Vapochromism and Magnetochemical Switching of a Nickel(II) Paddlewheel Complex by Reversible NH Uptake and Release.

Reaction of [NiCl (PnH) ] (1) (PnH=6-tert-butyl-pyridazine-3-thione) with NiCl affords the binuclear paddlewheel (PW) complex [Ni (Pn) ] (2). Diamagnetic complex 2 is the first example of a PW complex capable of reversibly binding and releasing NH . The NH ligand in [Ni (Pn) (NH )] (2⋅NH ) enforces major spectroscopic and magnetic susceptibility changes, thus displaying vapochromic properties (λ (2)=532 nm, λ (2⋅NH )=518 nm) and magnetochemical switching (2: S=0; 2⋅NH : S=1). Upon repeated adsorption/desorption cycles of NH the PW core remains intact. Compound 2 can be embedded into thin polyurethane films (2 ) under retention of its sensing abilities. Therefore, 2 qualifies as reversible optical probe for ammonia. The magnetochemical switching of 2 and 2⋅NH was studied in detail by SQUID measurements showing that in 2⋅NH , solely the Ni atom coordinated the NH molecule is responsible for the paramagnetic behavior.