Electronic effects on the interactions of complexes [Ru(phen)2(p-L)] (L=MOPIP, HPIP, and NPIP) with DNA

In order to explore the electronic effects of Ru(II) complexes binding to DNA, a series of Ru(II) complexes [Ru(phen)₂ (p-MOPIP)]²⁺ (1), [Ru(phen)₂ (p-HPIP)]²⁺ (2), and [Ru(phen)₂(p-NPIP)]²⁺ (3) were synthesized and characterized by elementary, ¹H NMR, and ES-MS analysis. The binding properties of these complexes to CT-DNA were investigated with spectroscopic methods and viscosity experiments. Furthermore, the computations for these complexes applying the density functional theory (DFT) method have also been performed. The results show that all of these complexes can well bind to DNA in intercalation mode and DNA-binding affinity of these complexes is greatly influenced by electronic effects of intercalating ligands. The intrinsic binding constants for 1, 2, and 3 are 0.20, 0.69, and 1.56 × 10⁵ M⁻¹, respectively. This order is in accordance with that of the electron-withdrawing ability of substituent [-OR < -OH < -NO₂]. Such a trend in electronic effects of Ru(II) complexes binding to DNA can be reasonably explained by the DFT calculations.     

Platinum(II) imidazo[4,5-f]-1,10-phenanthroline chloride and thiolate complexes: Synthesis and crystal structures

The planar aromatic imidazo[4,5-f]-1,10-phenanthroline ligands have been used to prepare platinum(II) chloride and thiolate complexes. The X-ray structures of two thiolate compounds are reported, which show column-like packing in the solid state due to intermolecular aromatic π-π interactions. The compounds absorb moderately in the visible region, owing to {charge-transfer-to-diimine} electronic transition.     

Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)2(mitatp)] and [Ru(bpy)2(nitatp)]

Two new ruthenium complexes [Ru(bpy)₂(mitatp)](ClO₄)₂1 and [Ru(bpy)₂(nitatp)](ClO₄)₂2 (bpy = 2,2′-bipyridine, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene, nitatp = 5-nitro-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) have been synthesized and characterized by elemental analysis, ¹H NMR, mass spectrometry and cyclic voltammetry. Spectroscopic and viscosity measurements proved that the two Ru(II) complexes intercalate DNA with larger binding constants than that of [Ru(bpy)₂(dppz)]²⁺ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine) and possess the excited lifetime of microsecond scale upon binding to DNA. Both complexes can efficiently photocleave pBR322 DNA in vitro under irradiation. Singlet oxygen (¹O₂) was proved to contribute to the DNA photocleavage process, the ¹O₂ quantum yields was determined to be 0.43 and 0.36 for 1 and 2, respectively. Moreover, a photoinduced electron transfer mechanism was also found to be involved in the DNA cleavage process.     

Experimental and DFT studies on the DNA-binding trend and spectral properties of complexes [Ru(bpy)2L] (L = dmdpq, dpq, and dcdpq)

The trend in DNA-binding affinities and the spectral properties of a series of Ru(II) polypyridyl complexes, [Ru(bpy)₂(dmdpq)]²⁺ (1), [Ru(bpy)₂(dpq)]²⁺ (2), [Ru(bpy)₂(cndpq)]²⁺ (3) (bpy = 2,2′-bipyridine; dpq = dipyrido[3,2-d:2′,3′-f]quinoxaline; dmdpq = di-methyl-dpq; dcdpq = di-cyano-dpq), have been experimentally and theoretically investigated. The DNA-binding constants K_b of the complexes were determined systematically with spectrophotometric titration. The density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were carried out for these complexes. The experimental results show that these complexes bind to DNA in intercalation mode, and the order of their intrinsic DNA-binding constants K_b is K_b(1) < K_b(2) ? K_b(3). The substituents on the intercalative ligands of the complexes play a very important role in the control of DNA-binding affinities of the complexes, in particular, the stronger electron-withdrawing substituent (-CN) on the intercalative ligand can greatly improve the DNA-binding property of the derivative complex. The trend in DNA-binding affinities as well as the spectral properties of metal-ligand charge-transition (¹MLCT) of this series of complexes can be reasonably explained by applying the DFT and TDDFT calculations and the frontier molecular orbital theory.     

Theoretical studies on DNA-binding, DNA-photocleavage and spectral properties of Co(III) complexes [Co(phen)2(L)] (L = pip, hpip, hnaip)

Theoretical studies on the DNA-binding, DNA-photocleavage and spectral properties of Co(III) polypyridyl complexes [Co(phen)₂(L)]³⁺ (L = pip, hpip, hnaip) have been carried out, using the density functional theory (DFT), Hartree-Fock (HF) and configuration interaction singles (CIS) methods. The optimized geometric structures of these Co(III) complexes in aqueous solution are more close to experimental data than those in vacuo at the B3LYP/LanL2DZ level. Based on the optimized geometric structures in solution, the electronic structures of these Co(III) complexes were analyzed and the trend in the DNA-binding constants (K_b) was reasonably explained. In particular, via the analysis of natural charges of the complexes in ground state and excited state, it is very interesting to find the following: under UV or visible light irradiation, the Co(Ш) polypyridyl complexes undergo an intra-molecular electron transfer from S₀ state to T₁ state, and the positive charges on the main-ligand in the T₁ state are greatly increased, so as to form a radical cation with strong oxidation ability. Meanwhile, the change in geometry of the complexes under light irradiation also helps to the radical cation easily approaching and further oxidating DNA-base-pairs. These results offer the theoretical explanation for the photo-induced oxidation-reduction mechanism which was experimentally proposed on DNA-photocleavage by Co(Ш) polypyridyl complexes. In addition, the electronic absorption spectra of these complexes were calculated and simulated in aqueous solution using the time dependent DFT (TDDFT) method, in satisfying agreement with experimental results, and the properties of experimental absorption bands have been theoretically explained in detail.     

Synthesis, structures and DNA binding of ternary transition metal complexes M(II)L with the 2,2-bipyridylamine (L = p-HB, M = Co, Ni, Cu and Zn)

New ternary transition metal complexes of formulations [Co(bpa)(p-HB)₂](bpa = 2,2′-bipyridylamine, p-HB = p-hydroxybenzenecarboxylic acid) (1), [Ni(bpa)(p-HB)(H₂O)₂]⁺(NO₃)⁻ · H₂O (2), , [Cu(bpa)(p-HB)Cl] (4) and [Zn(bpa)(p-HB)₂]₂ · 0.5H₂O (5) are prepared, their structural features are characterized by crystal structural studies, and their DNA binding propensity has been evaluated by fluorescence method. The molecular structure of complex 1 shows the six coordinate octahedral geometry with one bpa and two p-HB ligands, complex 2 is the cationic complex and has the six coordinate octahedral structure with one bpa, one p-HB and two aqua ligands, complex 3 is also the cationic complex of octahedral coordination with two bpa and one p-HB ligands, complex 4 is five coordinate distorted square pyramidal with one bpa, one p-HB and chloride ligands and complex 5 has the distorted octahedral coordination with two p-HB and one bpa ligands. In all of the complexes, both bpa and p-HB act as the bidentate N and O-donor ligands, respectively. The intermolecular H-bond networks, together with π-π interaction in their solid state are also described. The complexes show the competitive inhibition of ethidium binding to DNA, and the DNA binding propensity can be reflected as the relative order: 3 > 2 > 1 > 5 > 4, in which the cationic charged Ni(II) complexes 2 and 3 show the most effective inhibition ability.     

Ruthenium(II/III) mediated transformation of 1,2-bis(2′-pyridylmethyleneimino)benzene (L) to 2-(2′-benzimidazolyl)pyridine (L′H) and its in situ formed complexes with Ru(II): X-ray structure of trans-[Ru(PPh3)2(L′H)2](ClO4)2

A series of ruthenium (II) complexes of formulae trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ (1), [Ru(bpy)(L′H)₂](ClO₄)₂ (2), [Ru(bpy)₂(L′H)](ClO₄)₂ (3), cis-[Ru(DMSO)₂(L′H)₂]Cl₂ (4), and [Ru(L′H)₃](PF₆)₂ (5) (where L′H = 2-(2′-benzimidazolyl)pyridine) have been synthesized by reaction of the appropriate ruthenium precursor with 1,2-bis(2′-pyridylmethyleneimino)benzene (L). The complexes were characterized by elemental analyses, spectroscopic and electrochemical data. All the complexes were found to be diamagnetic and hence metal is in +2 oxidation state. The molecular structure of trans-[Ru(PPh₃)₂(L′H)₂](ClO₄)₂ has been determined by the single crystal X-ray diffraction studies. The molecular structure shows that Ru(II) is at the center of inversion of an octahedron with N₄P₂ coordination sphere. The ligand acts as a bidentate N,N′donor. The electronic spectra of the complexes display intense MLCT bands in the visible region.Cyclic voltammetric studies show quasi-reversible oxidative response at 0.99-1.32 V (vs Ag/AgCl reference electrode) due to Ru(III)/Ru(II) couple.     

An expeditious route to cis-Ru(bpy)2C12 (bpy = 2,2′-bipyridine) using carbohydrates as reducers

The tandem use of simple mono- or disaccharides and vitamin C as organic reducers allows the synthesis of the widely used starting material cis-Ru(bpy)₂Cl₂ (where bpy = 2,2′-bipyridine) from commercial ruthenium (III) chloride in less than half an hour. Notably, the reaction can be run in organic aqueous solvent or in only water, hence it can be adapted to substituted 2,2′-bipyridines.     

Synthesis and DNA threading properties of quaternary ammonium [Ru(phen)2(dppz)] derivatives

Ruthenium complexes with one dipyrido[3,2-a:2′-3′-c]phenazine (dppz) ligand, e.g. [Ru(phen)₂(dppz)]²⁺ (phen = phenanthroline), shows strong binding to double helical DNA and are well-known DNA “light-switch” molecules. We have here investigated four new [Ru(phen)₂(dppz)]²⁺ derivatives with different bulky quaternary ammonium substituents on the dppz ligand to find relationships between molecular structure and intercalation kinetics, which is considered to be of importance for antitumor applicability. Linear dichroism spectroscopy shows that the enantiomers of the new complexes exhibit very similar binding geometries (intercalation of dppz moiety between adjacent DNA base pairs) as the enantiomers of the parent [Ru(phen)₂(dppz)]²⁺ complex. Absorption spectra and luminescence properties provide further evidence for a final intercalative binding mode which has to be reached by threading of a bulky moiety between the strands of the DNA. Δ-enantiomers of all the new complexes show much slower association and dissociation kinetics than that of a reference complex without a cationic substituent. Kinetics were not very different whether the bulky quaternary group was derived from hexamethylene tetramine or 1,4-diazabicyclo-(2,2,2)octane (DABCO) or whether it had one or two positive charges. However, a complex in which the hexamethylene tetramine substituent is attached via a phenyl group showed a lowered association rate, in addition to an improved quantum yield of luminescence. A second positive charge on the DABCO substituent resulted in a much slower dissociation rate, suggesting that the distance from the Ru-centre and the amount of charge are both important for threading intercalation kinetics.     

A new arylimido derivative of polyoxometalate (Bu4N)2[Mo6O17(NAr)2] [Ar = 2,6-(CH3)2C6H3]: Synthesis, structure and physicochemical properties

A novel bifunctionalized arylimido derivative of hexamolybdate, (Bu₄N)₂[Mo₆O₁₇(NAr)₂] [Ar = 2,6-(CH₃)₂C₆H₃] (1), in which the two 2,6-dimethylaniline groups are bounded to hexamolybdate at the cis positions, was synthesized by a facile reaction of α-octamolybdate with 2,6-dimethylaniline using DCC as a dehydration agent. The existence of strong non-typical C-H?O hydrogen bonds plays an important role in crystal structure stabilization of compound 1. The results of fluorescence spectra show that the formation of a covalent bond between 2,6-dimethylaniline molecule and hexamolybdate could efficiently quench the fluorescence intensity of 2,6-dimethylaniline molecule, with a fluorescence quencher efficiency of 87.7%. Thermal analysis results indicate that two substituted 2,6-(CH₃)₂C₆H₃ molecules bonding to the same cluster dissociated at different temperature, in well agreement with the different MoN bond length in compound 1. The electrochemical behavior of modified 1-CPE has been studied in detail. Compared with the conventional polyoxometalate (POM)-modified electrode, 1-CPE presents a merit of remarkable stability over 500 cycles due to the insolubility of the POM nanoparticles, which is especially important for practical applications.     

Synthesis, characterization, and DNA-binding of chiral complexes delta- and lambda-[Ru(bpy)2(pyip)]2+

New chiral Ru(II) complexes delta and lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) [(bpy = 2,2'-bipyridine; pyip = (2-(1-pyrenyl)-1H-imidazo[4,5-f] [1,10]phenanthroline] were synthesized and characterized by elemental analysis, (1)H NMR, ESI-MS, IR, and CD spectra. Their DNA-binding properties were studied by means of UV-vis, emission spectra, CD spectra and viscosity measurements. A subtle but detectable difference was observed in the interaction of both enantiomer with CT-DNA. Spectroscopy experiments indicated that each of these complexes could interact with the DNA. The DNA-binding of the Delta-enantiomer was stronger than that of Lambda-enantiomer. DNA-viscosity experiments provided evidence that both Delta- and Lambda-[Ru(bpy)(2)(pyip)](PF(6))(2) bound to DNA by intercalation. At the same time, the DNA-photocleavage properties of the complexes were investigated too. Under irradiation with UV light, Ru(II) complexes showed different efficiency of cleaving DNA.     

Synthesis and characterization of three group 10 complexes containing nido-carborane diphosphine: [MCl(PPh3){7,8-(PPh2)2-7,8-C2B9H10}] (M = Ni, Pd, Pt)

Three group 10 complexes containing nido-carborane diphosphine, [NiCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] (1), [PdCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] · 1.25CH₂Cl₂ (2) and [PtCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] · 2.5CH₂Cl₂ (3) have been synthesized by the reactions of [M(PPh₃)₂Cl₂] (M = Ni, Pd, Pt) with closo carborane diphosphine 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ in ethanol. For complex 3, it could also be obtained under solvothermal condition. All three complexes were characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopy and X-ray structure determination. Single crystal structures show that their structures are similar to each other. In each complex, the nido [7,8-(PPh₂)₂-7,8-C₂B₉H₁₀]⁻, which resulted from the degradation of the initial closo ligand 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ during the reaction process, was coordinated bidentately through the P atoms to M(II) ion, and this resulted in a stable five-membered chelating ring between the bis-diphosphine ligand and the metal. The coordination mode of the metal can be described as a slightly distorted square-planar, in which the remaining two positions were occupied by one Cl⁻ and one PPh₃ group.     

Towards absolute asymmetric synthesis. Synthesis and crystal structure of stereochemically labile MCl2 (M = Co, Ni, Cu, Zn) complexes with diamine ligands

In search for new conglomerates, seven stereochemically labile complexes between MCl₂ (M = Co, Cu, Ni, Zn) and bidentate ligands, the commercially available N,N,N′-trimethylethane-1,2-diamine (trimeda) and the somewhat bulkier N-isopropyl-N,N′,N′-trimethylethane-1,2-diamine (itmeda), have been synthesized and characterized using single crystal X-ray diffraction. The trimeda and itmeda ligands exhibit chirogenic nitrogen centers and may form chiral metal complexes that are candidates for total spontaneous resolution. Copper(II) chloride forms the dimeric meso complexes [{CuCl₂(trimeda)}₂] (1) and [{CuCl₂(itmeda)}₂] (2), while [CoCl₂(trimeda)₂] (3) and [NiCl₂(trimeda)₂] (4) exhibit six-coordinate but chiral (R,R)- and (S,S)-complexes. Three examples of the chiral target complex, comprising four-coordinate stereochemically labile monomers, was successfully prepared, viz. [NiCl₂(itmeda)] (5), [ZnCl₂(itmeda)] (6), and [CoCl₂(itmeda)] (7).In all seven complexes, the λ-conformation of the five-membered trimeda-metal chelate ring corresponds to the (S)-configuration at nitrogen, and vice versa. Supramolecular interactions in 3 and 4 form hydrogen-bonded heterochiral ribbons. However, crystals of 5-7 display homochiral interactions resulting in polar phases. Weak CH-Cl interactions in 5 and 6 form homochiral layers. In 7, interactions form homochiral helices along the a-axis.     

Synthesis, characterization, DNA-binding and spectral properties of complexes [Ru(L)4(dppz)]2+ (L=Im and MeIm)

Two new Ru(II) complexes [Ru(L)(4)(dppz)](2+) (L=imidazole (Im), 1-methylimidazole (MeIm); dppz=dipyrido[3,2-a:2',3'-c]phenazine), have been synthesized and characterized in detail by elemental analysis, (1)H NMR, Electrospray ionization mass spectrometry (ESI-MS) and UV-visible (UV-Vis) spectroscopic techniques. The interaction of these complexes with calf thymus DNA (CT-DNA) has been explored by using electronic absorption titration, competitive binding experiment, circular dichroism (CD), thermal denaturation and viscosity measurements. The experimental results show that: both the two complexes can bind to DNA in an intercalation mode; the DNA-binding affinity of complex [Ru(Im)(4)(dppz)](2+)1 (K(b)=2.5 x 10(6)M(-1)) is greater than that of complex [Ru(MeIm)(4)(dppz)](2+)2 (K(b)=1.1 x 10(6)M(-1)). Moreover, it is very interesting to find that the circular dichroic spectrum of DNA-complex 1 adduct, in which both bands centered at 277 nm and 236 nm are all negative, is very different from those of DNA-complex 2 adduct and other Ru(II) complexes binding to DNA in general intercalation mode. It may be due to the hydrogen-bonding effect or the contribution of induced CD signals of complex 1. Another interesting finding is that the hypochromism of the complexes is not linear relation to their DNA-binding affinities. In order to deeply study these experimental phenomena and trends, the density functional theory (DFT) and time-dependent DFT (TDDFT) computations were carried out, and on the basis of the DFT/TDDFT results and the frontier molecular orbital theory, the trend in DNA-binding affinities, the spectral properties as well as the interesting phenomena of larger extent of hypochromism but relatively smaller K(b) values for the title complexes have been reasonably explained.     

Preparation, crystal structures and spectroscopic properties of novel [MCl3 − n(P)3 + n] (M = Co, Rh; n = 0, 1, 2 or 3) series of complexes containing tripodal tridentate phosphine, 1,1,1-tris(dimethylphosphinomethyl)ethane

Cobalt(III) and rhodium(III) complexes of the series of [M^IIICl_3 − n(P)_3 + n]ⁿ⁺ (M = Co or Rh; n = 0, 1, 2 or 3) have been prepared with the use of 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) and mono- or didentate phosphines. The single-crystal X-ray analyses of both series of complexes revealed that the M-P and M-Cl bond lengths were dependent primarily on the strong trans influence of the phosphines, and secondarily on the steric congestion around the metal center resulting from the coordination of several phosphine groups. In fact, the M-P(tdmme) bonds became longer in the order of [MCl₃(tdmme)] < [MCl₂(tdmme)(PMe₃)]⁺ < [MCl(tdmme)(dmpe)]²⁺ (dmpe = 1,2-bis(dimethylphosphino)ethane) < [M(tdmme)₂]³⁺ for both Co^III and Rh^III series of complexes, while the M-Cl bond lengths were shortened in this order (except for [M(tdmme)₂]³⁺). Such a steric congestion around the metal center can also account for the structural and spectroscopic characteristics of the series of complexes, [MCl(tdmme)(dmpm, dmpe or dmpp)]²⁺ (dmpm = bis(dimethylphosphino)methane, dmpp = 1,3-bis(dimethylphosphino)propane). The X-ray analysis for [CoCl(tdmme)(dmpm or dmpe)](BF₄)₂ showed that all Co-P bonds in the dmpm complex were shorter by 0.03-0.04 Å than those in the dmpe complex. Furthermore, the first d-d transition energy of the Co^III complexes and the ¹J_Rh-P(tdmme) coupling constants observed for the Rh^III complexes indicated an unusual order in the coordination bond strengths of the didentate diphosphines, i.e., dmpm > dmpe > dmpp.     

Synthesis, crystal structure, spectral properties and catalytic activity of hexakis(imidazole)manganese(II) bisindole-2-carboxylato bisneocuproine bisdimethyl sulfoxide solvates {[Mn(Im)6] · 2(2-IC) · 2(NC) · 2(DMSO)}

Synthesis, X-ray crystal structure and IR spectrum of {[Mn^II(Im)₆] · 2(2-IC) · 2(NC) · 2(DMSO)} (Im = imidazole, 2-HIC = indole-2-carboxylic acid, NC = 2,9-dimethyl-1,10-phenanthroline, DMSO = dimethyl sulfoxide) are reported. The manganese(II) ion has octahedral geometry with a MnN₆ core. The crystal structure is completed by two NC, two 2-IC⁻ and two DMSO solvate molecules. The individual cations are linked into chains running parallel to the a axis by four intermolecular hydrogen bonding involving two 2-IC⁻solvate. Moreover, these chains are connected by π-π stacking interactions which occur between neocuproine molecules related through inversion center. In IR spectroscopy, the compound spectrum is roughly similar to the imidazole one: (i) above 1800 cm⁻¹, the bands are broad, but when focussing on some of them a doublet structure can be found; (ii) below 1800 cm⁻¹, the bands are sharp and it is then possible to point out the modification of S-O band when this later is involved in bifurcated hydrogen bonding to a second solvate 2-IC⁻. The compound catalyses the disproportionation of H₂O₂; moreover an additional quantity of imidazole increases the reaction rate.     

Reactivity of the N-heterocyclic carbene complexes [Ru(IMes)2(CO)HX] (X = OH, Cl) with alkynes

Treatment of the 16-electron hydroxy hydride complex [Ru(IMes)₂(CO)H(OH)] (1, IMes = 1,3-bis-(2,4,6-trimethylphenyl)imidazol-2-ylidene) with HCCR affords the alkynyl species [Ru(IMes)₂(CO)H(CCR)] (R = Ph 3, SiMe₃, 4) and [Ru(IMes)₂(CO)(CCR)₂] (R = Ph, 5). Deuterium labelling studies show that the mono-alkynyl complexes are formed via hydrogen transfer from a coordinated alkyne ligand to Ru-OH, while bis-alkynyl formation is proposed to take place through hydrogen transfer to Ru-H. Both 3 and 5 readily coordinate CO to give the corresponding dicarbonyl species 6 and 7. Addition of HCCPh to the hydride chloride precursor [Ru(IMes)₂(CO)HCl] (2) results in a different reaction pathway involving alkyne insertion into the Ru-H bond to yield the alkenyl chloride complex [Ru(IMes)₂(CO)(CHCHPh)Cl] 8. Complexes 3-8 have been structurally characterised by X-ray crystallography.     

Syntheses and 1D structures of organic-inorganic hydrid polymers combining M(ClO4)2 (M = Cd, Zn) junctions and the semi-flexible bis-pyridyl ligand 3-pmpmd (N,N′-bis(3-pyridylmethyl)pyromellitic diimide)

Two 1D organic-inorganic coordination polymers, [Cd(3-pmpmd)(CH₃CN)₂(H₂O)₂]_n · 2n(ClO₄)₂ (1) and [Zn(3-pmpmd)_1.5(H₂O)₂]_n · 2n(ClO₄)₂ · nCH₃CN (2), were obtained from M(ClO₄)₂ (M = Cd, Zn) and the semi-flexible 3,3′-N-donor bis-pyridyl ligand 3-pmpmd: 1 has an 1D zigzag framework with 3-pmpmd in the Z_T-mode (anti, trans-) conformation, while 2 has an 1D rod and loop network with 3-pmpmd in both Z_T- and Z_C-mode (anti, cis-) conformations. Results showed that the metal ions could influence the coordination mode of a semi-flexible bis-pyridyl ligand.     

Ligand substitution in hexahalorhenate(IV) complexes: Synthesis, crystal structures and magnetic properties of NBu4[ReX5(DMF)] (X = Cl and Br)

The preparation, crystal structures, and magnetic properties of two rhenium(IV) mononuclear compounds of formula NBu₄[ReX₅(DMF)] with X = Cl (1) and Br (2) are reported. 1 and 2 are isostructural complexes which crystallize in the monoclinic system with the space group P2₁/n. The rhenium atom is six-coordinated with five X atoms and a DMF molecule forming a somewhat distorted octahedral surrounding [values of Re-X varying in the ranges 2.317(1)-2.358(1) (1) and 2.495(1)-2.518(1) Å (2)]. Magnetic susceptibility measurements on samples of 1 and 2 in the temperature range 1.9-300 K are interpreted in terms of magnetically isolated spin quartets with large values of the zero-field-splitting (|2D| is ca. 20.2 and 39.2 cm⁻¹ for 1 and 2, respectively).