The well-known tetradentate ligand 1,2-bis(pyridine-2-carboxamido)benzenate(2-), (bpb)2-, and its 4,5-dichloro analogue, (bpc)2-, are shown to be "noninnocent" ligands in the sense that in coordination compounds they can exist in their radical one- and diamagnetic two-electron-oxidized forms (bpbox1)- and (bpbox2)0 (and (bpcox1)- and (bpcox2)0), respectively. Photolysis of high-spin [(n-Bu)4N][FeIII(bpb)(N3)2] and its (bpc)2- analogue in acetone solution at room temperature generates the diamagnetic dinuclear complex [(n-Bu)4N][FeIV2(mu-N)(bpb)2(N3)2] and its (bpc)2- analogue; the corresponding cyano complex [(n-Bu)4N][FeIV2(mu-N)(bpb)2(CN)2] has been prepared via N3- substitution by CN-. Photolysis in frozen acetonitrile solution produces a low-spin ferric species (S = 1/2) which presumably is [FeIII(bpbox2)(N)(N3)]-, as has been established by EPR and Mössbauer spectroscopy. The mononuclear complexes [(n-Bu)4N][FeIII(bpb)(CN2)] (low spin), [Et4N][CoIII(bpb)(CN)2] and Na[CoIII(bpc)-(CN)2].3CH3OH can be electrochemically or chemically one-electron-oxidized to give [FeIII(bpbox1)(CN)2]0 (S = 0), [CoIII(bpbox1)(CN)2]0 (S = 1/2), and [CoIII(bpcox1)(CN)2]0 (S = 1/2). All complexes have been characterized by UV-vis, EPR, and Mössbauer spectroscopy, and their electro- and magnetochemistries have been studied. The crystal structures of [(n-Bu)4N][FeIII(bpb)(N3)2].1/2C6H6CH3, Na[FeIII(bpb)(CN)2], Na[CoIII(bpc)(CN)2].3CH3OH, [(n-Bu)4N][FeIV2(mu-N)(bpb)2(CN)2], and [(n-Bu)4N][FeIV2(mu-N)(bpb)(N3)2] have been determined by single-crystal X-ray diffraction.

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A binuclear tetraprotonated macrocyclic complex [Mg(2)(L(2)-H(4))(NO(3))(2)](NO(3))(2).6H(2)O (1) has been obtained by template condensation of 4-methyl-2,6-diformylphenol and 1,2-diaminoethane in the presence of magnesium acetate and nitrate. Complex 1 on reduction with NaBH(4), followed by the removal of magnesium, yields the 36-membered octaaminotetraphenol macrocyclic ligand H(4)L(1). The replacement of magnesium in 1 with copper(II) leads to the formation of the binuclear complex [Cu(2)L(3)(ClO(4))(2)] (2) derived from the [2+2] cyclization product of 4-methyl-2,6-diformylphenol and 1,2-diaminoethane. From H(4)L(1) a series of tetranuclear nickel(II) complexes 5-8 with the core cation [Ni(4)L(1)(&mgr;(2)-X)(2)(&mgr;(2)-H(2)O)(2)](2+) (X = NCS, N(3), OAc, or Cl) have been synthesized and characterized. The trinuclear complex [Ni(3)L(1)(acac)(2)(H(2)O)(2).2H(2)O (9), obtained by reacting nickel(II) acetylacetonate with H(4)L(1), on treatment with nickel(II) perchlorate produces the tetranuclear compound [Ni(4)L(1)(acac)(2)(H(2)O)(4)](ClO(4))(2) (10). Variable-temperature (4-300 K) magnetic susceptibility measurements have been carried out for the tetracopper(II) complex [Cu(4)L(1)(H(2)O)(4)](ClO(4))(4) (3) and the tetranickel(II) complexes [Ni(4)L(1)(&mgr;(3)-OH)(&mgr;(2)-H(2)O)(2)(ClO(4))](ClO(4))(2).2CH(3)COCH(3).H(2)O (4), [Ni(4)L(1)(&mgr;(2)-NCS)(2)(&mgr;(2)-H(2)O)(2)](ClO(4))(2).2CH(3)CN (5), [Ni(4)L(1)(&mgr;(2)-N(3))(2)(&mgr;(2)-H(2)O)(2)](ClO(4))(2).2CH(3)OH (6), [Ni(4)L(1)(&mgr;(2)-OAc)(2)(&mgr;(2)-H(2)O)(2)](ClO(4))(2).2H(2)O (7), and [Ni(4)L(1)(&mgr;(2)-Cl)(2)(&mgr;(2)-H(2)O)(2)]Cl(2).4H(2)O (8). The X-ray structure of 5 has been determined. The complex (C(50)H(70)N(12)O(14)Cl(2)S(2)Ni(4)) crystallizes in the triclinic space group P&onemacr; with a = 11.794(6) Å, b = 12.523(4) Å, c = 12.794(5) Å, alpha = 117.28(5) degrees, beta = 96.38(4) degrees, gamma = 109.65(3) degrees, and Z = 1. In the asymmetric unit each of the nickel(II) centers with distorted octahedral geometry is triply-bridged by a phenoxide group, a water molecule, and a N-bonded thiocyanate and these metal centers are further bridged to their symmetry-related counterparts by another phenoxide group. The experimental susceptibility data have been analyzed using appropriate Heisenberg spin coupling models (H = -2J(ij)()S(i)().S(j)()) and the best-fit spin exchange parameters obtained are as follows: J = -288(3) cm(-)(1) (3); J(1) = -8.1(2) cm(-)(1), J(2) = -10.2(2) cm(-)(1) (4); J(1) = -34.5(1.0) cm(-)(1), J(2) = -9.5(2.0) cm(-)(1) (5); J(1) = -34(1) cm(-)(1), J(2) = 11(2) cm(-)(1) (6); J(1) = -30(1) cm(-)(1), J(2) = -7.0(1.5) cm(-)(1) (7); J(1) = -32(1) cm(-)(1), J(2) = -4(1) cm(-)(1) (8).