Mixed ligand complexes of osmium(II)-2,2-bipyridine: synthesis, spectral characterization and electrochemical properties of bis-chelated-arylazoimidazole-bipyridine-osmium(II) and X-ray crystal structure of [(2,2-bipyridine)-bis-{1-methyl-2-(p-tolylazo)imidazole}osmium(II) hexafluorophosphate

Reaction of ctc-OsBr₂(RaaiR^′)₂ [RaaiR^′=1-alkyl-2-(arylazo)imidazole, p-R-C₆H₄-NN-C₃H₂-NN-1-R^′, where R=H (a), Me (b), Cl (c) and R^′=Me (2), Et (3) and CH₂Ph (4)] with 2,2^′-bipyridine (bpy) in presence of AgNO₃ in EtOH followed by the addition of NH₄PF₆ afforded a mixed ligand complex [Os(bpy)(RaaiR^′)₂](PF₆)₂. The structure of the complex, in one case [Os(bpy)(MeaaiMe)₂](PF₆)₂ · 4H₂O, has been confirmed by X-ray crystallography. The complexes are diamagnetic (low spin d⁶, s=0) and they show intense MLCT transition in the visible region (480-525 nm) and a weak transition at longer wavelength (>850 nm) in CH₃CN solution. Cyclic voltammetry of the complexes show two metal oxidation, Os(II)/Os(III) at 0.72-0.76 V and Os(III)/Os(IV) at 1.34-1.42 V and three successive ligand reductions.     

Cd(II)-NCS/NCO complexes of 1-alkyl-2-(arylazo)imidazole: Single crystal X-ray structure of [Cd(HaaiMe)2(SCN)2]

The reaction of Cd(OAc)₂ · 4H₂O and 1-alkyl-2-(arylazo)imidazole [RaaiR′ where R = H (a), Me (b); R′ = Me (1/3/5), Et (2/4/6)] and NH₄NCS/NaNCO in methanol in 1:2:2 mole ratio has afforded [Cd(RaaiR′)₂(NCS)₂] (3, 4) and [Cd(RaaiR′)₂(NCO)₂] (5, 6) complexes. The complexes are characterized by different physicochemical methods and in one case, the structure was confirmed by single crystal X-ray diffraction study for title compounds.     

Synthesis, structures, and magnetic properties of dicopper(II) and dinickel(II) complexes with a new bis(macrocycle), 7,7-(2-hydoxypropane-1,3-diyl)bis{3,7,11,17-tetraazabicyclo[11.3.1]- heptadeca-1(17),13,15-triene}

A new bis(macrocycle) ligand, 7,7^′-(2-hydoxypropane-1,3-diyl)-bis{3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),13,15-triene} (HL), and its dicopper(II) ([Cu₂(HL)Cl₂](NO₃)₂ · 4H₂O (4a), [Cu₂(HL)I₂]I₂ · H₂O (4b)) and dinickel(II) ([Ni₂(L)(OH₂)](ClO₄)₃ (5a), [Ni₂(L)(OH₂)]I₃ · 2H₂O (5b), [Ni₂(L)N₃](N₃)₂ · 7H₂O (5c)) complexes have been synthesized. The alkoxide bridged face-to-face structure of the dinickel(II) complex 5c has been revealed by X-ray crystallography, as well as the “half-opened clamshell” form of the bis(macrocyclic) dicopper(II) complex 4b. Variable temperature magnetic susceptibility studies have indicated that there exists intramolecular antiferromagnetic coupling (J=−33.8 cm⁻¹ (5a), −32.5 cm⁻¹ (5b), and −29.7 cm⁻¹ (5c)) between the two nickel(II) ions in the nickel(II) complexes.     

Dinuclear nickel(II) and zinc(II) complexes of 2,6-bis[{bis(2-pyridylmethyl)amino}methyl]-4-methylphenol

Reaction of the symmetrical proligand H₂L with metal(II) acetate and a counteranion to promote crystallisation has given the homodinuclear complexes [Zn₂L(OAc)₂](BF₄)]·2MeOH and [Ni₂L(OAc)₂](BF₄)]·2MeOH the crystal structures of which are reported. These show the presence of a triply bridging (μ-cresolato)bis(μ-carboxylato) dimetal core.     

Synthesis and crystal structures of trans-dichlorobis{tri(2-methylphenyl)stibine}palladium(II) and trans-dibromobis{tri(2-methylphenyl)stibine}palladium(II)

Tri(2-methylphenyl)stibine reacts with [PdX₂(cod)] or PdX₂ (X = Cl or Br) to give the trans-[PdX₂{Sb(2-Me- C₆H₄)₃}₂]. The single crystal X-ray structures of trans-[PdX₂{Sb(2-Me-C₆H₄)₃}₂] (X = Cl or Br) revealed that the palladium atom is a square planar environment with mutually trans-Sb(2-methylphenyl)₃ ligands. Iodine analogous of complex can also be prepared from trans metallation reaction with sodium iodine.     

Synthesis and characterization of 6-(p-chlorobenzoyl)-5,7,12,14-tetramethyl-benzo[b]-1,4,8,11-tetraazacyclo[14]tetradecinato(2-)nickel(II)

A nickel(II) complex with 6-(p-chlorobenzoyl)-5,7,12,14-tetramethyl-benzo[b]-1,4,8,11- tetraazacyclo[14]tetradecine was synthesized and characterized by measurements of NMR, IR and an electronic spectra. The X-ray crystal structure shows that the coordination geometry around the Ni atom is a square planar with the unsymmetrical tetraaza[14]annulene.     

The structure of the dichromium compound Cr2(μ-OH)2(μ-3,5Cl2-form)2(η-3,5Cl2-form)2

With exposure to trace amounts of air and moisture, the Cr₂(II, II) complex Cr₂(μ-3,5Cl₂-form)₄, where 3,5Cl₂-form is [(3,5-Cl₂C₆H₃)NC(H)N(3,5-Cl₂C₆H₃)⁻], undergoes an oxidative addition reaction. Structural information from the X-ray crystal structure of the edge-sharing bioctahedral (ESBO) Cr₂(III, III) product Cr₂(μ-OH)₂(μ-3,5Cl₂-form)₂(η²-3,5Cl₂-form)₂ (1) indicates 1 has a significantly longer Cr–Cr distance [2.732(2) Å] than Cr₂(μ-3,5Cl₂-form)₄ [1.9162(10) Å], but the shortest Cr–Cr distance in an ESBO Cr₂(III, III) complex recorded to date.     

Syntheses and structures of Group 12 metal thioacetate anions, [M(SC{O}Me)nCl4−n] (n=3 and 4) and [Cd2Cl2(SC{O}Me)4]

We have utilized the possibility of altering the ratio of reactants to result in tetrahedral anions, [M(SC{O}Me)_nCl_4−n]²⁻ (n=3, 4) and [Cd₂Cl₂(SC{O}Me)₄]²⁻. Complexes of the formula [Ph₄P]₂[M(SC{O}Me)₄] (M=Zn(II) (1), Cd(II) (2) or Hg(II) (3)) were synthesized by the reaction of thioacetate ligand with the metal salts and Ph₄PCl in 4:1:2 molar ratio in suitable solvents. The geometry of Zn(II) in 1 is nearly tetrahedral and the distortion in tetrahedron increases in the order of 1<2<3 as observed from the SMS angles in the crystal structures. The tendency of monoanionic complexes [Ph₄P][M(SC{O}Me)₃] to react with 1 mole equivalent of Ph₄PCl resulted in complexes of the type [Ph₄P]₂[M(SC{O}Me)₃Cl] (M=Cd(II) (4) or Hg(II) (5)). In the structures of 4 and 5, three sulfur atoms and one chloride atom occupy the corners of the tetrahedron around the metal centers. However, in a 4:2:2 or 2:1:2 molar reaction of Me{O}CS⁻ with CdCl₂ and Ph₄PCl in aqueous medium resulted in a chloro bridged dimer, [Ph₄P]₂[Cd₂(μ-Cl)₂(SC{O}Me)₄] (6) as determined by X-ray crystallography.     

Structural analysis and magnetic properties of the copper(II) dicyanamide complexes [Cu2(dmphen)2(dca)4], [Cu(dmphen)(dca)(NO3)]n and [Cu(4,4-dmbpy)(H2O)(dca)2] (dca=dicyanamide; dmphen=2,9-dimethyl-1,10-phenanthroline; 4,4-dmbpy=4,4-dimethyl-2,2-bipyridine)

The preparation, crystal structures and magnetic properties of three copper(II) compounds of formulae [Cu₂(dmphen)₂(dca)₄] (1), [Cu(dmphen)(dca)(NO₃)]_n (2) and [Cu(4,4^′-dmbpy)(H₂O)(dca)₂] (3) (dmphen=2,9-dimethyl-1,10-phenanthroline, dca=dicyanamide and 4,4^′-dmbpy=4,4^′-dimethyl-2,2^′-bipyridine) are reported. The structure of 1 consists of discrete copper(II) dinuclear units with double end-to-end dca bridges whereas that of 2 is made up of neutral uniform copper(II) chains with a single symmetrical end-to-end dca bridge. Each copper atom in 1 and 2 is in a distorted square pyramidal environment: two (1) or one (2) nitrile-nitrogen atoms from bridging dca groups, one of the nitrogen atoms of the dmphen molecule (1 and 2) and either one nitrile-nitrogen from a terminal dca ligand (1) or a nitrate-oxygen atom (2) build the equatorial plane whereas the second nitrogen atom of the heterocyclic dmphen fills the axial position (1 and 2). The copper-copper separations through double (1) and single (2) end-to-end dca bridges are 7.1337(7) (1) and 7.6617(7) (2). Compound 3 is a mononuclear copper(II) complex whose structure contains two neutral and crystallographically independent [Cu(4,4^′-dmbpy)(H₂O)(dca)₂] molecules which are packed in two different layer arrangements running parallel to the bc-plane and alternating along the a-axis. The copper atoms in both molecules have slightly distorted square pyramidal surroundings with the two nitrogen atoms of the 4,4^′-dmbpy ligand and two dca nitrile-nitrogen atoms in the basal plane and a water oxygen in the apical position. A semi co-ordinated dca nitrile-nitrogen from a neighbour unit [2.952(6) Å for Cu(2)-N] is in trans position to the apical water molecule in one of the two molecules, this feature representing part of the difference in supramolecular connections in the alternating layers referred to above. Magnetic susceptibility measurements for 1-3 in the temperature range 1.9-290 K reveal the occurrence of weak antiferromagnetic interactions through double [J=−3.3 cm⁻¹ (1), ] and single [J=−0.57 cm⁻¹ (2), ] dca bridges and across intermolecular contacts [θ=−0.07 K (3)].     

Synthesis, crystal structure and EPR of a hydrogen bonded two-dimensional network of Cu(II) complex with N-(2-hydroxybenzyl)-2-amino-1-ethanol

Hsalea (N-(2-hydroxybenzyl)-2-amino-1-ethanol) and its Cu(II) complexes, Cu(salea)₂ (1) and CuH₋₁(salea)·1.5H₂O (2), were prepared and characterized. X-ray structural analyses of 1 show that two amino N and two deprotonated phenoxy O atoms of the two ligands coordinate equatorially to Cu(II). Two alcoholic O atoms coordinate weakly at axial positions. Each molecule utilizes two alcoholic H atoms and two phenoxy O atoms to form hydrogen bonds with four surrounding molecules, leading to a two-dimensional network structure. EPR and electronic spectra of 1 are consistent with the elongated octahedral coordination polyhedron.     

A novel ferromagnetic coupling one-dimensional complex {Cu(II)(NIT3Py)2[N(CN)2]2(H2O)2}

The novel ferromagnetic coupling one-dimensional complex {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} (NIT3Py=2-(3^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group C2/c. The Cu(II) ion is in a distorted octahedral environment. The units of {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} were connected as one-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show that there are intramolecular ferromagnetic interactions and intermolecular antiferromagnetic interactions within the chain.     

Transition metal complexes of 2-amino-3,5-dihalopyridines: Synthesis, structures and magnetic properties of Cu(3,5-diCAP)2X2 and Cu(3,5-diBAP)2X2

A family of bis(2-amino-3,5-dihalopyridine)dihalocopper(II) compounds has been synthesized, including (3,5-diCAP)₂CuCl₂ (1), (3,5-diCAP)₂CuBr₂ (2), (3,5-diBAP)₂CuCl₂ (3), and (3,5-diBAP)₂CuBr₂ (4) [3,5-diCAP = 2-amino-3,5-dichloropyridine; 3,5-diBAP = 2-amino-3,5-dibromopyridine]. These complexes have been analyzed through single crystal X-ray diffraction and temperature dependant magnetic susceptibility. The compounds are all isostructural, forming bi-bridged chains with long Cu-X?Cu bridges in the crystal lattice. The two copper chloride compounds (1 and 3) exhibit weak antiferromagnetic interactions along these chains.     

Synthesis and structure of a lead(II)-citrate: {Na(H2O)3}[Pb5(C6H5O7)3(C6H6O7)(H2O)3]·9.5H2O

The reaction of lead(II) nitrate with trisodium citrate Na₃(C₆H₅O₇) in a 1:22.5 ratio at pH 4.8 provides crystals of {Na(H₂O)₃}[Pb₅(H₂O)₃(C₆H₅O₇)₃(C₆H₆O₇)]·9.5H₂O (1). The structure of 1 is two-dimensional and exhibits five distinct Pb(II) sites and four different modes of citrate bonding. The five lead sites all display hemidirected coordination geometries, that is, irregular distribution of neighboring oxygen atoms resulting in obvious gaps in the coordination spheres. Consequently, the lead coordination geometries exhibit proximal bonding to a number of oxygen donors, as well as distal interactions with nearest neighbors. The coordination numbers vary from 8 to 10, with ‘5+3’, ‘5+4’, ‘6+4’ and ‘7+3’ coordination modes where the first number refers to the proximal ligands and the second to the distal set. The four crystallographically distinct citrate groups include three with deprotonated carboxylate groups (C₆H₅O₇)³⁻ and one with a single protonated carboxyl group (C₆H₆O₇)². The citrate ligands bridge 3, 5, 7 and 7 lead sites. Three of the citrate groups exhibit tridentate chelation coordination to a lead site through two carboxylate oxygen donors and the hydroxyl groups. One citrate group projects an uncoordinated -OH group and a pendant protonated carboxyl group into the interlamellar domain. This latter carboxyl group coordinates to a sodium cation, which exhibits five coordinate geometry defined by three aqua ligands and the carbonyl oxygen of the -CO₂H groups in the basal plane and a citrate -OH donor in the apical position.     

Synthesis and crystal structure of the low-spin iron(II) complex [Fe(bpz)3](ClO4)2 · H2O (bpz=2,2-bipyrazine)

The crystal structure of the title compound [Fe(bpz)₃](ClO₄)₂ · H₂O (bpz=2,2^′-bipyrazine) has been determined by a single crystal X-ray diffraction study at 293(2) K. The complex is monoclinic, P2₁/c, a=17.263(3), b=9.983(2), c=17.921(4) Å, β=107.94(3)°, V=2938.3(10) ų, Z=4, R=0.073 and R_w=0.118. The structure is made up of tris-chelated [Fe(bpz)₃]²⁺ cations, uncoordinated perchlorate anions and crystallization water molecules. The iron atom exhibits a FeN₆ distorted octahedral geometry with average Fe-N bond length and N-Fe-N bidentate angle of 1.962(5) Å and 81.6(2)°. The value of the Fe-N bond distance and that of the room temperature magnetic moment are in agreement with a singlet ¹A₁ ground state. The structure of 1 is compared to those of other tris-chelated iron(II) complexes with bidentate nitrogen heterocycles.     

Synthesis and characterization of Cu(II) and Ni(II) complexes of a tripodal ligand containing imidazoles

Two complexes of the formula [MH₃L](ClO₄)₂ [M = Cu(II) (1), Ni(II) (2)] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with the ligand (H₃L) formed by the Schiff base condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 4-methyl-5-imidazolecarboxaldehyde and structurally and magnetically characterized. The structures of 1 and 2 are isomorphous with each other and with the iron(II) complex of H₃L which has been reported previously. The ligand, while potentially heptadentate, forms six coordinate complexes with both metal centers forming three M-N_imine and three M-N_imidazole bonds. The tren central N atom is at a nonbonded distance from M of 3.261 Å for 1 and 3.329 Å for 2. The neutral complex CuHL 3 was prepared by reaction of H₃L with Cu(OCH₃)₂ and the ionic complex Na[NiL] 4 was prepared by deprotonation of 2 with aqueous sodium hydroxide. Magnetic measurements of 1-3 are consistent with the spin-only values expected for S = 1/2 (d⁹, Cu(II)) and S = 1 (d⁸, Ni (II)) systems.     

Fluorous interactions in complexes of lead(II) hexafluoroacetylacetonate

Structure determinations for 2,2′-bipyridine and 1,10-phenanthroline adducts of lead(II) hexafluoroacetylacetonate, [Pb(bipy)₂(hfacac)₂] (1), [Pb(bipy)(hfacac)₂] (2), and [Pb(phen)(hfacac)₂] (3), show that the balance of intermolecular forces within the lattices is seemingly sensitive to the adduct stoichiometry but not to the nature of the heteroaromatic base. In 3, a structure, in which there is an apparent preference for CF/aromatic interactions over separate CF/CF and aromatic/aromatic interactions, is essentially identical at both 120 and 293 K.     

Conformational flexibility of 2,6-bis(pyrazol-1-ylmethyl)pyridine (L) in [(L)Co(H2O)3]Cl2 and [(L)Ni(H2O)2Cl]Cl·H2O. Molecular structures and non-covalent interactions

Using a non-planar tridentate ligand 2,6-bis(pyrazol-1-ylmethyl)pyridine (L⁵) two new coordination complexes [(L⁵)Co^II(H₂O)₃]Cl₂ (1) and [(L⁵)Ni^II(H₂O)₂Cl]Cl·H₂O (2) have been synthesized and structurally characterized. Complex 1 has N₃O₃ distorted octahedral environment around Co^II with coordination by L⁵ (two pyrazole and a pyridine nitrogen in a facial mode) and three water molecules. Complex 2 has N₃O₂Cl distorted octahedral geometry around Ni^II with meridional L⁵ coordination, two water molecules, and a Cl⁻ ion. Analysis of the crystal packing diagram reveals the involvement of solvent (water as metal-coordinated and as solvent of crystallization) and counteranion (Cl⁻) to play significant roles in generating 1D chains, involving O-H···Cl, and O-H···O interactions.     

A new series of iodocarbonyl ruthenium (II) complexes with unsymmetrical phosphine-phosphine sulfide ligands of the type Ph2P(CH2)nP(S)Ph2, n = 1-4: Isolation and structural investigation

Hexa-coordinated chelate complex cis-[Ru(CO)₂I₂(P∩S)] (1a) {P∩S = η²-(P,S)-coordinated} and penta-coordinated non-chelate complexes cis-[Ru(CO)₂I₂(P∼S)] (1b-d) {P∼S = η¹-(P)-coordinated} are produced by the reaction of polymeric [Ru(CO)₂I₂]_n with equimolar quantity of the ligands Ph₂P(CH₂)_nP(S)Ph₂ {n = 1(a), 2(b), 3(c), 4(d)} in dichloromethane at room temperature. The bidentate nature of the ligand a in the complex 1a leads to the formation of five-membered chelate ring which confers extra stability to the complex. On the other hand, 1:2 (Ru:L) molar ratio reaction affords the hexa-coordinated non-chelate complexes cis,cis,trans-[Ru(CO)₂I₂(P∼S)₂] (2a-d) irrespective of the ligands. All the complexes show two equally intense terminal ν(CO) bands in the range 2028-2103 cm⁻¹. The ν(PS) band of complex 1a occurs 23 cm⁻¹ lower region compared to the corresponding free ligand suggesting chelation via metal-sulfur bond formation. X-ray crystallography reveals that the Ru(II) atom occupies the center of a slightly distorted octahedral geometry. The complexes have also been characterized by elemental analysis, ¹H, ¹³C and ³¹P NMR spectroscopy.     

Manganese(II) complexes with croconate and 2-(2-pyridyl)imidazole ligands: Syntheses, X-ray structures and magnetic properties

The mixed-ligand complexes of manganese(II) of formula [Mn(pyim)₂(C₅O₅)] (1) and [Mn(pyim)(H₂O)(C₅O₅)]_n · 2.5nH₂O (2) [pyim = 2-(2-pyridyl)imidazole and  = croconate (dianion of 4,5-dihydroxy-4-cyclopentene-1,2,3-trione)] have been prepared and their structures determined by X-ray crystallographic methods. Compound 1 is a tris-chelated mononuclear complex where the manganese atom is six-coordinate: four nitrogen atoms from two pyim molecules and two oxygen atoms from a croconate group build a somewhat distorted octahedral surrounding around the metal atom. The resulting neutral mononuclear units are linked to each other through double bridges which are constituted by the imidazole N-H and the metal-coordinated croconate-oxygen atom, the metal-metal separation through this supramolecular pathway being 7.6856(11) Å. Compound 2 is a croconato-bridged manganese(II) uniform chain with an intrachain metal-metal distance of 7.5118(9) Å. A bidentate pyim group, a water molecule and four oxygen atoms from two bis-bidentate croconate ligands build an irregular seven-coordination polyhedron around each manganese atom in 2. The investigation of the magnetic properties of 2 in the temperature range 1.9-295 K has shown the occurrence of a weak antiferromagnetic interaction [J = −0.066 cm⁻¹ with the Hamiltonian defined as H = −J ∑_i S_i · S_i+1] through the bis-bidentate croconate. The ability of the bis-chelating croconate to mediante magnetic interactions between paramagnetic first-row transition metal ions is discussed and compared to that of the related oxalate ligand.     

Synthesis, structures and spectroscopic properties of platinum(II), copper(I) and zinc(II) complexes bearing 4-(p-dimethylaminophenyl)-6-phenyl-2,2′-bipyridine ligand

The reactions of 4-(p-dimethylaminophenyl)-6-phenyl-2,2′-bipyridine (HL) with three metal salts of platinum(II), copper(I) and zinc(II) provide the new complexes [Pt(L)(PPh₃)]ClO₄ (1), [Cu(HL)₂]BF₄ (2), [Cu(HL)(PPh₃)]BF₄ (3) and [Zn(HL)₂](ClO₄)₂ (4). All the structures of these four complexes have been characterized by single crystal X-ray diffraction, and their spectroscopic properties were investigated. Especially for complex 1, upon protonation, the excited state can be tuned from the intraligand charge transfer (ILCT) to the metal-to-ligand charge transfer (MLCT), and such switching in the excited state is acid/base reversible. The time-dependent density functional theory (TD-DFT) calculation was used to interpret the absorption spectra of complex 1, and the calculated result is consistent with those of experiments results. In contrast with 1, the lowest energy absorption at 410-650 nm of complexes 2 and 3 can be assigned to MLCT excited state. In solid state or solution complex 4 exhibits intense photoluminescence attributed to a ILCT transition in nature.