Sujittra Youngme

Synthesis, spectroscopic characterization, X-ray crystal structure and magnetic properties of oxalato-bridged copper(II) dinuclear complexes with di-2-pyridylamine

The syntheses and characterization of a series of dinuclear μ-oxalato copper(II) complexes of the general type [(NN) 1 or 2 Cu(C 2 O 4 )Cu(NN) 1 or 2 ] 2+ , where NN=didentate dpyam (di-2-pyridylamine) ligand, are described. The crystal structures of three representative complexes have been determined. The dinuclear-oxalate bridged compounds [Cu(dpyam) 4 (C 2 O 4 )](ClO 4 ) 2 (H 2 O) 3 (1) and [Cu 2 (dpyam) 4 (C 2 O 4 )](BF 4 ) 2 (H 2 O) 3 (2) crystallize in the non-centrosymmetric triclinic space group P which are isomorphous and isostructural. The compound [Cu 2 (dpyam) 2 (C 2 O 4 )(NO 3 ) 2 ((CH 3 ) 2 SO) 2 ] (3) crystallizes in the centrosymmetric monoclinic space group P with all Cu-oxalate contacts in the equatorial plane. All three complexes contain six-coordinate copper centres bridged by planar bis-didentate oxalate groups from the equatorial position of one chromophore to the equatorial position of the other one. Both chromophores in 1 and 2 exhibit the compressed octahedral Cu(II) geometry, while 3 displays an elongated octahedral Cu(II) environment. The IR, ligand field and EPR measurements are in agreement with the structures found. The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a very weak ferromagnetic interaction between the Cu(II) atoms for compound 1 and 2 , with a singlet–triplet energy gap ( J ) of 2.42 and 3.38 cm −1 , for compounds 1 and 2 , respectively. Compound 3 has a strong antiferromagnetic interaction with a J of −305.1 cm −1 , in agreement with coplanarity of the magnetic orbitals.

The coordination chemistry of mono and bis(di-2-pyridylamine)copper(II) complexes: preparation, characterization and crystal structures of [Cu(L)(NO2)2], [Cu(L)(H2O)2(SO4)], [Cu(L)2(NCS)](SCN)·0.5DMSO and [Cu(L)2(SCN)2]

Abstract The crystal structures of two mono(dpyam)copper(II) complexes, [Cu(dpyam)(NO2)2] (1) and [Cu(dpyam)(H2O)2(SO4)] (2) and two dithiocyanate compounds containing bis(dpyam)copper(II) units, [Cu(dpyam)2(NCS)](SCN)·0.5DMSO (3) and [Cu(dpyam)2(SCN)2] (4) have been determined by X-ray crystallography. The second orthorhombic form of the monomeric Cu(II) complex 1 was obtained by the reaction of di-2-pyridylamine (dpyam) with CuCl and NaNO2 in water–methanol solution. Each copper(II) ion in 1 exhibits a tetrahedrally-distorted square base of the CuN2O2 chromophore, with off-the-z-axis coordinated nitrito groups weakly bound in approximately axial positions. Complex 2 is an example of a polymeric copper(II) derivative containing the bidentate bridging sulfate ligand in the long-bonded axial positions. Each copper(II) ion in 2 shows an elongated tetragonal octahedral stereochemistry. The CuN4N′ chromophore of 3 involves a square-based pyramidal structure, slightly distorted towards a trigonal bipyramidal stereochemistry, τ=0.13. One of the SCN− anions is bonded to the copper(II) ion via the N atom in the axial position of the square pyramid. Complex 4 is centrosymmetric and octahedrally elongated, with the SCN− anions coordinating in axial positions via the S atom. The structures of complexes 1–4 and their ESR and electronic reflectance spectra are compared with those of related complexes.

Toward the design of ferromagnetic molecular complexes: magnetostructural correlations in ferromagnetic triply bridged dinuclear Cu(II) compounds containing carboxylato and hydroxo bridges.

In the present work we present a comprehensive study of the magneto-structural correlations of a series of ferromagnetic triply heterobridged Cu(II) dinuclear compounds containing [Cu(2)(mu-O(2)CR)(mu-OH)(mu-X)(L)(2)](2+) ions (where X = OH(2), Cl(-), OMe(-) and L = bpy, phen, dpyam) which have the particularity of being all ferromagnetic. The present theoretical study, based on hybrid density functional theory (DFT) calculations, leads to strong conclusions about the role of the pentacoordination geometry of the Cu(II) ions (square base pyramidal (SP) or trigonal bipyramidal (TBP) coordination) and the nature of the third bridging ligand in determining the final value of the magnetic coupling constants in this series of compounds. These investigations point toward the existence of a maximum value for the ferromagnetic interaction and may offer some useful information to synthetic chemists aiming at obtaining new compounds with enhanced ferromagnetism.

Coordination geometries in bis(di-2-pyridylamine)copper(II) complexes. Crystal structures and spectroscopic properties of [CuL2(H2O)2](S4O6), [CuL2(CF3SO3)2] and [CuL2(SO4)]2[CuL2(H2O)2](PF6)2.2H2O (L = di-2-pyridylamine)

Abstract The crystal structures of three compounds containing bis(di-2-pyridylamine)copper(II) complex units have been determined by X-ray crystallographic methods; [Cu(dpyam)2(OH2)2](S4O6) (1), [Cu(dpyam)2(CF3SO3)2] (2) and [Cu(dpyam)2(SO4)]2[Cu(dpyam)2(OH2)2](PF6)2·2H2O (3). In compound 1 the anions are uncoordinated, and each Cu(II) ion involves the elongated tetragonal octahedral geometry with two water molecules occupying the axial positions. Compound 2 consists of neutral mononuclear units, the Cu(II) environment being elongated tetragonal octahedral with two unidentate triflate anions coordinating in axial positions. Two crystallographically independent molecules are found in compound 3, one complex unit being centrosymmetric and octahedrally elongated, with two water molecules coordinated in the axial positions, the other predominately close to the distorted square-based pyramidal (4+1) stereochemistry of the CuN3ON′ chromophore which is best described as square-pyramidal cis-distorted octahedral (4+1+1*). The latter complex unit of compound 3 is the first example containing a cis-distorted octahedral coordination among the copper(II) complexes with divalent oxyanions.

Preparation, crystal structure, spectroscopic and magnetic characterisation of acetatobis(di-2-pyridylamine)copper(II) tetrafluoroborate and μ-carbonato-tetrakis(di-2-pyridylamine) dicopper(II) bistetrafluoroborate tetrahydrate

Abstract The crystal structures of [Cu(dpyam)2(O2CCH3)][BF4] (1) and [Cu2(dpyam)4(CO3)][BF4]2·4H2O (2) have been determined by X-ray analysis. 1 involves the distortion of the CuN4O2 chromophore towards a square pyramidal (4+1+1*) stereochemistry which is best described as involving a square-pyramidal distorted octahedral stereochemistry of the six-coordinate CuN4OO′ chromophore. Compound 2 has a dinuclear cation with five-coordinate copper(II) ions bridged asymmetrically by a bidentate carbonate ligand. Both copper(II) ions predominantly involve the distorted square-pyramidal (4+1) stereochemistry of the CuN3ON′ chromophore. The polycrystalline ESR spectra of 1 and 2 are exchange coupled and temperature independent. In 2 the room temperature effective magnetic moment of 1.34 μB indicates the partial spin pairing by antiferromegnetic coupling.

New series of triply bridged dinuclear Cu(II) compounds: synthesis, crystal structure, magnetic properties, and theoretical study.

Five new triply bridged dinuclear Cu(II) compounds have been synthesized, and their magnetic properties have been measured and characterized. The magnetic coupling constants (J) of these compounds plus a previously structurally characterized compound of the same type have been derived by appropriate fitting of the experimentally measured molar susceptibility variation with the temperature. Two of the compounds are ferromagnetically coupled, and three are antiferromagnetically coupled with J values in the [+150, -40] cm(-1) range. The validity of the structural aggregate Addisons parameter as a qualitative magneto-structural correlation is confirmed. The origin of the magnetic interactions and the magnitude of the magnetic coupling have been analyzed by means of density functional theory-based calculations using a variety of state of the art exchange-correlation potentials. It is shown that the long-range separated LC-ωPBE provides the overall best agreement with experiment for this family as well as for a set of previously reported hetero triply bridged dinuclear Cu(II) compounds, especially for ferromagnetic systems.

Influence of supramolecular bonding contacts on the spin crossover behaviour of iron(II) complexes from 2,2′-dipyridylamino/s-triazine ligands

Reactions of the related ligands 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(phenoxy)-(1,3,5)triazine (L1) and 2-(N,N-bis(2-pyridyl)amino)-4,6-bis(pentafluorophenoxy)-(1,3,5)triazine (L1(F)) with iron(II) thiocyanate produced two spin-crossover coordination compounds with distinct cooperative behaviours. trans-[Fe(L1)2(NCS)2]·2CH2Cl2 (1) displays a very gradual transition centred at T½ = 233 K, characterized by a ΔT80 (namely the temperature range within which 80% of the transition considered occurs) of 90 K, while that of fluorinated trans-[Fe(L1(F))2(NCS)2]·2CH3CN (3) is significantly more abrupt (and centred at T½ = 238 K), with a ΔT80 of 50 K, resulting from supramolecular contacts induced by the fluorinated phenol groups. The coordination compound equivalent to 1 with selenocyanate anions, namely trans-[Fe(L1)2(NCSe)2]·4CH2Cl2·4CH3OH (2), also exhibits SCO properties centred at T½ = 238 K, but the transition is very gradual (ΔT80 = 150 K). Light-induced excited spin-state trapping (LIESST) is effective although incomplete for 2 and 3, while it is complete with a T(LIESST) of 58 K for 1.

Synthesis, crystal structures and magnetism of planar and roof-shaped hydroxo-bridged dinuclear copper(II) compounds with di-2-pyridylamine as a ligand

Abstract The compounds [Cu(dpyam)(OH)Br] 2 (H 2 O) 4 ( 1 ), [Cu(dpyam)(OH)(CF 3 SO 3 )] 2 ( 2 ) and [Cu 2 (dpyam) 2 (OH) 2 (OH 2 )]Br 2 (H 2 O) 2 ( 3 ) have been synthesized and their crystal structures determined by X-ray crystallographic methods. Compound 1 crystallises in the triclinic system, space group P 1 . The lattice constants are a =8.892(1), b =9.346(1), c =9.358(1) A, α =112.2(1), β =108.3(1), γ =95.8(2)° with Z =1 and R 1 =0.0292. Compound 2 crystallises in the triclinic system, space group P 1 . The lattice constants are a =8.1616(5), b =9.4156(6), c =10.2921(6) A, α =72.58(2), β =72.48(4), γ =73.19(2)° with Z =1 and R 1 =0.0595. Crystals of 3 are orthorhombic with space group Cmc 2 1 . The lattice constants are a =15.979(1), b =8.550(1), c =18.237(1) A with Z =4 and R =0.0623. Compound 1 contains a dinuclear [Br(dpyam)Cu(OH) 2 Cu(dpyam)Br] unit with a dihedral angle between the CuO 2 planes of 179.9°. Each copper atom is in a square-pyramidal coordination environment; the basal plane consists of two bridging hydroxo groups and two dpyam ligands coordinated through their nitrogen atom. The fifth axial coordination site of each copper(II) ion is occupied by a Br atom, at a weak semi-coordination distance of 2.803(2) and 2.804(2) A. For compound 2 , the coordination geometry around each copper(II) ion is distorted elongated octahedral, CuN 2 O 4 . The equatorial positions are occupied by the two nitrogen atoms of dpyam and the two oxygen atoms of the bridging hydroxo groups, where the apical positions are occupied by oxygen atoms from both triflate groups. In the dinuclear units of compound 3 the triply-bridged Cu(II) ions show a distorted square pyramidal coordination. The fifth apical ligand is a longer bonded bridging water molecule for 3 , at distances of 2.220(2) A, which joins the basal CuN 2 O 2 planes in a roof-shaped configuration (dihedral angle 135.8 o ). The CuCu distances are 2.993(2), 2.964(2) and 2.849(2) A for compounds 1 , 2 and 3 , respectively. The magnetic susceptibility measurements revealed a ferromagnetic interaction between the Cu(II) atoms for compound 2 , with a singlet–triplet energy gap ( J ) around 83 cm −1 . Compound 1 has an antiferromagnetic interaction with a J of −48.6 cm −1 , whereas compound 3 is very weakly antiferromagnetic with J =−0.6 cm −1 .

The crystal structures and electronic properties of bis(di-2-pyridylamine)copper(II), bis(tetrafluoroborate) and bis[bis-aquabis(di-2-pyridylamine)copper(II)] sulfate heptahydrate

Abstract In the [Cu(C 10 H 9 N 3 ) 2 ][BF 4 ] 2 ( 1 ) complex, the Cu(II) ion is in a compressed tetrahedral environment of four N atoms from two di-2-pyridylamine ligands, with an average Cu–N distance of 1.962(7) A; the dihedral angle between the N–Cu–N planes of the two ligands is 55.0(2)°. The asymmetric unit of [Cu(C 10 H 9 N 3 ) 2 (H 2 O) 2 ][SO 4 ]·7H 2 O ( 2 ) contains two units of one-half [Cu(C 10 H 9 N 3 ) 2 ] moieties (the other half is inversion related), one sulfate and nine water molecules. Each Cu(II) ion involves the elongated rhombic octahedral CuN 4 O 2 chromophore, and is surrounded by four N atoms from the two inversion related dpyam ligands, with an average Cu–N distance of 2.019(2) A. The axial positions of Cu(1) are occupied by the centrosymmetrically related O atoms of the two water molecules at 2.496(3) A, giving it a tetragonally distorted Cu(1)N 4 O 2 octahedron. Similarly, the inversion related water oxygens at 2.465(3) A give a Cu(2)N 4 O 2 chromophore. The electronic and ESR spectra of 1 and 2 are consistent with the compressed tetrahedral and the elongated rhombic octahedral stereochemistries, respectively, as reported for other related complexes.

Drastic steric effects from, respectively, a hydrogen, a methyl and an ethyl group on the coordination network of a zinc(II)–4,4′-bipyridine–carboxylato ternary system

The combination of a [zinc(II)–4,4′-bpy] coordination moiety with, respectively, formato, acetato and propionato ligands leads to the formation of the compounds {[Zn3(4,4′-bpy)3.5(µ-O2CH)4 (H2O)2](ClO4)2(H2O)2}n (1), {[Zn3(4,4′-bpy)3(µ-O2CCH3)4(H2O)2](PF6)2(H2O)2}n (2) and {[Zn3(4,4′-bpy)4(µ-O2CCH2CH3)4](ClO4)2(4,4′-bpy)2(H2O)4}n (3). The molecular structures determined by single-crystal X-ray diffraction data reveal significant changes, which are apparently due to the sole different steric hindrance between a H atom (formato, compound 1), a methyl group (acetato, compound 2) and an ethyl group (propionato, compound 3). The three coordination materials have been fully characterized and their thermal decomposition behavior has been investigated. The 3D (1), 1D (2) and 2D (3) networks exhibit voids that contain the counter-ions and guest molecules as well, namely water for compounds 1 and 2, and water/4,4′-bpy for compound 3.