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Lanthanide pyrrole-2-carboxylates [{Ln(L)3(H2O)2}·H2O]n (Ln = Eu, Gd, Tb) were synthesized and investigated using single crystal X-ray diffraction and optical spectroscopy (luminescence, luminescence excitation and vibrational IR spectra). The europium pyrrole-2-carboxylate crystallizes as a 2D network structure in the P21/c space group. The Eu3+ coordination polyhedron formed by five carboxylic groups and two water molecules can be described as a distorted single-capped square antiprism. The luminescence spectra indicate a low symmetry of the charge distribution around the Ln3+ ion that corresponds to the C1 symmetry of the coordination environment of Eu3+ ion in the [{Eu(L)3(H2O)2}·H2O]n crystal lattice. The low-energy ligand–metal charge transfer (LMCT) state was identified in the europium compound. The shortening of the 5D0 (Eu3+) lifetime in the 230–295 K temperature region, when the compound is heated from 77 to 295 K, and the low luminescence intensity of the europium pyrrole-2-carboxylate are caused by the participation of the LMCT state in quenching processes. The energy of activation determined for the 5D0 – LMCT crossover is 3900 ± 100 cm−1.

Homo-trinuclear [Zn3(L)(μ2-OAc)2(H2O)].CH2Cl2 (1) and hetero-pentanuclear [Zn4(L)2Eu(NO3)3(H2O)] (2) and [Zn4(L)2Nd(NO3)3(H2O)]·CH3CH2OH (3) complexes containing a coumarin-skeleton bis(salamo) ligand H4L, were successfully prepared and characterized via the means of elemental analyses, single crystal X-ray crystallography, FT-IR, UV–Vis absorption spectroscopy and Hirshfeld surfaces analyses. Complex 1 is a 1:3 ((L)4−:ZnII) structure, and complexes 2 and 3 are 2:4:1 ((L)4−:ZnII:LnIII) structure. All ZnII atoms in complexes 1–3 occupied the N2O2 sites are five-coordinated with geometries of slightly distorted tetragonal pyramid and trigonal bipyramid. Rare earth metal (EuIII and NdIII) atoms are both coordinated with phenolic oxygen atoms, and eight-coordinated with the square antiprism geometries in complexes 2 and 3. Water molecules as coordinating solvents participate in the coordination. Supra-molecular structures are built by C H…π and hydrogen bonding interactions in complexes 1–3. Moreover, Hirshfeld surfaces analyses of complexes 1–3 were also analysed in detail. Most important of all, luminescences of complexes 1–3 were discussed.

Four new coordination polymers based on the use of the [Cr(pyim)(C2O4)2]− species as a metalloligand, namely [LiCr(pyim)(C2O4)2(MeOH)]n (1), {[CaCr2(pyim)2(C2O4)4]·2MeOH}n (2), {[SrCr2(pyim)2(C2O4)4(H2O)]·0.45MeOH·4.55H2O}n (3) and {[CdCr2(pyim)2(C2O4)4]·MeOH}n (4) [pyim = 2-(2′-pyridyl)imidazole] have been synthesized and characterized by elemental analyses, IR spectra and X-ray diffraction on single crystals. Complex 1 is a neutral heterobimetallic chain where the tris(chelated) chromium(III) unit acts as a bis-bidentate ligand towards {Li(MeOH)}+ fragments through its two oxalate ligands, each lithium ion being five-coordinate in a intermediate surrounding between square pyramidal and trigonal bipyramidal. The structure of 2 consists of neutral oxalato-bridged chromium(III)-calcium(II) double chains of single chirality [all the tris(chelated) chromium centres have the same chirality either Λ or λ] and methanol molecules of crystallization. Each calcium ion in 2 exhibits a square antiprism environment which is built by four bidentate oxalate ligands from four [Cr(pyim)(C2O4)2]− units. Neutral oxalato-bridged chromium(III)-strontium(II) double chains also occur in 3 with methanol and water molecules of crystallization, each alkaline-earth cation being nine-coordinate in a monocapped square antiprism environment which is defined by a water molecule and eight oxalate-oxygens from four [Cr(pyim)(C2O4)2]− units. The CrIII2MII2 loops [M = Ca (2) and Sr (3)] within each double chain are planar. The structure of 4 is also made of neutral oxalato-bridged chromium(III)-cadmium(II) double chains but in contrast to 2 and 3, the chirality of the tris(chelated) chromium unit in 4 is alternated in each loop and the adjacent CrIII2CdII2 loops are not planar but form a dihedral angle of 84.8°. The potential use of the [Cr(pyim)(C2O4)2]− entity as a metalloligand in designing heterobimetallic compounds is analyzed and discussed.

Two isostructural Dy(III) and Tb(III) complexes based on 5-azotriazolyl salicylic acid (H3ATSA) ligand of [Ln(HATSA)(OAc)(H2O)2]·4H2O [Ln = Dy (1), Tb (2)] have been synthesized and characterized by single-crystal X-ray diffraction analysis. Each Dy(III) and Tb(III) ion coordinates to eight oxygen atoms to form an eight-coordinated square antiprism geometry. The two-dimensional coordinated layers are further linked to a stable three-dimensional supramolecular network by π-π stacking interactions. The fluorescent and magnetic properties of 1 and 2 were investigated and discussed. The solid sample of 2 shows four characteristic emission bands at 490, 546, 585 and 622 nm for Tb(III) ion under excitation at 313 nm. The alternating current (ac) magnetic susceptibility for 1 shows an increase of frequency-dependent.

In this context, three isomorphic compounds were obtained, namely, [Ln2(L)2(NO3)4(H2O)2]·2CH3OH (Ln = Dy (1), Tb (2) and Er (3), HL = N′-(2-Hydroxybenzoyl) pyridine-2-carbohydrazonamide). In these compounds, LnIII ion locates in N2O7 coordination environment, forming a monocapped square antiprism configuration (C4v). Furthermore, two L− ligands coordinate to two LnIII centers in an antiparallel or “head-to-tail” fashion with tridentate unit and monodentate phenol-O−, resulting in a center of symmetry with LnIII⋯LnIII distances (intramolecular) of 6.751 A for 1, 6.708 A for 2 and 6.723 A for 3, respectively. Magnetic measurement reveals that 1 shows frequency-dependent out-of-phase (χ″) signals under a direct-current (dc) field, exhibiting single-molecule magnet (SMM) behavior with the anisotropy energy barrier (Ueff) of 16.0 K and the pre-exponential factor value (τ0) of 1.0 × 10−6 s. In addition, the luminescence properties of 1 and 2 were studied. Moreover, the semiconductor behaviors of 1–3 have been investigated by experimental measurements of UV−vis spectroscopy.

Five LnIII complexes based on indazole radical have been synthesized and characterized by X-ray crystal diffraction: [Ln(hfac)3(NITIn)(H2O)]·XCH2Cl2·YC7H16 (Ln = Pr(1), Sm(2), Gd(3), hfac = hexafluoroacetylacetone; NITIn = (3-(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl)indazole) and [Ln(hfac)3(NITIn)] (Ln = Tb(4), Dy(5)). Compounds 1–3 are isostructural and crystalize in P21/n space group, while compounds 4–5 crystalize in P21/c space group. In compounds 1–3, the coordination number around the lanthanide ion is nine, and the polyhedron is in distorted 4,4,4-tricapped trigonal prism (C4v) or muffin (Cs) environment finished by three bischelate hfac− ligands, one bidentate radical ligand and one water molecular. The coordination number around the lanthanide ion in 4–5 is eight, and the polyhedron is in distorted square antiprism (D4d) environment. DC magnetic studies show that Pr, Sm, Tb and Dy complexes are paramagnetic. In addition, Tb and Dy complexes exhibit slow frequency-dependence of ac magnetic susceptibilities, which indicates the presence of slow magnetic relaxation.

The one-step metal-promoted condensation reaction of salicylaldehyde with diethylenetriamine in the presence of rare earth metal ions carried out in the same experimental conditions produces two types of salicylaldimine complexes. The compounds were characterized by spectroscopic data (ESI-MS, IR, UV/Vis, luminescence) and X-ray crystallography. The complexes contain the deprotonated tetradentate C11H16N3O = (L1)1− N-(salicylidene)-diethylenetriamine or pentadentate C18H19N3O2 = (L2)2− N,N′-bis(salicylidene)-diethylenetriamine ligand as a result of the [1+1] or [2+1] Schiff base condensation, respectively. The metal ions are bonded to all the potential nitrogen and oxygen donor atoms. The crystal structures of the complexes reveal two different supramolecular architectures: a monomer in [Tm(C11H16N3O)2]NO3·CH3OH complex with formation of a two-dimensional self-assembled network and a dimer in [M2(C18H19N3O2)2(NO3)2] complexes (M = Y3+, Eu3+or Lu3+), although in all cases the metal ions are eight-coordinated with distorted square antiprism geometry.

The coordination chain {[Dy(dbm)3bpy]·C7H8}n (1) having only 4,4′-bipyridine as connector has been prepared in high yield and its structural and magnetic properties have been investigated. It is isostructural with the terbium analogue {[Tb(dbm)3bpy]·C7H8}n (2) and features units repeating in a 1D-zigzag fashion, where the metal is octa-coordinated in a distorted square antiprism geometry. Despite the 1D structure, the absence of paramagnetic connectors prevents the direct magnetic intrachain interaction among the lanthanide ions. In zero magnetic field, only a small fraction of the magnetization of 1 displayed slow dynamics with no dependence on temperature. Upon application of a 1 kOe magnetic field, a relaxation process appears, compatible with a mixed Raman/Direct mechanisms. Magnetic dilution in the diamagnetic Y(III)-based analogue revealed that actually two distinct relaxation processes are active for 1, whose temperature dependence can be interpreted again with a mixed Raman/Direct relaxation model. Compound 2 displayed only in-field slow relaxation, compatible with the models employed for 1.

We report three-dimensional (3D) cyanido-bridged Mn–Nb and Co–Nb bimetal assemblies, Mn II 2 [Nb IV (CN) 8 ]·(L) 2 · n H 2 O ( 1 : L = 5-aminopyrimidine, n = 5; 2 : L = 5-methylpyrimidine, n = 4), and Co II 2 [Nb IV (CN) 8 ] (4-pyridinealdoxime) 8 ·2H 2 O ( 3 ). The single-crystal X-ray structural analyses show that 1 and 2 consist of isomorphic 3D cyanido-bridged network (monoclinic, P 2 1 / n ) composed of square antiprism Nb sites and distorted octahedral Mn sites. Both 1 and 2 show ferrimagnetism with Curie temperatures ( T C ) of 32 and 34 K, respectively, which is caused by the antiferromagnetic superexchange interaction between Mn II ( S = 5/2) and Nb IV ( S = 1/2) through the CN groups. 3 has a 3D cyanido-bridged network (tetragonal, I 4 1 / a ) composed of a dodecahedral Nb site and axially distorted pseudo-octahedral Co site. This compound shows ferromagnetic ordering with a T C of 18 K. Magnetization versus rotation angle of single crystal reveals that 3 has a large coercive field of 15 000 Oe as crystal is oriented to a -axis, which is due to the strong magnetic anisotropy on distorted Co II .

Two isostructural mononuclear rare-earth complexes, [(dbm)2Er(dtc)(phen)] (1-Er) and [(dbm)2Tb(dtc)(phen)] (2-Tb) (dbm− = dibenzoylmethanoate anion, dtc− = diethyldithiocarbamate anion, phen = 1, 10-phenanthroline) were synthesized and structurally characterized by single-crystal X-ray diffraction analyses. Each complex consists of one sulfur-donor ligand, two oxygen-donor ligands and one auxiliary ligand, and Er3+/Tb3+ ion locates in a distorted square antiprism. Magnetic measurements show that 1-Er displays slow magnetic relaxation behavior under an applied field, and solid-state emission spectra reveal that 1-Er exhibits characteristic emissions of Er3+ ion in the visible and near-infrared regions, indicating the dual functionality of 1-Er. Neither slow relaxation of the magnetization nor characteristic emissions of Tb3+ ion were observed for 2-Tb.

A new type of multifunctional single ionic chiral dysprosium complex (DyL) was obtained by the reaction of Dy(NO3)3 and salen-type Schiff base ligand N,N′-bis(3,5-dichlorosalicylidene)-(1R,2R)-1,2-cyclohexylenediamine. In the synthesis reaction, Dy(III) was found not only to be the central metal to coordinate with two Schiff base ligands, but also the Lewis acid catalyst to promote the partial decomposition of salen-type Schiff base ligand. Complex DyL crystallizes in a chiral and polar space group P21. The central metal Dy(III) adopts eight-coordinated square antiprism geometry with Δ absolute configuration. Complex DyL exhibits good SHG and ferroelectric properties. The single-crystal sample of DyL displays an obvious ferroelectric behavior with a remnant polarization (Pr) of ca. 4.51 μC cm−2 and Ec of ca. 28.11 kV cm−1. The solid luminescent spectrum of DyL presents characteristic emission 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions of Dy(III).

The crystal structure of the complex (α R ,6 R )-Na[Gd(H 2 O)-AAZTA-C 2 H 4 COOBn]·3H 2 O·EtOH was determined by single crystal X-ray diffraction; the complex represents a bifunctional derivative of Gd-AAZTA, previously reported as original scaffold for the development of efficient contrast agents for MRI. The Gd(III) ion is nine coordinated with three nitrogens, five carboxylate oxygens and one water oxygen in a monocapped distorted square antiprism coordination polyhedron. Three of the five carboxylic groups are monodentate while a fourth is bidentate bridging an adjacent Gd ion with the formation of a polymeric structure. The influence on the overall structure of the propionate side arm introduced for conjugation purposes was discussed, and a computational approach to predict the structure of its (α R ,6 S ) isomer is presented and compared with the X-ray structure of the (α R ,6 R ) epimer.

A highly volatile air and moisture stable eight-coordinate samarium complex, [Sm(hfaa)3(pz)2] (hfaa = anion of hexafluoroacetylacetone and pz = pyrazole), has been synthesized and structurally characterized by single crystal X-ray diffraction. The complex crystallizes in the monoclinic space group P21/c and the coordination polyhedron around the samarium ion is best describable as a distorted square antiprism. The NMR spectrum reveals that both the pz units remain coordinated to the samarium in solution. The quantum yield of the complex is determined to be 0.012 in solution. The lifetime of the complex is found to be 0.039 ms (χ2 = 1.071). The experimental intensity parameter (ηSm) is calculated for the complex.

Phosphinoylated calixarenes feature high coordination ability toward f elements and a great potentiality toward actinide/rare earth separation. Here, we report three characteristic properties of a tetra-phosphinoylated p-tert-butylcalix[4]arene, B(4)bL(4) functionalized with phosphinoyl pendant arms: (i) its coordination ability toward Th(IV) complexation in organic medium, (ii) its ability to separate thorium from yttrium, lanthanum, and europium in three different organic media, and (iii) the X-ray crystal structure of the La complex. Thorium(IV) forms 1:1 and 1:2 (M:L) complexes with B(4)bL(4): Th(NO3)(4)(B(4)bL(4))(n)center dot xH(2)O (n = 1, x = 1, 1; n = 2, x = 4, 2). Spectroscopic data point to the inner coordination sphere of 1 and 2 containing nitrate ions and water molecules. Molecular modeling of 1 yielded an 8-coordinate species and its coordination polyhedron can be described as a distorted square antiprism while that for 2, a 9-coordinate species, as a distorted tricapped trigonal prism. The extraction study of tetravalent thorium and trivalent rare-earth (Y, La, Eu) ions from acidic nitrate media by B(4)bL(4) in chloroform shows thorium being much more extracted than the rare earths, with selectivity close to 100%. The extraction behavior can be easily modulated by changing the initial conditions (pH, nitrate concentration). The X-ray structure of [LaB(4)bL(4)(H2O)(5)] CH3CN center dot(ClO4)(3) points to the La-III ion lying on a C-4 axis and being 9-coordinated by the four O(P) atoms and five O atoms from water molecules. It is located in the middle of the void formed by the four O-CH2-PO(Me)(2) pendant arms. (C) 2011 Elsevier B.V. All rights reserved.

A mesogenic Schiff base, N , N ′-di-(4-hexadecyloxysalicylidene)diaminoethane, H 2 dhdsde (abbreviated as H 2 L 1 ) that exhibit smectic-C ( SmC ) mesophase, was synthesized and its structure studied by elemental analyses, mass, NMR & IR spectra and single crystal XRD (triclinic space group P 1 ¯ with Z = 1) techniques. Bi-dentate bonding of the Schiff base in the mesogenic La III complex was implied on the basis of IR & NMR spectral data. As per the spectral studies of the complexes, the Zwitterionic species of the ligand (H 2 L 1 ) coordinates to Ln III ion through two phenolate oxygens rendering the overall geometry around the metal ion to distorted square antiprism (Ln = La, Pr, Nd, Sm, Eu) and monocapped octahedron (Ln = Gd, Tb, Dy, Ho).

The coordination capability of the octaaza 24-membered (L1) and the tetraoxotetraaza 28-membered (L2) macrocycle ligands – with different sizes, nature and number of the donor atoms – has been investigated with nitrate and perchlorate Cd(II) salts. The complexes were prepared in 1:1 and 2:1 Cd:L molar ratio. The characterization by elemental analysis, IR, LSI mass spectrometry, conductivity measurements and 1H NMR spectroscopy, together with the crystal structure of the complexes [CdL1](NO3)2 · 0.5H2O, [CdL1](ClO4)2 and [CdL2(CH3CN)2](ClO4)2 · CH3CN · H2O confirms the formation of mononuclear complexes in all cases. The [CdL1](NO3)2 · 0.5H2O and [CdL1](ClO4)2 present a mononuclear endomacrocyclic structure with the metal ion coordinated by the eight donor nitrogen atoms from the macrocyclic backbone in a square antiprism geometry. The complex [CdL2(CH3CN)2](ClO4)2 · CH3CN · H2O is also mononuclear, but the cadmium ion is in an octahedral environment coordinated by four amine nitrogen atoms from the macrocyclic framework and two nitrogen atoms from two acetonitrile molecules. The ether oxygen atoms from the ligand are not coordinated.

A novel Eu(III) complex featuring three dibenzoylmethanate (DBM) ligands and a Lewis base ligand 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) was synthesized. This novel complex was characterized by 1 H NMR, FAB-MS, and elemental analyses. The structure of the complex was established by single crystal X-ray diffraction. The nonacoordinate europium ion features six oxygen atoms of the three DBM ligands and three nitrogen atoms from the TPTZ ligand, forming a distorted monocapped square antiprism. Spectroscopic studies revealed that the electronic absorption of the complex is essentially ligand-based, while the emission is characteristic of a Eu(III) ion. It is concluded that the metal-centered red emission is promoted by the ligand-assisted energy transfer, namely the antenna effects.

Substitution of a borane vertex by an isolobal transition metal vertex in a deltahedron can change the shape and apparent electron count. More specifically, in many metallaborane deltahedra with 9, 10, and 11 vertices some transition metal units are found to occur at degree 6 vertices. In the case of 9- and 10-vertex deltahedra this requires a change in the shape of the deltahedron from the metal-free closo borane deltahedra having only degree 4 and 5 vertices to alternative so-called isocloso deltahedra having a single degree 6 vertex. The change in electron count from 2 n +2 skeletal electrons for metal-free borane closo deltahedra having the maximum number of degree 4 and 5 vertices to 2 n skeletal electrons for metallaborane isocloso deltahedra with the metal at a single degree 6 vertex can be rationalized by a major change in the skeletal bonding topology from globally delocalized in the closo deltahedra to face-localized in the isocloso deltahedra. In this model the skeletal bonding in closo deltahedra with n vertices can be constructed from n two-center two-electron surface bonds and a single n -center core bond whereas the entire skeletal bonding in isocloso deltahedra can arise from n three-center two-electron bonds in n of the 2 n −4 faces. The isocloso metallaboranes with n vertices can be considered to be metal complexes of an open borane ligand having all triangular faces except for a single hexagonal face, which forms a hexahapto bond to the transition metal vertex similar to the hexahapto arenemetal bonds in arene metal complexes. The 10-vertex deltahedra (C 5 H 5 M) 2 C 2 B 6 H 8 (M=Co, Fe) discovered by Hawthorne and co-workers in the 1970s provide an early example of a structurally characterized closo / isocloso deltahedral pair of the same stoichiometry in which the cobalt derivative has the 2 n +2 skeletal electrons and geometry of the closo 10-vertex deltahedron (the bicapped square antiprism) whereas the iron derivative has only 2 n skeletal electrons and the different geometry of the isocloso 10-vertex deltahedron with one of the iron atoms at the unique degree 6 vertex.

Neodymium and europium complexes with 3-picoline- N -oxide and formula Ln(pic) 3 ·2(3-picNO)·H 2 O were synthesized and characterized by elemental analysis, IR absorption spectra, the visible absorption spectrum of the neodymium compound and the emission spectrum of the europium compound. The Eu complex, isomorphous with the neodymium, crystallizes in space group P 1 with Z =4. There are two crystallographic non-equivalent Eu(III) ions. Both are coordinated to nine oxygen atoms in the form of a distorted monocapped square antiprism, where one of the square faces is bent. The difference between the two environments is that in one the cap is over the square plane, whereas in the other it is over the distorted face of the antiprism.

Reactions of tetra-n-butylammonium thiocyanate with the appropriate lanthanide nitrate polyhydrate yield complexes of the general type [(n-C 4 H 9 ) 4 N] 3 [Ln(NCS) x (NO 3 ) y ]. [(n-C 4 H 9 ) 4 N] 3 [Pr(NCS) 2 (NO 3 ) 4 ] ( I ), [(n-C 4 H 9 ) 4 N] 3 [Nd(NCS) 4 (NO 3 ) 2 ] ( II ), and [(n-C 4 H 9 ) 4 N] 3 [Dy(NCS) 4 (NO 3 ) 2 ] ( III ) were crystallized from ethanol and characterized by single-crystal X-ray crystallography, IR spectroscopy, and other physical determinations. The coordination about the central lanthanide ion varied. For complex I , the geometric polyhedron is a bicapped square antiprism ( D 4 d ), while those for complexes II and III are best described as a dodecahedral prism ( D 2 d ). Details of the synthesis and selected bond distances and angles are presented and discussed.

A new crystalline strontium-copper ethylene glycol complex has been isolated and structurally characterized by single-crystal X-ray diffraction. The solution-phase complex has also been investigated as a possible molecular precursor for use in sol-gel synthesis of SrCuO2. [Sr(C2H6O2)5][Cu(C2H4O2)2]·C2H6O2 has been isolated by crystallization from an ethylene glycol/methylethylketone solution of the strontium-copper salt. Crystallographic data are as follows: orthorhombic, space group Pna21, a = 18.494(3), b = 9.3076(8), c = 16.615(3)A, V = 2860(2) A 3 , Z = 4, R = 0.044 . In this molecule, copper is coordinated by two bidentate ethylene glycolate ligands in roughly a square planar geometry. Strontium is coordinated by three bidentate ethylene glycol molecules and two monodentate ethylene glycol molecules; the eight-fold coordination resembles a highly-distorted square antiprism. An additional ethylene glycol of crystallization is present which does not directly coordinate the strontium ion. Copper and strontium ion complexes are held together by hydrogen bonding. The solution-phase bimetallic complex is hydrolytically unstable, giving rise to a ‘muddy’ brown precipitate upon exposure to water. The apparent decomposition is in direct contrast with hydrolysis of similar barium-copper complexes which gives rise to stable blue gels. This decomposition made the strontium-copper diol complex unsuitable for use in alkoxide sol-gel synthesis of strontium-copper oxides.

The 1,4,7-tris(carbamoylmethyl)-1,4,7-triazacyclononane (TCMT) ligand and its complexes with yttrium(III) and lutetium(III) have been prepared. [Y(TCMT)(CF3SO3)2(H2O)](CF3SO3) crystallizes in the centrosymmetric triclinic space group P1 (No. 2) with a = 10.3660(14), b = 11.7663(15), c = 13.3008(20) A, α = 72.079(10), β = 81.684(12), γ = 78.401(11)°, V = 1506.1(4) and Z = 2. The structure was refined to R = 5.64% for those 1758 reflections with |Fo| > 6σ(|Fo|). The nonacoordinate yttrium(III) ion has a bound water molecule, two bound triflate ions and a hexadentate TCMT ligand. The coordination geometry may be described as a 3:5:1 arrangement in which the C6N3 backbone occupies the ‘3’ sites and H2O the unique ‘1’ site, or alternatively as a capped square antiprism or as a distorted tricapped trigonal prism. The [Ln(TCMT)]3+ complexes dissociate completely in aqueous solution within 25 min at pH 6.0 and 37°C in the presence of Cu2+ as a trapping agent. Molecular mechanics calculations have been used to investigate the strain energy of the TCMT and 1,4,7-triazacyclononane-1,4,7-triacetate (NOTA) ligands in complexes that are 6-, 7- or 9-coordinate.

A single crystal X-ray analysis of the ammonium salt of Gd 3+ diethylenetriaminepentaacetate has shown that the compound has a binuclear structure in contrast to the corresponding sodium salt that has a mononuclear structure. Five oxygen atoms and three nitrogen atoms from a ligand molecule construct a distorted square antiprism around a Gd 3+ ion. One of the square planes is capped by an oxygen atom from the adjacent metal chelate molecule, resulting in the formation of a binuclear metal chelate. The coordination polyhedron including this oxygen atom is described as a tricapped trigonal prism. The binuclear structure is the result of well-developed hydrogen bonds that involve the ammonium ions.

The crystal structure of tetrabutylammonium tetrakis (4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione praseodymium(III), (C 4 H 9 ) 4 N(C 8 H 4 F 3 0 2 S) 4 Pr(III), has been determined using 2300 independent, visually estimated intensities and refined by full matrix least- squares methods to R =0.118, R w =0.149. The crystals are monoclinic with a =22.32(5), b =10.45- (2), c =12.23(3) A, β=96.7(4)°. The space group is P 2 /n with Z =2, requiring a 2-fold axis in both the anion and cation. The coordination sphere has an arrangement close to that of a square antiprism but with small distortions in the direction of a dodecahedron. PrO bond distances range from 2.42– 2.47 A.

The title compounds were prepared from the metal chlorides, NaS2PEt2 and Ph4AsCl in ethanol. The crystal structures have been determined from diffractometer data. [La(S2PEt2)4] [Ph4As]: triclinic, space group P 1 , with a = 10.748(3), b = 15.028(6), c = 16.544(6) A, α = 84.86(3), β = 84.04(3), γ = 84.73(4)°, R = 0.069. [Er(S2PEt2)4] [Ph4As]: isomorphous to above with a = 10.715(3), b = 15.084(2), c = 16.410(3) A, α = 85.11(1), β = 84.59(2), γ = 83.94(2)°, R = 0.066. The metal ions are surrounded by eight sulphur atoms (LaS = 2.981 A, ErS = 2.859 A) in an almost perfect D2d dodecahedral arrangement. Only minor distortion towards a square antiprism is observed.

A new compound, tetrakis(diacetamide)monoaquostrontium(II) perchlorate, Sr(CH3CONHCOCH3)4 H2(ClO4)2 has been synthesized and its structure determined from three dimensional X-ray diffraction data using monochromatic CuKα radiation. The unit cell is monoclinic, space group P21/m with dimensions a = 8.642(.9) A, b = 21.833(2), c = 8.652(.9), β = 78°41′ (1′) and Z = 2. Three dimensional intensity data were collected on the Enraf Nonius CAD-4 automated diffractometer. The crystal structure was determined by the heavy atom method and refined anisotropically by block diagonal least squares to a conventional unweighted R-factor of 0.083 The complex forms the nine-coordinate monocapped square antiprism (C4v), rather than the lower energy symmetrically tricapped trigonal prism (D3h). Eight of the coordinated oxygens are contributed by the four bidentate diacetamides and the ninth by the water. Two of the diacetamides bridge the equatorial planes while a third spans an edge of one equatorial plane and the fourth bridges the cap position and an equatorial plane. Two types of hydrogen bonding are present: (1) OH⋯O between water and perchlorate and (2) NH⋯O between amide and perchlorate. Strontium-oxygen bond distances fall within the range 2.54A to 2.69A.

The crystal structure of tetrakis(diacetamide)calcium(II) chlorate monohydrates [Ca(DA)4]ClO3)2·H2O, has been determined from three-dimensional X-ray data. The complex has the cell parameters a = 12.399(3) A, b = 7.900(2) A, c = 14.725(3) A, β = 98.35(2)°, Z = 2. The unit cell is monoclinic, space group P2/c. The structure was determined by direct methods and refined anisotropically by block-diagonal least squares to a conventional unweighted R of 0.11. The calcium ion is 8-coordinated and its coordination sphere can be described as a square antiprism formed by eight carbonyl oxygens from 4 diacetamide ligands; two ligands are related to the other two by a two-fold rotation axis. One of the amide nitrogens is hydrogen bonded to a chlorate oxygen. In addition, hydrogen bondingbetween an amide nitrogen and an uncoordinated water molecule results in the formation of infinite chains parallel to [100]. Calcium-oxygen distances fall within the range 2.41–2.44 A.

The crystal structure of Er(III)(salen)2(pipH) [salen=N,N′-ethylene-bis(salicylaldimine),pipH= piperidinium] has been determined by X-ray diffraction. The structure of the compound consists of [Er(salen)2]−1 anions and pipH+ cations. In the complex anion the erbium(III) ion is eight-coordinated by the donor atoms of two tetradentate salen ligands, forming a distorted square antiprism with approximate D2 symmetry. The ErO and ErN distances average respectively 2.270 and 2.511 A. This is the first structural determination of a lanthanide element complex with a tetradentate ligand.

Actinide ions, owing to their large ionic radius, generally present high coordination numbers and thorium(IV), which has the maximum ionic radius among the tetravalent actinides, can easily reach a coordination number nine or ten with chelating ligands. For the uranyl(IV) complexes prepared, the generale formulation of the type [UO2L2S]S, where the coordinate solvent molecule (S) can be replaced by more basic monodentate ligands as Ph3PO, dmso, dma or dmf, is supported by the elemental analysis as well as by t lowering of the vN-O stretching frequency and by the corresponding lowering of the P-O, S-O and C-O stretching frequencies upon coordination. For these complexes a coordination number seven, in an approximately pentagonal bipyramidal coordination geometry, can be reasonably attributed to the uranium atom. Thorium(IV) complexes of the type [ThL4S]· xS were obtained with the potentially five-membered chelate ligands HpyOO and HpyOS, whereas complexes of the type [Th(Quin)4]·xS were obtained with the six-membered chelate ligand HQuin. The coordinated solvent molecule in the first two complexes can be replaced by PH3PO, dmso, dma, dmf, as supported by the elemental analysis and by the i.r. spectra. It must be noted that [Th(Quin)4]·xS is, for instance, insoluble in dmso and remains uncharged. This behaviour seems to be ascribed to the observed tendency of thorium(IV) towards higher coordination number in complexes with five-membered chelate ligands, while it preferably maintains a coordination number eight, when forming complexes with six-membered chelate ligands. On the contrary Th(pyOO)4·2h2O or Th(PhOO)2·MeOH, well as Th(pyOS)4·H2O rapidly dissolve in dmso, giving rise to complexes formulable as ThL4·2dmso. These complexes can be formulated, from infrared evidences, as [ThL4(dmso)] dmso with the central metal ion nine-coordinated: a band at about 100 cm−1 was assigned to th vS-O stretching frequency of the coordinated molecule, whereas a second band at about 1025 cm−1 can be probably ascribed to the uncoordinated dmso. For a correct knowledge of the coordination geometry of the prepared complexes, crystals of Th(pyOS)4(dmf), suitable for an X-ray structural analysis, were grown from a dimethylformamide/ diethylether solution. Th(pyOS)4 dmf is a nine-coordinate chelate with eight donor atoms contributed by the four monoanionic bidentate ligands and the ninth by the solvent molecule. The coordination polyhedron is a distorted monocapped square antiprism with S(4) as cap. The thorium atom lies 1.38 A above the base of the polyhedron O(1), O(2), O(3), O(5) and 1.08 A below the base of the pyramidal cap S(1), S(2), S(3), O(4). The mean planes for the atoms comprising the two ‘square’ bases are approximately parallel with 2.4° between their normals. The lanthanum(III) complexes are of the type LnL3×H2O or Li[LNL4]xH2O, the coordination number seems to be most likely eight, even if the stoicheiometry of Ln(pyOO)3H2O and Ln(Quin)3 supports coordination number seven and six respectively. In these complexes however a partial oligomerization cannot be ruled out.

Crystals of tetrakis(biuret)strontium(II) perchlorate, [Sr((NH 2 CO) 2 NH) 4 ](ClO 4 ) 2 , are monoclinic with a = 11.21(1), b = 7.30(1), c = 14.52(1) A, β = 98.2(2)°, D obs = 1.976, D calcd (Z = 2) = 1.973 g/cm 3 , space group P2/c. 1526 independent reflections recorded photographically by the equi-inclination. Weissenberg technique using CuKα, the intensities of which were estimated visually, were used in the structure determination. The structure was solved by Patterson and Fourier methods and refined anisotropically by diagonal least squares to an R factor of 0.094. The strontium atoms are located at special positions related by inversion. The perchlorate moieties are ionic although extensive hydrogen bonding exists between them and the primary and secondary amines of biuret. The two biuret ligands in the asymmetric unit are bonded to strontium as bidentates via the carbonyl oxygens with a small twist (10.9, 12.0°) about the oxygen-oxygen line. The six membered rings formed by the chelate ligands with strontium are folded (49.6, 1.8°) about the oxygen-oxygen line. This is attributed to packing considerations. The co-ordination polyhedron is best described as approximately D 2 -222 distorted square antiprism with the bidentate ligands spanning opposite edges of the rectangular faces. To our knowledge this complex presents the first case of an eight co-ordinate non-transition metal complex, characterized by x-rays, where all of the ligands are non-ionic chemically identical oxygen donor bidentates.

The crystal structure of pentakis(diacetamide)barium(II) perchlorate, [Ba((CH 3 CO) 2 NH) 5 ](ClO 4 ) 2 , has been determined from three-dimentional X-ray diffraction data using Cukα radiation. The unit cell constants are a = 13.052(5)A, b = 14.406(6) A , c = 19.508(8) A and β = 107.6(3)°. The monoclinic colorless crystals belong to the space group P2 1 /c. The observed and calculated (Z = 4) densities are 1.608 g/ cm 3 and 1.602 g/cm 3 respectively. Two sets of intensity data (nkl and hnl) were recorded on film by the equi-inclination Weissenberg method and their intensities estimated visually. A total of 4041 independent reflections above background were used in the Patterson and Fourier summations for structure determination. The structure was refined by full-matrix least squares to an unweighted conventional R factor of 0.094. The five diacetamide molecules assume a modified trans—trans (diacetamide-B) configuration with a small twist from planarity (5–15°) about the oxygen—oxygen line as they bond as bidentates to barium forming a ten co-ordinated complex. The six membered rings formed by the diacetamide ligand with barium are folded to varying degrees (7–42°) about the oxygen-oxygen lines. The bonded oxygen atoms are located at the vertexes of a distorted symmetrically bicapped square antiprism (D 4d ). Barium-oxygen bond distances vary from 2.73(2) A to 2.91(2) A . The complex is unique in that it is the first reported case of a ten co-ordinated complex, characterized by X-rays, where all of the ligands are non-ionic, chemically identical bidentates. The hybrid orbitals of barium that could reasonably be involved in sigma covalent bonding with the oxygen atoms are sp 3 d 5 f z(5z 3 -3r 2 .

Reaction of YbCl 3 with NH 4 DPAP (HDPAP= 1,3-diphenyl-4-acetylpyrazol-5-one) in a 1:3 molar ratio results in the formation of the complex Yb(DPAP) 3 ·(H 2 O) 2 ·3EtOH, the crystal structure of which has been determined. The compound crystallizes in the monoclinic system, space group P 2 1 / n with Z = 4, unit cell parameters a = 16.067(2), b =22.254(3), c = 15.297(2) A and β= 99.46(3)°. The structure has been refined to R = 0.0501 (R w = 0.057) for 7201 indepedent reflections. The coordination polyhedron about the eight- coordinate ytterbium atom is a square antiprism. The three DPAP ligands are bidentate to the central metal ion, where two water molecules are also coordinated. The average bonding distances are YbO (DPAP) = 2.31(1) A, YbO (water) = 2.36(1) A. The complex has been further characterized by elemental analysis, TGA, DTA and IR spectroscopy.

The pentadentate ligand 2,6-diacetylpyridinedisemicarbazone, DAPSC, reacts with Th(NO 3 ) 4 in ethanolwater mixture and a di-μ-hydroxo Th(IV) dimer is formed. The compound [Th 2 (OH) 2 (DAPSC) 2 (NO 3 ) 2 (H 2 O) 2 ](NO 3 ) 4 ·4H 2 O ( I ) is monoclinic, space group P 2 1 / n with a = 10.705(1), b = 19.008(2), c = 11.782(1) A, β = 107.82(2)°, V = 2282(1) A 3 and Z = 2. Detailed X-ray structural analysis showed that each thorium atom in the complex is coordinated to one pentadentate DAPSC ligand, which is subjected to a considerable distortion, one bidentate nitrate group, one water ligand and two bridging hydroxo groups. The coordination number is ten and the best presentation of the polyhedron is that of a distorted bicapped square antiprism. The ThTh separation is 4.0181(6) A and the average ThO(H) bridge is 2.366 A. The structure was refined using 3185 reflections to an R value of 5.0%.

[Lu(OH 2 ) 8 ] [Na(12-crown-4) 2 ]Cl 4 ·2H 2 0 crystallizes at 5 °C from a reaction mixture of LuCl 3 ·6H 2 O and 12-crown-4 (in a 1:3 solution of CH 3 OH: CH 3 CN) following the addition of NaCl. The crystal structure of this complex has been determined by single crystal X-ray diffraction techniques. The title complex is monoclinic, P 2 1 /c , with a =15.265(2), b =14.203(2), c =16.030(1) A, β=94.570(9)°, and D c =1.67 g cm −3 for Z =4 formula units. Primarily organic and inorganic zones exist essentially in layers parallel to bc . The organic layers consist of [Na(12- crown-4) 2 ] + cations with the oxygen atoms forming a square antiprism around Na + (NaO=2.49(3) A average). The [Lu(OH 2 ) 8 ] 3+ cations (also essentially square antiprismatic, LuO=2.34(2) A), the chloride ions, and the two uncoordinated water molecules are hydrogen bonded forming a network in the b and c directions. The two unique cations are packed linearly along a in a staggered square face to square face arrangement.

The crystals of calcium diiodate(V) hexahydrate, Ca(IO3)2. 6H2O are orthorhombic, space group Fdd2 with 8 molecules in the unit cell. The structure consists of pyramidal anions joined to one another in chains by intermolecular I ... O interactions. The chains are held together by calcium ions and by hydrogen bonds between water molecules and anions. The coordination polyhedron around calcium can be described as a square antiprism, with distances Ca- O=2.43-2.57 A. In the pyramidal anion the distances between oxygen and iodine atoms are I-O=1.78, 1.90, 1.85 A. The environment of the iodine atom is approximately octahedral: the coordination is completed by two water molecules and by one oxygen atom of another anion.

The compound previously believed to be K 3 [Hg(NO 2 ) 5 ]H 2 O has been shown by crystal structure analysis to be correctly formulated K 3 [Hg(NO 2 ) 4 ]NO 3 , containing [Hg(NO 2 ) 4 ] 2− and nitrate as discrete anions. The nitrite ions are co-ordinated to the mercury through both oxygens, and thus function as bidentate chelates. The configuration of the eight oxygen atoms about the mercury is as the vertices of a severely distorted square antiprism.

Recently some uranyl mixed complexes, containing ethylenediaminetetraacetic (edta) and other anions have been synthesized and crystal structure of the (CH3H6)4[(UO2)2edtaF4] has been determined [1]. The edta group is shown to be a bridge hexadentate ligand with planar conformation of the NCN2CH2N fragment. As continuation of this work some other complexes of the U(IV) and Th(IV), namely M4[U(Th)edta(CO3)2]; M4[Uedta(c2O4)2]· 3H2O;M3[U(Th)edta·F3]; M2[UedtaCl2·4H2O]; U(Th)edta·6H2O (M CN3H+6) were synthesized and their properties such as conductivity in water solutions, IR-spectra, thermostability were investigated. The structure of the (CN3H6)3[UedtaF3] and isomorphous (CN3H6)3[ThedtaF3] was determined by X-ray analysis. The coordination polyhedron of these compounds was shown to be a distorted square antiprism with the cap over one base (C.N.9). The edta group is hexadentate and ethylenediamine fragment has gosh-conformation. The structure is constituted by the separate complex [U(Th)edtaF3]3− anions and (CH3H6)+ cations. the hydrogen bonds NH⋯O and NH⋯F are between anions and cations.

Various sulphato complexes of thorium have been prepared but the co-ordination number of thorium in such complexes has not been characterised. To establish the maximum co-ordination number of thorium we prepared (NH4)8Th(SO4)6·2H2O. It has been discussed and suggested by V. A. Golovnya and G. T. Boltova [1] that in the sulphate compounds of Ce(IV) and U(IV) the co-ordination number 8 is retained. In the lower sulphato complexes some of the water molecules cannot be removed easily; these water molecules are directly bonded to the central atom. The X-ray diffraction study of potassium thorium tetrasulphate tetrahydrate has shown that the coordination number of thorium is nine and a chain-like structure is observed. The structure is complex, and although the water molecules can be readily removed yet two water molecules are directly bonded to the thorium. All modes of bonding for sulphato groups are observed, that is, bidentate chelate, bidentate bridging, and monodentate. E. L. Muetterties and C. M. Wright [2] suggested that hexasulphato thorium ion, Th(SO4)8−6, isolated in the form of salts might be analogous to lanthanum case, since in La2(SO4)3·9H2O [3] the eicosahedron is established for the co-ordination of lanthanum ion. Twelve oxygen atoms are within 2.60–2.74 A. It was decided to undertake a three dimensional single crystal structure analysis to determine the nature of the thorium co-ordination. Experimental An irregular shaped crystal of 0.38 mm in diameter was mounted along the real c axis. Preliminary optical and X-ray examination indicated the crystals to be triclinic. The unit cell parameters, from the high angle precession data and Weissenberg data with Mo-Kα radiation were determined as: Ammonium thorium hexasulphate dihydrate: N8H32Th/S6O24·2H2O M = 988 Triclinic a = 9.82 A α = 57.95° b = 9.76 A β = 89.7° c = 10.40 A γ = 115.416° U = 729.58 A3Z = 1 μ(for MoKα = 63.74 cm−1 The space group P1 has been used so far for refinement. Zirconium filtered Mo-Kα radiation was used to collect equi-inclination Weissenberg data for the layers [khOhk10] and precession data for the layers hO1 and Ok1 by the multiple film technique. Structure Determination and Refinement Using 4051 unique reflections as the criterion a three dimensional Patterson synthesis was computed and there was no big peak except the origin peak. Thorium was put at the origin and to start the temperature factor for thorium was put as 2. The parameters for thorium only along with the scalefactor were refined for four cycles by block-diagonal least square refinement, which reduced the discrepancy index to 0.21. Twenty-one atoms were then put successfully and all were refined isotropically and the R factor was 18.4%. The oxygen atoms of sulphato groups were much distorted from tetrahedral configuration. Throughout the analysis the structure factors for neutral thorium, sulphur, oxygen and nitrogen were used. The R factor was not going down than 18%, indicating that either the space group is not P1 or while calculating the absorption correction the crystal should not be assumed as a sphere, rather all the faces of the crystal should be measured correctly. In conclusion, there are some prospects for refining this structure to a low R value. Discussion Although the structure is not finished completely, nevertheless, the salient features of the structure have been solved. The structure of sulphato complexes of thorium are suggested as isolated unit complexes, in which the sulphato groups are bonding to the central atom as unidentate or bidentate ligands and it was proposed that the maximum co-ordination number for thorium is retained as eight. On the other hand they may also be chain compounds in which some of the sulphato groups are acting as bridges. Bridging sulphates are presented in K4 (Th(SO4)4·2H2O)·2H2O [4]. X-ray diffraction study of (NH4)8Th(SO4)6·2H2O has confirmed that isolated unit structures are present and the sulphato groups have either the co-ordinating capacity of two or one. No bridging sulphates are present in the structure under discussion. The thoriumoxygen distances vary over a wide range (2.32 to 2.69 A). From the geometry of the interatomic distances it appears that thorium is ten co-ordinate. The co-ordination polyhedron is a distorted bicapped square antiprism. Bicapped square antiprism is observed in protactinium metal [5]. Out of the six sulphato groups four are bidentate, and two are mono-dentate. The oxygens of the water molecules are not taking part in the co-ordination. This proves that in hexa sulphato complexes all the molecules of water of crystallisation are removed easily. As the structure has not yet been refined to a high degree of accuracy there is some uncertainty about the precise details of the thorium co-ordination polyhedron. As there are only 6 ThS vectors in the Patterson the thorium and sulphur atoms must form a centrosymmetric arrangement. But the oxygens may show small differences from C1 symmetry and thus cause the difficulties of refinement which were observed. The determination of the actual distortions from this arrangement may take much further study.

Single crystals of U or Th(DBM)4-solvate, U or Th(TFBA)4 and Th(DBM)4-solvate or Th(TFBA)4 doped with U(IV), few tenths of cubic millimeters in size, have been grown at low temperature from benzene (DBM) or toluene (TFBA) solutions. Other conditions do not lead to so large single crystals. All tetrakis-dibenzoylmethanato crystals exchange benzene molecules giving solvate crystals. They only can be kept unchanged in benzene saturated atomsphere. The yet unknown structure of these solvates are slightly different from the known ‘dry’ orthorhombic U(DBM)4 (Pccn) [1, 2]. First investigation on U(DMB)4 solvate essentially shows a 15% increasing of the b parameter and a 20% increasing of the orthorhombic volume cell. Space group is Pcbb. This probably means that benzene molecules insert themselves between the U(DBM)4 layers of the dry crystals. In both structures, U lies on a C2 crystallographic axis parallel to z. The structure of the tetrakis-trifluorobenzoylmethanato crystals is known to be tetragonal (I41/a) [3]. Polarized high resolution spectra of all these single crystals have been obtained between 4000 and 20000 A in the temperature range 4−300 K, Some common features appear on these spectra. The thorium chelates show two bands. The Th(DBM)4:U(IV) and Th(TFBA)4:U(IV) which are the best resolved spectra among all the recorded ones, show about thirty vibronic bands, some of them having a width of 10 A at 4 K. A quite god polarization of Th(DBM)4:U(IV) spectra is surprising for such an orthorhombic lattice. This means that probably the two optical axes are so close together that the crystal appears at 4 K as uniaxial. The 4 K polarized spectra look like very accurately the σ and π U4+ spectra in β-ThBr4 and β-ThCl4 matrix or UCl4, all of them being uniaxial tetragonal crystals [4, 5] where point group symmetry of U4+ in D2d. So, point group symmetry of U(IV) is close to D2d or another group whose characteristic table is the same. These observations cannot be explained according to the above mentioned insertion of benzene molecules without any other changes in the positions of U in the lattice. In dry U(DBM)4, point group symmetry of U(IV) is D4d or C2 depending on whether the considered environment is a square antiprism of oxygen or the whole molecule. Spectra of Th(DBM)4:U(IV) have temporarily assigned on the D2d basis point group symmetry. Broadness of the lines leads to poorly significant values of the Fk and Bkq parameters. As expected for a tetragonal crystal and a S4 point group symmetry for U(IV), polarization of Th(TFBA)4:U(IV) is found and spectra of U(IV) are very different from those of D2d symmetry. σ lines are more numerous than π lines and this could indicate according to dipole selection rules for S4, that ground state is two fold degenerate. Unfortunately no spectra of U(IV) have today been assigned in a such symmetry. The spectra we have recorded could be a basis calculations.

Coordination compounds M(AH)nX3·mH2O, M = Pr, Nd, Eu, Gd, Dy, Ho, Er, Tm, Lu; X = Cl, NO3 n = 3, 4, 5; X = NCS, n = 3; m = 0, 1, 3; AHCH3CONHNH2 were isolated from water or ethanol solutions by reactions of lanthanide salts with acetylhydrazine. On the bases of IR and Raman Spectra investigations of the normal and deuterated complexes it was shown that all these compounds contain chelate metal-hydrazide rings. (M = Pr, Nd, Eu, Gd, Dy, Ho, Er, Tm, Lu). The crystal structure of compounds [Dy(AH)3(H2O)3]Cl3 (I), [Ho(AH)3(H2O)3]Cl3 (II), [Er(AH)4(H2O)](NO3)3 (III), [Pr(AH)5](NO3)3 (IV) were determined. The coordination numbers were found 9 in I–III and 10 in IV. The polyhedron of metals has the configuration of threecapped trigonal prism in I and II, the configuration of monocapped square antiprism in III and configuration of twocapped square antiprism in IV. The metal-ligand bond lengths (mid.) in complexes are: LnN: 2.571(1), 2.542 (iii), 2.760 A (IV); LnN(AH): 2.360 (I), 2.337 (III), 2.497 A (IV); LnO(H2O): 2.425 (I), 2.363 A (III). H-bonds type OH⋯O(Cl) and NH⋯(Cl) in complexes observed

Lanthanide complexes are known to form exceedingly labile species. Two rare exceptions to this rule are reported in the present paper. The ligand DOTA was found [1, 2] to form rigid lanthanide complexes in solution: the configuration of the ethylenediamine groups undergoes a very slow inversion as shown by NMR. Furthermore, the activation energy for this process is unusually large. An analysis of the solid state structure of Na+(EuDOTA·H2O−4H2O has now been carried out, The metal ions lie between two planes made up respectively by the four nitrogens of the macrocycle and by the four carboxylate groups. The metal ion is also coordinated to one water molecule and its coordination polyhedron is a slightly distorted capped square antiprism. This structure exhibits an axial symmetry (C4 axis) and the induced paramagnetic shifts can thus be reliably computed by the simple dipolar equation Δv = 3 cos2θ - 1/r3. The calculated dipolar shifts of (YbDOTA)− are in excellent agreement with the experimental shifts, thus indicating that the DOTA complexes are highly symmetrical and have exactly the same structure in the solid and in solution. The conformational properties of the paramagnetic lanthanide TETA complexes are no less surprising. Adding two −CH2 - units to the DOTA structure brings about drastic changes in both the conformation and the structure of the macrocyclic complexes. As shown by a crystallographic investigation of Na+(TbTETA)−·5H2O(NaCl)12, the metal ion lies in a distorted dodecahedral environmental of nitrogen atoms and carboxylate groups. This structure has an approximate C2 axis and the induced paramagnetic shifts can no longer be calculated by the simpler form of the dipolar equation but have to be computed by the complete two-term dipolar equation. In this case, the calculated shifts are once again in excellent agreement with the experimental shifts. Moreover, the TETA complexes exhibit a quite unusual conformational behavior: the two orthogonal trapezoids in the dodecahedron are slowly moving up and down and are exchanging their position. This leads to profound alterations of the NMR spectra with temperature except for the two protons of the two propylenediamine carbon atoms in β positions. These protons lie on both sides of a near-plane of symmetry, the values of their dipolar geometric factors are not altered by the conformational changes and accordingly, their NMR peaks are not involved in exchange processes. The DOTA and TETA complexes thus exhibit several intriguing features which have not been observed so far for other lanthanide complexes.