A new Schiff-base macrocycle is obtained by the lead(II) ion templated [2+2] condensation of 3,5-diacetyl-1H-1,2,4-triazole and 1,4-diaminobutane in the presence of sodium hydroxide. Transmetallation of the resulting dilead complex, Pb2(L2)(ClO4)21, in acetonitrile with two equivalents of CoCl2·6H2O leads to the isolation of an orange, six-coordinate complex, [CoII2(L2)(OH2)3(NCCH3)](ClO4)2·H2O·2CH3CN 2. Subsequent reaction of 2 with two equivalents of NaOCN or NEt4Cl yielded red–purple five-coordinate [CoII2(L2)(NCO)2] 3 and red five-coordinate [CoII2(L2)(Cl)2]·1.5CH3CN 4, respectively. In all three air-stable dicobalt complexes the macrocycles contain two high-spin cobalt(II) centers which are weakly antiferromagnetically coupled (2J = −3.0, −0.4, −3.5 cm−1 for 2, 3 and 4, respectively). Complexes 2–4 have been characterized by X-ray diffraction and are the first structurally characterised complexes of a triazolate-containing macrocycle to date.

The synthesis and structures of a dicobalt(II) complex and an unusual organometallic dicobalt(III) complex of the triazolate-containing Schiff-base macrocyclic ligand L2- are presented.

A series of structurally characterized copper complexes of two pyridazine-spaced cryptands in redox states + (I,I), (II,I), (II), (II,II) are reported. The hexaimine cryptand L(I) [formed by the 2 + 3 condensation of 3,6-diformylpyridazine with tris(2-aminoethyl)amine (tren)] is able to accommodate two non-stereochemically demanding copper(I) ions, resulting in [Cu(I)(2)L(I)](BF(4))(2) 1, or one stereochemically demanding copper(II) ion, resulting in [Cu(II)L(I)()](BF(4))(2) 3. Complex 3 crystallizes in two forms, 3a and 3b, with differing copper(II) ion coordination geometries. Addition of copper(I) to the monometallic complex 3 results in the mixed-valence complex [Cu(I)Cu(II)L(I)](X)(3) (X = PF(6)(-), 2a; X = BF(4)(-), 2b) which is well stabilized within this cryptand as indicated by electrochemical studies (K(com) = 2.1 x 10(11)). The structurally characterized, octaamine cryptand L(A), prepared by sodium borohydride reduction of L(I), is more flexible than L(I) and can accommodate two stereochemically demanding copper(II) ions, generating the dicopper(II) cryptate [Cu(II)(2)L(A)](BF(4))(4) 4. Electrochemical studies indicate that L(A) stabilizes the copper(II) oxidation state more effectively than L(I); no copper redox state lower than II,II has been isolated in the solid state using this ligand.

On binding a stereochemically demanding cation a symmetrical cryptand host generates a second non-identical site thereby offering a reliable route to certain types of heterobinuclear cryptates. Specifically, mononuclear complexes [CoIIL](BF4)2 (1) and [CuIIL](BF4)2 (2), of the symmetrical cryptand L [formed by the 3+2 condensation of 3,6-diformylpyridazine with tris(2-aminoethyl)amine (tren)], were reacted with 1 equiv. of Cu(MeCN)4BF4 to yield [CoIICuIL](BF4)3 (3) and [CuIICuIL](BF4)3 4, respectively.

3,6-Diformylpyridazine has been incorporated into a crypt ligand (L) for the first time by condensation with tris(2-aminoethyl)amine (tren). This crypt is shown to be an accommodating host, being able to encapsulate none, one or two metal ion guests. The free crypt, disilver(I) complex and monocobalt(II) complex have been structurally characterised. Electrochemical studies establish that the π-acceptor ligand L effectively stabilises the cobalt ion in the +2 oxidation state.