Spectral properties and bio-activity of copper(II) clofibriates, part III: crystal structure of Cu(clofibriate)2(2-pyridylmethanol)2, Cu(clofibriate)2(4-pyridylmethanol)2(H2O) dihydrate, and Cu2(clofibriate)4(N,N-diethylnicotinamide)2

New copper(II) clofibriates (clof, {2-(4-chlorophenoxy)-2-methylpropionic or 2-(4-chlorophenoxy)isobutyric acid}) of composition Cu(clof)₂L₂ (where L=2-pyridylmethanol (2-pymeth) (1), N-methylnicotinamide (Menia) (4), N,N-diethylnicotinamide (Et₂nia) (5), isonicotinamide (isonia) (7) or methyl-3-pyridylcarbamate (mpc) (8)), [Cu(clof)₂(4-pymeth)₂(H₂O)] · 2H₂O (4-pymeth=4-pyridylmethanol) (2 · 2H₂O) and Cu(clof)₂L (where L=4-pymeth (3) or Et₂nia (6)) have been prepared and spectroscopically characterized. All the Cu(clof)₂L₂ compounds seem to possess distorted octahedral copper(II) stereochemistry with differing tetragonal distortions. An X-ray analysis of 1 was carried out and it featured a tetragonal-bipyramidal geometry around the copper(II) atom. X-ray analysis of 2 · 2H₂O featured a square-pyramidal geometry around copper(II) atom. Both the Cu(clof)₂L compounds seem to consist of a binuclear unit of tetracarboxylate type bridging. An X-ray analysis of 6 revealed typical binuclear paddle-wheel type structure, consisting of two copper(II) atoms in square-pyramidal geometry bridged by four carboxylate anions in the xy-plane. All complexes under study were characterized by EPR and electronic spectroscopy. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi.     

Synthesis, structure, cytotoxic activities and DNA-binding properties of tetracopper(II) complexes with dissymmetrical N,N′-bis(substituted)oxamides as ligands

To compare the cytotoxicities and the DNA-binding properties in tetranuclear complexes with different bridging ligands, two tetracopper(II) complexes with formulae of [Cu₄(oxbe)₂Cl₂(bpy)₂]·4H₂O (1) and [Cu₄(oxbm)₂Cl₂(bpy)₂]·2H₂O (2) were synthesized, where H₃oxbe and H₃oxbm stand for N-benzoato-N′-(2-aminoethyl)oxamide and N-benzoato-N′-(1,2-propanediamine)oxamide, respectively, and bpy is 2,2′-bipyridine. Complex 1 was characterized by elemental analyses, IR and electronic spectra and single-crystal X-ray diffraction. The crystal structure reveals the presence of the circular tetranuclear copper(II) cations which are assembled by a pair of cis-oxamido-bridged dinuclear copper(II) units through carboxyl bridges. The crystal structure of complex 2 has been reported in our previous paper. However, the bioactivities were not studied. Cytotoxicities experiments reveal that both the two complexes exhibit cytotoxic effects against human hepatocellular carcinoma cell SMMC-7721 and human lung adenocarcinoma cell A549, and complex 1 has the better activities than those of complex 2. The results of the interactions between the two complexes and herring sperm DNA (HS-DNA) suggest that the two complexes interact with HS-DNA in the mode of intercalation with the intrinsic binding constants of 3.93 × 10⁴ M⁻¹ (1) and 2.48 × 10⁴ M⁻¹ (2). These results indicated that the bridging ligands may play an important role in the cytotoxicities and the DNA-binding properties of tetranuclear complexes.     

Supramolecular architectures based on di-, tri- and tetrameric complexes with N,N′-diacylhydrazide ligands

Five new complexes, [Co₃(HL₁)₂(Py)₈]·4CH₃OH (1), [Ni₃(HL₁)₂(Py)₄]₂·2DMF (2), [Co₃(H₂L₂)₂(Py)₈]·2NO₃ (3), [Ni₂(HL₂)(Py)₆] (4) and [Cu₄(HL₂)₂(Py)₄]·4DMF (5) (H₄L₁ = N-propionyl-4-hydroxysalicylhydrazide, H₄4-hopshz; H₅L₂ = N-(3-carboxy-cis-2-propenoyl)-4-hydroxysalicylhydrazide, H₅4-hocpshz) have been obtained from two N,N′-diacylhydrazide ligands and characterized by elemental analysis, FT-IR, X-ray diffraction and antimicrobial activities. These di-, tri-, and tetrameric complexes are connected into three-dimensional supramolecular architectures with interesting topologies through O-H?O, C-H?O and C-H?π interactions. 1-3 are linear trimeric complexes with the ligands triply-deprotonated. Topological analysis indicates that they exhibit 2D (4,4), 3D (6,8)-connected (3³4⁹5²6)(3⁴4¹²5⁷6⁴7) and 8-connected (4²⁵6³) net, respectively. 4 and 5 possess dimeric and tetrameric structures, which are extended into 7-connected (3³4¹³5³6) and 4-connected (4,4) net, respectively.     

Synthesis and transition metal complexes of 3,3-bis(1-vinylimidazol-2-yl)propionic acid, a new N,N,O ligand suitable for copolymerisation

The new N,N,O heteroscorpionate ligand 3,3-bis(1-vinylimidazol-2-yl)propionic acid (Hbvip) (5) was synthesised in five steps starting from 1-vinylimidazole. This ligand is closely related to 3,3-bis(1-methylimidazol-2-yl)propionic acid (Hbmip), but contains two vinyl linker groups which can be used for radical-induced polymerisation reactions. The κ³-N,N,O coordination behaviour of 5 was proven by the synthesis of the tricarbonyl complexes [Re(bvip)(CO)₃] (6), [Mn(bvip)(CO)₃] (7) and [Cu(bvip)₂] (8). To obtain good yields of 6, it was synthesised in water instead of THF. The ligand as well as all three complexes were characterised by X-ray crystallography. Copolymerisation of 5 with pure methyl methacrylate (MMA) or a combination of MMA and ethylene glycol dimethacrylate (EGDMA) led to the solid phases P1 and P2. Polymer-bound rhenium and manganese tricarbonyl complexes could be obtained by the reaction of deprotonated P1 with [MBr(CO)₅] (M = Re, Mn) and also by copolymerisation of 6 and 7 with MMA. In both cases, the facial tripodal binding behaviour was evidenced by IR spectra of the polymers. Furthermore, the content of metal incorporated in the polymers was determined by elemental analysis, AAS or ICP-OES measurements. Reaction of the deprotonated solid phase P1 with copper(II) chloride led to a blue solid-phase (P1-Cu). The UV-Vis absorption maximum of P1-Cu is found at 615 nm, which is almost identical to that found for 8. Thereby, it seems likely that P1 is flexible enough to form bisligand complexes with copper(II). This means that the copper centres act as a kind of crosslinking agents. In contrast, the heterogeneous reaction of P2 with copper(II) chloride yielded a lime green solid phase (P2-Cu). The bathochromic shift of the absorption maximum by 102 nm suggests one-sided bound copper centres.     

Syntheses, structures and properties of copper(II) complexes containing N-(2-hydroxybenzyl)-amino amide ligands

Four copper(II) complexes containing the reduced Schiff base ligands, namely, N-(2-hydroxybenzyl)-glycinamide (Hsglym) and N-(2-hydroxybenzyl)-l-alaninamide (Hsalam) have been synthesized and characterized. The crystal structures of [Cu₂(sglym)₂Cl₂] (1), [Cu₂(salam)₂(NO₃)₂] · H₂O (3), [Cu₂(salam)₂(NO₃)(H₂O)](NO₃) · 1.5H₂O (4), [Cu₂(salam)₂](ClO₄)₂ · 2H₂O (5) show that the Cu(II) atoms are bridged by two phenolato oxygen atoms in the dimers. The sglym ligand bonded to Cu(II) in facial manner while salam ligand prefers to bind to Cu(II) in meridonal geometry. Variable temperature magnetic studies of 3 showed it is antiferromagnetic. These Cu(II) complexes and [Cu₂(sglym)₂(NO₃)₂] (2), exhibit very small catecholase activity as compared to the corresponding complexes containing acid functional groups.     

Synthesis, spectroscopic, thermal and X-ray structure characterization of 1,3-propanediammonium tetrathiomolybdate and N,N,N′,N′-tetramethylethylenediammonium tetrathiomolybdate

The title compounds 1,3-propanediammonium tetrathiomolybdate, (1,3-pnH₂)[MoS₄], 1 and, N,N,N′,N′-tetramethylethylenediammonium tetrathiomolybdate, (tmenH₂)[MoS₄], 2, were prepared by reacting the ammonium salt of [MoS₄]²⁻ with the corresponding organic diamine. In 1 and 2 the organic diamines 1,3-propanediamine (1,3-pn) and N,N,N′,N′-tetramethylethylenediamine (tmen) are present in their diprotonated form. The reaction of 1 or 2 with [Ni(en)₃]Cl₂ · 2H₂O (en is ethylenediamine) results in the formation of the highly insoluble complex tris(ethylenediamine)Ni(II) tetrathiomolybdate, [Ni(en)₃][MoS₄], in quantitative yields. 1 and 2 have been characterized by chemical analysis, vibrational, UV-Vis and NMR spectroscopy, TG-DTA-MS and single crystal X-ray crystallography. Compound 1 is thermally more stable compared to 2. Both complexes decompose in a single step forming amorphous molybdenum sulfide. The structure of the title complexes can be described as consisting of tetrahedral [MoS₄]²⁻ dianions which accept a complex series of H-bonds from the organic dications. The strength and number of these hydrogen bonds affect the Mo-S bond lengths.     

New polymeric thiocyanatoiron(II) complex with N,N′-diethylnicotinamide - Synthesis, structure, magnetic and spectral properties

The iron(II) compound of formula [Fe(NCS)₂(dena)₂]_n (dena = N,N′-diethylnicotinamide) has been prepared by the reaction between iron(III) thiocyanate and dena in ethanol solution. The complex was characterized by elemental analysis, spectral and magnetic measurements. Single-crystal X-ray diffraction methods show that the complex, crystallizing in the triclinic space group, undergoes a phase transition between 220 K and 230 K, connected with the doubling of cell volume. Crystal structures at 230 K (1a; HT phase) and 150 K (1b; LT phase) are described and a transition mechanism is discussed. In both phases the compound has an extended chain structure, in which the neutral molecule of N,N′-diethylnicotinamide acts as a bridging ligand binding through pyridine N atom to one centre and through amide O atom to the neighbouring Fe centre. The Fe²⁺ ion has a slightly distorted trans-octahedral environment with FeO₂N₄ chromophore, and all Fe-O and Fe-N bonds in the typical for high-spin iron(II) compounds range. Variable-temperature magnetic susceptibility data in the temperature range 1.8-300 K show that iron(II) is high-spin S = 2(⁵T_2g) and as a result effects due to zero-field splitting are anticipated at low temperatures. The IR spectrum suggested the coordination of N,N′-diethylnicotinamide to the central atom of iron(II) as a bridging ligand and NCS group as a monodentate ligand.     

Polymorphism and weak antiferromagnetic interactions in dibromo[(−)-sparteine-N,N]copper(II)

Two polymorphic crystal structures of the title compound, dibromo[(−)-sparteine-N,N^′]copper(II), 1, were determined. The structures of two isomorphs of 1, 1a [orthorhombic, P2₁2₁2₁, a=11.0463(9) Å, b=11.9839(15) Å and c=12.7835(19) Å] and 1b [orthorhombic, P2₁2₁2₁, a=7.6779(9) Å, b=12.0927(14) Å and c=18.090(2) Å], are composed of the same basic structural unit, Cu(C₁₅H₂₆N₂)Br₂. The bond distances in the molecular structures of 1a and 1b are identical to each other within the esds. However, there are slight differences in the bond angles around the Cu(II) center and considerable differences in their packing structure. Crystal 1a exhibits weak anti-ferromagnetism (J=−1.89 cm⁻¹) as opposed to the magnetically isolated paramagnetism observed for the analogous dichloro[(−)-sparteine]copper(II), 2. The results of a magneto-structural investigation of 1a and 2, and other supporting evidence, suggest that the pathway for the weak antiferromagnetic super-exchange in 1a might be through a Cu-Br ? Br-Cu contact.     

Synthesis, characterization, and magnetic properties of new homotrinuclear bis(oxamato) copper(II) complexes with an asymmetric central N,N′-bridge

The new mononuclear bis(oxamato) complex [n-Bu₄N]₂[Cu(obbo)] (1) (obbo=o-benzyl-bis(oxamato)) has been synthesized as a precursor for trinuclear oxamato-bridged transition metal complexes. Starting from 1 the homotrinuclear complexes [Cu₃(obbo)(pmdta)₂(NO₃)](NO₃)·CH₂Cl₂·H₂O (2) and [Cu₃(obbo)(tmeda)₂(NO₃)₂(dmf)] (3) have been prepared, where pmdta = N,N,N′,N″,N″-pentamethyldiethylenetriamine, tmeda = N,N,N′,N′-tetramethylethylenediamine and dmf = dimethylformamide. The crystal structures of 1-3 were solved. The magnetic properties of 2 and 3 were studied by susceptibility measurements versus temperature. For the intramolecular J parameter values of −111 cm⁻¹ (2) and −363 cm⁻¹ (3) were obtained.     

N,N′-Bis(3-methoxysalicylidene)propane-1,2-diamine mononuclear 4f and heterodinuclear Cu-4f complexes: Synthesis, crystal structure and electrochemical properties

Reactions of H₂L [H₂L = N,N′-bis(3-methoxysalicylidene)propane-1,2-diamine] and Ln(NO₃)₃ · 6H₂O give rise to two different mononuclear 4f complexes, namely, {[(H₂L)La(NO₃)₃(MeOH)] · H₂O}_n (1) and [(H₂L)Nd(NO₃)₃] (2). Further additions of Cu(Ac)₂ · H₂O to the mononuclear 4f complexes yield expected heterodinuclear Cu-4f complexes [LCu(Me₂CO)Ln(NO₃)₃] (3, Ln = Nd; 4, Ln = Eu; 5, Ln = Dy). Complex 1 is a unique 1D polymeric chain structure, and 2 is one of the few structurally characterized discrete hexadentate salen-type mononuclear 4f complexes. Complexes 3-5 are similar to their analogues. However, they are prepared by a reversed synthetic route in contrast to their isomorphic complexes. Electrochemical behavior of heterodinuclear Cu-4f complexes 3-5 has been examined by cyclic voltammetry in acetonitrile. The redox potential of heterodinuclear Cu-4f complexes 3-5 shows significant anodic shift comparing to that of mononuclear copper complex (LCu). A tendency of anodic shift was observed in a sequence of 3 < 4 < 5. This results from the modulating effect of coordination geometry around Cu(II) ion on redox potential.     

Structural chemistry of dihalogenopalladium(II) and platinum(II) complexes of heteroleptic N,S- and N,Se-donor ligands based on the 2-organochalcogenomethylpyridine motif

The structural chemistry of dihalogenopalladium(II) and platinum(II) complexes of 2-organochalcogenomethylpyridine ligands is described. Complexes with a methyl group in the 6-position of the pyridyl ring, 6-MepyCH₂ER, form dimeric complexes [trans-PdX₂(μ-6-MepyCH₂SePh-N,Se)]₂ (X = Br (1), I (2)) or mononuclear complexes trans-PdI₂(6-MepyCH₂SR-N)₂ (R = Me (5), Ph (6)). Absence of a 6-methyl substituent results in the bidentate configuration observed for PdI₂(pyCH₂SePh-N,Se) (3) and PdI₂(4-MepyCH₂SMe-N,S) (4). Related platinum(II) complexes are mononuclear including PtCl₂(6-MepyCH₂SPh-N,S) (8) as an analogue of trimeric [trans-PdCl₂(μ-6-MepyCH₂SPh-N,S)]₃. Differences between palladium and platinum appear to result from a combination of steric and electronic factors.     

Insertion reactions of organic anhydrides into the M-O bond of CuOBu and Sb(OMe)3

The synthesis and structural characterization of the copper salts [Cu₂(2-Boc-benzoate)₄(dme)₂] (1), [Cu(2-Boc-benzoate)₂(tmeda)] (2), [Cu₂(2-Boc-benzoate)₂(dppm)] (3), [Cu(2-Boc-nicotinate)(PPh₃)₂] (4), [Cu₂{2-Boc-5,6-anhydride-naphthylcarboxylate}₂(dppm)₂] (5) [dme = 1,2-dimethoxyethane, dppm = bis(diphenylphosphino)methane, tmeda = N,N′-tetramethylethylenediamine, Boc = tert-butoxycarbonyl] prove that cyclic organic anhydrides and dianhydrides readily insert into the Cu-O bond of [CuO^tBu] forming carboxylate ligands with ester functionalities in the ligand periphery. [Sb(CO₂Ph-o-CO₂Me)₂(OMe)(tmeda)] (6) was synthesised by insertion reaction of Sb(OMe)₃ with phthalic anhydride.     

One-dimensional silver(I) and mercury(II) complexes with 1,4-bis(1-benzyl-benzimidazol-2-yl)cyclohexane (N-BBzBimCH)

The crystal structures of four Ag(I) and Hg(II) complexes of the ligand 1,4-bis(1-benzyl-benzimidazol-2-yl)cyclohexane (N-BBzBimCH) have been described, that is, [Hg₂(N-BBzBimCH)Cl₄] (1), [Hg(N-BBzBimCH)Br₂] (2), [Ag(N-BBzBimCH)](NO₃)(H₂O) (3) and [Ag₂(N-BBzBimCH)(CF₃OCO)₂] (4). All these compounds show 1D polymeric structures in the solid state. In complexes 1 and 4, the chloride ions and the trifluoroacetate groups bridge the [Hg₂(N-BBzBimCH)Cl₂] and [Ag₂(N-BBzBimCH)] fragments, respectively, to generate 1D polymers. While the bromide ions in complex 2 and nitrate groups in complex 3 are only serving as terminal ligands to suffice the coordination geometry of the metal centers. In all cases, weak intermolecular interactions such as C-H?X (X = Cl, Br) contacts, hydrogen bonds, π-π interactions and C-H?π stacking play important roles to extend the 1D chain structures to 2D network. Solid state fluorescence of these compounds was also studied.     

Exploring the coordination chemistry and reactivity of hemilabile N-alkylaminopyrazole ligands towards Pd(II)

Reaction of the N-alkylaminopyrazole (NN′N) ligands bis[(3,5-dimethyl-1-pyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethyl-1-pyrazolyl)methyl]isopropylamine (bdmai) with [PdCl₂(CH₃CN)₂] in a 1:1 M/L ratio in CH₂Cl₂ produces cis-[PdCl₂(NN′N)] (NN′N = bdmae (1), bdmai (2)). The solid state structure of complex 1 was determined by X-ray diffraction studies. The bdmae ligand is coordinated through the two N_pz atoms to the metal atom, which completes its coordination with two chlorine atoms in a cis disposition.Treatment of the corresponding ligand with [PdCl₂(CH₃CN)₂] in 1:1 M/L ratio in the presence of AgBF₄ and metathesis with NaBPh₄ in CH₂Cl₂/CH₃OH (3:1) gave [PdCl(bdmae)](BPh₄) (3), and in the presence of NaBPh₄ in CH₂Cl₂/CH₃CN (3:1) gave [PdCl(bdmai)](BPh₄) (4). Complexes 1 and 2 were again obtained when complexes 3 and 4 were heated under reflux in a solution of Et₄NCl in acetonitrile. These Pd(II) compounds were characterised by elemental analyses, conductivity measurements, IR, ¹H and ¹³C{¹H} NMR, HMQC and NOESY spectroscopies. The NMR studies of the complexes prove the rigid conformation of the ligands when they are complexed.     

Synthesis, crystal structures, DNA-binding properties, cytotoxic and antioxidation activities of several new ternary copper(II) complexes of N,N′-(p-xylylene)di-alanine acid and 1,10-phenanthroline

Three novel ternary copper(II) complexes, [Cu₂(phen)₂(l-PDIAla)(H₂O)₂](ClO₄)₂·2.5H₂O (1), [Cu₄(phen)₆(d,l-PDIAla)(H₂O)₂](ClO₄)₆·3H₂O (2) and [Cu₂(phen)₂(d,l-PDIAla)(H₂O)](ClO₄)₂·0.5H₂O (3) (phen = 1,10-phenanthroline, H₂PDIAla = N,N’-(p-xylylene)di-alanine acid) have been synthesized and structurally characterized by single-crystal X-ray crystallography and other structural analysis. Spectrometric titrations, ethidium bromide displacement experiments, CD (circular dichroism) spectral analysis and viscosity measurements indicate that the three compounds, especially the complex 3, strongly bind to calf-thymus DNA (CT-DNA). The intrinsic binding constants of the ternary copper(II) complexes with CT-DNA are 0.89 × 10⁵, 1.14 × 10⁵ and 1.72 × 10⁵ M⁻¹, for 1, 2 and 3, respectively. Comparative cytotoxic activities of the copper(II) complexes are also determined by acid phosphatase assay. The results show that the ternary copper(II) complexes have significant cytotoxic activity against the HeLa (Cervical cancer), HepG2 (hepatocarcinoma), HL-60 cells (myeloid leukemia), A-549 cells (pulmonary carcinoma) and L02 (liver cells). Investigations of antioxidation properties show that all the copper(II) complexes have strong scavenging effects for hydroxyl radicals and superoxide radicals.     

N,N-dimethylcarbamato complexes of zinc

By reaction of Zn₄O(O₂CNMe₂)₆ (1) with [NH₂Me₂][O₂CNMe₂] in toluene as medium, the homoleptic zinc compound [Zn(O₂CNMe₂)₂] (2) was obtained, which reverted back to the tetranuclear μ-oxo derivative by controlled hydrolysis. The reaction of ZnO in MeCN with an excess of [NH₂Me₂][O₂CNMe₂] in concentrated solution produced high yields of [Zn(O₂CNMe₂)₂] (2) or [NH₂Me₂][Zn₂(O₂CNMe₂)₅] · xMeCN, 3 · xMeCN, x = 1 or 2, depending on the experimental conditions.     

Structural comparison of (pentamethylcyclopentadienyl)iridium(III) azido complexes containing potentially N,S-bidentate N-heterocyclic thiolates: 2- or 8-quinolinethiolate and benzimidazole-2-thiolate

The crystal structures of mononuclear (azido)(pentamethylcyclopentadienyl)iridium(III) complexes bearing 2- or 8-quinolinethiolate (n-Sqn⁻), [Cp^∗Ir(N₃)(n-Sqn)] {n = 2 (1) or 8 (2); Cp^∗ = η⁵-C₅Me₅} have been determined by X-ray analysis. The 2-Sqn complex, 1, acquires severe steric strains in the four-membered κ²N,S chelate ring, while the 8-Sqn isomer, 2, forms a strain-free five-membered planar κ²N,S chelate ring. It has also been revealed that the corresponding benzimidazole-2-thiolate (Hbimt⁻) complex, which was obtained similarly to the above n-Sqn complexes from [Cp^∗Ir(N₃)₂]₂ and Na(Hbimt), takes an unsymmetrical dinuclear structure bridged by two Hbimt⁻ ligands with different bonding modes, [Cp^∗Ir(N₃){μ(S:N¹)-Hbimt}{μ(S:S)-Hbimt}Ir(N₃)Cp^∗] · MeOH (3).     

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

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

Structural and magnetic behavior of mono- and dinuclear nickel (II) complexes of N,N′-bis-(3,5-dipiperidin-1-yl-[2,4,6]triazin-1-yl)-pyridin-2-ylmethyl-ethane-1,2-diamine

Reaction of nickel (II) perchlorate with the ligand N,N′-bis-(3,5-dipiperidin-1-yl-[2,4,6]triazin-1-yl)-pyridin-2-ylmethyl-ethane-1,2-diamine yields an octahedral Ni(II) high-spin complex 1 ([C₄₀H₅₆N₁₄Ni(H₂O)(CH₃OH)](ClO₄)₂(CH₃OH)₂) with moderate zero-field splitting (ZFS) axial distortion parameter D/k_B = 5.37 K. The ligand contributes a N4 donor set; the remaining two coordinating positions are occupied by coordinating solvents molecules. Exchange of the coordinating solvents molecules in complex 1 to thiocyanate moieties leads to formation of complex 2 ([C₄₀H₅₆N₁₄Ni(NCS)₂](CHCl)₃) with an extended parameter D/k_B = 8.80 K. The analysis of the structural and magnetic properties of complexes 1 and 2 led to the design of dinuclear complex 3 ([C₄₀H₅₆N₁₄NiN₃]₂(ClO₄)₂(CH₃OH)₂), where two azido groups were utilized as bridging ligands. The double azido bridges in complex 3 cross each other to form a rarely observed non-coplanar (N₃)₂ structure. The magnetic behavior of complex 3 reveals ferromagnetic coupling interactions characterized by J/k_B = 23.25 K, D₁/k_B = 7.90 K, D₂/k_B = 0.54 K.     

Aromatic N-oxide bridged copper(II) coordination polymers: Synthesis, characterization and magnetic properties

The complexes [Cu₂(o-NO₂-C₆H₄COO)₄(PNO)₂] (1), [Cu₂(C₆H₅COO)₄(2,2′-BPNO)]_n (2), [Cu₂(C₆H₅COO)₄(4,4′-BPNO)]_n (3), [Cu(p-OH-C₆H₄COO)₂(4,4′-BPNO)₂·H₂O]_n (4), (where PNO = pyridine N-oxide, 2,2′-BPNO = 2,2′-bipyridyl-N,N′-dioxide, 4,4′-BPNO = 4,4′-bipyridyl-N,N′-dioxide) are prepared and characterized and their magnetic properties are studied as a function of temperature. Complex 1 is a discrete dinuclear complex while complexes 2-4 are polymeric of which 2 and 3 have paddle wheel repeating units. Magnetic susceptibility measurements from polycrystalline samples of 1-4 revealed strong antiferromagnetic interactions within the {Cu₂}⁴⁺ paddle wheel units and no discernible interactions between the units. The complex 5, [Cu(NicoNO)₂·2H₂O]_n·4nH₂O, in which the bridging ligand to the adjacent copper(II) ions is nicotinate N-oxide (NicoNO) the transmitted interaction is very weakly antiferromagnetic.