Preparation and Radical Oligomerization of anFe(II) Complex without Loss of Spin-Crossover Properties

 11-(4H-1,2,4-Triazol-4-yl)-undecylmethacrylate (1), a new ligand for Fe(II) spin-crossover (SCO) complexes containing a polymerizable group, was synthesized and characterized. The complex [Fe·1 ₃](BF₄)₂ (2) was obtained by reaction of 1 with Fe(BF₄)₂·6H₂O (molar ratio 1/Fe(II) = 3/1) in THF. Complex 2 showed a gradual spin-crossover between 80 and 230 K. The methacrylate units in the ligands of complex 2 could be oligomerized radically in solution (initiator: azoisobutyronitrile) without loss of the spin-crossover behaviour.     

Spin Transition of 1D, 2D and 3D Iron(II) Complex Polymers The Tug-of-War between Elastic Interaction and a Shock-Absorber Effect

Summary.  The structures of linear chain Fe(II) spin-crossover compounds of α,β- and α,ω-bis (tetrazol-1-yl)alkane type ligands are described in relation to their magnetic properties. The first threefold interlocked 3-D catenane Fe(II) spin-transition system, [μ-tris(1,4-bis(tetrazol-1-yl)butane-N1,N1′) iron(II)] bis(perchlorate), will be discussed. An analysis is made among the structures and the cooperativity of the spin-crossover behaviour of polynuclear Fe(II) spin-transition materials. Corresponding author. E-mail: koning@iacgu7.chemie.uni-mainz.de Received April 8, 2002; accepted April 18, 2002     

Synthesis and Characterization of a Phthalocyanine-Porphyrazine Hybridand its Palladium(II) Complex

Summary.  A phthalocyanine-porphyrazine hybrid molecule composed of three phthalonitrile units and one maleonitrile moiety was prepared by cyclomerization of the reactants in the presence of magnesium butoxide. Two thioether groups fused to β-pyrrol positions were complexed with PdCl₂. The compounds were characterized by ¹H NMR, IR, and UV/Vis spectroscopy as well as elemental analysis. Received May 23, 2000. Accepted June 26, 2000     

Synthesis, infrared spectra, thermal analyses and structural studies of half-sandwich Fe(III)/Fe(II) complex containing pyridine-2,6-dicarboxylate and 1,10-phenanthroline

A new pyridine-2,6-dicarboxylate iron(III)/iron(II) complex [Fe(phen)₃][Fe₂(PDC)₄]·3CH₃OH was synthesized and characterized (where PDC = pyridine-2,6-dicarboxylate, phen = 1,10-phenanthroline) by using elemental analysis, IR spectroscopy and thermal analyses (TGA and DTA). The molecular structure of the complex has been determined by single-crystal X-ray diffraction. The complex is mixed-ligands and the IR spectra display bands characteristic of coordinated mixed-ligand bases. All the IR results are in agreement with the X-ray crystal result. The bond lengths indicate that this complex has [Fe(phen)₃]²⁺ cation where Fe(II) ion is in typical low-spin state, and in counter ions, [Fe(PDC)₂]⁻ are both in high-spin state.     

Extraction of Unprotected Amino Acids by Mixed-Ligand Nickel(II) and Copper(II) Chelates

Summary.  Six mixed-ligand Nickel(II) and Copper(II) chelates with square-planar geometry of the formula [Ni/Cu(O-O)(S-tmpn)]B(C₆H₅)₄ were prepared, where O-O represents acetylacetonate, tropolonate, or hinokitiolate and S-tmpn is (S)-tetramethyl-1,2-propanediamine. The compounds were investigated with respect to their function as receptor for unprotected amino acids, taking advantage of their high solubilities in non-polar organic solvents. In liquid-liquid extraction experiments between a 1,2-dichloroethane phase containing the metal chelates and an aqueous phase containing amino acids (rac-phenylglycine, rac-phenylalanine, or rac-tryptophan), the nickel(II) chelates effectively extracted amino acids from the aqueous phases under neutral conditions, forming octahedral ternary chelates. Received February 19, 2001. Accepted April 2, 2001     

Bis-(bis-(1,3-diaminopropane)-copper(II) Tetracyanonickellate(II)) Tetrahydrate: Preparation, Characterization, and Crystal Structure of a Novel Molecular Tetracyanonickellate

Summary.  [Cu(tn)₂Ni(CN)₄]₂ċ4H₂O and Cu(tn)₂Ni(CN)₄ (tn = 1,3-diaminopropane) were prepared and characterized. The hydrate is unstable on air and readily dehydrates to Cu(tn)₂Ni(CN)₄. Crystal structure analysis of the hydrate at 150 K revealed a novel tetranuclear molecular structure of the tetracyanonickellate. The building elements are two [Cu(tn)₂]²⁺ cations (coordination numbers of Cu: 5 and 6, respectively), two [Ni(CN)₄)²⁻ anions, and crystal water. The two cations are linked by one tetracyanonickellate anion via bridging cyano groups placed in cis positions. The second anion is bound weakly (Cu-N = 2.82 ?) via one μ₂-bridging cyano ligand. The tetranuclear molecules and pairs of solvate water molecules are linked by strong hydrogen bonds, thus forming infinite planes which are linked in the third dimension by considerably weaker hydrogen bonds. Received May 9, 2000. Accepted (revised) August 21, 2000     

Structural Insights into Hysteretic Spin-Crossover in a Set of Iron(II)-2,6-bis(1H-Pyrazol-1-yl)Pyridine) Complexes

Bistable spin-crossover (SCO) complexes that undergo abrupt and hysteretic (ΔT_1/2) spin-state switching are desirable for molecule-based switching and memory applications. In this study, we report on structural facets governing hysteretic SCO in a set of iron(II)-2,6-bis(1H-pyrazol-1-yl)pyridine) (bpp) complexes – [Fe(bpp−COOEt)₂](X)₂ ⋅ CH₃NO₂ (X=ClO₄, 1 ; X=BF₄, 2 ). Stable spin-state switching – T_1/2=288 K; ΔT_1/2=62 K – is observed for 1 , whereas 2 undergoes above-room-temperature lattice-solvent content-dependent SCO – T_1/2=331 K; ΔT_1/2=43 K. Variable-temperature single-crystal X-ray diffraction studies of the complexes revealed pronounced molecular reorganizations – from the Jahn-Teller-distorted HS state to the less distorted LS state – and conformation switching of the ethyl group of the COOEt substituent upon SCO. Consequently, we propose that the large structural reorganizations rendered SCO hysteretic in 1 and 2 . Such insights shedding light on the molecular origin of thermal hysteresis might enable the design of technologically relevant molecule-based switching and memory elements.     

Synthesis and Properties of Complexes of Lead(II), Cadmium(II), and Zinc(II) with N-Phosphonomethylglycine

Summary.  Sparingly water soluble complexes of lead(II), cadmium(II), and zinc(II) with N-phosphonomethylglycine (glyphosate, NPMG) of the general formulae C₃H₆O₅NPPb, C₃H₆O₅NPCdċ2H₂O, and C₃H₆O₅NPZn were synthesized. The complexes were also precipited from a dilute Roundup solution, and their solubility in water was determined. Thermal, diffractometric, and IR spectrophotometric analyses were carried out. It was found that the metal is bonded to glyphosate through the oxygen atoms of the carboxylic and phosphonate groups; metal-nitrogen binding is absent in the above compounds. Studying the complexing behaviour in solution by UV spectrophotometry pointed out that a complex of the composition Pb(II) : NPMG=1:1 with an absorption band at 232 nm is formed. Its stability constant as determined by Job’s method is logK=5.9±0.1. Using potentiometric techniques, the dissociation constant of N-phosphonomethylglycine and the stability constants of its complexes with cadmium (II) and zinc (II) were determined. Received June 30, 1999/Accepted July 21, 1999.     

An Anionic Mn(III) Ethyleneglycolate Complex

Summary.  The crystal structure of consists of individual layers in which the anionic complexes form strings of vertex-sharing octahedral units. These strings are interconnected by units to form layers via Na-Cl and Na-O interactions. An outstanding feature of the compound are the unusually strong Jahn-Teller elongated trans- octahedra. Received April 25, 2000. Accepted May 8, 2000     

Preparation, Structure, and Thermal Decomposition of Co(II) Complexeswith 2,3- and 2,5-Dichlorobenzoic Acid and Imidazole

Summary.  The reaction products of Co(II)-2,3- and -2,5-dichlorobenzoate with imidazole (1, 2; CoL ₂⋯2imdċ2H₂O, L=C₇H₃Cl₂O, imd=imidazole) were characterized by their spectroscopic and thermochemical properties. The compounds crystallize in the monoclonic system with space group = P2₁/c, a=13.848(3), b=12.841(3) ?, c= 7.064(2) ?, β=98.12 °, V=1243.5(4) ?³, Z=2 for 1 and space group =P2₁/n, a=13.293(3), b= 6.964(2), c=13.800(3) ?, β=108.92(3) °, V=1208.6(4) ?³, Z=2 for 2. The complexes lose their crystal water in one step at 333 K and subsequently decompose to CoO with intermediate formation of Co₃O₄. Received August 9, 1999. Accepted (revised) February 11, 2000     

Thermochromism and Solvatochromism in Solution

Summary.  The thermochromic behaviour of various coordination compounds in solution is discussed, with a special focus on cyclic diamine chelates. Thermally induced spin-crossover phenomena of iron(II) complexes are also considered. The solvatochromic behaviour of mixed-ligand complexes is presented in detail. Received April 2, 2001. Accepted (revised) April 19, 2001     

Tuning the Helicity of (2,2′-Bidipyrrinato)-nickel(II) Complexes

Summary.  The influence of the terminal substituents of 2,2′-bidipyrrin ligands on the geometrical and spectroscopic properties of the respective nickel(II) complexes was investigated. Helicity was found to be an intrinsic structural feature of all 2,2′-bidipyrrins studied to date, including a species with minimum helical overlap. Surprisingly, no changes became apparent upon increasing the size of the terminal substituent from methyl to 1,4-butadiyl. t-Butyl groups at the termini, however, were found to be sterically too demanding to allow the formation of stable nickel(II) complexes. Received October 5, 2001. Accepted (revised) November 14, 2001     

Preparation, Characterization and Crystal Structure of [Be(NCSe)2(HCON(CH3)2)2]

 Di-N-selenocyanato-bis(N,N′-dimethylfor- mamide)beryllium (1) was prepared and characterized by chemical analyses, and single crystal X-ray structure analysis. Crystals of 1 are monoclinic with a = 1837.2 (8) pm, b = 547.1 (2) pm, c = 1435.6 (6) pm, β = 93.27 (4)°, space group C2/c, Z = 4. Beryllium is tetrahedrally coordinated by two N-bonded selenocyanate and two O-bonded N,N′-dimethylformamide ligands and intermolecular Se ⋯ Se as well as Se ⋯ H interactions are observed.     

Study of the Ternary Systems M(II)(NO3)2–LiNO3–H2O (M(II) 5 Mg, Ca, Sr, Ba) at 25°C

Summary.  The isothermal solubility diagrams of four aqueous systems containing lithium nitrate and nitrates of group IIA metals – magnesium, calcium, strontium, and barium – were studied at 25°C. No double salt formation was observed. The results were compared with similar nitrate and chloride systems. Some trends in the shape of the phase diagrams were observed. Hydration analysis was applied to the solubility branches, rendering information about ionic processes in saturated solutions. Further, the ratio of activity coefficients of the saturating solid phase in ternary and binary solutions (γ/γ₀) was obtained. Received April 13, 2001. Accepted June 15, 2001     

Synthesis and Properties of Glass-Forming Hydrazones II [1]. Hydrazones Containing Bicarbazolyl Units

Summary.  A series of new glass-forming hydrazones containing bicarbazolyl units were synthesized starting from 9-(2-(9H-carbazol-9-yl)-cyclobutyl)-9H-carbazole and 9-(6-(9H-carbazol-9-yl)-hexyl)-9H-carbazole, and their thermal properties were studied. The correlation between their inclination to form glasses and their chemical structures are discussed. The results of a preliminary investigation of the photoelectric properties of amorphous films of the title compounds are briefly reported. The highest hole drift mobility was observed for 9-(2-(9H-carbazol-9-yl)-cyclobutyl)-9H-carbazole-3-carbaldehyde N,N-diphenylhydrazone; at high electric fields, it approaches 1 · 10⁻³ cm²/Vs. Received September 17, 2001. Accepted (revised) October 16, 2001     

Electrometric Studies on the Ternary Complexes of M(II) With Chlorpromazine and Some Amino Acids

 The stability constants for the binary M(II)- chlorpromazine hydrochloride (CPZ) and the ternary complexes M(II)-chlorpromazine-amino acid, have been studied using pH-measurements. The amino acids (aa) are: glycine, glutamic acid, histidine and the metal ions are: Cu(II), Zn(II), Co(II), Ni(II) and UO₂(II). All experiments were carried out in the presence of 0.1 mol dm⁻³ KNO₃. The resulting stability constants of the binary and the ternary complexes were compared. It was observed that the stability of the ternary complexes-except for glutamic acid – are lower than of the binary ones. Received October 22, 1998. Revision March 14, 1999.     

Solid-Solute Phase Equilibria in Aqueous Solutions XVII [I]. Solubility and Thermodynamic Data of Nickel(II) Hydroxide

Summary.  The solubility of nickel(II) hydroxide (theophrastite) in water was determined as a function of temperature and ionic strength by the pH variation method. In each experiment the inert electrolyte medium was made up with sodium perchlorate. The experimental data were thermodynamically analyzed, and the standard solubility constant was extrapolated to zero ionic strength with the specific ion-interaction equation. Furthermore, the standard molar Gibbs energy and the enthalpy of formation for theophrastite, β-Ni(OH)₂, were evaluated. For all calculations, ChemSage and its optimizer routine were used. Received October 25, 2001. Accepted October 29, 2001     

Samarium(II) Iodide Promoted Tandem Reductive Fragmentation and Aldol Reaction

Summary.  We report a new reductive fragmentation/aldol tandem reaction in a 1,4-diketone induced by samarium(II) iodide. Due to the particular stereoelectronic situation in the molecule, an alternative pathway was avoided despite the fact that it would have greatly reduced the strain in the tricyclic molecule. Received February 23, 2001. Accepted March 7, 2001     

Structural, Spectroscopic, and Thermal Behaviour of Bis-(thiosaccharinate)-aqua-cadmium(II)

Summary.  The crystal structure of the title complex, [Cd(tsac)₂(H₂O)], has been determined by single crystal X-ray diffraction methods. It crystallizes in the monoclinic space group C2/c (a = 12.236(3), b = 8.919(3), c = 16.655(3) ?, β = 96.18(2)°, Z = 4). The molecular structure was solved from 1705 independent reflections with I > σ(I) and refined to R ₁ = 0.0489. Infrared and Raman spectra of the complex were recorded and are briefly discussed. Its thermal behaviour was investigated by thermogravimetry and differential thermal analysis. Received December 18, 2000. Accepted February 19, 2001     

Colorimetric Microdetermination of Mercury(II) with Some Quinoxaline Azo Compounds in Presence of an Anionic Surfactant

Summary.  A new simple, rapid, sensitive, and selective method is proposed for the microdetermination of mercury. Mercury(II) forms insoluble complexes with 2,3-dichloro-6-(2-hydroxy-3,5-dinitrophenylazo)-quinoxaline (1), 2,3-dichloro-6-(5-amino-3-carboxy-2-hydroxy-phenylazo)-quinoxaline (2), 2,3-dichloro-6-(2,7-dihydroxynaphth-1-ylazo)-quinoxaline (3), and 2,3-dichloro-6-(3-carboxy-2-hydroxy-naphth-1-ylazo)-quinoxaline (4) in aqueous acidic medium; the complexes can be made soluble by the action of an anionic surfactant. The solution of the pink coloured compounds is stable for at least 24 h. Beer’s law is obeyed over the concentration range from 0.1 to 2.8 μg · cm⁻³ of mercury. For a more accurate analysis, Ringbom optimum concentration ranges were found to be 0.25–2.5 μg · cm⁻³. The molar absorpitivity, Sandell sensitivity, and relative standard deviations were also calculated. A slight interference from Pd²⁺ and Cd²⁺ is exhibited by the first three ligands, whereas the last one is only negligibly affected by these metal ions. Strong interference from Ag(I) is evident for all ligands, whereas alkali, alkaline earth, and other transition metals tested posed negligible interference. 15 μg · cm⁻³ of Cd²⁺ and Pd²⁺ or 10 μg · cm⁻³ of Ag⁺ can be tolerated if 1.0 mg of potassium bromide and 2.0 mg of citrate as masking agents are added for the determination of 1.5 μg · cm⁻³ of mercury(II). The method was applied to the determination of methyl- and ethylmercury chloride and the analysis of environmental water samples. Received August 7, 2000. Accepted (revised) October 18, 2000