The aim of this investigation was to study the bonding patterns, geometry, and fluorescence properties of nickel(II) complexes with salicylaldehyde-based thiosemicarbazones [(2-OH-5-R1-C6H3)C(R2)=NNHC(=S)NHR3, LH2] by invoking the effect of substituents at the C-2 and N-1 atoms of the thio ligands and by using bipyridines/phenanthrolines as auxiliary ligands. The methodology used for the preparation of complexes involved initial binding of NiII with a thio ligand in an organic solvent to yield an insoluble solid of empirical composition [NiL], which was reacted further with a N,N-donor ligand. In this way, we have prepared a series of dinuclear complexes and two mononuclear complexes with stoichiometries [Ni2L2(bipy)(D)] [bipy = 2,2′-bipyridine, L = L1 (R1, R2, R3 = H), D = H2O 1; L = L2 (R1, R2 = H, R3 = Me), D = CH3OH 2; L =L3 (R1, R2 = H, R3 = Et), D = CH3OH 4; L = L3, D = H2O 5; L = L4 (R1 = Me, R2 = H, R3 = Me), D = CH3OH 6], [Ni2L32(bipy)] (3), [Ni2L32(dmbipy)(H2O)] (7, dmbipy = 4,4′-dimethyl-2,2′-bipyridine), [Ni2L52(bipy)2] (8, R1 = NO2, R2 = H, R3 = Me), [NiL6(bipy)] (9, R1 = NO2, R2 = H, R3 = Et), [NiL7(bipy)(H2O)] (10, R1 = H, R2 = Me, R3 = Et), [Ni2L32(4,4′-bipy)] (11, 4,4′-bipy = 4,4′-bipyridine), and [Ni2L72(4,4′-bipy)] (12). The dinuclear complexes involve (i) O,N3,S chelation with bridging N2 atoms to form trigonal-bipyramidal/square-planar complexes with a five-coordinate and a four-coordinate Ni center (3, 5:4-coordination) and octahedral/square-planar complexes (1, 2, 4–7, 6:4-coordination), (ii) O,N3,S chelation with S bridges to form octahedral/octahedral complexes (8, 6:6-coordination), and (iii) O,N3,S chelation to form square-planar/square-planar complexes (11, 12, 4:4-coordiantion). The mononuclear complexes involve O, N3,S chelation and have square-pyramidal (9) and octahedral (10) geometries. Complexes 1–10 are paramagnetic with μeff value in the range 2.97–3.38 μB. Complexes 2 and 3 exhibit fluorescence emission.