Synthesis, structure and characterization of new complexes [Fe2(μ-OMe)2(PAP)(X)4] (PAP= 1,4-di(2-pyridyl)aminophthalazine, X=Cl, OAc) and their oxidation catalysis

Two dinuclear iron(III) complexes with tetradentate N-donor ligand 1,4-di(2^′-pyridyl)aminophthalazine (PAP), [Fe₂(μ-OMe)₂(PAP)Cl₄] (2) and [Fe₂(μ-OMe)₂(PAP)(OAc)₄] (3) were prepared and characterized. Single crystal X-ray molecular structure of [Fe₂(μ-OMe)₂(PAP)Cl₄] · 2MeOH have been elucidated. The six-coordinate iron atoms are in distorted octahedral environment bridged by the oxygen atoms of two methoxy groups and the PAP ligand. The Mössbauer spectra of both complexes show one quadrupole doublet and the isomer shift and quadrupole splitting values indicate the presence of octahedral high-spin Fe^III ions. Complex 2 showed catalytic activity for alkane oxidation with hydrogen peroxide.     

Diverse coordination of polynuclear copper(II) complexes constructed from benzene tetracarboxylates

The reaction of aqueous solutions of the preformed 1:1 Cu(ClO₄)₂-polydentate amine with tetrasodium 1,2,4,5-benzene tetracarboxylate (Na₄bta) afforded three different types of polynuclear compounds. These include the tetranuclear complexes: [Cu₄(Medpt)₄(μ₄-bta)(ClO₄)₂(H₂O)₂](ClO₄)₂·2H₂O (1), [Cu₄(pmdien)₄(μ₄-bta)(H₂O)₄](ClO₄)₄ (2), [Cu₄(Mepea)₄(μ₄-bta)(H₂O)₂](ClO₄)₄(3), [Cu₄(TPA)₄(μ₄-bta)](ClO₄)₄·10H₂O (4) and [Cu₄(tepa)₄(μ₄-bta)](ClO₄)₄·2H₂O (5), the di-nuclear: [Cu₂(DPA)₂(μ₂-bta)(H₂O)₂]·4H₂O (6), [Cu₂(dppa)₂(μ₂-bta)(H₂O)₂]·4H₂O (7) and [Cu₂(pmea)₂(μ₂-bta)]·14H₂O (8) and the trinuclear complex [Cu₃(dppa)₃(μ₃-bta)(H₂O)_2.25](ClO₄)₂·6.5H₂O (9) where Medpt = 3,3′-diamino-N-methyldipropylamine, pmedien = N,N,N′,N″,N″-pentamethyldiethylenetriamine, Mepea = [2-(2-pyridyl)ethyl]-(2-pyridylmethyl)methylamine, TPA = tris(2-pyridylmethyl)amine, tepa = tris[2-(2-pyridyl)ethyl)]amine, DPA = di(2-pyridymethyl)amine, dppa = N-propanamide-bis(2-pyridylmethyl)amine and pmea = bis(2-pyridylmethyl)-[2-(2-pyridylethyl)]amine. The complexes were structurally characterized by elemental analyses, spectroscopic techniques, and by X-ray crystallography for complexes 1, 2, 4, 6, 7 and 9. X-ray structure of the complexes reveal that bta⁴⁻ is acting as a bridging ligand via its four deprotonated caboxylate groups in 1, 2 and 4, three carboxylate groups in 9 and via two trans-carboxylates in 6 and 7. The complexes exhibit extended supramolecular networks with different dimensionality: 1-D in 2 and 4 due to hydrogen bonds of the type O-H···O, 2-D in 1 and 7, and 3-D network in 6 as a result of hydrogen bonds of the types N-H···O and O-H···O. Magnetic susceptibility measurements showed very weak antiferromagnetic coupling between the Cu^II ions in 1-5, 7-9 (|J| = 0.02-0.87 cm⁻¹) and weak ferromagnetic coupling for 6 (J = 0.08 cm⁻¹).     

Synthesis and characterization of 8-quinolinolato vanadium(IV) complexes

Reaction of vanadium(III) chloride with 8-quinolinol (Hqn) gave a mononuclear vanadium(IV) complex, [VOCl₂(H₂O)₂] 1) · 2H₂qn · 2Cl · CH₃CN, and three dinuclear vanadium(IV) complexes: [V₂O₂Cl₂(qn)₂(H₂O)₂] (2) · Hqn, [V₂O₂Cl₂(qn)₂(C₃H₇OH)₂] (3), and [V₂O₂Cl₂(qn)₂(C₄H₉OH)₂] (4). Reaction of vanadium(III) chloride with 5-chloro-8-quinolinol (HClqn) gave four dinuclear vanadium(IV) complexes: [V₂O₂Cl₂(Clqn)₂(H₂O)₂] (5) · 2HClqn, [V₂O₂Cl₂(Clqn)₂(C₃H₇OH)₂] (6), [V₂O₂Cl₂(Clqn)₂(C₆H₅CH₂OH)₂] (7), and [V₂O₂Cl₂(Clqn)₂(C₄H₉OH)₂] (8) · 2C₄H₉OH. Reaction of vanadium(III) chloride with 5-fluoro-8-quinolinol (HFqn) gave two dinuclear vanadium(IV) complexes: [V₂O₂Cl₂(Fqn)₂(H₂O)₂] (9) · HFqn · 2H₂O and V₂O₂Cl₂(Fqn)₂(C₃H₇OH)₂] (10). X-ray structures of 1 · 2H₂qn · 2Cl · CH₃CN, 3, 4, 6, 7, 8 · 2 t-BuOH, and 10 have been determined. As to the mononuclear species 1 · 2H₂qn · 2Cl · CH₃CN, coordination of Hqn to vanadium does not occur, but protonation to Hqn occurs to give H₂qn⁺, which links 1’s through hydrogen bonding, while each of the dinuclear species has a terminal and a bridging qn (or Clqn, Fqn) ligand, giving rise to a (V-O)₂ ring. Magnetic measurements of 3, 4, 6, 7, and 10 in solid form show very weak antiferromagnetic behavior, and the effective magnetic moments are close to spin only value (2.44) of d¹-d¹ system, while ESR of 3 in THF shows dissociation to monomeric species. Change from mononuclear, 1, to dinuclear, 2, species was followed by the change of electronic spectrum.     

Mononuclear and unsymmetric dinuclear complexes of the tripodal ligand 2-hydroxyethyl-bis(2-{pyrid-2-yl}ethyl)amine

Reaction of bis(2-{pyrid-2-yl}ethyl)amine with 2-bromoethanol in the presence of Na₂CO₃ yields the title ligand, LH. Treatment of LH with the CuBr₂ or Zn(O₂CMe)₂ · 2H₂O yields pure crystalline [CuBr(LH)]Br · H₂O (1 · H₂O) and [Zn₂(O₂CMe)₂(μ-O₂CMe)(μ-L)] (2). Reaction of LH with Cu(O₂CMe)₂ · H₂O affords a low yield of [Cu₂Cl₂(μ-O₂CMe)(μ-L)] (3), the Cl⁻ ligands apparently originating from the CH₂Cl₂ crystallization solvent. Compound 1 · H₂O is a near-regular square-pyramidal complex with a neutral, protonated LH ligand. In contrast, 2 and 3 are both unusual unsymmetric dinuclear complexes, with a five-coordinate [ML(O₂CMe)] (M = Zn or Cu) unit linked to a second metal ion through the deprotonated ligand alkoxide donor and O,O′-bridging acetate ligand.     

Dicyanamido-metal(II) complexes. Part 4: Synthesis, structure and magnetic characterization of polynuclear Cu(II) and Ni(II) complexes bridged by μ-1,5-dicyanamide

The one pot aqueous reaction of M(ClO₄)₂ (M = Cu²⁺ or Ni²⁺) with N-methylbis[2-(2-pyridylethyl)]amine (MeDEPA) and N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethylenediamine (bpmen) and 1,4,7,10-tetraazacyclododecane (cyclen) in presence of sodium dicyanamide (Nadca) yielded dicyanamido-bridged polynuclear complex {[Cu(MeDEPA)(μ-1,5-dca)]ClO₄}_n (1), and two dinuclear complexes [Cu₂(bpmen)₂(μ-1,5-dca)]₂(ClO₄)₅dca (2) and [Ni(cyclen)(μ-1,5-dca)]₂(ClO₄)₂ (3). These complexes were characterized by IR and UV-Vis spectroscopy. Room temperature single-crystal X-ray studies have confirmed that the Cu(II) centers in 1 and 2 adopt geometries that are more close to trigonal bipyramidal (TBP) in 1 and close to square pyramidal (SP) in 2, whereas in 3, the Ni(II) centers are located in octahedral environment with doubly bridged μ-1,5-dca bonding mode. The intermolecular M···M distances in these complexes are in the range of 7.3-8.6 Å. Variable temperature magnetic susceptibility studies have confirmed that the dca-bridges mediate very weak antiferromagnetic interaction between the M(II) centers with J values of −0.35, −0.18 and −0.43 cm⁻¹ for 1, 2 and 3, respectively. The results are compared and discussed in the light of other related bridged μ-1,5-dca Cu(II) and Ni(II) complexes.     

Synthesis, characterization, and magnetic properties of new binuclear CuCu bis(oxamato) complexes

Two new neutral, binuclear Cu^IICu^II bis(oxamato) complexes with the formula [Cu₂(opba)(pmdta)(MeOH)] · 1/2MeOH · dmf (3) and [Cu₂(nabo)(pmdta)(MeOH)] (4), with opba = o-phenylene-bis(oxamato), nabo = 2,3-naphthalene-bis(oxamato), pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine and dmf = dimethylformamide have been synthesized and their crystal structures have been determined. The structure of 3 consists of dimeric [Cu₂(opba)(pmdta)(MeOH)] entities, joined together by mutual intermolecular Cu?O contacts of the Cu²⁺ ion of one [Cu(opba)]²⁻ complex fragment and one carboxylate atom of the oxamato group of a second [Cu(opba)]²⁻ complex fragment. The structure of 4 consists of neutral binuclear complexes joined together by hydrogen bonds and π-π interactions, giving rise to an unique supramolecular 1D-chain. The magnetic properties of 3 and 4 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter, identical values of (−114 ± 2) cm⁻¹ (3) and (−112 ± 2) cm⁻¹ (4) were obtained.     

Luminescent cadmium and zinc diphenate coordination polymers containing pyridyl-piperazine type ligands: Grids, diamondoid lattices, and a rare 4-connected net

Hydrothermal synthesis has afforded five d¹⁰ configuration divalent metal diphenate coordination polymers containing pyridyl-piperazine type ligands, which were structurally characterized by single-crystal X-ray diffraction. {[Cd(diphenate)(3-bpmp)(H₂O)]·0.5H₂O}_n (1, 3-bpmp = bis(3-pyridylmethyl)piperazine) has a double layer topology. Its perchlorate-containing analog {[Cd₃(diphenate)₄(H₂3-bpmp)(H3-bpmp)(H₂O)₂](ClO₄)·7H₂O}_n (2) possesses a very rare 4-connected 6⁵8 dmp topology based on anionic trinuclear nodes. {[Cd(diphenate)(4-bpfp)]·H₂O}_n (3, 4-bpfp = bis(4-pyridylformyl)piperazine) manifests a non-interpenetrated diamondoid lattice, while the related compound [Cd(diphenate)(4-bpmp)(H₂O)]_n (4, 4-bpmp = bis(4-pyridylmethyl)piperazine) has a simple (4,4) grid topology. {[Zn(diphenate)(4-bpmp)]·0.5H₂O}_n (5) displays a 2-fold interpenetrated diamondoid lattice. Luminescent properties of these materials are also reported.     

Synthesis, crystal structure, spectroscopic and magnetic properties of doubly and triply bridged dinuclear copper(II) compounds containing di-2-pyridylamine as a ligand

The dihydroxo-bridged dinuclear copper(II) compound [Cu₂(dpyam)₂(μ-OH)₂]I₂ (1) and the triply bridged dinuclear copper(II) compounds with a formato bridge [Cu₂(dpyam)₂(μ-O₂CH)(μ-OH)(μ-OMe)](ClO₄) (2) and [Cu₂(dpyam)₂(μ-O₂CH)(μ-OH)(μ-Cl)](ClO₄) · 0.5H₂O (3) (in which dpyam=di-2-pyridylamine) have been synthesized and their crystal structures determined by X-ray crystallographic methods. All three compounds are either centrosymmetric, or have a symmetry plane in the molecule. Compound 1 contains the [Cu₂(dpyam)₂(μ-OH)₂]⁺ unit and iodide anions. Each copper(II) ion is in a slightly tetrahedrally distorted square planar coordination with the square plane consisting of two nitrogen atoms of the dpyam ligand and two bridging hydroxo groups. The Cu-I distances of 3.321 Å are quite long and only involve a weak semi-coordination. Compound 2 contains a triply bridged dinuclear copper(II) species, the coordination environment around each copper(II) ion involves a distorted trigonal-bipyramidal CuN₂O₃ chromophore. In the dinuclear unit of compound 3, the triply bridged copper(II) ions show a distorted trigonal-bipyramidal coordination of the CuN₂O₂Cl chromophore. The Cu-Cu distances are 2.933(2), 3.023(1) and 3.036(1) Å for compounds 1, 2 and 3, respectively.The magnetic susceptibility measurements, measured from 5 to 280 K, revealed a weak antiferromagnetic interaction between the Cu(II) atoms for compound 1 with a singlet-triplet energy gap (J) of −15.3 cm⁻¹, whereas compounds 2 and 3 are ferromagnetic with J=62.5 and 79.1 cm⁻¹, respectively.     

Zinc complexes with tricarballylic acid and Lewis bases with zero- and two-dimensional structures

Three ternary zinc complexes of the open chain polycarboxylic acid, tricarballylic (1,2,3-propane-tricarboxylic) acid (PTCH₃) have been isolated and characterized with crystallographic and physicochemical techniques. [Zn(PTCH)(phen)(H₂O)]₂ · 4H₂O (1) (where phen = 1,10-phenanthroline) has a unique dinuclear structure, while [Zn(PTCH)(bpy)]_n · 3nH₂O (2) and [Zn(PTCH)(epy)]_n · 4nH₂O (3) (where bpy = 4,4′-bipyridine and epy = 1,2-bis(4-pyridine)ethane) have 2D polymeric structures. The bis-deprotonated ligand, in all three complexes, uses for coordination only two oxygen atoms, which belong to the same carboxylate in 1, and to two different carboxylates in 2 and 3.     

Synthesis, characterization, and cytotoxicity of trimethylplatinum(IV) complexes with 2-thiocytosine and 1-methyl-2-thiocytosine ligands

The reaction of [PtMe₃(MeOH)(bpy)][BF₄] (1) with the thionucleobases 2-thiocytosine (SCy, 2) and 1-methyl-2-thiocytosine (1-MeSCy, 3) resulted in the formation of the complexes [PtMe₃(bpy)(SCy-κS)][BF₄] (4) and [PtMe₃(bpy)(1-MeSCy-κS)] [BF₄] (5), respectively. The complexes were characterized by ¹H and ¹³C NMR spectroscopy as well as by single-crystal X-ray analyses of 4 · MeOH and 5. In 4 · MeOH two strong hydrogen bonds (N4-H?N3′: N4?N3′ 2.976(7) Å) between the thiocytosine ligands give rise to base pairing thus forming dinuclear cations [{PtMe₃(bpy)(SCy-κS)}₂]²⁺. In both complexes the platinum atom is octahedrally coordinated [PtC₃N₂S] by three methyl ligands, the 2,2′-bipyridine ligand and the κS coordinated nucleobase (configuration index: OC-6-33). The structural investigations gave evidence that the sulfur atoms of the nucleobase ligands in 4 · MeOH and 5 have to be regarded as sp³ and sp² hybridized, respectively. Thus, the ligand in 4 · MeOH has to be considered as the deprotonated thiol-amino form of thiocytosine being reprotonated at N1. In complex 5 the 1-MeSCy is coordinated in its thione-amino form. DFT-calculations of the base-paired dinuclear cation in 4 as well as of 4 itself gave proof of the strength of the hydrogen bond (8.5 kcal/mol) and exhibited that cation-anion interactions influence the conformation of the complex. In vitro cytotoxicity studies of 4 and 5 using nine different human tumor cell lines revealed moderate cytotoxic activity.     

Synthesis and structures of pyridinecarboxylate-containing zinc(II) complexes in dien and tren system

Four new zinc(II) complexes [Zn(dien)(μ-nic)]₂(BPh₄)₂·2CH₃OH (1), {[Zn(dien)(isonic)]BPh₄}_n (2), [Zn(tren)(nic)]BPh₄ (3) and [Zn(tren)(isonic)]BPh₄ (4) (dien/tren = diethylenetriamine/triethylenetriamine, nic/isonic = nicotinate/isonicotinate anion) were synthesized and structurally characterized by IR, ¹H NMR and single crystal X-ray diffraction. In the zinc(II) complexes of dien, both nicotinate and isonicotinate connect the zinc(II) ions via N,O-bis-monodentate mode. Complex 1 contains a centrosymmetric dinuclear unit bridged by two nicotinate anions in anti-parallel way. Complex 2 is characterized by an infinite one-dimensional zigzag chain bridged by isonicotinate anion in an end-to-end mode. The Zn···Zn distance is 6.782 for 1 and 8.805 Å for 2. While in the complexes of tren, both 3 and 4 are mononuclear complexes with nicotinate and isonicotinate coordinated to zinc(II) ion through only one oxygen atom of their carboxylate groups. The zinc(II) ions in all of the four complexes are in a distorted trigonal bipyramidal geometry. Complex 3 forms a dinuclear unit and complex 4 forms an infinite 2D sheet structure through intermolecular H-bonds. In all of the crystal lattices, the counterions act to balance the electronic charge at the same time to construct different 3D structures through noncovalent interactions such as C-H···π, N-H···π and van der Waals interactions.     

Diorganotin(IV) complexes of dipeptides containing the alpha-aminoisobutyryl residue (Aib): preparation, structural characterization, antibacterial and antiproliferative activities of [(n-Bu)2 Sn(H(-1)L)] (LH=H-Aib-L-Leu-OH, H-Aib-L-Ala-OH)

Two new organotin(IV) complexes with dianionic dipeptides containing the α-aminoisobutyryl residue (Aib) as ligands are described. The solid complexes [(n-Bu)₂Sn(H₋₁L_A)] · 2MeOH (1 · 2MeOH) (L_AH = H-Aib-L-Leu-OH) and [(n-Bu)₂Sn(H₋₁L_B)] · MeOH (2 · MeOH) (L_BH = H-Aib-L-Ala-OH) have been isolated and characterized by single-crystal X-ray crystallography and spectroscopic techniques (H₋₁L²⁻ is the dianionic form of the corresponding dipeptide). Complexes 1 · 2MeOH and 2 · MeOH are monomeric with similar molecular structures. The doubly deprotonated dipeptide behaves as a N(amino), N(peptide), O(carboxylate) ligand and binds to the Sn^IV atom. The five-coordinate metal ion has a distorted trigonal bipyramidal geometry. A different network of intermolecular hydrogen bonds in each compound results in very dissimilar supramolecular features. The IR, far-IR, Raman and ¹¹⁹Sn NMR data are discussed in terms of the nature of bonding and known structures. The antibacterial and antiproliferative activities as well as the effect of the new compounds on pDNA were examined. Complexes 1 and 2 are active against the gram-positive bacteria Bacillus subtilis and Bacillus cereus. The IC₅₀ values reveal that the two compounds express promising cytotoxic activity in vitro against a series of cell lines.     

Mononuclear and dinuclear model hydrolases of nickel and cobalt

Reaction between the dinuclear model hydrolases [M₂(μ-OAc)₂(OAc)₂(μ-H₂O)(tmen)₂]; M = Ni (1); M = Co (2) and trimethylsilyltrifluoromethanesulphonate (TMS-OTf) under identical reaction conditions gives the mononuclear complex [Ni(OAc)(H₂O)₂(tmen)][OTf] · H₂O (3) in the case of nickel and the dinuclear complex [Co₂(μ-OAc)₂(μ-H₂O)₂(tmen)₂][OTf]₂ (4) in the case of cobalt.Reaction of (3) with urea gives the previously reported [Ni(OAc)(urea)₂(tmen)][OTf] (5), whereas (4) gives [Co₂(OAc)₃(urea)(tmen)₂][OTf] (6) previously obtained by direct reaction of (2) with urea. Both (3) and (4) react with monohydroxamic acids (RHA) to give the dihydroxamate bridged dinuclear complexes [M₂(μ-OAc)(μ-RA)₂(tmen)₂][OTf]; M = Ni (7); M = Co (8) previously obtained by the reaction of (1) and (2) with RHA, illustrating the greater ability of hydroxamic acids to stabilize dinuclear complexes over that of urea by means of their bridging mode, and offering a possible explanation for the inhibiting effect of hydroxamic acids by means of their displacing bridging urea in a possible intermediate invoked in the action of urease.     

Synthesis and characterization of ether-derivatized aminophosphines and their application in C-C coupling reactions

Four new bis(phosphino)amine ligands (Ph₂P)₂N-C₆H₃-R, where R = 3,5-OMe (1), 2,5-OMe (2), 2,4-OMe (3) or 3,4-OMe (4), were prepared via aminolysis of the corresponding dimethoxyanilines with 2 equiv. of diphenylphosphine chloride in the presence of triethyl amine. Oxidation of these ligands with aqueous H₂O₂, elemental S₈ or Se powder afforded the corresponding chalcogen oxides 1a-4a, sulfides 1b-4b and selenides 1c-4c in good yields. Reaction of 1-4 with [MCl₂(cod)] (M = Pt, Pd; cod = cycloocta-1,5-diene) in equimolar ratios afforded cis-[MCl₂{(Ph₂P)₂N-C₆H₃-R}] (M = Pt; R = 3,5-OMe 1d, R = 2,5-OMe 2d, R = 2,4-OMe 3d, and R = 3,4-OMe 4d. M = Pd; R = 3,5-OMe 1e, R = 2,5-OMe 2e, R = 2,4-OMe 3e, and R = 3,4-OMe 4e). Similarly, reaction of [Cu(CH₃CN)₄]PF₆ with the 1-4 in 1:2 ratio gave [Cu{(Ph₂P)₂N-C₆H₃-R}₂]PF₆ (R = 3,5-OMe 1f, 2,5-OMe 2f, 2,4-OMe 3f and 3,4-OMe 4f). All new compounds were fully characterized by spectroscopy and elemental analysis and the molecular structures of seven representative compounds were determined by single-crystal X-ray crystallography. In addition, the palladium complexes were investigated as pre-catalysts in C-C coupling reactions.     

Mono and bimetallic Co Schiff base complexes: Coordination induced ligand imidazolidine ring cleavage and stabilization

2-(2′-Hydroxyphenyl) imidazoline ring grafted dinucleating diimine-diamine-tris-phenol ligand (H₃aeas) has been obtained from a two-step reaction of 2-hydroxy acetophenone, N,N′-bis-(2-aminoethyl)ethylenediamine and 2-hydroxy benzaldehyde. Reaction of the ligand with Co(ClO₄)₂·6H₂O and NEt₃ in MeOH-DCM solvent mixture yielded the monometallic complex [Co(aea)]ClO₄·H₂O (1) of imidazolidine ring hydrolyzed hexadentate proligand H₂aea. Any solvent derived MeO⁻ bridged Co₂ complex could not be obtained due to facile cobalt coordination assisted hydrolytic cleavage of substituted imidazolidine ring. When the reaction is carried out with Co(NO₃)₂·4H₂O and CoCl₂·6H₂O in presence of NH₄NCS and NaN₃ in MeOH-DCM and MeOH under aerobic conditions, preassembly of bimetallic [Co₂(μ-OMe)]⁵⁺ and [Co₂(μ-N₃)]⁵⁺ cores takes place on the solvent derived methoxido and azido clips through non-hydrolytic pathways in [(SCN)₂Co₂(μ-OMe)(μ-aeas)]·DMF (2), and cocrystals of [(N₃)₂Co₂(μ-OMe)(μ-aeas)] (3a) and [(N₃)₂Co₂(μ-N₃)(μ-aeas)] (3b), respectively.     

Synthesis, crystal structures and magnetic properties of the copper(II) complexes containing isophthalate anion as coligand

Two new dinuclear isophthalato-bridged copper(II) complexes [Cu₂(ntb)₂(μ-ipt)](ClO₄)₂·4CH₃OH·0.33H₂O (1), [Cu₂(bbma)₂(μ-ipt)(NO₃)(CH₃OH)]NO₃·CH₃OH (2) and one mononuclear complex [Cu(bbma)(ipt)(CH₃OH)_0.67(H₂O)_0.33]·2CH₃OH (3) containing tetradentate and tridentate poly-benzimidazole ligands were synthesized, where ntb is tris(2-benzimidazolylmethyl)amine, bbma is bis(benzimidazol-2-yl-methyl)amine and ipt is isophthalate dianion. All of the complexes were characterized by elemental analysis, IR spectra and X-ray crystallography. The structures of complexes 1 and 2 consist of μ-ipt bridging two Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry around the Cu(II) ions of both compounds has a distorted square pyramidal geometry. The Cu···Cu distances are 9.142 and 10.435 Å for 1 and 2, respectively. Complex 3 has a distorted square pyramidal geometry achieved by the three N-atoms of the bbma ligand, one isophthalate-oxygen atom and one oxygen atom from a coordinated methanol molecule. The magnetic susceptibility measurements at variable temperature over the 2-300 K range for complexes 1 and 2 are reported, with J values to be −0.013 and −0.32 cm⁻¹, respectively. The results show that the two complexes exhibit very weak antiferromagnetic interactions between the dinuclear copper(II) centers.     

Synthesis and structures of four new compounds of the copper(II)-carboxylate-pyridinecarboxamide system

The synthesis and structural characterization of four new copper compounds with formula [Cu(crot)₂(isn)₂(Hcrot)·H₂O] (1), [Cu(oda)(isn)₂] (2), [Cu(crot)₂(nia)₂·(H₂O)] (3) and [Cu(oda)(nia)] (4) (crot = trans-2-butenoate, oda = oxydiacetate, isn = isonicotinamide, nia = nicotinamide) is reported. The complexes extend into 3D supramolecular structures by means of hydrogen bonds. EPR spectra of powder samples of the compounds are reported.     

Influence of the counter anion and solvent in the structure of copper derivatives with the 2,3-bis(2-pyridyl)pyrazine ligand

Several compounds have been isolated from the reaction between different copper bis(acetylacetonato) derivatives and the potentially bridging ligand 2,3-bis(2-pyridyl)pyrazine (bppz). A compound of formula [Cu(tfacac)₂(bppz)] (1) is obtained when the substituted trifluoromethylacetylacetonato is used. The use of different anions and the unsubstituted acetylacetonato give rise to new derivatives of general formula [{Cu(acac)}₂(μ-bppz)₂]X₂ (X⁻ = BF₄⁻, 2; PF₆⁻, 3; BPh₄⁻, 4). In these compounds the bppz ligand is acting as a bridge by chelating one copper atom and bonding monodentate a second copper atom. The presence of anions with different coordination abilities introduces variations in the copper environment and geometry. When the non-coordinating tetraphenylborate is used different compounds depending on the nature of the solvent are obtained. The dimer 4 was isolated from a methanol/chloroform mixture, while in the absence of chloroform the monomeric compound of formula [Cu(acac)(bppz)(ROH)](BPh₄)·ROH (ROH = MeOH, 5) was obtained. When ethanol was used instead of methanol the analogous derivative 6 (R = EtOH) was isolated. Both species show a mononuclear structure with the copper atom five-coordinated by the chelating acac and bppz ligands and one hydroxo group occupying the apical position. A similar environment for the copper appears in [Cu(tfacac)(bppz)(MeOH)](BPh₄), 7, which shows a dimeric structure through hydrogen bonds interactions. The magnetic susceptibility data of the dimeric compounds show very weak antiferromagnetic interactions between the copper atoms, an expected fact since the bridging bppz ligand is not planar but the monodentate pyridine is more or less perpendicular to the other two aromatic rings, precluding the spin exchange via the π ligand electrons.     

Five-coordinate cobalt(II) complexes of tris(2-pyridylmethyl)amine (TPA): Synthesis, structural and magnetic characterization of a terephthalato-bridged dinuclear cobalt(II) complex

The cobalt(II) complexes [Co(TPA)Cl]ClO₄ (1), [Co(TPA)Br]ClO₄ (2), [Co(TPA)(H₂O)]Cl(ClO₄) (3) and [Co₂(TPA)₂(μ-tp)](ClO₄)₂ · 2H₂O (4) (TPA = tris(2-methylpyridyl)amine and tp = terephthalate dianion) were synthesized and structurally characterized by UV-vis and IR spectroscopy. The molecular structures of complexes 1 and 4 were determined by X-ray crystallography and their magnetic properties were measured over the temperature range 2-300 K. The coordination geometry around the central Co(II) in these compounds has a distorted trigonal bipyamidal geometry with four nitrogen atoms from the TPA ligand and the fifth coordination site is occupied by Cl⁻ ion in 1, Br⁻ ion in 2, coordinated oxygen atom from H₂O in 3 and by an oxygen atom supplied by the carboxylate group of the bridged terephthalato ligand in 4. The visible spectra of the complexes 1-3 in MeOH show strong distortion toward tetrahedral geometry. For complex 4, analysis of the infrared spectral data for the ν(COO⁻) stretching frequencies of the tp-carboxalato groups reveals the existence of the bis(monodentate) coordination mode for the bridged tp. X-ray data for 1 and 4 show that the former is mononuclear while the latter is dinuclear. The electronic spectrum of 4 in MeOH is in complete agreement with the assigned X-ray geometry around the Co(II) centers. The magnetic behavior of the mononuclear complex 1 is indicative of a high-spin compound with zero-field splitting. The best fit was obtained with ∣D∣ = 7.3 cm⁻¹, g = 2.25. The dinuclear complex 4 exhibits weak antiferromagnetic coupling with a coupling constant J = −0.8 cm⁻¹. The magnetic properties and the structural parameters of 4 are discussed in relation to the other related μ-terephthalato dinuclear Co(II) compounds. The geometry of the coordination sphere around 4 is unique - the CSD compilation listing only one other compound with such a geometry around the dinuclear Co(II) complex and its composition is far different from that in 4. However, they share a common feature of having a weakly antiferromagnetic coupling between Co(II) centers.     

Structural studies on 1:1 and 2:1 adducts of silver(I) cyanide with alkanediamine ligands

The crystal structures of two 1:1 ligand-silver(I) cyanide complexes, [Ag(CN)(en)] (en = ethane-1,2-diamine) (1) and [Ag(CN)(pn)] (pn = propane-1,2-diamine) (2), and of two 2:1 ligand-silver(I) cyanide compounds, [(AgCN)₂ · tn] (tn = propane-1,3-diamine) (3) and [(AgCN)₂ · bn] (bn = butane-1,4-diamine) (4), were determined from single-crystal X-ray diffraction data, collected at 173 K. In 1 and 2, mononuclear AgCN complexes are formed, in which silver(I) is coordinated by one cyanide and one chelating alkanediamine donor ligand. However, in the dinuclear adducts of 3 and 4, two AgCN units are connected by one alkane-1,n-diamine bridging ligand (n = 3, 4). The resulting molecules of 1-4 are cross-linked via N-H?N hydrogen bonds. Apart from these intermolecular contacts, comparatively short Ag(I)-Ag(I) distances of 3.182(1) Å (in 1), 3.267(1) Å (in 2), 3.023(2) Å (in 3) and 3.050(2) Å (in 4) occur.