Four cis-dioxomolybdenum complexes of general formula [MoO2(Ln)EtOH] (n = 1-4) and one oxomolybdenum(IV) complex [MoO(L4)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh3. The complexes are characterized by elemental analysis, electronic spectra, IR, 1H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole -N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO5 donor environment. © 2006 Elsevier Ltd. All rights reserved.

S GUPTA

A K BARIK

S PAL

A HAZRA

S ROY

R J BUTCHER

S K KAR

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Polyhedron

Reaction of 2 equiv. amount of copper(II) nitrate hexahydrate with 1 equiv. of 5-methyl-1-pyridin-2-yl-1H-pyrazole-3-carboxylic acid (PyPzCA) in presence of triethyl amine base afforded a 1D coordination polymeric compound [Cu 2(PyPzCA)2(H2O)3(NO 3)]NO3·H2O (1). Whereas, the same reaction when repeated with 1-(4,6-dimethyl-pyrimidin-2-yl)-5-methyl-1H- pyrazole-3-carboxylic acid (PymPzCA) instead of PyPzCA, a mononuclear compound [Cu(PymPzCA)]·2H2O·NEt3 (2) is formed. Both the complexes are crystallographically characterized. In 1, both the copper atoms (Cu1 and Cu2) have distorted square pyramidal geometry with N 2O3 chromophore while, in 2, the central copper atom has a distorted trigonal bipyramidal geometry with N4O chromophore. Complex 1, is a 1D coordination polymer where the metal centers being far apart and are involved in a weak ferromagnetic interaction which is quite unexpected. © 2011 Elsevier Ltd. All rights reserved.

A 1D Cu(II) coordination polymer exhibiting ferromagnetic interactions and a mononuclear Cu(II) complex of substituted pyrazole carboxylic acids: Synthesis, characterization and crystal structure

Ten new binuclear singly oxo-bridged molybdenum complexes (complexes 1-10) were prepared using five pyrimidine derived Schiff base ligands and two Mo(V) precursors (NH4)2MoOCl5 and (NH 4)2MoOBr5. The ligands are prepared by the condensation of 4,6-dimethyl 2-hydrazino pyrimidine with salicylaldehyde (for HL1), o-hydroxy acetophenone (for HL2) and substituted salicylaldehydes (for HL3, HL4 and HL5) respectively. These ligands are already reported as good donors for Mo(VI) state. The μ-oxo Mo(V) complexes reported here bears a distorted octahedral geometry around each Mo atom with either N2O2Cl or N 2O2Br chromophores. Fine variations in the spectroscopic behaviour of the complexes are observed in accordance with the varying electron donating properties of the ligands. All the complexes are unstable in solution and X-ray quality crystal of complex 1 could be isolated. All the complexes are characterized by IR and UV-Vis spectra.

Fulltext

Journal of Chemical Sciences

Synthesis, characterization and spectrochemical studies on a few binuclear Î¼-oxo molybdenum(V) complexes of pyrimidine derived Schiff base ligands

The varying coordination modes of the title ligand, L [5-methyl-1-(pyridin- 2-yl)-N′-[pyridin-2-ylmethylidene]pyrazole-3-carbohydrazide] towards the different metal centers is reported by preparation and characterization of Cu(II), Zn(II) and Cd(II) complexes, [Cu(L)NO3.H2O] (NO3) (1) [Zn(L)2](ClO4)2· 2DMF (2) and [Cd(L)(I)2] (3) respectively. In 1, the neutral ligand serves as tetradentate 4 N donor where both pyridine and pyrazole nitrogen atoms of pyridyl-pyrazole part are coordinatively active, leaving the carbonyl oxygen of the carbohydrazide part inactive. The same pyridine and pyrazole N atoms remain abstained from the coordination process towards the Zn(II) and Cd(II) metal centers. For 2 and 3 the ligand behaves as a tridentate NNO donor where the two nitrogen atoms come from azomethine, pyridine of pyridine-2-carbaldehyde parts and O from carbonyl oxygen atoms (carbohydrazide part). The complex 1 and 2 are distorted octahedral while complex 3 adopts distorted square pyramidal geometry. All the complexes are X-ray crystallographically characterized. © 2010 Elsevier Ltd. All rights reserved.

Syntheses, characterization, X-ray crystal structures and emission properties of copper(II), zinc(II) and cadmium(II) complexes of pyridyl-pyrazole derived Schiff base ligand - Metal selective ligand binding modes

Dioxomolybdenum(VI) complexes [MoO2(B1)H2O] (1), [MoO2(B2)EtOH] (2), [MoO2(B3)EtOH] (3) and [MoO2(B4)EtOH] (4) were synthesized using the Schiff base ligands H2B1(previously reported), H2B2, H2B3 and H2B4, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H2B1, H2B2 and H2B3 exhibit fluorescent emissions, and the most intense emission was obtained for H2B3. H2B4 is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H2B1, i.e. complex 1, shows quenched emission compared to H2B1. Again when Cu2+, Co2+ or Ni2+ ions are added to a solution of 1, in each case a new complex of Cu2+ Co2+ or Ni2+ is formed in solution and further quenching was observed. However, with Zn2+ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H2B1 (complex 5), produced by adding equivalent amount of Cu2+ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh3 produces complex [MoO(B3)CH3CN] (6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, 1H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H2B2 and H2B3, have been crystallographically characterized. © 2009 Elsevier Ltd. All rights reserved.

Modulation of fluorescence emission of 1-(2-pyridyl) pyrazole derived Schiff base ligands by exploiting their metal ion sensitive binding modes

The syntheses of dioxomolybdenum(VI) complexes were attempted using the Schiff base ligands HL1 and HL2. The ligands were prepared by the condensation of 4,6-dimethyl 2-hydrazino pyrimidine with salicyl aldehyde (for HL1) and o-hydroxy acetophenone (for HL2). When MoO2(acac)(2) was used as a metal precursor, HL1 yielded the normal ligand exchange product [MoO2(L-1)Cl] (1) in a medium acidified by HCl. However, instead of the normal product, HL2 produced two bis chloro dioxomolybdenum(VI) complexes [MoO2(L-3)Cl-2] (2) and [Mo2O5(L-3)Cl-2] (3) in the same reaction medium. Here, L-3 is a bidentate neutral ligand 2-(3,5-dimethyl-1-pyrazolyl) 4,6-dimethyl pyrimidine, which is afforded by a transformation of the used ligand. This ligand transformation reaction is probably triggered by molybdenum mediated C=N bond cleavage in the hydrazone part of HL2 followed by cyclization with acetylacetone released from the metal precursor. Again, when MoO2(acac)(2) was reacted with another related ligand H2L'(1), a bis salicyl hydrazone of 2,4-dihydrazino pyrimidine, in acidic medium, [MoO2(L-4)Cl] (4) was produced as the only product. Here, also a similar ligand transformation, but only to a partial extent, leads to the formation of the ligand HL4, the salicyl hydrazone of 2-hydrazino-4-(3,5-dimethyl-1-pyrazolyl) pyrimidine. HL4, thus produced in the reaction medium binds in a monoanionic fashion to the MoO22+ core to form the complex [MoO2(L-4)Cl] (4). The complexes are characterized by elemental analyses, electronic spectra, IR, H-1 NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1, 2, 3 and 4, as well as the ligand HL2, have been crystallographically characterized in order to probe into the structures and the ligand transformation process in a comprehensive way. (C) 2009 Elsevier Ltd. All rights reserved.

Molybdenum(VI) complexes of a few pyrimidine derived ligands and the study of metal mediated C = N bond cleavage resulting in ligand transformation during complex formation

A number of oxomolybdenum (VI) and (IV) complexes with potentially tridentate ONS donor Schiff bases of S-benzyl and S-methyl dithiocarbazates with salicylaldehyde have been synthesized. The Mo(VI) complexes are cis-dioxo, MoO2L (where L= H2L1 and H2L 2) with one coordination site available for substrate binding. The Mo(IV) complexes, MoOL, are derived from the corresponding Mo(VI)-dioxo complexes by oxo abstraction with PPh3. The complexes were characterized by elemental analysis, UV, IR and 1H NMR spectroscopy, magnetic susceptibility measurement, molar conductivities in solution and by cyclic voltammetry. Two of the complexes MoO2L1 and MoO2L2 were crystallographically characterized. The structures reveal that the molybdenum acceptor center is present in a distorted octahedral NO4S donor environment. © 2004 Published by Elsevier Ltd.

Synthesis, characterization and crystal structure of oxomolybdenum (VI) and (IV) complexes of some tridentate ONS donor ligands

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) &amp; 1.954(5) Å and 1.903(4) &amp; 1.916(5) Å in ligand A &amp; B, respectively where as that of Co - S (thiolato) is 2.217(2) and 2.255(2) Å 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. © 1997 Elsevier Science Ltd.

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

Dioxomolybdenum(VI) and -tungsten(VI) complexes with tetradentate aminobis(phenol)s

Anti-Corrosion Methods and Materials

Bruker AXS announces SMART BREEZE™

Dioxomolybdenum(VI) complexes with tri- and tetradentate aminobis(phenolate)s

Oxomolybdenum(VI) and (IV) complexes of pyrazole derived ONO donor ligands - synthesis, crystal structure studies and spectroelectrochemical correlation

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ISSN	0277-5387