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.