bluuebunny/crossref_metadata_2025 huggingface dataset:
Epipolar geometry estimation method based on maximizing image correlation
Authors: Hata Koichi , Eto Minoru
Published: February 2003

The authors proposed a method for estimation of epipolar geometry parameters based on correlation between two images. This method is characterized by the fact that, unlike conventional epipolar geometry estimation methods using correspondence of characteristic points between the images, it uses parametric block matching correlation with the results of block matching in the image approximated by a two‐dimensional function. This technique involves (1) performing block matching between the two images and obtaining the parametric block correlation function, and (2) minimizing the obtained parametric block correlation function by a robust estimation based on the epipolar geometry parameters, and estimating the epipolar geometry parameters. In the current study, the authors discussed a technique for estimating the epipolar geometry parameters by linear solution method, and then a technique for estimating the epipolar geometry parameters based on nonlinear solution method with those parameters set as initial values. Finally, it was shown by tests using real images that this method is suitable for estimating epipolar geometry parameters with highly correlated images. The tests confirmed that this technique is efficient for improving image quality in the course of image synthesis or improving encoding efficiency during image encoding. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(3): 73–81, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10137
Knowledge extraction from scenery images and recognition using fuzzy inference neural networks
Authors: Iyatomi Hitoshi , Hagiwara Masafumi
Published: February 2003

A new method of extracting various types of human knowledge from scenery images in linguistic form and labeling the various regions of unknown images in an effective manner is proposed. In this system, partitioning of the input/output space can be performed in a self‐organizing manner. Rule extraction is performed in parallel and automatically by using a knowledge extraction network (KEN). Depending on the type of image to be learned, two‐phase processing including a self‐organization phase and an LMS learning phase is performed by several KENs. The overall network output is then unified and knowledge extraction and region recognition are performed linguistically. Software that performs a series of such operations has been implemented and it has been confirmed that knowledge extraction and better image recognition can be performed linguistically even if human knowledge is not provided. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(3): 82–90, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10138
Numerical analysis of ultra‐short pulse wavelength conversion characteristics of LiNbO3 waveguide nonlinear‐optic devices
Authors: Ishizuki Hideki , Suhara Toshiaki , Nishihara Hiroshi
Published: February 2003

The pulse wavelength conversion characteristics of various nonlinear optical processes in LiNbO3 waveguide nonlinear optic devices are analyzed by the beam propagation method. Detailed data for estimation of device characteristics and for optimal device design for a 1.5‐µm‐band signal are presented. The following results are obtained. (1) The conversion efficiency of second harmonic generation decreases as the pulse width of the input pump wave is decreased, and is improved as the device length is increased in the range where the walkoff between the optical waves is short. (2) In difference frequency generation, the optical pulse width of the difference frequency is close to that of the input signal wave. In continuous wave pumping, high efficiency is realized by increasing the device length. (3) In cascade second harmonic generation/difference frequency generation, high efficiency can be realized by increasing the device length in both continuous wave pumping and difference frequency pumping. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(3): 11–20, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.1118
Post‐breakdown conduction mechanism of thin oxide films and their aspects
Authors: Komiya Kenji , Oka Takashi , Okada Naoki , Omura Yasuhisa
Published: February 2003

This study investigates extremely thin silicon oxide with thicknesses of 3 to 5 nm produced by various fabrication processes, and the post‐breakdown characteristics are studied. This paper describes the results of comparison. By analysis of the conduction characteristics after intrinsic breakdown, it is shown that there exist two conduction mechanisms—resistive and barrier type—for oxide films with thicknesses of 3.3 and 5.2 nm. These properties of the conduction characteristics are very similar to those reported for the soft breakdown state, which indicates that the conduction mechanisms essentially do not differ much between soft and intrinsic breakdown. It is also shown that the intrinsic breakdown process progresses in two stages in an oxide film with a thickness of 3.3 nm, in contrast to film with a thickness of 5.2 nm. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(3): 21–27, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.1119
Investigation of oxygen source from vapor phase and target for growth of Pb(Zr,Ti)O3 thin film
Authors: Kim Je‐Deok , Sasaki Kimihiro , Hata Tomonobu
Published: February 2003

The authors are engaged in the study of fast low‐temperature fabrication of strongly dielectric Pb(Zr,Ti)O3 [PZT] thin film by reactive sputtering, using a metal (ZrTi)‐oxide (PbO) composite target. In this approach, there is an interaction between the metal target and the oxide target, affecting the fabricated film. When the area ratio of the oxide target is increased, there appears a sputtering mode (called the quasi‐metallic mode) in which metal and oxide are sputtered simultaneously. The deposition mechanism of PZT thin film in the quasi‐metallic mode is investigated, and it is revealed that oxygen is supplied not from the gas source, but from PbO. It is also determined that when a sufficient amount of oxygen is not supplied to the surface of the growing PZT film, reevaporation of Pb occurs, resulting in a deficit of Pb. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(3): 28–34, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.1120
Synthesis and Reactivity of Organoimido Complexes of Chromium
Authors: Leung Wa‐Hung
Published: February 2003

Organoimido groups are excellent spectator ligands for high‐valent organometallic compounds due to their strong π‐donating capability. Of interest are imidochromium complexes that are used as catalysts for olefin polymerization. This microreview provides an overview of the organometallic chemistry of high‐valent imidochromium complexes. Synthetic routes to alkyl‐ and arylimido complexes of chromium in oxidation states VI−IV will be presented. The reactivity of imidochromium complexes including imido group transfer and cycloaddition will be described. The use of imidochromium complexes as catalysts for regioselective ring opening of epoxides will be discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Unexpected Effect of Cyclodextrins on Water‐Soluble Rhodium Complexes
Authors: Caron Laurent , Canipelle Mickael , Tilloy Sébastien , Bricout Hervé , Monflier Eric
Published: February 2003

As shown by 31P NMR spectroscopy, addition of β‐cyclodextrin or randomly methylated β‐cyclodextrin to an aqueous solution of [HRh(CO){P(m‐C6H4SO3Na)3}3] has no effect on the organometallic complex. In contrast, [HRh(CO){(p‐tBuC6H4)P(m‐C6H4SO3Na)2}3] can be partially converted in the presence of the same β‐cyclodextrin derivatives into the hydroxy complex [HORh(CO){(p‐tBuC6H4)P(m‐C6H4SO3Na)2}2], under nitrogen, or to the hydrido complex [HRh(CO)2{(p‐tBuC6H4)P(m‐C6H4SO3Na)2}2] under carbon monoxide. This remarkable difference of behavior was attributed to the fact that the phosphane (p‐tBuC6H4)P(m‐C6H4SO3Na)2 forms more stable inclusion complexes with the β‐cyclodextrin derivatives than the phosphane P(m‐C6H4SO3Na)3. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Complexes of Rhodium(I) and Iridium(I) with the Chiral Tridentate Phosphane Pigiphos: Structure and Reactivity Studies
Authors: Hintermann Lukas , Perseghini Mauro , Barbaro Pierluigi , Togni Antonio
Published: February 2003

The chiral ferrocenyltriphosphane Pigiphos [bis{(S)‐1‐[(R)‐2‐(diphenylphosphanyl)ferrocenyl]ethyl}cyclohexylphosphane] forms four‐coordinate complexes with IrI and RhI. The tridentate ligand assumes different conformations in the derivatives [Rh(CO)(Pigiphos)]OTf (4) and [IrCl(Pigiphos)] (1b), the latter also showing a drastic deviation from the square‐planar geometry. Reactivity studies have focussed on the more reactive 1b. The HCl and O2 adducts have been characterized in solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Preparation of Rhodium Catalysts Supported on Carbon Nanotubes by a Surface Mediated Organometallic Reaction
Authors: Giordano Roberto , Serp Philippe , Kalck Philippe , Kihn Yolande , Schreiber Joachim , Marhic Christiane , Duvail Jean‐Luc
Published: February 2003

The dimeric complex [Rh2Cl2(CO)4] was grafted to multi‐walled carbon nanotubes (MWNTs) previously oxidised with nitric acid and then treated with sodium carbonate to produce carboxylate groups on their outer surface. The grafting mechanism involves bridge‐splitting and substitution of ‐COO for Cl, as evidenced by the presence of NaCl in the samples. A further reduction/decomposition step under dihydrogen at 573 K afforded highly dispersed rhodium nanoparticles (≈︁1.5−2.5 nm). This novel rhodium‐supported carbon material (Rh/MWNT‐COONa) was tested as a catalyst for the hydrogenation of trans‐cinnamaldehyde and the hydroformylation of hex‐1‐ene in the liquid phase: in both cases it was found to be very selective, toward C=C double‐bond hydrogenation and the production of linear and branched aldehydes, respectively. A comparison was made between its catalytic activity and that of rhodium supported on pristine MWNTs and on nitric acid‐oxidised MWNTs. We observed that these latter catalysts have larger particle sizes and lower activities, thus confirming the efficiency of our grafting procedure. Moreover, the better results obtained when using MWNT‐COONa as support with respect to carboxylate‐containing activated carbon also point to the important role played by the mesoporous nature of the carbon nanotube support, which can ameliorate transfer processes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Syntheses, Crystal Structures, and Properties of Four Two‐Dimensional Network Complexes with Multidentate Bis(Schiff Base) Ligands
Authors: Ouyang Xing‐Mei , Fei Bao‐Li , Okamura Taka‐aki , Bu Hong‐Wei , Sun Wei‐Yin , Tang Wen‐Xia , Ueyama Norikazu
Published: February 2003

Four novel two‐dimensional coordination polymers [Ag2(L1)2](CF3SO3)2·H2O (1), [Ag3(L1)2](NO3)3·H2O (2), [Co(L1)2(SCN)2]·EtOH (3), and [Co(L2)2(SCN)2] (4) were obtained by reactions of the bis(Schiff base) ligand 1,2‐bis(4′‐pyridylmethyleneamino)ethane (L1) with silver(I) trifluoromethanesulfonate, silver(I) nitrate, and cobalt(II) thiocyanate, and 1,2‐bis(3′‐pyridylmethyleneamino)ethane (L2) with cobalt(II) thiocyanate, respectively. In complex 1, a 2D network structure was achieved by hydrogen bonding interactions between the two 1D chains, consisting of double‐stranded helicates, through solvate water molecules. The 2D network of complex 2 was formed by the coordination to a two‐coordinate silver(I) ion instead of hydrogen bonds as in complex 1. Complex 3 contains molecular square units, which are occupied by disordered ethanol molecules. Complex 4 exhibits a classic square‐grid network which is different from that of 3 due to the different terminal pyridyl groups in L1 (4‐pyridyl) and L2 (3‐pyridyl). These coordination polymers were characterized by X‐ray crystallography, electrospray mass spectrometry, cyclic voltammetry and magnetic measurements. The results show a 2D network superstructural diversity by the fine‐tuning of construction components. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture
Authors: Hintermann Lukas , Perseghini Mauro , Barbaro Pierluigi , Togni Antonio
Published: February 2003

The cover picture shows the X‐ray crystal structure of the complex [IrCl(Pigiphos)], where Pigiphos is a unique chiral tridentate ligand containing two ferrocenyl units. Enantiomerically pure triphosphanes are still quite rare and Pigiphos is particularly attractive because of its simple synthesis − one step from commercially available precursors. The study of the coordination chemistry of Pigiphos has shown that it can accomodate metal ions in essentially perfect square‐planar geometries (NiII, PdII, PhI). In case of an ocatahedral coordination sphere it can adopt both a facial or an equatorial configuration (RuII). However, the present [IrCl(Pigiphos)] complex displays a severe deviation from the expected square‐planar geometry and shows a dynamic behavior in solution. Synthesis, characterization, and reactivity of this and other Pigiphos complexes of Ir and Rh are presented in the article by P. Barbaro, A. Togni et al. on p. 601 ff.
Reactivity of B(C6F5)3 with Oxovanadium(V) Complexes VOL3 (L = OCH2CF3, NEt2): Formation of the Organometallic Vanadium(V) Complex [VO(μ‐OCH2CF3)(OCH2CF3)(C6F5)]2 and the Lewis Acid Adduct [(Et2N)3VO·B(C6F5)3]
Authors: Wolff Fabien , Choukroun Robert , Lorber Christian , Donnadieu Bruno
Published: February 2003

Treatment of the oxovanadium(V) complex [VO(OCH2CF3)3]2 (3) with the Lewis acid B(C6F5)3 leads to aryl/alkoxy group exchange and formation of the unexpected organometallic oxovanadium(V) [VO(μ‐OCH2CF3)(OCH2CF3)(C6F5)]2 (1), while reaction of B(C6F5)3 and [VO(NEt2)3] produces the Lewis acid adduct [(Et2N)3VO·B(C6F5)3] (2). The crystal structures of 1, 2 and 3 were determined. 51V NMR chemical shifts for complexes 1−3 and [VO(NEt2)3] are discussed. A concentration‐dependant monomer‐dimer equilibrium for 3 is observed in solution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Formation and Reactivity of a Tantalocene Trihydride Containing an Aminoethyl‐Functionalised Ligand
Authors: Poulard Cyril , Perrey Danièle , Boni Gilles , Vigier Estelle , Blacque Olivier , Kubicki Marek M. , Moïse Claude
Published: February 2003

The complex [Cp*{C5H4(CH2CH2NMe2)}TaCl2] (1) was synthesised by reaction of the lithium salt LiC5H4(CH2CH2NMe2) with the tantalum compound [Cp*TaCl3(PMe3)]. Reduction of 1 with NaAl(H)2(OCH2CH2OMe)2 leads to the trihydride derivative [Cp*{C5H4(CH2CH2NMe2)}TaH3] (2). The oxidation of 2 in THF with ferrocenium ion leads to a cationic dihydride intermediate [Cp*{C5H4(CH2CH2NMe2)}TaH2]PF6 (3) with an intramolecular stabilization by the aminoethyl side‐chain of the cyclopentadienyl ligand. The hemilabile character of the functionalised cyclopentadienyl ligand was checked by treating 3 with electron‐donating ligands (e.g. phosphanes, sulfides, anions); in all cases, no displacement of the amino group was observed. When treated with HBF4, 2 undergoes a loss of the hydride and the resulting cation can be isolated as a solvento adduct by carrying out the reaction in dimethyl sulfide. Acidolysis of 2 in the presence of an excess of trifluoroacetic acid affords the compound [Cp*{C5H4(CH2CH2NHMe2)}TaH(OCOCF3)2](CF3COO) (5). Microanalytical and NMR spectroscopic data for these complexes are given. The X‐ray crystal structures are reported for [Cp*{C5H4(CH2CH2NMe2)}TaH2]PF6 (3) and [Cp*{C5H4(CH2CH2NHMe2)}TaH(OCOCF3)2](CF3COO) (5). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Investigations on 1‐Metallaindanes
Authors: Goedheijt Marcel Schreuder , Nijbacker Tom , Horton Andrew D. , Kanter Franciscus J. J. de , Akkerman Otto S. , Bickelhaupt Friedrich
Published: February 2003

1‐Mercuraindane (6) was prepared in three steps from 1‐bromo‐2‐(2‐bromoethyl)benzene (3) and converted into 1‐magnesaindane (1) by reaction with magnesium. In solution,6was observed to occur in a remarkable dimer/trimer equilibrium, whereas1forms a dimer. From1and dichlorozirconocene, the 1‐zirconaindane2was obtained, which reacted with B(C6F5)3to form the adduct13. According to spectroscopic data,13is formed by attack of the β‐methylene carbon atom at the boron atom and has a zwitterionic structure with weak interactions between the zirconium ion and one of theortho‐fluorine atoms. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
A Complex‐Based Soft Template Route to PbSe Nanowires
Authors: Liu Yuanfang , Cao Jinbo , Zeng Jinghui , Li Cun , Qian Yitai , Zhang Shuyuan
Published: February 2003

PbSe nanowires with an average size of 8 × 350 nm were synthesized by the reaction of Pb(NO3)2 and Se powder at 60 °C under ambient pressure. A mixture of arachidic acid (AA, n‐C19H39COOH) and octadecylamine (ODA), which could form a complex with Pb2+, was employed as a soft template to control the morphology of the resultant PbSe nanowires. The products were characterized by X‐ray powder diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy. The photoluminescence (PL) spectrum of the PbSe nanowires is presented. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cobalt Chloride Complexes of N3 and N4 Donor Ligands
Authors: Kooistra T. Martijn , Hekking Koen F. W. , Knijnenburg Quinten , de Bruin Bas , Budzelaar Peter H. M. , de Gelder René , Smits Jan M. M. , Gal Anton W.
Published: February 2003

A number of cobalt(II) chloride complexes of pyridine/amine N3 and N4 donors have been prepared and structurally characterised. Even though they are paramagnetic, assignment of the 1H NMR signals was possible in several cases. With the exception of tpa, which formed a cationic monochloride complex, all new complexes have cis‐coordinated chlorides. Nevertheless, only the relatively rigid pyp ligands gave rise to (low) ethene polymerisation activity on activation with MAO. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Reactions of cis‐2,3‐Dimethylaziridine, 3‐Pyrroline and Pyrrolidine with Me3Al and Me3Ga: Adducts and Dimeric Amides
Authors: Zhang Yuankui , Budzelaar Peter H. M. , Smits Jan M. M. , Gelder René de , Hageman Paul R. , Gal Anton W.
Published: February 2003

The reactions of Me3Al and Me3Ga with cis‐2,3‐dimethylaziridine (1‐H), 3‐pyrroline (2‐H) and pyrrolidine (3‐H) have been investigated. At room temperature, monomeric adducts [Me3M·LH] are obtained (M = Al, Ga; L = 1−3). [Me3Al·1‐H] is the first example of a structurally characterized adduct of an aziridine and a group 13 metal. On heating in mesitylene, all adducts except [Me3Ga·2‐H] evolve methane to form the corresponding amides; the Ga complexes require somewhat higher temperatures for this reaction. In contrast to the unsubstituted aziridine derivatives (which are trimers), dimethylaziridine amides Me2M‐1 are dimers, as shown by X‐ray crystallography. NMR spectroscopic data suggest the occurrence of a cis‐trans equilibrium for these dimers in solution. For the pyrroline and pyrrolidine derivatives, the X‐ray structures suggested large changes in the C−C and C−N bond lengths on formation of the adducts and amides. However, DFT calculations reveal that these changes are artefacts, and that the real bond length changes are fairly modest. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Structures of Alkaline‐Earth Metal Supersilanides: tBu3SiMX and tBu3Si−M−SitBu3 (M = Be, Mg; X = Cl, Br)
Authors: Lerner Hans‐Wolfram , Scholz Stefan , Bolte Michael , Wiberg Nils , Nöth Heinrich , Krossing Ingo
Published: February 2003

The alkaline‐earth metal silanides, (tBu3Si)2Be and (tBu3Si)2Mg, have been synthesized from the reaction of the sodium silanide tBu3SiNa with BeCl2 in Bu2O and MgBr2 in THF. The bissupersilylmagnesium THF adduct [(tBu3Si)2Mg(THF)2] reacts with GaBr3 in benzene at ambient temperature to form tBu3SiGaBr2 and tBu3SiMgBr(THF). The structures of bissupersilyl silanides, (tBu3Si)2Be and (tBu3Si)2Mg(THF)2, and the Grignard analogue, tBu3SiMgBr(THF), have been determined by X‐ray structure analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Chelating Ligand 1,3‐Bis(pyrazol‐1′‐yl)propane (Bpp) Enforces a Tetrahedral Geometry in Both CuII and CuI Species
Authors: Flinzner Kristel , Stassen Arno F. , Mills Allison M. , Spek Anthony L. , Haasnoot Jaap G. , Reedijk Jan
Published: February 2003

The ligand 1,3‐bis(pyrazol‐1′‐yl)propane (bpp) has been prepared by reacting 1,3‐dichloropropane with two equivalents of pyrazole. After reaction of bpp with copper(II) tetrafluoroborate, three different compounds were obtained, two with CuII and one with CuI as cation, depending on the preparative method. The formation of single crystals of these compounds was only observed when 1‐(3‐chloropropyl)pyrazole (ppc) was present in the solution. The single‐crystal X‐ray structures of [Cu(bpp)2](BF4)2 and [Cu(bpp)2](BF4) show that bpp acts as a didentate chelating ligand to form an uncommon eight‐atom chelate ring with the copper ion. Two polymorphs of the CuII complex were characterized. In each of them, the metal atoms possess a distorted tetrahedral geometry. In the copper(I) complex the metal center is present in a less‐distorted tetrahedral coordination sphere. The spectroscopic properties of the compounds are in agreement with the structural data. Cyclic voltammetry measurements showed a redox wave at 0.92 V vs. Ag/AgCl. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and X‐ray Structures of Tin(IV) and Lead(II) Complexes with Heterocyclic Thiones
Authors: Sousa‐Pedrares Antonio , Casanova María I. , García‐Vázquez José A. , Durán María L. , Romero Jaime , Sousa Antonio , Silver Jack , Titler Philip J.
Published: February 2003

Tin(IV) and lead(II) complexes of 3‐(trifluoromethyl)pyridine‐2‐thione (3‐CF3‐pySH) and 5‐(trifluoromethyl)pyridine‐2‐thione (5‐CF3‐pySH) have been synthesised. The compounds [Sn(3‐CF3‐pyS)4] (1), [Sn(5‐CF3‐pyS)4] (2), [Pb(3‐CF3‐pyS)2] (3), and [Pb(5‐CF3‐pyS)2] (4) were obtained by addition of the appropriate ligand to a methanol solution of tin(II) chloride or lead acetate in the presence of triethylamine. The complex [Sn(5‐CF3‐pyS)4] was also prepared by electrochemical oxidation of a tin anode in a cell containing an acetonitrile solution of the ligand 5‐(trifluoromethyl)pyridine‐2‐thione. The X‐ray crystal structure of [Sn(3‐CF3‐pyS)4] reveals a dodecahedral coordination geometry around SnIV, with the four thionate ligands acting in a bidentate (N,S) manner. [Sn(5‐CF3‐pyS)4] also consists of monomeric neutral molecules with the tin(IV) atom in an octahedral geometry with two bidentate (N,S) ligands and two monodentate S ligands. The molecular structure of [Pb(3‐CF3‐pyS)2] shows the metal in a five‐coordinate geometry with the stereochemically active lead(II) lone pair in an equatorial position of a trigonal bipyramid. Spectroscopic data for the complexes (IR, NMR, FAB, and Mössbauer spectra) are discussed and related to the structural information. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Reactivity of the First η6‐Rhodium(I) and η6‐Iridium(I) Complexes of 2,6‐Bis(trimethylsilyl)phosphinines
Authors: Doux Marjolaine , Ricard Louis , Mathey François , Floch Pascal Le , Mézailles Nicolas
Published: February 2003

It has been shown that 2 equiv. of 2,3,5,6‐tetraphenylphosphinine (2) react with [Rh(COD)2][BF4] to yield the bis(η1‐phosphinine)RhI complex 6, whose X‐ray crystal structure is presented. On the other hand, 2,6‐bis(trimethylsilyl)phosphinines 4 and 5 react with Rh+ and Ir+ precursors to yield the first (η6‐phosphinine)RhI and ‐IrI complexes 7−10, and 11−12, respectively. The X‐ray crystal structure of complex 8 is presented. Reaction of these η6‐phosphinine complexes with water or ethanol yields the first (η5‐phosphacyclohexadienyl)RhI and ‐IrI complexes 13−17, resulting from the formal 1,1‐addition of RO− and H+. DFT calculations comparing isoelectronic (η6‐phosphinine)‐ and (η6‐benzene)Fe0 and ‐RhI complexes allows the rationalization of the large difference in reactivity of these complexes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Electrospray Behavior of Lacunary Keggin‐Type Polyoxotungstates [XW11O39]p− (X = Si, P): Mass Spectrometric Evidence for a Concentration‐Dependent Incorporation of an MOn+ (M = WVI, MoVI, VV) Unit into the Polyoxometalate Vacancy
Authors: Bonchio Marcella , Bortolini Olga , Conte Valeria , Sartorel Andrea
Published: February 2003

ESI‐MS analysis provides a straightforward tool for the solution characterization of highly charged mono‐lacunary Keggin‐type polyoxotungstates α‐[XW11O39]p− (X = Si, P; p = 8, 7). Doubly and triply charged quasi‐molecular ion peaks were identified on the basis of both the theoretical simulation of the isotopic cluster distributions and the fragmentation modes observed with MS/MS technique. This approach allows the characterization of the inorganic polyanions transferred into the gas‐phase with associated alkali metal cations (Li+, Na+). Indeed, the ESI‐MS spectrum was found to be dependent on the counterion nature and on the initial concentration of the polyoxotungstate. While lithium salts at millimolar concentration represent the best choice for the analytical protocol, upon dilution the inorganic structure rearranges to a saturated Keggin dodecametalate complex. This phenomenon is induced by the electrospray ionization process and was exploited to produce gas‐phase ions of monosubstituted species formed through incorporation of molybdenum and vanadium into the polyoxotungstate framework. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis and Structure of Redox‐Active Heterotetranuclear Molecular Polygons by Self‐Assembly of Two Ferrocene‐Bridged Bis(pyridines) with Two Transition Metals
Authors: Lindner Ekkehard , Zong Ruifa , Eichele Klaus , Weisser Ulrike , Ströbele Markus
Published: February 2003

The macrocyclic complexes [(η5‐C5H4C2‐4‐py)2Fe]2Ni2(NO3)4 (2), [(η5‐C5H4C2‐3‐py)2Fe]2Ag2(ClO4)2 (4), and [(η5‐C5H4C2‐3‐py)2Fe]2Pd2Cl4 (5) were obtained by reaction of [Ni(H2O)6](NO3)2, AgClO4, and PdCl2(COD) with the ligands (η5‐C5H4C2‐4‐py)2Fe (1) and (η5‐C5H4C2‐3‐py)2Fe (3), respectively, under high dilution conditions (Scheme 1). The molecular motifs of 2, 4, and 5 were studied by single‐crystal X‐ray structural investigations. Elemental analyses and 1H NMR and IR spectra were also used to confirm the structures. Compound 2 represents an unsymmetric paddlewheel, in which the centers of the four Cp rings define a nearly ideal rectangle with dimensions of 20.2 × 3.3 Å. In principle, macrocycles 4 and 5 can also be described as rectangles, however, due to the 3‐positioned nitrogen donors with deformed edges (17.4 × 3.3 Å for 4). In contrast to the offset packing of the molecules in 2, the macrocycles in the crystal of 4 are aligned, with trapped acetonitrile molecules in between. The intra‐ and intermolecular Ag−Ag distances are 3.50 and 3.79 Å, respectively. Cyclovoltammetric studies reveal chemically reversible ferrocene‐based redox reactions of 1−4. Although no electronic communication was observed between the two identical ferrocene units, a weak through‐bond electronic interaction between ferrocene and nickel, or silver, was established. In 2 a weak antiferromagnetic interaction between the nickel atoms was also found. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Orientation‐ and Temperature‐Dependent Rotational Behavior of Imidazole Ligands (L) in β‐[Ru(azpy)2(L)2](PF6)2 Complexes
Authors: Velders Aldrik H. , Quiroga Adoracion Gomez , Haasnoot Jaap G. , Reedijk Jan
Published: February 2003

The synthesis and characterization of the cis bifunctional coordinated ruthenium(II) complexes β‐[Ru(azpy)2(MeIm)2](PF6)2 (β‐MeIm) and β‐[Ru(azpy)2(MeBim)2](PF6)2 (β‐MeBim) (azpy = 2‐phenylazopyridine, MeIm = 1‐methylimidazole and MeBim = 1‐methylbenzimidazole) is reported. In β‐MeIm the two MeIm ligands can both freely rotate around the Ru−N axes on the NMR timescale. In β‐MeBim the two MeBim ligands appear restricted in their rotation around the Ru−N axes, which becomes slow on the NMR timescale at low temperatures. In contrast to the analogous complexes α‐[Ru(azpy)2(MeBim)2](PF6)2 and cis‐[Ru(bpy)2(MeBim)2](PF6)2, only one atropisomer is observed for the two MeBim ligands in β‐MeBim. The orientation of the MeBim ligands appears to correspond to an HT isomer which is similar to the orientation of the MeBim ligands in the most abundant atropisomer found in the related α‐[Ru(azpy)2(MeBim)2](PF6)2. A stacking interaction between the phenyl ring of one azpy and one MeBim ligand is likely to stabilize the observed atropisomer of β‐MeBim, and is such that the rotation of the phenyl ring of one of the two azpy ligands is restricted. At very low temperatures this rotation, or flipping of the phenyl ring between two identical positions, is in the slow‐exchange range on the NMR timescale. (© Wiley‐VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)
New Molecular Charge‐Transfer Salts of TM‐TTF and BMDT‐TTF with Thiocyanate and Selenocyanate Complex Anions [TMTTF = Tetramethyltetrathiafulvalene; BMDT‐TTF = Bis(methylenedithio)tetrathiafulvalene]
Authors: Mas‐Torrent Marta , Turner Scott S. , Wurst Klaus , Vidal‐Gancedo José , Veciana Jaume , Day Peter , Rovira Concepció
Published: February 2003

Three new charge‐transfer salts of tetrathiafulvalene (TTF)‐based donors with thiocyanato‐ or selenocyanato‐metal complex anions have been synthesised. The salts isolated were [BMDT‐TTF]4[Cr(NCS)6] (1), [TM‐TTF]4[Cr(NCS)6]·2CH3CN (2) and [TM‐TTF]4[Cr(NCSe)6]·2CH3CN (3) [BMDT‐TTF = bis(methylenedithio)tetrathiafulvalene and TM‐TTF = tetramethyltetrathiafulvalene]. Single crystals of compound 1 crystallise in the monoclinic C2/c space group with a = 37.286(3), b = 10.0539(6), c = 21.069(2) Å, β = 124.348(4)°, V = 6520.9(9) Å3 and Z = 4. Compound 3 was also suitable for an X‐ray diffraction study, however the anionic part, [Cr(NCSe)6]− was highly disordered and the best solution gave a final R factor of 16.4%. A solution was found for the monoclinic space group C2/m with a = 13.787(3), b = 19.507(3), c = 14.735(5) Å, β = 102.90(3)°, V = 3862.9(17) Å3 and Z = 2. For compound 1 there are several S···S close atomic contacts between the donors and acceptors, but there is no discernible magnetic exchange between ions. Such an interaction was previously observed in related salts such as [TTF][Cr(NCS)4(phenanthroline)2] and [donor][M(NCS)4(isoquinoline)2] [M = Cr, Fe and donor = TTF, BEDT‐TTF or TM‐TTF (tetramethyltetrathiafulvalene)]. Compounds 1 to 3 are all paramagnetic semiconductors in which the magnetic susceptibility is dominated by the Cr‐containing anions. The structure‐function relationship, along with a comparison with related compounds, indicates that there is no long‐range magnetic order because there are no π‐stacking interactions between donor and acceptor; these types of interactions are seen in all of the bulk magnets of this type in which the donor spin is magnetically coupled to the anion. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Syntheses and Structures of Layered Copper(II) Diphosphonates with Mixed Ligands
Authors: Yin Ping , Peng Yang , Zheng Li‐Min , Gao Song , Xin Xin‐Quan
Published: February 2003

This paper describes the syntheses and crystal structures of two new copper(II) diphosphonates with mixed ligands: [Cu3(hedpH)2(4,4′‐bipy)(H2O)2]·2H2O (1) and [Cu3(hedpH)2(4,4′‐azpy)(H2O)2]·1.6H2O (2) (hedp = 1‐hydroxyethylidenediphosphonate, 4,4′‐bipy = 4,4′‐bipyridine, 4,4′‐azpy = 4,4′‐azobispyridine). Both adopt a two‐dimensional layer structure containing neutral ladder‐like chains of {Cu3(hedpH)2(H2O)2}n linked by 4,4′‐bipy or 4,4′‐azpy ligands. The adjacent layers are held together by strong hydrogen bonds, thus generating a three‐dimensional network with rectangular shaped channels. The lattice water is found in these channels. The magnetic properties of compounds 1 and 2 have also been investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis, Crystal Structures and Magnetism of a Series of Heptanuclear Rare‐Earth‐Centered Trigonal Prism Clusters
Authors: Liu Qin‐De , Li Jun‐Ran , Gao Song , Ma Bao‐Qing , Kou Hui‐Zhong , Ouyang Liang , Huang Rui‐Li , Zhang Xi‐Xiang , Yu Kai‐Bei
Published: February 2003

A series of heptanuclear rare‐earth‐centered trigonal prism clusters [LnCu6(μ‐OH)3(HL)2(L)4]·(ClO4)2·25H2O (Ln = La−Ho and Y; H2L = iminodiacetic acid) was synthesized and their crystal structures were determined by X‐ray diffraction. The rare‐earth center and the copper ions are bridged by three μ3‐OH and six μ2‐O moieties from the carboxyl groups of six different ligands. The rare earth ion is nine‐coordinate and the coordination polyhedron is an unusual, highly symmetrical tricapped trigonal prism (C3h). The cluster has an interesting, highly symmetrical eclipsed structure (C3h) which utilizes the central rare earth cation as a template. The temperature‐dependence of the magnetic susceptibility of the cluster series was investigated and was found to vary with the central rare‐earth ions. The magnitude of the antiferromagnetic interaction constants J between Cu2+ ions in [LaCu6] and [YCu6] were compared and estimated to be −24 cm−1 and −7 cm−1, respectively, indicating a significant effect of the central diamagnetic ions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Spectroscopic and Structural Characterizations of Novel Water‐Soluble Peroxo[polyaminocarboxylato bis(N‐oxido)]niobate(V) Complexes
Authors: Bayot Daisy , Tinant Bernard , Mathieu Benoît , Declercq Jean‐Paul , Devillers Michel
Published: February 2003

New water‐soluble peroxo complexes of niobium(V) with polyaminocarboxylic acids (PAC) have been prepared and characterized by IR and NMR (1H, 13C, 15N) spectroscopy, as well as by thermal analysis. The synthesis in presence of excess H2O2 leads to the oxidation of the nitrogen atoms of the PAC ligand into N‐oxide groups. The compounds obtained correspond to the general formula (AI)3[Nb(O2)2(LO2)]·xH2O·yH2O2 [AI = NH4+ or CN3H6+ (gu) and L = edta, pdta] in which H4LO2 refers to the bis(N‐oxide) derivative of the PAC ligand. The crystal structures of the guanidinium derivatives of the (edta)‐ and (pdta)Nb complexes have been determined, both showing an eight‐coordinate Nb atom with two bidentate peroxo ligands and a quadridentate PAC bis(N‐oxido) ligand, resulting in a distorted dodecahedral geometry. The structure of the guanidinium derivative of the edta bis(N‐oxido) ligand is also described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Pyridine‐ and 3‐/6‐Methylpyridine‐2‐tellurolate Complexes of Palladium(II) and Platinum(II)
Authors: Dey Sandip , Jain Vimal K. , Singh Jaspreet , Trehan Veena , Bhasin Kuldip K. , Varghese Babu
Published: February 2003

The reaction of py2Te2 or (3‐MeC5H3N)2Te2 with Na2PdCl4 in methanol yields an insoluble brown complex, [PdCl(TeNC5H3R)]n (R = H or Me). Several reactions of pyTe−, (3‐MeC5H3N)Te−, or (6‐MeC5H3N)Te− with various palladium(II) and platinum(II) complexes have been carried out. Complexes of the types [MCl(Te−N)(PR3)], [Pt(Te−N)2(dppe)], [Pt(Te−N)2(PPh3)2], and [Pt2(μ‐Te−N)2(dppe)2][BPh4]2 [M = Pd or Pt; Te−N = pyTe, (3‐ or 6‐MeC5H3N)Te] have been prepared and characterized by elemental analyses, UV/Vis, IR, and NMR (1H, 31P, 195Pt) spectroscopy. The complexes [MCl(Te−N)(PR3)] show irreversible oxidation and reduction by CV in DMF. The molecular structure of [PdCl{Te(3‐MeC5H3N)}(PPh3)] (2c) has been established by single‐crystal X‐ray diffraction analysis. The palladium atom is bound to the chelating 3‐methylpyridinetellurolate ligand, a chlorine atom and a PPh3 ligand. The pyrolysis of [PdCl{Te(3‐MeC5H3N)}(PR3)] (PR3 = PEt3 or PPh3) at 340 °C yields PdTe. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Selective Synthesis of N‐Methylanilinooligosilanes
Authors: Böhme Uwe , Günther Betty , Rittmeister Ben
Published: February 2003

Defined crystalline amino‐substituted organosilanes were prepared by reaction of N‐methylaniline with 1,1,2,2‐tetrachloro‐1,2‐dimethyldisilane. It is possible to selectively prepare mono‐, di‐, and triaminodisilanes depending on the reactant ratio. The X‐ray structure analyses of 1,2‐dichloro‐1,2‐dimethyl‐1,2‐bis(N‐methylanilino)disilane (2), 1‐chloro‐1,2‐dimethyl‐1,2,2‐tris(N‐methylanilino)disilane (3), and 1,2‐dimethyl‐1,1,2,2‐tetrakis(N‐methylanilino)disilane (4) were performed. The absolute structure of 2 was determined by crystallographic methods. Compound 2 is a useful reagent for preparing a variety of other aminoorganodisilanes like [Me(PhMeN)2Si]2 (4), [FMe(PhMeN)Si]2 (12), [(PhCC)Me(PhMeN)Si]2 (13), [(p‐MeC6H4)Me(PhMeN)Si]2 (14), and [(PhCH2)Me(PhMeN)Si]2 (15). Other chloroorganooligosilanes also react with N‐methylaniline to give PhMeN[SiMe2]2Cl (5), PhMeN[SiMe2]2NMePh (6), Cl[SiMe2]3NMePh (7), PhMeN[SiMe2]3NMePh (8), Cl[SiMe2]4NMePh (9), MeClSi[Si(NMePh)ClMe]2 (10), and MeSi[Si(NMePh)ClMe]3 (11). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Synthesis, X‐ray Structure and Properties of a Trinuclear Mixed‐Valence CoIII‐CoII‐CoIII Complex with Carboxamido N and Sulfinato S Donors
Authors: Rat Mathieu , Sousa Rodolphe Alves de , Tomas Alain , Frapart Yves , Tuchagues Jean‐Pierre , Artaud Isabelle
Published: February 2003

Air oxidation of the six‐coordinate (Et4N)2[Co(N2S2)(CN)(CH3CN)] complex derived from N,N′‐(3‐mercapto‐3‐methylbutyryl)‐o‐phenylenediamine results in the formation of the trinuclear mixed‐valence complex (Et4N)4{CoII[CoIII{N2(SO2)2}(CN)(OH)]2} (3) where the thiolates have been oxidized to sulfinates. Its X‐ray structure reveals a linear arrangement of cobalt ions with bridging hydroxides and sulfinates. All cobalt ions are in a distorted octahedral environment. The mixed‐valence nature of this complex has been demonstrated by temperature‐dependent magnetic susceptibility measurements and by EPR spectroscopy both in the solid state and in solution. These data are in agreement with a high‐spin CoII. The IR spectrum shows the typical vibrations of cyanide and sulfinate at 2130 cm−1 (νCN), 1175 (νas/SO2) and 1030 cm−1 (νs/SO2). Trapping of CoII by chelex chromatography after treatment with aqueous HCl, or ” in situ” in aqueous solution, yields six‐coordinate low‐spin complexes with two different axial ligands Na3[Co{N2(SO2)2}(CN)(Cl)] (5a) and (Et4N)2[Co{N2(SO2)2}(CN)(H2O)] (5b). The pKa of the bound water molecule was estimated as 10.1 by pH‐metric titration. While 3 and 5a were inactive toward acetonitrile hydration, 5b catalyzes acetamide formation at 50 °C and pH 4.7 and 7 with low efficiency. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Influence of Functional Group Orientation on the Structure of Zinc 1,1,4‐Trimethylthiosemicarbazide Dicarboxylates: Probing the Limits of Crystal Engineering Strategies
Authors: Burrows Andrew D. , Harrington Ross W. , Mahon Mary F. , Teat Simon J.
Published: February 2003

The reaction of [Zn(tmtsc)2](NO3)2 [tmtsc = 1,1,4‐trimethylthiosemicarbazide, MeNHC(S)NHNMe2] with a range of sodium dicarboxylates has been shown to lie on the borderline between commonly used crystal engineering strategies. The products exhibit a wide range of structural diversity with the main driving force being the relative orientation of the carboxylate groups. Thus, fumarate leads to the hydrogen‐bonded aggregate [Zn(tmtsc)2(OH2)][fumarate] (2) in which cations and anions are linked by hydrogen bond donor‐donor acceptor‐acceptor (DD:AA) interactions, whereas isophthalate and (+)‐camphorate lead to coordination polymers [Zn(tmtsc)(μ‐isophthalate)] (3a) and [Zn(tmtsc)(μ‐camphorate)] (4) with the metal centres linked by bridging dicarboxylate ligands. In the case of isophthalate, a hydrated product [Zn(tmtsc)(μ‐isophthalate)]·H2O (3b) was also characterised, although microanalysis and powder X‐ray diffraction revealed this to be a minor product. Incorporation of water was shown to lead to a change in carboxylate coordination mode from η1 in 3a to η2 in 3b. Use of terephthalate leads to the compound [{Zn(tmtsc)(OH2)}2(μ‐terephthalate)][terephthalate]·2H2O (5), in which half of the terephthalates bridge metal centres, to form dimers, and the remainder link the dimeric cations through DD:AA hydrogen bond interactions. Homophthalate leads to discrete dimers [Zn(tmtsc)(μ‐homophthalate)]2 (6), whereas acetylenedicarboxylate yields the unexpected compound [Zn(tmtsc)2(OH2)][O2CCH=CC(O)N(Me)C(=NNMe2)S]2·H2O (7) in which the dicarboxylate has reacted with tmtsc to give a 2‐hydrazono‐4‐oxo‐1,3‐thiazolidineacetate, which is subsequently trapped in the solid state by DD:AA hydrogen bonding interactions with [Zn(tmtsc)2(OH2)]2+. All products were characterised by single crystal X‐ray crystallography, and the representational nature of these crystal structures to the bulk materials was confirmed by microanalysis and powder diffraction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Consequences of forest fires on the hydrogeological response of mountain catchments: a case study of the Riale Buffaga, Ticino, Switzerland
Authors: Conedera Marco , Peter Larissa , Marxer Peter , Forster Felix , Rickenmann Dieter , Re Lorenza
Published: February 2003

The debris flow of 28 August 1997 which occurred in the Riale Buffaga, a torrent channel in the territory of the village of Ronco s./Ascona (Ticino, Switzerland), has been simulated with a good degree of reliability due to the existence of morphologic surveys of the torrent channel preceding the flood event and the presence of a rain gauge that registered the rainfall event at a resolution of 10 minutes. With these data it is possible to conduct a quantitative analysis of the effect of a forest fire on the hydrogeological response of a given catchment. In the case at hand, a 10‐year rainfall event caused a 100‐ to 200‐year flood event. This result clearly quantifies the possible consequences of a forest fire in terms of territorial safety. Copyright © 2003 John Wiley & Sons, Ltd.
Modelling the effect of vegetation on channel pattern in bedload rivers
Authors: Murray A. Brad , Paola Chris
Published: February 2003

We modify a simple numerical stream‐pattern model to examine the effect of sediment stabilization by roots on the channel pattern of bedload rivers. In the model, vegetation enhances bank resistance to erosion, causing the development of a single channel instead of a rapidly changing, multiple channel (braided) pattern. Net aggradation resulting from a high sediment supply, however, causes frequent avulsions that destroy vegetation locally, leading to the development of a multiple‐channel pattern. A stability diagram representing multiple model runs predicts whether a river will exhibit single or multiple channels, based on plant‐enhanced bank strength, and on the time scale of plant development relative to a time scale for change in unvegetated channels. A second stability diagram predicts the way in which the amplitude and period of a fluctuating imposed sediment load influence whether a single or multiple‐channel pattern develops. Copyright © 2003 John Wiley & Sons, Ltd.
Deforestation of water‐repellent soils in Galicia (NW Spain): effects on surface runoff and erosion under simulated rainfall
Authors: Benito E. , Santiago J.L. , de Blas E. , Varela M.E.
Published: February 2003

At three adjacent sites in steeply sloping woodland in Galicia (NW Spain), surface runoff and associated erosion under simulated rainfall (64 mm h−1) were measured on five occasions between June 1998 and July 1999. Two of the three sites had recently been deforested and topsoil added, and one of these two had been sown with grass, which was germinating at the onset of the study. Deforestation greatly increased runoff and erosion rates, and the recovery of plant cover reduced erosion. All three soils were very hydrophobic due to high levels of poorly humified organic matter, which led to higher runoff rates than expected, especially during dry periods. However, great structural stability prevented there being a significant correlation between runoff rate and soil erosion. Copyright © 2003 John Wiley & Sons, Ltd.
The influence of bedrock‐derived acidity in the development of surface and underground karst: evidence from the Precambrian carbonates of semi‐arid northeastern Brazil
Authors: Auler Augusto S. , Smart Peter L.
Published: February 2003

Very extensive cave systems are developed in Precambrian Una Group carbonates in the Campo Formoso area, eastern Brazil. In contrast, the area is largely devoid of significant surface karst landforms, as would be expected given its semi‐arid climate. The caves in the area display many morphological features characteristic of deep‐seated hypogenic caves, such as lack of relationship with the surface, ramiform/network pattern, abrupt variations of passage cross‐sections and absence of fluvial sediments, but do not show evidence of vertical passages marking the ascending path of acidic water nor present extensive gypsum or acid clay mineral deposits. Hydrochemical analyses of present‐day ground water indicate that oxidation of bedrock sulphide is an active process, and sulphuric acid may be the main agent driving carbonate dissolution in the area. A shallow mode of speleogenesis is thus proposed, in which sulphuric acid produced through the oxidation of sulphide beds within the carbonates controls cave initiation and development. Moreover, the geological situation of the area in an ancient stable passive margin precludes the possibility of deep‐seated sources of acidity.

Under dry climate, due to the absence of recharge, solutional landforms will be largely subdued in the surface. Hypogenic processes, if present, are likely to predominate, producing a landscape characterized by a marked disparity in the comparative degree of development between surface and underground landforms. Rates of karst landform development have traditionally been analysed through a climatic perspective, runoff being the main controlling factor in promoting karst development. This view needs to be reassessed in the light of the growing awareness of the importance of climate‐independent processes related to hypogenic sources of acidity. Copyright © 2003 John Wiley & Sons, Ltd.