Vapochromism and Magnetochemical Switching of a Nickel(II) Paddlewheel Complex by Reversible NH3 Uptake and Release

Abstract

Reaction of [NiCl2(PnH)4] (1) (PnH=6-tert-butyl-pyridazine-3-thione) with NiCl2 affords the binuclear paddlewheel (PW) complex [Ni2(Pn)4] (2). Diamagnetic complex 2 is the first example of a PW complex capable of reversibly binding and releasing NH3. The NH3 ligand in [Ni2(Pn)4(NH3)] (2⋅NH3) enforces major spectroscopic and magnetic susceptibility changes, thus displaying vapochromic properties (λmax(2)=532 nm, λmax(2⋅NH3)=518 nm) and magnetochemical switching (2: S=0; 2⋅NH3: S=1). Upon repeated adsorption/desorption cycles of NH3 the PW core remains intact. Compound 2 can be embedded into thin polyurethane films (2P) under retention of its sensing abilities. Therefore, 2 qualifies as reversible optical probe for ammonia. The magnetochemical switching of 2 and 2⋅NH3 was studied in detail by SQUID measurements showing that in 2⋅NH3, solely the Ni atom coordinated the NH3 molecule is responsible for the paramagnetic behavior.