Nityananda Saha

Spectroscopic, structural and antibacterial properties of copper(II) complexes with bio-relevant 5-methyl-3-formylpyrazole N(4)-benzyl-N(4)-methylthiosemicarbazone

The coordination behaviour of the title ligand, 5-methyl-3-formylpyrazole N(4)-benzyl-N(4)-methylthiosemicarbazone(HMPz4BM), is reported with solid state isolation of copper(II) complexes, [Cu(HMPz4BM)X2] (X = Cl, Br, NO3, ClO4 and BF4) which have been spectroscopically and structurally characterised. I.r. data for the free ligand and its Cu(II) complexes indicate that HMPz4BM exhibits a neutral NNS tridentate function via the pyrazolyl nitrogen(tertiary), azomethine nitrogen and thione sulphur. Electronic spectral data are suggestive of a square pyramidal environment for the seemingly pentacoordinated Cu(II) species. E.s.r parameters (RT and LNT) of the reported copper(II) complexes are indicative of a dxx2–y2 ground state for the reported species. Cyclic voltammograms of Cu(II) complexes show a quasireversible CuII/CuIII couple and also an irreversible CuII/CuI couple. X-ray crystallography of a representative species, [Cu(HMPz4BM)(NO3)2] (C2/c, monoclinic ), has unambiguously documented the conjectural findings from i.r. data that coordinating sites of the title ligand are pyrazolyl (tertiary)nitrogen, azomethine nitrogen and the thione sulphur (NNS); and the oxygen of one of the nitrate ions has occupied the basal plane; the fifth coordination position has been occupied by the oxygen of another nitrate ion in a square pyramidal geometry. The antibacterial properties of the ligand and its copper(II) complexes studied on microorganism, Staphylococcus aureus have pointed out that most of the complexes have higher activities than that of the free ligand.

Synthesis and spectroscopic characterisation of cobalt(III) and nickel(II) complexes with 5-methyl-3-formylpyrazole-N(4)-dibutylthiosemicarbazone (HMPzNBu2): X-ray crystallography of [Co(MPzNBu2)2]NO3·H2O (I) and [Ni(HMPzNBu2)2](ClO4)2 (II)

Abstract New cobalt(III) and nickel(II) complexes of 5-methyl-3-formylpyrazole-N(4)-dibutylthiosemicarbazone (HMPzNBu2), [Co(MPzNBu2)2]X·H2O and [Ni(HMPzNBu2)2]X2 (X=Cl, Br, ClO4, BF4 and NO3), respectively, have been synthesised and physico-chemically characterised by magnetic measurements (polycrystalline state), 1H NMR [for Co(III) complexes], electronic and IR spectra. The reported species are all cationic complexes, behaving as 1:1 [for Co(III) complexes] and 1:2 [for Ni(II) complexes] electrolytes in MeOH. Electronic spectral features of the diamagnetic Co(III) and paramagnetic Ni(II) species classify them as six-coordinate distorted octahedral ones. IR spectra (4000–200 cm−1) indicate a monoprotic tridentate (NNS) function of HMPzNBu2 coordinating to the central Co(III) via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulfur atom; while for the Ni(II) complexes, HMPzNBu2 behaves as neutral NNS tridentate, bonding to Ni(II) through the pyrazolyl iminic nitrogen, azomethine nitrogen and thioketo sulfur. 1H NMR data (in DMSO-d6 at 300 MHz) for the uncomplexed ligand and those of its Co(III) complexes are commensurate with the propositions of bonding sites envisaged from IR data. X-ray crystallographic data of I (P 1 , triclinic) and of II (C2/c, monoclinic) have authenticated CoN4S2 and NiN4S2 octahedral coordination, respectively; in both I and II; the pair of coordinating ligands are nearly orthogonal to each other with the difference that while in I, the pair of ligands are monodeprotonated, in II, the same pair of ligands are neutral.

Synthesis and spectroscopic characterisation of cobalt(III) complexes with S-benzyl dithiocarbazate of 5-methyl-3-formyl pyrazole (HMPzSB): X-ray crystal structure of [Co(MPzSB)2]Cl

Abstract The coordination mode of the title ligand, HMPzSB (synthesized for the first time and characterised by elemental analysis, mass, IR and PMR spectral parameters), is reported by solid state isolation and physicochemical identification of cobalt(III) complexes, [Co(MPzSB)2]X (X = Cl, ClO4 and BF4). Electronic spectral features of these diamagnetic CoIII species classify them as six-coordinate distorted octahedral ones. IR spectra (4000-200 cm−1) of HMPzSB and its complexes are indicative of an uninegative tridentate NNS function of the title ligand through the Pyrazolyl (2N) nitrogen, azomethine nitrogen and thiolato sulphur atom. 1H-NMR data (in d6-DMSO at 300 MHz) of the uncomplexed ligand and its CoIII species are commensurate with the tridenticity (NNS) of the deprotonated form of HMPzSB. X-ray crystallographic studies of [Co(MPzSB)2]Cl has authenticated that the geometry of the species is distorted octahedral, as envisaged, with the two deprotonated primary ligand systems (MPzSB−). The CoN (azomethine) and CoN (pyrazolyl) bond lengths are 1.898(4) & 1.954(5) A and 1.903(4) & 1.916(5) A in ligand A & B, respectively where as that of CoS (thiolato) is 2.217(2) and 2.255(2) A in the two ligands. The extended planarity of the dithiocarbazate moiety and the pyrazolyl ring of the primary ligand system are maintained because of the ligation phenomenon to CoIII.

Synthesis, characterisation and coordinating properties of a new pyrazole-derived thiosemicarbazone, a potential antiviral agent: Co(III), Ni(II) and Cu(II) complexes of neutral and deprotonated 5(3)-methylpyrazole-3(5)-aldehydothiosemicarbazone

Abstract The title compound (abbreviated as MPzATSH) has been synthesised and physico-chemically (IR, PMR and mass spectrum) characterised for the first time. The ligational behaviour of the thiosemicarbazone has been demonstrated by isolation and characterisation of its complex species with Co(III), Ni(II) and Cu(II) with different counterions. Magnetic and spectral features indicate Co(MPzATS)2X (X = Cl, Br, ClO4, BF4, NO3 or 1 2 SO4) as the diamagnetic octahedral species with the ligand in the deprotonated thiol form, while Ni(MPzATSH)2X2 and Cu(MPzATSH)X2 are proposed as octahedral complexes with the ligand in the neutral “thione” form.

Metal complexes of pyrimidine-derived ligands—III: Tris-complexes of Co(III), Ni(II) and Cu(II) fluoroborates, perchlorates and iodides with 3,5-dimethyl-1-(4′,6′-dimethyl-2′-pyrimidyl) pyrazole, a potential anti-tumour agent

Tris-complex of Co(II), Ni(II), Cu(II) fluoroborates, perchlorates and iodides with the title ligand conform to the composition M(DPymPz)3X2, nH2O [M = Co(II), Ni(II), Cu(II); X = ClO4, BF4 and I, n = 0,2]. Physico-chemical characterisations of the complex species have been made from electronic and vibrational spectra, magnetic susceptibility measurements in the solid state and conductivity measurements in solution. Electronic spectral features together with the corresponding ligand field parameters suggest an overall octahedral environment for the pyrazolyl nitrogen (tertiary) and one of the pyrimidyl nitrogens as bonding sites in forming these complexes while the anion (X) retains its identity (as in free form) in the said species.

Coordinating properties of a pyrazole-derived carbohydrazide, a potential ligand of biological importance: Ni(II) complexes of neutral and deprotonated 5(3)-methylpyrazole-3(5)-carbohydrazide

Abstract Ni(II) complexes of 5(3)-methylpyrazole-3(5)-carbohydrazide (MPCH) and its deprotonated anion (MPC) have been isolated and characterised in the solid state. Magnetic and electtronic spectral features classify both the bis-complexes Ni(MPCH)2X2·2H2O and the mono-chelates Ni(MPC)X·2H2O[X = Cl, Br, I, NO3, BF4, ClO4, SCN or 0.5SO4] as grossly octahedral ones. The IR spectra indicate that in the bis-derivatives the ligand is bidentate through the pyrazolyl-ring nitrogen and the kenotic oxygen of the hydrazide residue and that in the monochelates, the deprotonated ligand functions primarily as a (ONN) tridentate finally forming polymeric quasi-octahedral species through involvement of additional donor site (amide-nitrogen) of the hydrazide residue; the counterion (X) is coordinated in majority of the complex species.

Synthesis and structural characterisation of new iron(III) complexes with biologically relevant pyrazolyl thiosemicarbazones

Abstract New iron(III) complexes of 5-methyl-3-formylpyrazole-N(4)-dipropylthiosemicarbazone (HMPzNPr2) and 5-methyl-3-formylpyrazole-N(4)-dibutylthiosemicarbazone (HMPzNBut2), [Fe(MPzNPr2)2]NO3·H2O (I) and [Fe(MPzNBut2)2]ClO4·H2O (II), respectively, have been synthesised for the first time and physico-chemically characterised by magnetic measurements (polycrystalline state), electronic, IR and EPR spectra. Both are cationic complexes containing two monodeprotonated tridentate ligands with NNS donor sites and an anionic counterpart; the complex species behave as 1:1 electrolytes in MeOH. IR spectra (4000–200 cm−1) indicate the co-ordination to central iron(III) via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atom. EPR data (RT and LNT) reveal the presence of a spin-paired iron(III) cation with d2xz d2yz d1xy configuration. X-ray crystallographic data of I and II (both P1, triclinic) have authenticated a FeN4S2 octahedral co-ordination in both the complex ions, as envisaged from spectral data. In both species, the two azomethine nitrogen atoms are trans to each other, while the pyrazolyl ring nitrogen atoms and the thiolato sulphurs are in cis positions.

Synthesis and spectroscopic characterisation of copper(II) complexes with 5-methyl-1-(2′-pyridyl) pyrazole-3-carboxamide (MPyPzCA): X-ray crystal structure of [Cu(MPyPzCA)2(H2O)](ClO4)2

Abstract The coordination mode of the title ligand, MPyPzCA (synthesised for the first time and characterised by elemental analyses, mass, IR and PMR spectral parameters), is reported by solid state isolation and physicochemical identification of copper(II) complexes, Cu(MPyPzCA)2X2.H2O (X=Cl/Br/NO3/ClO4). Magnetic and electronic spectral features classify the reported complexes as six coordinate distorted octahedral ones. IR spectra (4000–200 cm−1) of MPyPzCA and its complexes indicate different denticity of the two ligand moities namely neutral bidentate function through pyrazolyl 2N and pyridyl 1′N of one ligand (A) and the neutral tridentate behaviour through pyrazolyl 2N, pyridyl 1′N and the amidic oxygen of the second ligand system (B). The sixth apical coordination site is occupied by a water molecule in the perchlorate complex (as evident by X-ray data) or by the counter ion, X (X=Cl/Br/NO3). The electrochemical studies demonstrate easy oxidative nature of Cu(II) in the reported species. X-ray crystallographic studies of the perchlorate complex, [Cu(MPyPzCA)2(H2O)](ClO4)2, (Pna21, orthorhombic), has substantiated the conjecture that the geometry is distorted octahedral. The Cu-N (pyrazolyl) and Cu-N (pyridyl) bond lengths are 2.001(3) and 1.969(3) A and 2.020(4) and 2.206(4) A in the ligand systems, A and B. respectively; Cu-O (amidic oxygen) for ligand system B and Cu-O (water) bond lengths are 2.783(3) and 2.010(3) A, respectively. The crystal structure is highly stabilised through extensive hydrogen bonding.

Metal complexes of pyrimidine-derived ligands. VII. Palladium(II), platinum(II) and rhodium(III) complexes with 3,5-dimethyl-1 -(4′, 6′-dimethyl-2′-pyrimidyl)pyrazole, a potential anti-cancer agent

Abstract Using 3,5-dimethyl-1-(4′,6′-dimethyl-2′-pyrimidyl)pyrazole (DPymPz) as a coordinating ligand, palladium(II), platinum(II) and rhodium(III) complexes of the type [M(DPymPz)X 2 ] (M = Pd(II), X = Cl, Br, I, SCN, ClO 4 , NO 2 , NO 3 ; M = Pt(II), X = Cl, Br, SCN, NO 2 ) and [Rh(DPymPz) 2 X 3 ] (X = Cl, Br, I) habe been isolated in the solid state and characterized on the basis of analytical, magnetic and spectral (diffuse reflectance, UV-Vis, IR and 1 H NMR) properties, together with powder X-ray diffraction studies. The Pd(II) and Pt(II)complexes are square-planar as expected and the Rh(III) species have pseudo-octahedral geometry. The calculated ligand field parameters are in favour of the proposed stereochemistry of the complexes. IR data point out the pyrazolyl nitrogen (tertiary) and one of the pyrimidyl nitrogens of DPymPz as bonding sites in forming these complexes.

Synthesis and spectroscopic studies of cobalt(III) complexes with 5-methyl-3-formylpyrazole-N(4)-diethylthiosemicarbazone (HMPzNEt2): X-ray crystallography of [Co(MPzNEt2)2]ClO4·2H2O (I) and [Co(MPzNEt2)2]BF4·2H2O (II)

Abstract The co-ordination mode of the title ligand, HMPzNEt2 (synthesised for the first time and characterised by elemental analyses, mass, IR and 1H NMR spectral parameters), is reported by solid state isolation and physico-chemical identification of cobalt(III) complexes, [Co(MPzNEt2)2]X·2H2O (X=Cl, Br, ClO4, BF4 and NO3). Electronic spectral features of these diamagnetic Co(III) species classify them as six co-ordinate distorted octahedral ones. IR spectra (4000–200 cm−1) indicate that the Co(III) complexes have monoanionic tridentate NNS co-ordination of the title ligand through the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulfur atoms. 1H NMR data (in CDCl3 at 300 MHz) for the uncomplexed ligand and those of its Co(III) complexes are commensurate with the NNS function of the monodeprotonated HMPzNEt2, as ascertained from downfield shift of the relevant protons adjacent to the bonding sites. X-ray crystallographic data of I and II (both P1, triclinic) have authenticated a CoN4S2 octahedral co-ordination in both the complex ions.