Synthesis, characterization and properties of nickel(II)pseudohalide complexes of types [Ni(pap)₂(X)₂], [Ni(pap)₂(X)]₂(Y)₂ and [Ni(pap)(N₃)₂]_n [pap=2-(phenylazo)pyridine; X=N₃^ˉ, NCSˉ, NCOˉ; Y=ClO₄ˉ, PF₆ˉ]

2474-2479Three different types of nickel(II)pseudohalide compounds, viz. red-brown [Ni(pap)2(X)2] [pap=2-(phenylazo)pyridine; X=N3ˉ, 1; NCSˉ, 2; NCOˉ 3], greenish-brown [Ni(pap)2(X)]2(Y)2  (X= N3ˉ , Y=ClO4ˉ, 4; X= N3ˉ  , Y=PF6ˉ , 5; X=NCOˉ, Y=ClO4ˉ, 6; X= NCOˉ, Y= PF6ˉ, 7) and brownish-green, [Ni(pap)(N3)2]n (8) have been prepared and characterised on the basis of microanalytical, spectroscopic, magnetic, electrochemical and other physicochemical properties. In IR, v(N=N) stretching frequency is observed at considerably lower frequencies (-1370 cm-1) than the free ligand value (1425 cm-1) indicating substantial Ni (II)→ pap π-back bonding and in electronic spectra, the MLCT bands show characteristic lower energy shifts in going from mono- to polynuclear compounds via dinuclear ones. Room temperature magnetic measurements show uniformly two-electron paramagnetism for each nickel(II) ion in these complexes. Electrochemical electron transfer study reveals nearly- reversible responses corresponding to NiIII/NiII couple in acetonitrile solutions. On the negative side of SCE, multiple ligand reductions pertaining to azo reductions are observable

Synthesis, characterisation and redox behaviour of mixed ligand complexes of osmiurn(II/III/IV)

2772-2777A group of mixed-tris chelates of osmium(II), (III) and (IV) of the general formula [OsL'L2]z+ [L' = N-((pyridin-2-yl )formylidene) aniline (pfan) or N-((pyridin-2-yl)benzylidene)aniline (pban); L = 2,2'-bipyridyl (bipy), 2-(III-tolylazo)pyridine (tapy) or quinolin-8-olate (oxin); z = 1-3] have been prepared, isolated as their perchlorates and characterised by physicochemical, magnetic and spectroscopic methods. The complexes exhibit several spinallowed and spin-forbidden charge-transfer transitions in the 1000-200 nm region. In MeCN solutions the chelates display osmium(IV)-osmium(III) and osmium(III)-osmium(II) couples in the range -0.4 to 1.6 V vs SCE. The stability of metal oxidation levels is discussed in terms of the electrochemical result s and correlated to the π-acceptor properties of these ligands. On the negative side of SCE, successive ligand reductions in bipy/tapy complexes are observed involving diimine (-N=C-C=N-)/ azoimine (-N=N-C=N-) group

Synthesis, structure and luminescence behaviour of zinc(II) complexes containing hexadentate N-donor Schiff bases

2427-2432Six hexacoordinated zinc(II) complexes of the type [Zn(L)](Y)2 [L = N-(1-pyridin-2-yl-formylidene)-N'-[2-({2-[(1-pyridin-2-ylformylidene)amino]ethyl}amino)ethyl]ethane- 1,2-diamine (pfad), Y = ClO4 (1a), Y = PF6 (1b); L = N-(1-pyridin-2-ylmethylidene)-N'-[2-({2 -I(1-pyridin-2-ylmethylidene)amino)ethyl]amino)ethyl)ethane- 1,2-diamine (pmad), Y = ClO4ˉ (2a), Y= PF6- (2b); L = N-(l-pyridin-2-ylbenzylidene)-N'-[2-({2-[(l-pyridin-2 ylbenzylidene)amino]-ethyl]amino)ethyl]ethane- 1,2-diamine (pbad), Y = ClO4ˉ (3a), Y = PF6- (3b)] have been synthesised and characterized on the basis of microanalytical, spectroscopic and other physicochemical properties. Structural analysis of 3a reveals that zinc(II) adopts a distorted octahedral environment with a ZnN6 chromophore ligated by two pyridine N atoms (N1, N1*), two imine N atoms (N2, N2*) and two amine N atoms (N3, N3*) in cis-trans-cis orientation. Spectral properties show that the other complex ions are iso-structural with the dication in 3a.</b

Synthesis, characterization and properties of nickel(II)pseudohalide complexes of types [Ni(pap)₂(X)₂], [Ni(pap)₂(X)]₂(Y)₂ and [Ni(pap)(N₃)₂]_n [pap=2-(phenylazo)pyridine; X=N₃^ˉ, NCSˉ, NCOˉ; Y=ClO₄ˉ, PF₆ˉ]

2474-2479Three different types of nickel(II)pseudohalide compounds, viz. red-brown [Ni(pap)2(X)2] [pap=2-(phenylazo)pyridine; X=N3ˉ, 1; NCSˉ, 2; NCOˉ 3], greenish-brown [Ni(pap)2(X)]2(Y)2 &nbsp;(X= N3ˉ , Y=ClO4ˉ, 4; X= N3ˉ &nbsp;, Y=PF6ˉ , 5; X=NCOˉ, Y=ClO4ˉ, 6; X= NCOˉ, Y= PF6ˉ, 7) and brownish-green, [Ni(pap)(N3)2]n (8) have been prepared and characterised on the basis of microanalytical, spectroscopic, magnetic, electrochemical and other physicochemical properties. In IR, v(N=N) stretching frequency is observed at considerably lower frequencies (-1370 cm-1) than the free ligand value (1425 cm-1) indicating substantial Ni (II)→ pap π-back bonding and in electronic spectra, the MLCT bands show characteristic lower energy shifts in going from mono- to polynuclear compounds via dinuclear ones. Room temperature magnetic measurements show uniformly two-electron paramagnetism for each nickel(II) ion in these complexes. Electrochemical electron transfer study reveals nearly- reversible responses corresponding to NiIII/NiII couple in acetonitrile solutions. On the negative side of SCE, multiple ligand reductions pertaining to azo reductions are observable

Heteroleptic tris-complexes of ruthenium(II/III) containing one bidentate Schiff base: Synthesis, characterisation and link-up of oxidation levels

1239-1244A series of mixed-tris chelates of ruthenium(II) and -(III) of general formula [RuLʹL2]z+ [Lʹ = N-((pyridin-2-yl)formylidene)aniline (pfan ), N-((pyridin-2-y l)benzylidene)aniline (pban), N((pyridin-2-yl)formylidene)benzylamine (pfba) or N-((pyridin-2-yl)benzylidene)benzylamine (pbba): L = 2,2ʹ-bipyridine (bpy), z = 2 or 3; L = 2-(m -tolylazo)pyridine (tap), z = 2] have been prepared, isolated as their perchlorates and characterised by physicochemical, magnetic and spectroscopic methods. The ruthenium (II) and rutheniun(III ) complexes, respectively exhibit several MLCT and LMCT charge- transfer transitions in the 200-900 nm region . In MeCN solutions all the compounds exhibit ruthenium(III)ruthenium(II) couple, and additionally bpy complexes show ruthenium(IV)-ruthenium(III) response. The stability of metal oxidation levels is discussed in terms of the electrochemical results and correlated to the π-acceptor properties of these ligands. On the negative side of SCE successive ligand reductions are observable involving diimine/azoimine group

Synthesis, characterisation and redox behaviour of mixed ligand complexes of osmium(II/III/IV)-phosphines

1112-1118The reaction of [OsX2 L2] [X = Cl or Br; L = 2-(m-tolylazo)pyridine (tapy), 1; L = quinolin-8-olate (oxin), 2] with tertiary phosphine (PR3 = PPh3 or PPh2Me) bases in boiling aqueous alcohol affords complexes of the types [OsX(PR3)L2]z + (L = tapy, Z = 1, 3; L = oxin, Z = 0, 5) and [Os(PR3)2 L2]n+ (L =tapy,n = 2, 4;L = oxin, n = 0, 6), which when charged isolated as their perchlorates. The osimum(IV) counterparts [OsX(PR3)-(oxin2)1+ (7) and osimum(III) species [Os(PR3)2 (oxin)2]1+ (8) of [OsX(PR3)(oxin)2] (5) and [Os(PR3)(oxin)2] (6), respectively are also stable enough for isolation by oxidation with cerium(IV). The new complexes have been characterized by spectroscopic, magnetic, electrochemical and other physicochemical results. Using 1H NMR results (δMe of tapy/PPh2Me) in selected cases the stereochemistry of OsL2 fragment in these mixed L-PR3 complexes has been proposed. The diamagnetic osmium(II) complexes display a number of spin -allowed and spin -forbidden MLCT transitions whereas LMCT bands are seen in paramagnetic osmium (III) and osmium(IV) compounds. All the complexes are electroactive and exhibit osmium (III) - osmium (II) response in MeCN solutions; additionally, oxin complexes show osmium(IV)osmium(III) couple within accessible potential window. The stability of metal oxidation levels is discussed in terms of the electrochemical results and correlated to the π-acceptor strengths of these ligands

Synthesis, structure and properties of [Co(L)(NO₃)]ClO₄.2H₂O (L = tetradentate Schiff bases): Example of chelating nitrate

1565-1570The synthesis and characterization of three mononuclear cobalt (II) complexes of the type [Co(L)(NO3 )]ClO4.2H2O [L = N,N'-(bis(pyridin -2-yl) formylidene)butane- 1 ,4-diamine (bpfd). 1 ; N,N'-(bis(pyridin -2-yl) me thylidene)butane- l, 4-diamine (bpmd). 2; and N,N' -(bis(pyridin -2-yl)benzylidene)butane-1 ,4-diamine (bpbd), 3] are described here. In IR, the presence of v(NO3) band at ~1380 cm-1 with distinct splittings is strongly suggestive of coordination of nitrate instead of its simple counter anionic view. X-ray diffraction studies of [Co(bpfd )(NO3)] ClO4.2H2O (1), has been made for the exact knowledge of its coordination sphere. Structural analysis reveals cobalt(II) centre in a distorted octahedral environment with a CoN4O2 chromophore ligated by four N atoms of the tetradentate Schiff base along with two O atoms of nitrate in a chelating fashion. The tetradenlate chelator is folded in the butylenic pan. The mononuclear units in 1 are engaged in intermulecular C-H. . O and O-H .. . O hydrogen bondings leading to a 2D sheet. Electrochemical electron transfer studies in MeCN solutions show an oxidative response presumably due to cobalt(III)-cobalt(II) couple. All the complexes display intraligand 1(π-π*) fluorescence and intraligand 3(π-π*) phosphorescence in glassy solutions (MeOH at 77 K)

Synthesis, characterization and properties of mono-, di- and polynuclear nickel(II) pseudohalide complexes containing bidentate Schiff bases. X-ray structure of [Ni(Ni,Np)₂(NCS)₂] [Ni,Np = N-((pyridin-2-yl)benzylidene) benzylamine]

9-17Three different types of nickel(II) pseudohalide compounds, [Ni(Ni,Np)₂(X)₂] [Ni,Np = N-((pyridin-2-yl)benzylidene) benzylamine; X = N₃⁻, 1; X = NCS⁻, 2; X = NCO-, 3], [Ni(Ni,Np)₂(X)]₂(Y)₂ [X = N₃⁻, Y = ClO4⁻, 4; X = N₃⁻, Y = PF6⁻, 5; X = NCO⁻, X = ClO4⁻, 6; X = NCO⁻, Y = PF6⁻, 7] and [Ni(Ni,Np)(N₃)2]n (8) have been prepared and characterized using microanalytical, spectroscopic and other physicochemical results. Single crystal X-ray study of one of the mononuclear compounds, [Ni(Ni,Np)₂(NCS)₂] (2) has been done. Structural analysis reveals that the metal center in 2 adopts a distorted octahedral geometry with an NiN6 chromophore coordinated through four N atoms of two bidentate L units and two N atoms of terminal thiocyanate in mutual cis orientation. The mononuclear units in 2 are engaged in intermolecular weak C-H…S hydrogen bonding to give a 1D chain. Electrochemical electron transfer study reveals nearly-reversible responses to NiIII/NiII couple in acetontrile solutions. High-energy intraligand 1(π-π *) fluorescence at room temperature and intraligand ³ (π-π*) phosphorescence in glassy solutions (MeOH at 77 K) are seen in all the complexes

Synthesis, structure and properties of [Cu(L)(NCO)]X (L = tetradentate schiff bases; X = ClO₄, PF₆)

1901-1905Four copper(II) complexes of the type [Cu(L)(NCO)]X (1-4) [L=N,N' -(bis(pyridin-2-yl)formylidene)butane-1 ,4-diamine (bpfd) or N,N'-(bis(pyridin-2-yl)benzylidene)butane-1 ,4-diamine (bpbd); X = ClO4, PF6] have been synthesised and characterised on the basis of microanalytical, spectroscopic, magnetic, electrochemical and other physicochemical properties. X-ray diffraction study of complex 1 (L= bpfd, X = ClO4 ) reveals copper(II) ion in a distorted trigonal bipyramidal environment through coordination of the metal centre by two pyridine N atoms and two imine N atoms of the schiff base with the fifth position occupied with N atom of terminal NCO'. The tetradentate chelator is folded in the butylenic part. I R spectra of the complexes show asymmetric and symmetric stretching vNCO vibrations at ~ 2250 and ~1320 cm-1 respectively indicating N-bonding of NCO'. Electrochemi cal electron transfer study reveals CUII-CUI reduction in methanolic solutions