Abstract
As a probe of the dinucleating ability of the known but little studied bis‐bidentate ligand 3,5‐di(2‐pyridyl)‐4‐(1__H__‐pyrrol‐1‐yl)‐4__H__‐1,2,4‐triazole (pldpt) its reactivity towards MX~2~·6H~2~O (M = Co^II^, Ni^II^ and Zn^II^; X = ClO~4~^–^ and BF~4~^–^) as well as Cu(ClO~4~)~2~·6H~2~O, in a 1:1 metal‐to‐ligand molar ratio in MeCN, has been investigated. In the case of Co^II^, Ni^II^ and Zn^II^, these reactions gave dinuclear complexes M^II^~2~(pldpt)~2~X~4~(MeCN)~m~(H~2~O)~n~, whereas for Cu^II^ initially the mononuclear complex [Cu^II^(pldpt)~2~(ClO~4~)~2~] was isolated, followed by the dinuclear complex Cu^II^~2~(pldpt)~2~(MeCN)~2~(H~2~O)~2~~4~. The use of the strongly polar aprotic co‐solvent DMF resulted in the partial breakdown of the initial dinuclear entities in the case of Co^II^ and Ni^II^ but not in the case of Zn^II^. In all five of the structurally characterised dinuclear complexes the (N′,N^1^,N^2^,N′′)~2~ double‐bridging coordination mode is realised with distorted octahedral N~4~Y~2~‐coordinated metal centres (Y = DMF, H~2~O or MeCN). The two mononuclear complexes feature the common trans‐(N′,N^1^)~2~ coordination mode with axial DMF or ClO~4~^–^ co‐ligands. The near‐perpendicular orientation [82.4(3)–88.8(1)°] of the π‐electron‐rich 4‐(1__H__‐pyrrol‐1‐yl) substituent with respect to the triazole ring of pldpt, observed in all of these structures, means that no π‐interactions are expected between these rings so any electronic interaction is likely to be small. Whether a di‐ or mononuclear complex of pldpt forms is therefore primarily determined by a number of other factors, including the reaction stoichiometry, the nature of the counterions and the solvent, as well as the relative solubility of the various possible products. Clearly the nature of the N^4^ substituent can have a major impact on the last of these factors. Magnetic studies carried out on the dinuclear complexes revealed that the triazole bridges mediate relatively weak antiferromagnetic coupling between the two metal centres. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)