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

Reaction of [NiCl2(PnH)(4)] (1) (PnH=6-tert-butyl-pyridazine-3-thione) with NiCl2 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 NH3. The NH3 ligand in [Ni-2(Pn)(4)(NH3)] (2.NH3) enforces major spectroscopic and magnetic susceptibility changes, thus displaying vapochromic properties (lambda(max)(2)=532 nm, lambda(max)(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 (2(P)) 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.

Automated summary

The reaction of [NiCl2(PnH)(4)] with NiCl2 yields a binuclear paddlewheel complex capable of reversibly binding and releasing NH3, showing distinctive vapochromic properties and magnetochemical switching. Detailed SQUID measurements reveal that in the complex, only the Ni atom coordinated to the NH3 molecule is responsible for its paramagnetic behavior.