EPR and NMR study of the spin-crossover transition in bis(4,4'-bi-1,2,4-triazole)bis(thiocyanato)iron hydrate and bis(4,4'-bi-1,2,4-triazole)bis(selenocyanato)iron hydrate. X-ray structure determination of Fe(4,4'-bi-1,2,4-triazole)2(SeCN)2.cntdot.H2O