| Summary: | Pyridyl- and indoleninyl-substituted pyrimido[1,2-<i>b</i>]indazole were synthesised in good to high yields from the condensation reaction of 1,3-dialdehydes with 3-aminoindazoles. The structural features of the compounds were determined by NMR (<sup>1</sup>H, <sup>13</sup>C and <sup>19</sup>F), FT-IR and HR-MS. The spectroscopic assignments were confirmed by X-ray crystallography for two derivatives, i.e., 9-Bromo-3-(pyridin-4-yl)pyrimido[1,2-<i>b</i>]indazole (<b>1b</b>) and 10-Methoxy-3-(pyridin-4-yl)pyrimido[1,2-<i>b</i>]indazole (<b>1c</b>), which further provides support for significant delocalisation of π-electron density over the entire fused ring system. The molecular packing was assessed by conventional methods together with Hirshfeld surface analyses. In <b>1b</b>, the molecular packing features pyrimidyl-N–H···N(pyrimidyl), π(pyrazolyl)···π(pyrimidyl) and Br···N interactions within a two-dimensional array. In <b>1c</b>, pyrimidyl-C–H···N(pyrazolyl) and pyridyl-C–H···O(methoxy) interactions feature within a three-dimensional architecture.
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