Synthesis, spectroscopic characterization, and magnetic properties of unusual 3,5-dialkyl-1,2,4-triazole compounds containing N-bridging isothiocyanato ligands. X-ray structure of trinuclear bis[(.mu.-thiocyanato-N)bis(.mu.-3,5-diethyl-1,2,4-triazole-N1,N2)bis(thiocyanato-N)(3,5-diethyl-1,2,4-triazole-N1)nickel(II)-N,N1,N1']nickel(II) dihydrate