in benzene byproducts: HCl; absence of air and moisture; slow addn. of slight excess ligand to metalchloride, refluxing for 6 h; solvent removal; can be recrystallized (warm hexane); elem. anal.;

Na#Hg in tetrahydrofuran byproducts: NaCl; (N2), glovebox, dark; mixing niobium compd., AsP3, C4H8O, 0.5percent Na/Hg, stirring (20 min, 22°C), evapn., addn. of (C2H5)2O, filtration, evapn., addn. of P4 in C6D6, evapn., addn. of C4H8O, freezing, addn. of AsCl3 in toluene, stirring for 20 min; heating (22°C), filtration through Celite, concn., NMR;