Metal derivatives of N1-substituted thiosemicarbazones: Synthesis, structures and spectroscopy of nickel(II) and cobalt(III) complexes

Reactions of nickel(II) and cobalt(II) salts with various N1-substituted thiosemicarbazones [R1R2C2N3–N2H–C1(S)–N1HR3, H2L; R1 = C6H5-, R2 = H, H2L1(R3 = Me); H2L2(R3 = Ph), R1 = 2-OHC6H4-, R2 = H, H2L3(R3 = Me), H2L4(R3 = Et), H2L5(R3 = Ph); R2 = Me, H2L6(R3 = Me), R2 = Me, H2L7(R3 = Et) and R2, R3 = H, Me, H2L8(R1 = C4H3S), H2L9(R1 = C4H3O)] are described. Reactions of Ni(OAc)2 with the ligands having R1 as phenyl group at C2 carbon (H2L1, H2L2) gave complexes, [Ni(κ2-N3, S-HL)2] (HL− = HL1, 1; HL2, 2). Other ligands with R1 as 2-hydroxyphenyl groups, namely, H2L3–H2L7, with Ni(OAc)2 yielded rust colored compounds, {Ni(κ3-O, N3, S–L)} (L2− = L3–L7) which after the addition of PPh2-CH2-PPh2 yielded dinuclear, [Ni2(κ3-O, N3, S–L)2(μ-P, P–PPh2–CH2–PPh2)] (L2− = L3, 3; L4, 4; L5, 5) and mononuclear, [Ni(κ3-O, N3, S–L)(κ1-P–PPh2–CH2–PPh2)] (L2− = L6, 6; L7, 7) complexes. Likewise, {Ni(κ3-O, N3, S-L5} with 2-phenylpyridine(2-Phpy) has yielded a mononuclear complex, [Ni(κ3-O, N3, S–L5)(κ1-N-2-Phpy)] 8. The geometry around Ni metal center can be formally described as square planar in each of complexes 1–8. Reactions of CoCl2 with H2L8 and H2L9 involved oxidation of CoII to CoIII and yielded octahedral complexes, [Co(κ2-N, S–HL)3] (HL− = HL8, 9; HL9, 10).

Graphical abstractThiosemicarbazones, R1R2C2–N3–N2H–C1(S)–N1HR3, with R1 as phenyl group at C2 carbon have formed bis square planar NiII complexes (1, 2) while with 2-hydroxyphenyl group formed mononuclear square planar (6–8) and dinuclear complexes (3–5). The variation of substituents (R2) at C2 carbon of 2-hydroxyphenyl (R1) based thiosemicarbazones, has changed the coordination behavior of PPh2–CH2–PPh2, For R2 = H, it shows bridging (4) and for R2 = Me, it shows monodentate (7) coordination behavior. Furan- and thiophene-based thiosemicarbazones have formed tris octahedral CoIII complexes (9, 10).Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Benzaldehyde thiosemicarbazones have formed only trans square planar N3, S-chelated nickel(II) complexes. ► The substituents at C2 carbon of thiosemicarbazones alter coordination modes of PPh2–CH2–PPh2. ► Octahedral tris [CoL3] complexes of thiophene- and furan-2-carbaldehyde-thiosemicarbazones represent new examples.