fac-/mer-[RuCl3(NO)(P-N)] (P-N = [o-(N,N-dimethylamino)phenyl]diphenylphosphine): Synthesis, characterization and DFT calculations

Complex fac-[RuCl₃(NO)(P-N)] (1) was synthesized from the reaction of [RuCl₃(H₂O)₂(NO)] and the P-N ligand, o-[(N,N-dimethylamino)phenyl]diphenylphosphine) in refluxing methanol solution, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) was obtained by photochemical isomerization of (1) in dichloromethane solution. The third possible isomer mer,cis-[RuCl₃(NO)(P-N)] (3) was never observed in direct synthesis as well as in photo- or thermal-isomerization reactions. When refluxing a methanol solution of complex (2) a thermally induced isomerization occurs and complex (1) is regenerated.The complexes were characterized by NMR (³¹P{¹H}, ¹⁵N{¹H} and ¹H), cyclic voltammetry, FTIR, UV-Vis, elemental analysis and X-ray diffraction structure determination. The ³¹P{¹H} NMR revealed the presence of singlet at 35.6 for (1) and 28.3 ppm for (2). The ¹H NMR spectrum for (1) presented two singlets for the methyl hydrogens at 3.81 and 3.13 ppm, while for (2) was observed only one singlet at 3.29 ppm. FTIR Ru-NO stretching in KBr pellets or CH₂Cl₂ solution presented 1866 and 1872 cm⁻¹ for (1) and 1841 and 1860 cm⁻¹ for (2). Electrochemical analysis revealed a irreversible reduction attributed to Ru^II-NO⁺ → Ru^II-NO⁰ at −0.81 V and −0.62 V, for (1) and (2), respectively; the process Ru^II → Ru^III, as expected, is only observed around 2.0 V, for both complexes.Studies were conducted using ¹⁵NO and both complexes were isolated with ¹⁵N-enriched NO. Upon irradiation, the complex fac-[RuCl₃(NO)(P-N)] (1) does not exchange ¹⁴NO by ¹⁵NO, while complex mer,trans-[RuCl₃(NO)(P-N)] (2) does. Complex mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′) was obtained by direct reaction of mer,trans-[RuCl₃(NO)(P-N)] (2) with ¹⁵NO and the complex fac-[RuCl₃(¹⁵NO)(P-N)] (1′) was obtained by thermal-isomerization of mer,trans-[RuCl₃(¹⁵NO)(P-N)] (2′).DFT calculation on isomer energies, electronic spectra and electronic configuration were done. For complex (1) the HOMO orbital is essentially Ru (46.6%) and Cl (42.5%), for (2) Ru (57.4%) and Cl (39.0%) while LUMO orbital for (1) is based on NO (52.9%) and is less extent on Ru (38.4%), for (2) NO (58.2%) and Ru (31.5%).     

Manganese(III) complexes of N2O2 donor 5-bromosalicylideneimine ligands: Combined effects of electron withdrawing substituents and chelate ring size variations on electrochemical properties

A series of mononuclear manganese(III) complexes of formulae [Mn(L)(X)(H₂O)] (1-13) and [Mn(L)(X)] (14-17) (X = ClO₄, F, Cl, Br, I, NCS, N₃), derived from the Schiff bases of 5-bromosalicylaldehyde and different types of diamine (1,2-diaminoethane, 1,2-diaminopropane, 1,3-diaminopropane and 1,4-diaminobutane), have been synthesized and characterized by the combination of IR, UV-Vis spectroscopies, cyclic voltammetry and by X-ray crystallography. The redox properties of all the manganese(III) complexes show grossly identical features consisting of a reversible or quasireversible Mn^III/Mn^II reduction. Besides Mn^III/Mn^II reduction, the complexes 4, 5, 10, 13 and 16 also show reversible or quasireversible Mn^III/Mn^IV oxidation. A linear correlation has been found for the complexes 5, 7, 11 and 13 [Mn(L²)(X)(H₂O)] (X = F, Cl, Br, I) when E_1/2 [Mn^III/Mn^II] is plotted against Mulliken electronegativities (χ_M). The effect of the flexibility of the ligand on redox potential has been studied. It has been observed that the manganese(II) state is stabilized with increasing flexibility of the ligand environment. The crystal structure of 6 shows an octahedral geometry.     

Activity of homobimetallic ruthenium alkylidene complexes on intermolecular [2+2+2] cyclotrimerisation reactions of terminal alkynes

The activity of homobimetallic ruthenium alkylidene complexes, [(p-cymene)Ru(Cl)(μ-Cl)₂Ru(Cl)(CHPh)(PCy₃)] [Ru-I] and [(p-cymene)Ru(Cl)(μ-Cl)₂Ru(Cl)(CHPh)(IPr)] [Ru-II], on intermolecular [2+2+2] cyclotrimerisation reactions of monoynes has been investigated for the first time. It was found that these complexes can catalyse the chemo and regioselective cyclotrimerisation reactions of alkynes at both 25 and 50 °C in polar, aprotic solvents. The catalytic activity of [Ru-I] and [Ru-II] was compared to other well-known ruthenium catalysts such as Grubbs first generation catalyst [RuCl₂(CHPh)(PCy₃)₂] [Ru-III], [RuCl(μ-Cl)(p-cymene)]₂ [Ru-IV] and [RuCl₂(p-cymene)PCy₃] [Ru-V] complexes. To examine the effect of the steric hinderance of substrates on the regioselectivity of the reaction, a series of sterically hindered silicon containing alkynes (1a, 1b, 1c) were used. It was shown that the isomeric product distribution of the reaction shifts from 1,2,4-trisubstituted arenes to 1,3,5-trisubstituted arenes as the steric hinderance on the substrates increases. These homobimetallic ruthenium alkylidene complexes also catalysed regio- and chemo-selective cross-cyclotrimerisation reactions between silicon-containing alkynes (1a, 1b, 1c) and aliphatic alkynes (1d-g).     

Electronic structures and reactivity aspects of ruthenium-nitrosyls

Nitrosyl complexes with {Ru-NO}⁶ (4(ClO₄)₃) and {Ru-NO}⁷ (4(ClO₄)₂) configurations have been isolated in the selective molecular framework of [Ru(tpm)(pap)(NO)]ⁿ⁺ (tpm = tris(1-pyrazolyl)methane and pap = 2-phenylazopyridine). The DFT optimized structures of [Ru^II(tpm)(pap)(NO⁺)]³⁺ (4³⁺) and [Ru^II(tpm)(pap)(NO)]²⁺ (4²⁺) predict that the Ru-N-O groups in the complexes are in almost linear and bent geometries, respectively. In agreement with largely NO centered reduction a sizeable shift in ν(NO) frequency of 324 cm⁻¹ has been observed on moving from {Ru^II-NO⁺} state in 4³⁺ to {Ru^II-NO) state in 4²⁺. The DFT proposed NO centered spin in {Ru^II-NO) (4²⁺) (Mulliken spin-densities: 0.860 (NO) and 0.087 (Ru)) has been evidenced by its free radical EPR spectrum with g = 1.989. The strongly electrophilic {Ru^II-NO⁺} state in 4³⁺ (ν(NO): 1962 cm⁻¹) can be transformed to the corresponding complex (3⁺) in the presence of nucleophile, OH⁻ with k = 2.03 × 10⁻¹ M⁻¹ s⁻¹ at 298 K in CH₃CN. On irradiation with light the acetonitrile solution of [Ru^II(tpm)(pap)(NO⁺)]³⁺ (4³⁺) undergoes facile photorelease of NO (k_NO, s⁻¹ = 0.1 × 10⁻¹ and t_1/2, s = 69.3) with the concomitant formation of the solvate [Ru^II(tpm)(pap)(CH₃CN)]²⁺ (2²⁺). The photoreleased NO can be trapped as an Mb-NO adduct.     

Interaction of Pt(II) and Pd(II) complexes of terpyridine with 1-methylazoles: A combined experimental and density functional study

The synthesis and characterization of several complexes of the composition [{M(terpy)}_n(L)](ClO₄)_m (M = Pt, Pd; L = 1-methylimidazole, 1-methyltetrazole, 1-methyltetrazolate; terpy = 2,2′:6′,2″-terpyridine; n = 1, 2; m = 1, 2, 3) is reported and their applicability in terms of a metal-mediated base pair investigated. Reaction of [M(terpy)(H₂O)]²⁺ with 1-methylimidazole leads to [M(terpy)(1-methylimidazole)](ClO₄)₂ (1: M = Pt; 2: M = Pd). The analogous reaction of [Pt(terpy)(H₂O)]²⁺ with 1-methyltetrazole leads to the organometallic compound [Pt(terpy)(1-methyltetrazolate)]ClO₄ (3) in which the aromatic tetrazole proton has been substituted by the platinum moiety. For both platinum(II) and palladium(II), doubly metalated complexes [{M(terpy)}₂(1-methyltetrazolate)](ClO₄)₃ (4: M = Pt; 5: M = Pd) can also be obtained depending on the reaction conditions. In the latter two compounds, the [M(terpy)]²⁺ moieties are coordinated via C5 and N4. X-ray crystal structures of 1, 2, and 3 are reported. In addition, DFT calculations have been carried out to determine the energy difference between fully planar [Pd(mterpy)(L)]²⁺ complexes Ip-IVp (mterpy = 4′-methyl-2,2′:6′,2″-terpyridine; L = 1-methylimidazole-N3 (I), 1-methyl-1,2,4-triazole-N4 (II), 1-methyltetrazole-N3 (III), or 3-methylpyridine-N1 (IV)) and the respective geometry-optimized structures Io-IVo. Whereas this energy difference is larger than 70 kJ mol⁻¹ for compounds I, II, and IV, it amounts to only 0.8 kJ mol⁻¹ for the tetrazole-containing complex III, which is stabilized by two intramolecular C-H?N hydrogen bonds. Of all complexes under investigation, only the terpyridine-metal ion-tetrazole system with N3-coordinated tetrazole appears to be suited for an application in terms of a metal-mediated base pair in a metal-modified oligonucleotide.     

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

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

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.     

Hybrid scorpionate/cyclopentadienyl titanium and zirconium complexes with alkoxide and imido ligands

The reactivity of hybrid scorpionate/cyclopentadienyl ligand-containing trichloride zirconium complexes [ZrCl₃(bpzcp)] (1) [bpzcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethylcyclopentadienyl] and [ZrCl₃(bpztcp)] (2) [bpztcp = 2,2-bis(3,5-dimethylpyrazol-1-yl)-1-tert-butylethylcyclopentadienyl] toward several lithium alkoxides has been carried out. Thus, alkoxide-containing complexes [ZrCl₂(OR)(bpzcp)] (R = Me, 3; Et, 4; ⁱPr, 5; (R)-2-Bu, 6), [ZrCl₂(OR)(bpztcp)] (R = Me, 7; Et, 8; ⁱPr, 9; (R)-2-Bu, 10) and [Zr(OR)₃(bpztcp)] (R = Et, 11; ⁱPr, 12) were prepared by deprotonation of the appropriate alcohol group with BuⁿLi followed by reaction with 1 or 2. In addition, the imido-complex [Ti(N^tBu)Cl(bpztcp)(py)] (13) were also prepared. The structures of these complexes have been proposed on basis of spectroscopic and DFT methods.     

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.     

Chalcogenide-capped triruthenium clusters: X-ray structures of [Ru3(CO)6(μ3-CO){P(C4H3S)3}(μ-dppm)(μ3-O)] and [(μ-H)2Ru3(CO)6{P(C4H3S)3}(μ-dppm)(μ3-S)]

Treatment of [Ru₃(CO)₉{P(C₄H₃S)₃}(μ-dppm)] (1) [dppm = bis(diphenylphosphino)methane] with molecular oxygen in benzene at 60 °C affords oxo-capped [Ru₃(CO)₆(μ₃-CO){P(C₄H₃S)₃}(μ-dppm)(μ₃-O)] (2), while with elemental sulfur and selenium related chalcogenide-capped clusters [Ru₃(CO)₆(μ₃-CO){P(C₄H₃S)₃}(μ-dppm)(μ₃-E)] (3, E = S; 5, E = Se) and bis(chalcogenide) clusters [Ru₃(CO)₆{P(C₄H₃S)₃}(μ-dppm)(μ₃-E)₂] (4, E = S; 6, E = Se) result. Reaction of 1 with H₂S in refluxing THF affords the previously reported [(μ-H)₂Ru₃(CO)₇(μ-dppm)(μ₃-S)] (7) together with the new sulfido-capped dihydride [(μ-H)₂Ru₃(CO)₆{P(C₄H₃S)₃}(μ-dppm)(μ₃-S)] (8). All new compounds have been characterized by spectroscopic data, and 2 and 8 by single-crystal X-ray diffraction analyses. Oxo-capped 2 consists of a triangular ruthenium framework capped on opposite sides by oxo and carbonyl groups, while 8 consists of a ruthenium triangle by a capping sulfido ligand and two inequivalent bridging hydride ligands.     

Synthesis, characterisation and crystal structures of a few coordination complexes of nickel(II), cobalt(III) and zinc(II) with N′-[(2-pyridyl)methylene]salicyloylhydrazone Schiff base

Four new coordination complexes, Ni^II(L)₂ (1), [Co^III(L)₂]ClO₄ (2), [Zn(HL)(L)]ClO₄ · H₂O (3) and [Zn(L)₂][Zn(L)(HL)]ClO₄ · 7H₂O (4) (where L is a monoanion of a Schiff base ligand, N′-[(2-pyridyl)methylene]salicyloylhydrazone (HL) with NNO tridentate donor set), have been synthesised and systematically characterised by elemental analysis, spectroscopic studies and room temperature magnetic susceptibility measurements. Single crystal X-ray diffraction analysis reveals that 1 is a neutral complex, while 2-4 are cationic complexes. Among them, 4 is a rare type of cationic complex with two molecules in the asymmetric unit. The ligand chelates the metal centre with two nitrogen atoms from the pyridine and imino moieties and one oxygen atom coming from its enolic counterpart. All the reported complexes show distorted octahedral geometry around the metal centres, with the two metal-N (imino) bonds being significantly shorter than the two metal-N (Py) bonds.     

Syntheses, characterization, and DFT investigation of new mononuclear acetonitrile- and chloro-ruthenium(II) terpyridine complexes

A series of mononuclear acetonitrile complexes of the type [Ru(CH₃CN)(L)(terpy)]²⁺ {L = phen (1), dpbpy (3), and bpm (5)}, and their reference complexes [RuCl(L)(terpy)]⁺ {L = phen (2), dpbpy (4), and dpphen (6)} were prepared and characterized by electrospray ionization mass spectrometry, UV-vis spectroscopy, and cyclic voltammograms (CV). Abbreviations of the ligands (Ls) are phen = 1,10-phenanthroline, dpbpy = 4,4′-diphenyl-2,2′-bipyridine, bpm = 2,2′-bipyrimidine, dpphen = 4,7-diphenyl-1,10-phenanthroline, bpy = 2,2′-bipyridine, and terpy = 2,2′:6′,2″-terpyridine. The X-ray structures of the two complexes 2 and 3 were newly obtained. The metal-to-ligand charge transfer (MLCT) bands in the visible region for 1, 3, and 5 in acetonitrile were blue shifted relative to those of the reference complexes [RuCl(L)(terpy)]⁺. CV for all the [Ru(CH₃CN)(L)(terpy)]²⁺ complexes showed the first oxidation wave at around 0.95 V, being more positive than those of [RuCl(L)(terpy)]⁺. The time-dependent-density-functional-theory approach (TDDFT) was used to interpret the absorption spectra of 1 and 2. Good agreement between computed and experimental absorption spectra was obtained. The DFT approach also revealed the orbital interactions between Ru(phen)(terpy) and CH₃CN or Cl⁻. It is demonstrated that the HOMO-LUMO energy gap of the acetonitrile ligand is larger than that of the Cl⁻ one.     

Synthesis, characterization and antibacterial activity of Fe, Co, Cu and Zn complexes probed by transmission electron microscopy

We synthesized iron(III), cobalt(II), copper(II) and zinc(II) complexes [Fe^III(HBPClNOL)Cl₂]·H₂O (1), [Co^II(H₂BPClNOL)Cl₂] (2), [Cu^II(H₂BPClNOL)Cl]Cl·H₂O (3), and [Zn^II(HBPClNOL)Cl] (4), where H₂BPClNOL is the ligand (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine). The complexes obtained were characterized by elemental analysis, IR and UV-visible spectroscopies, electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (MS/MS), and cyclic voltammetry. X-ray diffraction studies were performed for complexes (3) and (4) revealing the presence of mononuclear and dinuclear structures in solid state for (3). However, the zinc complex is mononuclear in solid state. Biological studies of complexes (1)-(4) were carried out in vitro for antimicrobial activity against nine Gram-positive bacteria (Staphylococcus aureus strains RN 6390B, COL, ATCC 25923, Smith Diffuse, Wood 46, enterotoxigenic S. aureus FRI-100 (SEA+), FRI S-6 (SEB+) and SEC FRI-361) and animal strain S. aureus LSA 88 (SEC/SED/TSST-1+). The following sequence of inhibition promoted by the complexes was observed: (4) > (2) > (3) > (1), showing the effect of the metal on the biological activity. To directly observe the morphological changes of the internal structure of bacterial cells after the treatment, transmission electron microscopy (TEM) was employed. For the most active complex [Zn^II(HBPClNOL)Cl] (4), granulation deposits around the genetic material and internal material leaking were clearly detected.     

Photoactive trans ammine/amine diazido platinum(IV) complexes

The synthesis and characterisation of eight new octahedral Pt^IV complexes of the type trans,trans,trans-[Pt(N₃)₂(OH)₂(NH₃)(Am)] where Am = methylamine (2), ethylamine (4), thiazole (6), 2-picoline (8), 3-picoline (10), 4-picoline (12), cyclohexylamine (14), and quinoline (16) are reported, including the X-ray crystal structures of complexes 2, 8, and 14 as well as that of two of the precursor Pt^II complexes (trans-[Pt(N₃)₂(NH₃)(methylamine)] (1) and trans-[Pt(N₃)₂(NH₃)(cyclohexylamine)] (13)). Irradiation with UVA light rapidly induces loss in intensity of the azide-to-Pt^IV charge-transfer bands and gives rise to photoreduction of platinum. These complexes have potential for use as photoactivated anticancer agents.     

Probing valence and spin situations in selective ruthenium-iminoquinonoid frameworks. An experimental and DFT analysis

The ruthenium-iminoquinone complexes, [Ru(tpm)(Cl)(Q)]⁺ [tpm = tris(1-pyrazolyl)methane, Q = 3,5-di-tert-butyl-N-aryl-1,2-benzoquinonemonoimine, where aryl = C₆H₅, [1]⁺; m-(OCH₃)₂C₆H₃, [2]⁺; m-(Cl)₂C₆H₃, [3]⁺] have been synthesized. The sensitive bond distances of “Q” in [1](ClO₄) and [2](ClO₄), C-O: 1.294(8), 1.281(2) Å; C-N: 1.352(8), 1.335(2) Å; and C-C(meta): 1.366(10)/1.367(9) Å, 1.364(2)/1.353(2) Å, respectively, and other analytical as well as theoretical (DFT) events suggest the valence configuration of [Ru^III(tpm)(Cl)(Q_Sq⁻)]⁺ for [1]⁺-[3]⁺. The paramagnetic [1]⁺-[3]⁺ show sharp ¹H NMR spectra with strikingly small J of 1.8-3.0 Hz. The DFT calculations on [1]⁺ predict that the triplet (S = 1) state exists above (1004 cm⁻¹) the singlet (S = 0) ground state. [1]⁺ exhibits μ = 2.2 BM at 300 K which diminishes to 0.3 BM near 2 K due to the steady decrease in the ratio of triplet to singlet population with the lowering of temperature. [1]⁺-[3]⁺ exhibit one oxidation and two successive reductions each in CH₃CN. Experimental and DFT analyses collectively establish the valence configurations at the non-innocent {Ru-Q} interface along the redox chain as [(tpm)(Cl)Ru^III(Q_Q^o)]²⁺ ([1]²⁺-[3]²⁺) → [(tpm)(Cl)Ru^III(Q_Sq⁻)]⁺ ([1]⁺-[3]⁺) → [(tpm)(Cl)Ru^II(Q_Sq⁻)] ↔ [(tpm)(Cl)Ru^III(Q_Cat)] (1-3) → [(tpm)(Cl)Ru^II(Q_Cat)]⁻ ([1]⁻-[3]⁻). The spectral features of [1]ⁿ-[3]ⁿ (n = +2, +1, 0) have been addressed based on the TD-DFT calculations on [1]ⁿ.     

Controlled nitric oxide photo-release from nitro ruthenium complexes: The vasodilator response produced by UV light irradiation

Preliminary pharmacological studies of various nitric oxide (NO) photo-releasing agents are reported based on the flash-photolysis studies of the nitro ruthenium complexes cis-[Ru^II(NO₂)L(bpy)₂]⁺ (bpy = 2,2′-bipyridine and L = pyridine, 4-picoline and pyrazine) and [Ru^II(NO₂)(bpy)(terpy)]⁺ (terpy = terpyridine) in physiological medium. The net photoreactions under these conditions are two primary photoproducts, in (I) there is Ru^II-NO₂ photoaquation, where the photoproducts are Ru^II-H₂O plus and (II) homolytic dissociation of NO from a coordinated nitrito to derive the Ru^II-OH₂ specie and NO. Based on photochemical processes, the nitro ruthenium complexes were incorporated in water in oil (W/O) microemulsion and used in the vasorelaxation induced experiment. Denuded rat aortas were contracted with KCl and nitro ruthenium complexes in microemulsion were added. Perfusion pressures were recorded while arteries were irradiated at 355 nm The time to reach maximum relaxation was longer for [Ru^II(NO₂)(bpy)(terpy)]⁺ complex (ca. 50 min, n = 6) than for cis-[Ru(NO₂)L(bpy)₂]⁺ with L = py and 4-pic complex (ca. 28 min, n = 6) and cis-[Ru(NO₂)(bpy)₂ (pz)]²⁺ complex (ca. 24 min, n = 5).     

Novel Cu, Co and Pb supramolecular networks of pyridine-2,6-dicarboxylate (pydc) in cooperation with a bent dipyridyl spacer via coordinative, hydrogen-bonding and aromatic stacking interactions

Reaction of M(OAc)₂ (M^II = Cu^II for 1, Co^II for 2, and Pb^II for 3) with pyridine-2,6-dicarboxylic acid (H₂pydc) in presence of a dipyridyl spacer 2,5-bis(4-pyridyl)-1,3,4-oxadiazole (bpo) affords three novel metal-organic supramolecular networks [Cu₂(bpo)(pydc)₂(H₂O)₃] · 2.75H₂O(1), [Co(bpo)(pydc)(H₂O)₂] · (H₂O) (2) and [Pb(pydc)]_n (3), which have been structurally determined by single-crystal X-ray diffraction. The dimeric Cu-pydc coordination framework bridged by a bpo spacer in 1 is hydrogen-bonded to four others to result in a two-dimensional (2-D) sheet array. The neutral monomeric molecules in 2 have an ordered 3-D stacking stabilized via hydrogen bonds and significant π-π interactions in the lattice, possessing large porous channels with the inclusion of guest solvates. In coordination polymer 3, the Pb^II ion takes the unusual distorted capped trigonal prismatic geometry (PbNO₆) and each pydc dianion binds to four Pb^II centres to form a 2-D infinite network. The thermal stabilities of these complexes have also been investigated.     

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.     

Syntheses, crystal structures and magnetic properties of trinuclear and [3 × 1 + 1 × 2] pentanuclear complexes derived from a compartmental ligand: Role of solvent on nuclearity and number of components

Reaction of [Cu^IIL⊂(H₂O)] (H₂L = N,N′-ethylenebis(3-ethoxysalicylaldimine)) with nickel(II) perchlorate in 1:1 ratio in acetone produces the trinuclear compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂ (1). On the other hand, on changing the solvent from acetone to methanol, reaction of the same reactants in same ratio produces the pentametallic compound [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)]·2MeOH (2A), which loses solvated methanol molecules immediately after its isolation to form [(Cu^IIL)₂Ni^II(H₂O)₂](ClO₄)₂·2[Cu^IIL⊂(H₂O)] (2B). Clearly, formation of 1 versus 2A and 2B is solvent dependent. Crystal structures of 1 and 2A have been determined. Interestingly, compound 2A is a [3 × 1 + 1 × 2] cocrystal. The cryomagnetic profiles of 1 and 2B indicate that the two pairs of copper(II)···nickel(II) ions in the trinuclear cores in both the complexes are coupled by almost identical moderate antiferromagnetic interaction (J = −22.8 cm⁻¹ for 1 and −26.0 cm⁻¹ for 2B).     

{Ru-NO} and {Ru-NO} configurations in [Ru(trpy)(tmp)(NO)] (trpy = 2,2:6′,2′′-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline): An experimental and theoretical investigation

The ruthenium-nitrosyl complexes [Ru^II(trpy)(tmp)(NO⁺)](ClO₄)₃ ([4](ClO₄)₃) and [Ru^II(trpy)(tmp)(NO)](ClO₄)₂ ([5](ClO₄)₂) with {Ru-NO}⁶ and {Ru-NO}⁷ configurations, respectively (trpy = 2,2′:6′,2′′-terpyridine, tmp = 3,4,7,8-tetramethyl-1,10-phenanthroline) have been isotaled. The nitrosyl complexes [4]³⁺ and [5]²⁺ have been generated by following a stepwise synthetic procedure: [Ru^II(trpy)(tmp)(X)]ⁿ, X/n = Cl/+ (1⁺) → CH₃CN/2+ (2²⁺) → NO₂/+ (3⁺) → NO⁺/3+ (4³⁺) → NO/2+ (5²⁺). The single-crystal X-ray structures of two precursor complexes [1]ClO₄ and [3]ClO₄ have been determined. The DFT optimized structures of 4³⁺ and 5²⁺ suggest that the Ru-N-O geometries in the complexes are linear (177.9°) and bent (141.4°), respectively. The nitrosyl complexes with linear (4³⁺) and bent (5²⁺) geometries exhibit ν(NO) frequencies at 1935 cm⁻¹ (DFT: 1993 cm⁻¹) and 1635 cm⁻¹ (DFT: 1684 cm⁻¹), respectively. Complex 4³⁺ undergoes two successive reductions at 0.25 V (reversible) and −0.48 V (irreversible) versus SCE involving the redox active NO function, Ru^II-NO⁺ ? Ru^II-NO and Ru^II-NO → Ru^II-NO⁻, respectively, besides the reductions of trpy and tmp at more negative potentials. The DFT calculations on the optimized 4³⁺ suggest that LUMO and LUMO+1 are dominated by NO⁺ based orbitals of around 65% contribution along with partial metal contribution of ∼25% due to (dπ)Ru^II → π∗(NO⁺) back-bonding. The lowest energy transitions in 4³⁺ and 5²⁺ at 360 nm and 467 nm in CH₃CN (TD-DFT: 364 and 459 nm) have been attributed to mixed MLLCT transitions of tmp(π) → NO⁺(π∗), Ru(dπ)/tmp(π) → NO⁺(π^∗) and Ru(dπ)/NO(π) → trpy(π^∗), respectively. The paramagnetic reduced species 5²⁺ exhibits an anisotropic EPR spectrum with g₁ = 2.018, g₂ = 1.994, g₃ = 1.880 (〈g〉 = 1.965 and Δg = 0.138) in CH₃CN, along with ¹⁴N (I = 1) hyperfine coupling constant, A2 = 35 G at 110 K due to partial metal contribution in the singly occupied molecular orbital (DFT:SOMO:Ru (34%) and NO (53%)). Consequently, Mulliken spin distributions in 5²⁺ are calculated as 0.115 for Ru and 0.855 for NO (N, 0.527; O, 0.328). The reaction of moderately electrophilic nitrosyl center in 4³⁺ with the nucleophile, OH⁻ yields the nitro precursor, 3⁺ with the second-order rate constant value of 1.7 × 10⁻¹ M⁻¹ s⁻¹ at 298 K in CH₃CN-H₂O (10:1). On exposure to light (Xenon 350 W lamp) both the nitrosyl species, 4³⁺ ({Ru^II-NO⁺}) and 5²⁺ ({Ru^II-NO}) undergo photolytic Ru-NO bond cleavage process but with a widely varying k_NO, s⁻¹ (t_1/2, s) of 1.56 × 10⁻¹(4.4) and 0.011 × 10⁻¹(630), respectively.