The Effect of C‐2 Substituents of Salicylaldehyde‐Based Thiosemicarbazones on the Synthesis, Spectroscopy, Structures, and Fluorescence of Nickel(II) Complexes

Abstract

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.

Synthesis, structure investigation and biological evaluation of 2-thiophene N(4)-phenylthiosemicarbazone and its three metal derivatives

“…In the past few decades, many transition metal complexes likely Co(II) [17], Ni(II) [18][19], Cu(II) [20], Zn(II) [21], Pd(II) [22][23][24], Ag(I) [25], Au(I) [26] and Pt(II) [26] related to thiosemicarbazones have been prepared and their cytotoxic activities have been investigated using different cell line cultures. However, the mechanism of action is still controversial in many respects and has not been completely identified including ribonucleotide reductase inhibition, metal dependent radical damage, DNA binding, and inhibition of protein synthesis, etc.…”

Synthesis, Structural Characterization, and Biological Application of p-[N,N-bis(2-chloroethyl) Aminobenzaldehyde Thiosemicarbazone and Its Nickel (II) Complex

“…[1][2][3][4][5] Though the versatility of thiosemicarbazone ligands for binding and deprive cells of essential metal ions has been well established, this can be valid for tridentate (NNS donor, must to act as chemotherapeutic agents) ligands, with their high formation constants, but it is in striking contrast with the fact that the metal complexes are systematically more active than the ligands by themselves. Recently, the structural and biological activity of substituted thiosemicarbazone derived from p-fluorobenzaldehyde, [6] salicylaldehyde, [7][8][9] 2-hydroxy-1-naphthaldehyde, [10] thiophene-2,3-dicarboxaldehyde, [11] and p-[N,N-bis(2-chloroethyl)amino]benzaldehyde [12,13] also supports the synergic activity of the complex against various biological samples than the corresponding free thiosemicarbazone. As a part of continuing interest in this area of research, we have investigated coordination behavior of a new square planar nickel(II) complex of simple thiosemicarbazone and characterized it by using spectral techniques.…”

Stabilization of CuII–I Bonds Using 2‐Benzoylpyridine Thiosemicarbazones – Synthesis, Structure, Spectroscopy, Fluo­rescence, and Cyclic Voltammetry

“…[42] For example, copper(II) halides (Cl/Br) with neutral thiosemicarbazones involved the deprotonation of the -N 2 H moiety to form copper(II) complexes (Scheme 4), as represented in Equation (1). The resulting complexes have anionic thiosemicarbazone ligands and are either four-coordinate square-planar {Cu II X(NNS)} complexes (Scheme 4, structure IV), [24,26,36,38,[42][43][44][45][46][47] or five-coordinate square-pyramidal complexes with bridging halogen or sulfur atoms and {Cu II X(μ-S) 2 NN} (Scheme 4, structure V) [24] and {Cu II (μ-X) 2 NNS} (Scheme 4, structure VI; X = Cl or Br in IV-VI) coordination cores. [45] On the other hand, the reactions of thiosemicarbazones with copper(I) …”

“…with thiosemicarbazones and bipyridine or phenanthroline coligands displayed similar fluorescent behavior; however, the much higher emission intensity (FI) was attributed to the coligands. [32][33][34][35][36] The cyclic voltammograms of the ligands and complexes in acetonitrile have been recorded (Table 4) gands. Complexes 3, 6, and 9 with coordinated chlorido ligands showed only oxidation responses at E a = 0.756, 0.744, and 0.750 V, respectively, which are attributed to irreversible electrochemical behavior ( Figure 13).…”