Transition metal halide salts of 8-methylquinolinium: Synthesis and structures of (8-methylquinolinium)2 MX4·nH2O (M = Cu, Co, Zn; X = Cl, Br; n = 0, 1)

The reactions of metal(II) chlorides and bromides with 8-methylquinoline (8-mequin) in neutral and acidic solutions were investigated. The reaction with ZnCl₂, ZnBr₂, CoCl₂, CoBr₂, CuCl₂ or CuBr₂ with the appropriate HX in water or aqueous ethanol gave complexes of the formula (8-mequin)₂MX₄ (1, M = Cu, X = Cl; 2, M = Cu, X = Br; 3, M = Co, X = Cl; 4, M = Co, X = Br) or (8-mequin)₂ZnX₄·nH₂O (5, X = Cl, n = 0; 6, X = Br, n = 0; 7, X = Cl, n = 1; 8, X = Br, n = 1). Crystals of 1, 2 and 4-8 suitable for single crystal X-ray diffraction were obtained and the structures reported. Compounds 1 and 2 crystallize in the monoclinic space group C2/c, while 4-8 crystallize in the triclinic space group, . Variable temperature magnetic susceptibility data indicate very weak interactions for the copper compounds 1 and 2, while the magnetic behavior of 3 and 4 is dominated by single ion anisotropy, with weaker antiferromagnetic interactions.     

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.     

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).     

Investigation of the MSO4 · xH2O (M = Zn, x = 7; M = Cd, x = 8/3)/methyl 2-pyridyl ketone oxime reaction system: A novel Cd(II) coordination polymer versus mononuclear and dinuclear Zn(II) complexes

The reactions of methyl 2-pyridyl ketone oxime, (py)C(Me)NOH, with MSO₄ · xH₂O (M = Zn, x = 7; M = Cd, x = 8/3), in the absence of an external base, have been investigated. The synthetic study has led to the two new complexes [Zn(SO₄){(py)C(Me)NOH}(H₂O)₃] · H₂O (1 · H₂O) and [Zn₂(SO₄)₂{(py)C(Me)NOH}₄] · (py)C(Me)NOH [2 · (py)C(Me)NOH], and the coordination polymer [Cd(SO₄){(py)C(Me)NOH}(H₂O)]_n · [Cd(SO₄){(py)C(Me)NOH}(H₂O)₂]_n (3). In the three complexes the organic ligand chelates through its nitrogen atoms. The sulfate anion in 1 · H₂O is monodentate; the complex molecule is the mer isomer considering the positions of the aqua ligands. The Zn^II centers in 2 · (py)C(Me)NOH are bridged by two syn, anti η¹:η¹:μ₂ ligands; each metal ion has the cis-cis-trans disposition of the coordinated sulfate oxygen, pyridyl nitrogen and oxime nitrogens, respectively. The molecular structure of 3 is unique consisting of two different linear and ladder - type chains. π-π stacking interactions and/or hydrogen bonds lead to the formation of interesting supramolecular architectures in the three complexes. The thermal decomposition of complex 3 has been studied. Characteristic vibrational (IR, Raman) bands are discussed in terms of the nature of bonding and the structures of the three complexes.     

Chemistry at the apical position of square-pyramidal copper(II) complexes: Synthesis, crystal structures, and magnetic properties of homopolynuclear complexes with azido bridges containing [Cu(AA)(BB)] moieties (AA = acetylacetonate; BB = 1,10-phenanthroline, bipy = 2,2′-bipyridine)

Three new homopolynuclear complexes with azido bridges have been obtained by using [Cu(AA)(BB)]⁺ building-blocks (AA = acetylacetonate; BB = 1,10-phenanthroline or 2,2′-bipyridine). The reaction between [Cu(acac)(phen)(H₂O)](ClO₄) and NaN₃ leads to a mixture of two compounds: a binuclear complex, [{Cu(acac)(phen)}₂(μ_1,3-N₃)](ClO₄) · 2H₂O (1), and a linear tetranuclear one, [{Cu(acac)(phen)(ClO₄)}₂{Cu(phen)(μ_1,1-N₃)₂}₂] (2). The reaction between [Cu(acac)(bipy)(H₂O)](ClO₄) and NaN₃ affords also a mixture of two compounds: [{Cu(acac)(bipy)}₂(μ_1,3-N₃)]₃(ClO₄)₃ · 3.75H₂O (3) and [Cu(acac)(bipy)(N₃)][Cu(acac)(bipy)(H₂O)](ClO₄) (4). The X-ray crystal structures of compounds 1-4 have been solved (for compound 4 the crystal structure was previously reported). In compounds 1 and 3, two {Cu(AA)(BB)} fragments are bridged by the azido anion in an end-to-end fashion. Two isomers, cis and trans with respect to azido bridge, were found in crystal 3. The structure of compound 2 consists of two Cu(II) central cations bridged by two μ_1,1-azido ligands, each of them being also connected to a {Cu(acac)(phen)} fragment through another μ_1,1-azido ligand. The cryomagnetic properties of the compounds 1 and 2 have been investigated and discussed. The magnetic behaviour of compound 1 shows the absence of any interactions between the metallic ions. In the tetranuclear complex 2, the magnetic interactions between the external and central copper(II) ions(J₁), and between the central metallic ions (J₂) were found ferromagnetic (J₁ = 0.36 cm⁻¹, J₂ = 7.20 cm⁻¹).     

Polymorphism in [(polyamine)Co(NO2)x]Y crystals caused by changes in torsional angles of the (amine)N-Co-N-O fragments (x = 2, Y = NO3: x = 3, Y = 0)

Herein, we report the synthesis and characterization of a third polymorph of trans-[Co(2,3,2-tet)(NO₂)₂]NO₃, III, crystallizing in space group (No. 2) obtained during an attempt to reproduce the synthesis of a previously reported polymorph, I (for more details of polymorphs I and II, see Introduction and references cited therein). The cations of polymorphs I and II differ primarily by the angles that the planes of the two -NO₂ ligands make with one another; the former being considerably larger than that in II. Polymorph III resembles II in that the torsional angular differences between the trans-nitro ligands are also small, but differ notably from that in I.The structure of the compound [(5-Me-(dpt)Co(NO₂)₃], was determined also. The space group is P2₁/n, with two molecules in the asymmetric unit, whose occupancies are 65% and 35% for molecules IVa and IVb, respectively. Again, the two differ by the torsional angles of the nitro ligands, specially two of them whose angular orientations are vastly different. Molecules IVa and IVb are compared with a previously obtained polymorph V of this same compound reported earlier. Once more, V is closely related in stereochemistry to IVb, but differs markedly from IVa in nitro torsional angles.In all cases, the Co(amine) fragments are closely super-imposable and the differences in nitro torsional angles are the result of the availability of several amine hydrogens of the basal plane with which to make intra-molecular hydrogen bonds. Clearly, these hydrogen bonds must be of very similar strength and the barriers to rotation of the -NO₂ ligands must have energies similar to the energetics of the hydrogen bonds causing the torsional motions.     

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).     

Three novel coordination networks dependent upon H2btze ligand [H2btze = 1,2-bis(tetrazol-5-yl) ethane]

Three novel metal-organic frameworks, [Zn(btze)]_n (1), [Zn(btze)(H₂O)]_n (2) and [Mn(btze)(H₂O)₄]_n·(H₂O)₂ (3) [btze = 1,2-bis(tetrazol-5-yl) ethane anion], were synthesized and characterized by elemental analysis, IR spectroscopy, X-ray crystallography and thermogravimetric analysis. The crystal structures study reveal that 1 displays a 3D framework, 2 displays a 2D layer structure and 3 displays a 1D polymeric chain. The luminescence properties of 1-3 were investigated at room temperature in solid state.     

Thiodiacetato-copper(II) chelates with or without N-heterocyclic donor ligands: molecular and/or crystal structures of [Cu(tda)]n, [Cu(tda)(Him)2(H2O)] and [Cu(tda)(5Mphen)] · 2H2O (Him = imidazole, 5Mphen = 5-methyl-1,10-phenanthroline)

Three new thiodiacetato-Cu(II) chelates have been synthesized and studied by X-ray crystallography and by thermal, spectral and magnetic methods. [Cu(tda)]_n (1) is a 3D-polymer with a pentadentate tda, which acts with a fac-O₂ + S(apical)-tridentate chelating conformation and as a twofold anti, syn-μ-η¹:η¹ carboxylate bridge. In its square pyramidal Cu(II) coordination (type 4 + 1) four O(carboxylate) donors define a close regular square base, but the Cu-S(apical) bond deviates 27.4° from the perpendicular to the mean basal plane. Each anti,syn-bridging carboxylate group exhibits two C-O (average 1.26(1) Å) and two Cu-O bonds (average 1.958(7) Å), which are very similar in length to each other. In contrast, the mixed-ligand complexes of [Cu(tda)(Him)₂(H₂O)] (compound 2, distorted octahedral, type 4 + 1 + 1) and [Cu(tda)(5Mphen)] · 2H₂O (compound 3, distorted square pyramidal, type 4 + 1) have molecular structures and the tda ligand displays only a fac-O₂ + S(apical)-tridentate conformation. The Cu-S(apical) bond lengths (2.570(1), 2.623(1) or 2.573(1) Å for 1, 2 or 3, respectively) are shorter than those previously reported for closely related Cu(II)-tda derivatives. The different tda ligand roles in their Cu(II) derivatives are rationalized on the basis of crystal packing forces driving in the absence or presence of auxiliary ligands (with two or three N-donor atoms).     

Hybrid materials composed of tetravanadate motifs: Synthesis, structure and magnetic properties of the open framework structure solids [{M(C5H5N)4}2]V4O12 (M = Cu, Co)

Two new inorganic-organic hybrid materials - [{M(C₅H₅N)₄}₂]V₄O₁₂ (M = Cu, 1; M = Co, 2) have been synthesized and characterized by spectroscopic methods, X-ray powder diffraction, thermogravimetry, magnetometry and complete single crystal structure analysis. The structures of 1-2 are comprised of layers containing centrosymmetric {V₄O₁₂} rings connected to {M(C₅H₅N)₄} units by V-O-M bridges (M = Cu, 1; M = Co, 2). The layers are parallel to the (1 0 1) crystal planes and there are pyridine stacking interactions between layers. The effective magnetic moment, μ_eff, values for 1 and 2 are 1.9 μ_B and 3.9 μ_B, respectively, indicating some orbital contributions in each case. Both compounds exhibit Curie-Weiss magnetic behavior over the entire range above the critical temperature.     

Cd (II)-M (II) hetero-nuclear coordination polymers: Synthesis, structure and photo-electric properties (M = Fe, Co, Cd)

Three Cd (II)-M (II) hetero-nuclear coordination polymers, [FeCd₂(Hcit)₂(H₂O)₂]_n (1), [CoCd₂(BTC)₂(H₂O)₄]_n (2) and [Cd₃(Hcit)₂(H₂O)₂]_n (3) (H₄cit = citric acid, H₃BTC = 1,3,5-benzenetricarboxyl acid), were synthesized through hydrothermal method. They were characterized through elemental analysis, IR spectra, UV-Vis absorption spectra, X-ray powder diffraction, single-crystal X-ray diffraction and surface photovoltage spectra (SPS). Structural analysis indicates that 1 and 3 possess 2D structures, which are further connected to 3D structures by hydrogen bonds. 2 is a 3D Cd-Co coordination polymer bridged by BTC³⁻ groups. The SPS show that 1 and 2 present positive photovoltage response in 300-550 nm, but the photovoltage response of 3 appears in 300-400 nm. It is indicated that the limits of SPS response bands of polymers 1 and 2 are wider than those of 3 because of introduction of the other transition metal ions. There is a good corresponding relationship between SPS and UV-Vis absorption spectra.     

Synthesis and characterization of Fe(III)(3-CH3O-qsal)2PF6 · nH2O (n = 0, 2)

Compounds Fe^III(3-CH₃O-qsal)₂PF₆ · nH₂O (n = 0, 2) (1, 1 · 2H₂O) were synthesized and characterized: the structure of 1 and the magnetic properties of both compounds were determined. Compound 1 · 2H₂O presents properties characteristic of high-spin Fe(III), while 1 presents properties of low-spin Fe(III) with an onset of a gradual spin crossover at ca. 300 K.     

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

New ternary transition metal complexes of formulations [Ni(bpa)(p-AB)Cl]_n · 3nH₂O (bpa = 2,2′-bipyridylamine, p-AB = aminobenzenecarboxylic acid) (1), [Cu(bpa)(p-AB)Cl] · H₂O (2), [Zn(bpa)(p-AB)₂] · H₂O (3) are prepared, their structural features are characterized by crystal structural studies, and their DNA binding propensity has been evaluated by fluorescence and viscosity method. In complex 2 and 3, both bpa and p-AB act as the bidentate N and O-donor ligand, respectively. While in complex 1, p-AB acts as a rare tridentate ligand. In the packing pattern of each complex, π-π interaction in their solid state is 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: 1 > 2 > 3.     

A series of d transition metal coordination complexes: Structures and comparative study of surface electron behaviors (n = 9, 8, 7, 6, 5)

Ten transition metal coordination complexes [Cu₂(phen)(p-tpha)(μ-O)]_n1, [Cu(m-tpha)(imH)₂]_n2, [Ni(5-Haipa)₂(H₂O)₂]_n3, [Ni(phen)₂(H₂O)₂]·btc·[Ni(H₂O)₆]_0.5·9H₂O 4, [Co(2,5-pdc)(H₂O)₂]_n·nH₂O 5, [Co₂(2,5-pdc)₂(H₂O)₆]_n·2nH₂O 6, [Fe(2,5-Hpdc)₂(H₂O)₂]·H₂O 7, [Co(C₆H₄NO₂)₃]·H₂O 8, [Fe₂(μ₂-btec)(μ₂-H₂btec)(bipy)₂(H₂O)₂]_n9, [Mn(phen)(2,5-pdc)(H₂O)₂]·H₂O 10 (H₄btec = 1,2,4,5-benzenetetracarboxylic acid, phen = 1,10-phenanthroline, 2,5-H₂pdc = 2,5-pyridine-dicarboxylic acid, p-tpha = p-phthalic acid, m-tpha = m-phthalic acid, bipy = 2,2′-bipyridine, 5-H₂aipa = 5-aminoisophthalic acid, imH = imidazole, H₃btc = 1,3,5-benzenetricarboxylic acid) were synthesized through hydrothermal method. They were characterized by UV-Vis absorption spectra, single-crystal X-ray diffraction and surface photovoltage spectra (SPS). Structural analysis indicated that the complexes 1, 2, 3, 5, 6 and 9 were linked into infinite structures bridged by organic acid ligands. The other four complexes were molecular complexes and further connected to 2D or 3D structures by the hydrogen bonds. The SPS of complexes 1-10 indicate that there are positive response bands in the range of 300-800 nm showing different levels of photo-electric conversion properties. The intensity, position, shape and the number of the response bands in SPS are obviously different since the structure, species, valence, dⁿ electrons configuration and coordinated environment of the center metals are different. There are good relationships between SPS and UV-Vis spectra.     

X-ray powder and single crystal structures of two unprecedented families of bpca-based 1-D magnetic chains (Hbpca = bis(2-pyridylcarbonyl)amine)

Two unprecedented families of bpca-based mono-dimensional complexes Cu(bpca)(X) (X = CN, 1; N₃, 2) and [Cu_1 − xFe_x(bpca)](ClO₄) (x = 0, 3; 0.23, 4) were synthesised. The structure of 1 was solved ab initio from X-ray powder diffraction data and refined by Rietveld methods. The complexes 3-4 were characterised by X-ray single crystal diffraction. In 1 the cyano ligand coordinates the metal centres, the Cu centres forming a zigzag 1-D chain along the (0 0 1) direction, while in 3-4, the bpca ligand itself acts as the link towards the metal ions which are arranged in a linear 1-D chain running parallel to the (0 0 1) direction. An infrared spectroscopy study confirmed these coordination modes. The magnetic properties of both chain families were studied. 1-2 do not show significant magnetic interactions, whereas the magnetic behaviour for 3-4 suggests dominant antiferromagnetic interactions between the metal ions within the chains. The magnetic behaviour of 3 was analysed using the Padé approximation of the Bonner-Fisher model for S = 1/2 antiferromagnetic chains. The J value was estimated as 10 K.     

Synthesis, structures, luminescence/magnetic properties of complexes of the M/1-hydroxybenzotriazole, M = cobalt, nickel, silver, zinc and copper

Five novel complexes, Co(OBt)₂ · 7H₂O (1) (OBt = 1-hydroxybenzotriazole ion), Ni₃(OBt)₆ · 6H₂O (2), [Ag(OBt)(HOBt)]_n (3), [Zn(OBt)₂]_n (4) and [Cu₂(OBt)₄ · 3H₂O]_n (5) were synthesized by hydrothermal method and characterized by elemental analysis, IR spectroscopy, TGA, XRPD, and single-crystal X-ray diffraction. The results from single-crystal X-ray diffraction indicate that 1-5 are zero-dimensional (0D), zero-dimensional, one-dimensional (1D), and three-dimensional (3D) frameworks, respectively. In particular, 3 is twin crystal; 4 possesses of double-stranded chains; 5 crystallizes in orthorhombic space group P2₁2₁2₁ with a helical chain in its structure. The luminescence properties and the magnetic properties of the five complexes were investigated.     

Novel long bipyridine-type linking ligands containing an intervening naphthalene fragment: [Zn(L)(NO3)2], [Zn(L)(NO3)2], and [Cd(L)1.5(NO3)2] (L = (4-py)-CHN-C10H6-NCH-(4-py); L = (3-py)-CHN-C10H6-NCH-(3-py))

Novel bipyridine-type linking ligands L¹ ((4-py)-CHN-C₁₀H₆-NCH-(4-py)) and L² ((3-py)-CHN-C₁₀H₆-NCH-(3-py)), a pair of isomers due to possessing different pairs of terminal pyridyl groups, were prepared by the Schiff-base condensation. In ligand L¹, the N?N separation between the terminal pyridyl groups is 16.0 Å, with their nitrogen donor atoms at the para positions (4,4′). The corresponding N?N separation in ligand L² is 14.2 Å, with the nitrogen donor atoms at the meta positions (3,3′). 1-D zigzag-chain coordination polymers [Zn(L¹)(NO₃)₂] (1) and [Zn(L²)(NO₃)₂] (2) were prepared by reactions of Zn(NO₃)₂ · 6H₂O with ligands L¹ and L², respectively, by solution diffusion. Polymer 3, [Cd(L¹)_1.5(NO₃)₂], prepared from Cd(NO₃)₂ · 4H₂O and L¹, exhibits a 1-D ladder structure, whose repeating ladder unit consists of four Cd metals and four L¹ ligands to create a large 76-membered ring with dimensions of 20.8 × 20.8 Å. All products were structurally characterized by X-ray diffraction.     

Formation and stabilization of five-coordinate iron(II) verdoheme analogues by axial weakly coordinating anion ligation. X-ray crystal structures of [(OEOPFe)2O](X)2 (X = AsF6, SbF6)

The effect of weakly coordinating anions, , as axial ligands on the formation and coordination chemistry of verdoheme analogues have been examined. Two new five-coordinate and stable iron(II) verdoheme analogues, [OEOPFe^IIX], where OEOP is the monoanion of octaethyloxoporphyrin and X = AsF₆ and SbF₆, have been isolated. The compounds have been characterized by different spectroscopic methods as well as elemental analysis. ¹H NMR spectroscopy and magnetic moment measurements show that the [OEOPFe^IIX] are paramagnetic and iron is five-coordinate. Exposure of dichloromethane solutions of [OEOPFe^IIX] (X = AsF₆ (2), SbF₆ (3)) to dioxygen result in their transformation into the μ-oxo bridged compounds, [(OEOPFe)₂O](X)₂ (X = AsF₆ (4), SbF₆ (5)). The structures of 4 and 5 have been determined by X-ray diffraction analysis, both are structurally similar with a P2₁/c space group in the monoclinic crystal system.     

Reaction of [MCl2(CH3CN)2] (M = Pd(II), Pt(II)) compounds with N1-alkylpyridylpyrazole-derived ligands

Palladium(II) and platinum(II) complexes with N-alkylpyridylpyrazole-derived ligands, 2-(1-ethyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L¹) and 2-(1-octyl-5-phenyl-1H-pyrazol-3-yl)pyridine (L²), cis-[MCl₂(L)] (M = Pd(II), Pt(II)), have been synthesised. Treatment of [PdCl₂(L)] (L = L¹, L²) with excess of ligand (L¹, L²), pyridine (py) or triphenylphosphine (PPh₃) in the presence of AgBF₄ and NaBPh₄ produced the following complexes: [Pd(L)₂](BPh₄)₂, [Pd(L)(py)₂](BPh₄)₂ and [Pd(L)(PPh₃)₂](BPh₄)₂. All complexes have been characterised by elemental analyses, conductivity, IR and NMR spectroscopies. The crystal structures of cis-[PdCl₂(L²)] (2) and cis-[PtCl₂(L¹)] (3) were determined by a single crystal X-ray diffraction method. In both complexes, the metal atom is coordinated by one pyrazole nitrogen, one pyridine nitrogen and two chlorine atoms in a distorted square-planar geometry. In complex 3, π-π stacking between pairs of molecules is observed.     

Acid-base behavior of a simple metal bis(dithiolate) system: Synthesis, crystal structure and spectroscopy of [Bu4N]2[M(ppdt)2] (M = Ni, Pt; ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate)

The syntheses, crystal structures and properties of compounds [Bu₄N]₂[Ni(ppdt)₂] (1) and [Bu₄N]₂[Pt(ppdt)₂] (2) (ppdt = pyrido[2,3-b]pyrazine-2,3-dithiolate) have been described. Compound 1 crystallizes in P2₁/c space group (monoclinic system), whereas compound 2 crystallizes in C2/c space group (monoclinic system). The crystal structures of both compounds 1 and 2 have been characterized by C-H?S and C-H?N hydrogen bonding interactions between cation and anions resulting in three-dimensional supramolecular networks in the crystals of 1 and 2, respectively. The acid-base behavior of the ground states of both [Bu₄N]₂[Ni(ppdt)₂] (1) and [Bu₄N]₂[Pt(ppdt)₂] (2) and also the excited state of compound [Bu₄N]₂[Pt(ppdt)₂] (2) in solutions has been studied. The pH dependent changes in the charge transfer absorption and emission spectra are attributed to the protonation on an imine nitrogen of the ppdt ligand. The ground-state basicity constants of the two complexes 1 and 2 have been determined from spectrophotometric analysis by titrating with an weak acid, yielding pK_b1 = 8.0 for complex [Bu₄N]₂[Ni(ppdt)₂] (1) and pK_b1 = 7.8 for complex [Bu₄N]₂[Pt(ppdt)₂] (2). The excited-state basicity constant pK_b1^* for complex [Bu₄N]₂[Pt(ppdt)₂] (2) has been determined by a thermodynamic equation using a Förster analysis yielding the value of 1.8. The complex 2 is electrochemically irreversible with an oxidation potential of E_1/2 = +0.41 V versus Ag/AgCl in methanol.