Nickel complexes of thiohydrazonates. 3. Crystal and molecular structures of [2,4-pentanedione bis(thioacethydrazonato)]nickel(II)-acetonitrile adduct, tetrabutylammonium [2,4-pentanedione bis(thioacethydrazonato)]nickelate(II), and [pentanetrione 2,4-bis(thioacethydrazonato)]nickel(II)