in pentane Irradiation (UV/VIS); irradiation (25°C/12 - 18 h/366 nm, 450 watt water cooled medium-pressure mercury lamp) of vigorously stirred suspension in dry N2-satd. pentane (Schlenck technique);; filtration from ppt. (washed with pentane); evapn. of filtrate to dryness; chromy.;;