The synthesis and structure of heteroleptic tris(diimine)ruthenium(II) complexes

The reactions of bidentate diimine ligands (L2) with cationic bis(diimine)[Ru(L)(L1)(CO)Cl]+ complexes (L, L1, L2 are dissimilar diimine ligands), in the presence of trimethylamine-N-oxide (Me3NO) as a decarbonylation reagent, lead to the formation of heteroleptic tris(diimine) ruthenium(II) complexes, [Ru(L)(L1)(L2)]2+. Typically isolated as hexafluorophosphate or perchlorate salts, these complexes were characterised by UV-visible, infrared and mass spectroscopy, cyclic voltammetry, microanalyses and NMR spectroscopy. Single crystal X-ray studies have elucidated the structures of K[Ru(bpy)(phen)(4,4'-Me(2)bpy)](PF(6))(3).1/2H(2)O, [Ru(bpy)(5,6-Me(2)phen)(Hdpa)](ClO(4))(2), [Ru(bpy)(phen)(5,6-Me(2)phen)](ClO(4))(2), [Ru(bpy)(5,6'-Me(2)phen)(4,4'-Me(2)bpy)](PF(6))(2).EtOH, [Ru(4,4'-Me(2)bpy)(phen)(Hdpa)](PF(6))(2).MeOH and [Ru(bpy)(4,4'-Me(2)bpy)(Hdpa)](ClO(4))(2).1/2Hdpa (where Hdpa is di(2-pyridyl)amine). A novel feature of the first complex is the presence of a dinuclear anionic adduct, [K(2)(PF(6))(6)](4-), in which the two potassium centres are bridged by two fluorides from different hexafluorophosphate ions forming a K(2)F(2) bridging unit and by two KFPFK bridging moieties.     

Synthesis,characterization and biological application of cyclometalated heteroleptic platinum(II) complexes

A series of square planar cyclometalated heteroleptic platinum(II) complexes of the type [(C^N)Pt(O^O)] [where, O^O is a β‐diketonato ligand of acetylacetone (acac), C^N = cyclometalating 7‐(4‐fluorophenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L¹), 7‐(4‐chlorophenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L²), 7‐(4‐bromophenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L³), 7‐(4‐methoxyphenyl)‐5‐phenylpyrazolo[1,5‐a]pyrimidine (L⁴), 5‐phenyl‐7‐(p‐tolyl)pyrazolo[1,5‐a]pyrimidine (L⁵)] have been design, synthesized and characterized. All compounds have been screened for biological studies like in vitro antibacterial, in vitro cytotoxicity, cellular level cytotoxicity, absorption titration, viscosity measurements, fluorescence quenching analysis, molecular docking and DNA nuclease. The intrinsic binding constants (K_b) of compounds with HS‐DNA has been obtained in range of 2.892–0.242 × 10⁵ M^?1. All the compounds bound with HS DNA by partial intercalative mode of binding. MIC study has been carried out against Gram^(+ve) and Gram^(?ve) bacterial species. In vitro cytotoxicity against brine shrimp lethality bioassay has been also carried out. The LC₅₀ values of the ligands and complexes have been found in range of 56.49–120.22 μg/mL and 6.71–11.96 μg/mL, respectively.     

Synthesis and characterization of heteroleptic iron(II) thiolate complexes with weak iron-arene interactions

Selective preparation and characterization of a series of heteroleptic thiolate complexes of iron(II) are described. The compounds were synthesized by treatment of iron bis-amide Fe{N(SiMe₃)₂}₂ (1) with 1 equiv. of terphenyl thiols HS(2,6-(aryl)₂C₆H₃) followed by addition of another equivalent of different thiol. An amide-thiolate intermediate [{(Me₃Si)₂N}Fe]₂(μ-SDpp)₂ (2; Dpp = 2,6-Ph₂C₆H₃) was isolated from the 1:1 reaction of 1 and HSDpp. The X-ray crystal structures of all new thiolate complexes have been determined. The compounds crystallize as monomers or dimers, dependent on the substituents. They consist of distorted tetrahedral or trigonal-planar iron centers with weak interactions between the aromatic rings of thiolate ligands, where the Fe-C(arene) contact is 2.272(2) Å at shortest. The stronger iron-arene interaction appears to induce more pyramidalized geometry at the iron center.     

Synthesis of mononuclear and dinuclear ruthenium(II) tris(heteroleptic) complexes via photosubstitution in bis(carbonyl) precursors

A novel, and quite general, approach for the preparation of tris(heteroleptic) ruthenium(II) complexes is reported. Using this method, which is based on photosubstitution of carbonyl ligands in precursors such as [Ru(bpy)(CO)(2)Cl(2)] and [Ru(bpy)(Me(2)bpy)(CO)(2)](PF(6))(2), mononuclear and dinuclear Ru(II) tris(heteroleptic) polypyridyl complexes containing the bridging ligands 3,5-bis(pyridin-2-yl)-1,2,4-triazole (Hbpt) and 3,5-bis(pyrazin-2-yl)-1,2,4-triazole (Hbpzt) have been prepared. The complexes obtained were purified by column chromatography and characterized by HPLC, mass spectrometry, 1H NMR, absorption and emission spectroscopy and by electrochemical methods. The X-ray structures of the compounds [Ru(bpy)(Me(2)bpy)(bpt)](PF(6))x0.5C(4)H(10)O [1x0.5C(4)H(10)O], [Ru(bpy)(Me(2)bpy)(bpzt)](PF(6))xH(2)O (2xH(2)O) and [Ru(bpy)(Me(2)bpy)(CH(3)CN)(2)](PF(6))(2)xC(4)H(10)O (6xC(4)H(10)O) are reported. The synthesis and characterisation of the dinuclear analogues of 1 and 2, [{Ru(bpy)(Me(2)bpy)}(2)bpt](PF(6))(3)x2H(2)O (3) and [{Ru(bpy)(Me(2)bpy)}(2)bpzt](PF(6))(3) (4), are also described.     

Synthesis and spectroscopic characterization of CN-substituted bipyridyl complexes of Ru(II)

A series of ruthenium complexes having the general form [Ru(bpy)(3-n)(CN-Me-bpy)(n)](PF(6))(2) (where bpy = 2,2'-bipyridine, CN-Me-bpy = 4,4'-dicyano-5,5'-dimethyl-2,2'-bipyridine, and n = 1-3 for complexes 1-3, respectively) have been synthesized and characterized using a variety of steady-state and nanosecond time-resolved spectroscopies. Electrochemical measurements indicate that the CN-Me-bpy ligand is significantly easier to reduce than the unsubstituted bipyridine (on the order of ～500 mV), implying that the lowest energy (3)MLCT (metal-to-ligand charge transfer) state will be associated with the CN-Me-bpy ligand(s) in all three compounds. Comparison of the Huang-Rhys factors derived from spectral fitting analyses of the steady state emission spectra of complexes 1-3 suggests all three compounds are characterized by excited-state geometries that are less distorted relative to their ground states as compared to [Ru(bpy)(3)](PF(6))(2); the effect of the more nested ground- and excited-state potentials is reflected in the unusually high radiative quantum yields (13% (1), 27% (2), and 40% (3)) and long (3)MLCT-state room-temperature lifetimes (1.6 μs, 2.6 μs, and 3.5 μs, respectively) for these compounds. Coupling of the π* system into the CN groups is confirmed by nanosecond step-scan IR spectra which reveal a ～40 cm(-1) bathochromic shift of the CN stretching frequency, indicative of a weaker CN bond in the (3)MLCT excited state relative to the ground state. The fact that the shift is the same for complexes 1-3 is evidence that, in all three complexes, the long-lived excited state is localized on a single CN-Me-bpy ligand rather than being delocalized over multiple ligands.     

Synthesis and characterization of rigid +2 and +3 heteroleptic dinuclear ruthenium(II) complexes

Synthesis and characterization of the dinuclear ruthenium coordination complexes with heteroleptic ligand sets, [Cl(terpy)Ru(tpphz)Ru(terpy)Cl](PF₆)₂(7) and [(phen)₂Ru(tpphz)Ru(terpy)Cl](PF₆)₃(8), are reported. Both structures contain a tetrapyrido[3,2-α:2′,3′-c:3′′,2′′-h:2′′,3′′-j]phenazine (tpphz) (6) ligand bridging the two metal centers. Complex 7 was obtained via ligand exchange between, RuCl₂(terpy)DMSO (5) and a tpphz bridge. Complex 8 was obtained via ligand exchange between, [Ru(phen)₂tpphz](PF₆)₂(4) and RuCl₂(terpy)DMSO (5). Metal-to-ligand-charge-transfer (MLCT) absorptions are sensitive to ligand set composition and are significantly red-shifted due to more electron donating ligands. Complexes 7–9 have been characterized by analytical, spectroscopic (IR, NMR, and UV–Vis), and mass spectrometric techniques. The electronic spectral properties of 7, 8, and [(phen)₂Ru(tpphz)Ru(phen)₂](PF₆)₄(9), a previously reported +4 analog, are presented together. The different terminal ligands of 7, 8, and 9 shift the energy of the MLCT and the π–π* transition of the bridging ligand. These shifts in the spectra are discussed in the context of density functional theory (DFT). A model is proposed suggesting that low-lying orbitals of the bridging ligand accept electron density from the metal center which can facilitate electron transfer to nanoparticles like single walled carbon nanotubes and colloidal gold.     

Synthesis and characterisation of N-1,10-phenanthrolin-5-ylalkylamides and their photosensitising heteroleptic Ru(II) complexes

In the context of our studies on ruthenium(II) complexes containing polyazaheterocyclic ligands as functionalised photosensitisers for singlet molecular oxygen generation in heterogeneous phase, we describe the synthesis and spectroscopic characterisation of different amide-functionalised N-1,10-phenanthrolin-5-ylalkylamides. These chelators are used to obtain heteroleptic [Ru(phen)₂L]²⁺ complexes, where L stands for 2-iodo-N-1,10-phenanthrolin-5-ylacetamide (5-iap), 4-oxo-4-(1,10-phenanthrolin-5-ylamino)butanoic acid (5-suap), 5-oxo-5-(1,10-phenanthrolin-5-ylamino)pentanoic acid (5-glap) and tert-butyl 4-oxo-4-(1,10-phenanthrolin-5-ylamino)butylcarbamate (BOC-5-ngap). The spectroscopic data, excited state lifetimes and quenching rate constants with O₂ (ca. 3.7×10⁹ L mol⁻¹ s⁻¹) of these novel complexes are also reported.     

Synthesis, characterization and some properties of amide-linked porphyrin-ruthenium(II) tris(bipyridine) complexes

A new molecular dyad, comprised of a zinc-porphyrin and a ruthenium(II) tris(bipyridine) complex linked through an amide bond has been synthesized and characterized by ¹H, ¹³C NMR, UV-vis, mass-spectrometry and elemental analysis. The electrochemistry as well as the steady-state emission properties were investigated. The redox behavior of the dyad exhibits a favorable reversible characteristic. Substantial quenching of porphyrin emission was found when the Q band of 5 and 5-Zn was selectively photoexcited. This observation suggests a quenching mechanism with possible intramolecular electron transfer or energy transfer between the Ru(bpy)₃ moiety and the porphyrin free-base or Zn porphyrin moieties.     

Synthesis and characterization of two intensely colored tris(benzoylcyanoxime)iron(II) anionic complexes

Two intensely blue-colored complexes, P(C 6H 5) 4[Fe(BCO) 3] ( 1) and Na[Fe(BCO) 3] ( 2), where BCO (-) is the benzoylcyanoxime anion, have been prepared and characterized in solution and in the solid state. The crystal structure of 1 has been determined at several temperatures (100, 155, 225, and 293 K) and consists of layers of P(C 6H 5) 4 (+) cations and [Fe(BCO) 3] (-) anions. The latter exist as a pair of fac-Delta and Lambda enantiomers in a monoclinic unit cell in the P2(1)/ n space group. Iron(II) has a trigonal-prismatic N 3O 3 coordination environment with average Fe-N and Fe-O bond distances of 1.866 and 1.956 A, respectively, bonds that are unusually short and indicate a (1)A 1g low-spin ground state for iron(II). A sample of 1 prepared with iron-57 has been studied by Mossbauer spectroscopy between 4.2 and 430 K and found to be low-spin iron(II) in studied temperature range. The stepwise formation constants for 1 in aqueous solution at 296 K and pH of 7 are log beta 1 = 0.85 +/- 0.1, log beta 2 = 3.55 +/- 0.15, and log beta 3 = 6.36 +/- 0.15. Both 1 and 2 exhibit irreversible oxidation of iron(II) at approximately 1.0 V, indicating a significant degree of the ligand-to-iron charge transfer. Thus, 1 and 2 are rare examples of highly colored iron(II) anionic complexes that do not contain aromatic heterocyclic amine ligands, such as bipyridine or phenanthroline.     

Substituted pyridazines as ligands in homoleptic (fac and mer) and heteroleptic Ru(II) complexes

This article reports the preparation of a range of phenyl, pyridyl and pyrazinyl substituted pyridazines via the inverse electron demand [2 + 4] Diels-Alder reaction between 3,6-di(2-pyridyl)-1,2,4,5-tetrazines (bptz) and 3,6-di(2-pyrazinyl)-1,2,4,5-tetrazines (bpztz) and suitable dienophiles including acenaphthalene. The resulting polyaromatic compounds vary systematically in the number of aromatic substituents and the number and position of N-heteroatoms. For four of these compounds, the effect of the molecular changes on the solid-state structures were investigated using single crystal X-ray crystallography. The pyridazines were used as bidentate ligands in {M(II)(bipy)(2)} and tris(homoleptic) complexes (M = Fe, Ru). The optical and electrochemical properties of these complexes reflect the electron accepting character of the new ligands. The facial and meridional isomers of the tris complexes could be separated by column chromatography (on silica), thus allowing a spectral comparison of their absorption and emission properties. The solid-state structures of several of the metal complexes are discussed, including that of the facial isomer of the tris Ru(II) complex of 3,6-bis(2-pyridyl)-4,5-bis(4-pyridyl)pyridazine--a potential preformed geometric motif for the predirected construction of supramolecular assemblies.     

Synthesis, characterization and DNA-binding characteristics of Ru(II) molecular light switch complexes

A series of four polypyridyl Ru(II) complexes such as [Ru(L)₄(PIP)]²⁺ and [Ru(L)₄PPIP]²⁺ where L is 4-amino pyridine and Pyridine (PIP?=?2-phenylimidazo[4,5-f] [1, 10] phenanthroline), (PPIP?=?2-(4??-phenoxy-phenyl) imidazo[4,5-][1, 10]phenanthroline) have been synthesized and characterized by elemental analysis, physicochemical methods such as UV?Cvis, IR and NMR spectroscopic techniques. The DNA-binding behavior of these complexes was investigated by electronic absorption titrations, fluorescence spectroscopy, viscosity measurements and salt-dependent studies. The experimental results indicate that all these complexes can bind to DNA through an intercalation mode, the DNA-binding affinities of these complexes follow the order [Ru(4-APy)₄(PPIP)]²⁺(1)?>?[Ru(Py)₄PPIP]²⁺(2)?>?[Ru(4-APy)₄(PIP)]²⁺(3)?>?[Ru(Py)₄PIP]²⁺(4). Noticeably, these complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA. Further, all four complexes screened for their antimicrobial activity indicate that the complexes show appreciable activity against Escherichia coli and Neurospora Crassa. In addition, in the presence of Co²⁺, the emission of DNA-[Ru(L₄)PPIP/PIP]²⁺ can be quenched and recovered by the addition of EDTA, which exhibited the DNA ??light switch?? properties.     

Synthesis,characterization, and transfer hydrogenation of Ru(II)-N-heterocyclic carbene complexes

A new series of ruthenium(II) N-heterocyclic carbene complexes [RuL^1,2,3(p-cymene)Cl₂] (3a–c) (where L is a N-heterocyclic carbene), have been synthesized via transmetalation. The new ruthenium(II)-NHC complexes were applied to transfer hydrogenation of acetophenone derivatives and aldehydes using 2-propanol as a hydrogen source and KOH as a co-catalyst. The results show that the corresponding alcohols could be obtained in good yield with high catalyst activity (up to 100%) under mild conditions. [RuL¹(p-cymene)Cl₂] (3a) is much more active than the other complexes in transfer hydrogenation. Reactions, catalyzed by 3a–c, showed the highest reaction rates and yields of alcohol when the substrates bear more electron-withdrawing substituents. All new compounds were characterized by IR, elemental analysis, LC–MS (ESI), and NMR spectroscopy.     

Synthesis, characterization, and OFET properties of amphiphilic heteroleptic tris(phthalocyaninato) europium(III) complexes with hydrophilic poly(oxyethylene) substituents

A series of amphiphilic heteroleptic tris(phthalocyaninato) europium complexes with hydrophilic poly(oxyethylene) heads and hydrophobic alkoxy tails {Pc[(OC2H4)2OCH3]8}Eu{Pc[(OC2H4)2OCH3]8}Eu[Pc(OCnH2n + 1)8] (n = 6, 8, 10,12) (1-4) were designed and prepared from the reaction between homoleptic bis(phthalocyaninato) europium compound {Pc[(OC2H4)2OCH3]8}Eu{Pc[(OC2H4)2OCH3]8} and metal-free 2,3,9,10,16,17,23,24-octakis(alkoxy)phthalocyanine H2Pc(OCnH2n + 1)8 (n = 6, 8, 10,12) in the presence of Eu(acac)3.H2O (Hacac = acetylacetone) in boiling 1,2,4-trichlorobenzene (TCB). These novel sandwich triple-decker complexes have been characterized by a wide range of spectroscopic methods and have been electrochemically studied. With the help of the Langmuir-Blodgett (LB) technique, these typical amphiphilic triple-decker complexes have been fabricated into organic field effect transistors (OFET) with an unusual bottom contact configuration. The devices display good OFET performance with the carrier mobility for holes in the direction parallel to the aromatic phthalocyanine rings, which shows dependence on the length of the hydrophobic alkoxy side chains, decreasing from 0.46 for 1 to 0.014 cm2 V(-1) s(-1) for 4 along with the increase in the carbon number in the hydrophobic alkoxy side chains.     

Synthesis of heteroleptic bis(diimine)carbonylchlororuthenium(II) complexes from photodecarbonylated precursors

The reactions of bidentate diimine ligands (L2) with binuclear [Ru(L1)(CO)Cl2]2 complexes [L1 not equal to L2 = 2,2'-bipyridine (bpy), 4,4'-dimethyl-2,2'-bipyridine (4,4'-Me2bpy), 5,5'-dimethyl-2,2'-bipyridine (5,5'-Me2bpy), 1,10-phenanthroline (phen), 4,7-dimethyl-1,10-phenanthroline (4,7-Me2phen), 5,6-dimethyl-1,10-phenanthroline (5,6-Me2phen), di(2-pyridyl)ketone (dpk), di(2-pyridyl)amine (dpa)] result in cleavage of the dichloride bridge and the formation of cationic [Ru(L1)(L2)(CO)Cl]+ complexes. In addition to spectroscopic characterization, the structures of the [Ru(bpy)(phen)(CO)Cl]+, [Ru(4,4'-Me2bpy)(5,6-Me2phen)(CO)Cl]+ (as two polymorphs), [Ru(4,4'-Me2bpy)(4,7-Me2phen)(CO)Cl]+, [Ru(bpy)(dpa)(CO)Cl]+, [Ru(5,5'-Me2bpy)(dpa)(CO)Cl]+, [Ru(bpy)(dpk)(CO)Cl]+, and [Ru(4,4'-Me2bpy)(dpk)(CO)Cl]+ cations were confirmed by single crystal X-ray diffraction studies. In each case, the structurally characterized complex had the carbonyl ligand trans to a nitrogen from the incoming diimine ligand, these complexes corresponding to the main isomers isolated from the reaction mixtures. The synthesis of [Ru(4,4'-Me2bpy)(5,6-Me2bpy)(CO)(NO3)]+ from [Ru(4,4'-Me2bpy)(5,6-Me2bpy)(CO)Cl]+ and AgNO3 demonstrates that exchange of the chloro ligand can be achieved.     

Synthesis and characterization of picolinato and nicotinato cobalt(II) complexes containing tris(2-benzimidazolylmethyl)amine

Two new mononuclear cobalt(II) complexes [Co(ntb)(pic)](ClO₄) · (CH₃OH)_2.35 (1) and [Co(ntb)(nic)](ClO₄) · CH₃OH (2) were synthesized and structurally characterized, where ntb is tris(2-benzimidazolylmethyl)amine, pic is the anion of picolinic acid, and nic is the anion of nicotinic acid. The X-ray analysis indicates that the Co(II) center is six-coordinate in distorted octahedral and five-coordinate in distorted trigonal bipyramidal geometry for 1 and 2, respectively. In 1, the picolinate anion coordinates to Co(II) in a bidentate μ₂-N,O chelating mode. In 2, the nicotinate anion coordinates with Co(II) through a monodentate carboxylate oxygen. 1-D chain structures were formed by intermolecular hydrogen bonds in the two complexes and π–π interactions are important for the stabilization of the structures.     

Synthesis and structural characterization of ruthenium(II) complexes bearing phosphine-pyrazolyl based tripod ligands

Phosphine-pyrazolyl based tripod ligands ROCH₂C(CH₂Pz)₂(CH₂PPh₂) (R = H, Me, allyl; Pz = pyrazol-1-yl) were efficiently synthesized and characterized. Reactions of these ligands with [Ru(η⁶-p-cymene)Cl₂]₂ afforded complexes of the type [Ru(η⁶-p-cymene)Cl₂](L) (6-8) in which the ligands exhibit κ¹-P-coordination to the metal center. Complex [Ru(η⁶-p-cymene)Cl₂{Ph₂PCH₂C(CH₂OH)(CH₂Pz)₂}] (6) underwent chloride-dissociation in CH₂Cl₂/MeCN to give complex [RuCl(η⁶-p-cymene){κ²(P,N)-Ph₂PCH₂C(CH₂OH)(CH₂Pz)₂}][Cl] (9). Complexes 6-9 demonstrated poor to moderate catalytic activity in the transfer hydrogenation of acetophenone. All these complexes were fully characterized by analytical and spectroscopic methods and their molecular structures were determined by X-ray crystallographic study.     

Synthesis,spectral characterization and catalytic applications of Ru(II) complexes with amide ligands

Ruthenium(II) complexes of the type, RuCl₂(NO)(PPh₃)(L₂) (where L = amide ligand) have been synthesized and characterized on the basis of their elemental analysis IR, ¹H-, ¹³C-, ³¹P-NMR spectra. Amide ligand behaved as a bidentate ligand. The probable structures of these complexes have been discussed. They were used as catalysts for the hydrolysis of drugs viz. rivastigmine tartrate and neostigmine bromide. The percent yields of hydrolyzed products of these drugs were determined spectrophotometrically.     

Synthesis,characterization, antitumor,and cytotoxic activity of mononuclear Ru(II) complexes

In the search for antitumor active metal complexes several ruthenium complexes have been reported to be promising. A series of mononuclear Ru(II) complexes, [Ru(T)₂(S)]²⁺, where T?=?2,2′-bipyridine/1,10-phenanthroline and S?=?CH₃-bitsz, Cl-bitsz, Br-bitsz, tmtsz, dmtsz, have been prepared and characterized by UV-Vis, IR, ¹H-NMR, FAB-mass spectroscopy, and elemental analysis. The complexes were subjected to in vivo anticancer activity against a transplantable murine tumor cell line Ehrlich's ascitic carcinoma (EAC) and in vitro cytotoxic activity against human cancer cell line Molt 4/C₈, CEM, and murine tumor cell line L1210. Ruthenium complexes showed promising biological activity especially in decreasing tumor volume and viable ascitic cell counts. Treatment with these complexes prolonged the life span of EAC-tumor-bearing mice by 10–48%. In vitro evaluation of these ruthenium complexes revealed cytotoxic activity from 0.21 to 24?µmol?L^?1 against Molt 4/C₈, 0.16–19?µmol?L^?1 against CEM, and 0.75–32?µmol?L^?1 against L1210 cell proliferation, depending on the nature of the compound.     

Synthesis of monomeric Fe(II) and Ru(II) complexes of tetradentate phosphines

rac-Bis[{(diphenylphosphino)ethyl}-phenylphosphino]methane (DPPEPM) reacts with iron(II) and ruthenium(II) halides to generate complexes with folded DPPEPM coordination. The paramagnetic, five-coordinate Fe(DPPEPM)Cl(2) (1) in CD(2)Cl(2) features a tridentate binding mode as established by (31)P{(1)H} NMR spectroscopy. Crystal structure analysis of the analogous bromo complex, Fe(DPPEPM)Br(2) (2) revealed a pseudo-octahedral, cis-α geometry at iron with DPPEPM coordinated in a tetradentate fashion. However, in CD(2)Cl(2) solution, the coordination of DPPEPM in 2 is similar to that of 1 in that one of the external phosphorus atoms is dissociated resulting in a mixture of three tridentate complexes. The chloro ruthenium complex cis-Ru(κ(4)-DPPEPM)Cl(2) (3) is obtained from rac-DPPEPM and either [RuCl(2)(COD)](2) [COD = 1,5-cyclooctadiene] or RuCl(2)(PPh(3))(4). The structure of 3 in both the solid state and in CD(2)Cl(2) solution features a folded κ(4)-DPPEPM. This binding mode was also observed in cis-[Fe(κ(4)-DPPEPM)(CH(3)CN)(2)](CF(3)SO(3))(2) (4). Addition of an excess of CO to a methanolic solution of 1 results in the replacement of one of the chloride ions by CO to yield cis-[Fe(κ(4)-DPPEPM)Cl(CO)](Cl) (5). The same reaction in CH(2)Cl(2) produces a mixture of 5 and [Fe(κ(3)-DPPEPM)Cl(2)(CO)] (6) in which one of the internal phosphines has been substituted by CO. Complexes 2, 3, 4, and 5 appear to be the first structurally characterized monometallic complexes of κ(4)-DPPEPM.     

Magnetostructural correlations in heteroleptic nickel(II) complexes

Heteroleptic nickel(II) complexes with the general formula Ni(L)_m(H₂O)_n(X)_k, have been synthesized and structurally characterized; L stands for neutral N-donor ligands: 4-benzofuropyridine (bzfupy), dimethylfuropyridine (Me₂fupy) and 1,2-dimethylimidazole (Me₂iz), X = acetate or Cl⁻. The structures of the complexes [Ni(bzfupy)₂(ac)₂(H₂O)₂], [Ni(Me₂fupy)₂(H₂O)₄](ac)₂ and [Ni(Me₂iz)₄(H₂O)₂]Cl₂ · 3H₂O are formed from {NiO₂O′₂N₂}, {NiO₄N₂} and {NiN₄O₂} chromophores, respectively. These complexes and two other previously characterized complexes, [Ni(pz)₄(ac)₂], pz – pyrazole, and [Ni(L^NN)₂(H₂O)₂], L^NN – bidentate chelating ligand, were subjected to magnetochemical investigation down to 2 K (susceptibility and magnetization measurements). They show magnetic behaviour typical for zero-field splitting systems. The axial parameter of the zero-field splitting, D, adopts either positive or negative values and correlates with the axial distortion of the coordination polyhedra.