Terephthalate Complex Research Articles

Effect of solvent in the solvothermal synthesis of nickel(II)-terephthalate complex

This research aims to replace the use of dimethylformamide (DMF) with a greener solvent in the solvothermal synthesis of nickel(II)-terephthalate complex. Effect of solvent on the crystallinity degree, thermal stability, and band gap energy of the synthesized complex are also studied. The synthesis was carried out using solvothermal method at 150 0C for 10 hours with a Ni(II) : terephthalate acid mol ratio of 1:1 in several H2O:DMF solvent compositions (1:0; 1:1; and 0:1). The precipitated products underwent characterization using ATR-IR, P-XRD, SEM, TGA, Surface Area Analyzer, and UV-DRS. Findings revealed the successful formation of the Ni(II)-terephthalate complex using three different solvent compositions (H2O/DMF = 1:0, 1:1, and 0:1). This suggests that the complex can be synthesized using more environmentally friendly solvents, potentially reducing or substituting the use of DMF solvent. However, the solvent affects the characteristics of the synthesized complex, in which green block microcrystalline solid was obtained when using water as the solvent, meanwhile green aggregates with lower crystallinity degree was precipitated out when using DMF or H2O-DMF. The Ni(II)-terephthalate complexes obtained from the H2O and H2O-DMF solvents are different to that of from the DMF solvent, but they both has identical powder diffraction pattern with previously reported compound of [Ni3(OH)2(C8H4O4)2(H2O)4].2H2O. Furthermore, the use of water as the solvent increase the crystallinity degree and thermal stability of the complex but the band gap energy of the synthesized Ni(II)-terephthalate complex compared to that of obtained from the DMF solvents.

Cobalt Organic Framework Supported over Carbon-Based Materials as Novel Catalysts in the Hydrolysis of Sodium Borohydride

It is no secret that the global supplies of fossil fuel resources have been steadily dwindling. While there is no consensus on when the reserves will be completely depleted, there has been an effort among scientists to find a new, sustainable energy source for the future. It is generally agreed that such a source needs to not only be abundant, but also avoid the harmful biproducts of current fuel sources. Some proposed energy sources include solar, wind, geothermal and more. While each of these sources have their benefits, they also have their drawbacks and the cost to install and maintain these sources, as well as the environmental damage done during their construction can offset their benefits. One potential new energy source can be found in hydrogen gas. Hydrogen is not only the most abundant element in the universe, but its gaseous form can be burned to produce only energy and water [1-12]. The biggest hurdle a hydrogen economy faces is in the storage of the highly combustible gas. An interesting method of storing hydrogen is via adsorption within the chemical structure of a molecule. Sodium borohydride (NaBH4) for example is a chemical that contains 10.8% hydrogen by weight and steadily releases hydrogen gas when mixed with water.1 In order to efficiently utilize this reaction a catalyst is required. Typical catalysts are often precious metals like platinum, gold, and palladium, which tend to be expensive to use. By forming these metals into nanoparticles, their surface area can be increased, which increases their catalytic potential, however, these nanoparticles have a tendency to agglomerate in solution. Previous work by this team explored the catalytic capability of these metals and notes the use of carbon-based support structures can mitigate this agglomeration.2-4 This study aims to expand on those studies by using cobalt nanoparticles, which is a more cost-effective metal. Two novel Cobalt terephthalate complexes were combined with graphene and multiwalled carbon nanotubes (MWCNT) respectively, then tested for their ability to catalyze the hydrolysis of sodium borohydride. These materials were characterized using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Powdered X-ray diffraction (P-XRD), and Fourier Transform Infrared spectroscopy (FTIR). It was observed that after a single reaction, our materials appeared to be converted into cobalt borohydrides. The hydrogen produced for each material was 73 mL and 76 mL for the graphene and MWCNT materials, respectively. This study provides a possible method for producing cheaper, cleaner energy for a more sustainable future.

Supported Manganese Organic Framework as Catalyst for Hydrogen Evolution Reaction

The dependence on fossil fuels has caused significant harmful impact on the environment. The combustion of fossil fuels increases the harmful greenhouse gases including carbon dioxide and methane. The pollution not only worsens the impact of global warming but also affects human health. Many renewable energy sources have been discovered to replace fossil energy, but it is a challenge to find a cheap and effective energy source. Hydrogen arises as a potential candidate due to its high energy density and abundance. However, hydrogen was difficult to store. Hydrogen was often stored in liquid form at high pressure and extremely low temperature conditions. Another method of effectively storing hydrogen is by using hydrogen feedstock materials such as sodium borohydride. Sodium borohydride can be stored at room temperature and has a high gravimetric hydrogen capacity of 10% by weight. However, the process of extracting hydrogen from the materials was slow so it required catalysts. Many precious metal catalysts such as gold and silver catalyst have been applied to improve hydrogen generation reaction, but those metal catalysts were expensive to create. Additionally, those metal catalysts were often agglomerate and impossible to reuse. In this study, we used a non-precious metal complex supported over carbon-based materials to catalyze the hydrogen evolution reaction. We discovered a novel method of synthesizing manganese terephthalate complex at room temperature. The metals complex was coupled with graphene (G) and multiwalled carbon nanotubes (MWCNT) to increase its durability and efficiency. Each material was characterized by Powdered X-ray diffraction (P-XRD), Fourier Transform Infrared (FTIR) spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). During the reaction with sodium borohydride, we discovered that the manganese terephthalate complex converted to manganese boride and further improved the catalysis process. In the first trial, the reaction catalyzed by Mn complex coupled with MWCNT produced 25ml of hydrogen. At the fifth reuse trials, the amount of generated hydrogen (~44 ml) was nearly doubled. A similar phenomenon was observed in Mn complex coupled with graphene. This study introduces a novel method in synthesizing a stable, cheap and efficient catalyst for hydrogen evolution.

Synthesis of iron oxide nanocubes and their incorporation with luminescent lanthanide (Ln = Tb/ Eu)-Terephthalate complex in silica nanospheres using a reverse microemulsion method

Luminescent magnetic nanocomposites are of interest because of their promising applications in the biomedical field. This article reports the preparation of silica-coated lanthanide terephthalate complexes, Ln-TA (Ln = Tb and Eu) containing luminescent magnetic nanocomposites. Cubic-shaped iron oxide nanoparticles were synthesized through the thermal decomposition of the iron-oleate complex. Then, polymerization of tetraethyl ortho silicate in a water-in-oil reverse microemulsion in the presence of previously prepared iron oxide nanocubes and a terbium (Tb3+)/europium (Eu3+)-terephthalate (TA) complex was performed to obtain luminescent magnetic Fe3O4@Ln-TA (Ln = Tb, Eu)/SiO2 nanocomposites. The size (8.9 nm) and cubic shape of magnetic core were determined via transmission electron microscopy and the superparamagnetic behavior using a vibrating sample magnetometer. Energy dispersive X-ray analysis and inductively coupled plasma optical emission spectroscopy found that the luminescent Tb-TA and Eu-TA complexes were incorporated in the magnetic silica nanocomposites. The nanocomposites, Fe3O4@Ln-TA/SiO2, exhibited distinct luminescent green and red emission peaks and showed promise as a T1 contrast agent for magnetic resonance imaging.

Green synthesis and properties of nickel terephthalate complex with 2,2'-bipyridine

Green synthesis of nickel terephthalate complex with 2,2′-bipyridine involves the preparation of intermediate nickel terephthalate followed by complexation with 2,2′-bipyridine. The resulting substance was tested as an adsorbent for solidphase extraction of technogenic pollutants.

Exploring zinc terephthalate complexes through multinuclear ssNMR and in situ reaction monitoring by Raman spectroscopy

Exploring zinc terephthalate complexes through multinuclear ssNMR and <i>in situ</i> reaction monitoring by Raman spectroscopy

Electrocatalytic Properties of 3D Hierarchical Graphitic Carbon-Cobalt Nanoparticles for Urea Oxidation.

A 3D hierarchical graphitic carbon nanostructure encapsulating cobalt(0)/cobalt oxide nanoparticles (CoGC) has been prepared by solid-state pyrolysis of a mixture of anthracene and cobalt 2,2′-bipyridine terephthalate complex at 850 °C. Based on the Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods, the prepared material has high surface area (186.8 m2 g–1) with an average pore width of 205.5 Å. XPS reveals the functionalization of carbon with different oxygen-containing groups, such as carboxylic acid groups. The presence of metallic cobalt nanoparticles with cubic and hexagonal crystalline structures encapsulated in graphitized carbon is confirmed using XRD and TEM. Raman spectroscopy indicates a graphitization degree of ID/IG = 1.02. CoGC was cast onto a glassy carbon electrode and used for urea electrooxidation in an alkaline solution. The electrochemical investigation shows that the newly prepared CoGC has a promising electrocatalytic activity toward urea. The specific activity is 128 mA cm–1 mg–1 for the electrooxidation of 0.3 M urea in 1 M KOH at a relatively low onset potential (0.31 V vs Ag/AgCl). It can be mainly attributed to the morphological structure of carbon and the high reactivity of cobalt nanoparticles. The calculated charge-transfer resistance, Rct, of the modified electrode in the presence of urea (10.95 Ω) is significantly lower than that in the absence of urea (113.5 Ω), which indicates electrocatalytic activity. The value of charge-transfer rate constant, ks, for the anodic reaction is 0.0058 s–1. Electrocatalytic durability in 1000 s chronoamperometry of the modified electrode suggests high structure stability. The modified electrode retained about 60% of its activity after 100 cycles as indicated by linear sweep voltammetry.

Cobalt-carbon/silica nanocomposites prepared by pyrolysis of a cobalt 2,2'-bipyridine terephthalate complex for remediation of cationic dyes.

Recently, carbon nanostructures have attracted interest because of their unique properties and interesting applications. Here, CoC@SiO2-850 (3) and CoC@SiO2-600 (4) cobalt–carbon/silica nanocomposites were prepared by solid-state pyrolysis of anthracene with Co(tph)(2,2′-bipy)·4H2O (1) complex in the presence of silica at 850 and 600 °C, respectively, where 2,2′-bipy is 2,2′-bipyridine and tph is the terephthalate dianion. Moreover, Co(μ-tph)(2,2′-bipy) (2) was isolated and its X-ray structure indicated that cobalt(ii) has a distorted trigonal prismatic coordination geometry. 2 is a metal–organic framework consisting of one-dimensional zigzag chains within a porous grid network. 3 and 4 consist of cobalt(0)/cobalt oxide nanoparticles with a graphitic shell and carbon nanotubes embedded in the silica matrix. They were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS revealed that the nanocomposites are functionalized with oxygen-containing groups, such as carboxylic acid groups. In addition, the presence of metallic cobalt nanoparticles embedded in graphitized carbon was verified by XRD and TEM. The efficiency of 3 for adsorption of crystal violet (CV) dye was investigated by batch and column experiments. At 25 °C, the Langmuir adsorption capacity of 3 for CV was 214.2 mg g−1 and the fixed-bed column capacity was 36.3 mg g−1. The adsorption data were well fitted by the Freundlich isotherm and pseudo-second-order kinetic model. The adsorption process was spontaneous and endothermic.

Saudis claim success at investor conference

Saudi Arabian firms claimed success at the country’s controversial Future Investment Initiative, held last week in Riyadh. A few firms, including JPMorgan Chase and Bloomberg, boycotted the event to punish the Saudi government over its alleged responsibility in the death of journalist Jamal Khashoggi early this month in Turkey. National oil company Saudi Aramco says it signed 15 memoranda of understanding worth a total of $34 billion. However, many of the announced projects, such as a petrochemical complex with France’s Total and a gasification unit with Air Products & Chemicals, were already ongoing. Saudi chemical maker SABIC signed a deal with the German photovoltaics firm Schmid to build a $430 million silicon plant in Jubail, Saudi Arabia. SABIC also said it will spend nearly $1 billion to provide raw materials to a polyethylene terephthalate complex the Chinese firm Pan Asia PET is building in Jazan, Saudi Arabia. Saudi Aramco is

Generation of Hydrogen through the Hydrolysis of Feedstock Materials Via Ni(II) and Ni-MOF Catalysts

Within the last decade, the development of environmental and economically viable fuel cell technology has come in response to the push to decrease the use of fossil fuels. Current fuel cell technology has lacked in the fueling of the cell with a viable hydrogen source. Materials with a high hydrogen weight percent, such as sodium borohydride (NaBH4, 10.8% wt), provide a viable source in the presence of a metal catalyst. Metal organics frameworks (MOFs) have seen an exponential growth in interest for industrial applications such as catalysis, filtrations and storage.1 Their use as catalysts for the hydrolysis of hydrogen feedstock materials has the potential to improve current fuel cell technology by providing a metal catalyst with a high surface area. In this study, NiCl2• 6H2O was coordinated to the organic ligands of disodium terephthalate (C8H4Na2O4 (Na2BDC)) to synthesize the nickel terephthalate complex (Ni-MOF) in an aqueous media.3 The Ni-MOF was synthesized at room temperature (RT), with crystal formation occurring instantly, a highly desirable time frame for industrial applications.3 The catalytic efficiency of the Ni-MOF catalyst was also tested in aqueous solution with the hydrogen feedstock material, NaBH4, in varying conditions of pH, temperature and concentration.1,4 These efficiencies were compared to the catalytic capabilities of NiCl2 • 6H2O as a reducing catalyst. The Ni-MOF was characterized via surface area analysis for surface area and pore volume, powdered x-ray diffraction (PXRD) for crystallization, thermogravimetric analysis (TGA) for thermo-stability and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) to determine the chemical composition of the framework. The hydrolysis of NaBH4 via the Ni-MOF showed an overall increase in hydrogen volume produced and production rate over the metal-salt catalyst. Increased volumes of 43.56 mL to 70.03 mL were seen for the MOF at 303 K and similar increases for each of the other temperature trials as well as variation to pH of solution. Increases were also seen for the activation energy of the catalysts from 56.23 kJ mol-1 to 62.55 kJ mol-1 when coordinated into the nickel framework. Through TGA analysis the framework was found to be stable up to 620 K. Overall, the synthesis of Ni-MOF from NiCl2 • 6H2O and disodium terephthalate, provides an easy synthesis that increases the catalytic efficiencies while maintaining green chemistry properties. References Huff C., Long J., Aboulatta A., Heyman A., Abdel-Fattah T.M., ECS Journal of Solid State Science and Technology (2017), 6 (10), M115-M118Schlesingehr H.I.; Brown, H.C.; Finholt A.E.; Gilbreath J.R.; Hoekstra H.R.; Hyde E.L.; Sodium Borohydride, Its Hydolysis and its Use as a Reducing Agent in the Generation of Hydrogen; Am. Chem. Soc., (1953), 75 (1), pp 215–219Sánchez-Sánchez M., Getachew N., Díaz K., Díaz-García M., Chebudeb Y., Díaz I.; Green Chem., 17, 1500–1509 (2015)Walter, J.C.; Zurawski, A.; Montgomery, D.; Thornburg, M.; Revankar, S.; Sodium borohydride hydrolysis kinetics comparison for nickel, cobalt, and ruthenium boride catalysts; of Power Sources 179 (2008) 335–339

Green Synthesis of Nickel Terephthalate MOF at Room Temperature for the Catalysis of Hydrogen Generation

In this study, the metal salt, Ni(II) Chloride, was reacted to the organic ligands of disodium terephthalate (C8H4Na2O4) to synthesize the nickel terephthalate complex as metal organic framework (Ni-MOF) in aqueous media. The Ni-MOF was synthesized at room temperature (RT), with crystal formation occurring instantly and continuing to increase for up to a week. The catalytic efficiency of the Ni-MOF catalyst was also tested in aqueous solution with sodium borohydride. Reduction of sodium borohydride via the Ni-MOF showed an overall increase in hydrogen production over the metal-salt catalyst with increased volumes of 43.56 mL to 70.03 mL for the MOF at 303 K. The rates of reaction were also increased for the Ni-MOF over the nickel metal salt from 0.006 min-1 to 0.02 min-1 as a second order reaction.

Study of thermal decomposition of a zinc(II) monomethyl terephthalate complex, [Zn(CH3O–CO–C6H4COO)2(OH2)3]·2H2O

In this contribution, we report the thermal decomposition and thermo-X-ray diffraction analyses of a ZnII monomethyl terephthalate complex, [Zn(CH3O–CO–C6H4COO)2(OH2)3]·2H2O. Both XRD and temperature-dependent T-XRD patterns for the title compound in the thermal decomposition process (temperature range 30–300 °C) present diffraction peaks reminiscent of ordered, crystalline structure of the starting complex [Zn(CH3O–CO–C6H4COO)2(OH2)3]·2H2O. Crystallization and coordination water molecules of the title complex are eliminated in successive steps, and then the anhydrous complex decomposes to ZnO (the total experimental mass loss of 84.80 % versus the theoretical mass loss, 84.23 %). The formation of ZnO of wurtzite structure (hexagonal phase, space group P63 mc) as spherical nanoparticles with average size of 58 nm has been confirmed by XRD, SEM and EDX analyses performed on the final product.

An anti-ferromagnetic terephthalate-bridged trigonal prismatic dinuclear manganese(II) complex: Synthon of rare anion⋯ π interaction promoting dimensionality

A dinuclear compound [Mn2(L)2(μ-tp)](PF6)2⋅3.57H2O (1) [L = N,N′-(bis(pyridin-2-yl)benzy-lidene)-1,3-propanediamine and tp = terephthalate dianion] has been isolated and characterized on the basis of microanalytical, spectroscopic and other physicochemical properties. X-ray structural study showed interesting bis(bidentate) bridging motif of tp in the dicationic dinuclear unit [Mn2(μ-tp)]2+. Each manganese(II) centre adopts a rare distorted trigonal prismatic geometry with an MnN4 O 2 chromophore. Chelation of the tetradentate Schiff base (L) along with bis(bidentate) bridging of two O atoms of tp complete hexacoordination around each manganese(II) centre. The dinuclear units of 1 are associated through cooperative C-H⋯F hydrogen bonds and π ⋯ π, C-H⋯ π and rare anion⋯ π interactions to promote the dimensionality in a graded manner. Variable temperature magnetic susceptibility measurement of 1 in the 2–300 K temperature range revealed weak anti-ferromagnetic interaction presumably due to long bridging arm of tp. Synthesis, crystal structure and magnetic behavior of a dinuclear manganese(II) terephthalate complex with tetradentate N-donor Schiff base has been described. Interesting trigonal prismatic geometry around metal ion was observed in the complex. The dinuclear units of 1 are the source of rare anion⋯ π interactions to promote the dimensionality of compound.

The effect of oxygen ion beam bombardment on the properties of tin indium oxide/polyethylene terephthalate complex

The tin indium oxide (ITO) films were deposited onto the polyethylene terephthalate (PET) surface that has been bombarded by an O ion beam. The variation of the O bombardment time resulted in the production of ITO/PET complex with different properties. Characterization by four-point probe measurement after the bending fatigue test showed that the adhesion property of the ITO/PET complex could be improved by the increase of O bombardment time while little change of electrical resistivity was observed. Scanning electron microscopy results showed that after the bending fatigue test, the nano scale seams and micro scale trenches appeared at the surface of the ITO/PET complex. The former was only the cracks of ITO film, which has little influence on the continuity and electrical resistivity of ITO film. On the contrary, the micro scale trenches were caused by the peeling off of ITO chips at the cracks, which mainly influenced the continuity and electrical resistivity of ITO film. With the increase of O bombardment time, the number and length of the micro scale trenches decreased. X-ray photoelectron spectrometry characterization showed that with the increase of O bombardment time, parts of the methylene C bonds were transformed into CO bonds, which could be broken to form COIn(Sn) bonds at the initial stage of ITO film growth. By these COIn(Sn) crosslink bonds, the ITO film could adhere well onto the PET and the ITO/PET complex display better anti-bending fatigue property. Finally, in the context of the application of the ITO/PET complex as a flexible electrode substrate, the present work reveals a simple way to crosslink them, as well as the physicochemical mechanism happening at the interface of complex.

Coordination Assembly of ZnII/CdII Terephthalate with Bis-Pyridinecarboxamide Tectons: Establishing Net Entanglements from [3 + 3] Interpenetration to High-Connected Self-Penetration

Four polymeric d10 metal terephthalate complexes incorporating bis-pyridinecarboxamide building blocks were prepared to explore the effect of the central metal ion or the fluorine substituent of the ligand on the topology and entanglement of coordination networks. The combination of ZnII terephthalate with a fluorinated ligand leads to a noninterpenetrated coordination layer with honeycomb (hcb) topology for complex 1. Interestingly, the other three materials display the unusual entangling coordination networks. For 2, the reaction of zinc terephthalate with nonfluorinated ligand affords three-dimensional diamond (dia) architecture of [3 + 3] interpenetration, while the CdII terephthalate complexes 3 and 4 with the two types of bis-pyridinecarboxamide tectons show the isostructural self-penetrating framework with unique 8-connected (417.611) topology.

Supramolecular architecture of cadmium(II)–terephthalate complexes having a tridentate or tetradentate Schiff base as blocking coligand

Two new cadmium(II)–terephthalate complexes, ∞ 1 { [ Cd 2 ( μ - terephthalate ) 2 ( L 1 ) 2 ] · 9 H 2 O } ( 1) and [{Cd(H 2O)(L 2)} 2(μ-terephthalate)](terephthalate) · 10H 2O ( 2), where L 1 = ( E)- N 1, N 1-diethyl- N 2-(1-(pyridin-2-yl)ethylidene)ethane-1,2-diamine; L 2 = N, N′-bis-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine; terephthalate = benzene - 1 , 4 - dicarboxylate - O 2 C - C 6 H 4 - CO 2 - ) have been synthesized by a conventional solution method. Characterization by single crystal X-ray crystallography shows that compound 1 is composed of 1-D polymeric zig-zag chains with distorted pentagonal-bipyramidal cadmium centers. Compound 2 consists of centrosymmetric dinuclear complexes with a distorted pentagonal-bipyramidal cadmium center in which one terephthalate ligand bridges the metal centres and another terephthalate anion with water of crystallization forms a H-bonding network.

A Novel Reaction Pathway in Olefin-Deuterium Exchange Reaction inside the Micropores of Rh(II) Dicarboxylate Polymer Complexes

Abstract Three dimensional microporous polymers of Rh fumarate or Rh terephthalate complexes exhibited high catalytic activity for hydrogen exchange and hydrogenation of olefins at 200 K. The hydrogen exchange reaction takes place only inside the nanopores of the complexes without complete scission of C–H bond of olefin molecule.

Imide and anhydride bridged organoiron dinuclear homo and hetero dichalcogeno carboxylate complexes [CpFe(CO)2ECO(C6H4)CO]2NH and [CpFe(CO)2ECO(C6H4)CO]2O; E = S, Se

Organoiron thio- and seleno-terephthaloyl chloride complexes CpFe(CO)2ECO(C6H4)COCl (E = S and Se) react with NaOH and NaNH2 to give quantitative yields of the acid Cp(CO)2ECO(C6H4)CO2H and the amide CpFe(CO)2ECO(C6H4)CONH2 respectively. These amide and acid derivatives react with the terephthaloyl chloride complexes to give a new series of imide-bridged [CpFe(CO)2ECO(C6H4)CO]2NH and anhydride-bridged [CpFe(CO)2ECO(C6H4)CO]2O organoiron dinuclear homo and hetero dichalcogeno terephthalate complexes. The complexes were characterized by elemental analysis, i.r. and 1H-n.m.r. spectra.

Polyketone and complex formation of some halatopolymers

AbstractThe possibility of a number of halatopolymers forming complexes with pyridine and their ability to produce ketones by pyrolytic decarboxylation have been investigated. Of all the halatopolymer‐forming divalent metal (i.e., Mg2+, Ca2+, Ba2+, Zn2+, Cd2+, Mn2+, and Pb2+) dicarboxylates (i.e., suberate, sebacate, dodecanedioate, and terephthalate) investigated only Cd2+ yielded polyalkylene ketone on pyrolysis and formed complexes with pyridine. The polyalkylene ketones were infusible, and no solvents were found for them which suggests a cross‐linked molecular structure. Complexes formed by the cadmium aliphatic dicarboxylates were unstable but highly viscous in solution. Cadmium‐pyridine terephthalate complexes were on the contrary very stable.