Donald G. VanDerveer

Enhanced Metal Ion Selectivity of 2,9-Di-(pyrid-2-yl)-1,10-phenanthroline and Its Use as a Fluorescent Sensor for Cadmium(II)

The metal ion complexing properties of the ligand DPP (2,9-di-(pyrid-2-yl)-1,10-phenanthroline) were studied by crystallography, fluorimetry, and UV-visible spectroscopy. Because DPP forms five-membered chelate rings, it will favor complexation with metal ions of an ionic radius close to 1.0 A. Metal ion complexation and accompanying selectivity of DPP is enhanced by the rigidity of the aromatic backbone of the ligand. Cd2+, with an ionic radius of 0.96 A, exhibits a strong CHEF (chelation enhanced fluorescence) effect with 10(-8) M DPP, and Cd2+ concentrations down to 10(-9) M can be detected. Other metal ions that cause a significant CHEF effect with DPP are Ca2+ (10(-3) M) and Na+ (1.0 M), whereas metal ions such as Zn2+, Pb2+, and Hg2+ cause no CHEF effect with DPP. The lack of a CHEF effect for Zn2+ relates to the inability of this small ion to contact all four donor atoms of DPP. The structures of [Cd(DPP)2](ClO4)2 (1), [Pb(DPP)(ClO4)2H2O] (2), and [Hg(DPP)(ClO4)2] (3) are reported. The Cd(II) in 1 is 8-coordinate with the Cd-N bonds to the outer pyridyl groups stretched by steric clashes between the o-hydrogens on these outer pyridyl groups and the central aromatic ring of the second DPP ligand. The 8-coordinate Pb(II) in 2 has two short Pb-N bonds to the two central nitrogens of DPP, with longer bonds to the outer N-donors. The coordination sphere around the Pb(II) is completed by a coordinated water molecule, and two coordinated ClO4(-) ions, with long Pb-O bonds to ClO4(-) oxygens, typical of a sterically active lone pair on Pb(II). The Hg(II) in 3 shows an 8-coordinate structure with the Hg(II) forming short Hg-N bonds to the outer pyridyl groups of DPP, whereas the other Hg-N and Hg-O bonds are rather long. The structures are discussed in terms of the fit of large metal ions to DPP with minimal steric strain. The UV-visible studies of the equilibria involving DPP and metal ions gave formation constants that show that DPP has a higher affinity for metal ions with an ionic radius close to 1.0 A, particularly Cd(II), Gd(III), and Bi(III), and low affinity for small metal ions such as Ni(II) and Zn(II). The complexes of several metal ions, such as Cd(II), Gd(III), and Pb(II), showed an equilibrium involving deprotonation of the complex at remarkably low pH values, which was attributed to deprotonation of coordinated water molecules according to: [M(DPP)(H2O)]n+ <==> [M(DPP)(OH)](n-1)+ + H+. The tendency to deprotonation of these DPP complexes at low pH is discussed in terms of the large hydrophobic surface of the coordinated DPP ligand destabilizing the hydration of coordinated water molecules and the build-up of charge on the metal ion in its DPP complex because of the inability of the coordinated DPP ligand to hydrogen bond with the solvent.

A Supramolecular Tetra‐Keggin Polyoxometalate [Nb4O6(α‐Nb3SiW9O40)4]20−

: Giant polyoxometalates with catalytic, magnetic, and antiviral properties, which are in part attributable to their structures, are currently of great interest. Herein is described the synthesis and characterization of 1, a structurally novel tetrameric complex from Keggin ions (see picture). This complex is stable under the physiological conditions of the stomach (pH 1-2), which is interesting since related keggin anions are among the least toxic and yet most potent antiviral agents of the more than 300 polyoxometalates investigated biologically and pharmacologically.

Temperature dependent structural and transport properties of the type II clathrates A8Na16E136 (A=Cs or Rb and E=Ge or Si)

Variable temperature single-crystal structure analyses for Cs8Na16Si136, Rb8Na16Si136, Cs8Na16Ge136, and Rb8Na16Ge136 are reported along with electrical and thermal transport measurements on two polycrystalline specimens. The strong temperature dependence of the atomic displacement parameters for the alkali-metal atoms is indicative of significant disorder associated with the “rattling” alkali-metal atoms inside the two different polyhedra (sixteen dodecahedra and eight hexakaidecahedra per cubic unit cell) that makeup the type II clathrate hydrate framework. This disorder can lead to low lattice thermal conductivities. Transport measurements show these compounds to be metallic. The potential of type II clathrates for thermoelectric applications is discussed.

Diastereoselective reactions of an acyclic α-lithiated sulfide: a case of thermodynamic control

Abstract The CLi bond α to sulfur in an acyclic sulfide thermodynamically favors one configuration (96:4). This allows for the diastereoselective functionalization of sulfide 4 .

A CONVERGENT SYNTHESIS OF (+)-PANCRATISTATIN BASED ON INTRAMOLECULAR ELECTROPHILIC AROMATIC SUBSTITUTION

Abstract A convergent formal synthesis of (+)-pancratistatin ( 1 ) is reported. Specifically, an optically active adduct of piperonyl bromide and acetonated conduritol A was converted to a late-stage intermediate from the Danishefsky-Lee synthesis of 1 . The carbon skeleton was established via intramolecular electrophilic aromatic substitution within the piperonylated conduritol. Some competitive cationic rearrangement was observed in this operation, being dependent on the degree to which a 2-substituent in the piperonyl domain favors attack ipso to the piperonyl benzylic carbon.

Strong Metal Ion Size Based Selectivity of the Highly Preorganized Ligand PDA (1,10-Phenanthroline-2,9-dicarboxylic Acid) with Trivalent Metal Ions. A Crystallographic, Fluorometric, and Thermodynamic Study

The selectivity of the rigid ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) for some M(III) (M = metal) ions is presented. The structure of [Fe(PDA(H)(1/2))(H(2)O)(3)] (ClO(4))(2).3H(2)O.(1)/(2)H(5)O(2) (1) is reported: triclinic, P1, a = 7.9022(16) A, b = 12.389(3) A, c = 13.031(3) A, alpha = 82.55(3) degrees , beta = 88.41(3) degrees , gamma = 78.27(3) degrees , V = 1238.6(4) A(3), Z = 2, R = 0.0489. The coordination geometry around the Fe(III) is close to a regular pentagonal bipyramid, with Fe-N lengths averaging 2.20 A, which is normal for a 1,10-phenanthroline type of ligand coordinated to seven-coordinate Fe(III). The Fe-O bonds to the carboxylate oxygens average 2.157 A, which is rather long compared to the average Fe-O length of 2.035 A to carboxylates in seven-coordinate Fe(III) complexes. The structure of 1 supports the idea that the Fe(III) is too small for ideal coordination in the cleft of PDA, and the structure shows that the Fe(III) adapts to this by inducing numerous small distortions in the structure of the PDA ligand. The log K(1) values for PDA at 25 degrees C in 0.1 M NaClO(4) were determined by UV spectroscopy with Al(III) (log K(1) = 6.9), Ga(III) (log K(1) = 9.7), In(III) (log K(1) = 19.7), Fe(III) (log K(1) = 20.0), and Bi(III) (log K(1) = 26.2). The low values of log K(1) for PDA with Al(III) and Ga(III) are because these ions are too small for the cleft in PDA, which requires a large metal ion with an ionic radius (r(+)) of 1.0 A. In(III) and Fe(III) (r(+) = 0.86 and 0.72 A for a coordination number (CN) of 7) are somewhat too small for the cleft in PDA but may adapt by increasing the coordination number, which increases the metal ion size, and have high log K(1) values. Very large log K(1) values are found, as expected, for Bi(III) (r(+) = 1.17 A, CN = 8), which fits the cleft quite well. Fluorescence studies show that Y(III) produces the largest CHEF (chelation enhanced fluorescence) effects, followed by La(III) and Lu(III), in the PDA complexes. Metal ions with nonfilled d or f subshells produce very large quenching of the fluorescence, as do heavy-metal ions such as In(III) and Bi(III), which have large spin-orbit coupling effects. The Al(III)/PDA complex produced an intense broad band at longer wavelength than the pi*-pi emissions of the PDA ligand, which is at a maximum at pH 6, and the possibility that this might reflect an exciplex, where one PDA ligand in the Al(III) complex pi-stacks with the excited state of a second PDA ligand, is discussed.

Main group metal halide complexes with sterically hindered thioureas XI. Complexes of antimony(III) and bismuth(III) chlorides with a new bidentate thiourea — 1,1′-methylenebis(3-methyl-2H-imidazole-2-thione)

Abstract A new bidentate ligand, mbit, [mbit=1,1′-methylenebis (3-methyl-2H-imidazole-2-thione)] was synthesized and characterized along with two new pnictogen complexes - SbCl3mbit and BiCl3mbit. A single crystal X-ray structure of SbCl3mbit gave the following cell parameters: space group P21/c, a = 11.812(9), b = 7.699(4), c = 18.100(9) A, β = 101.29(5)°, Z = 4, V = 1614.2 A3, Do = 1.92 g/cm3, Dc = 1.927 g/cm3 (λ = 0.71069 A). The structure refined to a conventional R=0.042. The local geometry around the antimony atom was distorted octahedral with bridging sulfur atoms creating long zigzag chains of octahedra sharing vertices cis to each other. Two chlorine atoms are trans to each other, and the third chlorine is trans to the bridging sulfur. The Sb—S bridges are 3.41 A in length. There is no strong evidence for a stereoactive lone pair in the coordination sphere of antimony. The ligand forms an eight-membered ring with the antimony atom included. Solid state IR data showed little change in ligand vibrational modes normally sensitive to coordination, and solution state proton NMR gave evidence for a high degree of association.

The versatile chemistry and noncentrosymmetric crystal structures of salt-inclusion vanadate hybrids.

Three unique structure types of the vanadate-based mixed-metal oxide systems (salt)·MnII-Vv-O and (salt)·CuII-Vv-O are presented, with a focus on the role of the asym. vanadate units. Lattice parameters were obtained for (CsCl)2Mn(VO3)2, (CsBr)2Mn(VO3)2, (RbCl)2Mn(VO3)2, (CsCl)2Cu(VO3)2, (CsCl)Mn2(V2O7), (KCl)2Cu(VO3)2, (RbCl)2Cu(VO3)2 and (CsBr)2Cu(VO3)2. The two structure types found in the (AX)2M-(VO3)2 series differ in the propagation direction of the metavanadate chains which is thought to be due to the presence (or absence) of a Jahn-Teller distortion of the metal (d9 Cu2+ vs. d5 Mn2+) ion.

Chiral bimetallic complexes from chiral salen metal complexes and mercury (II) halides and acetates: the anionic groups interact with Cu(II) in apical position

Abstract A series of chiral bimetallic complexes have been prepared containing both Cu(II) and Hg(II) metal centers. The complexes possess chiral salen ligands which host Cu(II) in the center of the cis-N2O2 chromophore and Hg(II) via two oxygen atoms of the chromophore. Halogen and acetate groups from mercury salts interact with the Cu(II) center. The X-ray crystallographic data of 11 reveals a short distance of Cl⋯Cu (3.22–3.26 A). EPR study also discloses a strong interaction, in particular, of acetate group with Cu.

Synthesis and characterization of N -(alky(aryl)carbamothioyl)cyclohexanecarboxamide derivatives and their Ni(II) and Cu(II) complexes

N-(R-carbamothioyl)cyclohexanecarboxamides (R: diethyl, di-n-propyl, di-n-butyl, diphenyl and morpholine-4) and their Ni(II) and Cu(II) complexes have been synthesized and characterized by elemental analyses, FT-IR and NMR methods. N-(diethylcarbamothioyl)cyclohexanecarboxamide, HL1, C12H22N2OS, crystallizes in the orthorhombic space group P212121, with Z = 4, and unit cell parameters, a = 6.6925(13) Å, b = 9.0457(18) Å, c = 22.728(5) Å. The conformation of the HL1 molecule with respect to the thiocarbonyl and carbonyl moieties is twisted, as reflected by the torsion angles O1–C6–N2–C5, C6–N2–C5–N1 and S1–C5–N2–C6 of 1.68°, −67.47° and 115.50°, respectively. The structure of HL1 also shows a delocalization of the π electrons of the thiocarbonyl group over the C–N bonds. The ring puckering analysis shows that the cyclohexane ring has a chair conformation. The bis(N-(morpholine-4-carbonothioyl)cyclohexane carboxamido)nickel(II) complex, Ni(L5)2, C24H38N4NiO4S2, crystallizes in the monoclinic space group P21/c, with Z = 4, and unit cell parameters, a = 16.919(3) Å, b = 8.3659(17) Å, c = 19.654(4) Å, β = 107.43(3)°. Ni(L5)2 is a cis-complex with a slightly distorted square-planar coordination of the central nickel by two oxygen and two sulfur atoms.