Scientist Spotlights in Secondary Schools: Student Shifts in Multiple Measures Related to Science Identity after Receiving Written Assignments.

Based on theoretical frameworks of scientist stereotypes, possible selves, and science identity, written assignments were developed to teach science content through biographies and research of counter-stereotypical scientists-Scientist Spotlights (www.scientistspotlights.org). Previous studies on Scientist Spotlight assignments showed significant shifts in how college-level biology students relate to and describe scientists and in their performance in biology courses. However, the outcomes of Scientist Spotlight assignments in secondary schools were yet to be explored. In collaboration with 18 science teachers from 12 schools, this study assessed the impacts of Scientist Spotlight assignments for secondary school students. We used published assessment tools: Relatability prompt; Stereotypes prompt; and Performance/Competence, Interest, and Recognition (PCIR) instrument. Statistical analyses compared students' responses before and after receiving at least three Scientist Spotlight assignments. We observed significant shifts in students' relatability to and descriptions of scientists as well as other science identity measures. Importantly, disaggregating classes by implementation strategies revealed that students' relatability shifts were significant for teachers reporting in-class discussions and not significant for teachers reporting no discussions. Our findings raise questions about contextual and pedagogical influences shaping student outcomes with Scientist Spotlight assignments, like how noncontent Instructor Talk might foster student shifts in aspects of science identity.

A non-luminescent polymorph of [(cyclohexyl isocyanide)2Au]PF6 that becomes luminescent upon grinding or exposure to dichloromethane vapor.

The discovery of a third, non-luminescent crystalline polymorph of [(C6H11NC)2Au]PF6 is reported. Remarkably, crystals of this polymorph are sensitive to mechanical pressure or to exposure to dichloromethane vapor. In both cases, the conversion produces the yellow, green luminescent polymorph of [(C6H11NC)2Au]PF6 and not the colorless, blue luminescent polymorph.

Unsymmetrical Coordination of Bipyridine in Three-Coordinate Gold(I) Complexes.

The unsymmetrical coordination of gold(I) by 2,2'-bipyridine (bipy) in some planar, three-coordinate cations has been examined by crystallographic and computational studies. The salts [(Ph3P)Au(bipy)]XF6 (X = P, As, Sb) form an isomorphic series in which the differences in Au-N distances range from 0.241(2) to 0.146(2) Å. A second polymorph of [(Ph3P)Au(bipy)]AsF6 has also been found. Both polymorphs exhibit similar structures. The salts [(Et3P)Au(bipy)]XF6 (X = P, As, Sb) form a second isostructural series. In this series the unsymmetrical coordination of the bipy ligand is maintained, but the gold ions are disordered over two unequally populated positions that produce very similar overall structures for the cations. Although many planar, three-coordinate gold(I) complexes are strongly luminescent, the salts [(R3P)Au(bipy)]XF6 (R = Ph or Et; X = P, As, Sb) are not luminescent as solids or in solution. Computational studies revealed that a fully symmetrical structure for [(Et3P)Au(bipy)]+ is 7 kJ/mol higher in energy than the observed unsymmetrical structure and is best described as a transition state between the two limiting unsymmetrical geometries. The Au-N bonding has been examined by natural resonance theory (NRT) calculations using the "12 electron rule". The dominant Lewis structure is one with five lone pairs on Au and one bond to the P atom, which results in a saturated (12 electron) gold center and thereby inhibits the formation of any classical, 2 e- bonds between the gold and either of the bipy nitrogen atoms. The nitrogen atoms may instead donate a lone pair into an empty Au-P antibonding orbital, resulting in a three-center, four-electron (3c/4e) P-Au-N bond. The binuclear complex, [µ2-bipy(AuPPh3)2](PF6)2, has also been prepared and shown to have an aurophillic interaction between the two gold ions, which are separated by 3.0747(3) Å. Despite the aurophillic interaction, this binuclear complex is not luminescent.

Role of Anions and Mixtures of Anions on the Thermochromism, Vapochromism, and Polymorph Formation of Luminescent Crystals of a Single Cation, [(C6H11NC)2Au].

Noncoordinating anions, which generally play a subordinate role in coordination chemistry, alter the structure, the luminescence, as well as the thermochromic and vapochromic behaviors of salts of the two-coordinate cation, [(C6H11NC)2Au]+. Thus whereas the yellow polymorphs of [(C6H11NC)2Au](PF6) and [(C6H11NC)2Au](AsF6) contain single chains of cations and are vapochromic, yellow [(C6H11NC)2Au](SbF6) does not form the same polymorph and is not vapochromic but contains two distinct chains of cations connected through aurophilic interactions. Mixed crystals such as [(C6H11NC)2Au](PF6)0.50(AsF6)0.50 have been prepared by adding diethyl ether to a dichloromethane solution containing equimolar amounts of [(C6H11NC)2Au](PF6) and [(C6H11NC)2Au](AsF6). The initial (kinetic) product for the three combinations of anions ((PF6)-/(AsF6)-, (PF6)-/(SbF6)-, and (AsF6)-/(SbF6)-) was a precipitate of fine yellow needles with a green emission, which were gradually transformed at rates that depended on the anions present into colorless crystals with a blue emission. Whereas neither polymorph of [(C6H11NC)2Au](PF6) nor [(C6H11NC)2Au](SbF6) is thermochromic, the colorless mixed crystal [(C6H11NC)2Au](PF6)0.50(SbF6)0.50 is thermochromic and converts from blue-emitting to green-emitting at 87-95 °C. The temperature required to transform a crystal of the type [(C6H11NC)2Au](PF6)n(AsF6)1-n from colorless (blue-emitting) to yellow (green-emitting) increases as the fraction of hexafluorophosphate ion in the crystal increases. The yellow crystals of [(C6H11NC)2Au](PF6)0.75(AsF6)0.25, [(C6H11NC)2Au](PF6)0.50(AsF6)0.50, and [(C6H11NC)2Au](PF6)0.25(AsF6)0.75 are vapochromic, whereas the yellow crystals of [(C6H11NC)2Au](PF6)0.50(SbF6)0.50 and [(C6H11NC)2Au](AsF6)0.50(SbF6)0.50 are not.

Seeing luminescence appear as crystals crumble. Isolation and subsequent self-association of individual [(C6H11NC)2Au]+ ions in crystals.

Non-luminescent, isostructural crystals of [(C6H11NC)2Au](EF6)·C6H6 (E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. Previous studies have shown that the two-coordinate cation, [(C6H11NC)2Au]+, self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual [(C6H11NC)2Au]+ ions are isolated from one another. In [(C6H11NC)2Au](BArF24) ((BArF24)- is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of [(C6H11NC)2Au](EF6) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates [(C6H11NC)2Au](EF6)·C6H6. These two solvates are isostructural and contain columns in which cations and benzene molecules alternate. With the benzene molecules separating the cations, the shortest distances between gold ions are 6.936(2) Å for E = As and 6.9717(19) Å for E = Sb. Upon removal from the mother liquor, these crystals crack due to the loss of benzene from the crystal and form luminescent powders. Crystals of [(C6H11NC)2Au](SbF6)·C6H6 that powder out form a pale yellow powder with a blue luminescence with emission spectra and powder X-ray diffraction data that show that the previously characterized [(C6H11NC)2Au](SbF6) is formed. In the process, the distances between the gold(i) ions decrease to ∼3 Å and half of the cyclohexyl groups move from an axial orientation to an equatorial one. Remarkably, when crystals of [(C6H11NC)2Au](AsF6)·C6H6 stand in air, they lose benzene and are converted into the yellow, green-luminescent polymorph of [(C6H11NC)2Au](AsF6) rather than the colorless, blue-luminescent polymorph. Paradoxically, the yellow, green-luminescent powder that forms as well as authentic crystals of the yellow, green-luminescent polymorph of [(C6H11NC)2Au](AsF6) are sensitive to benzene vapor and are converted by exposure to benzene vapor into the colorless, blue-luminescent polymorph.

Vapoluminescent Behavior and the Single-Crystal-to-Single-Crystal Transformations of Chloroform Solvates of [Au2 (µ-1,2-bis(diphenylarsino)ethane)2 ](AsF6 )2.

The mono- and di-chloroform solvates of [Au2 (µ-1,2-bis(diphenylarsino)ethane)2 ](AsF6 )2 undergo single-crystal-to-single-crystal transformations that result in gain (over 12 hours) or slow loss (over five years) of only one chloroform molecule. The change in solvation results in changes in the structure and luminescence of the digold cation. The cation consists of a pair of slightly bent As-Au-As units that are connected through the two bridging dpae ligands and by aurophilic interactions with Au⋅⋅⋅Au contacts of 3.05152(15) Šin the disolvate or 2.9570(5) Šin the monosolvate.