl-2-mercaptoimidazole (Hmimt) was employed, no stable compound was obtained. We also synthesized [Phen2Ag](O3SCF3) (Phen=1,10-phenanthroline) and its reaction with K[HB(3,5-Me2pz)3] yielded the complex {Phen[HB(3,5-Me2pz)3]Ag}, which is not fluxional in solution. Instead only unmanageable material was obtained from the reaction between (Hmimt)2Ag(O3SCF3) and K[HB(3,5-Me2pz)3]. Finally, the gold(I) complex [HB(3,5-Me2pz)3]Au(PPh3)2 was obtained when the reaction between PPh3AuCl and [HB(3,5-Me2pz)3] was carried out in presence of 1 equiv of PPh3. The solid state structures of {[HB(3,5-Me2pz)3]Ag(PPh2Me)} and {[HB(3,5-Me2pz)3]Ag(P-o-tolyl3)}, show that the silver(I) atoms are in a strongly distorted tetrahedral environment, with the [HB(3,5-Me2pz)3]− donor acting in the tridentate form. The Ag–P and Ag–N bond distances in {[HB(3,5-Me2pz)3]Ag(PPh2Me)} are 2.336(2) A and 2.316(6), 2.336(5) and 2.329(6) A, respectively; they are shorter than in the more sterically hindered {[HB(3,5-Me2pz)3]Ag(P-o-tolyl3)} (Ag–P: 2.375(2) A; Ag–N: 2.361(4) A). The ligand bite N–Ag–N ranges from 82.1(2)° to 84.8(2)°, whereas the N–Ag–P angle ranges from 125.1(1) to 134.1(1)°.

X-ray diffraction structure determinations of HOAt and HOOBt, two well-known additives for peptide bond formation, are reported in conjunction with those of seven derivatives of HOBt, HOAt, and HOOBt, five of which originate from Nα-protected α-amino acids. In the crystal state the two additives are found in the 1-hydroxy tautomeric form. In contrast to six derivatives which crystallize as esters, one, Fmoc-(N)OBt, is observed in the isomeric amide-type (urethane) form.

We have synthesized by solution methods and fully characterized the Nα-blocked heptapeptide methylamide mBrBz-[L-Iva-L-(αMe)Val]2-L-(αMe)Phe-L-(αMe)Val-L-Iva-NHMe, fully based on conformationally constrained Cα-methylated α-amino acids. An X-ray diffraction investigation of the Nα-benzyloxycarbonylated analogue showed that in the crystal state both independent molecules (A and B) in the asymmetric unit of the peptide adopt a fully developed, regular, right-handed 310-helical structure, although molecule A would be slightly distorted at the C-terminal residue. Solution conformational analysis on the mBrBz-blocked peptide was carried out in CDCl3 by means of NMR spectroscopy. For structure determination we performed restrained molecular dynamics simulations in CDCl3 based on a search of the conformational space derived from a simulated annealing strategy. For this peptide the NMR observables can be described by a single backbone conformation, more specifically a rigid 310-helix spanning the amino acid seque...

(Trialkyl- and (triarylphosphine)silver(I) derivatives containing anionic tris(1H-pyrazol-1-yl)borates were prepared from AgX (X = CF3SO3 or NO3), PR3 (R = phenyl, benzyl, cyclohexyl, 2,4,6-trimethylphenyl, or o-, m-, and p-tolyl) or PMePh2, and M[HB(pz)3] [M = K or Na; pzH = pyrazole in general; in detail, pyrazole (PzH), 3,5-dimethylpyrazole (3,5-Me2PzH), or 4-bromopyrazole (4-BrPzH)] and characterized through analytical and spectral (IR; 1H, 13C, and 31P NMR) measurements. These air stable, light-sensitive complexes are not electrolytes in CH2Cl2 and acetone. In these solvents they decompose even with strict exclusion of oxygen and light. The solid-state structures show that the silver atom adopts a distorted tetrahedral geometry. Crystal data with Mo Kα (λ = 0.710 70 A) at 293 K: [HB(Pz)3]Ag(PPh3), C54H50Ag2B2N12P2, a = 15.082(2) A, b = 19.728(2) A, c = 9.432(1) A, α = 94.8(1)°, β = 107.4(1)°, γ = 87.8(1)°, triclinic, P1, Z = 2; [HB(Pz)3]Ag[P(o-tolyl)3], C30H31AgBN6P, a = 14.461(2) A, b = 14.461(2) ...

A straightforward procedure for the preparation of enantiopure phosphorothioates and diastereopure phosphorothioamidates of 2,2′,6,6′-biphenyltetrol is presented. Basic alcoholysis of compounds trans -3 and cis -3 proceeds in high diastereoselectivity to give only two of the six possible acyclic phosphorothioamidates 4a and 4b (or 5a and 5b). When diastereopure 4 and 5 are subjected to acid alcoholysis they lead to enantiopure cyclic phosphorothioates trans -6 and trans-7, respectively. All compounds prepared are solid, air stable and possess a C2 symmetry axis. Due to restricted rotation around the C1-C1′ bond, compounds 4a, 4b, 5a, 5b, 6 and 7 exist as stable atropisomers at rt. However for compounds trans-3 and cis-3, the bridged biphenyl system intercorverts at rt with a half-life of 6 h. The structure of compounds trans- 2,trans- 3, and 5a has been confirmed by X-ray analysis. Phosphorothioates and phosphorothioamidates can be tested as agrochemicals since these classes of compounds can inhi...

Three trismalonatoferrate compounds (20% enriched in57Fe) NaBa (FeMa3)·3H2O (1), [Na3 (FeMa3]2·8H2O (2), and Na 3)O·1/2 Sol (3) (Ma is the malonato anion and Sol is a solvate molecule) have been prepared and their X-ray crystal structures determined. The Mossbauer spectra exhibit a broadened line at 293 and 4.2 K indicating the presence of spin relaxation effects. The spectra data, fitted following Afanas'ev and Wickman models, point to the presence of spin-spin isotropic relaxation mechanism.

The synthesis of 2,3-dibromobenzonorbornadiene 11 by high temperature bomination of 2-bromobenzonorbornadiene 9 allows the synthesis of the benzoannelated trimers, syn - and anti -5,18:6,11:12,17-trimethanotrinaphthylene 8 . The syn isomer is a basket shaped molecule that displays unusual geometric and electronic features including bond length fixation of the central benzene ring as shown by X-ray diffraction (exocyclic bond 1.41 A, endocyclic bond 1.36 A).

The preparation of a number of biaryldithiols from biaryldiols is discussed. A key reaction is the Newman-Kwart thermorearrangement of bisthiocarbamates and crucial variables of temperature and reaction time have been identified. Alternative approaches to 3,3′-disubstituted dithiols via ortho metallation are presented. The benefit of using such disubstituted compounds is illustrated with representative examples of the stereochemical features of the derived carbanions in reactions with prochiral electrophiles. © 1997 Published by Elsevier Science Ltd.

A complete series of N- and C-blocked, monodispersed homo-oligopeptides to the pentamer level from 1-aminocycloheptane-1-carboxylic acid (Ac7c), an α-amino acid conformationally restricted through Ciα ←→ Ciα cyclization, and three tripeptides with Ac7c combined with Ala, Leu, and Val residues have been synthesized by solution methods and fully characterized. The solution conformational preferences have been determined by IR absorption and 1H NMR spectroscopy. In addition, the molecular structures of three derivatives (Ac7c hydantoin, ClCH2CO-Ac7c-OH, and Z-Ac7c-OH; Z = benzyloxycarbonyl) and four peptides [the dipeptide Z-Ac7c-L-Ala-OMe, the tripeptides Z-Ac7c-(L-Ala)2-OMe and Z-(Ac7c)3-OBut, the tetrapeptide Z-(Ac7c)4-OBut, and the pentapeptide Z-(Ac7c)5-OBut] have been assessed in the crystal state by X-ray diffraction. The results obtained confirm the tentative conclusions put forward on the basis of our previous preliminary study, namely that β-bends and 310-helices are preferentially adopted by Ac7c-based peptides. A comparison with the structural tendencies extracted from published work on peptides from α-aminoisobutyric acid, the prototype of Cα,α-dialkylated glycines, and the other extensively investigated members of the class of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n = 3–6, 8, 9) is made and the implications for the use of the Ac7c residue in conformationally constrained analogues of bioactive peptides are briefly discussed.

A series of tin(IV) and organotin(IV) hydridotris(4-bromo-1H-pyrazol-1-yl)borates has been prepared. The compounds of general formula RnSnCl4−n−1[HB(4-Br-pz)3] (where R = Me or Ph, n = 0, 1, 2, or 3) are rigid in solution and contain a six-coordinate tin(IV) site with a tridentate ligand. They were characterised by IR, 1H, 13C, 119Sn NMR, and 119Sn Mossbauer spectroscopy. Their stability towards self-decomposition decreases with increasing number of Sn-bonded aryl or alkyl groups. The compound MeCl2Sn[HB(4-Br-pz)3] crystallises in the space group R 3 (no. 148), trigonal, with a=35.520(2), b=35.520(2), and c=8.688(1) A , γ=120° .

Terminally blocked, isotactic homopeptides from the sterically demanding α-methylvaline of general formula Y-[L-(αMe)Val]n-OtBu (Y = Z, pBrBz, Ac; n = 2–8) have been prepared step-by-step in solution and fully characterized. The conformations preferred in solution (β-turn and right-handed 310-helix) have been assessed by FT-IR, 1H NMR and CD spectroscopy. The molecular and crystal structures of the Z-protected trimer, hexamer, heptamer and octamer have been determined by X-ray diffraction. In the crystal state, while the trimer is folded in a type III β-turn conformation, the longest homopeptides form well-developed, regular, right-handed 310-helices. The screw sense in the helix of the pBrBz-blocked octamer has been confirmed to be right-handed by solid-state and solution CD spectroscopy. The possible exploitation of these peptide helices as rigid and precise molecular rulers is discussed.

Syntheses of Ph 2 Pb(dmit) ( 3 ), [Q] [Ph 2 Pb(dmit)I] ( 5 , Q = NEt 4 or 1,4-Me 2 -pyridinium), (Ph 3 Pb) 2 (dmit) ( 4 ) and Pb(dmit) ( 6 ) are reported [H 2 -dmit = 4,5-dimercapto-1,3-dithiole-2-thione]. Compound 3 was produced from Ph 2 Pb(OAc) 2 and [NEt 4 ] 2 [Zn (dmit) 2 ], while 4 was obtained from Ph 3 PbOAc and either Na 2 (dmit) or [NEt 4 ] 2 [Zn(dmit) 2 ]. The ionic species, 5 , were obtained by addition of [Q] I to 3 ( eg. for Q = 1,4-Me 2 -pyridinium) or from reaction of Ph 2 PbI 2 with [NEt 4 ] 2 [Zn(dmit) 2 ]. Reaction of either Pb(OAc) 2 or Pb(NO 3 ) 2 with [NEt 4 ] 2 [Zn(dmit) 2 ] produced 6 . NMR spectra, including the solid state spectra for 3 , have been obtained. X-ray crystallography revealed 4 to be a monomeric compound with each Pb atom having a distorted tetrahedral geometry. The CPbS bond angles are less and the CPbC bond angles greater than ideal tetrahedral angles. The dmit ligand is effectively inserted between two phenyl rings of different Ph 3 Pb groups in 4 , with short non-bonded CC and CS distances of 3.4–3.7 A. Cyctic voltammetric studies of 3 and of 4 in DMF have also been carried out.

From the (attempted) recrystallization of samples of Me 2 SnCl · Tp ∗ Me [ Tp ∗ Me = hydridotris (3,4,5- trimethyl -1 H- pyrazol-l-yl ) borate, C18H28N6B−] in dichloromethane-acetonitrile at sub-ambient temperature, two crystalline compounds were obtained, 1 {bis(3,4,5-Me3-pyrazole)dichlorodimethyltin(IV) SnC14H20N4Cl2} and 2 {3,4,5-Me3-pyrazolechlorodimethyltin, chlorodimethyltinoxide, di-μ-oxo-dimer Sn2C10OH22N2 Cl2}. This last structure displays a planar Sn2O2 ring around an inversion centre; the two tin atoms are penta-coordinate with differently distorted geometries.

The crystal and molecular structure of dimethyl(L-tryptophyl-L-alaninato)tin(IV)–methanol (1/1) has been determined by X-ray crystallography. The tin atom, bonding to two methyl carbons [Sn–C(1) 2.107(6), Sn–C(2) 2.121(8)A; C(1)–Sn–C(2) 123.8(3)°], terminal amino nitrogen [Sn–Namino 2.272(5)A], deprotonated peptide nitrogen [Sn–Npeptide 2.064(5)A] and terminal carboxylate [Sn–Ocarboxylate 2.174(5)A], has a five-co-ordinated trigonal-bipyramidal environment. An extended hydrogen-bond network gives rise to one-dimensional polymeric chains. The molecular dynamics of three tryptophan-containing dipeptide complexes with R2SnIV(dipeptide dianion = Trp-AlaO, R = Me or Ph; dipeptide dianion = TrpTyrO, R = Me) have been investigated by variable-temperature 119Sn Mossbauer spectroscopy. The complexes behaved as Debye solid and, in particular, the calculated mean-square displacements of the tin atom confirm the occurrence of monomeric structures in such complexes interconnected through hydrogen bonds, which appear to be much stronger in SnMe2(Trp-AlaO) and SnMe2(Trp-TyrO) than in SnPh2(Trp-AlaO).

Five tin(IV) and organotin(IV) hydridotris(4-chloro-3,5-dimethyl-1H-pyrazol-1-yl)borates have been synthesized and characterized by 1H, 13C and 119Sn NMR and 119mSn Mossbauer spectroscopy. The tin atom has a more or less distorted octahedral coordination both in the solid state and in solution. The X-ray crystal structures of trichlorotin(IV) and dichlorophenyltin(IV) hydridotris [4-chloro-3,5-dimethyl-1H-pyrazol-1-yl)borates confirm these inferences.

The interaction of iron(III) halides with 18-crown-6 or 15-crown-5 ethers has led to the isolation of several complexes, two of which, [FeCl3(H2O)2] (15-crown-5) and H(FeBr4) (15-crown-5)2(H2O)2, yielded crystals suitable for single crystal X-ray structural analysis. The chloro complex crystallizes in the monoclinic P21 (No. 4) space group with Z = 2, a = 8.574(1), b = 13.714(2), c = 8.223(1) A, β = 107.9 (1)°. The crystals contain trigonal bipyramidal [FeCl3(H2O)2] moieties hydrogen bonded to a partially disordered 15-crown-5 ether to form a polymeric chain oriented along the crystallographic c-axis. The bromo complex crystallizes in the cubic Fd3 (No. 203) space group with Z = 8, a = 19.500(2) A. The compound contains tetrahedral FeBr4− anions which have no bonding interaction with the 15-crown-5 ether, which simply acts as a dielectric medium to separate the anions. A study of the thermal decomposition of the compounds was performed by thermogravimetric analysis. IR and Mossbauer spectral measurements indicate that the decomposition products are water, acetaldehyde, dioxane, chlorine or bromine, carbon dioxide, carbon monoxide, and mixtures of hydrated iron(II) halides and iron oxides.

The heterobimetallic complex syn-[Cr(CO)3(μ,η:η-indenyl)Rh(COD)] was obtained of syn-[Cr(CO)3(μ,η:η-indenyl(Rh(CO)2] with COD. The stereochemistry was retained in the exchange reaction as confirmed by 1H and 13C NMR measurements and by X-ray diffractometric analysis. In spite of great distortion, the COD complex is quite stable. An unusual bonding interaction between the hybrid CO orbitals of the Cr(CO)3 group and the s-orbital of methine hydrogen atoms of COD is inferred on the basis of spectroscopic and X-ray structural data.

The steric course of the catalytic decomposition of the chiral diazoxazepanedione 1 to 2-pyrrolone 3 was clarified by the X-ray diffraction study of the enantiomerically pure pyrrolidine 5 , obtained by reductive cleavage of the unisolated intermediate bicyclic compound 2 .

The reaction of RhCl 3 ·3H 2 O with ( EEE )-1,5,9-cyclododecatriene in alcohols gives a red polymeric solid compound with chlorine bridges, 1 , in which the hydrocarbon moiety has been reported to be bonded to the metal via an η 3 -allylic bond. Re-examination of this reaction has led to the isolation of soluble derivatives obtained by breaking the chlorine bridges with chelating diphosphines and diamines. An X-ray analysis on single crystals of a diphosphino and a diamino derivative, indicates that the cyclo-olefin residue with composition C 12 H 17 has undergone isomerization. The two double bonds not involved in the bonding to the metal are 5,8 rather than 5,9.

The five-co-ordinate complexes [CuII(tren)(H2O)]Cl21, [CuII(tren)(HAde)]Cl22, [CuII(tren)(HAde)]-[NO3]23 and [CuII(tren)(Ade)]Cl·2H2O 4[tren = tris(2-aminoethyl)amine and HAde = neutral adenine] have been synthesized and characterized. The geometry and structures of the complexes were studied by electronic and IR spectra and, in addition, the structure of complex 4 has been determined by X-ray crystallography. The physicochemical data for complexes 2 and 3 support the presence of neutral adenine co-ordinated to CuII, whereas in complex 4 the adenine molecule is bound in its monoanionic form, as confirmed by the X-ray analysis [monoclinic, space group P21/a, a= 15.001(2), b= 8.422(1), c= 15.039(2)A, β= 105.90(6)°, Z= 4; R= 0.065 for 2596 unique diffraction data]. The co-ordination polyhedron around the Cu2+ ion is approximately trigonal bipyramidal, with the equatorial sites occupied by the three primary amino nitrogen atoms and the axial positions occupied by the tertiary amino nitrogen and the imidazole N9 nitrogen from the adenine monoanion. The Cu–N(9) distance is rather short at 1.965(9)A. Such selective metal bonding in adenine is very probably promoted by the trigonal-bipyramidal geometry around CuII and by the relatively low steric hindrance of the CuII(tren) moiety.

Several thermally stable M[L]2 complexes were obtained from the appropriate metal chlorides in aqueous solution (M = Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) with potassium hydridotris[(3-Me-1H-pyrazol-1-yl)borate]. They have been investigated by elemental analysis, conductivity measurements, IR spectroscopy and, where possible, by 1H and 13C NMR. The X-ray crystal structure of nickel(II)bis[hydridotris(3-Me-1H-pyrazol-1-yl)borate] has been resolved. Two discrete units with octahedral NiN6 sites are present. The NiN bond lengths range from 2.097(5) to 2.134(4) A and the NNiN bond angles from 87.8(2) to 92.4(2)°.

Terminally blocked, syndiotactic linear homo-peptides from Cα,α-disubstituted glycines Iva and (αMe)Val have been prepared to the hexapeptide and tripeptide amide levels, respectively, by solution methods and fully characterized. The molecular and crystal structures of pBrBz-(D-lva-L-lva)2-OBut methanol solvate, pBrBz-(D-lva-L-lva)2-D-lva-OBut methanol solvate, and Z-D-(αMe)Val-L-(aMe)Val-D-(aMe)Val-NHPri(pBrBz =p-bromobenzoyl, Z = benzyloxycarbonyl) were determined by X-ray diffraction. While the Iva pentapeptide and the (αMe) Val tripeptide amide are folded in an (incipient) left-handed 310-helical conformation, the Iva tetrapeptide adopts a double β-bend conformation of the II′–III type. The FTIR absorption and 1H NMR analyses support our contention that in chloroform solution, the longest syndiotactic homo-peptides may be folded in well developed 310-helical structures. This is the first structural study reported on regularly alternating (D–L) peptides based on conformationally constrained α-amino acids.

The molecular and crystal structures of one derivative and three homopeptides (from the di-to the tetrapeptide level) of the chiral, Cα, α-disubstituted glycine Cα-methyl, Cα-benzylglycine [(αMe)Phe], have been determined by x-ray diffraction. The derivative is mClAc-D-(αMe)Phe-OH, and the peptides are pBrBz-[D-(αMe)Phe]2-NHMe, pBrBz-[D-(αMe)Phe]3-OH hemihydrate, and pBrBz-[D-(αMe)Phe]4-OtBu sesquihydrate. All (αMe)Phe residues prefer ϕ,ψ torsion angles in the helical region of the conformational map. The dipeptide methylamide and the tripeptide carboxylic acid adopt a β-turn conformation with a 1 4 CO…HN intramolecular H bond. The structure of the tripeptide carboxylic acid is further stabilized by a 1 4 CO…HO intramolecular H bond, forming an “oxy-analogue” of a β-turn. The tetrapeptide ester is folded in a regular (incipient) 310-helix. In general, the relationship between (αMe)Phe chirality and helix screw sense is opposite to that exhibited by protein amino acids. A comparison is made with the conclusions extracted from published work on homopeptides from other Cα-methylated α-amino acids. © 1993 John Wiley & Sons, Inc.

The reaction of 9H,10H-4b,9a([1,2]benzenomethano)indeno[1,2-a]indene (triptindan, TRIP) with Cr(CO)6 in Bu2O/THF (9:1) affords a monocomplex (A) together with two bis-Cr(CO)3 complexes (B and C) and one tris-Cr(CO)3 complex (D). The relative yields of the four complexes as well as their tendency to lose Cr(CO)3 are related to stabilizing intramolecular factors. All the Cr(CO)3 units of the complexes A, B, and D are coordinated in the isoclined orientation with respect to the polar axis of the ligand, whereas complex C bears one isoclined and one anticlined Cr(CO)3 unit. The results of X-ray measurements support the hypothesis of weak attractive electronic interactions bonds between the oxygen atoms of the carbonyl groups and polarized faces of benzene rings.

The formylketenyl platinum complex, trans-bis(tricyclohexylphosphine)(η1-formylketenyl)(hydride)platinum(II), trans-(PCy3)2(H)Pt[η1-C(CHO)CO] (1), reacts with acids causing the cleavage of the PtC bond and generating the species C3H2O2 which is trapped by an excess of 1. The reaction gives rise to the formation of the addition product trans-(PCy3)2(H)Pt(C6H3O4), where C6H3O4 is an α-pyrone ligand σ-bonded to Pt. The crystal structure of the Pt α-pyrone derivative has been determined. The crystal are monoclinic, space group P21/a, with a = 19.404(9), b = 11.889(6), c = 18.534(9), β = 91.3(1)°, Z = 4. The plane of the α-pyrone ligand is almost orthogonal to the coordination plane of Pt. IR, 1H and 31P NMR and mass spectra also support the structure.

The series of lanthanide(III) complexes Ln(NCS)3(THF)4[Ln = lanthanide(III) ion, THF = tetrahydrofuran] has been synthesized and examined by X-ray diffractometric methods. The study has shown that four oxygen atoms (THF) and three nitrogen atoms (NCS) are arranged around the Ln3+ ions according to well-defined coordination geometries: the square antiprism (SQA) for eight-coordination and the pentagonal bipyramid (PB) for seven-coordination. The dimeric square antiprismatic structures (Ln = Nd, Gd, Eu, Dy and Er) have been previously described. Here we report the crystal structure of Yb(NCS)3(THF)4. The coordination geometry of the metal ion consists of a slightly distorted pentagonal bipyramid, in which two nitrogen atoms (NCS) are in the apical positions and four oxygens atoms (4THF) and one nitrogen (NCS) lie in the equatorial plane. A correlation between the two coordination arrangements (SQA) and (PB) is discussed.

The oxidative ability toward the alcoholic function of a series of peroxomolybdenum complexes has been evaluated by measuring the oxidation rates and the nature of the products in the oxidation of two model alcohols, i.e . cyclohexanol and 1-octanol. Included in the series are two complexes, i.e . [MoO(O 2 ) 2 (C 6 H 5 COO)] − (Bu) 4 N + and [2MoO(O 2 ) 2 (MeOH) 2 (MoO(O 2 )O) 2 (MeO) 2 ] 2− [(Bu) 4 N + ] 2 which have been synthesized for the first time and characterized by X-ray analysis. On the basis of the reactivity data and of the structural features of the oxidants, the requisites that allow the peroxomolybdenum complexes to act as effective and selective oxidants of the alcoholic function have been selected. The necessary requisite appears to be the anionic nature of the oxidant. An important role is also played by the availability of a free or releasable coordination site on the complexes. Such a site should be the second apical position of the species which in all cases displays pentagonal pyramid or bipyramid geometry. Some preliminary mechanistic considerations based on the results obtained are presented envisaging the coordination of the substrate as an alkoxo derivative prior to the oxidation step.

The compounds [SnMe 2 X 2 (Hmimt)], [SnMe 2 X 2 (Hmimt) 2 ] and (Et 4 N)[SnMe 2 X 3 (Hmimt)] (X = Cl or Br; Hmimt = 1-methyl-2(3 H )-imidazolinethione) have been prepared and characterized by conductivity measurements and by IR, Raman, Mossbauer and 1 H, 13 C and 119 Sn NMR spectroscopy. The structure of [SnMe 2 Cl 2 (Hmimt)] was determined by X-ray diffraction. Its crystals are triclinic, space group P 1 , with a 9.702(2), b 9.375(2), c 7.119(1) A,α 68.1(2),s 86.6(2), γ 85.6(2)°, U 598.7 A 3 , Z = 2, R = 0.062, R w = 0.058 and consist of chlorine-bridged [SnMe 2 Cl 2 (Hmimt)] dimers in which the hexacoordinate tin atoms have distorted octahedral environments and the thiones are S-bonded. Neighbouring dimers are linked by NH … Cl bonds. Mossbauer and vibrational data suggest octahedral coordination for the tin atom in [SnMe 2 X 2 (Hmimt) 2 ] and (Et 4 N)[SnMe 2 X 3 (Hmimt)].

Terminally blocked homodi- and homotripeptides from (αMe)Val, a C α,α -disubstituted glycine, were prepared by solution methods and fully characterized. The preferred conformation in CHCl 3 solution was assessed by FTIR and 1 H NMR as a function of concentration and addition of perturbing agents. The molecular and crystal structures of the dipeptide and tripeptide amides, Z-(D-(αMe)Val] n -NHiPr (n= 2, 3) were also determined by X-ray diffraction. While the dipeptide amide adopts a type-III' β-turn conformation stabilized by a 1←4 C=O...H-N intramolecular H bond, the tripeptide amide is folded in an incipient left-handed 3 10 -helix

The thiocyanate complexes Ln(NCS)3 · (THF)4 (Ln = Nd, Eu and Er) have been prepared and their structure was studied in the solid state by X-ray diffractometric methods. They crystallize in the monoclinic space group P21/a with a ranging from 19.279(9) for Nd to 18.980(9) A for Er; b, c and β have almost constant values: b = 8.11 ± 0.01 A, c = 17.68 ± 0.05 A and β = 111.0 ± 0.03°. A peculiar feature of these complexes is the octa-coordination, the dimeric nature and the fact that in the molecule the NCS groups are coordinated as mono (LnNCS) and bidentate (LnNCSLN) ligands. The structural units assume an almost undistorted square antiprismatic coordination geometry; they are linked through bridges of NCS groups. The Ln ⋯ S distances range from 3.10 (Nd) to 3.26 A (Er); these values correspond to rather weak bond interactions, but are unambiguously recognized as coordinating values in geometrical terms.

With the aim to obtain further insight into the nature of the Ni(II)-nitrogen bond in complexes with nucleobases, we have synthesized two novel Ni(II) ternary complexes constituted by Ni(II), tris(2-aminoethyl)amine (tren) and neutral adenine (AdH) or imidazole (ImH). The reaction of NiCl2·6H2O with tren and imidazole yields the ternary [Ni(tren)(ImH)(H2O)]Cl2·H2O complex and the same reaction with adenine instead of imidazole gives the ternary [Ni(tren)(AdH)Cl]Cl complex. The complexes have been studied by spectrophotometric and spectroscopic measurements and by X-ray diffraction. The ternary complex of adenine is monoclinic, space groupC2/c, and exhibits a pseudo-octahedral geometry, being Ni(II) coordinated to the four nitrogen atoms of the tetradentate tren ligand, to a Cl− ion and to the pyrimidine N3 site of a neutral adenine. Such an exclusive Ni-N3 bonding [2.081(4)A] is now reported for the first time. The ternary complex of imidazole is monoclinic, space groupP21/n. Its pseudo-octahedral geometry is similar to that found in the above adenine complex although a water molecule instead of a Cl− ion is now present in the coordination sphere. In fact, Ni(II) is coordinated to tetradentate tren, to the imidazole N1 nitrogen and to a water molecule. Electronic and1H NMR spectra in solution indicate that the octahedral structures found in the solid state are substantially maintained in solution. Furthermore, the present investigation suggests that the adenine Ni-N3 and imidazole Ni-N1 bonds have the same chemical nature, involving mainly σ- and only partiallyπ-bonding. The Ni-N3 bonding is discussed in connection with biological implications and possible applications.

The preparation of compound 1, a conformational study in solution and the unexpectedly facile rearrangement into 2 via photochemical intramolecular [2+2]-cycloaddition is described: the structure of these compounds have been investigated by NMR and X-ray diffraction.

The interaction of cis-[Pt(PMe3)2(H2O)2]2+ with 1-methylcytosine (4-amino-1-methyl-1H-pyrimidin-2-one)(myct) and cytidine (4-amino-1-β-D-ribofuranosyl-1H-pyrimidin-2-one)(Cyd) has been investigated by 1H and 31P NMR spectroscopy. The compounds cis-[Pt(PMe3)2(myct)2][NO3]2 and cis-[Pt(PMe3)2(Cyd)2][NO3]2 have been isolated and the molecular structure of the nucleobase derivative determined by single-crystal X-ray diffraction techniques. The crystals of cis-[Pt(PMe3)2-(mcyt)2][NO3]2 are triclinic, space group P, with a= 12.363(2), b= 11.479(2), c= 9.645(2)A, α= 87.5(2). β= 73.9(2), γ= 84.5(2)° and Z= 2. The structure was solved by heavy-atom methods and refined by least-squares techniques to R(F)= 0.067 for 4112 observed reflections with F 7δ(F). The platinum atom is in a distorted square-planar environment with the phosphine ligands in cis position [P–Pt–P 94.5(3)°] and the two N(3)-bonded nucleobases in a head-to-til arrangement. The interbase dihedral angle is 94.2(3)° and the platinum co-ordination plane forms a dihedral angle of 74.1(3)° with the pyrimidine ring planes. The Pt–P and Pt–N(3) bond distances are 2.256(5), 2.254(5) and 2.092(9), 2.108(9)A, respectively. Strong interbase [NH2(4)⋯ O(2′) 2.95(1)A] and base–nitrate anion hydrogen bonds are observed. The 13C and 195Pt NMR data of these nucleobase and nucleoside adducts are also reported and discussed.