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Reduction of [([Formula: see text])2][As6]2 with triphenylantimony and tetrabutylammonium chloride produced the diradical 5,5'-bis(1,3,2,4-dithiadiazolyl) [[Formula: see text]-[Formula: see text]] in high yield as a black solid with widely ranging magnetic susceptibilities (e.g., 0.6 to 2.6 μB), which on oxidation with AsF5 regenerated [([Formula: see text])2][AsF6]2. The identity of [[Formula: see text]-[Formula: see text]] was established from EPR, vibrational, and mass spectra. Ab initio molecular orbital [MPW1PW91/6-311G(2df)] calculations show the lowest energy structure to consist of two coplanar rings separated by a C—C single bond (1.444 Å), reflected in the comparison of the vibrational spectra of the diradical with that of [([Formula: see text])2][AsF6]2 and the calculated spectra. Confidence in the calculated [MPW1PW91/6-311G(2df)] structure of the diradical is supported by the excellent agreement between the calculated and X-ray single crystal structure geometries of [[Formula: see text]]2 and [([Formula: see text])2]2+ in [([Formula: see text])2][AsF6]2. The molecular orbitals indicate the diradical is essentially disjoint, confirmed by a very small (0.07 kJ mol–1) GVB-PP(TC-SCF)/6-311G* calculated singlet–triplet energy gap. Accordingly, the EPR spectrum of the diradical (in tetrahydrofuran, 293 K) shows a simple 3-line pattern (g = 2.0043, a(14N) = 1.11 mT) with no observable exchange coupling between the two radical centers. Mechanical grinding of the diradical results in a large increase in paramagnetism (e.g., from 1.03 to 2.55 μB) that is unprecedented in main group chemistry. The X-ray diffraction data of the ground and unground powder are consistent with a second order phase change on grinding. Attempts to obtain crystals of the diradical by sublimation led instead to numerous decomposition and rearrangement products, including 4-cyano-1,2,3,5-dithiadiazolyl [NC-[Formula: see text]], monoclinic space group C2/c, a = 9.46(2) Å, b = 7.625(5) Å, c = 13.17(2) Å, β = 107.94(4)°, Z = 8. The structure consists of axially symmetric, co-facial, cis dimers linked to form strands through two sets of C[Formula: see text]Nδ–···Sδ+ contacts. More efficient and larger scale preparations of [SNS][AsF6] and [([Formula: see text])2][AsF6]2 are reported. Key words: 5,5'-bis(1,3,2,4-dithiadiazolyl), diradical, paramagnetism, mechanical grinding, second order phase change, 4-cyano-1,2,3,5-dithiadiazolyl.

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Penelitian ini bertujuan (1) mengembangkan instrumen evaluasi kinerja guru yang valid dan reliabel, (2) mengevaluasi kinerja guru Fisika, Biologi, dan Kimia SMA yang sudah terser-tifikasi/menerima tunjangan profesi. Populasi penelitian yaitu seluruh guru Fisika, Biologi dan Kimia SMA tersertifikasi/pene-rima tunjangan profesi yang berada di Kota Banda Aceh, Kabupaten Aceh Besar dan Kabupaten Pidie. Validitas konstruk instrumen yang dikembangkan dibuktikan melalui analisis fak-tor, dan reliabilitasnya diestimasi dengan rumus alpha Cron-bach. Analisis tingkat kinerja ditentukan dengan persentase. Hasil penelitian menunjukkan: (1) instrumen yang dikembang-kan terdiri atas 33 butir pernyataan, dan memiliki koefisien reliabilitas konsistensi internal sebesar 0,953; (2) kinerja guru Fisika, Biologi, dan Kimia SMA yang sudah lulus sertifikasi dan sudah menerima tunjangan belum seluruhnya berkinerja tinggi; (3) kinerja guru Kimia relatif lebih baik dari pada kinerja guru Biologi dan guru Fisika. Kata kunci: evaluasi, kinerja guru, validitas, reliabilitas ______________________________________________________________AN EVALUATION OF THE PERFORMANCE OF CERTIFIED SCIENCE TEACHERS (PHYSICS, CHEMISTRY AND BIOLOGY) OF SENIOR HIGH SCHOOLS Abstract This study was aimed at (1) developing a valid and reliable performance evaluation instruments for teachers, and (2) evaluating the level of Physics, Biology and Chemistry teachers of senior high schools who have been certified and received theprofession allowance. The population of this study included all certified Physics, Biology and Chemistry teachers of senior high schools who have received profession allowance in Banda Aceh, Aceh Besar, and Pidie. The construct validity of the instrument developed was assessed through factor analysis, and the reliability was estimated by using Cronbach’s Alpha formula. The level of teachers’performance was analyzed by the percentage. The result of the research shows that (1) the instrument developed consists of 33 items, and has an internal consistency reliability coefficient of 0,953, (2) not all certified high school teachers who have received profession allowance and teach Physics, Biology and Chemistry show high performance, and (3) the performance of Chemistry teachers is relatively higher than that of Physics and Biology teachers. Keywords: evaluation, teachers’ performance, validity, reliability

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