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.     

Synthesis and characterization of Os(II)(dpop′) (dpop′ = dipyrido(2,3-a;3′,2′-j)phenazine) complexes with 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)

New Os(II) complexes including [Os(dpop′)₂](PF₆)₂ (dpop′= dipyrido(2,3-a;3′,2′-j)phenazine) and a series of mixed ligand [Os(dpop′)(N-N)Cl]PF₆ (N-N = 2,2′-bipyridine(bpy); 2,2′-bipyrimidine(bpm) and 2,3-bis(2-pyridyl)pyrazine(dpp)) were synthesized. The Os dπ → dpop′ π^∗ MLCT transitions for [Os(dpop′)₂]²⁺ are observed at lower energy than for Os dπ → tpy π^∗ (tpy = 2,2′:6′,2″-terpyridine) and Os dπ → tppz π^∗ (tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine) (The ligand abbreviations tpd, tpp and tpypz have also appeared in the literature for 2,3,5,6- tetrakis(2-pyridyl)pyrazine in addition to tppz.) MLCT transitions in the comparative [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The Os dπ → dpop′ π^∗ MLCT transitions are observed at lower energy in mixed bidentate ligand N-N systems compared with [Os(dpop′)₂]²⁺. Cyclic voltammetry shows more positive osmium oxidation, and less negative ligand reduction potentials for [Os(dpop′)₂]²⁺ as compared to [Os(tpy)₂]²⁺ and [Os(tppz)₂]²⁺ complexes. The osmium oxidation potentials in mixed ligand [Os(dpop′)(N-N)Cl]⁺ complexes are at less positive potential than for the [Os(dpop′)₂]²⁺ ion. NMR results show different chemical shifts for ring protons either trans or cis to dpop′ in mixed ligand systems, and also show two geometrical isomers for the [Os(dpop′)(dpp)Cl]⁺ complex. The [Os(dpop′)(dpp)Cl]⁺ geometric isomer with the pyrazine ring of dpp trans to dpop′ is found more predominate by 1.0/0.7 over the isomer with the pyrazine ring of dpp cis to dpop′ and that inter-conversion of geometric isomers does not occur in room temperature solution on the NMR timescale.     

Effect of H-bonding on the ambivalence of SCN towards copper(II)

Condensations of 2-(2-aminoethyl)pyridine with 4-methylimidazole-5-carboxaldehyde and 1-methyl-2-imidazolecarboxaldehyde generate the tridentate N donor ligands L and L′ respectively. Reactions of Cu(NCS)₂ with L and L′ yield respectively CuL(SCN)(NCS) (1) containing a CuN₄S core and CuL′(NCS)₂ (2) having a CuN₅ core. Both the cores are square pyramidal with SCN⁻ bound in 1 at the axial position through the S end. This differential behaviour of SCN⁻ in the two complexes despite the ligands being very similar, is investigated by DFT calculations at the B3LYP/TZV level. It is found that DFT calculations predict isolation of the Cu(ligand)(NCS)₂ species for both the ligands L and L′. Presence of an offsetting intermolecular H-bonding between the N atom of the thiocyanate and the N-H proton of the ligand L of an adjacent molecule makes the binding of SCN⁻ via the S end feasible in 1 resulting in the H-bonded dimer Cu₂L₂(SCN)₂(NCS)₂. The strength of the H-bond is estimated as 27.1 kJ mol⁻¹ from the DFT calculations. The question of such H-bonding does not arise with L′ as it lacks in a similar H atom. Dimeric 1 represents a case of two non-interacting spins.     

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.     

Copper-thioarylazoimidazole complexes: Structures, photochromism and redox interconversion between Cu(II) ↔ Cu(I) and correlation with DFT calculation

Reaction of Cu(ClO₄)₂·6H₂O, SRaaiNR′ (1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole) and NH₄SCN (1:1:2 mol ratio) affords distorted square pyramidal, [Cu^II(SRaaiNR′)(SCN)₂] (3) compound while identical reaction with [Cu(MeCN)₄](ClO₄) yields -SCN- bridged coordination polymer, [Cu^I(SRaaiNR′)(SCN)]_n (4). These two redox states [Cu^II and Cu^I] are interconvertible; reduction of [Cu^II(SRaaiNR′)(SCN)₂] by ascorbic acid yields [Cu^I(SRaaiNR′)(SCN)]_n while the oxidation of [Cu^I(SRaaiNR′)(SCN)]_n by H₂O₂ in presence of excess NH₄SCN affords [Cu^II(SRaaiNR′)(SCN)₂]. They are structurally confirmed by single crystal X-ray diffraction study. Cyclic voltammogram of the complexes show Cu(II)/Cu(I) redox couple at ∼0.4 V and azo reductions at negative to SCE. UV light irradiation in MeCN solution of [Cu^I(SRaaiNR′)(SCN)]_n (4) show trans-to-cis isomerisation of coordinated azoimidazole. The reverse transformation, cis-to-trans, is very slow with visible light irradiation while the process is thermally accessible. Quantum yields (?_t→c) of trans-to-cis isomerisation are calculated and free ligands show higher ? than their Cu(I) complexes. The activation energy (E_a) of cis-to-trans isomerisation is calculated by controlled temperature experiment. Copper(II) complexes, 3, do not show photochromism. DFT and TDDFT calculation of representative complexes have been used to determine the composition and energy of molecular levels and results have been used to explain the solution spectra, photochromism and redox properties of the complexes.     

[Ni(L)(MeCN)]complex cation as a template for the assembly of extended I3 · I5 and I5 · I7 polyiodide networks {L=2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane}. Synthesis and structures of [Ni(L)(MeCN)]I8 and [Ni(L)(MeCN)]I12

The compounds [Ni(L)(MeCN)]I₈ (1) and [Ni(L)(MeCN)]I₁₂ (2) have been obtained from the reactions of the complexes [Ni(L)(L^′)][BF₄]_(2 + n) {L=2,5,8-trithia[9](2,9)-1,10-phenanthrolinophane; L^′=MeCN, Cl⁻, Br⁻, I⁻; n=charge of L^′} with an excess of I₂ (molar ratios of 6, 10 and 20 have been used), in the presence of the stoichiometric amount of I⁻ (as Bu₄ⁿNI) necessary to balance the charge of the complex cation [Ni(L)(L^′)]^(2 + n)+. An X-ray diffraction analysis shows that, independently of the nature of L^′, both 1 and 2 contain the complex cation [Ni(L)(MeCN)]²⁺, which is therefore capable of templating two different polyiodide networks based on interacting I₃⁻/I₅⁻ and I₅⁻/I₇ units, respectively. The solid state FT-Raman spectra of 1 and 2 are discussed based on their structural features.     

Photophysical properties, X-ray structures, electrochemistry, and DFT computational chemistry of osmium complexes

We report the synthesis of phosphorescent divalent osmium complexes of the form [Os(N-N)₂(L-L) or Os(L-L)₂(N-N)]²⁺ (PF₆)₂ where N-N is a derivative of 1,10-phenanthroline, and L-L is a diarsine or diphosphine ligand: 1,2-bis(dimethylphosphino)ethane, 1,2-bis(dicyclohexylphosphino)ethane, or 1,2-bis(dimethylarseno)benzene. X-ray structures have been determined, luminescent and electrochemical properties have been measured and DFT calculations have been performed on the complexes. The emission lifetime of complexes of structure Os(II)(L-L)₂(N-N) are longer than the those of Os(II)(N-N)₂(L-L). The DFT calculations show that there is significant mixing of the π−π^∗ into the dπ−π^∗ charge-transfer state for the complexes of the form Os(II)(L-L)₂(N-N) resulting in a longer lived excited state. Through DFT calculations we were able to conclude that the HOMO of the complexes is a d orbital on the osmium while the LUMO is the b₁(ψ) π^∗ system of the phenanthroline. However, we found that the HOMO did not have the correct symmetry to enable strong charge transfer to the phenanthroline to be observed, and the strong MLCT transition observed in the spectra is the metal d HOMO(−1) to the b1 π^∗ LUMO of the phenanthroline.     

Novel Pt(II) and Pt(IV) complexes with 3-amino-5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione. Synthesis, physicochemical, chemometric and pharmacological investigation

Platinum(II) and platinum(IV) complexes with 3-amino-5-methyl-5-(4-pyridyl)-2,4-imidazolidenedione (L) with general formulaе cis-[PtL₂X₂]·nH₂O and [PtL₂Cl₄], where X = Cl⁻, Br⁻, I⁻ and n = 2-4) were synthesized. The novel compounds were fully characterized by elemental analysis, IR, ¹H, ¹³C, ¹⁹⁵Pt NMR spectra, thermal analysis and molar conductivity. The geometry of Pt(II) complexes and of the organic ligand in the gas phase were optimized using the hybrid DFT method B3LYP with LANL2DZ and 6-31G** basis sets. Some physicochemical parameters as dipole moment, HOMO, LUMO energies and ESP charges were calculated. The comparison of the bond length and angles, obtained from the X-ray analysis and DFT calculations is realized. The cytotoxic effects of these complexes in human T-cell leukemia KE-37 (SKW-3) are reported.     

Exploring the properties of mixed valence cyanide bridged dinuclear complexes: Solvent stabilization of electronic isomers

We report here the synthesis and properties of a family of mixed-valence cyanide-bridged dinuclear complex ions trans-[(L′L₄Ru^II(μ-NC)Fe^III(CN)₅]⁻ (with L = pyridine or 4-dimethylaminopyridine (dmap) and L′ = pyridine, 4-methoxypyridine (meopy) or 4-dimethylaminopyridine)) whose properties could be adjusted smoothly by changing the acceptor properties of the solvent and the σ donor properties of the L′ pyridine ligand. In solution these complexes exhibit an intense solvent-dependent MM′CT (Ru^II → Fe^III) absorption in the near infrared region. Analysis of this band in different complexes and solvents suggests an enhanced interaction as the energies of the metal centers come closer. From this trend the anion trans-[(dmap)₅Ru(μ-NC)Fe(CN)₅]⁻ (dmap = 4-dimethylaminopyridine) in water is expected to belong to the class II-III, but its spectral properties indicates a ground state with Ru(III)-Fe(II) character. The stabilization of this electronic isomer is probably related to the better donor properties of the hexacyanoferrate(II) moiety and its stronger interaction with water.     

Effect of solvent environment on the CO band position in the infrared spectrum of trans-[Fe(CN)4(CO)2]

Density functional theory (DFT) is used to understand the effect of hydrogen bonding solvents on the CO band position in the infrared (IR) spectrum of a mono-iron complex, trans-[Fe^II(CN)₄(CO)₂]²⁻. This mono-iron complex has received much attention recently due its potential relation to the biosynthesis of Fe-only hydrogenase enzymes. Our calculations show that the polar solvent molecules preferentially hydrogen bond to the cyano ligands in this complex. The effect of such hydrogen bonding on the electron density distribution is analyzed in terms of the population in natural bond orbitals (NBO). Our results show that the presence of hydrogen bonding to the cyano ligands decreases the extent of back bonding from the metal to the carbonyl ligand. This results in decreased electron density in the π^∗ orbitals of the carbonyl bond leading to a strengthening of the CO bond and a consequent blue shift in the IR band position of the carbonyl group. We also show that the extent of blue shift correlates with the number of nearest neighbor solvent molecules.     

The cyanocarbanion (C[C(CN)2]3) as monodentate ligand: Synthesis, structure and magnetic properties of [Mn2(bpym)3(tcpd)2(H2O)2] (tcpd = (C[C(CN)2]3) and bpym = 2,2′-bipyrimidine)

One-pot reaction between MnCl₂·4H₂O, K₂tcpd (tcpd²⁻ = [C₁₀N₆]²⁻ = (C[C(CN)₂]₃)²⁻ = 2-dicyanomethylene-1,1,3,3-tetracyanopropanediide anion) and 2,2′-bipyrimidine (bpym = C₈H₆N₄) in aqueous solution yields the new compound [Mn₂(bpym)₃(tcpd)₂(H₂O)₂] (1). The molecular structure of 1 consists of a centrosymmetrical binuclear complex which includes unprecedented unidentate tcpd ligands with two bidentate and a bis-chelate bpym units. Examination of the intermolecular distances reveals that the dinuclear units are held together by hydrogen bonds involving coordinated water molecules and two nitrile groups of the tcpd ligand, giving rise to a 2D structure overall. Variable-temperature magnetic susceptibility data show the occurrence of slight antiferromagnetic coupling (J = −0.58 cm⁻¹) between the Mn(II) ions through bridging bpym (the exchange Hamiltonian being defined as ).     

Long-distance magnetic coupling in dinuclear copper(II) complexes with oligo-para-phenylenediamine bridging ligands

Two novel dinuclear copper(II) complexes of formulae [Cu₂(tren)₂(bpda)](ClO₄)₄ (2) and [Cu₂(tren)₂(tpda)](ClO₄)₄ (3) containing the tripodal tris(2-aminoethyl)amine (tren) terminal ligand and the 4,4′-biphenylenediamine (bpda) and 4,4″-p-terphenylenediamine (tpda) bridging ligands have been synthesized and structurally, spectroscopically, and magnetically characterized. Their experimentally available electronic spectroscopic and magnetic properties have been reasonably reproduced by DFT and TDDFT calculations. Single crystal X-ray diffraction analysis of 2 shows the presence of dicopper(II) cations where the bpda bridging ligand adopts a bismonodentate coordination mode toward two [Cu(tren)]²⁺ units with an overall non-planar, orthogonal anti configuration of the N-Cu-N threefold axis of the trigonal bipyramidal Cu^II ions and the biphenylene group. The electronic absorption spectra of 2 and 3 in acetonitrile reveal the presence of four moderately weak d-d transitions characteristic of a slightly distorted trigonal bipyramid stereochemistry of the Cu^II ions. TDDFT calculations on 2 identify these transitions as those taking place between the four lower-lying, doubly occupied a₂ (d_yz)², b₂ (d_xz)², b₁ (d_xy)², and a₁ (d_x²-y²)² orbitals and the upper, singly occupied a₁ (d_z²)¹ orbital of each trigonal bipyramidal Cu^II ion. Variable-temperature magnetic susceptibility measurements of 2 and 3 show the occurrence of moderate (J = −8.5 cm⁻¹) to weak intramolecular antiferromagnetic couplings (J = −2.0 cm^-1) [H = −JS₁·S₂ with S₁ = S₂ = S_Cu = ½] inspite of the relatively large copper-copper separation across the para-substituted biphenylene- (r = 12.3 Å) and terphenylenediamine (r = 16.4 Å) bridges, respectively. DFT calculations on 2 and 3 support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction between the two unpaired electrons occupying the d_z² orbital of each trigonal bipyramidal Cu^II ion through the predominantly π-type orbital pathway of the oligo-p-phenylenediamine bridges, as reported earlier for the parent compound [Cu₂(tren)₂(ppda)](ClO₄)₄·2H₂O (1) with the 1,4-phenylenediamine (ppda) bridging ligand. Finally, a rather slow exponential decay of the antiferromagnetic coupling (-J) with the number of phenylene repeat units, -(C₆H₄)_n- (n = 1-3), has been found both experimentally and theoretically along this series of oligo-p-phenylenediamine-bridged dicopper(II) complexes. These results further support the ability of linear π-conjugated oligo-p-phenylene spacers to transmit the exchange interaction between the unpaired electrons of the two Cu^II centers with intermetallic distances in the range of 7.5-16.4 Å.     

Two new supermolecular structures of organic-inorganic hybrid compounds: [Zn(phen)(SO4)(H2O)2]n and [Cu(phen)(H2O)2] · SO4 (phen = 1,10-phenanthroline)

Two new organic-inorganic hybrid compounds [Zn(phen)(SO₄)(H₂O)₂]_n (1) and [Cu(phen)(H₂O)₂] · SO₄ (2) have been prepared by conventional aqueous solution synthesis and characterized by single-crystal X-ray diffraction, IR spectroscopy, thermal gravimetric analysis (TGA) and fluorescent spectroscopy. In compound 1, the sulfate group adopts bidentate mode to coordinate with two Zn(II) ions to form one-dimensional polymer. The one-dimensional polymers are further linked together via the intermolecular hydrogen-bonding and π-π stacking interactions to form a 3D supramolecular framework. Compound 2 is build up of discrete [Cu(phen)(H₂O]²⁺ cations and SO₄²⁻ anions to form a three-dimensional framework via hydrogen-bonding and π-π stacking interactions. Furthermore, the luminescent properties of both 1 and 2 were studied. The complexes 1 and 2 excited at 280 nm wavelength produced characteristic luminescence features, arising maybe due to the π-π transitions.     

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

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

Complexes of N-thiophosphorylthioureas RNHC(S)NHP(S)(OiPr)2 (HL) (R = pyridin-2-yl, pyridin-3-yl, 6-amino-pyridin-2-yl) with copper(I): Crystal structures of Cu(PPh3)nL (n = 1, 2)

Reaction of the potassium salts of N-thiophosphorylated thioureas of common formula RNHC(S)NHP(S)(OiPr)₂ [R = pyridin-2-yl (HL^a), pyridin-3-yl (HL^b), 6-amino-pyridin-2-yl (HL^c)] with Cu(PPh₃)₃I in aqueous EtOH/CH₂Cl₂ leads to mononuclear [Cu(PPh₃)₂L^a,b-S,S′] (1, 2) and [Cu(PPh₃)L^c-S,S′] (3) complexes. Using copper(I) iodide instead of Cu(PPh₃)₃I, polynuclear complexes [Cu_n(L-S,S′)_n] (4-6) were obtained. The structures of these compounds were investigated by IR, ¹H, ³¹P{¹H} NMR spectroscopy, ES-MS and elemental analyses. The crystal structures of Cu(PPh₃)₂L^b (2) and Cu(PPh₃)L^c (3) were determined by single-crystal X-ray diffraction.     

Formation and structural chemistry of the unusual cyanide-bridged dinuclear species [Ru2(NN)2(CN)7] (NN = 2,2′-bipyridine or 1,10-phenanthroline)

Crystallisation of simple cyanoruthenate complex anions [Ru(NN)(CN)₄]²⁻ (NN = 2,2′-bipyridine or 1,10-phenanthroline) in the presence of Lewis-acidic cations such as Ln(III) or guanidinium cations results, in addition to the expected [Ru(NN)(CN)₄]²⁻ salts, in the formation of small amounts of salts of the dinuclear species [Ru₂(NN)₂(CN)₇]³⁻. These cyanide-bridged anions have arisen from the combination of two monomer units [Ru(NN)(CN)₄]²⁻ following the loss of one cyanide, presumably as HCN. The crystal structures of [Nd(H₂O)_5.5][Ru₂(bipy)₂(CN)₇] · 11H₂O and [Pr(H₂O)₆][Ru₂(phen)₂(CN)₇] · 9H₂O show that the cyanoruthenate anions form Ru-CN-Ln bridges to the Ln(III) cations, resulting in infinite coordination polymers consisting of fused Ru₂Ln₂(μ-CN)₄ squares and Ru₄Ln₂(μ-CN)₆ hexagons, which alternate to form a one-dimensional chain. In [CH₆N₃]₃[Ru₂(bipy)₂(CN)₇] · 2H₂O in contrast the discrete complex anions are involved in an extensive network of hydrogen-bonding involving terminal cyanide ligands, water molecules, and guanidinium cations. In the [Ru₂(NN)₂(CN)₇]³⁻ anions themselves the two NN ligands are approximately eclipsed, lying on the same side of the central Ru-CN-Ru axis, such that their peripheries are in close contact. Consequently, when NN = 4,4′-^tBu₂-2,2′-bipyridine the steric bulk of the t-butyl groups prevents the formation of the dinuclear anions, and the only product is the simple salt of the monomer, [CH₆N₃]₂[Ru(^tBu₂bipy)(CN)₄] · 2H₂O. We demonstrated by electrospray mass spectrometry that the dinuclear by-product [Ru₂(phen)₂(CN)₇]³⁻ could be formed in significant amounts during the synthesis of monomeric [Ru(phen)(CN)₄]²⁻ if the reaction time was too long or the medium too acidic. In the solid state the luminescence properties of [Ru₂(bipy)₂(CN)₇]³⁻ (as its guanidinium salt) are comparable to those of monomeric [Ru(bipy)(CN)₄]²⁻, with a ³MLCT emission at 581 nm.     

Oxoselenide triangular molybdenum clusters: Synthesis and characterization of [Mo3SeO3(acac)3(py)3]PF6

New cluster complex [Mo₃SeO₃(acac)₃(py)₃]⁺ was obtained by ligand substitution in the aqua complex [Mo₃SeO₃(H₂O)₉]⁴⁺. Crystal structure was determined for [Mo₃SeO₃(acac)₃(py)₃]PF₆·C₆H₅CH₃. The complex was characterized by ⁷⁷Se NMR, electrospray mass-spectrometry, and cyclic voltammetry. DFT calculations were used to confirm the assignment of chemical shift and to study Mo-Mo bonding in the cluster core.     

Synthesis, characterization, structures and DNA-binding properties of complexes [Ru(bpy)2(L)] (L = ptdb, ptda and ptdp) with asymmetric intercalative ligands

A series of Ru(II) polypyridyl complexes [Ru(bpy)₂(ptdb)](ClO₄)₂ (1), [Ru(bpy)₂(ptda)](ClO₄)₂ (2) and [Ru(bpy)₂(ptdp)](ClO₄)₂ (3) with asymmetric intercalative ligands have been synthesized and characterized by EA, mass spectra, ¹H NMR and cyclic voltammetry. The crystal structure of complex 1 has been determined. The DNA-binding properties of the complexes were investigated by absorption titration, luminescence spectroscopy and viscosity measurements. The experimental results suggest that all these complexes bind to DNA in an intercalation mode. The results also show that the order of DNA-binding affinities (A) of this series of complexes is A(1) < A(2) < A(3). It is further confirmed that a ligand planarity of the complexes is a very important factor in affecting the DNA-binding behaviors of such complexes. Theoretical studies for these complexes were also carried out with the density functional theory (DFT) method. The trend in the DNA-binding affinities of this series of complexes can be reasonably explained by the synthetical considerations of the calculated planarity of intercalative ligands, some frontier molecular orbital energies of the complexes and the planarity area (S) of the intercalative ligands.     

Structural diversity and optical properties in the M-X-isonicotinic (M = Zn, Cd; X = Cl, Br, I) system: New zero-, one-, two- and three-dimensional inorganic-organic hybrids

Assembly of isonicotinic acid ligand (HL) with metal halide, five new hybrid complexes [CdI₂(C₅H₄NCOOH)(C₅H₄NHCOO)] · H₂O (1), Na_n[ZnCl₂(C₅H₄NCOO)]_n · 2nH₂O (2), [CdX(C₅H₄NCOO)]_n (X = Br (3), I (4)) and [Cd₃Cl₂(OH)₂(C₅H₄NCOO)₂]_n (5) were obtained, which display a variety of structural motifs, ranging from zero-dimensional to complicated three-dimensional networks. Complex 1 possesses an isolated unit MX₂ that is further connected into 3D networks through hydrogen bonding and π-π stacking interactions. Complex 2 is characterized by an infinite one-dimensional chain of zinc atoms bridged by L⁻ ligands. While complexes 3 and 4 possess X-bridging ^∞₁[CdX_2/2] inorganic chains connected by L⁻ ligands to form a 2D hybrid network structure. In the case of 5, the cadmium(II) cation is bridged by μ₃-Cl atom and μ₃-OH⁻ group to form a 2-D ^∞₂[Cd_6/2Cl_6/3(μ₃-OH)₂] inorganic layer which is further extended into 3-D framework by bridging L⁻ ligand via Cd-N and Cd-O bonds. The optical properties of 1, 4, and 5 in the solid state are investigated at room temperature and time-dependent DFT (TDDFT) calculation using the B3LYP functional has been performed on 1. The result indicated that the emission band of 1 is attributed to an admixture of MLCT (metal-to-ligand charge-transfer) and LLCT (ligand-to-ligand charge-transfer).     

Dinitrosyl iron complexes [E5Fe(NO)2] (E = S, Se): A precursor of Roussin’s black salt [Fe4E3(NO)7]

[PPN][Se₅Fe(NO)₂] (1) and [K-18-crown-6-ether][S₅Fe(NO)₂] (2′) were synthesized and characterized by IR, UV-Vis, EPR spectroscopy, magnetic susceptibility, and X-ray structure. [PPN][Se₅Fe(NO)₂] easily undergoes ligand exchange with S₈ and (RS)₂ (R = C₇H₄SN (5), o-C₆H₄NHCOCH₃ (6), C₄H₃S (7)) to form [PPN][S₅Fe(NO)₂] and [PPN][(SR)₂Fe(NO)₂]. The reaction displays that [E₅Fe(NO)₂]⁻ (E = Se (3), S (4)) facilely converts to [Fe₄E₃(NO)₇]⁻ by adding acid HBF₄ or oxidant [Cp₂Fe][BF₄] in THF, respectively. Obviously, complexes 1 and 2′ serve as the precursors of the Roussin’s black salts 3 and 4. The electronic structure of {Fe(NO)₂}⁹ core of [Se₅Fe(NO)₂]⁻ is best described as a dynamic resonance hybrid of {Fe⁺¹(NO)₂}⁹ and {Fe⁻¹(NO⁺)₂}⁹ modulated by the coordinated ligands. The findings, EPR signal of g = 2.064 for 1 at 298 K, implicate that the low-molecular-weight DNICs and protein-bound DNICs may not exist with selenocysteine residues of proteins as ligands, since the existence of protein-bound DNICs and low-molecular-weight DNICs in vitro has been characterized with a characteristic EPR signal at g = 2.03. In addition, complex 2′ treated human erythroleukemia K562 cancer cells exposed to UV-A light greatly decreased the percentage survival of the cell cultures.