A series of dinickel(II) complexes with the 24-membered macrocyclic hexaazadithiophenol ligand H(2)L(Me) was prepared and examined. The doubly deprotonated form (L(Me))(2-) forms complexes of the type [(L(Me))Ni2II(mu-L')](n+) with a bioctahedral N(3)Ni(II)(mu-SR)(2)(mu-L')Ni(II)N(3) core and an overall calixarene-like structure. The bridging coordination site L' is accessible for a wide range of exogenous coligands. In this study L'=NO(3)(-), NO(2)(-), N(3)(-), N(2)H(4), pyrazolate (pz), pyridazine (pydz), phthalazine (phtz), and benzoate (OBz). Crystallographic studies reveal that each substrate binds in a distinct fashion to the [(L(Me))Ni(2)](2+) portion: NO(2)(-), N(2)H(4), pz, pydz, and phtz form mu(1,2)-bridges, whereas NO(3)(-), N(3)(-), and OBz(-) are mu(1,3)-bridging. These distinctive binding motifs and the fact that some of the coligands adopt unusual conformations is discussed in terms of complementary host-guest interactions and the size and form of the binding pocket of the [(L(Me))Ni(2)](2+) fragment. UV/Vis and electrochemical studies reveal that the solid-state structures are retained in the solution state. The relative stabilities of the complexes indicate that the [(L(Me))Ni(2)](2+) fragment binds anionic coligands preferentially over neutral ones and strong-field ligands over weak-field ligands. Secondary van der Waals interactions also contribute to the stability of the complexes. Intramolecular ferromagnetic exchange interactions are present in the nitrito-, pyridazine-, and the benzoato-bridged complexes where J=+6.7, +3.5, and +5.8 cm(-1) (H=-2 JS(1)S(2), S(1)=S(2)=1) as indicated by magnetic susceptibility data taken from 300 to 2 K. In contrast, the azido bridge in [(L(Me))Ni(2)(mu(1,3)-N(3))](+) results in an antiferromagnetic exchange interaction J=-46.7 cm(-1). An explanation for this difference is qualitatively discussed in terms of bonding differences.

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A novel amine-thiolate ligand, H 3 3‚6HCl (N,N′,N′′-tris-[2-thio-3-aminomethyl-5-tert-butylbenzyl]-1,1,1-tris-(aminomethyl)ethane), has been synthesized and used in the preparation of dinuclear complexes of Fe, Co, and Ni. The nonadentate N 6 S 3 ligand H 3 3 is formally derived from the symmetric tridentate N 2 S ligand H 1 1 (2,6-bis(aminomethyl)-4-tert-butylthiophenol). It provides two dissimilar octahedral N 3 S 3 and N′ 3 S 3 coordination sites to give complexes with a central N 3 M(µ 2 -SR) 3 MN′ 3 core structure (N and N′ denote primary and secondary amine nitrogen atoms, respectively). The complexes of H 3 3 exist as dinuclear [M II 2 (3)] + , [M III M II (3)] 2+ , or [M III 2 -(3)] 3+ species which are all accessible by chemical or electrochemical reduction/oxidation. The following complexes were isolated as microcrystalline solids: [Co III 2 (3)][ClO 4 ] 3 (4b), [Ni III Ni II (3)][BPh 4 ] 2 (5b), and [Fe III Fe II (3)][BPh 4 ] 2 (6b). The chemical and physicochemical properties of the respective species are very similar to those of Fe, Co, and Ni complexes of H 1, and support the formulation of 4b-6b as discrete dinuclear species with a central N 3 M(µ 2 -SR) 3 MN′ 3 core. NMR spectra of diamagnetic cobalt complexes 4a and 4b reveal the complexes to be C 3h and C 3 symmetric, respectively, in the solution state. The crystal structure determination of [Co III 2 (1) 3 ][Fe(CN) 6 ]‚7MeOH‚3H 2 O (4c) (monoclinic, space group C2/c, a ) 28.037(2) Å, b ) 17.861(1) Å, c ) 25.727(2) Å, ) 90.24(1)°, and Z ) 8) reveals 4c to consist of dinuclear [Co III 2 (1) 3 ] 3+ trications featuring two fac-octahedral N 3 Co III (SR) 3 units bridged at the thiolate sulfur atoms. Compound 4c represents the first structurally characterized M III 2 complex of H 1 1. The ability of H 3 3 to form heterodinuclear complexes is demonstrated with the synthesis of [Co III Ni II (3)][BPh 4 ] 2 (7) and its linkage isomer [Ni II Co III (3)][BPh 4 ] 2 (8). All complexes undergo two electrochemically and chemically reversible one-electron-transfer reactions which convert the respective [M 2 (3)] n+ species. For M III 2 /M III M II (E 1 1/2 ) and M III M II / M II 2 (E 2 1/2 ): -0.40 V, -0.84 V (M ) Co), +0.49 V, +0.05 V (M ) Ni), +0.21 V, -0.33 V (M ) Fe) vs SCE.Heterodinuclear complexes 7 and 8 also give rise to two consecutive one-electron-transfer processes at E 1 1/2 (Ni III/II ) and E 2 1/2 (Co III/II ): +0.55 V, -0.71 V (for 7) and +0.60 V, -0.86 V (for 8), respectively. Comparison of the electrochemical properties of [Co III Ni II (3)] 2+ and [Ni III Ni II (3)] 2+ reveals the Ni III/II redox potential in the dinuclear complexes to be influenced by the oxidation state of the adjacent metal ion. At 77 K the mixed-valent Ni III Ni II (S ) 3 / 2 spin ground states) and Fe III Fe II complexes (S ) 1 / 2 spin ground states) exhibit localized and delocalized valencies, respectively, as indicated by UV-vis, EPR, and 57 Fe Mössbauer spectroscopy. IntroductionFace-sharing bioctahedral complexes of the type Y 3 M(µ 2 -X) 3 MY 3 (Chart 1), where ...

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A coordinatively unsaturated dinuclear Ni(II) complex of the tridentate ligand 2,6-di(aminomethyl)-4-tert-butyl-thiophenol (HL) has been synthesized and investigated in the context of ligand binding and oxidation state changes. The starting complex [L(2)Ni(2)][BPh(4)](2) (1) is readily prepared from NaL, NiCl(2).6H(2)O, and NaBPh(4) in methanol. Compound 1.CH(3)CN.CH(3)OH crystallizes from an acetonitrile/methanol mixed-solvent system in monoclinic space group P2(1)/n with a = 21.940(4) Å, b = 13.901(3) Å, c = 23.918(5) Å, beta = 110.00(3) degrees, and Z = 4. The structure consists of dinuclear [L(2)Ni(2)](2+) cations with two distorted planar cis-N(2)S(2)Ni coordination units joined by the thiophenolate sulfur atoms. The molecule has idealized C(2)(v)() symmetry. Complex 1 readily adds another 1 equiv of HL to afford the pale green complex [L(3)Ni(2)]Cl (2). The dinuclear structure and its formulation as a 3:2 complex (six-coordinate Ni ions) is derived from UV spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction of its oxidation product, [L(3)Ni(2)](2+). The dication was prepared by chemical oxidation of 2 with iodine in DMF and isolated as the dark brown BPh(4)(-) salt, [L(3)Ni(2)][BPh(4)](2).CH(3)OH (3), which crystallizes in monoclinic space group P2(1)/c with a = 23.678(5) Å, b = 20.090(4) Å, c = 16.797(3) Å, beta = 106.16(3) degrees, and Z = 4. Complex 3 is the first structurally characterized example that features a bioctahedral N(3)Ni(&mgr;(2)-SR)(3)NiN(3) core. Distortions from D(3)(h)() symmetry suggest that 3 is a trapped-valence Ni(II)Ni(III) compound. The Ni-S and Ni-N bond lengths vary from 2.2975(9) to 2.4486(12) Å and from 2.027(3) to 2.120(3) Å, respectively. On the CV time scale complex 2 undergoes two reversible electron-transfer reactions at E(1/2) = -0.02 and +0.44 V vs SCE, affording 3 and the transient dark green trication [L(3)Ni(2)](3+) (tau(1/2) approximately 15 min at 295 K), respectively. While 2 is EPR silent, the EPR spectrum of a powdered sample of 3 reveals g( perpendicular) = 4.0 and g( parallel) = 2.09 at 77 K, consistent with an S = (3)/(2) spin state of the mixed-valent Ni(II)Ni(III) complex.