Synthesis and structure of iron (III) and iron (II) complexes in S4P2 environment created by diethyldithiocarbamate and 1,2-bis(diphenylphosphino)ethane chelation: Investigation of the electronic structure of the complexes by Mössbauer and magnetic studies

Iron (II) and iron (III) complexes, [Fe^II(DEDTC)₂(dppe)] · CH₂Cl₂ (1), [Fe^II(ETXANT)₂(dppe)] (2) (DEDTC = diethyldithiocarbamate, ETXANT = ethyl xanthate, dppe = 1,2-bis (diphenylphosphino) ethane), and [Fe^III(DEDTC)₂(dppe)] [Fe^IIICl₄] (3) have been synthesized and characterized. Since 3 contains two magnetic centers, an anion metathesis reaction has been conducted to replace the tetrahedral FeCl₄⁻ by a non-magnetic BPh₄⁻ ion producing [Fe^III(DEDTC)₂(dppe)]BPh₄ (4) for the sake of unequivocal understanding of the magnetic behavior of the cation of 3. With the similar end in view, the well-known FeCl₄⁻ ion, the counter anion of 3, is trapped as PPh₄[Fe^IIICl₄] (5) and its magnetic property from 298 to 2 K has been studied. Besides the spectroscopic (IR, UV-Vis, NMR, EPR, Mass and XPS) characterization of the appropriate compounds, especially 2, others viz. 1, 3 and 4 have been structurally characterized by X-ray crystallography. While Fe^II complexes, 1 and 2, are diamagnetic, the Fe^III systems, namely the cations of 3, and 4 behave as low-spin (S = 1/2) paramagnetic species from 298 to 50 K. Below 50 K 3 shows gradual increase of χ_MT up to 2 K suggesting ferromagnetic behavior while 4 exhibits gradual decrease of magnetic moment from 60 to 2 K, indicating the occurrence of weak antiferromagnetic interaction. These conclusions are supported by the Mössbauer studies of 3 and 4. The Mössbauer pattern of 1 exhibits a doublet site for diamagnetic (2-400 K) Fe^II. The compounds 1, 2 and 4 encompass interesting cyclic voltammetric responses involving Fe^II, Fe^III and Fe^IV.     

Synthesis and structural characterization of the mono- and diphosphine-containing diiron propanedithiolate complexes related to [FeFe]-hydrogenases. Biomimetic H2 evolution catalyzed by (mu-PDT)Fe2(CO)4[(Ph2P)2N(n-Pr)

As the new H-cluster models, six diiron propanedithiolate (PDT) complexes with mono- and diphosphine ligands have been prepared and structurally characterized. The monophosphine model complex (μ-PDT)Fe₂(CO)₅[Ph₂PNH(t-Bu)] (1) was prepared by reaction of parent complex (μ-PDT)Fe₂(CO)₆ (A) with 1 equiv of Ph₂PNH(t-Bu) in refluxing xylene, whereas A reacted with 1 equiv of Me₃NO · 2H₂O in MeCN at room temperature followed by 1 equiv of Ph₂PH to give the corresponding monophosphine model complex (μ-PDT)Fe₂(CO)₅(Ph₂PH) (2). Further treatment of 2 with 1 equiv of n-BuLi in THF at −78 °C followed by 1 equiv of CpFe(CO)₂I from −78 °C to room temperature afforded monophosphine model complex (μ-PDT)Fe₂(CO)₅[Ph₂PFe(CO)₂Cp] (3), whereas the diphosphine model complexes (μ-PDT)Fe₂(CO)₄(Ph₂PC₂H₄PPh₂) (4), (μ-PDT)Fe₂(CO)₄[(Ph₂P)₂N(n-Pr)] (5) and (μ-PDT)Fe₂(CO)₄[(Ph₂P)₂N(n-Bu)] (6) were obtained by reactions of A with ca.1 equiv of the corresponding diphosphines in refluxing xylene. All the new model complexes were characterized by elemental analysis, spectroscopy and particularly for 1 and 3-6 by X-ray crystallography. On the basis of electrochemical and spectroelectrochemical studies, model 5 was found to be a catalyst for HOAc proton reduction to H₂, and for this electrocatalytic reaction an ECCE mechanism was proposed.     

Bioinspired FeIIICdII and FeIIIHgII complexes: synthesis, characterization and promiscuous catalytic activity evaluation

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe^IIICd^II(L)(μ-OAc)₂]ClO₄·0.5H₂O (1) complex containing the unsymmetrical ligand H₂L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)}-aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe₂^IIIHg₂^II(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) and [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe^III₂Hg^II₂(L)₂(OH)₂](ClO₄)₂·2CH₃OH (2) can be converted to (3) by the fixation of atmospheric CO₂ since the crystal structure of the tetranuclear organometallic complex [Fe^IIIHg^II(L)(μ-CO₃)Fe^IIIHg^II(L)](ClO₄)₂·H₂O (3) with an unprecedented {Fe^III(μ-O_phenoxo)₂(μ-CO₃)Fe^III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe^III-bound hydroxo group on the CO₂ molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe^III centers in 3 are antiferromagnetically coupled (J = − 7.2 cm^− 1) and that the Fe^III-OR-Fe^III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k_H/k_D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe^III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe^III…Hg^II distance could be responsible for the lower catalytic effectiveness of 2.     

Phosphorus-carbon(pyridyl) bond cleavage on reacting diphenyl-2-pyridylphosphine with triiron dodecacarbonyl

The reaction of [Fe₃(CO)₁₂] with diphenyl-2-pyridylphosphine (PPh₂Py) in refluxing toluene for 1 h afforded three compounds, [Fe₂(CO)₆(μ-PPh₂)(μ-κ²-C,N-C₅H₄N)] (1), [Fe(CO)₄(κ¹-P-PPh₂Py)] (2), and [Fe(CO)₃(κ¹-P-PPh₂Py)₂] (3) in 23%, 10% and 3.5% yields after work-up, respectively. The PPh₂Py ligand acts as a terminal P-donor ligand in 2 and 3, while in 1 it underwent a selective phosphorus-carbon(pyridyl) bond cleavage to afford phosphido- and pyridyl-bridged ligands. The complexes were characterized by elemental analysis, FAB-mass, FTIR, ¹H and ³¹P-{¹H}NMR spectroscopies. Compounds 1 and 2 were also characterized by X-ray single crystal.     

Syntheses, structures and magnetic properties of heterobimetallic complexes based on a new tetracyanometalate precursor

A new mononuclear tetracyanometallic complex, (n-Bu₄N)[(dbphen)Fe(CN)₄] (1, dbphen = 5,6-dibromo-1,10-phenanthroline), has been prepared by reacting [(dbphen)Fe^II(py)₂(SCN)₂] and KCN in water and further oxidized with chlorine. With the use of 1 as building block, two trinuclear Fe₂M complexes, [(dbphen)₂Fe₂(CN)₈Cu(Me₃tacn)]·3H₂O (2), [(dbphen)₂Fe₂(CN)₈Ni(dabhctd)]·2H₂O (3) and a chain complex of squares [(dbphen)₂Fe₂(CN)₈Co(MeOH)₂]_n (4), have been synthesized and structurally characterized. Magnetic studies show ferromagnetic coupling between Fe^III and M^II (M = Cu, 2; Ni, 3) ions bridged by cyanides in complexes 2 and 3, while complex 4 exhibits meta-magnetic behavior.     

Neighbouring metal induced oxidative addition at the iron centre amongst the iron-arylpyridylphosphine complexes

Complexes of the type (η⁴-BuC₅H₅)Fe(CO)₂(P) (P = PPh₂Py 3, PPhPy₂4, PPy₃5; Py = 2-pyridyl) were satisfactorily prepared. Upon treatment of 3 with M(CO)₃(EtCN)₃ (M = Mo, 6a; W, 6b), the pyridyl N-atom could be coordinated to the metal M, which then eliminates a CO ligand from the Fe-centre and induced an oxidative addition of the endo-C-H of (η⁴-BuC₅H₅). This results in a bridged hydrido heterodimetallic complex [(η⁵-BuC₅H₄)Fe(CO)(μ-P,N-PPh₂Py)(μ-H)M(CO)₄] (M = Mo, 7a, 81%; W, 7b, 76%). The reaction of 4 or 5 with 6a,b did not give the induced oxidative addition, although these complexes contain more than one pyridyl N-atom. The reaction of 4 with M(CO)₄(EtCN)₂ (M = Mo, 9a; W, 9b) produced heterodimetallic complexes [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′-PPhPy₂)M(CO)₄] (M = Mo, 10a, 81%; W, 10b, 83%). Treatment of 5 with 6a,b gave [(η⁴-BuC₅H₅)Fe(CO)₂(μ-P:N,N′,N″-PPy₃)M(CO)₃] (M = Mo, 12a, 96%; W, 12b, 78%).     

Synthesis, crystal structures, electrochemical and magnetic properties of polynuclear {Fe4} and {Fe8Na4} carboxylate/picolinate clusters

Reaction of sodium picolinate with Fe^III oxo-centered carboxylate triangles in MeCN in the presence of PPh₄Cl yields (PPh₄)[Fe₄O₂(O₂CR)₇(pic)₂] (R = Ph (1), Bu^t (2)). Omitting the phosphonium cation produces [Fe₈Na₄O₄(O₂CPh)₁₆(pic)₄(H₂O)₄] (3), which contains two Fe₄Na₂ units bridged by two picolinate ligands. X-ray crystal structures of 1 and 3 are reported.Voltammetric profiles in MeCN show four one-electron reduction steps for complexes 1 and 2. Variable-temperature magnetic susceptibility measurements in polycrystalline samples of 1 and 3 reveal strong antiferromagnetic couplings leading to S = 0 ground states.     

Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set

The synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn^III₂(L-3Н)₂(CH₃ОH)₄]·2CH₃ОH (1) and [Mn^III₂(L-3Н)₂(Py)₄]·2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]-4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn₂N₄} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = −3.6 cm⁻¹, Θ = −2.02 K for 1 and g = 2.00, J = −3.7 cm⁻¹, Θ = 1.43 K for 2.     

Synthesis and reactivity of osmium (VI) nitrido complexes containing pyridine-carboxylato ligands

A series of osmium(VI) nitrido complexes containing pyridine-carboxylato ligands Os^VI(N)(L)₂X (L = pyridine-2carboxylate (1), 2-quinaldinate (2) and X = Cl (a), Br (1b and 2c) or CH₃O (2b)) and [Os^VI(N)(L)X₃]⁻ (L = pyridine-2,6-dicarboxylate (3) and X = Cl (a) or Br (b)) have been synthesised. Complexes 1 and 2 are electrophilic and react readily with various nucleophiles such as phosphine, sulfide and azide. Reaction of Os^VI(N)(L)₂X (1 and 2) with triphenylphosphine produces the osmium(IV) phosphiniminato complexes Os^VI(NPPh₃)(L)₂X (4 and 5). The kinetics of nitrogen atom transfer from the complexes Os^VI(N)(L)₂Br (2c) (L = 2-quinaldinate) with triphenylphosphine have been studied in CH₃CN at 25.0 °C by stopped-flow spectrophotometric method. The following rate law is obtained: −d[Os(VI)]/dt = k₂[Os(VI)][PPh₃]. Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) reacts also with [PPN](N₃) to give an osmium(III) dichloro complex, trans-[PPN][Os^III(L)₂Cl₂] (6). Reaction of Os^VI(N)(L)₂Cl (L = 2-quinaldinate) (2a) with lithium sulfide produces an osmium(II) thionitrosyl complex Os^II(NS)(L)₂Cl (7). These complexes have been structurally characterised by X-ray crystallography.     

New pyridyl modified phosphines: Synthesis and late transition-metal coordination studies

Using a phosphorus based Mannich condensation reaction the new pyridylphosphines {5-Ph₂PCH₂N(H)}C₅H₃(2-Cl)N (1-Cl) and {2-Ph₂PCH₂N(H)}C₅H₃(5-Br)N (1-Br) have been synthesised in good yields (60% and 88%, respectively) from Ph₂PCH₂OH and the appropriate aminopyridine. The ligands 1-Cl and 1-Br display variable coordination modes depending on the choice of late transition-metal complex used. Hence P-monodentate coordination has been observed for the mononuclear complexes AuCl(1-Cl) (2), AuCl(1-Br) (3), RuCl₂(p-cymene)(1-Cl) (4), RuCl₂(p-cymene)(1-Br) (5), RhCl₂(Cp^∗)(1-Cl) (6), RhCl₂(Cp^∗)(1-Br) (7), IrCl₂(Cp^∗)(1-Cl) (8), IrCl₂(Cp^∗)(1′-Cl) (8′), IrCl₂(Cp^∗)(1-Br) (9), cis-/trans-PdCl₂(1-Cl)₂ (10), cis-/trans-PdCl₂(1-Br)₂ (11), cis-PtCl₂(1-Cl)₂ (12) and cis-PtCl₂(1-Br)₂ (13). Reaction of Pd(Me)Cl(cod) (cod = cycloocta-1,5-diene) with either 1 equiv. of 1-Br or the known pyridylphosphines 1′-Cl, 1-OH or 1-H gave the P/N-chelate complexes Pd(Me)Cl(1-Br-1-H) (14)-(17). All new compounds have been fully characterised by spectroscopic and analytical methods. Furthermore the structures of 4, 5, 10 and 16 · (CH₃)₂SO have been elucidated by single crystal X-ray crystallography. A crystal structure of the dinuclear metallocycle trans,trans-[PdCl₂{μ-P/N-{Ph₂PCH₂N(H)}C₅H₄N}]₂ · CHCl₃, 18 · CHCl₃, has also been determined. Here 1-H bridges, using both P and pyridyl N donors, two dichloropalladium centres affording a 12-membered ring with the PdCl₂ units adopting a head-to-tail arrangement.     

Biotechnological application of homo- and heterotrinuclear iron(III) furoates for cultivation of iron-enriched Spirulina

New trinuclear iron(III) furoates with the general formula [Fe₃O(α-fur)₆(R-OH)₃]X, where α-fur C₄H₃OCOO, R = CH₃ (1), C₂H₅ (2), n-C₃H₇ (3), n-C₄H₉ (4), X = NO₃⁻ (1-4); [Fe₃O(α-Fur)₆(DMF)(CH₃OH)₂]NO₃ (5); [Fe₃O(α-Fur)₆(H₂O)(CH₃OH)₂]Cl (6); [Fe₂MO(α-Fur)₆(L)(H₂O)₂], where L = THF (7-9), DMF (10-12), M = Mn²⁺ (7, 10), Co²⁺ (8, 11), Ni²⁺ (9, 12) and [Fe₂MO(α-Fur)₆(3Cl-Py)₃], where M = Mn²⁺ (13), Co²⁺ (14), Ni²⁺ (15); have been prepared and investigated by Mössbauer and IR spectroscopy. The X-ray crystal structure for the 1·2CH₃OH complex indicates that it crystallizes in the monoclinic crystal system (P2₁/n) and has a structure typical of μ₃-O-bridged trinuclear iron(III) compounds. Coordination compounds 1, 4, 7, 8 can be used as regulators of the biochemical composition of cyanobacterium Spirulina platensis biomass. The supplementation of these compounds, in concentrations exceeding 5-10 mg/l, increases the content of iron, amino acids, peptides and carbohydrates in Spirulina.     

Nickel(II) and iron(II) mononuclear complexes with 1-methylimidazole-2-aldoximate: New building units for molecule-assembled magnetic materials

A new class of mononuclear metal complexes with 1-methylimidazole-2-aldoximate (miao) has been synthesized and characterized: trans-Ni^II(Cl)₂(Hmiao)₂ (1), trans-Ni^II(miao)₂(py)₂ (2), NO-trans-Ni^II(miao)₂(phen) (3), and NO-trans-Fe^II(miao)₂(phen) (4). The crystal structures of 2, 3, and 4 have been determined by single-crystal X-ray crystallography. Compound 1 having the protonated miao ligand (i.e., Hmiao) is a precursor for synthesizing 2 and 3. Compound 2 is an octahedral Ni^II complex surrounded by two miao bidentate ligands and two monodentate ligands of pyridine in a trans-arrangement. Compound 3 is a cis-type octahedral Ni^II complex with two miao ligands and a bidentate ligand of 1,10-phenanthroline, in which the ligand arrangement around Ni^II center is found in an NO-trans form. Compound 4 is an isostructural Fe^II derivative of 3. Compounds 1, 2, and 3 exhibit paramagnetic nature with an S = 1 spin and a positive zero-field splitting, among which it for 3 is overlapped with intermolecular ferromagnetic interaction (zJ/k_B = +0.16 K). Compound 4 is diamagnetic due to the existence of low-spin Fe^II ion.     

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.     

Supramolecular architectures based on di-, tri- and tetrameric complexes with N,N′-diacylhydrazide ligands

Five new complexes, [Co₃(HL₁)₂(Py)₈]·4CH₃OH (1), [Ni₃(HL₁)₂(Py)₄]₂·2DMF (2), [Co₃(H₂L₂)₂(Py)₈]·2NO₃ (3), [Ni₂(HL₂)(Py)₆] (4) and [Cu₄(HL₂)₂(Py)₄]·4DMF (5) (H₄L₁ = N-propionyl-4-hydroxysalicylhydrazide, H₄4-hopshz; H₅L₂ = N-(3-carboxy-cis-2-propenoyl)-4-hydroxysalicylhydrazide, H₅4-hocpshz) have been obtained from two N,N′-diacylhydrazide ligands and characterized by elemental analysis, FT-IR, X-ray diffraction and antimicrobial activities. These di-, tri-, and tetrameric complexes are connected into three-dimensional supramolecular architectures with interesting topologies through O-H?O, C-H?O and C-H?π interactions. 1-3 are linear trimeric complexes with the ligands triply-deprotonated. Topological analysis indicates that they exhibit 2D (4,4), 3D (6,8)-connected (3³4⁹5²6)(3⁴4¹²5⁷6⁴7) and 8-connected (4²⁵6³) net, respectively. 4 and 5 possess dimeric and tetrameric structures, which are extended into 7-connected (3³4¹³5³6) and 4-connected (4,4) net, respectively.     

Synthesis and characterization of ruthenium(II) complexes based on diphenyl-2-pyridylphosphine and their applications in transfer hydrogenation of ketones

Synthesis and characterization of the ruthenium complexes [RuH(CO)Cl(κ¹-P-PPh₂Py)₂(PPh₃)] (1) and [Ru(CO)Cl₂(κ¹-P-PPh₂Py)(κ²-P-N-PPh₂Py)] (2) containing diphenyl-2-pyridylphosphine (PPh₂Py) are described. Spectral and structural data suggested linkage of the PPh₂Py in κ¹-P bonding mode in 1 and both the κ¹-P and κ²-P-N bonding modes in 2. The complex 1 reacted with N,N-donor bases viz., ethylenediamine (en), N,N′-dimethyl-(ethylenediamine) (dimen), 1,3-diaminopropane (diap), 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen) and di-2-pyridylaminomethylbenzene (dpa) to afford cationic complexes of formulation [RuH(CO)(κ¹-P-PPh₂Py)₂(N-N)]⁺ (3-8) [N-N = en, 3; dimen, 4; diap, 5; bipy, 6; phen, 7; and dpa, 8], which have been isolated as their tetrafluoroborate salts. The complexes under investigation have been characterized by elemental analyses, spectroscopic and electrochemical studies. Molecular structures of 2, 3, 6, and 8 have been determined by single crystal X-ray diffraction analyses. Further, the complexes 1-8 act as effective precursor catalyst in transfer hydrogenation of acetophenone/ketones in basic 2-propanol.     

New supramolecular complexes generated from Mn, Fe, Co, Zn, Fe with a bent dipyridyl ligand: Metal- and anion-directed assembly

Assemblies of an angular dipyridyl ligand 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (4-bpo) with a series of metal perchlorate afford five new supramolecular complexes with the general formula of [M(4-bpo)₂(H₂O)₄] · (4-bpo)₂ · (anion) · (solvent), in which M = Mn^II for 1, Fe^II for 2, Co^II for 3, Zn^II for 4, and Fe^III for 5. Although similar molecular structures and compositions are found for these mononuclear complexes, they display two types of supramolecular lattices. Complexes 1, 4 and 5 similarly crystallize in space group P2/n or P2/c. The complex cations, free 4-bpo and lattice water are linked to generate 2D layered frameworks with the aid of hydrogen bonding, and the counter anions are located within and between (also methanol in 5) these 2D arrays. However, complexes 2 and 3 are isostructural in space group . Two types of alternate 2D layers consisting of complex cations and free 4-bpo components, respectively, are observed with the anions and lattice water locating between them. These motifs are interlinked by complicated hydrogen-bonding to form a 3D intercalated network. Moreover, when Co(NO₃)₂ is used instead of Co(ClO₄)₂ in the assembly of 3, a 1D polymeric chain complex {[Co(4-bpo)(H₂O)₂(NO₃)₂](H₂O)₃}_n (6) is generated. These results indicate that the choice of metal ion and anion exerts a significant influence on governing the target complexes. A comparison of the structural features for all metal perchlorate complexes with 4-bpo is also briefly discussed.     

Copper(II) complexes with monocarboxylate ligands bearing different substituent groups: Synthesis and spectroscopic studies

In our continuing efforts to explore the effects of substituent groups of ligands in the formation of supramolecular coordination structures, seven new Cu^II complexes formulated as [Cu₂(L¹)₄(DMF)₂] (1), {[Cu₂(L¹)₄(Hmta)](H₂O)_0.75}_∞ (2), [Cu₂(L²)₄(2,2′-bipy)₂] (3), [Cu₂(L³)₄(H₂O)₂] (4), [Cu₂(L³)₄(Hmta)]_∞ (5), [Cu₂(L³)₄(Dabco)]_∞ (6) and [Cu₂(L³)₄(Pz)]_∞ (7) with three monocarboxylate ligands bearing different substituent groups HL¹-HL³ (HL¹ = phenanthrene-9-carboxylic acid, HL² = 2-phenylquinoline-4-carboxylic acid, HL³ = adamantane-1-carboxylic acid, Hmta = hexamethylenetetramine, 2,2′-bipy = 2,2′-bipyridine, Dabco = 1,4-diazabicyclo[2.2.2] octane and Pz = pyrazine), have been prepared and characterized by X-ray diffraction. In 1, 2 and 4-7, each Cu^II ion is octahedrally coordinated, and carboxylate acid acts as a syn-syn bridging bidentate ligand. While each Cu^II ion in 3 is penta-coordinated in a distorted square-pyramidal geometry. 1 and 4 both show a dinuclear paddle-wheel block, while 2, 5, 6 and 7 all exhibit an alternated 1D chain structure between dinuclear paddle-wheel units of the tetracarboxylate type Cu₂-(RCO₂)₄ and the bridging auxiliary ligands Hmta, Dabco and Pz. Furthermore, 3 has a carboxylic unidentate and μ_1,1-oxo bridging dinuclear structure with the chelating auxiliary ligand 2,2′-bipy. Moreover, complexes 1-6 were characterized by electron paramagnetic resonance (EPR) spectroscopy.     

Synthesis, reactivity, and structures of dialuminum complexes containing linked ketiminate ligands

Linked bis(ketimine) (1) can be prepared with the reaction of excess 2,4-pentanedione and 4,4′-methylene-bis(2,6-diisopropylaniline) in methanol in the presence of catalytic amount of formic acid. The dialuminum alkyl complexes containing the linked bis(ketiminate) dianionic ligands, [OC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₂-4)AlR₂]₂CH₂ (2, R = Me; 3, R = Et), were prepared by a reaction of 2 equiv AlR₃ with [OC(Me)CHC(Me)NH(2,6-ⁱPr₂C₆H₂-4)]₂CH₂ in methylene chloride. Reactions of 2 with 2 and 4 equiv of I₂ gave corresponding aluminum iodo complexes 4 and 5, respectively. Treatment of 5 with 2 equiv of AgBF₄, however, gave a diboron complex, [OC(Me)CHC(Me)N(2,6-ⁱPr₂C₆H₂-4)BF₂]₂CH₂ (6), in 18% isolated yield. All new complexes have been characterized by ¹H and ¹³C NMR spectroscopy and complexes 2, 3, and 6 are also confirmed by X-ray diffraction.     

A high-spin Fe(II)/low-spin Fe(III) redox couple featuring the hydro[tris(4-chloro-3,5-dimethyl-pyrazolyl)]borate ligand: Synthesis, spectroscopic and X-ray crystallographic characterization

The white homoleptic high-spin iron(II) complexes Fe[Tp^Me2,4Cl]₂ (1) was isolated in quantitative yield from reaction mixtures containing 1 equiv of FeCl₂(THF)_1.5 and 2 equiv of K[Tp^Me2,4Cl] (Tp^Me2,4Cl = hydrotris[(4-chloro-3,5-dimethyl-pyrazolyl)]borate). Its purple low-spin iron(III) counterparts 1[O₃SCF₃] and 1[PF₆] were synthesized and isolated in 85% yields upon treatment of 1 with 1 equiv of silver triflate and silver hexafluorophosphate, respectively. The three paramagnetic compounds are air and thermally stable as solids and in solution; they were characterized by elemental analyses, IR, magnetic susceptibility measurements, ¹H NMR, and Mössbauer spectroscopy. In addition, 1[PF₆] was authenticated by a single-crystal X-ray diffraction. The two scorpionate ligands are κ³-N,N′,N′′ ligated to the central Fe^III ion, forming an almost perfect FeN₆ octahedron with an average Fe-N bond distance of 1.9551(18) Å. In addition, complex 1 which oxidizes reversibly at E_1/2 = 0.483 V/SCE (ΔE_p = 94 mV), remains high-spin (S = 2) when the temperature is lowered to 2 K.     

Hydrothermal synthesis, crystal structures and properties of new Fe, Co, Ni, and Zn complexes with 6-quinolinecarboxylate: Interplay of coordinative and noncovalent interactions

Reactions of Fe^II, Co^II, Ni^II, and Zn^II salts with 6-quinolinecarboxylic acid (HL) under the hydrothermal conditions afford three monomeric complexes [M(L)₂(H₂O)₄] (M = Fe^II for 1, Co^II for 2, and Ni^II for 3) and a 1-D polymeric species {[Zn(L)₂(H₂O)] · H₂O}_n (4). The crystal structures of the ligand HL and these four complexes have been determined by using the X-ray single-crystal diffraction technique. The results suggest that complexes 1-3 are isostructural, displaying novel 3-D pillar-layered networks through multiple intermolecular hydrogen bonds, whereas in coordination polymer 4, the 1-D comb-like coordination chains are extended to generate a hydrogen-bonded layer, which is further reinforced via aromatic stacking interactions. Solid-state properties such as thermal stability and fluorescence emission of the polymeric Zn^II complex 4 have also been investigated.