The influence of substituents at the C2carbon of N1-substituted thiosemicarbazones, {C4H3X–C2(CH3)N3–N2H–C1(S)N1HR2} (X = O, S) on the geometry of nickel(ii) complexes has been investigated. The presence of a methyl group at the C2position of 2-acetylfuran-N1-substituted thiosemicarbazones {(C4H3O)–C2(CH3)N3–N2H–C1(S)N1HR2, R2= CH3, HaftscN–Me; C2H5, HaftscN–Et; C6H5, HaftscN–Ph} induces unusual coordination by the furan ring and yielded high spin octahedral nickel(ii) complexes, [Ni(κ3-O, N3, S-aftscN–R2)2], CH31, C2H52, and 2[Ni((κ3-O, N3, S-aftscN–Ph)2] 3(μeff= 2.98, 1; 2.96, 2; 2.92, 3). With 2-acetylthiophene-N1-substituted thiosemicarbazones, {(C4H3S)-C2(CH3)N3-N2H–C1(S)N1HR2, R2= CH3, HattscN–Me; C2H5, HattscN–Et; C6H5, HattscN–Ph}, N3, S chelated low spin transsquare planar complexes, {[Ni(κ3-O, N3, S-attscN–R2)2], R2= CH3, 4; C2H5, 5; C6H5, 6} with pendant thiophene rings have been obtained. The bigger sized sulfur atoms of the thiophene rings form short intramolecular contacts with the deprotonated hydrazinic nitrogen atoms (SN2) inhibiting its lability for possible coordination to nickel(ii). Complexes have one independent molecule (1) or two independent molecules (2, 3) in their respective crystal lattices. The simultaneous presence of methyl groups at the C2and N1atoms of 2-acetylthiophene-N1-methylthiosemicarbazone (HattscN–Me) have facilitated the binding of triphenylphosphine in three-coordinate copper(i) halide complexes, [CuX(η1-S-HattscN–Me)(Ph3P)] (X, Br, 7; Cl, 8), which represent an unusual donor set of ligands, namely, triphenylphosphine, sulfur of a thio-ligand and a halide. [ABSTRACT FROM AUTHOR]