Crystallographic elucidation of purely structural, thermal and light-induced spin transitions in an iron(II) binuclear complex.

The intricate phase diagram of the binuclear iron(II) spin-crossover complex [{Fe(3-bpp)(NCS)(2)}(2)(4,4'-bypiridine)].2CH(3)OH where 3-bpp is 2,6-bis(pyrazol-3-yl)pyridine has been investigated by variable temperature single crystal X-ray diffraction including a study into the effect of photo-irradiation. This sample is known to exhibit an incomplete spin transition at low temperature. At room temperature, in phase I, iron ions are all crystallographically equivalent, adopting the high spin state (HS). X-Ray structural investigation has revealed two phase transitions in the range (300-30 K). The first transition (T approximately 161 K) leading to phase II is of a purely structural nature and corresponds to a break in symmetry as a result of a twist of the two rings of 4,4'-bipyridine; the two iron sites of the binuclear unit becoming crystallographically independent but remaining all HS. The second structural transition corresponds to the spin crossover, one of the two Fe(II) ions of the binuclear complex being in the low spin state (LS) in phase III. The crystal structure shows an ordered HS-LS crystal packing where HS and LS sites are clearly identified and not randomly distributed in the metal ion sites as often observed. Moreover, light irradiation of single crystals in phase III at 30 K, leading to phase III*, induces a light-induced spin-state trapping (LIESST) effect corresponding to the full conversion of all the iron sites to HS. The crystal packing in phase III* is closer to that of phase III than to those observed in the other HS phases, I and II. This reveals an unusual differentiation between the thermal and light-induced HS states. A deeper analysis of the structural properties first demonstrates the key role of the bipyridine bridge in the peculiar preliminary pure structural transition shown by the title compound. Elsewhere, it also shows that the molecular packing is strongly dependent on the nature of the external perturbation contrary to the iron coordination sphere geometry that appears to be only dependent on the spin state. Moreover, in the HS phase II, the distortion of the iron sites that will subsequently undergo a spin crossover demonstrates some differences with the distortion of the iron sites that remain HS. The predominant role of the iron environment distortion in the spin crossover phenomenon is thus clearly evidenced.

Low temperature single crystal X-ray diffraction: advantages, instrumentation and applications.

The benefits of carrying out single crystal X-ray diffraction (SXRD) experiments at low temperatures have long been recognised by the scientific community, as clearly demonstrated by the massive increase in publications reporting the use of low temperature SXRD in the past 15 years. This tutorial review will summarise the advantages, many of them now often forgotten by its practitioners or never known by the newcomers to the field, of performing single crystal X-ray diffraction experiments at low temperatures. The instrumentation currently available to university laboratories, which has been greatly improved over the past 5 years, will also be briefly described and a few different examples covering a range of applications will be presented.

trans-Diaqua(2,2'-biquinoline-N,N')(nitrato-O,O')nickel(II) nitrate hydrate.

The structure of the title compound, [Ni(NO(3))(C(18)H(12)N(2))(H(2)O)(2)]NO(3) x H(2)O, is composed of monomers with the nickel ion octahedrally coordinated to a bidentate biquinoline ligand, a bidentate nitrate anion and two water molecules, and is stabilized by a nitrate counter-ion and a hydrate water molecule. There is a fairly complex hydrogen-bonding scheme involving all the water H atoms and five different nitrate O atoms.

Mu-oxo-bis[eta5-1,2-dicarbaundecarboato)bis(N,N-dimethylacetamidinato)-tantalum] dichlooromethane hemisolvate.

The structure of the title compound, [Ta2O(C2B9H11)2(C4H9N2)4]*0.5CH2Cl2, contains two (C2B9H11)Ta[NC(Me)NMe2]2 units bridged by a nearly linear [Ta-O-Ta 163.4 (4) degrees ] mu-oxo ligand. The dichloromethane molecule lies on a twofold axis.

Cigarette smoking during pregnancy and risk of preeclampsia: a systematic review.

In this systematic review of the existing evidence regarding the relationship between cigarette smoking during pregnancy and preeclampsia, studies were found through searches of MEDLINE (1966-October 31, 1998), Embase, Popline, CINAHL, Lilacs, bibliographies of identified studies, and proceedings of meetings on preeclampsia, and also through contact with relevant researchers. No language restrictions were imposed. Only cohort and case-control studies dealing with the relationship between cigarette smoking and preeclampsia were considered. Assessment of methodologic quality and data extraction of each study were carried out by 2 authors working independently. Typical relative risks and odds ratios with 95% confidence intervals were calculated for cohort and case-control studies, respectively, with both fixed and random effects models. Twenty-eight cohort studies and 7 case-control studies including a total of 833,714 women were included. All cohort studies reported an inverse association between cigarette smoking during pregnancy and incidence of preeclampsia (typical relative risk, 0.68; 95% confidence interval, 0.67-0.69). The findings were similar for case-control studies (typical odds ratio, 0.68; 95% confidence interval, 0.57-0.81). An inverse dose-response relationship was also found. Pooled data from cohort and case-control studies showed a lower risk of preeclampsia associated with cigarette smoking during pregnancy.

Epidemiology of eclampsia in Colombia.

OBJECTIVE: To measure the incidence of eclampsia, its maternal and perinatal outcomes and patterns of presentation of this disease in our environment. METHOD: Retrospective descriptive study of 164 cases of eclampsia managed at the Hospital Universitario del Valle, Cali, Colombia from September 1993 to August 1995. Information was collected from reviews of hospital case-notes. RESULTS: The incidence of eclampsia was 8.1/1000 deliveries. Maternal mortality was 6.1%. Fifty-seven percent of seizures occurred antepartum, 22% during labor, and 21% after delivery. Sixty-nine cases (42%) presented preterm. Ninety-eight women (60%) were nulliparous. Approximately one quarter of the women did not have hypertension or significant proteinuria at the time of seizures. Twenty percent of all women had at least one major complication. Perinatal mortality was 12.8%. Antepartum and postpartum cases were more severe than intrapartum cases. CONCLUSION: Eclampsia occurs in one in 124 deliveries in Cali, Colombia and is associated with high maternal and perinatal morbidity and mortality.

Triple-marker test as screening for Down syndrome: a meta-analysis.

The effectiveness of triple-marker testing as screening for Down syndrome needs to be evaluated by means of formal meta-analytic techniques. We did a MEDLINE search to identify studies evaluating the detection of Down syndrome by use of the triple-marker test. Reference lists of articles were also checked. Papers published in either English, French, or German from 1966 to November 1996 were eligible for this review. Twenty cohort studies were identified. Results of sensitivities and false-positive rates from different subgroups of the study sample were compared by using summary receiver-operating characteristic curve analysis. Medians of sensitivities and false-positive rates were also estimated. A total of 194,326 patients were included. In women of all ages, the medians for sensitivities were 67, 71, and 73 percent when the cutoffs used were 1:190-200, 1:250-295, and 1:350-380, respectively. The median false-positive rates fluctuated between 4 and 8 percent. For women at or above 35 years old, the medians of sensitivity and false-positive rate were 89 and 25 percent, respectively, when the chosen cutoff was 1:190-200. In patients below 35 years old, the median sensitivity was 57 percent if the cutoff used was 1:250-295. Summary receiver-operating characteristic curves showed that 1:190 was the best cutoff for predicting Down syndrome. The triple-marker testing is an effective screening method of detecting Down syndrome pregnancies. It is less effective in younger than in older age groups and may be offered as an alternative to amniocentesis to pregnant women over 35.

Case-control study of risk factors for complicated eclampsia.

OBJECTIVE: To identify risk factors associated with complicated eclampsia. METHODS: Twenty-four patients with eclampsia complicated by intracerebral hemorrhage, pulmonary edema, renal, hepatic, or respiratory failure, disseminated intravascular coagulation, abruptio placentae, pulmonary aspiration, or hemolysis, elevated liver enzymes, low platelets syndrome were compared retrospectively with 101 uncomplicated eclamptic controls. Information on maternal demographic factors, medical and obstetric histories, and maternal and perinatal outcomes was retrieved and analyzed by univariate and multivariate analysis. RESULTS: By multiple logistic regression, the only risk factors associated with the development of complicated eclampsia were maternal age over 26 years (adjusted odds ratio [OR] 6.3, 95% confidence interval [CI] 2.17, 18.48), multiparity (adjusted OR 4.5, 95% CI 1.55, 13.60) and no prenatal care (adjusted OR 3.3, 95% CI 1.25, 9.60). CONCLUSION: Maternal age above 26 years, multiparity, and no prenatal care are the maternal risk factors identified for the development of complicated eclampsia.