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A series of lanthanide(III) oxamate complexes of formula Na[Eu(4-HOpa)4(H2O)]∙2H2O (1), Na[Gd(4-HOpa)4(H2O)]∙2H2O (2), Na[Dy(4-HOpa)4(H2O)]∙2H2O (3), and Na[Ho(4-HOpa)4(H2O)]∙2H2O (4) (4-HOpa = N-4-hydroxyphenyloxamate) were synthesized and characterized. The crystal structures of complexes 1–4, as well as the oxamate ligand in the ethyl ester acid form (Et[4-HOpa]), were elucidated by single crystal X-ray diffraction. 1–4 are isostructural, and they crystallize in the P21/n space group of the monoclinic system. The crystal structures of 1–4 consist of mononuclear lanthanide(III) complex anions, [Ln(4-HOpa)4(H2O)]− (Ln = Eu3+, Gd3+, Dy3+, and Ho3+), coordinated sodium(I) countercations, and crystallization water molecules, resulting in a 2D NaILnIII supramolecular coordination network. The coordination sphere of Ln3+ ions consists of square-face capped square antiprism (SAPRS-9). Magnetic properties were investigated for 1–4 in the 2–300 K temperature range using polycrystalline samples. Complex 2 exhibits an unusual and rare slow-relaxation of the magnetization for Gd3+ ions under DC applied field of 1.0 kOe, behaving as a field-induced single-ion magnet as occurs for the Dy3+ complex 3. The Eu3+ complex 1 has a nonmagnetic ground state, while the Ho3+ compound 4 behave as a paramagnet, and do not exhibit relaxation of the magnetization with or without an applied field.

The reaction of the lanthanide(III) β-diketonate salt (Dy(beac)3·2H2O) with a bidentate chelating ligand 5-(2-hydroxy-5-methylbenzylidene)-8-hydroxylquinoline (HL) afforded the tetranuclear Dy(III) cluster, [Dy4(μ3-OH)2L6(beac)4]·10CH3CN (1). The elemental analysis (EA), powder X-ray diffraction (PXRD), single-crystal X-ray diffraction and magnetic properties of 1 have been characterized. The X-ray structural analysis reveals that cluster 1 contains one Dy4 center with a rhombus-shaped arrangement, and each Dy(III) ion of 1 is located in a distorted square antiprism geometrical configuration. Magnetic properties study indicate that 1 shows single-molecule magnet behavior with larger energy barrier (ΔE/kB) of 78.3 K and τ0 = 4.4 × 10−7 s.

A cerium(III) complex, [Ce2(NA)6(H2O)4] (1) and an erbium(III) complex, [Er2(2-AMB)6(H2O)4]·3H2O (2), where NA = nicotinic acid and 2-AMB = 2-aminobenzoic acid, have been prepared and characterized by IR spectroscopy, thermogravimetric analysis and X-ray crystallography. The single crystal analysis reveals that both complexes are dinuclear. In 1, the two cerium(III) ions are bridged by carboxylate groups of four nicotinate ligands. Each cerium atom in 1 is nine-coordinate and exhibits a distorted monocapped square antiprism geometry. The Ce(III) ions are coordinated by seven oxygen atoms of the carboxylate groups and two oxygen atoms of water molecules. In 2, each Er(III) ion is eight-coordinated adopting a distorted ErO8 dodecahedral geometry. The Er(III) ions are bound to four oxygen atoms of the chelating carboxylate ligands, to one oxygen each from the two bridiging carboxylates, and two oxygen atoms of water molecules. In 2 there is an intramolecular hydrogen bond forming a six-membered ring between the NH2 group and one of the carboxylate oxygens in each of the six 2-AMB ligands. In the crystal packing, the molecules of 1 and 2 are associated through O(or N)–H⋯O and O–H⋯N hydrogen bonds. In 2 the intermolecular hydrogen bonding results in a 3D supramolecular network structure.

The synthesis, crystal structures, and magnetic properties of a nonanuclear dysprosium complex [Dy9(μ3-OH)8(μ4-OH)2(N3)8{(py)2C(OCH3)O}8](OH)·4H2O (1, (py)2C(OCH3)OH = the hemiacetal form of di-2-pyridyl ketone) and a tetranuclear dysprosium complex [Dy4(μ4-O)(μ-N3)2(μ-OCH3)2(L)4](OH)2·3.5CH3OH (2, HL = 2-(benzothiazol-2-yl-hydrazonomethyl)-6-methoxyphenol) have been prepared and structural characterization. Nine DyIII ions in 1 form a sandglass with the eight DyIII atoms at the apexes and one DyIII ion located at the center of a square antiprism formed by eight DyIII ions, while four DyIII ions in 2 form an irregular tetrahedron. Complexes 1 and 2 have been investigated by direct current (dc) and alternating current (ac) susceptibility measurements. The ac susceptibility studies revealed that complexes 1 and 2 exhibit slow magnetic relaxation. Moreover, complex 2 shows two-step thermal magnetic relaxation with their energy barriers of about 15 K and 2.68 K, respectively. The orientations of the magnetic anisotropy of DyIII ions in 1 and 2 were also estimated by electrostatic calculations.

A series of mononuclear [Ln(L)(H2O)(NO3)(solv)]·solv, (Ln = Pr (1), Nd (2), Sm (3), Eu (4), Gd (5), Tb (6–6a), Dy (7); solv = DMF, DMSO, H2O) and L = 2,4-bis(2-hydroxybenzylidenehydrazino)-6-methoxy-s-triazine complexes were prepared. The lanthanide(III) ions are nine-coordinated in the complexes and are bound to the O atoms of bidentate nitrate, three N and two O atoms of a pentadentate L ligand and one O atom from water and one O atom from dimethylformamide with a spherical capped square antiprism coordination environment in 1–7. The compounds have been characterized by means of elemental analysis, IR spectroscopy, UV–Vis spectroscopy, X-ray diffraction, and thermal analysis. Lanthanide-centered emission of the complexes is overlapped by the ligand emission.

Seven novel mixed-ligand complexes, [Ln(Hpma)2(phen)2(OAc)]·2H2O (Ln = La (1), Ce (2) and Nd (3)), [Er(Hpma)2(phen)(OAc)(H2O)]·EtOH·H2O (4), [Yb(Hpma)3(phen)]·2EtOH (5) and [Ln(Hpma)3(phen)(H2O)]·4H2O (Ln = Nd (6) and Gd (7)) (Hpma = N-(2,6-dimethylphenyl)oxamate; phen = 1,10-phenanthroline) were prepared in the presence of NaOH. Complexes 1–3 are isostructural and each metal ion is ten-coordinate, adopting a distorted sphenocorona geometry, with continuous shape measures of 2.702, 2.677 and 2.592, respectively. In contrast, the nona-coordinate complexes 4, 6 and 7 displayed spherical capped square antiprism molecular geometry, while the Yb(III) complex is bonded to three bidentate Hpma– ligands and one phen, forming a square antiprism structure (coordination number = 8). Besides the strong Ln(III)-ligand bonds as the main driving force for coordination, the relatively weak hydrogen bonds (O H∙∙∙O and N H∙∙∙O), C H∙∙∙O contacts, C H∙∙∙π, N H∙∙∙π and offset π-π interactions between the aromatic rings, play a key role in crystal packing. The UV–Vis-NIR absorption spectra of the metal complexes are associated with the π → π* transitions of phen and the Laporte-forbidden f-f transitions of the Nd(III), Er(III) and Gd(III) ions from the 4I9/2, 4I15/2 and 8S7/2 ground states, respectively, to the various excited J-levels. Cytotoxicity studies revealed antiproliferative activity in MCF-7 cells (p 0.05) for all the compounds, except for the positive control curcumin; indicating that the target compounds do not exert adverse effects on the immune system monocytes.

Bi(III) as its oxide combined with 2,4,6-pyridine tricarboxylic acid, H2pdc-COOH, and various pyridine-derived additives in dimethylformamide (dmf) under solvothermal conditions produced three novel bismuth coordination polymers, {[Bi(μ-pdc-COO)2][NH2Me2]3}n, 1, {[Bi(μ-pdc-COO)2][C5H7N2]3·C5H6N2}n, 2, and {[Bi2(μ-pdc-COO)2(μ-pdc-COOH)(pdc-COOH)][NH2Me2]4·2dmf·NHMe2}n, 3. The anionic coordination network topologies are two-dimensional, chains-of-loops and ladders, respectively, but the local 8-coordinate environments about the bismuth(III) centres are in each case between that of a square antiprism and that of a hexagonal bipyramid. When the 4-carboxy substituent in H2pdc-COOH is replaced by another potentially coordinating substituent to give 4-R-2,6-pyridine dicarboxylic acid, H2pdc-R (R = OH, NH2, Cl), the salts obtained contain discrete centrosymmetric dinuclear 8-coordinate bismuth anions with either double O-bridges between the metal centres, [Bi2(μ-pdc-R)2(pdc-R)2(dmf)2][NH2Me2]2 (R = OH, NH2), 4 and 5, or double carboxylate bridges with one long Bi–O bond, [Bi2(μ-pdc-NMe2)2(pdc-NMe2)2(dmf)2][NH2Me2]2, 6 (R = Cl, but replaced by dimethylamine during the reaction). The structures and supramolecular networks of 1–6 are described and compared as an exploration of alternatives to the conventional carboxylate-based organic linking units.

Centrosymmetric, acetato-bridged dinuclear coordination compounds with the formulae [La2(Hphen)2(OAc)4(H2O)2]·DMF·H2O (1), [Ln2(HNic)2(OAc)4(H2O)2]·DMF·H2O (Ln = La (2) and Nd (3)) and [Ln2(HNic)2(OAc)4(H2O)2]·DMF (Ln = Er (4) and Yb (5)) (H2phen = (E)-N'-(2-hydroxybenzylidene)benzohydrazide and H2Nic = (E)-N'-(2-hydroxybenzylidene)nicotinohydrazide) were isolated from the reactions of lanthanide acetates and hydrazones, and characterised by elemental analyses, IR spectroscopy, UV–Vis spectroscopy, X-ray diffraction studies and SHAPE 2.1. The nine-coordinate distorted spherical capped square antiprism complexes 1–3 crystallise in the triclinic space group P-1, while the eight-coordinate triangular dodecahedron (D2d) Er(III) and Yb(III) complexes belong to the monoclinic system (space group P21/c). Geometry optimisation of the monoanionic forms of the hydrazone ligands (Hphen– and HNic–) were performed at the DFT/B3LYP/aug-cc-pVTZ level of theory. Natural population analysis (NPA) and molecular electrostatic potential (MEP) maps indicated that the most preferred sites for electrophilic attack in the anionic ligands were the phenolate and carbonyl oxygen atoms, and the azomethine nitrogen atoms. Cytotoxic studies of the compounds on breast cancer (MCF-7), endometrial carcinoma (HEC-1A) and human monocytic (THP-1) cell lines using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl tetrazolium bromide (MTT) assay revealed that the hydrazone ligands and complexes 1–4 are partially cytotoxic against MCF-7 cells, while the Schiff bases and complexes 3–5 significantly inhibit cell growth in HEC-1A cells.

The macrocyclic ligand salt [H2LH2](ClO4)2, derived from the [2+2] condensation process involving 4-methyl-2,6-diformylphenol and 1,3-diaminopropane, has been used to synthesize the sandwich-type lanthanide(III) complexes [Ln(LH2)2](ClO4)3·2H2O (1–6, Ln = La–Eu, except Pm), [Ln(LH2)2](ClO4)3·CH3CN (7–13, Ln = Gd–Lu, except Er) and [Ln(LH2)(LH)](BPh4)2 (14–16, Ln = La, Nd and Sm). The X-ray crystal structures of the compounds 1, 7, 12, 13, 14 and 15 have been determined. In the isostructural [Ln(LH2)2](ClO4)3·CH3CN complexes of Gd (7), Yb (12) and Lu (13), the two macrocyclic ligands are considerably folded, albeit to different extents, and not symmetrically bound to the metal center. In these compounds, the metal center is coordinated with two imine nitrogen atoms and two phenolate oxygen atoms of each of the ligands (LH2), whose two other uncoordinated imine nitrogens are protonated and intramolecularly hydrogen-bonded with the phenolate oxygens. The structures determined for the La (14) and Nd (15) complexes of [Ln(LH2)(LH)](BPh4)2 are found to be identical. In these complexes, the ligand LH contains one N–H⋯O hydrogen-bonded unit, as against two in the ligand LH2. The [Ln(N2O2)2] coordination polyhedron in all the cases is a distorted square antiprism, although the extent of distortion in 7, 12 and 13 is less compared to that in 14 and 15. 1H NMR spectra of the [Ln(LH2)2]3+complexes in solution indicate a C2 symmetry. The 1H and 13C NMR signals of the EuIII complex 6 have been assigned on the basis of COSY, DEPT, HMQC and NOESY spectra. The photoluminescence spectra of the Sm(III) (5) and Eu(III) (6) complexes have been studied in a methanol–ethanol (1:4) glassy matrix at 77 K. The luminescence intensity of the hypersensitive 5D0 → 7F2 transition in 6 increases with the addition of triethylamine due to the formation of [Eu(LH2)(LH)]2+ and [Eu(LH)2]+ species, which in turn partially attenuate the quenching effect of the N–H⋯O oscillators on the emitting states of the metal ion.

The hydrothermal reactions of SrCl 2 with 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium (Na 2 H 2 Tiron) and 1,10-phenanthroline ligands yielded two strontium complexes of general formula [Sr 2 (Tiron) 2 (phen) 2 (H 2 O) 3 ]·2H 2 phen·2H 2 O ( 1 ) and [Sr 3 (Tiron) 2 (phen) 3 (H 2 O) 5 ]·Hphen·0.5H 2 phen·8H 2 O ( 2 ) (phen = 1,10-phenanthroline). Complexes 1 – 2 were characterized by X-ray single crystal diffraction, elemental analyses, FT-IR, and thermogravimetric analyses. Complex 1 feathers a pentdentate Tiron-bridged dinuclear structure, where Sr1 and Sr2 ions exhibit bicapped trigonal prism and monocapped square antiprism geometries, respectively, interconnected through edge-sharing. Complex 2 is a pentdentate and hexadentate Tiron-bridged trinuclear one, where Sr1 and Sr2 ions all exhibit bicapped trigonal prism geometries, interlinked via edge-sharing, and Sr3 ion exhibits a rare triangular prism geometry. The luminescent properties were also studied, and the results exhibit that the luminescence emissions of complexes 1 – 2 happen the bathochromic shifts, compared with the ligands.

EuIII and TbIII complexes with a benzoate and a tripod N7 ligand, [LnIII(H3L)benzoate](ClO4)2·H2O·2MeOH (LnIII = EuIII and TbIII; H3L = tris[2-(((imidazol-4-yl)methylidene)amino)ethyl]amine), were synthesized and crystallized into an isomorphous structure. Each LnIII ion is coordinated by one tripod ligand and one benzoate, resulting in a nona-coordinated capped square antiprism geometry. The solid-state emission spectra displayed sharp bands of the f–f transitions. TbIII complex exhibits a magnetic anisotropy and the ac susceptibility measurements exhibited an out-of-phase signal under 1000 G bias field, indicative slow relaxation of magnetization.

Two thorium(Th) complexes with lactate or formate have been synthesized and characterized. Th(C3H5O3)4(H2O)2 (1) [C3H5O3H = lactic acid] has a mononuclear structure with ten-fold coordinated Th polyhedron in deformed bicapped square antiprism by four chelating lactate ligands via both carboxylate O and the alcohol O atoms in addition to two coordinated water molecules. The lactate ligands are enantiomer with equal proportion of R- and S-isomers. [Th6(O)4(OH)4(HCO2)12(H2O)6]·5H2O (2) [HCO2H = formic acid] is a hexanuclear Th nanocluster constructed by four oxo-, four hydroxyl, twelve μ2-bridging formate ligands and six water molecules. The calculated bond valence sums are in good agreement with the presence of equal numbers of oxo- and hydroxyl groups in the cluster. Thermal studies confirmed that both complexes lost water molecules first followed by the decomposition of the organic ligands to form ThO2 as the final product. The presence of bridging OH-groups in both complexes has been proven by Raman spectroscopy.

The series of cobaltathiaboranes CpCoSBnHn (n = 6, 7, 8, 9, 10) related to the experimentally known CpCoSB8H8 and CpCoSB10H10 have been investigated by density functional theory. The lowest energy CpCoSBnHn (n = 6–10) structures are the closo deltahedra in accord with expectations for these 2n + 2 Wadean skeletal electron systems. In the lowest energy such structures the sulfur atom is located at a lowest degree vertex and the cobalt atom at a highest degree vertex. An alternative bicapped octahedral CpCoSB6H6 structure having the sulfur atom at a degree 3 capping vertex lies only ∼7 kcal/mol above the bisdisphenoid global minimum. For the 12-vertex CpCoSB10H10 system the three possible structures based on a B10CoS regular icosahedron lie more than 50 kcal/mol in energy below any non-icosahedral structures. The relative energy ordering of ortho < meta < para for these icosahedral CpCoSB10H10 structures is the opposite of the relative energy ordering of para < meta < ortho for the well-known icosahedral dicarbaboranes C2B10H10. One of the low-energy nine-vertex CpCoSB7H7 structures B7CoS-3 (Fig. 3) appears to be a frozen intermediate in the diamond-square-diamond process interconverting two isomeric tricapped trigonal prisms through a capped square antiprism intermediate.

A series of mononuclear lanthanide(III) coordination compounds Ln-1a with the “lasso-type” protection have been synthesized based on the flexible [1+1] pendant-arm Schiff-base macrocyclic ligand H2L1a. X-ray structure analysis reveals that the central ten-coordinate Ln(III) ion in every compound adopts distorted bicapped square antiprism geometry which is surrounded by one macrocycle and two axial chelating nitrates. Photophysical measurements have demonstrated that the macrocyclic ligand can serve as an effective sensitizer for Sm(III) ion. The relative compound Sm-1a shows efficient luminescence. Especially, the quantum yields are as high as about 1.48 ± 0.03 and 0.24 ± 0.02% for Sm(III) ion in solid state and methanol, respectively. The fluorescence lifetime is 42.3 μs in solid state together with 24.5 μs in methanol. It is proposed that the macrocyclic ligand plays an important role in guaranteeing the effective match of energy levels for Sm(III) central ion and constructing unique cavity microenvironment to shield the Sm(III) ion emitter from possible quenching effects.

Five new lanthanide tetrahydrofuran-2-carboxylate (THFC) complexes [Ln(THFC)2(H2O)2]·L·H2O (Ln = Eu; L = Cl−, Br−, NO3− and Ln = Tb; L = Cl−, NO3−) have been synthesized. The crystal structures of four compounds were solved by the X-ray diffraction method. The Ln3+ ions are coordinated to eight oxygen atoms: six oxygen atoms are provided by two tridentate bridging-cyclic THFC ligands, and the other two by water molecules. The Ln3+ coordination polyhedron can be described as a distorted square antiprism. The structures consist of planar layers linked by hydrogen bonds through outer-sphere L anions and H2O molecules. The influence of the L anion on the Eu3+ luminescence center is analyzed with the help of luminescence and IR vibrational spectroscopy. The distortions of the square antiprism increase with the size of the L outer-sphere anions. Consequently, the lowering of the symmetry of the crystal field around the Eu3+ ion appears as an extra splitting of the 7FJ levels under the influence of the crystal field components of the second and fourth ranks.

The mixed-ligand lanthanide(III) complexes derived from the tetraiminodiphenolate (L1H2) or octaiminotetraphenolate (L2H4) macrocyclic ligands and acetate (OAc−) or benzoate (OBz−) anions have been synthesized and structurally characterized. With the ligand combination L1H2 and OBz−, either the dimeric complexes [{Ln(L1H2)}2(μ2-η1:η1-OBz)4](ClO4)2 (Ln = La (1), Nd (2) and Eu (3)) or the monomeric complexes [Ln(L1H2)(η2-OBz)2](ClO4)·n solvent (Ln = Tb (4), Lu (5) and Y (6)) have been obtained. The X-ray crystal structures of 1, 4 and 6 have been determined, of which 4 and 6 have the same structure. L1H2 and OAc− combination affords the dimeric complexes [{Ln(L1H2)(η2-OAc)(μ-OAc)}2](ClO4)2 (Ln = La (7), Nd (8) and Y (9)) and the structure of 9 has been determined. In complexes 1–9, L1H2 uses two imino nitrogens and the two phenolate oxygens for metal coordination, while the other two uncoordinated imine nitrogens are protonated and intramolecularly hydrogen-bonded to the phenolate oxygens. The metal centre in all the cases is 8-coordinate and has distorted square antiprism geometry. With the octaiminotetraphenolate macrocyclic ligand (L2H4) dinuclear complexes of composition [Ln2(L2H4)(OAc)2(NO3)4]·nH2O (Ln = La (10), Pr (11), Nd (12) and Y (13)) have obtained. The structures determined for 11 and 12 have shown that they are isostructural and there are two independent molecules (A and B) in the unit cell. The molecule A has the bond types [Ln2(L2H4)(η2-OAc)2(η2-NO3)2(η1-NO3)2] and its 9-coordinate metal centre obtains a tricapped trigonal prismatic geometry, while the molecule B is [Ln2(L2H4)(η2-OAc)2(η2-NO3)4] whose 10-coordinate metal centre has a sphenocorona geometry. In these compounds, four uncoordinated imine nitrogens are protonated and hydrogen-bonded to the phenolate oxygens. The luminescence spectra of [{Eu(L1H2)}2(μ-OBz)4]2+ (32+) in acetonitrile (at 298 K) and in acetonitrile-toluene glassy matrix (at 77 K) have been studied.

In this paper, we report the syntheses, crystal structures, and magnetic properties of two manganese(II)–octacyanoniobate(IV)-based magnets: MnII2[NbIV(CN)8](3-pyridinemethanol)8·2H2O (1) and MnII2[NbIV(CN)8](3-aminopyridine)8·2H2O (2). 1 and 2 possess 3D network structures where a [Nb(CN)8]4− ion is connected to four Mn ions, and a Mn ion is connected to two [Nb(CN)8]4− ions via bridged cyanides. The coordination geometry of [Nb(CN)8] in 1 is square antiprism, while that in 2 is dodecahedron. Magnetic measurements show that 1 and 2 are ferrimagnets with Curie temperatures (TC) of 24 and 43 K, respectively, although the coordination numbers of the bridged CN groups around Nb and Mn ions are the same. The difference in TC can be understood by considering the difference in the coordination geometries of [Nb(CN)8]. Molecular orbital calculations of [NbIV(CN)8] using the discrete variational (DV)-Xα method indicate that the population of the 2p orbital on the bridged N with a dodecahedron geometry is larger than that with a square antiprism geometry. The calculation results suggest that the charge population of the 2p orbital on the cyano-nitrogen affects the superexchange interaction for the magnetic orbital of Nb C N Mn, which determines the TC value.

The synergistic solvent extraction of five selected lanthanoid ions (La3+, Nd3+, Eu3+, Ho3+ and Lu3+) with 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (HL) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-(dimethylphosphinoylmethoxy)calix[4]arene, (S) in CHCl3 has been studied. It was found that in presence of this phosphorus-containing calix[4]arene the lanthanoid ions have been extracted as [LnL3S2]. The values of the equilibrium constants and the separation factor have been calculated. The influence of the synergistic agent on the extraction process has been discussed. Elemental analysis, IR, 1H NMR, 19F NMR spectra and X-ray have shown that the complex of Eu(III) with HL is eight coordinated and its composition can be represented with the formula [EuL2(C2H5OH)4]Cl as well as that the coordination polyhedron is distorted square antiprism. The stoichiometry ([EuL2S]Cl) and the structure of the solid complex of Eu(III) with HL and S were proposed using elemental analysis, IR, 1H NMR, 19F NMR and 31P NMR data.

Schiff bases, obtained by condensation of N,N′-(1R,2R)-cyclohexanediamine with 2-hydroxy-5-chlorobenzaldehyde or 2-hydroxy-3,5-dichlorobenzaldehyde and of (±)cyclohexanediamine and salicylaldehyde, have been used as ligands for cerium(IV). The complexes were characterized by circular dichroism (CD), 1H NMR,13C NMR and nuclear Overhauser effect (NOE) studies. X-ray crystal structures determined for: [Ce(IV)((1R,2R)(−)chxn(3,5-diClba)2)2] and [Ce(IV)(±)(chxn(salal)2)2] revealed different orientation of a pair of Schiff base ligands in the coordination sphere. In [Ce(IV)((1R,2R)(−)chxn(3,5-diClba)2)2] two ligands form a sandwich with the cerium(IV) ion positioned between two layers of dichlorophenolic moieties. CD spectra in acetonitrile solution revealed exciton coupled π → π∗ and LMCT transitions. CD data are characteristic for distortion of the chelate ring from planarity and λ conformation of the cyclohexane bridge. NOE difference spectroscopy for the Schiff bases (saturated –HC N–) demonstrate correlations of the azomethine protons with the protons of the phenyl ring and the cyclohexane’s CH protons, and a weak correlation with the hydroxyl group. In the case of the cerium(IV) complexes, the strongest NOE (saturated H–C N) was observed with the phenyl ring’s hydrogen atoms, a slightly weaker correlation to the cyclohexane’s CH2 protons, and a much weaker NOE to the cyclohexyl’s CH2 protons. Results of spectral analyses suggest central ions in a distorted square antiprism geometry with the two basal N2O2 chromophore group. The X-ray crystallography study also confirmed antiprismatic distortion from planarity in obtained complexes.

Using the chiral ligands LSS (+)-4,5-pinene bipyridine and LRR (−)-4,5-pinene bipyridine ( Scheme 1 ), two novel Eu(III)-based complexes with the formula [Eu(DBM)3L] (LSS in 1, LRR in 2, DBM = dibenzoylmethanate) have been successfully synthesized and characterized by X-ray single crystal determination and spectroscopic methods. The crystal structure analysis of 1 and 2 reveal that they crystallize in the chiral space group P21 of the monoclinic system. The central Eu(III) ion is eight-coordinated in a geometrical environment intermediate between a square antiprism and a dodecahedron. The CD spectra reflect that complexes 1 and 2 are enantiomers. When ground in daylight, complexes 1 and 2 exhibit brilliant triboluminescence at room temperature.

Adducts of lanthanide β-diketonates of the general formula LnL3(TPTZ) were synthesized and structurally characterized by single crystal X-ray diffraction [Ln = Eu3+, Tb3+, Er3+; L is the conjugate base of dibenzoylmethane (DBM), 1-benzoylacetone (BA), thenoyltrifluoroacetone (TTA), or 4,4,4-trifluoro-1-phenyl-1,3-butanedione (BTFA); TPTZ = 2,4,6-tri(2-pyridyl)-1,3,5-triazine, a rigid Lewis base with a large π system]. The lanthanide ion in each of these complexes is nonacoordinate with six β-diketonate oxygen atoms and three TPTZ nitrogen atoms, forming a coordination polyhedron best describable as a monocapped square antiprism. Characteristic red, green, and near infrared luminescence was observed for the Eu3+, Tb3+, and Er3+ complexes, respectively. All complexes showed significantly enhanced luminescence quantum yields when compared with the corresponding aqua analogues, with one of the Eu3+ complexes displaying a quantum yield of 69.7% in chloroform.

Two new Eu(III) complexes featuring 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate (hfac) and a rigid Lewis base ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (tptz), [ Eu ( hfac ) 2 ( H 2 O ) ( EtOH ) ( tptz ) ] [ CF 3 CO 2 - ] (1) and Eu(hfac)3(tptz) (2), were synthesized. Their structures were established by single crystal X-ray diffraction. The europium ion in each of these complexes is nona-coordinate with six oxygen and three nitrogen atoms forming a coordination polyhedron best describable as a monocapped square antiprism. The difference in the composition and structure between these two complexes is caused by simply reversing the order of ligand (hfac and tptz) addition during the complex synthesis, and is rationalized in terms of the structural and electronic properties of the ligands and the overall steric bulk of the coordination sphere. Both complexes display characteristic Eu(III)-originated red emission upon UV excitation. The high quantum yields observed, 52% (1) and 60% (2), are rationalized in terms of the strong absorptions of both hfac and tptz ligands near the excitation wavelength (295 nm), an interpretation consistent with the well-established mechanism of ligand-mediated energy transfer for lanthanide-based light emission.

Three different uranium trichloride hydrates of the formulas UCl3 · 2H2O · 2CH3CN, UCl3 · 6H2O and UCl3 · 7H2O have been isolated from methylcyanide solutions of UCl4, with a 1–5% water content, by reduction with liquid zinc amalgam. The crystal and molecular structures of the hydrates have been determined by X-ray single crystal analysis. UCl3 · 2H2O · 2CH3CN crystallizes in the triclinic system (space group P 1 ¯ ) forming infinite zigzag chains in the [0 1 0] direction. The coordination polyhedron of the uranium atom is a bicapped trigonal prism, formed by two oxygen atoms of the water molecules, four bridging chlorine atoms, one terminal chlorine atom and one nitrogen atom of the methylcyanide molecule. UCl3 · 6H2O crystallizes in the monoclinic system (space group P2/n), with a monomeric structure. The uranium ion is eight-coordinated by two chlorine atoms and six oxygen atoms of the water molecules, which form a distorted square antiprism. UCl3 · 7H2O crystallizes in the triclinic system in the space group P 1 ¯ . The characteristic feature of this structure are [(H2O)7UCl2U(H2O)7]4+ dimers. The coordination polyhedra, in the form of a tricapped trigonal prism, are linked through the complex network of the hydrogen bonds. UCl3 · 6H2O and UCl3 · 7H2O are isostructural with their lanthanide analogues.

The adduct Eu(NTA)3 · bipy was prepared by the reaction of Eu(NTA)3 · 2H2O with 2,2′-bipyridine in a 1:1 ratio in chloroform [NTA = 1-(2-naphthoyl)-3,3,3-trifluoroacetonate]. Recrystallization of the complex from a chloroform/diethyl ether solvent mixture gave crystals suitable for X-ray diffraction. The structure contained chloroform molecules in partially occupied sites and was found to be different from the two forms previously reported for the same adduct (one unsolvated and the other containing isopropanol molecules). A single eight-coordinate geometry was found for Eu(NTA)3 · bipy · 0.44CHCl3, corresponding to a distorted square antiprism, with the bidentate ligands spanning opposite sides of the ‘square’ faces. A 2:1 (host-to-guest) inclusion compound comprising β-cyclodextrin (CD) and Eu(NTA)3 · bipy was obtained by co-precipitation from a mixed water/ethyl acetate solvent mixture. The formation of a true inclusion complex was supported by powder XRD, thermogravimetric analysis and 13C CP MAS NMR spectroscopy. Photoluminescence spectroscopy indicated the presence of only one low-symmetry environment for the Eu3+ cations in non-included Eu(NTA)3 · bipy and the inclusion compound. However, upon encapsulation of the complex in β-CD, some of the Eu3+ intra-4f6 5D0 → 7F0–4 lines shifted in energy, and the number of Stark components for the 5D0 → 7F1–2 transitions increased, indicating a lowering of the symmetry of the Eu3+ local coordination environment. The room temperature excitation spectrum of the inclusion compound revealed an enhancement of the Eu3+ sensitized process as a result of encapsulation of the Eu(NTA)3 · bipy molecules.

The hexadentate trans(O5O6)-K[Co(1,3-pddadp)] · 3H2O complex (where 1,3-pddadp represents the 1,3-propanediamine-N,N′-diacetate-N,N′-di-3-propionate ion) has been characterized by single-crystal X-ray crystallography. The complex crystallizes in the P2/c space group of the monoclinic crystal system. In the crystal structure of trans(O5O6)-K[Co(1,3-pddadp)] · 3H2O the potassium ions and two solvent water molecules (O1W and O3W) are settled on a twofold axis of symmetry. The octahedral complex units trans(O5O6)-[Co(1,3-pddadp)]− are bridged by carboxylate oxygen atoms with the potassium ions to build a two-dimensional polymer structure, separated by layers formed by hydrogen bonded water molecules and carboxylate oxygens. The coordination polyhedra around K1 and K2 are found to be distorted square antiprism and twisted bi-capped trigonal prism, respectively. Conformational analysis of the three possible geometrical isomers (trans(O5), trans(O5O6) and trans(O6)) of the [Co(1,3-pddadp)]− complex, was performed using the Consistent Force Field (CFF) program, with the parameters developed previously for edta-type complexes and new parameters for Co(III). Molecular mechanics (MM) calculations reproduced very well the crystallographically characterized structures (trans(O5O6)-[Co(1,3-pddadp)]− and trans(O6)-[Co(1,3-pddadp)]−).

[Cd(phen)2(CA)]n (I, where phen is 1,10-phenanthroline and CA2− is the dianion of 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone) has been synthesized and its crystal structure has been determined by single-crystal X-ray diffraction at room temperature. The crystal of I is built from infinite chains of chloranilate-bridged cadmium(II) leading to a zig-zag structure, with the phenanthroline ligands being stacked between the chains. These interactions assist the formation of a closely packed 3D structure. The coordination environment of cadmium(II) – very scarce in its chemistry – is square antiprismatic. The polymer was also characterized with spectroscopic (IR, Raman, DRS) and thermogravimetric (TG, DTA) techniques.

Reaction of 2,6-bis(phenylhydrazone)pyridine with Ln(NO3)3 · 6H2O nitrate (Ln=Y, Pr, Sm and Er) produces mononuclear complexes. The crystal structures of [Ln(C23H19N5O2)(H2O)(NO3)] (Ln=Y or Er) and {[Ln(C23H19N5O2)(C23H20N5O2)](H2O)2((CH3)2SO)} (Ln=Pr or Sm) were determined. Coordination of the dianionic and the monoanionic ligands in the complexes is via the pyridyl nitrogen, hydrazino nitrogen and iminol oxygen. The crystal structures were determined. In the isostructural complexes (Ln=Y, Er) the lanthanide ion have exactly the same coordination, being an irregular polyhedron with coordination number of eight. In the isostructural complexes (Ln=Pr, Sm) the lanthanide ion assumes a ten co-ordinated geometry for both metal ions. The coordination polyhedron around each lanthanide atom in both complexes is best described as a distorted bicapped square antiprism.

An extended MM3 model has been used to identify all low energy configurations for U(IV) complexes with catecholate and aquo ligands. Both stochastic and systematic conformational analyses of [U(cat)n(OH2)8–2n] 4–2n complexes, n ¼ 1–4, establish that 20 of the 67 possible stereochemistries are minima on the MM3 potential surface. The stable stereochemistries are reported for each stoichiometry and, where possible, the results are compared with experimental data and with the predictions from prior repulsion energy calculations. 2003 Published by Elsevier Ltd.

The glycine–alanine conjugated ligands of cyclen (1,4,7,10,-tetraazacyclododecane) 1 and 2, possessing methyl and benzyl alanine esters respectively, and the corresponding lanthanide complexes 1La, 1Eu, 1Tb, 1Yb, 2La, 2Eu, and 2Tb were designed with the aim of mimicking the nature of the hydrophobic cavity of ribonucleases. X-ray crystallographic investigations showed that 2Tb has a typical monocapped square antiprism geometry, where the Tb(III) ion is central, coordinating to the four amino moieties of the cyclen ring and four of the oxygens of amide carbonyl groups of the glycine residues of the four pendant arms, with the ninth coordinated site being occupied by a water molecule. All the complexes were shown to promote the hydrolysis of the phosphodiester bond of 2-hydroxypropyl p-nitrophenyl phosphate (HPNP, τ1/2=5.78×103 h) with 1Tb being the most efficient in promoting such hydrolysis at pH 7.4 and at 37 °C for the 1Ln family with τ1/2=4.9 h. For the 2Ln family, 2La was most effective in promoting hydrolysis of HPNP, with τ1/2=3.7 h. The rate of hydrolysis was also investigated for 1La and 2La as function of pH, with both complexes displaying bell-shaped pH dependence within the physiological pH range. For 1Ln the highest activity was observed at pH 7.0, with τ1/2=4.6 h, whereas for 2La it occurred at pH 7.4. Beyond pH 8, the rate of both complexes was shown to be almost linearly increased. The ability of 1Eu and 2Eu to cleave a 23-mer sequence from the mRNA of the GAG–HIV gene was also investigated. It was found that both gave rise to cleavage of the sequence at every nucleotide residue after 4 h of incubations at pH 7.4 and 37 °C.

The title compounds were synthesized by direct fusion of the corresponding elements in appropriate atomic ratios at 700 °C, and the structures were determined by single-crystal X-ray diffraction. They contain isolated deltahedral clusters of lead with charge of 4−. The clusters in Rb 4 Pb 9 and Cs 10 K 6 Pb 36 are Pb 9 4− . They are nido according to their charge, but their shapes do not always correspond to the classical nido geometry, a monocapped square antiprism. Some are differently distorted tricapped trigonal prisms. The relationship between these different geometries is discussed, and new classification for such clusters is proposed. The A 3 A′Pb 4 compounds are isostructural and contain isolated tetrahedra of Pb 4 4− .

Two novel ligands, 2-(4′-dimethylaminophenyl)imidazo[4,5-f]1,10-phenanthroline (L1) and 3-ethyl-2-(4′-dimethylaminophenyl)imidazo[4,5-f]1,10-phenanthroline (L2), and their europium(III) complexes with dibenzoylmethanate (DBM), Eu(DBM)3(L1) and Eu(DBM)3(L2), were synthesized and characterized by IR, UV–Vis and fluorescence spectroscopy, and thermogravimetric and differential thermal analyses (TG–DTA). The fluorescent intensity of Eu(DBM)3(L2) is 18 times that of Eu(DBM)3(L1). The crystal structures of Eu(DBM)3(L1) and L2 were determined by single crystal X-ray diffraction. Each europium atom is coordinated by six oxygen atoms of three bidentate DBM anions and two nitrogen atoms from one bidentate L1, forming a distorted square antiprism. Highly resolved fluorescence spectroscopy of Eu(DBM)3(L1) at 77 K revealed one Eu(III) site.

This paper presents the hydrothermal synthesis of a series of new isomorphous bis-dipicolinato lanthanide complexes: Ln(Hdipic)(dipic) with Ln=Eu, Gd, Tb, Dy, Ho, Er, Yb, and dipic=2,6-pyridinedicarboxylate. A structural study has been realised for the Ho3+ complex. It crystallises in a two-dimensional network, where sheets are parallel to the (100) plane. The luminescent properties of the analogous Eu3+ complex have been investigated. The composition of the 7FJ levels is consistent with a true C1 local symmetry: six oxygen and two nitrogen atoms forming a distorted square antiprism. The 5D0 emission lifetime is only slightly shorter than in [Eu(dipic)3]3− in solution, but the ligand to metal energy transfer is much less efficient.

A series of nine new lanthanide(III) complexes of the type [Ln(PBH)2(NO3)2]NO3·xH2O (PBH=2-pyridinecarboxaldehyde benzoylhydrazone) have been prepared and studied by IR, UV–Vis and mass spectra. In addition the crystal structures of PBH·H2O and [Er(PBH)2(NO3)2]NO3·1.5H2O have been solved. Erbium atom is ten-coordinate and the coordination polyhedron is best described as a distorted bicapped square antiprism.

The combination of EuCl3·6H2O with the trifunctional ligand 2,6-[(C6H5)2P(O)CH2]2C5H3NO, in a 1:2 ratio, produces the coordination complex [Eu{[(C6H5)2P(O)CH2]2C5H3NO}2(H2O)2]Cl3·9H2O. The molecular structure of the complex has been determined by single-crystal X-ray diffraction methods. The N,P,P′-trioxide ligands each bind to the central Eu(III) ion in a tridentate fashion along with two water molecules. The eight inner sphere oxygen atoms surrounding the Eu(III) ion form a square antiprism. These results are discussed in the context of the structures formed by lanthanide nitrates.

The title compound crystallises as a hexane hemisolvate from 1 : 1 : 1 or 2: 1 :2 reaction mixtures of the lithium primary amide (BuN)-N-t(H)Li, potassium t-butoxide (BuOK)-O-t, and the diamine TMEDA in hexane solution. An X-ray crystallographic study reveals that it exists as a discrete cage species with a central oxo (O2-) anion, coordinated to the eight cations of a surrounding 16-vertex (Li8O8) polyhedron, two opposing sides of which are each bridged by a TMEDA-chelated K+ cation. Made up of mu(3)O-Li-3 and mu(2)O-Li-2 interactions, the Li8O8 polyhedron can be regarded in common terminology for alkali metal based structures, as an incomplete stack arrangement of two tetrameric (Li-O)(4) cyclic rings. The eight Li+ cations form a distorted dodecahedron and the eight alkoxide O atoms form a distorted square antiprism. (C) 1998 Elsevier Science Ltd. All rights reserved.

The title complex [K3Yb(TTHA)(H2O)5], where TTHA6− is triethylenetetraaminehexaacetic acid anion was synthesized in aqueous solution, and its crystal structure was determined by X-ray diffraction. In the complex, the ytterbium ion is coordinated by four nitrogen atoms and five carboxyl oxygen atoms of the same TTHA6− anion. The coordination number of the ytterbium ion is 9, and its coordination polyhedron can be described as a distorted monocapped square antiprism. Each Yb(TTHA)3− is further connected by K+ ions through carboxyl groups of TTHA6− ion to form a three dimensional network structure.

The neodymium nitrate complex with 1,4-bis(phenylsulfinyl)butane(bphsb)[Ln(bphsb)2(NO3)3]n has been synthesized and characterized. The X-ray crystal structure determination of the complex indicates that bphsb and neodymium(III) ion form a polymeric chain involving 18-membered macrocycles, each macrocycle comprising two neodymium(III) ions. The adjacent metal centres are linked by the bridging ligand. Each neodymium ion is ten-coordinated and the coordination geometry is a distorted 4,4-bicapped square antiprism. The IR and absorption spectra of solid and solution for the complex were also studied.

Various dithiocarbamates of AsIII, SbIII and BiIII with diethyldithiocarbamic acid (dedtc), N-methylaminoethanoldithiocarbamic acid (nmedtc) and N,N′-iminodiethanoldithiocarbamic acid were subjected to cyclic voltammetric reduction studies with a glassy carbon working electrode. One-electron reduction processes occurs around −1.0 V for As and Sb complexes and around −0.5 V for Bi complexes which are completely irreversible. Attachment of the polar ends of the molecule is indicated by the pre- and post-reduction adsorption processes. As the number of −CH2CH2OH groups increases, the peak currents increase. In the case of Bi complexes, the reduction process tends to become reversible. In addition, the larger peak current associated with the third response indicates the possible reduction of Bi(dtc)2(DMF)n. In all the complexes the dtc− ion was lost from M(dtc)3− species, with oxidation around +0.6 V in the reverse scans. The crystal structures of As(deadtc)3 (1), Sb(deadtc)3 (2) and Bi(deadtc)3 (3) were determined by single crystal X-ray analysis. The coordination polyhedron in As(deadtc)3 is a distorted trigonal antiprism, with three strong (2.33–2.35 A) and three weak (2.82–2.86 A) AsS bonds. Sb(deadtc)3 has a coordination polyhedron which can be described as a distorted pentagonal pyramid. One of the SbS bonds is very short (2.46 A) and differences between others are not significant owing to the larger size of antimony compared with arsenic. The stereochemical requirement of the lone pair on Sb has a more pronounced effect in disturbing the neighbouring atoms than that observed in the corresponding As compounds. The binuclear Bi2(deadtc)6 complex is centrosymmetric, two bidentate ligands being bridged in such a way that each sulfur atom is simultaneously bonded to both metal ions. The resulting coordination polyhedron can be described as a distorted square antiprism. The asymmetry in the MS (M  As, Sb, Bi) bonds is a consequence of the stereochemical requirement for the ligand and the lone pair of electrons on the metals. This is supported by the valence bond sums (VBS) calculated for the complexes.

The title complex, K[KLa(HTTHA)(H2O]·8H2O, was synthesized in aqueous solution and its crystal structure was determined by X-ray diffraction. In the complex, the ten-coordinated lanthanum ion is bonded by four nitrogen atoms and six carboxyl oxygen atoms of the same triethylenetetraaminehexaacetic acid (H6TTHA) molecule. The coordination polyhedron of lanthanum can be described as a distorted bicapped square antiprism. The crystal is composed of one dimensional infinite chains.

Two β-ketoiminato complexes of zirconium, di[bis-trifluoroacetylacetone-ethylenediiminato]zirconium Zr(enTFA2)2 (1), and di[bis-trifluoroacetylacetone-trimethylenediiminato]zirconium, Zr(trimenTFA2)2 (2), have been obtained in high yield from the reaction of ZrCl4 and the sodium salt of the corresponding Schiff base. The compounds have been characterized by elemental analysis, NMR, mass spectrometry and X-ray structure determination. The coordination geometry around the zirconium atom is a dodecahedron in 1 and a square antiprism in 2. The increase of the aliphatic bridging chain of the ligand does not produce significant changes in the ZrOav bond distances [2.101(2) in 1 and 2.086(4) A in 2] while the ZrNav bond distances are lengthened [2.432(4) in 1 and 2.491(5) A in 2].

The title complex was synthesized in aqueous solution and its crystal structure was determined by X-ray diffraction. The complex is binuclear, with copper and yttrium ions connected by four bridging carboxyl groups from four alanine molecules. The yttrium ion is coordinated by four oxygen atoms from four carboxyl groups and four oxygen atoms of four water molecules with the coordination number eight, taking a square antiprism arrangement.

The lanthanide nitrate complexes with 1,8-bis(quinolyloxy)-3,6-dioxaoctane (L) have been prepared in tetrahydrofuran. These new complexes with the general formula [Ln(NO3)3(OH2)3]2 · L3(Ln = La, Nd, Sm, Er, Y) have been characterized by elemental analysis, IR spectra and conductivity measurements. The structure of the complex [Er(NO3)3(OH2)3]2 · L3·L2H2O has been determined by single crystal X-ray diffraction. The erbium(III) ion is nine-coordinate, bonded to three bidentate nitrate groups and three water molecules. The acyclic oligoether molecule is hydrogen bonded to these three coordinated water molecules. The average Er-O(nitrate) and Er-O(water) distances are 2.421(4)A and 2.307(4)A, respectively. The average O(water) ··· O(L) and O(water) ··· N(L) hydrogen bonded separations are 2.830A and 2.795A, respectively. The coordination geometry of the erbium(III) ion is a distorted monocapped square antiprism.

A barium complex with pyruvic acid isonicotinoyl hydrazone (H 2 L) has been synthesized and its crystal structure was determined by X-ray diffraction analyses. There is one complex unit, Ba(HL) 2 (H 2 O), with eight lattice water molecules in the asymmetric unit. The nine-coordinated barium has a distorted, monocapped square antiprism configuration.

The composition and crystal structure of the title complex are very different from those of α-alanine-lanthanide complexes reported previously. The structure of this complex comprises two kinds of polymer chains, both with dimeric repeat units. The two chains are very similar, taking a parallel and alternate arrangement in the lattice. In each dimeric unit, two praseodymium ions are connected by four carboxyl groups from β-alanine, two using simple bridges and two using tridentate bridges. A symmetry centre exists in each dimeric unit. The other two carboxyl groups link the units to each other by simple bridges. With two coordination water molecules for each central ion, the praseodymium ions are nine-coordinated, forming distorted, monocapped, square antiprism polyhedrons. A number of hydrogen bonds exist in the crystal.

Heterodecatungstates of the general formula X W 10 O 36 − where X = Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Th and U) have been studied by 17O and 183W NMR spectroscopy. It is shown that the structure of the heteropolyanions, where X occupies a centre of a square antiprism formed by two W5O18 ligands and which was determined in the crystalline state, is retained in aqueous solution. Completely resolved 17O and 183W NMR spectra for all atoms, even for the nearest oxygen atoms, have been recorded. From the analysis of the isotropic shifts, the contact and dipolar contributions have been estimated for all constituting atoms. The possible σ- and π-mechanisms of the spin transfer are considered. The negative spin density determines the dominant contact shift for the oxygen and tungsten nearest to X. The large pseudo-contact (ligand centred) contributions are estimated for the nearest oxygen and tungsten atoms. The positive spin density due to the σ-mechanism and large dipolar contribution gives rise to the observed chemical shift for the internal oxygen atom. The other oxygen atoms experience a mostly dipolar contribution with other terms probably cancelling each other. Temperature dependences of the chemical shifts are discussed. Copyright © 1996 Elsevier Science Ltd

Two lanthanide complexes, Ln 2 (Ileu) 4 (ClO 4 ) 6 · 8H 2 O, were synthesized in aqueous solution (where Ln  Nd or Er, Ileu = l -isoleucine). The crystal structure of the neodymium complex was determined by X-ray diffraction. The complex is a binuclear molecule, each neodymium ion is coordinated by four carboxylic oxygen atoms from four l -isoleucine and four oxygen atoms from H 2 O, forming a square antiprism coordination polyhedron.

A three-dimensional Huckel method recently developed for cluster compounds has been used to investigate polyhedral rearrangements of organic molecules as well as main-group inorganic clusters. The method starts from information about atomic connectivity and number of cluster electrons, familiar and convenient concepts for chemists. Calculations lead to diagrams that show how molecular orbital (MO) energy levels and second moment scaled total energies correlate between different structural forms. We consider diamond-square-diamond (DSD) framework reorganization mechanisms for pseudo-rotations of the closo-boranes. For B 5 H 5 2− and B 9 H 9 2− , the single DSD mechanism is not allowed by the principle of conservation of orbital symmetry. DSD rearrangements are allowed for the other closo-boranes we studied here, with increasing activation energies, B 8 H 8 2− ∼ B 11 H 11 2− 7 H 7 2− ∼ B 10 H 10 2− 6 H 6 2− , depending on the number of square faces opened during rearrangement. MO correlation diagrams and corresponding total energy curves for various numbers of cluster electrons provide visual rationalizations of observed structural trends with different numbers of cluster electrons. In particular, we discuss framework reorganizations for square to tetrahedron, hexagon to trigonal prism, hexagon to octahedron and cube to square antiprism.

The dinuclear complexes of 1,5-bis(1′-phenyl-3'-methyl-5'-pyrazolone-4')-l,5-pentanedione (H2L) with samarium, Sm2LL3 · 7H2OO (1) and Sm2LL3,, · 5DMF (2), have been synthesized. The X-ray crystal structure of Sm2LL3 · 5DMF has been determined. In complex 2. each L bonds two samarium atoms with its two ;-diketona-diketonate groups. The L acts as a bridging ligand. There are two DMF molecules bonded to each samarium atom. The coordination number of the two samarium atoms is eight (six oxygen atoms from three B--diketonates and the other two oxygen atoms from two DMF carbonyls). The eight atoms around the samarium make up a distorted square antiprism configuration. There are large differences between coordinated and uncoordinated DMF molecules.