title: Synthesis and Characterization of a Tetrapodal NO4(4-) Ligand and Its Transition Metal Complexes.
abstract: We present the synthesis and characterization of alkali metal salts of the new tetraanionic, tetrapodal ligand 2,2'-(pyridine-2,6-diyl)bis(2-methylmalonate) (A4[PY(CO2)4], A = Li(+), Na(+), K(+), and Cs(+)), via deprotection of the neutral tetrapodal ligand tetraethyl 2,2'-(pyridine-2,6-diyl)bis(2-methylmalonate) (PY(CO2Et)4). The [PY(CO2)4](4-) ligand is composed of an axial pyridine and four equatorial carboxylate groups and must be kept at or below 0 °C to prevent decomposition. Exposing it to a number of divalent first-row transition metals cleanly forms complexes to give the series K2[(PY(CO2)4)M(H2O)] (M = Mn(2+), Fe(2+), Co(2+), Ni(2+), Zn(2+)). The metal complexes were comprehensively characterized via single-crystal X-ray diffraction, (1)H NMR and UV-vis absorption spectroscopy, and cyclic voltammetry. Crystal structures reveal that [PY(CO2)4](4-) coordinates in a pentadentate fashion to allow for a nearly ideal octahedral coordination geometry upon binding an exogenous water ligand. Additionally, depending on the nature of the charge-balancing countercation (Li(+), Na(+), or K(+)), the [(PY(CO2)4)M(H2O)](2-) complexes can assemble in the solid state to form one-dimensional channels filled with water molecules. Aqueous electrochemistry performed on [(PY(CO2)4)M(H2O)](2-) suggested accessible trivalent oxidation states for the Fe, Co, and Ni complexes, and the trivalent Co(3+) species [(PY(CO2)4)Co(OH)](2-) could be isolated via chemical oxidation. The successful synthesis of the [PY(CO2)4](4-) ligand and its transition metal complexes illustrates the still-untapped versatility within the tetrapodal ligand family, which may yet hold promise for the isolation of more reactive and higher-valent metal complexes.
authors.affiliation: Departments of Chemistry, ‡Molecular and Cell Biology, and #Chemical and Biomolecular Engineering and the §Howard Hughes Medical Institute, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division and &Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Jordan C
authors.initials: JC
authors.lastname: Axelson
authors.affiliation: Departments of Chemistry, ‡Molecular and Cell Biology, and #Chemical and Biomolecular Engineering and the §Howard Hughes Medical Institute, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division and &Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Miguel I
authors.initials: MI
authors.lastname: Gonzalez
authors.affiliation: Departments of Chemistry, ‡Molecular and Cell Biology, and #Chemical and Biomolecular Engineering and the §Howard Hughes Medical Institute, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division and &Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Katie R
authors.initials: KR
authors.lastname: Meihaus
authors.affiliation: Departments of Chemistry, ‡Molecular and Cell Biology, and #Chemical and Biomolecular Engineering and the §Howard Hughes Medical Institute, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division and &Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Chang
authors.affiliation: Departments of Chemistry, ‡Molecular and Cell Biology, and #Chemical and Biomolecular Engineering and the §Howard Hughes Medical Institute, University of California , Berkeley, California 94720, United States.|Chemical Sciences Division and &Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Long