Outer-sphere Anion Research Articles

Laminated dihydrazone Zn(II) coordination polymer with prospects for sensory and multifunctional biomedical applications

This study introduces a new laminated coordination polymer, {[Zn3(HL)2(H2O)6](SO4)2⋅1.5dmf·2.5H2O}n (1), synthesized through the direct interaction of ZnSO4·7H2O with dihydrazone Schiff base ligand (H2L = 2,6-diacetylpyridine bis(isonicotinoylhydrazone)) at room temperature. Comprehensive characterization of the compound, employing various methods (SCXRD, PXRD, IR, TGA) revealed different coordination surrounding of metal atoms and a combination of photoluminescent properties and biological activity. The polymeric layers are corrugated along the b-axis, mutually intertwined forming channels filled with outer sphere anions (SO42-) and solvent molecules (water and dmf). It was shown that solvent molecules have a decisive influence on the photoluminescent properties of the compound. The partial removal of water molecules leads to increased photoluminescence, the intensity of which doubles compared to the synthesized crystals. Furthermore, the compound demonstrates robust antibacterial effects against four Gram+ positive and two Gram- negative bacteria. In addition, its impact on cell proliferation, both in cancerous and non-cancerous cells, reveals the compound's antiproliferative effect on breast cancer cells in vitro, coupled with biocompatibility with human fibroblasts. This multifaceted approach positions the synthesized polymer as a promising candidate with vast potential for applications in luminescent materials and biomedical research.

Bis(phenanthrolinyl)amine manganese complexes with pseudo-trigonal prismatic geometry

Two manganese(II) complexes supported by an isoamyl-substituted bis(phenanthrolinyl)amine ligand have been prepared and characterized. Determination of the molecular structures through X-ray crystallography demonstrated that the triflate compound crystallizes as a monomeric species with an outer-sphere anion, while the chloride complex exists as a dimer containing bridging chloride ligands in the solid state. Importantly, these structures revealed a coordination environment about the metal centre that is best described as pseudo-trigonal prismatic in both cases. Computational analysis found an optimized geometry for the triflate complex in a high-spin state that is consistent with the experimental observations, while the low-spin calculation showed a significant shift toward octahedral geometry. These results and their contrast with previously reported data provide evidence for the influence of electronic structure and metal ion size on molecular geometry in this system.

Spin Crossover in Iron(II) Complexes with Polynitrogen Heterocyclic Ligands and Outer-Sphere Boron Cluster Anions (Review)

The results of synthesis and study of magnetically-active iron(II) complexes with polynitrogen heterocyclic ligands and outer-sphere boron cluster anions have been considered. Derivatives of 1,2,4-triazole, tris(pyrazol-1-yl)methane, and 2,6-bis(imidazol-2-yl)pyridine have been used as ligands, decahydro-closo-decaborate, dodecahydro-closo-dodecaborate, decachloro-closo-decaborate, and 1,5,6,10-tetra(R)-7,8-dicarba-nido-undecaborates (R = H, Cl, Br) have been studied as outer-sphere anions. A number of iron(II) complexes showing spin crossover accompanied by thermochromism in the majority of cases has been obtained. Effect of ligand nature and cluster anion on temperature (Tc) and spin transition character has been considered. In particular, it has been shown that introduction of substituent increasing electron density over the system of conjugated three-centered two-electron bonds in cluster anion leads to increase in the field strength of ligand bound to anion via network of hydrogen bonds.

The effect of outer-sphere anions on the spectroscopic response of metal-binding chemosensors.

Ion pair receptors typically contain two separate binding sites, for the metal and the anion respectively. Here we report a less synthetically demanding approach, whereby we prepared a family of ion pair sensors based on a rhodamine fluorescent scaffold containing a tunable cation binding motif. When exposed to ion pairs, a competition for the metal ion is established between these ligands and anions. Structural and spectroscopic evidence showed that anions bind through weaker secondary interactions in the metal's outer coordination sphere and their presence influences the optical spectroscopic properties of the coordination complex in distinctive ways. The relationship between the binding site's metal affinity and its tunable properties, and the sensors' discriminatory power for anions was explained as a function of the metal ion's binding preferences. These effects were also exploited to discriminate cations and anions concurrently through multivariate data analysis methods.

Influence of Outer-Sphere Anions on the Photoluminescence from Samarium(II) Crown Complexes.

Three samarium(II) crown ether complexes, [Sm(15-crown-5)2]I2 (1), [Sm(15-crown-5)2]I2·CH3CN (2), and [Sm(benzo-15-crown-5)2]I2 (3), have been prepared via the reaction of SmI2 with the corresponding crown ether in either THF or acetonitrile in good to moderate yields. The compounds have been characterized by single crystal X-ray diffraction and a variety of spectroscopic techniques. In all cases, the Sm(II) centers are sandwiched between two crown ether molecules and are bound by the five etheric oxygen atoms from each crown ether to yield 10-coordinate environments. Despite the higher symmetry crystal class of 1 (R3c), the samarium center resides on a general position, whereas in 2 and 3 (both in P21/c) the metal centers lie upon inversion centers. Moreover, the complexes in 2 and 3 are approximated well by D5d symmetry. The molecule in 1, however, is distorted from idealized D5d symmetry, and the crown ethers are more puckered than observed in 2 and 3. All three complexes luminesce in the NIR at low temperatures. However, the nature of the luminescence differs between the three compounds. 1 exhibits broadband photoluminescence at 20 °C but at low temperatures transitions to narrow peaks. 2 only exhibits nonradiative decay at 20 °C and at low temperatures retains a mixture of broadband and fine transitions. Finally, 3 displays broadband luminescence regardless of temperature. Spin-orbit (SO) CASSCF calculations reveal that the outer-sphere iodide anions influence whether broadband luminescence from 5d → 4f or fine 4f → 4f transitions occur through the alteration of symmetry around the metal centers and the nature of the excited states as a function of temperature.

Metal-Organic Phase-Change Materials for Thermal Energy Storage.

The development of materials that reversibly store high densities of thermal energy is critical to the more efficient and sustainable utilization of energy. Herein, we investigate metal-organic compounds as a new class of solid-liquid phase-change materials (PCMs) for thermal energy storage. Specifically, we show that isostructural series of divalent metal amide complexes featuring extended hydrogen bond networks can undergo tunable, high-enthalpy melting transitions over a wide temperature range. Moreover, these coordination compounds provide a powerful platform to explore the specific factors that contribute to the energy density and entropy of metal-organic PCMs. Through a systematic analysis of the structural and thermochemical properties of these compounds, we investigated the influence of coordination bonds, hydrogen-bond networks, neutral organic ligands, and outer-sphere anions on their phase-change thermodynamics. In particular, we identify the importance of high densities of coordination bonds and hydrogen bonds to achieving a high PCM energy density, and we show how metal-dependent changes to the local coordination environment during melting impact the entropy and enthalpy of metal-organic PCMs. These results highlight the potential of manipulating order-disorder phase transitions in metal-organic materials for thermal energy storage.

Perrhenate and Pertechnetate Complexes of U(IV), Np(IV), and Pu(IV) with Dimethyl Sulfoxide as an O-Donor Ligand.

A series of new dimethyl-sulfoxide-containing pertechnetates and perrhenates of tetravalent U, Np, and Pu were synthesized and structurally characterized by the X-ray diffractometry. In all the synthesized compounds, the actinide atoms were coordinated by eight DMSO molecules with or without an extra XO4- anion in the coordination sphere. This resulted in the square antiprismatic or capped square antiprismatic coordination of An atoms. Three or four XO4- anions play the role of outer-sphere anions. The electron and IR spectra of the compounds correlated with their crystal structure.

Synthesis, Structure, and Cytotoxicity of Pd(II) and Cu(II) Complexes with 1-Terpenyl-3-Thiosemicarbazides of Pinane and para-Menthane Series

PdL1,2Cl2·H2O (I, II) and CuL1Cl2·H2O (III) complexes (L1 and L2 are 1-terpenyl-3-thiosemicarbazides of pinane and para-menthane series, respectively) are obtained. Single crystals of complexes I and [PdL3Cl2] (IV) (L3 is the product of hydrochlorination of ligand L2) have been grown. According to XRD data, crystal structures of I, IV consist of complex cations [PdLCl]+ and outer-sphere anions Cl−. The coordination polyhedron N2SCl is a distorted square. L1 and L3 are tridentate ligands. Free ligands L1, L2 and complexes I-III are studied using IR spectroscopy; conclusions on the structure of the Cu(II) complex are inferred from the analysis of obtained data. Cytotoxic properties of L1, complexes I and III, as well as the carboplatin pharmaceutic are studied on the Hep2 (human larynx carcinoma) cell line. Complexes I and III are shown to be moderately cytotoxic: they are twice as less toxic with respect to Hep2 cells than carboplatin that is used in the experiment as the reference complex.

Complexes of Np(VI) with Cyclobutanecarboxylic Acid Anions and Single-Charged Cations in the Outer Sphere: [NH4][NpO2(cbc)3], [C(NH2)3][NpO2(cbc)3], and [N(CH3)4][NpO2(cbc)3

Three new Np(VI) complexes with cyclobutanecarboxylic acid anions and single-charged outer-sphere anions: ammonium, [NH4][NpO2(cbc)3] (I), guanidinium, [C(NH2)3][NpO2(cbc)3] (II), and tetramethyl-ammonium, [N(CH3)4][NpO2(cbc)3] (III), were synthesized and studied by single-crystal X-ray diffraction. The coordination surrounding of the Np atoms in I–III is a hexagonal bipyramid with three bidentate cyclic C4H7COO− anions in the equatorial belt. In compounds I and II, the outer-sphere $$\rm{NH}_4^+$$ and $$\rm{C}(NH_2)_3^+$$ cations are linked with the anionic complexes [NpO2(cbc)3]− to form a three-dimensional framework via N–H⋯O hydrogen bonding. In complex III, large outer-sphere $$\rm{N}(CH_3)_4^+$$ cations cause differences in the structure of the anionic complexes [NpO2(cbc)3]−.

Spin crossover in homo- and heteroligand iron(II) complexes with tris(pyrazol-1-yl)methane derivatives

The studies concerning coordination compounds of various salts of iron(II) with tris(pyrazol-1-yl)methane derivatives (HC(pz)3) are discussed. The results of a number of studies on the synthesis and investigation of the homo- and heteroligand iron(II) complexes with tris(3,5- dimethylpyrazol-1-yl)methane (HC(3,5-Me2pz)3) are considered. The study of the temperature dependence μeff (T) showed that the spin crossover (SCO) 1A1↔5T2 observed in a series of the compounds discussed is accompanied by thermochromism (color change pink (purple) ↔ colorless). Specific features of the SCO and their dependence on the outer-sphere anion in the iron(II) complexes are discussed. The data of the recently published work devoted to the synthesis of the iron(II) complexes with three N-substituted HC(pz)3 derivatives (general formula xL, where x = H, CH2C6H5 (Bn) and p-SO3C6H4CH3 (Ts)) are considered.

Theoretical study of oxoborate complexes with MO 4 n− tetraoxo anions in the inner and outer spheres of the B20O30 cluster

The energies and structural and spectroscopic characteristics of endohedral (MO4©B20O 30 − ) and exohedral (MO4 · B20O 30 − ) isomers of oxoborate complexes with MO 4 − tetraoxo anions with 32 valence electrons located in the inner and outer spheres of the B20O30 cluster have been calculated by the density functional theory method (B3LYP). It has been demonstrated that, among the endohedral MO4©B20O 30 − clusters with strong multiply charged anions (VO 4 3− , CrO 4 2− , PO 4 3− , SO 4 2− , AsO 4 3− , SeO 4 2− , etc.), the isomer in which a “guest” tetrahedron MO4 is located at the center of the B20O30 cage and bonded to it through internal oxygen bridges M-O*-B is the most favorable one. Among the exohedral analogues MO4 · B20O 30 − , two most favorable isomers contain the “capping” MO4 tetrahedron bonded to the B20O30 cage through two and three external M-O-B bridges. For the complexes with doubly charged SO 4 2− and SeO 4 2− anions, the third exohedral isomer in which the sulfite or selenite group MO3 is bidentately coordinated to the oxidized B20O29(OO) cage with one peroxide bridge turns out to be close in energy to the above two isomers. For the systems with high negative charge n, the exohedral isomers are much more favorable than the endohedral isomer; however, with decreasing charge, the difference in energy between them decreases to ~10–18 kcal/mol, so that the exo–endo transition between them can require moderate energy inputs. For the endohedral complexes with singly charged ClO 4 − and BrO 4 − anions, two isomers with close energies are preferable in which the central atoms of the guest tetrahedra are reduced to the state of singly charged ions, while the oxoborate cage is oxidized to B20O26(OO)4 with four peroxide groups B-O-O-B and retains its closed (closo) structure. In the most favorable isomer of the complexes with multicharged ortho-anions BO 4 5− , CO 4 4− , and NO 4 3− , the outersphere anion is reduced to, respectively, borate, carbonate, and nitrate bidentately coordinated to the oxidized B20O29(O)2 cage with an open structure and two strongly elongated terminal B-O bonds. The results are compared with the data of previous calculations of endohedral and exohedral vanadate complexes MO4©V20O 50 − and MO4 · V20O 50 − with the same guest anions MO 4 − .

Tantalum Dimethyldithiocarbamate Complexes

The reaction of Ta(NMe2)5 with CS2 gave the tantalum(V) dimethyldithiocarbamate complex [Ta(MeDtc)4](MeDtc) (I). An ionic structure of the complex with a dodecahedral coordination of the tantalum atom was determined for toluene (I · Tol) and THF (I · THF) solvates by X-ray diffraction (CCDC no. 1544283 and no. 1544284, respectively). The reaction of I with CH2Cl2 leads to exchange of the outersphere anion to give the known complex [Ta(MeDtc)4]Cl (II). The cyclic voltammogram of II in CH3CN exhibits a quasi-reversible transition at E 1/2 =–0.735 V corresponding to the TaV/TaIV pair.

Structural Role of Isonicotinic Acid in U(VI), Np(VI), and Pu(VI) Complexes with TcO4-, ReO4-, and ClO4- Ions.

A series of new pertechnetate, perrhenate, and perchlorate compounds of hexavalent U, Np, and Pu containing isonicotinic acid were synthesized. Their crystal structures were determined by X-ray diffractometry. In all compounds, actinide atoms are found in pentagonal bipyramidal surroundings. They are coordinated by 2 to 4 isonicotinic acid molecules which exist in zwitterionic form as a result of N atom protonation. If only 2 or 3 isonicotinic acid molecules are present in the surroundings of an actinide (An) atom, TcO4- or ReO4- anions act as monodentate ligands. Otherwise, XO4- play the role of outer sphere anions. Electron and IR spectra of the compounds correlate with their crystal structure.

Intermolecular interactions and spin states of complexes [Fe(3-MeO-Qsal)2]Y (Y = PF6, BF4)

Compounds [Fe(3-MeO-Qsal)2]Y (Y = PF6, BF4) have been prepared by diffusion method and studied in temperature range 5–300 K by EPR and magnetic susceptibility methods. The coexistence of spatially separated high-spin (solvated) and low-spin (unsolvated) fractions in the studied compounds has been established. It has been shown that change in the type of outer-sphere anion leads to change in the character of intermolecular interactions in the high-spin fraction and has no effect on the parameters and character of interactions of paramagnetic centers in the low-spin fraction.

Structure and spin crossover in an iron(II) compound with tris(pyrazol-1-yl)methane and the complex Eu(dipic)2(Hdipic)]2– anion

An iron(II) complex with tris(pyrazol-1-yl)methane (HC(Pz)3) of the composition [Fe(HC(Pz)3))2]·[Eu(dipic)2(Hdipic)]·2H2O, containing an outer-sphere complex anion, is synthesized. The compound is examined by single crystal and powder X-ray diffraction, UV-Vis and IR spectroscopies, and static magnetic susceptibility. The investigation of the temperature dependence χ(T) in the temperature range 80-470 K reveals that the polycrystalline phase of the compound undergoes spin-crossover 1А1 ⇔ 5Т2. The transition is accompanied by thermochromism (color change pink ⇔ white).

Controlled Redox Chemistry at Cerium within a Tripodal Nitroxide Ligand Framework.

Ligand reorganization has been shown to have a profound effect on the outcome of cerium redox chemistry. Through the use of a tethered, tripodal, trianionic nitroxide ligand, [((2-tBuNOH)C6 H4 CH2 )3 N](3-) (TriNOx (3-) ), controlled redox chemistry at cerium was accomplished, and typically reactive complexes of tetravalent cerium were isolated. These included rare cationic complexes [Ce(TriNOx )thf][BAr(F) 4 ], in which Ar(F) =3,5-(CF3 )2 -C6 H3 , and [Ce(TriNOx )py][OTf]. A rare complete Ce-halide series, Ce(TriNOx )X, in which X=F(-) , Cl(-) , Br(-) , I(-) , was also synthesized. The solution chemistry of these complexes was explored through detailed solution-phase electrochemistry and (1) H NMR experiments and showed a unique shift in the ratio of species with inner- and outer-sphere anions with size of the anionic X(-) group. DFT calculations on the series of calculations corroborated the experimental findings.

The Dark Side of Hydrogen Bonds in the Design of Optical Materials: A Charge‐Density Perspective

A combined investigation of the structural, electronic, and optical properties of three crystalline nonaaqualanthanoid(III) triflates, [Ln(H2 O)9 (CF3 SO3 )3 ], has provided unambiguous experimental evidence for charge redistribution in the first coordination sphere of a lanthanide ion as a result of hydrogen bonds with outer-sphere anions. As well as resulting in charge transfer from the noncoordinated anions to the coordinated water molecules, these hydrogen bonds give rise to a new excited state, an hydrogen-bond-induced charge-transfer state, which is observed experimentally for the first time. This state was shown to be responsible for the previously unknown negative aspect of hydrogen bonds with a lanthanide-bound water molecule: rather than increasing the luminescence efficiency of the complex, they can lead to additional quenching that is unfavorable for the task-specific design of optical materials.

Outer-sphere anion recognition by a cyclen-based octadentate europium(iii) complex: pH dependent recognition of ortho-phthalic acid

An octadentate cyclen-based europium complex with amidic and hydroxyalkyl pendent moieties exhibits pH dependent ligand denticity associated with anion recognition. Unusually high hydration numbers are determined for ortho-phthalate ternary outer-sphere complexes for which modulation of lanthanide-based luminescence is observed.

Influence of outer-sphere anions in europium tetrahydrofuran-2-carboxylates on the Eu3+ luminescence center, analyzed by methods of X-ray diffraction and optical spectroscopy

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.

Crystal structure of hexakis(thiourea)-bis((μ-perchlorato-O,O’)-(perchlorato-O)-bismuth) diperchlorate

The complex[Bi2(Tu)6(ClO4)4](ClO4)2 (I) (Tu is thiourea) was synthesized and studied by X-ray diffraction. The crystallographic data of I are: a = 14.205(1) A, b = 13.083(1) A, c = 22.078(2) A, β = 96.182(1)°, V = 4079.1(7) A3, space group C2/c, Z = 4. The molecule is located on a twofold axis and consists of the binuclear cation [Bi2(Tu)6(ClO4)4]2+ and two outer-sphere anions Cl 4 − . The Bi-S bond lengths are 2.61–2.62 A. For each terminal and bridging ClO 4 − ion, one Bi-O distance varies from 2.744 to 3.048 3.269 structure contains a hydrogen bond network involving all hydrogen atoms. The IR and Raman spectroscopy data confirm the thiourea coordination by the sulfur atom.