Biomedical subjects
Publications and source records attributed to Thomas C. W. Mak.
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The lanthanide hypophosphite complexes Ln(H(2)PO(2))(3) (Ln = La, Pr, Nd) and Ln(H(2)PO(2))(3).H(2)O (Ln = La, Pr) crystallize in the space group P&onemacr; (No. 2), Z = 2. The lattice constants for La(H(2)PO(2))(3) are a = 6.7912(6) Å, b = 7.0801(8) Å, c = 8.863(1) Å, alpha = 82.64(1) degrees, beta = 74.43(1)( o), gamma = 71.91(1) degrees; for La(H(2)PO(2))(3).H(2)O, a = 7.2291(4) Å, b = 7.983(1) Å, c = 8.934(1) Å, alpha =110.57(1) degrees, beta = 98.26(1) degrees, gamma = 104.35(1) degrees. In both structures hypophosphite ions bridge adjacent 8-coordinate lanthanide ions to give infinite chains. Infrared and Raman spectra (300-20 K) are shown to be consistent with the crystallographic data, with 52 of the 54 fundamental hypophosphite modes of vibration assigned. The electronic spectra of the anhydrous compounds consist mainly of bands due to pure electronic electric dipole transitions. Two-center vibronic transitions observed in the (3)H(4) --> (1)D(2) spectrum of Pr(H(2)PO(2))(3) are not well-simulated by a model with dipole-dipole interaction terms between the two centers. The energy level scheme of Pr(3+) in Pr(H(2)PO(2))(3) was fitted to a model Hamiltonian for a C(2)(v)() site symmetry Pr(3+) ion, including configuration interaction of 4f(2) with 4f6p. Theoretical crystal field parameters were in reasonable agreement with those derived from the energy level fitting. The results highlight the C(2)(v)() (k even) and C(1) (k odd) distortions from the ideal D(4)(d)() antiprismal structure, which slightly modify the 4f(2) energy level scheme, and largely determine the spectral intensities in Pr(H(2)PO(2))(3), respectively. The derived energy level scheme of Nd(H(2)PO(2))(3) is similar to that for 8-coordinated Nd(3+) in NdCl(3).6H(2)O.
The new compounds UO(2)(H(2)PO(2))(2).H(2)O (1) and UO(2)(H(2)PO(2))(2).H(3)PO(2) (2) crystallize in the space groups P2(1)/n and P2(1)2(1)2(1), respectively, each with Z = 4. For 1, a = 7.686(2) Å, b = 9.275(2) Å, c = 11.027(2) Å, alpha = 90 degrees, beta = 92.32(3) degrees, gamma = 90 degrees; for 2, a = 7.1572(4) Å, b = 7.2363(6) Å, c = 17.554(2) Å, alpha = beta = gamma = 90 degrees. Each uranium atom, situated at a general position, has a distorted pentagonal bipyramidal coordination geometry, and U-O-P-O-U bridges form differently oriented chains in 1 and a three-dimensional network structure in 2. H(3)PO(2) serves as a terminal monodentate ligand in 2. The infrared and Raman spectra of 1 and 2 show (i) characteristic uranyl modes of vibration; (ii) partially resolved unit cell group modes of hypophosphite anions; and (iii) bands due to water and H(3)PO(2), respectively. The C(1) site symmetry in these compounds makes their spectral properties useful in evaluating the presence of additional electronic transitions not identified in the analyses of higher symmetry uranyl compounds. In the region between 20 000 and 29 000 cm(-)(1), 12 electronic transitions have been located and assigned. The luminescence from both compounds is weak due to competing nonradiative processes, and the major differences from that of UO(2)(2+) at centrosymmetric sites arise from the electric dipole intensity enhancement of the zero-phonon line and the appearance of progressions in the uranyl antisymmetric stretching mode. Water and hypophosphite modes are identified in the luminescence of 1 and 2, respectively. The anharmonicities of uranyl stretching modes in 1 are compared with those in other uranyl systems. The Franck-Condon analysis of the absorption and emission spectra of 1 show a U-O bond length increase of 5 +/- 1 pm on excitation from to sigma(u)delta(u), compared with values ranging from 4 to 9 pm for other uranyl systems.
3,4-Bis(trimethylsilyl)-1H-pyrrole (5) was employed as a key precursor to generate a highly strained and reactive five-membered cyclic cumulene, namely 1-tert-butoxycarbonyl-3,4-didehydro-1H-pyrrole (4). The transient existence of 4 at room temperature was confirmed by trapping reactions with furan, acrylonitrile, and benzene, affording cycloadducts 13-15. The choice of the electron-withdrawing tert-butoxycarbonyl group as the N-substituent was essential because it was able to adjust the electron density of 11a and 11b. As a result, monoiodonium triflates 12a and 12b were obtained, respectively. On the contrary, N-tert-butyl-3,4-bis(trimethylsilyl)-1H-pyrrole (9) led instead to the bisiodonium triflate 10 upon treatment with the Zefirov reagent.
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Direct chlorination of 1-CH(3)-CB(11)H(11)(-) in glacial acetic acid gave the highly chlorinated carborane anion 1-CH(3)-CB(11)Cl(11)(-), and treatment of 1-CH(3)-CB(11)H(11)(-) with ICl in triflic acid afforded the highly iodinated carborane anion 1-CH(3)-CB(11)I(11)(-). Under similar or more vigorous reaction conditions, however, the reaction of 1-CH(3)-CB(11)H(11)(-) with Br(2) in triflic acid did not proceed to completion. The highly brominated carborane anion 1-CH(3)-CB(11)Br(11)(-) was achieved via a sealed-tube reaction. This new method has led to the isolation of 1-H-CB(11)X(11)(-) (X = Cl, Br, I) and 1-Br-CB(11)Br(11)(-) in high yield. The lithiation of 1-H-CB(11)X(11)(-) resembles that of its parent anion CB(11)H(12)(-). Treatment of these lithio species with methyl iodide gave the methylated carborane anions 1-CH(3)-CB(11)X(11)(-). These new weakly coordinating anions were fully characterized by (1)H, (13)C, and (11)B NMR, IR, and negative-ion MALDI MS spectroscopy. Some were further confirmed by single-crystal X-ray analysis.
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A series of Ru(II) complexes of the ONNS donor ligand mono(4-(4-tolyl)thiosemicarbazone) of 2,6-diacetylpyridine (L(2)H) synthesized by using three different ruthenium-containing starting materials RuCl(3).xH(2)O, Ru(PPh(3))(3)Cl(2), and [Ru(NH(3))(5)Cl]Cl(2) are reported. Chemical and electrochemical studies of the complexes [Ru(L(2))(PPh(3))(2)]ClO(4) (1), [Ru(L(2))(PPh(3))(2)]Cl (2), [Ru(L(2))(PPh(3))]ClO(4).EtOH (3), [Ru(L(2))(PPh(3))(bpy)]ClO(4) (4), [Ru(L(2))(PPh(3))(ophen)]ClO(4) (5), [Ru(L(2))(2)] (6), and [Ru(L(2))(L(2)H)]Cl (7) have been carried out. The structure of the compound [Ru(L(2))(PPh(3))(2)]ClO(4) (1) has been determined by single-crystal X-ray diffraction techniques. The crystals are triclinic, space group P&onemacr; with a = 12.716(1) Å, b = 13.213(1) Å, c = 15.951(1) Å, alpha = 87.66(1) degrees, beta = 73.81(1) degrees, gamma = 70.93(1) degrees, and Z = 2, where the deprotonated ligand mono(4-(4-tolyl)thiosemicarbazone) of 2,6-diacetylpyridine (L(2)) is chelated to the Ru(II) center through the oxygen of the carbonyl group, pyridine ring nitrogen, imine nitrogen, and the thiolate sulfur atoms. Strong coordination of the carbonyl group suggested from its IR spectral characteristics has been confirmed from the appreciable shortening of the Ru-O bond and lengthening of the C=O bond in the structure of 1.
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The new Schiff base ligand 2-chlorobenzaldehyde thiosemicarbazone (L, 1) has been synthesized and characterized by spectral techniques and single-crystal X-ray analysis. Crystals of 1 are monoclinic, space group P2(1)/n with a = 12.964(4) Å, b = 5.131(5) Å, c = 4.970(1) Å, beta = 94.32(2) degrees, and Z = 4. The thiosemicarbazone moiety adopts a configuration with N(1) cis to N(3) and places the E configuration about both the bonds C(1)-N(2) and C(2)-N(3). The monodentate behavior of the neutral ligand (L) has been investigated in two cadmium halides CdL(2) Br(2) (2) and CdL(2)I(2) (3). Compound 2 crystallizes in space group Cc witha = 8.175(1) Å, b = 14.176(1) Å, c = 21.073(1) Å, beta = 94.02(1) degrees, and Z = 4. Compound 3 crystallizes in space group P&onemacr; with a = 10.9577(1) Å, b = 16.174(1) Å, c = 7.878(1) Å, alpha = 100.50(1) degrees, beta = 109.39(1) degrees, gamma = 83.67(1) degrees, and Z = 2. The coordination geometry about the cadmium(II) atom in compound 2 conforms to a tetrahedral configuration with two sulfur atoms from two unequivalent neutral ligands and two bromide atoms. Whereas the coordination geometry about the cadmium(II) atom in compound 3 is (4 + 1) distorted trigonal bipyramidal with two iodide atoms and one sulfur atom in the equatorial plane, the other thiosemicarbazone sulfur and the iodide atom I(1a) of an adjacent moiety occupy the axial positions. Compound 2 exhibits powder SHG efficiencies ca. 20 times that of urea, whereas compound 3 does not exhibit any SHG efficiency. Theory and experiment suggested that intermolecular contact is the main factor controlling the SHG efficiencies of compounds.