A Back‐to‐Back Ligand with Dipyrazolylpyridine and Dipicolylamine Metal‐Binding Domains

Reaction of 4‐bromomethyl‐2,6‐bis(pyrazol‐1‐yl)pyridine with dipicolylamine yields 4‐bis(pyrid‐2‐ylmethyl)aminomethyl‐2,6‐bis(pyrazol‐1‐yl)pyridine ( L ). Treatment of L with [MCl 2 (NCPh) 2 ] (M = Pd, Pt) in the presence of AgPF 6 affords [MCl( L )]PF 6 , whose palladium or platinum centre is bound exclusively by the dipicolylamino moiety of L , as established by NMR spectroscopy. The pendant dipyrazolylpyridine residue in these compounds is complexed by iron(II) to form [Fe{MCl(μ‐ L )} 2 ][PF 6 ] 4 (M = Pd, 1 ; M = Pt, 2· n H 2 O). The nitromethane solvate crystal of 1 contains low‐spin iron centres at 150 K. However, dried 1 and 2· n H 2 O are predominantly high‐spin at room temperature, undergoing very gradual thermal spin transitions upon cooling to ≤ 50 % completeness. The platinum compound also undergoes a thermal spin transition in CD 3 NO 2 solution, with T 1/2 = 253 K.