Novel heteroligand complexes of Co(II), Cu(II), Ni(II) and Mn(II) formed by 2,2′-dipyridyl or 1,10-phenanthroline and phosphortriamide ligands: Synthesis and structure

This paper presents examples of mixed-ligand Co(II), Cu(II), Ni(II) and Mn(II) complexes, with a distorted octahedral coordination geometry, with 2,2′-dipyridyl or 1,10-phenanthroline and phosphortriamide ligands. The complexes of the general type ML₂·Lig (where M = Co(II), Cu(II), Ni(II), Mn(II); L⁻ = {Cl₃C(O)NP(O)R₂}⁻ (R = NHBz, NHCH₂CHCH₂, NEt₂); Lig = 2,2′-dipyridyl or 1,10-phenanthroline) were synthesised and characterised by means of X-ray diffraction, IR and UV–Vis spectroscopy. The phosphortriamide ligands are coordinated via oxygen atoms of phosphoryl and carbonyl groups involved in six-membered metal cycles. The additional ligands 2,2′-dipyridyl or 1,10-phenanthroline are coordinated to the central atom, forming five-membered cycles.     

Influence of dicarboxylic acids on self-assembly process: Syntheses and structural characterization of new Ag(I) complexes derived from mixed ligands

Using the principle of crystal engineering, three new silver metal–organic coordination polymers, [Ag₂(L1)₂(L2)]·2H₂O (1), [Ag₂(L1)₂(L3)]·H₂O (2), [Ag₂(L1)₂(L4)]·2H₂O (3) (L1 = 2-aminopyrimidine, L2 = oxalate anion, L3 = glutarate anion and L4 = 1,4-naphthalenedicarboxylate anion) have been synthesized by solution phase reactions of silver nitrate with various dicarboxylic acids and cooperative heterocyclic 2-aminopyrimidine ligand under the ammoniacal conditions. All the complexes have been characterized by elemental analyses, IR spectra and X-ray diffraction. In complex 1, L1 ligands are coordinated to Ag(I) metal centers in rare tridentate fashions, forming one-dimensional (1-D) ladder-like structure, which is interlinked by L2 anions to generate 2-D pleated molecular sheet. Complex 2 displays an interesting two-dimensional (2-D) tongue-and-groove structure containing a new kind of “T-shaped” unit. Meanwhile, each of 2-D bilayers is interlocked by four adjacent identical motifs to form three-dimensional (3-D) 5-fold interpenetrating conformation with weak Ag···Ag interactions. In complex 3, L1 ligands are coordinated to the Ag(I) ions to form 1-D polymeric chain. And L4 anions, acting as bridging linkers through corresponding μ²-carboxylates, link a pair of Ag(I) atoms from adjacent chains to yield 3-D supramolecular network. The structures of complexes 1–3 which span from 2-D to 3-D networks suggest that dicarboxylate anions play important role in the formation of such coordination architectures.     

Facile strategies for the synthesis and crystallization of linear trinuclear nickel(II)-Schiff base complexes with carboxylate bridges: Tuning of coordination geometry and magnetic properties

Three new linear trinuclear nickel(II) complexes, [Ni₃(salpen)₂(OAc)₂(H₂O)₂]·4H₂O (1) (OAc = acetate, CH₃COO⁻), [Ni₃(salpen)₂(OBz)₂] (2) (OBz = benzoate, PhCOO⁻) and [Ni₃(salpen)₂(OCn)₂(CH₃CN)₂] (4) (OCn = cinnamate, PhCHCHCOO⁻), H₂salpen = tetradentate ligand, N,N′-bis(salicylidene)-1,3-pentanediamine have been synthesized and characterized structurally and magnetically. The choice of solvent for growing single crystal was made by inspecting the morphology of the initially obtained solids with the help of SEM study. The magnetic properties of a closely related complex, [Ni₃(salpen)₂(OPh)₂(EtOH)] (3) (OPh = phenyl acetate, PhCH₂COO⁻) whose structure and solution properties have been reported recently, has also been studied here. The structural analyses reveal that both phenoxo and carboxylate bridging are present in all the complexes and the three Ni(II) atoms remain in linear disposition. Although the Schiff base ligand and the syn–syn bridging bidentate mode of the carboxylate group remain the same in complexes 1–4, the change of alkyl/aryl group of the carboxylates brings about systematic variations between six- and five-coordination in the geometry of the terminal Ni(II) centres of the trinuclear units. The steric demand as well as hydrophobic nature of the alkyl/aryl group of the carboxylate is found to play a crucial role in the tuning of the geometry. Variable-temperature (2–300 K) magnetic susceptibility measurements show that complexes 1–4 are antiferromagnetically coupled (J = −3.2(1), −4.6(1), −3.2(1) and −2.8(1) cm⁻¹ in 1–4, respectively). Calculations of the zero-field splitting parameter indicate that the values of D for complexes 1–4 are in the high range (D = +9.1(2), +14.2(2), +9.8(2) and +8.6(1) cm⁻¹ for 1–4, respectively). The highest D value of +14.2(2) and +9.8(2) cm⁻¹ for complexes 2 and 3, respectively, are consistent with the pentacoordinated geometry of the two terminal nickel(II) ions in 2 and one terminal nickel(II) ion in 3.     

Spectroscopic investigations on AsH(XΣ) radical using CCSD(T) theory in combination with correlation-consistent quintuple basis set

The equilibrium internuclear separations, harmonic frequencies and potential energy curves of the AsH(X³Σ⁻) radical have been calculated using the coupled-cluster singles–doubles–approximate-triples [CCSD(T)] theory in combination with the series of correlation-consistent basis sets in the valence range. The potential energy curves are all fitted to the Murrell–Sorbie function, which are used to reproduce the spectroscopic parameters such as D_e, ω_eχ_e, α_e, B_e and D₀. The present D₀, D_e, R_e, ω_e, ω_eχ_e, α_e and B_e obtained at the cc-pV5Z basis set are of 2.8004 eV, 2.9351 eV, 0.15137 nm, 2194.341 cm⁻¹, 43.1235 cm⁻¹, 0.2031 cm⁻¹ and 7.3980 cm⁻¹, respectively, which almost perfectly conform to the measurements. With the potential obtained at the UCCSD(T)/cc-pV5Z level of theory, a total of 18 vibrational states is predicted when the rotational quantum number J is set to equal zero (J = 0) by numerically solving the radial Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are determined when J = 0 for the first time, which are in excellent agreement with the experiments.     

Synthesis and structure of indenylnickel(II) chlorides bearing free N-heterocyclic carbene ligands and their catalysis for styrene polymerization

The reaction of (R-Ind)₂Ni (Ind = C₉H₇, indenyl) with an equivalent of a bulky aryl-substituted imidazolium salt in CH₂Cl₂/THF at 45 °C results in the corresponding N-heterocyclic carbene (NHC) indenylnickel(II) chloride of the type (R-Ind)Ni(L)Cl [R = 1-H, L = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr), 1; R = 1-Me, L = IPr, 2] in high yield. Complexes 1 and 2 were characterized by elemental analysis, NMR spectroscopy and X-ray crystallography. The resulted NHC indenylnickel(II) complexes are capable of polymerizing styrene in the presence of NaBPh₄ to give atactic polystyrene with M_n values in the range of 10⁴. The present studies show a close relationship between the structure and catalytic activity of the NHC indenylnickel(II) halides (including the previously reported indenylnickel(II) halides bearing alkyl-substituted NHC ligands), and complex 2 shows the highest catalytic activity. In comparison with its phosphine analogue (1-Me-Ind)Ni(PPh₃)Cl, complex 2 shows significant improvements in stability and catalytic performance.     

Hydrogen bond strength in chromates with kröhnkite-type chains, K2Me(CrO4)2·2H2O (Me = Mg, Co, Ni, Zn, Cd)

Infrared spectra of the title compounds with kröhnkite-type infinite octahedral–tetrahedral chains, K₂Me(CrO₄)₂·2H₂O (Me = Mg, Co, Ni, Zn, Cd), are presented in the regions of the uncoupled O–D stretching modes of matrix-isolated HDO molecules (isotopically dilute samples) and water librations. The strengths of the hydrogen bonds are discussed in terms of the respective O_wO bond distances, the Me–water interactions (synergetic effect), the proton acceptor capability of the chromate oxygen atoms as deduced from Brown's bond valence sum of the oxygen atoms. The spectroscopic experiments reveal that hydrogen bonds of medium strength are formed in the chromates. The hydrogen bond strengths decrease in the order Cd > Zn > Ni > Co in agreement with the decreasing covalency of the respective Me–OH₂ bonds in the same order, i.e. decreasing acidity of the water molecules. The infrared band positions corresponding to the water librations confirm the claim that the hydrogen bonds in K₂Cd(CrO₄)₂·2H₂O are stronger than those formed in K₂Mg(CrO₄)₂·2H₂O on one hand, and on the other—the hydrogen bonds in K₂Ni(CrO₄)₂·2H₂O are stronger than those in K₂Co(CrO₄)₂·2H₂O.     

Novel coordination polymers with ferrocene-containing dicarboxylate ligand: Syntheses, crystal structures and properties

A new ferrocene-containing dicarboxylate ligand, L = 5-ferrocene-1,3-benzenedicarboxylic acid, has been prepared. Self-assembly of L, M(II) salts (M = Co and Zn) and chelating ligands dpa or phen (dpa = 2,2′-dipyridylamine and phen = 1,10-phen) gave rise to four new coordination polymers {[Co(L)(dpa)] · 2MeOH}_n (1), {[Zn(L)(dpa)] · 2MeOH}_n (2), {[Co(L)(phen)(H₂O)] · MeOH} (3), [Zn(L)(phen)(H₂O)] · MeOH (4). The isostructural complexes 1 and 2 possess 1D helical chain structures with 2₁ screw axes along the b-direction, and the right- and left-handed helical chains are alternate arrayed into 2D layer structures through hydrogen-bonding interactions; while isostructural complexes 3 and 4 are 1D linear chain structures with phen and ferrocene groups of L as pendants hanging on the different sides of the main chain. A structural comparison of complexes 1–4 demonstrated that the characteristics of subsidiary ligands and slight difference in coordination models of L play very important role in the construction of the complexes. In addition, the redox properties of complexes 1–4, as well as the magnetic properties of complexes 1 and 3 are also investigated.     

Chiral imidazole metalloenzyme models: Synthesis and enantioselective hydrolysis for α-amino acid esters

Chiral imidazole hydrolytic metalloenzyme models with characteristics of chiral centers directly link to imidazole N-atoms and varieties in both alkyl chain length and number of alkyl chains, have been synthesised and investigated for enantioselective hydrolysis of Boc-α-amino acid esters. The result indicates that both hydrolysis rates and enantioselectivities are increased with increases in the alkyl chain length and the number of the alkyl chains in the lipophilic chiral imidazole-type surfactants in many cases. The lipophilic chiral imidazole 4d ((S)-1-hexadecoxy-2-(1-imidazolyl)-propane), which has one long alkyl chain, shows higher hydrolysis rate and enantioselectivity (k_D = 132.5 × 10⁻⁵, k_D/k_L = 5.38), 5d ((S)-1,5-dihexadecoxy-2-(1-imidazolyl)-pentane), which has two long alkyl chains, shows the highest hydrolysis rate and enantioselectivity (k_D = 201.5 × 10⁻⁵, k_D/k_L = 11.72). Additionally, the effects of the metals, the additives, the solvents and the substrates on the hydrolysis rates and enantioselectivities are examined.     

Synthesis, characterization and biological evaluation of a novel Cu(II) complex with the mixed ligands 2,6-pyridinedicarboxylic acid and 2-aminopyridine

A novel bridged binuclear Cu(II) complex with mixed ligands, di-μ-(2-aminopyridine(N,N′))-bis[(2,6-pyridinedicarboxylate)aquacopper(II)] tetrahydrate, formulated as [Cu(μ-ap)(dipic)(H₂O)]₂·4H₂O (1) (dipic = 2,6-pyridinedicarboxylate, ap = 2-aminopyridine), has been synthesized and characterized by elemental, spectral (IR and UV–Vis.), thermal analysis, magnetic measurements and single crystal X-ray diffraction analysis. The central Cu(II) ion resides on a centre of symmetry in a distorted square-pyramid coordination environment comprising of two N atoms, one from dipic and one from the ap ring, two carboxylate O atoms from dipic, and one O atom from water. Intermolecular N–HO and O–HO hydrogen bonds and π–π stacking interactions seem to be effective in the stabilization of the crystal structure. The free ligands and the complex were also evaluated for their antimicrobial and radical scavenging activities (DPPH = 1,1-diphenyl-2-picrylhydrazyl hydrate) using in vitro microdilution methods. Antimicrobial screening of the free ligands and their complex showed that the free ligands and the complex possess antifungal activity against Candida sp.     

A 3D porous indium(III) coordination polymer involving in-situ ligand synthesis

The hydrothermal reaction of In³⁺ and 1,2,4-benzenetricarboxylic acid with the presence of piperazine leads to the generation of a novel 3D porous coordination polymer, [H₃O][In₂(btc)(bdc)(OH)₂]·5.5H₂O (1), (btc=1,2,4-benzenetricarboxylate, bdc=1,4-benzenedicarboxylate). Compound 1 crystallizes in orthorhombic space group Pbca with a=16.216(7) Å, b=13.437(6) Å, c=31.277(14) Å, and Z=8. It is interesting to find that the in-situ decarboxylation reaction of 1,2,4-benzenetricarboxylate (btc) partially transformed into 1,4-benzenedicarboxylate (bdc) occurs. The 16 indium(III) centers were linked by four btc, four bdc and two μ₂-OH ligands to form a box-girder. The adjacent box-girders are further connected by the bdc and btc ligands to generate a novel porous metal–organic framework containing nanotubular open channel with a cross-section of approximately 11.5×11.3 Å². The micropores are occupied by lattice water molecules, and the solvent-accessible volume of the unit cell was estimated to be 3658.6 Å³, which is approximately 53.7% of the unit-cell volume (6815.4 Å³).     

Co(III) complexes of Me-salpn and Me-salbn and the ring size effect on the coordination modes and electrochemical properties: The crystal structures of trans-[Co(Me-salpn)(py)2]PF6 and cis-α-[Co(Me-salbn)(4-Mepy)2]BPh4 · 4-Mepy

The synthesis and characterization of a series of cobalt(III) complexes of the general type [Co(N₂O₂)(L₂)]⁺ are described. The N₂O₂ Schiff base ligands used are Me-salpn (H₂Me-salpn = N,N′-bis(methylsalicylidene)-1,3-propylenediamine) (1–3) and Me-salbn (H₂Me-salbn = N,N′-bis(methylsalicylidene)-1,4-butylenediamine) (4–5). The two ancillary ligands L include: pyridine (py) 1, 3-metheylpyridine (3-Mepy) 2, 1-methylimidazole (1-MeIm) 3, 4-methylpyridine (4-Mepy) 4 and pyridine (py) 5. These complexes have been characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structures of trans-[Co^III(Me-salpn)(py)₂]PF₆, 1, and cis-α-[Co^III(Me-salbn)(4-Mepy)₂]BPh₄ · 4-Mepy, 4, have been determined by X-ray diffraction. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the complexes exerts a noticeable influence on the inner coordination sphere of the Co(III) ion. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Co^III–Co^II is electrochemically irreversible, which is accompanied by the dissociation of the axial (R-py)–cobalt bonds. It has also been observed that the Co(III) state is stabilized with increasing the flexibility of the ligand environment.     

Synthesis, EPR spectrum and X-ray structure of tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κS,S′)platinate(III)

The new salt, tetra-n-butylammonium bis(benzene-1,2-dithiolato(2−)-κ²S,S′)platinate(III), [NBu₄][Pt(C₆H₄S₂)₂] (1), has been synthesized in ethanol/water, and fully characterized by single crystal X-ray structure determination. The central platinum in the complex ion [Pt(bdt)₂]⁻ is tetracoordinated by the S atoms of the bdt²⁻ ligands (bdt²⁻ is benzene-1,2-dithiolate) in a square-planar geometry. The well-resolved frozen solution EPR spectrum exhibits rhombic symmetry. The room temperature effective magnetic moment (μ_eff = 1.80 Bohr magneton) is in line with this spectrum and strongly supports the Pt(III) oxidation state in 1. This observation is in excellent agreement with previous results reported on closely related Ni(III), Pd(III) and Pt(III) species.     

Chelate structures of 5-(H/Br)-2-hydroxybenzaldehyde-4-allyl-thiosemicarbazones (H2L): Synthesis and structural characterizations of [Ni(L)(PPh3)] and [Ru(HL)2(PPh3)2]

The reactions of 5-R-2-hydroxybenzaldehyde-4-allyl-thiosemicarbazone {R: H (L¹); Br (L²)} with [M^II(PPh₃)nCl₂] (M = Ni, n = 2 and M = Ru, n = 3) in a 1:1 molar ratio have given stable solid complexes corresponding to the general formula [Ni(L)(PPh₃)] and [Ru(HL)₂(PPh₃)₂]. While the 1:1 nickel complexes are formed from an ONS donor set of the thiosemicarbazone and the P atom of triphenylphosphine in a square planar structure, the 1:2 ruthenium complexes consist of a couple from each of N, S and P donor atoms in a distorted octahedral geometry. These mixed-ligand complexes have been characterized by elemental analysis, IR, UV–Vis, APCI-MS, ¹H and ³¹P NMR spectroscopies. The structures of [Ni(L²)(PPh₃)] (II) and [Ru(L¹H)₂(PPh₃)₂] (III) were determined by single crystal X-ray diffraction.     

Salicylaldoxime in manganese(III) carboxylate chemistry: Synthesis, structural characterization and physical studies of hexanuclear and polymeric complexes

The use of salicylaldehyde oxime (H₂salox) in manganese(III) carboxylate chemistry has yielded new members of the family of hexanuclear compounds presenting the [Mn₆(μ₃-O)₂(μ₂-OR)₂]¹²⁺ core, complexes [Mn^III₆(μ₃-O)₂(O₂CPh)₂(salox)₆(L₁)₂(L₂)₂] (L₁ = py, L₂ = H₂O (1); L₁ = Me₂CO, L₂ = H₂O (2); L₁ = L₂ = MeOH (3)). Addition of NaOMe to the acetonitrile reaction mixture, afforded the 1D complex [Mn^III₃Na(μ₃-O)(O₂CPh)₂(salox)₃(MeCN)]_n (4), whereas addition of NaClO₄ to the acetone reaction mixture afforded an analogous 1D complex [Mn^III₃Na(μ₃-O)(O₂CPh)₂(salox)₃(Me₂CO)]_n (5). The structures of 1–3 present the [Mn₆(μ₃-O)₂(μ₂-OR)₂]¹²⁺ core and can be described as two [Mn₃(μ₃-O)]⁷⁺ triangular subunits linked by two μ₂-oximato oxygen atoms of the salox²⁻ ligands, which show the less common μ₃-κ²O:κO′:κN coordination mode. The benzoato ligands are coordinated through the usual syn,syn-μ₂-κO:κO′ mode. The 1D polymeric structures of 4 and 5 consist of alternating [Mn₃(μ₃-O)]⁷⁺ subunits and Na⁺ atoms linked through two μ₃-κ²O:κO′:κN and one μ₄-κ²O:κ²O′:κN salox²⁻ ligands as well as one syn,anti-μ₂-κO:κO′ benzoato ligand. DC and AC magnetic susceptibility studies on 1 revealed the stabilization of an S = 4 ground state, and indications of single-molecule magnetism behavior, whereas the DC experimental data from polycrystalline sample of 5 are indicative of antiferromagnetic interactions within the [Mn₃] subunit. Solid state ¹H NMR data of 1 were used to probe the spin-lattice relaxation of the system.     

Hydrothermal synthesis, crystal structures, and properties of Co and Ni supramolecular complexes with 2,4,6-trimethyl benzoate and 4,4′-bipyridyl

Two new coordination complexes, viz. [Co(tmb)₂(4,4′-bpy)₂(H₂O)₂](Htmb)₂ (1) and {[Ni(tmb)₂(μ-4,4′-bpy)₂(H₂O)₂](4,4′-bpy)}_n (2), have been hydrothermally synthesized by reaction of the corresponding metal acetate with 2,4,6-trimethylbenzoic acid (Htmb) and 4,4′-bipyridyl (4,4′-bpy). X-ray single-crystal diffraction suggests that complex 1 represents a discrete mononuclear species in which the central metal ion is coordinated by the terminal carboxylate moiety and the 4,4′-bipyridyl ligand. The crystal structure of complex 2 reveals a 1D chain coordination polymer in which the Ni(II) ions are connected by the bridging 4,4′-bipyridyl ligands. In both cases, the coordination arrays are further extended via hydrogen bonding interactions to generate 3D supramolecular networks. Complexes 1 and 2 have also been characterized by spectroscopic (IR and UV/Vis), thermal (TGA) and magnetic susceptibility measurements. In addition, both complexes exhibit antimicrobial activity.     

Olefin epoxidation catalyzed by [Ru(TDL)(tmeda)H2O] complexes (TDL = tridentate Schiff-base ligand; tmeda = tetramethylethylenediamine)

Mixed-chelate complexes of ruthenium have been synthesized using tridentate Schiff-base ligands (TDLs) derived from condensation of 2-aminophenol or 2-aminobenzoic acid with aldehydes (salicyldehyde, 2-pyridinecarboxaldehyde), and tmeda (tetramethylethylenediamine). [Ru^III(hpsd)(tmeda)(H₂O)]⁺ (1), [Ru^III(hppc)(tmeda)(H₂O)]²⁺ (2), [Ru^III(cpsd)(tmeda)(H₂O)]⁺ (3) and [Ru^III(cppc)(tmeda)(H₂O)]²⁺ (4) complexes (where hpsd²⁻ = N-(hydroxyphenyl)salicylaldiminato); hppc⁻ = N-(2-hydroxyphenylpyridine-2-carboxaldiminato); cpsd²⁻ = (N-(2-carboxyphenyl)salicylaldiminato); cppc⁻ = N-2-carboxyphenylpyridine-2-carboxaldiminato) were characterized by microanalysis, spectral (IR and UV–vis), conductance, magnetic moment and electrochemical studies. Complexes 1–4 catalyzed the epoxidation of cyclohexene, styrene, 4-chlorostyrene, 4-methylstyrene, 4-methoxystyrene, 4-nitrostyrene, cis- and trans-stilbenes effectively at ambient temperature using tert-butylhydroperoxide (t-BuOOH) as terminal oxidant. On the basis of Hammett correlation (log k_rel vs. σ⁺) and product analysis, a mechanism involving intermediacy of a [Ru–O–OBu^t] radicaloid species is proposed for the catalytic epoxidation process.     

Effect of substituents on the photoluminescence performance of Ir(III) complexes: Synthesis, electrochemistry and photophysical properties

We have prepared and characterized a series of substituted imidazole ligands namely dmmppi, dmmpfpi, dmdmppi and dmdmpfpi. These compounds will readily undergo cyclometalation with iridium trichloride and form di-irrido and the six coordinated iridium(III) dopants of the substituted imidazole ligands. They emit green colour both in solid and in solution phase. The peak emission wavelength of the dopants (λ_max = 428–497 nm) can be finely tuned depending upon the electronic properties of the phenyl, fluorophyenyl, methoxy phenyl and dimethoxyphenyl substituents as well as their positions in the imidazole ring. These iridium complexes namely Ir(dmmppi)₂(pic) 1a, Ir(dmmpfpi)₂(pic) 1b, Ir(dmdmppi)₂(pic) 1c and Ir(dmdmpfpi)₂(pic) 1d were characterized by ¹H NMR, MS and elemental analysis. All these iridium complexes 1a–1d show unusual high HOMO levels (E_HOMO = 5.21–5.41 eV) and high phosphorescence. These complexes emit green light with exceedingly high efficiency.     

Hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands: Imidazole and oxazole ring Lewis basicity,Ni(II)/Pd(II) complex structures and spectra

Fourteen new organic molecules A1–A4, B1–B5, C1–C4 and D and a series of transition metal(II) complexes (Ni1–Ni9 and Pd1–Pd2b) were synthesized and studied in order to characterize the hemilability of 2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands (A1–A4 = 2-R²-6-(4,5-diphenyl-1R¹-imidazol-2-yl)pyridines, R¹ = H or CH₃, R² = H or CH₃; B1–B5 = 1-R²-2-(pyridin-2-yl)-1R¹-phenanthro[9,10-d]imidazoles/oxazoles, R¹ = H or CH₃, R² = H or CH₃; C1–C4 = 2-(6-R²-pyridin-2-yl)-1H-imidazo/oxazo[4,5-f][1,10]phenanthrolines, R² = H or CH₃; D = 2-mesityl-1H-imidazo[4,5-f][1,10]phenanthroline). They were also used to study the substituent effects on the donor strengths as well as the coordination chemistries of the imidazole/oxazole fragments of the hemilabile ligands.All the observed protonation–deprotonation processes found within pH 1–14 media pertain to the imidazole or oxazole rings rather than the pyridyl Lewis bases. The donor characteristics of the imidazole/oxazole ring can be estimated by spectroscopic methods regardless of the presence of other strong N donor fragments. The oxazoles possessed notably lower donor strengths than the imidazoles. The electron-withdrawing influence and capacity to hinder the azole base donor strength of 4,5-azole substituents were found to be in the order phenanthrenyl (B series) > 4,5-diphenyl (A series) > phenanthrolinyl (C series). An X-ray structure of Ni5b gave evidence for solvent induced ligand reconstitution while the structure of Pd2b provided evidence for solvent induced metal–ligand bond disconnection.Interestingly, alkylation of 1H-imidazoles did not necessarily produce the anticipated push of electron density to the donor nitrogen. Furthermore, substituents on the 4,5-carbons of the azole ring were more important for tuning donor strength of the azole base. DFT calculations were employed to investigate the observed trends. It is believed that the information provided on substituent effects and trends in this family of ligands will be useful in the rational design and synthesis of desired azole-containing chelate ligands, tuning of donor properties and application of this family of ligands in inorganic architectural designs, template-directed coordination polymer preparations, mixed-ligand inorganic self-assemblies, etc.     

Organotin(IV) 4-nitrophenylethanoates: Synthesis, structural characteristics and intercalative mode of interaction with DNA

Four new organotin(IV) carboxylates, [Bu₂SnL₂] (1), [Et₂SnL₂] (2), [Bu₃SnL]_n (3), [Me₃SnL]_n (4), where L = 4-nitrophenylethanoates, were synthesized and characterized by elemental analysis, FT-IR and multinuclear NMR (¹H and ¹³C). Spectroscopic results authenticated the coordination of ligand to the organotin moiety via COO group while X-ray single crystal analysis revealed bidentate chelating mode of coordination of ligand in complex 2 and a bridging behavior in complexes 3 and 4. Cyclic voltammetric (CV) technique was used to evaluate the electrochemical, kinetic and thermodynamic parameters of complexes 1-4, interacting with DNA. The linearity of the plots between the peak current (I) and the square root of the scan rate (ν^1/2) indicated the electrochemical processes to be diffusion controlled. The diffusion coefficients of the free (D_f) and DNA bound forms (D_b), standard rate constants (ks) and charge transfer coefficients (α) were determined by the application of Randle–Sevcik, Nicholson and Kochi equations. Furthermore, the binding constants evaluated from voltammetric data revealed the following increasing order of binding strength: 2 < 1 < 4 < 3. For 1 and 2, the activity against prostate cancer cell lines (PC-3) was found consistent with the order obtained from voltammetric behavior.