Square-pyramidal Geometry Research Articles

Catena-Poly[[[2,4-dichloro-6-{[(2-hydroxyethyl)imino]methyl}phenolato-κ3N,O,O']-copper(II)]-μ-chlorido]monohydrate]: Synthesis, structural, spectroscopic and luminescent properties

ABSTRACTA new chloride bridged polymeric Cu(II) complex, [Cu(HL)(μ-Cl).H2O]n, 1, (H2L = 2,4-dichloro-6-{[(2-hydroxyethyl)imino]methyl}phenol) has been synthesized and characterized by elemental-spectral analysis, crystal structure analysis and photoluminescence measurements. The Copper(II) atom is five-coordinate in a slightly distorted square-pyramidal geometry (τ = 0.085), with one N and two O atoms of the Schiff base ligand and one Cl atom defining the basal plane and a symmetry-related Cl atom occupying the apical position. The bridging Cl atom lies in apical position for one Cu(II) ion and basal for the other, and it makes this structural arrangement unusual. The linked moieties form polymeric zigzag chains running along the c axis. This zigzag chains connect each other with intramolecular and intermolecular O–H···O hydrogen bonds, which form 3D structure through π−π interactions. Furthermore, the photoluminescence properties of H2L and 1 were investigated, they exhibit unique bright green visible emissions in the solid state, under the excitation of 349 nm UV light. The strong luminescence emission of them makes 1 a potentially useful photoactive material in photo-physical chemistry.

Nickel, Ruthenium, and Rhodium NCN-Pincer Complexes Featuring a Six-Membered N-Heterocyclic Carbene Central Moiety and Pyridyl Pendant Arms

NCN pincer ligand precursor 1·HX (X = Cl, PF6), having a six-membered N-heterocyclic carbene central moiety and pyridyl pendant arms, was prepared via N–C cross-coupling of 2-bromo-6-tert-butylpyridine with propane-1,3-diamine, followed by ring closure with triethylorthoformate. The free ligand 1 was not accessible via deprotonation, yet its copper(I) complex 2 was prepared by reacting 1·HCl with CuI and potassium hexamethyldisilazide. It was used further as a transmetalation agent to prepare nickel(II) and ruthenium(II) dihalide NCN-pincer complexes 3a, 4a, and 4b, featuring a distorted square-pyramidal geometry at the metal, with the carbene ligand in the axial position. The rhodium(III) NCN-pincer complex 6b was obtained from 2 and [Rh(cod)Cl]2 via transmetalation followed by oxidation with Cu(I) in THF. The rhodium(III) NCC-pincer complex 9b was prepared under similar conditions in acetonitrile, where a spontaneous rollover cyclometalation occurred. Complex 9b has a distorted octahedral geometry, with the acetonitrile ligand trans to the carbene. Very short Ru–CNHC and Rh–CNHC bonds were measured in complexes 4a, 4b, and 9b. Halogen exchange was observed by 1H and 13C NMR spectroscopy in both ruthenium and rhodium systems during the transmetalation stage, and the purification was accomplished by pushing the respective equilibrium with excess halide.

Synthesis, properties and structure of copper(II) complexes of quinolyl azo derivatives of pyrazole-5-one(thione)

The interaction of 5-methyl-2-phenyl-4-[(8-quinolylhydrazono)]pyrazol-3-one (2) and 5-methyl-2-phenyl-4-(8-quinolylhydrazono)pyrazole-3-thione (4) with copper(II) acetate monohydrate under reflux in ethanol results in the formation of copper(II) azo chelates incorporating CuN4O2 (5) and CuN3S2 (6) chromophores. All the compounds were characterized with FT-IR, EPR, X-ray absorption spectroscopy and magnetic measurements. The structures of complexes 5 and 6 were determined by X-ray single-crystal diffraction. Complex 5 adopts a pseudo-octahedral geometry with a cis disposition of the oxygen atoms around the copper(II) centre, whilst in 6 the copper(II) ion displays a square-pyramidal geometry with a {N3S2} ligand environment.

Photocytotoxic Copper(II) Complexes with Schiff-Base Scaffolds for Photodynamic Therapy.

Photodynamic therapy (PDT) is a promising and minimally invasive method for the treatment of superficial diseases, and photosensitizers with high phototoxicity indices (defined as (IC50dark )/(IC50irradiation )) are essential for the development of ideal photosensitizing properties for this technology. Herein, we report a series of photocytotoxic copper(II) complexes [Cu(R QYMP)(dppn)] (R QYMP=N,N,O-tridentate Schiff-base derivatives, dppn=benzo[i]dipyrido[3,2-a;2',3'-c]phenazine), the structures of which have been confirmed by mass spectrometry and FTIR spectroscopy. X-ray crystallography revealed that the CuN4 O core of the [Cu(cumyl QYMP)(dppn)](ClO4 ) complex (3) has a distorted square-pyramidal geometry. Phototoxicity indices of 329 against human squamous cell carcinoma (SCC15) and 296 against basal cell carcinoma (BCC) cell lines have been determined with [Cu(3-OMe QYMP)(dppn)](ClO4 ) (4). This can be attributed to the formation of reactive oxygen species, cell apoptosis, and caspase-3 activation, indicating high potential of complex 4 as a photosensitizer candidate in PDT. Thus, copper complexes bearing suitable Schiff-base ligands with a dppn co-ligand may be considered for the design of efficient metal-based anticancer agents for PDT.

Two CuII complexes of 3,4,5-tri-methyl-1H-pyrazole.

The crystal structure of complexes of 3,4,5-tri-methyl-1H-pyrazole with CuCl2·2H2O and Cu(NO3)2·2.5H2O are presented, namely di-μ-chlorido-bis[chloridobis(3,4,5-trimethyl-1H-pyrazole-κN2)copper(II)], [Cu2Cl4(C6H10N2)4] (1) and aquatetrakis(3,4,5-trimethyl-1H-pyrazole-κN2)copper(II) dinitrate, [Cu(C6H10N2)4(H2O)](NO3)2 (2), and compared to the previously determined structures for 3-methyl-1H-pyrazole and 3,5-di-methyl-1H-pyrazole. CuCl2 forms a 2:1 ligand-to-metal chloride-bridged complex with 3,4,5-tri-methyl-1H-pyrazole, with a square-pyramidal coordination geometry about each copper(II) center. Similarly to the previously obtained 3,5-di-methyl-1H-pyrazole complex with CuCl2, the pyrazole ligands are cis to each other, with two chloride ions bridging the two copper(II) centers, and a terminal chloride ion occupying the axial position. Cu(NO3)2 forms a 4:1 ligand-to-metal complex with 3,4,5-tri-methyl-1H-pyrazole that is also arranged in a square-pyramidal geometry about CuII. The newly obtained copper(II) complex has the same coordination geometry as the 3,5-di-methyl-1H-pyrazole complex, including an axial water mol-ecule, two nitrate ions hydrogen-bonded to the water mol-ecule, and four pyrazole ligands in the equatorial plane, suggesting that similar steric forces are at play in the formation of these complexes.

Role of steric crowding of ligands in the formation of hydroxido bridged di- and trinuclear copper(II) complexes: Structures and magnetic properties

Two new trinuclear copper(II) complexes, [(CuL1)3(μ3-OH)](ClO4)2 (1) and [(CuL2)3(μ3-OH)](ClO4)2·5H2O (2), and one new dinuclear Cu(II) complex, [(CuL3)2(μ2-OH)(CH3OH)]ClO4 (3), have been synthesized using three tridentate NNO donor Schiff bases, HL1, HL2 and HL3 (HL1 = 1-((2-aminoethylimino)methyl)naphthalen-2-ol, HL2 = 1-((2-(methylamino)ethylimino)methyl)naphthalen-2-ol and HL3 = 1-((2-(dimethylamino)ethylimino)methyl)naphthalen-2-ol), respectively and structurally characterized by single-crystal X-ray diffraction. Complexes 1 and 2 consist of trinuclear [(CuL)3(μ3-OH)]2+ units, whereas 3 contains dinuclear [(CuL)2(μ2-OH)]+ unit along, with perchlorate anions which are needed to balance the charge. In each of the complexes, all the copper atoms are five-coordinated with a distorted square-pyramidal geometry, except for complex 1 in which one of the Cu(II) ions of the trinuclear unit is six-coordinate, being weakly coordinated to one of the perchlorate anions to form an elongated distorted octahedron. The equatorial plane consists of the bridging oxygen of the central OH− group together with three atoms (NNO) from the Schiff base. The phenoxido oxygen atom of the Schiff base coordinates to the axial position of the Cu(II) ion of another subunit to form the cyclic trimer in 1 and 2 and dimer in 3. Magnetic measurements of complexes 1–3 in the 2–300 K temperature range indicate antiferromagnetic coupling in the complexes with J = −8.85, −4.86 and −50.60 cm−1 for 1–3 respectively. Density Functional Theory has also been performed in order to estimate the exchange coupling constants in these three complexes. The theoretically calculated J values are in good agreement with the experimental values.

New cationic and neutral copper(II) complexes containing 7-hydroxy-4-oxo-4[H]-chromene derived ONO pincer ligands: Synthesis, characterization and in vitro biological evaluations

New Schiff base ligands are prepared by the condensation of 7-hydroxy-3-formylchromone with semicarbazone and phenyl semicarbazone. The complexation of these ligands with Cu(II) ion is proposed in the light of spectral studies (IR, UV–Vis, 1H NMR, 13C NMR, Mass and ESR). In the complexes 1 and 2, the ligands coordinate to the Cu(II) ion in a neutral fashion via ONO donor atoms. The single crystal XRD studies reveal a slightly distorted square-pyramidal geometry for cationic complex (1) and an octahedral geometry for neutral complex (2). Preliminary biological studies such as DNA and Protein binding are carried out by using absorption and emission titration methods. Observation of intercalative mode of binding with Calf Thymus DNA (CT-DNA) is confirmed by means of viscosity measurements. The micro-environmental changes occurring in Bovine Serum Albumin (BSA) and Human Serum Albumin (HSA) are monitored via three dimensional (3D) fluorescence studies. The compounds ability in inhibiting microbial growth is tested against different pathogens. MCF-7 (human breast cancer) and A549 (human lung carcinoma) cell lines are utilized to check the anticancer potential of the synthesized compounds by using MTT, LDH and NO assays. The results show that complexes 1 and 2 exhibited potent cytotoxic activity over standard drug cisplatin.

Polyoxometalate-Assisted, One-Pot Synthesis of a Pentakis[(triphenylphosphane)gold]ammonium(2+) Cation Containing Regular Trigonal-Bipyramidal Geometries of Five Bonds to Nitrogen.

Novel intercluster compounds consisting of pentakis[(triphenylphosphane)gold]ammonium(2+) cation (1) and Keggin polyoxometalate (POM) anions, i.e., {[Au(PPh3)]5(μ5-N)}3[α-PM12O40]2 (1-PW for M = W; 1-PMo for M = Mo), were synthesized in 30-36% yield by one-pot reaction of the protonic acid form of the Keggin POMs, H3[α-PM12O40]·nH2O (n = 13 for M = W; n = 15 for M = Mo) with monomeric (triphenylphosphane)gold(I) carboxylate [Au(RS-pyrrld)(PPh3)] [RS-Hpyrrld = (RS)-2-pyrrolidone-5-carboxylic acid] in the presence of aqueous NH3 at a molar ratio of 2:15:x (x = 3 for 1-PW; x = 7.5 for 1-PMo). These compounds resulted from the nitrogen-centered phosphanegold(I) clusterization of in situ generated monomeric phosphanegold(I) units, [Au(PPh3)]+ or [Au(L)(PPh3)]+ (L = NH3 or solvent), during the carboxylate elimination of [Au(RS-pyrrld)(PPh3)] in the presence of the Keggin POMs and aqueous NH3. The products 1-PW and 1-PMo were characterized by elemental analysis, Fourier transform infrared, thermogravimetric and differential thermal analyses (TGA/DTA), X-ray crystallography, and solid-state cross-polarization magic-angle-spinning (CPMAS) (31P and 15N) and solution (31P{1H} and 1H) NMR spectroscopy. The lattice contained three independent {[Au(PPh3)]5(μ5-N)}2+ cations, of which two took regular trigonal-bipyramidal (TBP) geometries and the third took a distorted, square-pyramidal (SP) geometry. These geometries are in contrast to those reported by Schmidbaur's group for {[Au(PPh3)]5(μ5-N)}2+ cations as BF4 salts. Density functional theory and ONIOM calculations for {[(L3P)Au]nN}(n-3)+ (L = H or Ph; n = 4-6) showed that the pentacoordinate cluster is energetically most stable and its TBP structure is only 1.6 kcal mol-1 more stable than its SP structure, in accordance with the experimental facts.

New diorganotin(IV) complexes of salicylaldehyde based hydrazones bearing furan heterocycle moiety: X-ray structural investigation of dimethyltin(IV) and diphenyltin(IV) complexes

Some new diorganotin(IV) derivatives formulated as R2SnL (where R = Me, Bu, Ph and Oct) were obtained upon treatment of diorganotin(IV) precursors with acylhydrazones [H2La = N'-(2-hydroxy-3-methoxybenzylidene)furan-2-carbohydrazide, H2Lb = N'-(5-chloro-2-hydroxybenzylidene)furan-2-carbohydrazide and H2Lc = N'-(2-hydroxy-5-nitrobenzylidene)furan-2-carbohydrazide] derived from Schiff base condensation of furan-2-carbohydrazide and substituted salicylaldehydes in methanol in appropriate molar ratio. The enolic tridentate chelating mode of the acylhydrazones towards the diorganotin moieties [R2Sn(IV)]2+ was ascertained by micro-analysis and various spectroscopic techniques viz., Fourier-transform infrared (FT-IR), multinuclear (1H, 13C and 119Sn) magnetic resonance (NMR) and electrospray ionization mass (ESMS) spectrometry. The single crystal X-ray diffraction investigation of Me2SnLb and Ph2SnLb demonstrates that they crystallize in monoclinic space groups ‘P 21’ and ‘P 21/c’ respectively, and comprised of crystallographically discrete 2 and 4 molecules in their respective unit cells. Both mononuclear complexes adopt a highly distorted square-pyramidal geometry (SP) wherein the imine nitrogen preferably occupies the apical site whereas the more electronegative enolic and phenolic oxygen atoms of the ligand and two carbon atoms of the methyl/phenyl groups of the organotin(IV) moiety align themselves equatorially around the five-coordinated tin center in a square plane. Diorganotin(IV) derivatives were also analyzed in air by thermo-gravimetric (TG, DTG and DTA) techniques to elucidate their thermal stability and decomposition trends.

The coordination of a multidentate NxOy-donor (x and y ≤ 2) oxazolidine-based ligand with Cd(II) and Hg(II); Structural, spectral, and theoretical studies

Two binuclear complexes, fac-[Cd2(AEPC)2(μ-Cl)2Cl2] (1) and [Hg2(AEPC)2(μ-Cl)2Cl2] (2), of 2-(2-(pyridin-2-yl)oxazolidin-3-yl)ethanol (AEPC) were prepared and identified by elemental analysis, FT-IR, 1H NMR spectroscopies, and single-crystal X-ray diffraction. All coordination modes of 2-(pyridin-2-yl)oxazolidine derivatives were studied by analysis of the Cambridge Structural Database (CSD) for determination of coordination behaviors of the AEPC ligand with metals. In the crystal structure of 1, the cadmium ion has a distorted octahedral geometry and CdN2OCl3 environment in which each ligand acts as an NN′O-donor. In the crystal structure of 2, the AEPC acts as NN′-donor toward the mercury ion to form a square-pyramidal geometry with three chloride ions. Each complex contains four chiral centers with a center of inversion and Ci symmetry. In the crystal networks of the complexes, the alcohol groups of the ligands participate in hydrogen bonding and form (28) and (44) hydrogen bond motifs (observed for 1). In addition to the hydrogen bonds, the crystal network is stabilized by π–π stacking interactions between pyridine rings of the AEPC ligands of adjacent complexes. The thermodynamic stability of the isolated complexes and their charge distribution patterns were studied by DFT and NBO analysis.

Bis{μ-2,2'-[(3,4-di-thia-hexane-1,6-di-yl)bis-(nitrilo-methanylyl-idene)]bis-(4-bromo-phenolato)-κ4O,N,N',O'}dicopper(II).

The crystal structure of the title compound, [Cu2(C18H12Br2N4O2S2)2], consists of binuclear complex units which lie across inversion centres and are connected by weak Cu-O coordination bonds forming chains along the b axis. The CuII ion is five-coordinated by two N atoms and two O atoms of the chelating ligand and one symmetry-related O atom forming a square-pyramidal coordination geometry. In the crystal, short S⋯Br contacts connect neighbouring chains into a two-dimensional network parallel to (101).

Pentacoordinated Chloro-Iron(III) Complexes with Unsymmetrically Substituted N2O2 Quadridentate Schiff-Base Ligands: Syntheses, Structures, Magnetic and Redox Properties

Since their development in the 1930s, Schiff-base complexes have played an important role in the field of coordination chemistry. Here, we report the synthetic, spectral, structural, magnetic and electrochemical studies of two new pentacoordinated neutral chloro-iron(III) complexes (3,5) supported by dianionic [N2O2]2− tetradentate Schiff-base ligands unsymmetrically substituted by either a pair of acceptor (F and NO2) or donor (ferrocenyl and OCH3) groups. The electron-withdrawing Schiff-base proligand 2 and the complexes 3 and 5 were prepared in good yields (79–86%). Complex 3 was readily obtained upon reaction of 2 with anhydrous iron chloride under basic conditions, while the bimetallic derivative 5 was synthesized by condensation of the free amino group of the ferrocenyl-containing O,N,N-tridentate half-unit 4 with 5-methoxysalicylaldehyde in the presence of FeCl3. The three new compounds were characterized by elemental analysis, FT-IR, UV–Vis, mass spectrometry and in the case of 2 by multinuclear NMR spectroscopy. The crystal structures of 3 and 5 revealed that in the two five-coordinate monomers, the iron atom showed distorted square-pyramidal geometry, with the N and O atoms of the Schiff-base ligand occupying the basal sites and the chlorine atom at the apex of the pyramid. Magnetic measurements showed a high-spin configuration (S = 5/2) for the Fe(III) ion in 3 and 5. Reduction associated with the Fe(III)/Fe(II) redox couple occurred at −0.464 and −0.764 V vs. Ag/Ag+, and oxidation taking place at the Schiff-base ligand was observed at 1.300 and 0.942 V vs. Ag/Ag+ for 3 and 5, respectively. A high-electronic delocalization of the Schiff-base ligand substituted by fluoro and nitro groups stabilizes the Fe(II) oxidation state and shifts the redox potential anodically.

Synthesis, Characterization, and Catalytic Properties of Iridium Pincer Complexes Containing NH Linkers

A series of tert-butyl-substituted pincer ligands based on 1,3-diaminobenzene and 3-aminophenol scaffolds, tBu4PXCYP (1e, X = Y = NH; 1f, X = NH; Y = O) and the corresponding iridium hydridochloro complexes (tBu4PXCYP)IrHCl (2e, X = Y = NH; 2f, X = NH; Y = O) were prepared with moderate yields and high purity and were fully characterized by 1H and 31P NMR spectroscopy. Unsymmetrical hybrid pincer ligands R2PNCOPtBu2 (1g, R = isopropyl; 1h, R = cyclohexyl) were prepared conveniently in high yield via a one-pot procedure by judiciously choosing reaction conditions and base; the corresponding iridium hydrido chloro complexes iPr2PNCOPtBu2IrHCl (2g) and Cy2PNCOPtBu2IrHCl (2h) were synthesized by the reaction of [IrCl(COE)2]2 with ligands. X-ray crystallography reveals that these iridium pincer complexes adopt similar square-pyramidal geometries and exhibit strong intermolecular hydrogen bonding between the NH linker and chloride ions of the adjacent iridium complex in the solid state. 1H NMR chemical shifts o...

Crystal structure of aqua-(1H-pyrazole-κN2)(pyridine-2,6-di-carboxyl-ato-κ3O2,N,O6)copper(II) dihydrate.

In the title compound, [Cu(C7H3NO4)(C3H4N2)(H2O)]·2H2O, the CuII atom is coordinated by three O atoms and two N atoms, provided by a tridentate pyridine-2,6-di-carboxyl-ate (pdc), one pyrazole and one water ligand, forming a slightly distorted square-pyramidal geometry [range of O-Cu-O and O-Cu-N bond angles = 79.55 (8)-166.22 (10)°]. The water mol-ecule is positioned at the apical position. In the crystal, the complex mol-ecule and the two crystallographically independent non-coordinating water mol-ecules are linked into a supra-molecular layer structure parallel to the ab plane via O-H⋯O and N-H⋯O hydrogen bonds.

A new copper(II) coordination polymer containing chains of interconnected paddle-wheel antiferromagnetic clusters.

The construction of supramolecular architectures based on inorganic-organic coordination frameworks with weak noncovalent interactions has implications for the rational design of functional materials. A new crystalline binuclear copper(II) one-dimensional polymeric chain, namely catena-poly[[[tetrakis(μ-4-azaniumylbutanoato-κ2O:O')dicopper(II)(Cu-Cu)]-μ-chlorido-[diaquadichloridocopper(II)]-μ-chlorido] bis(perchlorate)], {[Cu3Cl4(C4H9NO2)4(H2O)2](ClO4)2}n, was obtained by the reaction of 4-aminobutyric acid (GABA) with CuCl2·2H2O in aqueous solution. The structure was established by single-crystal X-ray diffraction and was also characterized by IR spectroscopy and magnetic measurements. The crystal structure consists of [{Cu2(GABA)4}{CuCl4(H2O)2}]+ cations and isolated perchlorate anions. Two symmetry-related CuII centres are bridged via carboxylate O atoms into a classical paddle-wheel configuration, with a Cu...Cu distance of 2.643 (1) Å, while bridging Cl atoms complete the square-pyramidal geometry of the metal atoms. The Cl atoms connect the paddlewheel moieties to a second CuII atom lying on an octahedral site, resulting in infinite helical chains along the c axis. The packing motif exhibits channels containing free perchlorate anions. The crystal structure is stabilized by hydrogen bonds between the perchlorate anions, the coordinated water molecules and the ammonium groups of the polymeric chains. The magnetic analysis of the title compound indicates a nontrivial antiferromagnetic behaviour arising from alternating weak-strong antiferromagnetic coupling between neighbouring CuII centres.

Novel binuclear diorganotin(IV) complexes of adipic acid dihydrazone containing flexible aliphatic spacer: X-ray structural characterization of dimethyltin(IV) complex

Three novel binuclear diorganotin(IV) derivatives formulated as (R2Sn)2L (where R = Me, Bu and Ph) of a new symmetrical adipodihyrazone ligand, 1,6-bis(5-hydroxy-3-methyl-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl)hexane-1,6-dione (H4L) derived from the Schiff base condensation of adipic acid dihydrazide and benzoylacetone in a 1:2 M ratio were synthesized. The micro-analysis and various spectroscopic techniques viz., infrared (IR), multinuclear (1H, 13C and 119Sn) magnetic resonance (NMR) spectroscopy and electrospray ionization mass (ESMS) spectrometry were employed to establish the chelating mode of the dihyrazone ligand towards the diorganotin moieties [R2Sn(IV)]2+. The single crystal X-ray diffraction analysis of complex, (Me2Sn)2L reveals that it crystallizes in monoclinic space group ‘P 21/n’ and consists of crystallographically discrete molecules. The complex has been investigated to prefer a highly distorted trigonal-bipyramidal geometry (TBP) over the square-pyramidal geometry (SP) around each tin centre wherein the more electronegative enolic and benzoylic oxygen atoms of the ligand are aligned axially, and two carbon atoms of the methyl groups attached to the tin metal atom and the imine nitrogen atom of the ligand aligned themselves equatorially around the tin centre in a trigonal plane. Thermal decomposition patterns of the dimethyl- and diphenyltin(IV) derivatives in air were also investigated by TG, DTG and DTA techniques.

Three VO2+ complexes of the pyridoxal-derived Schiff bases: Synthesis, experimental and theoretical characterizations, and catalytic activity in a cyclocondensation reaction

Three oxovanadium(IV) complexes of the pyridoxal Schiff bases have been newly synthesized and characterized. The used Schiff bases were N,N′-dipyridoxyl(ethylenediamine), N,N′-dipyridoxyl(1,3-propanediamine) and N,N′-dipyridoxyl(1,2-benzenediamine). Also, the optimized geometry, assignment of the IR bands and the Natural Bond Orbital (NBO) analysis of the complexes have been computed using the density functional theory (DFT) methods. Dianionic form of the Schiff bases (L2−) acts as a tetradentate N2O2 ligand. The coordinating atoms of the Schiff base are the phenolate oxygens and imine nitrogens, which occupy four base positions of the square-pyramidal geometry of the complexes. The oxo ligand occupies the apical position of the [VO(L)] complexes. In the optimized geometry of the complexes, the coordinated Schiff bases have more planar structure than their free form. Due to the high-energy gaps, all of the complexes are predicted to be stable. Good agreement between the experimental values and the DFT-computed results supports suitability of the optimized geometries for the complexes. The investigated complexes show high catalytic activities in synthesis of the tetrahydrobenzo[b]pyrans through a three-component cyclocondensation reaction of dimedone, malononitrile and some aromatic aldehydes. The complexes catalyzed the reaction in solvent free conditions and the catalysts were found to be reusable.

Aqua-chlorido-(2-{[6-(di-methyl-amino)-pyrimidin-4-yl]sulfan-yl}pyrimidine-4,6-di-amine)-copper(II) chloride hydrate.

A copper(II) complex of the non-symmetric bidentate ligand 2-{[6-(di-methyl-amino)-pyrimidin-4-yl]sulfan-yl}pyrimidine-4,6-di-amine (L1) is reported. The single-crystal X-ray structure of aqua-[aqua/chlorido-(0.49/0.51)](2-{[6-(di-methyl-amino)-pyrimidin-4-yl]sulfan-yl}pyrimidine-4,6-di-amine)-copper(II) 0.49-chloride 1.51-hydrate, [CuCl1.51(C10H13N7S)(H2O)1.49]Cl0.49·1.51H2O or [(L1)Cl1.51(H2O)1.49Cu]0.49Cl·1.51H2O, exhibits distorted square-pyramidal geometry around the metal centre, with disorder in the axial position, occupied by chloride or water. The six-membered metal-chelate ring is in a boat conformation, and short inter-molecular S⋯S inter-actions are observed. In addition to its capacity for bidentate metal coordination, the ligand has the ability to engage in further supra-molecular inter-actions as both a hydrogen-bond donor and acceptor, and multiple inter-actions with lattice solvent water mol-ecules are present in the reported structure.

A copper(II) paddle-wheel structure of tranexamic acid: di-chloro-tetra-kis-[μ-4-(ammonio-meth-yl)cyclo-hexane-1-carboxyl-ato-O,O']dicopper(II) dichloride hexa-hydrate.

Tranexamic acid [systematic name: trans-4-(amino-meth-yl)cyclo-hexane-1-carb-oxy-lic acid], is an anti-fibrinolytic amino acid that exists as a zwitterion [trans-4-(ammonio-meth-yl)cyclo-hexane-1-carboxyl-ate] in the solid state. Its reaction with copper chloride leads to the formation of a compound with a copper(II) paddle-wheel structure that crystallizes as a hexa-hydrate, [Cu2Cl2(C8H15NO2)4]2+·2Cl-·6H2O. The asymmetric unit is composed of a copper(II) cation, two zwitterionic tranexamic acid units, a coordinating Cl- anion and a free Cl- anion, together with three water mol-ecules of crystallization. The whole structure is generated by inversion symmetry, with the Cu⋯Cu axle of the paddle-wheel dication being located about a center of symmetry. The cyclo-hexane rings of the zwitterionic tranexamic acid units have chair conformations. The carboxyl-ate groups that bridge the two copper(II) cations are inclined to one another by 88.4 (8)°. The copper(II) cation is ligated by four carboxyl-ate O atoms in the equatorial plane and by a Cl- ion in the axial position. Hence, it has a fivefold O4Cl coordination sphere with a perfect square-pyramidal geometry and a τ5 index of zero. In the crystal, the paddle-wheel dications are linked by a series of N-H⋯Cl hydrogen bonds, involving the coordinating and free Cl- ions, forming a three-dimensional network. This network is strengthened by a series of N-H⋯Owater, Owater-H⋯Cl and Owater-H⋯O hydrogen bonds.

Crystal structure and spectroscopic characterization of a cobalt(II) tetraazamacrocycle: completing a series of first-row transition-metal complexes.

The tetraazamacrocyclic ligand 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMC) has been used to bind a variety of first-row transition metals but to date the crystal structure of the cobalt(II) complex has been missing from this series. The missing cobalt complex chlorido(1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane-κ4N)cobalt(II) chloride dihydrate, [CoCl(C14H32N4)]Cl·2H2O or [CoIICl(TMC)]Cl·2H2O, crystallizes as a purple crystal. This species adopts a distorted square-pyramidal geometry in which the TMC ligand assumes the trans-I configuration and the chloride ion binds in the syn-methyl pocket of the ligand. The CoII ion adopts an S = 3/2 spin state, as measured by the Evans NMR method, and UV-visible spectroscopic studies indicate that the title hydrated salt is stable in solution. Density functional theory (DFT) studies reveal that the geometric parameters of [CoIICl(TMC)]Cl·2H2O are sensitive to the cobalt spin state and correctly predict a change in spin state upon a minor perturbation to the ligand environment.