Synthesis and spectral characterization of zinc(II) complexes of N(4)-substituted thiosemicarbazone derived from salicylaldehyde: Structural study of a novel –OH free Zn(II) complex

Latheef, Leji; Manoj, E.; Kurup, M.R. Prathapachandra

doi:10.1016/j.poly.2007.05.023

Cited by 45 publications

(14 citation statements)

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“…2,2′‐Bipyridine and dmbipy have yielded distorted trigonal‐bipyramidal Cu II complexes [CuL(L′)] (L′ = dmbipy, L is an O , N , S ‐chelating dianion; R 1 = 2‐HO‐C 6 H 4 , R 2 = H, R 3 = Ph, cycohexyl; L′ = bipy, R 1 = 2‐HO‐C 6 H 4 , R 2 = H, R 3 = Ph, Me) 9,10,44. Likewise, Zn II has formed a five‐coordinate complex [ZnL(bipy)] (R 1 = 2‐HO‐C 6 H 4 , R 2 = H, R 3 = cycohexyl) 11. In contrast, in the absence of bipyridines, bis(thiosemicarbazone) ligands have formed mononuclear complexes with various metal centers with octahedral (Zn II , Cd II ,25 and Ni II )33, square‐pyramidal (Zn II ,25,28 Hg II ,25 Ga III , and In III ),26 or square‐planar (Ni II , Cu II , and Zn II ) geometries 27,30,31.…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2013

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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.

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Section: Resultsmentioning

confidence: 99%

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

et al. 2013

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“…They have been evaluated over the last 50 years as antiviral, antibacterial, and anticancer therapeutics, and biological activities of them are a function of parent aldehyde or ketone moiety [2][3][4][5][6][7]. Thiosemicarbazone is an important group of multidentate ligands and usually coordinates with the metal through the imine nitrogen and sulfur atom [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Synthesis, spectroscopic characterization, crystal structures, and theoretical studies of (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone

et al. 2010

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Two thiosemicarbazones, (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone (24-MBTSC (1)) and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone (25-MBTSC (2)), derived from 2,4-dimethoxybenzaldehyde and 2,5-dimethoxybenzaldehyde, respectively, with thiosemicarbazide have been synthesized and their structures were characterized by elemental analyses, FT-IR, 1 H NMR spectroscopy, and X-ray single-crystal diffraction analysis. Molecular orbital calculations have been carried out for 1 and 2 by using an ab initio method (HF) and also density functional method (B3LYP) at 6-31G basis set. Compound 1 crystallizes in the monoclinic system, space group P2 1 /c, with a = 8.1342(5) Å , b = 18.1406(10) Å , c = 8.2847(6) Å , b = 109.7258(17)°, V = 1150.75(12) Å 3 , and Z = 4, whereas compound 2 crystallizes in the orthorhombic system, space group Pbca, with a = 11.0868(6) Å , b = 13.1332(6) Å , c = 15.9006(8) Å , V = 2315.2(2) Å 3 , and Z = 8. The compounds 1 and 2 displays a trans-configuration about the C=N double bond.

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“…We explored the binding of this molecular switch to Zn II , which has been shown to bring about CCD in RCs, CDFs, and the deprotonation of hydrazones, [8] to discern whether the deprotonation process could be useful in activating the molecular rotor.…”

mentioning

confidence: 99%

“…As it happens, the coordination of transition metals to hydrazones can lead, in certain cases, to N À H deprotonation. [8] With this possibility in mind, we set out to develop a new switching mechanism that takes advantage of the CCD process.…”

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Switching through Coordination‐Coupled Proton Transfer

Robbins

Aprahamian

2011

Angew Chem Int Ed

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The binding of transition metals, such as Zn 2+ , Ni 2+ , and Cd 2+ , with protein residues often leads to proton displacement. [1] This process occurs, for example, in the reaction centers (RCs) of photosynthetic bacteria, [2] and leads to conformational changes and modification of the pK a values of the surrounding amino acid residues. These changes eventually slow down the photosynthetic process. A similar deprotonation event also takes place in cation-diffusion facilitators (CDFs), in which the coordination-coupled deprotonation (CCD) provides the energetic basis for metal efflux.[3] The CCD process has considerable potential for molecular switches, [4] as it opens the way to a new and far-reaching switching mechanism in which acid modulations [5] can be brought about without the addition of protons.[6] This possibility could be of interest, for example, in cases in which molecular switches need to be activated under mild or neutral conditions. The CCD process in RCs and CDFs is associated with metal binding to histidine residues. Therefore, NÀH-containing molecular switches, such as the pH-activated hydrazone-based rotary switches [7] that we have been developing, might be suitable for mimicking this bioinorganic process. As it happens, the coordination of transition metals to hydrazones can lead, in certain cases, to N À H deprotonation.[8] With this possibility in mind, we set out to develop a new switching mechanism that takes advantage of the CCD process.We recently reported the four-step pH-activated switching cycle of a tristable hydrazone-based molecular switch (QPH) with a quinolinyl group as the stator and an ethyl 2-pyridylacetate derivative as the rotor.[7b] This molecular switch can be viewed as a tridentate ligand that can accommodate a transition metal by coordination with either the pyridine or carbonyl moiety in the rotor, the quinolinyl group in the stator, and the imine or N À H nitrogen atoms in the axle. We explored the binding of this molecular switch to Zn II , which has been shown to bring about CCD in RCs, CDFs, and the deprotonation of hydrazones, [8] to discern whether the deprotonation process could be useful in activating the molecular rotor.The UV/Vis spectrum of QPH in CH 3 CN shows an absorption maximum at l max = 393 nm (Figure 1). Upon titration with zinc(II) perchlorate (Zn(ClO 4 ) 2 ), the absorption maximum shifted bathochromically with an accompanying hyperchromic change that reached saturation at 8 equivalents of Zn 2+ (l max = 452 nm). This shift in UV/Vis absorption is an indication that Zn 2+ coordinates strongly with QPH. A Job plot (see Figure S4 in the Supporting Information) derived from the UV/Vis spectra shows a vertex around 0.65, which suggests a 2:1 binding stoichiometry between QPH and Zn 2+ .[9] The fact that no isosbestic points were observed during the UV/Vis titrations indicates that more than two chromophoric species are involved in the process, and thus the binding stoichiometry cannot be 1:1. Binding constants were determined as K 1 = 5.7 10 5 m ...

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Synthesis and spectral characterization of zinc(II) complexes of N(4)-substituted thiosemicarbazone derived from salicylaldehyde: Structural study of a novel –OH free Zn(II) complex

Cited by 45 publications

References 38 publications

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

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

Synthesis, spectroscopic characterization, crystal structures, and theoretical studies of (E)-2-(2,4-dimethoxybenzylidene)thiosemicarbazone and (E)-2-(2,5-dimethoxybenzylidene)thiosemicarbazone

Switching through Coordination‐Coupled Proton Transfer

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