SYNTHESIS AND STRUCTURE ELUCIDATION OF 1,2,4-TRIAZINO [4,3-b] 1,2,4-TRIAZINES, 1,2,4-TRIAZINO [3,4-C] 1,2,4-TRIAZINES AND 1,2,4-TRIAZINO [4,3-dl l,2,4-TRIAZINES (Journal of Sciences, Islamic Republic of Iran)