Side-on coordination mode of a pyrazolyl group in the structure of a divalent [Sm{B(3-Mepz)}] 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(CHBN)], was synthesized from the reaction of SmI with potassium tetrakis(3-methyl-1H-pyrazol-1-yl)borate, denoted K[B(3-Mepz)], in tetrahydrofuran.