STRUCTURE AND PHYSICAL-PROPERTIES OF TRIGONAL MONOPYRAMIDAL IRON(II),COBALT(II), NICKEL(II), AND ZINC(II) COMPLEXES

A series of trigonal monopyramidal complexes of the tripodal ligand tr is((N-rert-butylcarbamoyl)methyl)aminato, [1(But)](3-), have been synt hesized and characterized. The structures of [Co1(But)](-), [Zn1(But)] (-), and [Ni1(But)](-) confirm that trigonal monopyramidal coordinatio n geometry occurs in these complexes where the three amidate nitrogens are arranged in the trigonal plane and the amine nitrogen is bonded a pically to the metal ions. The solid-state structures of [Co1(But)](-) , [Zn1(But)](-), and [Ni1(But)](-) are nearly identical indicating tha t the trigonal ligand [1(But)](3-) enforces the trigonal monopyramidal structure in these metal ions. Crystal data: K[Co1(But)].0.5DMF cryst allizes in the monoclinic space group C2/c, with cell dimensions a = 1 8.844(4) Angstrom, b = 9.809(3) Angstrom, c = 28.715(13) Angstrom, bet a = 102.70 degrees, and Z = 8; (NEt4)[Zn1(But)].THF crystallizes in th e monoclinic space group P2(1)/c, with cell dimensions a = 13.244(3) A ngstrom, b = 11.285(5) Angstrom, c = 25.625(3) Angstrom, beta = 104.45 (1)degrees and Z = 4. The H-1 NMR spectrum of the diamagnetic [Zn1(But )](-) also suggests that the complex retains its C-3 symmetry in solut ion. Room-temperature magnetic susceptibility measurements show that [ Fe1(But)](-), [Co1(But)](-), and [Ni1(But)](-) are high spin. The cycl ic voltammetry of [Co1(But)](-) and [Ni1(But)](-) at a glassy carbon s urface and at a scan rate of 100 mV s(-1) shows quasi-reversible one e lectron oxidation at E-1/2 = 0.77 (Delta E-p = 93 mV, i(pc)i(pa)(-1) = 0.69) and 0.56 (Delta E-p = 75 mV, i(pc)i(pa)(-1) = 0.79) V versus SC E, respectively. However, at slower scan rates these redox processes b ecome irreversible and attempts to isolate the oxidized products at ro om temperature were unsuccessful. The chemical oxidation of [Ni1(But)] (-) with [Fe(bpy)(3)](3-) in 1:1 propionitrile-DMF mixture at -75 degr ees C generated a EPR-active species (77 K, g(1) = 2.29, g(2) = 2.16, g(3) = 2.03, a(3) = 20 G) assigned to a Ni(III) complex with rhombic s ymmetry. [Fe1(But)](-) shows one irreversible oxidation (E-p,E-a = 0.0 5 V versus SCE) under the same conditions. These results are consisten t with [1(But)](3-) being able to stabilize trigonal monopyramidal com plexes of low-valent metal ions.