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We present a pulsational stability analysis of hot post-asymptotic giant branch (AGB) H-deficient pre-white dwarf stars with active He-burning shells. The stellar models employed are state-of-the-art equilibrium structures representative of PG1159 stars derived from the complete evolution of the progenitor stars, through the thermally pulsing AGB phase and born-again episode. On the basis of fully nonadiabatic pulsation computations, we confirmed theoretical evidence for the existence of a separate PG1159 instability strip in the log Teff-log g diagram characterized by short-period g-modes excited by the ε-mechanism. This instability strip partially overlaps the already known GW Vir instability strip of intermediate/long-period g-modes destabilized by the classical κ-mechanism acting on the partial ionization of C and/or O in the envelope of PG1159 stars. We found that PG1159 stars characterized by thick He-rich envelopes and located inside this overlapping region could exhibit both short and intermediate/long periods simultaneously. As a natural application of our results, we study the particular case of VV 47, a pulsating planetary nebula nucleus (PG1159 type) that is particularly interesting because it has been reported to exhibit a rich and complex pulsation spectrum including a series of unusually short pulsation periods. We found that the long periods exhibited by VV 47 can be readily explained by the classical κ-mechanism, while the observed short-period branch below ≈300 s could correspond to modes triggered by the He-burning shell through the ε-mechanism, although more observational work is needed to confirm the reality of these short-period modes. Were the existence of short-period g-modes in this star convincingly confirmed by future observations, VV 47 could be the first known pulsating star in which both the κ-mechanism and the ε-mechanism of mode driving are simultaneously operating., Facultad de Ciencias Astronómicas y Geofísicas

We present the results of a multisite photometric campaign on the pulsating sdB star Balloon 090100001. The star is one of the two known hybrid hot subdwarfs with both long- and short-period oscillations. The campaign involved eight telescopes with three obtaining UBVR data, four B-band data, and one Stromgren uvby photometry. The campaign covered 48 nights, providing a temporal resolution of 0.36microHz with a detection threshold of about 0.2mmag in B-filter data. Balloon 090100001 has the richest pulsation spectrum of any known pulsating subdwarf B star and our analysis detected 114 frequencies including 97 independent and 17 combination ones. The strongest mode (f_1) in the 2.8mHz region is most likely radial while the remaining ones in this region form two nearly symmetric multiplets: a triplet and quintuplet, attributed to rotationally split \ell=1 and 2 modes, respectively. We find clear increases of splitting in both multiplets between the 2004 and 2005 observing campaigns, amounting to 15% on average. The observed splittings imply that the rotational rate in Bal09 depends on stellar latitude and is the fastest on the equator. We use a small grid of models to constrain the main mode (f_1), which most likely represents the radial fundamental pulsation. The groups of p-mode frequencies appear to lie in the vicinity of consecutive radial overtones, up to the third one. Despite the large number of g-mode frequencies observed, we failed to identify them, most likely because of the disruption of asymptotic behaviour by mode trapping. The observed frequencies were not, however, fully exploited in terms of seismic analysis which should be done in the future with a larger grid of reliable evolutionary models of hot subdwarfs., accepted for publication in MNRAS

Aims. We present a new method that investigates the evolutionary history of the pulsating DB white dwarf GD 358 using asteroseismology. This is done considering the internal C/O profile, which describes the relative abundances of carbon and oxygen from the core of the star to its surface. Different evolutionary channels lead to the generation of different C/O profiles, and these affect the pulsation periods. Methods. We used the C/O profiles associated with white dwarfs that evolved through binary evolution channels where the progenitor experienced one or two episodes of mass loss during one or two common envelope (CE) phases, and two profiles from single-star evolution. We computed models using these different profiles and used a genetic algorithm (GA) to optimize the search in the parameter space for the best fit to the observed pulsation periods. We used three-parameter models, adjusting the stellar mass (M� ), the effective temperature (Teff), and the helium mass of the external layer (MHe). Results. Our results suggest that binary evolution profiles may provide a better match to the pulsation periods of GD 358. The best fit to the observations is obtained using a profile related to an evolutionary history where two episodes of mass loss happen during two CE phases, the first during the RGB (red giant branch) stage. The values obtained are Teff = 24 300 K, M� = 0.585 M� ,a nd log (MHe/M� ) = −5.66. The best-fit model has a mass close to the mean mass for DB white dwarfs found in various works and a temperature consistent with UV spectra obtained with the IUE satellite.

Aims. We searched for photometric variability in a sample of hot, hydrogen-deficient planetary nebula nuclei (PNNi) with “PG 1159” or “O VI” spectral type, most of them embedded in a bipolar or elliptical planetary nebula envelope (PNe). These characteristics may indicate the presence of a hidden close companion and an evolution affected by episodes of interaction between them. Methods. We obtained time-series photometry from a sample of 11 candidates using the Nordic Optical Telescope (NOT) with the Andalucia Faint Object Spectrograph and Camera (ALFOSC), modified with our own control software to be able to observe in a high-speed multi-windowing mode. The data were reduced on-line with the real time photometry (RTP) code, which allowed us to detect periodic variable stars with small amplitudes from CCD data in real time. We studied the properties of the observed modulation frequencies to investigate their nature. Results. We report the first detection of low-amplitude pulsations in the PNNi VV 47, NGC 6852, and Jn 1. In addition, we investigated the photometric variability of NGC 246. Time-series analysis shows that the power spectra of VV 47, NGC 6852, and NGC 246 are variable on time scales of hours. Power spectra from consecutive nights of VV 47 and NGC 6852 show significant peaks in different frequency regions. The same type of variability is present in NGC 246 in 2 observing runs separated by 3 days. Changes are also found in the power spectra of VV 47 and NGC 246 during the same night. The VV 47 power spectra are peculiar since they present modulation frequencies in a wide range from 175 to 7600 μ Hz. This is different from the previously known pulsating PNNi where no frequencies are found above ~3000 μ Hz. The high-frequency modulation observed in VV 47 may be due to g -modes triggered by the ϵ -mechanism, observed for the first time.

International audience; This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 ?Hz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after removal of all linear combinations. In taking into account other frequencies present during the 1996 WET campaign and those present in earlier data, which do not show up in the 1999 data set, we find a total of 43 independent frequencies. This makes HL Tau 76 the richest ZZ Ceti star in terms of number of observed pulsation modes. We use those pulsation frequencies to determine as much as possible of the internal structure of HL Tau 76. The pulsations in HL Tau 76 cover a wide range of periods between 380 s and 1390 s. We propose an identification for 39 of those 43 frequencies in terms of ?=1 and ?=2 non-radial g-modes split by rotation. We derive an average rotation period of 2.2 days. The period distribution of HL Tau 76 is best reproduced if the star has a moderately "thick" hydrogen mass fraction log qH ? -7.0. The results presented in this paper constitute a starting point for a detailed comparison of the observed periods with the periods calculated for models as representative as possible of HL Tau 76.

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt 5 (5.5 plus or minus 1.9) x 10(exp -15) ss(sup -1), after correcting for proper motion. Our results are consistent with previous P values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is |P||P(raised dot)|greater than or equal to 1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.13 s is only slightly less than the present measurement for another DAV, G117-B15A, for the period 215.2 s, establishing this mode in ZZ Ceti as the second most stable optical clock known, comparable to atomic clocks and more stable than most pulsars. Constraining the cooling rate of ZZ Ceti aids theoretical evolutionary models and white dwarf cosmochronology. The drift rate of this clock is small enough that we can set interesting limits on reflex motion due to planetary companions.

We report on the 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23 to June 8, 2000. We acquired more than 232 000 independent measurements and detected the non-radial g-modes consistent with degree ℓ = 1 and radial order 8 to 20 and their linear combinations up to 6th order. We also detect, for the first time, a high amplitude ℓ = 2 mode, with a period of 796 s. In the 2000 WET data, the largest amplitude modes are similar to those detected with the WET observations of 1990 and 1994, but the highest combination order previously detected was 4th order.

In this article we present the results of more than 180 hours of time-series photometry on the low gravity (log g = 5.4, T e f f = 29 300 K, log He/H = -3.0 by number) sdB pulsating star HS 2201+2610, obtained between September 2000 and August 2001. The temporal spectrum is resolved and shows 5 close frequencies: three main signals at 2860.94, 2824.10 and 2880.69 μHz, with amplitudes of about 1%, 0.5% and 0.1% respectively, are detected from single run observations; two further peaks with very low amplitude (

Equimolar (1:1:1) mixed-ligand Cu(II) complexes with iminodiacetato (IDA) or N-methyl-IDA (MIDA) and N-methyl-imidazole (1MeImH) or ImH, respectively, have been prepared and characterized by thermal, spectral, magnetic and X-ray diffraction methods. [Cu(MIDA) (ImH)] (I) crystallizes in the monoclinic system P21/n (a = 12.465(3), b = 5.999(1), c = 14.733(3) A, β = 111.91(1)°, Z = 4, R = 0.043, Rw = 0.047). The Cu(II) atom exhibits a flattened square base byramidal coordination (type 4 + 1). The N and two O atoms of the tridentate MIDA and one N of ImH form the square base; one longer CuO bond with the next MIDA ligand in the chain complex completes the Cu(II) five-coordination. [Cu(IDA) (1MeImH) (H2O)2]·H2O (II) crystallizes in the orthorhombic system Pna21 (a = 14.733(2), b = 7.721(1), c = 11.288(1) A, Z = 4, R = 0.041, Rw = 0.043). The N and two O atoms from IDA and one N from 1 MeImH define a square coordination; two longer CuOH2 bonds complete the unsymmetrical elongated octahedral coordnation of Cu(II) (type 4 + 1 + 1). The polar NH bonds of ImH in I and of IDA in II as well as the OH bonds of the water molecules of the latter compound are involved in hydrogen bonds. The stepwise water loss in II is explained on the basis of its structural role in the Cu(II) coordination and/or in the crystal packing.

Diaqua(iminodiacetato)copper(II), [Cu(IDA)(H2O)2] (I), reacts with 2-methylimidazole to yield [Cu(IDA)(2MeImH)]·nH2O (n = 3, 1/2) or [Cu(IDA)(2MeImH)2]2·4H2O. However, the reaction of I with 4MeImH (even in excess) only gives the 1:1:1 ternary complex in the form of the ‘remote’ tautomer derivative [Cu(IDA)(5MeImH)]·H2O. This compound crystallizes in the monoclinic system, space group P21/n (a = 13.875(1), b = 5.748(1), c = 14.739(3) A, β = 106.32(1)°, Z = 4; final R = 0.059 and Rw = 0.060 for 1169 independent reflections). The crystal consists of H2O molecules non-bonded to the metal and zigzag chains of the complex. The Cu(II) atom shows a flattened square base pyramidal coordination (type 4+1). One N of 5MeImH and one N and two O of the same IDA ligand are at the coordination square base. One longer CuO bond with the next adjacent IDA ligand of the chain complex accomplishes the Cu(II) distorted five-coordination. The new mixed-ligand copper(II) complexes were characterized by thermal, spectral and magnetic methods. The results are discussed in connection with the reported data for analogous compounds with an unsubstituted imidazole ligand.

A search programme for pulsating subdwarf B stars was conducted with the Nordic Optical Telescope on La Palma over 59 nights between 1999 and 2009. The purpose of the programme was to significantly extend the number of rapidly pulsating sdB stars to better understand the properties of this new group of variable compact stars. Candidates were selected initially from the HS and HE surveys, but were supplemented with additional objects from other surveys. Short sequences of time-series photometry were made on the candidates to determine the presence of rapid pulsations. In total twenty new pulsators were found in this survey, most of which have already been published and some extensively studied. We present four new short period pulsators, bringing the total of such pulsators up to 49. We also give limits on pulsation amplitudes for 285 objects with no obvious periodic variations, summarise the results of the survey, and provide improved physical parameters on the composite pulsators for which only preliminary estimates were published earlier., 17 pages, accepted for publication in A&A

Homonuclear compounds [M(H 2 O) 6 [M 2 L 2 (H 2 O) 2 ]·4H 2 O (M(II)Co(II) or Zn(II), L 3− =anion of N , N -bis(carboxymethyl)-β-alanine or ((2-carboxyethyl)imino)diacetic acid) have been synthesized and characterized by chemical analysis, magnetic susceptibility data and/or IR spectra, thermal analysis and X-ray diffraction method. They are isostructural and crystallize in the triclinic system, space group P 1 with Z =1. The crystal structure was determined for the cobalt(II) compound ( a =8.732(7)- b =9.751(6), c =9.918(5) A, α=99.96(4), β=110.88(5), γ=103.79(5), V =734.6A 3 , D meas =1.80 g cm −3 , D exp =1.80 g cm −3 ,μ=1.767 mm − (MoKα)). Final R =0.034 and R w =0.043 for 3145 independent observed reflections. This compound consists of both centrosymmetric hexaaquocobalt(II) cations (Co(1)-OW(1)=2.046(2), (Co(1)-OW(2)=2.077(2), Co(1)-OW(3)=2.119(2) A) and anions [Co 2 L 2 (H 2 O ) 2 ] 2− , and non-coordinated water molecules. In the homodinuclear chelate anions, each cobalt(II) atom is bonded to one water molecule (Co( 2 )-OW(4)=2.098(2) A) and one tetradentate chelating ligand L 3− (Co(2)−N=2.134(2), Co(2)−O(5)=2.113(2), Co(2)−O(13)=2.081 (2), Co(2)-O(23)=2.101(2) A). The dimer has an imposed C i symmetry. One carboxylate oxygen atom from the β-alanine arm acts as a bridge between the two cobalt atoms so completing the octahedral coordination of cobalt. The values of the distances Co(2)−Co(2 i ) and the angle at the oxygen atom Co(2)−O(5)−Co(2 i ) are 3.2934(7) A and 103.5(1) o respectively.

Context. PG 1159-035, a pre-white dwarf with Teff ≃ 140000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star. Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters. Methods. We used all available WET photometric data from 1983, 1985, 1989. 1993 and 2002 to identify the pulsation periods. Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M⊙= 0.59 ±0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at rc/R* = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period Prot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for ℓ = 1 modes and less than 50% for ℓ = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars., La lista completa de autores que integran el documento puede consultarse en el archivo., Facultad de Ciencias Astronómicas y Geofísicas, Instituto de Astrofísica de La Plata

We report on the first pointed X-ray observations with XMM-Newton and RXTE satellites of the X-ray source RXJ0757.0+6306=HT Cam. We detect a strong 515s X-ray modulation confirming the optical photometric period found in 1998, which definitively assigns this source to the intermediate polar class of magnetic cataclysmic variables. The lack of orbital sidebands in the X-rays indicates that the X-ray period is the spin period of the accreting white dwarf. Simultaneous ultraviolet and optical B-band photometry acquired with the XMM-Newton Optical Monitor and coordinated optical UBVRI photometric data acquired at the Nordic Optical Telescope (La Palma) show that the optical pulse is in phase with the X-rays and hence originates in the magnetically confined accretion flow. The lack of ultraviolet spin modulation suggests that accretion-induced heating on the white dwarf surface is not important in this source. Spectral analyses of XMM-Newton EPIC and RGS spectra show that HT Cam has a multi-temperature spectrum and, contrary to most intermediate polars, it does not suffer from strong absorption. With its 86min orbital period, HT Cam is then the third confirmed system of this class below the 2-3hr period gap accreting at a low rate., Comment: 14 pages, 10 figures. Accepted for publication in Astronomy & Astrophysics Main Journal

BPM 37093 is the only hydrogen-atmosphere white dwarf currently known which has sufficient mass (~ 1.1 M_sun) to theoretically crystallize while still inside the ZZ Ceti instability strip (T_eff ~ 12,000 K). As a consequence, this star represents our first opportunity to test crystallization theory directly. If the core is substantially crystallized, then the inner boundary for each pulsation mode will be located at the top of the solid core rather than at the center of the star, affecting mainly the average period spacing. This is distinct from the "mode trapping" caused by the stratified surface layers, which modifies the pulsation periods more selectively. In this paper we report on Whole Earth Telescope observations of BPM 37093 obtained in 1998 and 1999. Based on a simple analysis of the average period spacing we conclude that a large fraction of the total stellar mass is likely to be crystallized., Comment: 7 pages, 3 figures, 3 tables, accepted for Astronomy & Astrophysics

HR 1217 is one of the best-studied rapidly oscillating Ap (roAp) stars, with a frequency spectrum of alternating even- and odd-� modes that are distorted by the presence of a strong, global magnetic field. Several recent theoretical studies have found that within the observable

WOS: 000182039700036, We have acquired new time series photometry of the two pulsating DB white dwarf stars KUV 05134+2605 and PG 1654+160 with the Whole Earth Telescope. Additional single-site photometry is also presented. We use all these data plus all available archival measurements to study the temporal behaviour of the pulsational amplitudes and frequencies of these stars for the first time. We demonstrate that both KUV 05134+2605 and PG 1654+160 pulsate in many modes, the amplitudes of which are variable in time; some frequency variability of PG 1654+160 is also indicated. Beating of multiple pulsation modes cannot explain our observations; the amplitude variability must therefore be intrinsic. We cannot find stable modes to be used for determinations of the evolutionary period changes of the stars. Some of the modes of PG 1654+160 appear at the same periods whenever detected. The mean spacing of these periods (approximate to40 s) suggests that they are probably caused by non-radial gravity-mode pulsations of spherical degree l = 1. If so, PG 1654+160 has a mass around 0.6 M.. The time-scales of the amplitude variability of both stars (down to two weeks) are consistent with theoretical predictions of resonant mode coupling, a conclusion which might however be affected by the temporal distribution of our data.

We report 323 hours of nearly uninterrupted time series photometric observations of the DBV star GD 358 acquired with the Whole Earth Telescope (WET) during May 23rd to June 8th, 2000. We acquired more than 232 000 independent measurements. We also report on 48 hours of time-series photometric observations in Aug 1996. We detected the non-radial g-modes consistent with degree l=1 and radial order 8 to 20 and their linear combinations up to 6th order.We also detect, for the first time, a high amplitude l=2 mode, with a period of 796s. In the 2000 WET data, the largest amplitude modes are similar to those detected with the WET observations of 1990 and 1994, but the highest combination order previously detected was 4th order. At one point during the 1996 observations, most of the pulsation energy was transferred into the radial order k=8 mode, which displayed a sinusoidal pulse shape in spite of the large amplitude. The multiplet structure of the individual modes changes from year to year, and during the 2000 observations only the k=9 mode displays clear normal triplet structure. Even though the pulsation amplitudes change on timescales of days and years, the eigenfrequencies remain essentially the same, showing the stellar structure is not changing on any dynamical timescale., 34 pages, 14 figures, WET data, accepted to A&A

HR1217 is a prototypical rapidly oscillating Ap star that has presented a test to the theory of nonradial stellar pulsation. Prior observations showed a clear pattern of five modes with alternating frequency spacings of 33.3 μHz and 34.6 μHz, with a sixth mode at a problematic spacing of 50.0 μHz (which equals 1.5 × 33.3 μHz) to the highfrequency side. Asymptotic pulsation theory allowed for a frequency spacing of 34 μHz, but hipparcos observations rule out such a spacing. Theoretical calculations of magnetoacoustic modes in Ap stars by Cunha (2001) predicted that there should be a previously undetected mode 34 μHz higher than the main group, with a smaller spacing between it and the highest one. The 20th extended coverage campaign of the Whole Earth Telescope (XCov20) has discovered this frequency as predicted by Cunha (2001). Amplitude modulation of several of the pulsation modes between the 1986 and 2000 data sets has also been discovered, while important parameters for modelling the geometry of the pulsation modes have been shown to be unchanged. With stringent selection of the best data from the WET network the amplitude spectrum shows highest peaks at only 50 μmag and formal errors on the determined amplitudes are 14 μmag. Some lessons for future use of WET for the highest precision photometry on bright stars are discussed.

Hot subdwarf stars (hot sds) are blue subluminous objects. Only a few determinations are available to date regarding the study of such aspects as rotation, microturbulent velocities or the magnetic nature of these objects. Over 26 sdBs are known to date to be multiperiodic rapid oscillators. This project presents preliminary results of new observations and models of a sample of pulsating and non-pulsating hot sds, including considerations on mass loss and eventual magnetic properties.

We present results from a multisite (‘Whole Earth Telescope’) photometric campaign on PG 1336−018, the close eclipsing binary system containing a pulsating subdwarf B (sdB) star. The main part of the campaign (1999 April) resulted in ~172 h of observations, representing a coverage of about 47 per cent, and additional data were obtained outside the core campaign. Periodogram analysis shows that the light variations are dominated by three frequencies near 5757, 5585 and 5369 μHz (~174, 179 and 186s, respectively), although many frequencies are present, particularly in the range 5000–6000 μHz (~200–170 s). We identify, with some confidence, 28 frequencies down to a semi-amplitude of 0.0005 in fractional intensity (equivalent to about 0.5 mmag). It is clear that the pulsation frequencies of PG 1336−018 have changed substantially since the 1996 discovery observations were made, and that amplitude changes occur, at least in the dominant three frequencies, on relatively short time-scales (of the order of a day). On the assumption that the pulsating star is phase-locked in the binary system, we have searched for rotational splitting of frequencies near the orbital and half of the orbital period, but the results are confused by aliasing at those frequencies (due to the data gaps caused by the eclipses). A preliminary model qualitatively matches the distribution of frequencies in PG 1336−018, with some good individual correspondences, but cannot be considered adequate because geometric cancellation should hide some of the modes which are apparently detected. Analysis of the pulsations during eclipse recovers three of the strongest modes, but the limited eclipse data – which can, at best, be only about 9 per cent of the total – do not allow mode identification at this stage. Simulations indicate that an overall coverage of about 80 per cent would be required for this to be viable. An attempt was made to determine phase shifts in the pulsation frequencies as a way of directly measuring the size of the binary orbit, but the uncertainties in the method are comparable to the light travel time across the orbit (probably less than a second).

High-speed photometry BD+254655 was obtained using the TromsO-Texas photometer during the 2000 campaign at the CST with an integration time of 5 sec, while PG0856+121 and BS16545-49 were observed during the 2002 campaign at the IAC80 telescope with an integration time of 10 seconds.

In this article we present the first results of about 95 hours of time-series photometry on the low gravity sdB pulsating star HS 2201+2610, obtained from a multi-site time-series campaign in September-October 2000. The temporal spectrum of HS 2201+2610 shows 3 close frequencies at 2860.9, 2824.1 and 2880.8 μHz with amplitudes of about 1 %, 0.4 % and 0.1 % respectively. Due to the small number of excited modes, a mode identification is possible in principle but not easy; no clear signatures of rotational splitting are seen.

μ-(N,N,N′,N′-Tetrakis(carboxymethyl)cystaminato (4−))-bis(imidazole)diaquodicopper dihydrate, [Cu2- (TCC)(ImH)2(H2O)2]·2H2O (I) (where TCC = (O2- CCH2)2NC2H4SSC2H4N(CH2CO2)24−), has been obtained in good yield by reaction of [Cu2 (TCC)(H2O)2]·4H2O (II) with excess of imidazole (ImH) in water. The new product I has been characterized by chemical analysis, TG-DTA diagram, infrared, reflectance and ESR spectra and the single- crystal X-ray diffraction method. The compound crystallizes in the monoclinic system, space group P21/n (a = 20.800(2), b = 10.191(2), c = 13.419(2) A, β = 92.41(1)°). Final R = 0.036 and Rw, = 0.035 for 2784 independent observed reflections. Instead of the polynuclear layered crystal structure of II, the crystal of I consists of hydrogen bonded water molecules and discrete dinuclear units [Cu2(TCC)- (ImH)2(H2O)2] linked together in a tridimensional hydrogen bonding network. Both crystallographic independent copper atoms of the mixed dinuclear unit show analogous distorted elongated octahedral coordination (of the type 4 + 1 + 1). The two CuN(ImH) bonds are shorter than the homologous bond in a variety of copper(II)imidazole derivatives, lying in the lowest limit of the corresponding bond lengths in Cu(II)(ImH)aminoacidato (or peptide) complexes (1.95–1.98 A). However, the ImH ligands do not play any π acceptor role (the CuN(ImH) bonds are tilted with respect to the ImH planes, which are twisted with respect to the mean equatorial coordination planes of the copper(II) atoms). By reacting ImH with II to give I, the copper coordinated water molecule in the equatorial position in II is replaced by an ImH molecule in I and moves to an apical position; this results in the lengthening of the CuS(disulfide) bonds, from 2.721(3) A in II to 2.959(2) A, average in I.