Vapochromism and Magnetochemical Switching of a Nickel(II) Paddlewheel Complex by Reversible NH 3 Uptake and Release

Reaction of [NiCl 2 ( PnH ) 4 ] ( 1 ) ( PnH =6‐ tert ‐butyl‐pyridazine‐3‐thione) with NiCl 2 affords the binuclear paddlewheel (PW) complex [Ni 2 ( Pn ) 4 ] ( 2 ). Diamagnetic complex 2 is the first example of a PW complex capable of reversibly binding and releasing NH 3 . The NH 3 ligand in [Ni 2 ( Pn ) 4 (NH 3 )] ( 2 ⋅NH 3 ) enforces major spectroscopic and magnetic susceptibility changes, thus displaying vapochromic properties ( λ max ( 2 )=532 nm, λ max ( 2 ⋅NH 3 )=518 nm) and magnetochemical switching ( 2 : S =0; 2 ⋅NH 3 : S =1). Upon repeated adsorption/desorption cycles of NH 3 the PW core remains intact. Compound 2 can be embedded into thin polyurethane films ( 2 P ) under retention of its sensing abilities. Therefore, 2 qualifies as reversible optical probe for ammonia. The magnetochemical switching of 2 and 2 ⋅NH 3 was studied in detail by SQUID measurements showing that in 2 ⋅NH 3 , solely the Ni atom coordinated the NH 3 molecule is responsible for the paramagnetic behavior.