A) VCl3 reduction solution (saturated): 800 mg VCl3 (p.a., Merck) was partly dissolved in a small amount of ultrapure water (app. 20 mL), 8.4 mL HCl (37 wt.%) was added and diluted to 100 mL with ultrapure water. Using this procedure leads to a particle- free solution which is stable for at least a month.