First published as an Advance Article on the web 23rd May 2006 DOI: 10.1039/b603443h Three new salts RBzPy+[Ni(a-tpdt)2]

R = H, Br, F) were prepared and structurally and magnetically characterized. A common structural feature of these compounds is the arrangement of the anions with thiophenic sulfur atoms connecting to a coordinating sulfur atom of a neighbouring anion, placed almost perpendicular to each other. The cations are positioned with the pyridine rings inserted between thiophenic rings of anions, maximizing p–p interactions. Depending on the cation substitution structural differences and variable degrees of cis–trans disorder in the anions are observed, which affect the magnetic properties. HBzPy[Ni(a-tpdt)2] displays dominant ferromagnetic interactions and cluster glass behaviour at low temperatures, BrBzPy[Ni(a-tpdt)2] shows dominant antiferromagnetic interactions with a magnetic anomaly at y6 K and FBzPy[Ni(a-tpdt)2] magnetic behavior is dominated by weak ferromagnetic interactions but without magnetic ordering down to 1.5 K