bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal Structure and Excited Optical Nonlinearity of a 1D Polymeric [W2O2S6Cu4(NCMe)4]n Cluster
Authors: Zheng Hegen , Zhou Jianliang , Lappert Michael F. , Song Yinglin , Li Yizhi , Xin Xinquan 
Published: May 2004

AbstractThe self‐assembly reaction of (NH4)2(WOS3) with CuBr in the presence of PCy3 (PCy3 = tricyclohexylphosphane) in MeCN gives rise to a novel 1D polymeric compound [W2O2S6Cu4(NCMe)4]n (1) with solvent MeCN coordinated to the copper atom. This situation is unprecedented in the W(Mo)/Cu/S system. The excited state absorption and refraction of 1 in CH3CN solution were studied by using the Z‐scan technique with laser pulses of 40 ps pulse‐width at a wavelength of 532 nm. The compound possesses an optical self‐focusing performance. The positive nonlinear refraction is attributed to population transitions between singlet states. Compound 1 displays a strong excited‐state absorption, which induces an asymmetry between the peak and valley. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Crystal Structure and Properties of Ba11FeTi27O66.5
Authors: Vanderah Terrell A. , Siegrist Theo , Roth Robert S. , Ramirez Arthur P. , Geyer Richard G. 
Published: May 2004

AbstractThe crystal structure of Ba11FeTi27O66.5 was determined using single‐crystal and powder X‐ray diffraction methods. This phase crystallizes in the monoclinic space group C2/m (No. 12) (a = 23.324(1) Å, b = 11.388(1) Å, c = 9.8499(3) Å, β = 90.104(3)°; Z = 2; ρcalcd. = 4.98 g/cm3), and exhibits a 10‐layer structure built from close‐packed [O,(Ba,O)] layers with a stacking sequence (cchhc)2. Octahedral sites are occupied by a mixture of Fe3+ and Ti4+, with some preferential ordering suggested by analysis of bond valence sums. The structure features vertex‐, edge‐, and face‐sharing of the [Ti(Fe)O6] octahedra. Indexed X‐ray powder diffraction data for a polycrystalline specimen are given. Ba11FeTi27O66.5 and the 8‐layer phase Ba4Fe2Ti10O27 are built from the same types of polyhedral layers, some of which feature vacant sites between two Ba ions, which substitute for three oxygens in a row. The single‐crystal results suggest that the basic structural formula of the phase is A11B28O66+x, with the value of x (and hence the Fe/Ti ratio) determined by partial occupancy of one of these vacant sites. Variation of this occupancy factor with synthesis temperature may account for apparent slight differences in the stoichiometry of this phase in polycrystalline and single‐crystal form. However, solid solution formation was not observed for polycrystalline specimens. A comparison of the crystal structure obtained for Ba11FeTi27O66.5 with that previously proposed for “Zr4+‐stabilized Ba2Ti5O12” indicates that the phase “Ba2Ti5O12” is actually a ternary compound which forms upon addition (either deliberately or inadvertently) of a trivalent ion such as Fe3+ or Al3+. The specimens Ba11Al2Ti26O66, Ba11Al2Ti24Sn2O66, and Ba11Al2Ti24Zr2O66 were also prepared and were found to form the A11B28O66+x‐type phase. Ba11FeTi27O66.5 exhibits paramagnetic behavior that deviates somewhat from the Curie−Weiss Law below 75 K. Application of this formalism to the 1/χ vs. T data above 75 K yields an effective moment consistent with the presence of high‐spin Fe3+ (S = 5/2), and a negative Weiss constant (about −25 K) indicating weak cooperative magnetic interactions that are overall antiferromagnetic. The relative permittivity and dielectric loss tangent of a sintered polycrystalline disk were measured at 5.33 GHz, yielding values (corrected for theoretical density) of 55 and 7.7(±0.3) × 10−4, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Film Polymerization − A New Route to the Synthesis of Insoluble Polyimides Containing Functional Nickel(II) Schiff Base Units in the Main Chain
Authors: Di Bella Santo , Consiglio Giuseppe , Leonardi Nicoletta , Failla Salvatore , Finocchiaro Paolo , Fragalà Ignazio 
Published: May 2004

AbstractThe synthesis and characterization of a new, amino‐derivatized functional bis(salicylaldiminato)NiII complex is reported. It is a useful and reactive precursor in the synthesis of polyimide thermosets. Thus, the first synthesis of a polyimide containing a nonlinear optical NiII Schiff base complex in the main chain is achieved by thermally controlled film polymerization. Polymerization was monitored on silicon substrates by FT‐IR spectroscopy. The polymer film possesses characteristics analogous to those of the insoluble polymer obtained by polymerization in solution, as evidenced by FT‐IR spectroscopy and TGA analysis. The present approach might represent a general strategy for achieving thin films of insoluble, functional polymers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Palladacyclopentadiene Complexes with Mono‐ and Didentate Imidato Ligands: Synthesis, Hemilabile Behaviour and Catalytic Application in the Stille Reaction
Authors: Serrano José Luis , Fairlamb Ian J. S. , Sánchez Gregorio , García Luis , Pérez José , Vives Jorge , López Gregorio , Crawforth Catherine M. , Taylor Richard J. K. 
Published: May 2004

AbstractThe binuclear hydroxo complex [NBu4]2[Pd2{C4(COOMe)4}2(μ‐OH)2] (1) has been prepared by addition of two equivalents of NBu4OH to polymeric [Pd{C4(COOMe)4}]n. Complex 1 has been successfully employed as a precursor to three novel binuclear imidate‐bridged complexes [NBu4]2[Pd2{C4(COOMe)4}2(μ‐imidate)2] [imidate = succinimidate (suc) 2, phthalimidate (pht) 3 or maleimidate (mal) 4] in which the imidate group displays a bidentate N,O‐coordination mode. The hemilabile behaviour of the imidate ligands has been investigated by reaction with a variety of P, N and S ligands, affording the corresponding mononuclear derivatives [NBu4][Pd{C4(COOMe)4}(imidate)L] [L = PPh3 (2a, 3a or 4a), P(p‐C6H4F)3 (2b, 3b or 4b), PBu3 (2c, 3c or 4c), py (2d, 3d or 4d), p‐MeC6H4NH2 (2e, 3e or 4e), tetrahydrothiophene (2f, 3f or 4f)] with terminal N‐bonded imidate ligands. The characterization of the new complexes involved spectroscopic methods (IR, FAB, 1H, 13C, 19F and 31P NMR) and X‐ray crystallographic analysis for 1, 4b and 4e. The mononuclear derivatives are shown to catalyse the Stille cross‐coupling of benzyl bromide 7 with ethyl Z‐vinylstannyl carboxylate (8) in high yields. Yields and reaction times are dependent on the presence and type of imidate ligand, which suggests an important role for it in the catalytic cycle. (© Wiley‐VCH Verlag GmbH and Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis and Characterisation of the First Three‐Dimensional Mixed‐Metal‐Center Inorganic‐Organic Hybrid Framework with N‐(Phosphonomethyl)iminodiacetate
Authors: Almeida Paz Filipe A. , Shi Fa‐Nian , Klinowski Jacek , Rocha João , Trindade Tito 
Published: May 2004

AbstractUsing crystal engineering concepts, the first three‐dimensional (3D) mixed‐metal‐centre inorganic‐organic hybrid frameworks incorporating N‐(phosphonomethyl)iminodiacetate (pmida4−) were synthesised under mild hydrothermal conditions (100 °C) and characterised structurally. The crystal structures, obtained by the displacement of the coordinated water molecules in [Co2V2O2(pmida)2(H2O)10]·2(H2O) (1) [P21/c monoclinic space group, Z = 2, a = 9.996(2) Å, b = 14.854(3) Å, c = 10.781(2) Å, β = 110.90(3)° and V = 1495.5(5) Å3] by the rod‐like bridging 4,4′‐bipyridine (4,4′‐bpy) ligand — [CdVO(pmida)(4,4′‐bpy)(H2O)2]·(4,4′‐bpy)0.5·H2O (2) and [CoVO(pmida)(4,4′‐bpy)(H2O)2]·(4,4′‐bpy)0.5 (3) — are isostructural and were also determined in the P21/c monoclinic space group (Z = 4) by single‐crystal X‐ray diffraction studies at low temperature (180 K): for 2, a = 9.1267(18) Å, b = 17.610(4) Å, c = 15.361(3) Å, β = 93.06(3)° and V = 2465.3(9) Å3; for 3, a = 8.7734(18) Å, b = 17.264(4) Å, c = 15.507(3) Å, β = 93.94(3)° and V = 2343.2(8) Å3. All the crystal structures contain centrosymmetric dimeric [V2O2(pmida)2]4− units connected to neighbouring M2+ cations (Cd2+ for 2, and Co2+ for 1 and 3) through the phosphonate group. In 2 and 3, extended two‐dimensional [MVO(pmida)(H2O)2]n layers are formed, with the 4,4′‐bpy molecules acting as pillars between adjacent layers, leading to porous 3D supramolecular structures, [MVO(pmida)(4,4′‐bpy)(H2O)2]∞, with a topology resembling that of the NbO net. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Coordination Chemistry of 1,3‐Bis(2‐pyridylimino)‐ and 1,3‐Bis(2‐thiazolylimino)soindole Copper Complexes: Investigation of Their Catalytic Behavior in Oxidation Reactions
Authors: Meder Markus B. , Gade Lutz H. 
Published: May 2004

AbstractThe copper complexes [Cu(4‐MeBPI)(OAc)] (4), [Cu(4‐Me‐10‐tBuBPI)(OAc)] (5) and [Cu(BTI)(OAc)] (6) [BPI = 1,3‐bis(2‐pyridylimino)isoindole, BTI = 1,3‐bis(2‐thiazolylimino)isoindole] were prepared by reaction of the protio ligands with copper(II) acetate. Compounds 4 and 6 were characterized by X‐ray diffraction, establishing distorted square‐planar coordination geometries of the copper ions. Two monoclinic modifications of 6 (6a and 6b) were found, both crystallizing in the space group P21/c, but possessing different cell parameters. In contrast to 6a, which is monomeric in the crystal, the second monoclinic modification 6b has a more complicated crystal structure, which is composed of both monomeric complex units such as those found in 6a and infinite chains of coordination polymers. The copper atoms in the polymeric chains of 6b display fivefold coordination and a ligand polyhedron that is an intermediate form between a trigonal‐bipyramidal and a square‐pyramidal geometry. The allylic peroxylation of cyclohexene with tBuOOH (70% aqueous solution) catalyzed by 4 and 6 (0.17 mol %) gave tert‐butylperoxy‐3‐cyclohexene with selectivities of 86% and 80% (based on cyclohexene) and turnover frequencies of 63 h−1 and 18 h−1, respectively. The peroxylation reaction is thought to proceed according to a Haber−Weiss radical chain mechanism. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Synthesis of a Novel Organoiridium(I) Fluoro Complex
Authors: Gorol Michael , Mösch‐Zanetti Nadia C. , Roesky Herbert W. , Noltemeyer Mathias , Schmidt Hans‐Georg 
Published: May 2004

AbstractCyclooctadienefluorotriphenylphosphaneiridium(I) [IrF(C8H12)(PPh3)] (3) was prepared and its structure determined by single crystal X‐ray diffraction analysis. Complex 3 crystallises in the monoclinic space group P21/n. The lattice parameters are a = 931.9(3) pm, b = 1629.4(7) pm, c = 1592.9(7) pm, α = γ = 90°, β = 92.85(3)°. Number of molecules per unit cell is 4. The square planar iridium complex 3 exhibits an Ir−F bond length of 201.3(5) pm. 3 was obtained in Teflon tubes, whereas the use of glass vessels led to cyclooctadiene‐bis(triphenylphosphane)iridium(I)‐pentafluorosilicate(IV) ([Ir(C8H12)(PPh3)2][SiF5]) (4). The composition of 4 was confirmed by single crystal X‐ray diffraction analysis. 4 crystallises in the monoclinic space group P21/c. The lattice parameters are a = 1157.4(9) pm, b = 1864.4(9) pm, c = 1922.5(17) pm, α = γ = 90°, β = 96.16(7)°. The number of molecules per unit cell is 4. The square‐planar coordinated iridium cation [Ir(C8H12)(PPh3)2]+ is separated from the trigonal bipyramidal [SiF5]− anion by 461.1 pm (shortest Ir···F distance) and thus it is assumed that no interactions occur between the fluorine and iridium atoms. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Zinc Guanidinate Complexes and Their Application in Ring‐Opening Polymerisation Catalysis
Authors: Coles Martyn P. , Hitchcock Peter B. 
Published: May 2004

AbstractThe insertion reaction between 1 equiv. of carbodiimide, R′N=C=NR′, and the zinc bis(amide) [Zn{N(SiMe3)2}2] affords the homoleptic zinc(II) guanidinate compounds [Zn{(Me3Si)2NC(NR′)2}2] (3, R′ = iPr; 4, R′ = Cy) in preference to the monosubstituted compounds. Compound 3 also results from the protonation reaction of 1 equiv. of the neutral guanidine (Me3Si)2NC(NiPr)(NHiPr) (2) with [Zn{N(SiMe3)2}2] or ZnMe2. In contrast, the N‐dimethylguanidine analogue Me2NC(NiPr)(NHiPr) (1) reacts cleanly with 1 equiv. of ZnMe2 to afford the dimeric species [Zn{Me2NC(NiPr)2}Me]2 (5). Attempted protonation of the Zn−C bond in 5 with 2,6‐di‐tert‐butylphenol resulted in preferential reaction at the Zn−N bond and formation of the mixed (aryloxo)methyl complex [Zn(OAr)Me·{Me2NC(NiPr)(NHiPr)}] (6), isolated as the guanidine adduct. Heating of 6, in an attempt to promote methane elimination, afforded a small amount of the dimetallic complex [{Zn(OAr)}2(μ‐{Me2NC(NiPr)2})(μ‐NMe2)] (7) as a result of the extrusion of NMe2− from the guanidine‐based ligand. The amine‐elimination reaction between [Zn{N(SiMe3)2}2] and 1 equiv. of 1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidine (hppH) proceeds smoothly to afford the mixed (guanidinate)(amide) complex [Zn(hpp){N(SiMe3)2}]2 (8), which forms a dimer in the solid state. Crystal structures of compounds 3−8 are reported and a preliminary study of the activity of 8 in the ring‐opening polymerisation of lactide is described. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004
Can the cyclo‐P5 Ligand Introduce Basicity at the Transition Metal Center in Metallocenes? A Hybrid Density Functional Study on the cyclo‐P5 Analogues of Metallocenes of Fe, Ru and Os
Authors: Padma Malar E. J. 
Published: May 2004

AbstractDensity functional theory (DFT) calculations and natural population analysis (NPA) performed on metallocenes of Fe, Ru and Os triad reveal that the cyclo‐P5 ligand introduces basicity at the metal center. All‐electron calculations at the B3LYP/6‐311+G* level yield NPA charges of 0.28, −0.28 and −0.91 at the iron center in [FeCp2], [FeCp(η5‐P5)] and [Fe(η5‐P5)2], respectively. The same trend in the charges is observed even when the core electrons of the metal are replaced by effective core potentials (ECPs). The accumulation of negative charge at the metal center is found to be similar in the cyclo‐P5 analogues of ruthenocene and osmocene. Thus, for example, the net NPA charges on Ru and Os in the decaphosphametallocenes are predicted to be −0.6 to −0.9, respectively, at different levels of calculations involving ECPs. The natural orbital populations show a small transfer of electron density from each phosphorus atom to the metal center, leading to a significant build‐up of negative charge on the metal in [M(η5‐P5)2]; this is a new feature observed in the transition metals bound to cyclo‐P5 ring. This finding is indeed supported by the indirect evidence observed by Scherer and co‐workers from the diamagnetic behavior in an iridium derivative of Fe(P5), that the Fe atom is negatively charged while one of the P atoms is positively charged. Natural bond orbital analysis reveals that the extent of covalent bond formation between the metal and the ligand is more pronounced for the cyclo‐P5 than the cyclopentadienyl ligand. While Cp retains 56−68% of aromaticity, the P5 ring exhibits 26−51% aromaticity as compared to the free anionic rings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Oxalato‐Bridged [CuIICrIII] and [MnIICrIII] Binuclear Complexes: Synthesis, Crystal Structures, Magnetic and EPR Investigations
Authors: Marinescu Gabriela , Visinescu Diana , Cucos Andrei , Andruh Marius , Journaux Yves , Kravtsov Victor , Simonov Yurii A. , Lipkowski Janusz 
Published: May 2004

AbstractTwo new heterobinuclear complexes, [(bipy)(C2O4)Cr(μ‐C2O4)Cu(Hfsaaep)(H2O)]·2H2O (1) and [(phen)(C2O4)Cr(μ‐C2O4)Mn(phen)2(N3)]·H2O (2) have been obtained by using bis(oxalato)chromium(III) anions, [Cr(AA)(C2O4)2]−, as building blocks [AA = 2,2′‐bipyridine (bipy); 1,10‐phenanthroline (phen)]. The crystal structures of the two complexes have been solved. These complexes comprise neutral oxalato‐bridged CrIII−CuII and CrIII−MnII units. The [Cr(AA)(C2O4)2]− anion acts as a bidentate ligand toward CuII in compound 1 and as a monodentate ligand toward MnII in compound 2. The copper(II) ion in 1 exhibits a slightly distorted square bipyramidal stereochemistry, with the aqua ligand and one of the bridging oxalato oxygen atoms disposed in the apical positions [Cu(1)−O(1w) = 2.360(3) Å and Cu(1)−O(4) = 2.504(2) Å]. The second bridging oxalato oxygen atom [Cu(1)−O(2) = 2.0747(18) Å] and the N,N,O‐type Hfsaaep ligand are located in the basal plane. The distance between the CrIII and CuII ions across the bridging oxalate unit is 5.506 Å. The MnII ion in compound 2 is hexacoordinate (two chelating phen ligands, one oxalato bridging oxygen, and one terminal azido group). The intermolecular CrIII···MnII distance is 5.257 Å. The magnetic properties of the two complexes have been investigated. The magnetic coupling between CrIII and CuII in 1 was found to be ferromagnetic (J = +1.4 cm−1). The nature of the ground state (S = 2) has been further confirmed by plotting the magnetization‐versus‐field curve. An antiferromagnetic interaction was found between CrIII and MnII in compound 2 (J = −1.9 cm−1). The magnetization‐versus‐field curve indicates the occurrence of a crossover between the Zeeman components: MS = −1 (ground state S = 1), MS = −2, from the first excited state (S = 2), and MS = −3, from the second excited state. The EPR spectra of the two compounds are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Reaction Chemistry of 1,4‐Dilithio‐1,3‐diene and 1‐Lithio‐1,3‐diene Derivatives
Authors: Xi Zhenfeng 
Published: May 2004

AbstractThe organolithium compounds, 1,4‐dilithio‐1,3‐diene and 1‐lithio‐1,3‐diene derivatives, show unprecedented reaction patterns with organic substrates. The 1,4‐dilithio‐1,3‐dienes react with aldehydes or ketones via deoxygenation of the C=O moieties to afford cyclopentadiene derivatives; pyridine derivatives are obtained in excellent yields when these organolithium reagents are treated with nitriles. In addition to novel reaction patterns, the experimental results have demonstrated that both the mono‐ and the dilithio reagents are synthetically useful building blocks. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Come together: longitudinal comparisons of Pettigrew's reformulated intergroup contact model and the common ingroup identity model in Anglo‐French and Mexican‐American contexts
Authors: Eller Anja , Abrams Dominic 
Published: May 2004

AbstractBoth Anglo‐French and Mexican‐American relations are embedded in histories of conflict. Within these intergroup contexts, two longitudinal field studies of contact tested Pettigrew's (1998) reformulated model of the intergroup contact theory and Gaertner and Dovidio's (2000) Common Ingroup Identity Model (CIIM). In Pettigrew's model, intergroup friendship is accorded a special role and the contact‐bias relation is mediated by changing behaviour, ingroup reappraisal, generating affective ties, and learning about the outgroup. Pettigrew's integration of the three central models of contact generalization into a time‐sequence holds that contact first elicits decategorization, then salient categorization, and finally recategorization. In the CIIM, these three levels of categorization—plus a fourth, dual identity—are conceptualized to be mediators in the contact‐bias relation. Results point to the crucial importance of intergroup friendship and underline the mediating roles of learning about the outgroup, behaviour modification, and generating affective ties, but not ingroup reappraisal in Pettigrew's model. As for the CIIM, in Study 1 interpersonal and intergroup levels were most central, while in Study 2 the dual identity and superordinate group levels were most effective. The implications of the findings are discussed with reference to the likely stability of these effects in different intergroup contexts. Copyright © 2004 John Wiley & Sons, Ltd.
The ‘why’ and ‘why not’ of job search behaviour: their relation to searching, unemployment experience, and well‐being
Authors: Vansteenkiste Maarten , Lens Willy , De Witte Siegfried , De Witte Hans , Deci Edward L. 
Published: May 2004

AbstractTwo studies (n = 273 and 254) used self‐determination theory (SDT) to examine unemployed people's motivation both to search and not to search for a job. The self‐regulation questionnaire format (Ryan & Connell, 1989) was used to assess participants' autonomous and controlled job‐search motivation (the ‘why’ of job search) as well as their amotivation for searching. Additionally, both autonomous and controlled motivation for not searching (the ‘why not’ of job search) was assessed. Results provide validity for these five motivational constructs and indicate, in line with SDT, that the constructs predicted reports of search behaviour, affective experiences, and well‐being. The addition of autonomous and controlled motivation for not searching contributed additional predictive power beyond the motivational constructs that focused only on searching. Copyright © 2004 John Wiley & Sons, Ltd.
Characterization and Assessment of the Microjet Electrode as a Detector for HPLC
Authors: Cannan Susan , Unwin Patrick R. 
Published: May 2004

AbstractThe microjet electrode (MJE) is characterized as a detector for high performance liquid chromatography (HPLC). Voltammetric measurements of the oxidation of hydroquinone (HQ) allow mass transport to be determined for the MJE detector configuration, and the factors controlling the conversion efficiency of the device to be well understood. The current‐time response to the flow injection analysis of volumes of solution in the 10–80 μL range has been established, and the limit of detection of this method has been determined. The latter was found to approach that of UV absorbance measurements, which is particularly encouraging, given that HQ has a relatively strong chromophore (ε=2 290.8 cm−1 mol−1 L). This detection system is a robust and simple arrangement with the capability of analyzing large volumes of eluent at typical analytical HPLC flow rates.
The Modification of Screen‐Printed Carbon Electrodes with Amino Group and Its Application to Construct a H2O2 Biosensor
Authors: Gao Qiang , Yang Fan , Ma Ying , Yang Xiurong 
Published: May 2004

AbstractElectrooxidation of thionine on screen‐printed carbon electrode gives rise to the modification of the surface with amino groups for the covalent immobilization of enzymes such as horseradish peroxidase (HRP). The biosensor was constructed using multilayer enzymes which covalently immobilized onto the surface of amino groups modified screen‐printed carbon electrode using glutaraldehyde as a bifunctional reagent. The multilayer assemble of HRP has been characterized with the cyclic voltammetry and the faradaic impedance spectroscopy. The H2O2 biosensor exhibited a fast response (2 s) and low detection limit (0.5 μM).
A Markov regime switching approach for hedging stock indices
Authors: Alizadeh Amir , Nomikos Nikos 
Published: May 2004

AbstractIn this paper we describe a new approach for determining time‐varying minimum variance hedge ratio in stock index futures markets by using Markov Regime Switching (MRS) models. The rationale behind the use of these models stems from the fact that the dynamic relationship between spot and futures returns may be characterized by regime shifts, which, in turn, suggests that by allowing the hedge ratio to be dependent upon the “state of the market,” one may obtain more efficient hedge ratios and hence, superior hedging performance compared to other methods in the literature. The performance of the MRS hedge ratios is compared to that of alternative models such as GARCH, Error Correction and OLS in the FTSE 100 and S&P 500 markets. In and out‐of‐sample tests indicate that MRS hedge ratios outperform the other models in reducing portfolio risk in the FTSE 100 market. In the S&P 500 market the MRS model outperforms the other hedging strategies only within sample. Overall, the results indicate that by using MRS models market agents may be able to increase the performance of their hedges, measured in terms of variance reduction and increase in their utility. © 2004 Wiley Periodicals, Inc. Jrl Fut Mark 24:649–674, 2004