Nickel complexes of eight differently substituted 2,2′‐bidipyrrins have been prepared and fully characterized. The X‐ray analyses of three of these complexes revealed helical chiral molecules. Despite the tetrahedral deviation from the square‐planar coordination geometry at the metal centres, all compounds were found to be diamagnetic in nature. For (3,3′,4,4′,8,8′,9,9′‐octaethyl‐10,10′‐dimethyl‐6,6′‐diphenyl2,2′‐bidipyrrinato)nickel, a separation into the enantiomers by chiral MPLC could be achieved, and the first CD spectra of enantiomerically pure tetrapyrrole helicates are reported. An electrochemical study of the new complexes allowed a first insight into the electronic structure of (2,2′‐bidipyrrinato)nickel(II), disclosing a rather high energy HOMO and metal−ligand interaction similar to that observed in metalloporphyrins.

Copper(II) and palladium(II) complexes of two 2,2′‐bidipyrrin ligands were prepared and examined, in comparison with the known nickel(II) complexes of these ligands, by means of X‐ray crystallography, cyclic voltammetry, and spectroelectrochemistry. All compounds are of helical geometry with coordination environments of the metal centres displaying very small tetrahedral distortions for palladium and very large ones for copper complexes. Porphyrinoid behaviour was found for the one‐ and two‐electron oxidations of all complexes studied, as well as for the reductions of the PdII species. On the other hand, the reduction of the CuII complexes shows some special features, which may be explained from the results of spectroelectrochemical studies as related to the particular non‐planarity of these compounds. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

The first dinuclear iron(II) complexes of any 4-substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazole ligands, [Fe(II)2(adpt)2(H2O)1.5(CH3CN)2.5](BF4)4 and [Fe(II)2(pldpt)2(H2O)2(CH3CN)2](BF4)4, are presented [where adpt is 4-amino-3,5-di(2-pyridyl)-4H-1,2,4-triazole and pldpt is 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole]. Both dinuclear complexes feature doubly triazole bridged iron(II) centers that are found to be [high spin-high spin] at all temperatures, 4-300 K, and to exhibit weak antiferromagnetic coupling. In the analogous monometallic complexes, [Fe(II)(Rdpt)2(X)2](n+), the spin state of the iron(II) center was controlled by appropriate selection of the axial ligands X. Specifically, both of the chloride complexes, [Fe(II)(adpt)2(Cl)2] x 2 MeOH and [Fe(II)(pldpt)2(Cl)2] x 2 MeOH x H2O, were found to be high spin whereas the pyridine adduct [Fe(II)(adpt)2(py)2](BF4)2 was low spin. Attempts to prepare [Fe(II)(pldpt)2(py)2](BF4)2 and the dinuclear analogues [Fe(II)2(Rdpt)2(py)4](BF4)4 failed, illustrating the significant challenges faced in attempts to develop control over the nature of the product obtained from reactions of iron(II) and these bis-bidentate ligands.