Side-on coordination mode of a pyrazolyl group in the structure of a divalent [Sm{B(3-Mepz)4}2] complex (3-Mepz is 3-methylpyrazol-1-yl)

The discovery of polypyrazolylborate ligands allowed the development of various chemical fields and these ligands are an alternative to cyclopentadienyl, because both ligands have the same charge and donate the same number of electrons, as well as adopting the same facial geometry. Easy control of the bulkiness of polypyrazolylborate ligands is possible by modification of the substituents in the 3- and 5-positions of the pyrazolyl rings. The title complex, bis[tetrakis(3-methyl-1H-pyrazol-1-yl)borato]samarium(II), [Sm(C16H20BN8)2], was synthesized from the reaction of SmI2with potassium tetrakis(3-methyl-1H-pyrazol-1-yl)borate, denoted K[B(3-Mepz)4], in tetrahydrofuran. The X-ray structure analysis revealed an unusual side-on coordination mode of a 3-methylpyrazolyl group through an N=N group in the B(3-Mepz)4ligand. The distortion is defined by the B—N—N—Sm torsion angle [85.5 (4)°]. This is in contrast to the structure of the similar divalent samarium complex [Sm(Tp^{{\rm Me}_2})2] [Tp^{{\rm Me}_2} is tris(3,5-dimethylpyrazol-1-yl)borate], which displays normal κ3-bonding modes of the Tp^{{\rm Me}_2} ligands.

Efficient Synthesis and Properties of a Novel Unsymmetrical Photochromic Diarylethene Material Based on Pyrazolyl Group

An unsymmetrical diarylethene derivative was synthesized, and its photochromic properties and fluorescence switch were investigated in detail. The results showed that this compound exhibited reversible photochromism, undergoing reversible cyclization and cycloreversion reactions upon alternating irradiation with UV and visible light both in solution and in PMMA film, and its absorption maxima were observed at 574 nm in hexane and at 579 nm in PMMA amorphous film, respectively, upon irradiation with 297 nm UV light. The diarylethene 1a in hexane solution exhibited relatively strong fluorescence at 413 nm when excited at 322 nm. The fluorscence intensity is highest at the concentration of 1.0×10-4 mol/L when excited at 322 nm.