Preparation, characterization and X-ray analysis of [Co-2(Cl)(2)tpmc](BF4)(2). Comparative structural analysis with the complexes having analogous geometries and ligands

A novel binuclear Co(II) complex, [Co-2(Cl)(2)tpmc](BF4)(2) (tpmc=N,N,N",N"'-tetrakis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane), was prepared and structurally characterized by X-ray diffraction analysis at low temperature. The complex crystallizes in P2(1)/c space group of the monoclinic crystal system, and its crystals are isomorphic with those Of [Cu-2(Br)(2)tpmc](ClO4)(2) complex. In the crystal structure the complex cations [Co-2(Cl)(2)tpmc](2+) are settled around the inversion centres. Cobalt(II) is exo coordinated with four macrocyclic N atoms, and Cl- supplements the fifth coordination site. Based on the index of trigonality, the coordination polyhedron formed around Co(II) ion is described as distorted trigonal bipyramid. Two metal centres are at a distance of 5.710 angstrom. This is the first Co(II) complex for which X-ray analysis confirmed a chair conformation of tpmc ligand. IR, EPR (X-band) and UV/VIS absorption and reflectance spectra, molar conductivities and magnetic measurements (SQUID) are used to study the investigated complex. A comparative structural analysis with some of the described Co(II) and Cu(II) complexes of analogous geometries and type of pendant azamacrocyclic ligands was also done

Excited States of the Phthalimide Chromophore and Their Exciton Couplings: A Tool for Stereochemical Assignments

The electronically excited states of the phthalimide chromophore have been studied by means of linear dichroism (LD) of samples partially oriented in poly(vinyl alcohol) films, magnetic circular dichroism (MCD), and circular dichroism (CD) spectroscopy. On the basis of the LD measurements, the low-energy tail (340-320 nm) of the first absorption band is assigned to an out-of-plane polarized pi-->pi* transition (I). At higher energy, the electronic spectrum is resolved into contributions from five pi-->pi* transitions: II(300 nm, long-axis polarized), III (275 nm, short-axis polarized), IV (235 nm, short-axis polarized), V (220 nm, long-axis polarized), and VI (similar to 210 nm, short-axis polarized). The results from semiempirical (INDO/S-CI) and ab initio (CIS/6-31+G(d)) MO calculations compare well with the proposed assignments of the excited states. Degenerate exciton interaction between electric-dipole-allowed transitions of two phthalimide chromophores is observed in the electronic absorption spectra of the achiral bis-phthalimides 2a-c and in the CD spectrum of the chiral bis-phthalimide 3a. For the latter compound, the solid-state geometry has been determined by X-ray diffraction analysis. Good agreement between experimental and computed CD spectra confirms that the coupled-oscillator exciton model provides the basis for a reliable nonempirical method for the assignment of absolute configuration for this class of compounds. Nondegenerate exciton coupling between phthalimide and benzoate or phenyl chromophores is born out in the CD spectra of homochiral molecules 3c and 3d with the rigid cyclohexane skeleton. Finally, the exciton coupling method is used to make stereochemical assignments for the acyclic, conformationally flexible derivatives 4a-c and 5b

Second sphere coordiantion complexes via hydrogen bonding: synthesis, spectroscopic characterization, crystal structures and packing of cis-diazidobis(ethylenediamine)cobalt(III) cations with complex fluoroanions

Crystals of cis-diazidobis(ethylenediamine)cobalt(III) tetrafluoroborate nitrate [cis-Co(en)(2)(N-3)(2)](2) (BF4) (NO3) I and cis-diazidobis (ethylenediamine)cobalt(III) hexafluorosilicate, [cis-Co(en)(2)(N-3)(2)](2)(SiF6) Il have been obtained by slowly mixing the separately dissolved cis-diazidobis(ethylenediamine)cobalt(III) nitrate with sodium salt of tetrafluoroborate and hexafluorosilicate, in aqueous medium in 1: 1 and 2:1 molar ratio, respectively. Elemental analyses and spectroscopic techniques (IR, UV/visible, H-1 and C-13 NMR) were studied for characterizing the complex salts. Single crystal X-ray structure determinations revealed supramolecular assemblies via hydrogen bonding network between ionic groups and NH2 group of coordinated ethylenediamine molecules, i.e. second-sphere coordination

Role of second-sphere coordination in anion binding: Synthesis, characterisation and X-ray structure of hexaamminecobalt(III) chlorise hydrogen phthalate trihydrate and sodium hexamminecobalt(III) benzoate monohydrate

In an effort to utilize [Co(NH3)6]3+cation as a new host for carboxylate ions, orange coloured crystalline solids of composition [Co(NH3)6]Cl(C8H5O4)2·3H2O (1) and Na[Co(NH3)6](C7H5O2)4·H2O (2) were obtained by reacting hot aqueous solutions of hexaamminecobalt(III) chloride with potassium hydrogen phthalate and sodium benzoate in 1:3 molar ratio, respectively. The title complex salts were characterized by elemental analyses and spectroscopic studies (IR, UV/Visible and NMR). Single crystal X-ray structure determinations revealed the formation of second-sphere coordination complexes based on hydrogen bond interactions. In complex salt 1 only two out of three ionisable chloride ions present in [Co(NH3)6]Cl3 were replaced by two ions whereas in complex salt 2 all the three ionisable chloride ions present in [Co(NH3)6]Cl3 were replaced and the final product was an adduct with another mole of sodium benzoate in solid state. The crystal lattice is stabilized by electrostatic forces of attraction and predominantly N–H⋯O interactions

Novel Chiral Pyromellitdiimide (1,2,4,5-Benzenetetracarboxydiimide) Dimers and Trimers: Exploring Their Structure, Electronic Transitions and Exciton Coupling

The chiral but highly symmetrical acyclic and cyclic pyromellitic diimide dimers and trimers 2-5 have been obtained and characterized for the first time. The pyromellitdiimide chromophores in these molecules are linked by a rigid diequatorially 1,2-disubstituted cyclohexane skeleton. The structures of the compounds have been determined in detail by molecular modeling and, in the case of cyclic dimer 4 and trimer 5, by means of X-ray diffraction analysis. The electronically excited states of the pyromellitdiimide chromophore (1a) have been studied in these and other model compounds by means of linear dichroism (LD), magnetic circular dichroism (MCD), and circular dichroism (CD) spectroscopy. CD spectra of the rigid cyclic trimer 5 have provided the most detailed information on the excited states of the pyromellitdiimide chromophore. The low-energy tail (340-360 nm) of the absorption envelope can be assigned to out-of-plane polarized n-pi* transitions (I, II). The higher energy bands are due to contributions from up to six pi-pi* transitions, these being polarized either along the long (IV-VI, VIII) or short axis (III, VII). The results of ab initio CIS/cc-pVDZ and semiempirical INDO/S-CI calculations have been compared with the experimental data. CD Cotton effects in the region 200260 nm, which result from exciton interactions between electric dipole allowed transitions of two pyromellitdiimide chromophores in compounds 2-5, provide reliable and useful information concerning the conformation and absolute configuration of these molecules, which may be extrapolated to other oligoimide systems

Novel Chiral Pyromellitdiimide (1,2,4,5-Benzenetetracarboxydiimide) Dimers and Trimers: Exploring Their Structure, Electronic Transitions and Exciton Coupling

The chiral but highly symmetrical acyclic and cyclic pyromellitic diimide dimers and trimers 2-5 have been obtained and characterized for the first time. The pyromellitdiimide chromophores in these molecules are linked by a rigid diequatorially 1,2-disubstituted cyclohexane skeleton. The structures of the compounds have been determined in detail by molecular modeling and, in the case of cyclic dimer 4 and trimer 5, by means of X-ray diffraction analysis. The electronically excited states of the pyromellitdiimide chromophore (1a) have been studied in these and other model compounds by means of linear dichroism (LD), magnetic circular dichroism (MCD), and circular dichroism (CD) spectroscopy. CD spectra of the rigid cyclic trimer 5 have provided the most detailed information on the excited states of the pyromellitdiimide chromophore. The low-energy tail (340-360 nm) of the absorption envelope can be assigned to out-of-plane polarized n-pi* transitions (I, II). The higher energy bands are due to contributions from up to six pi-pi* transitions, these being polarized either along the long (IV-VI, VIII) or short axis (III, VII). The results of ab initio CIS/cc-pVDZ and semiempirical INDO/S-CI calculations have been compared with the experimental data. CD Cotton effects in the region 200260 nm, which result from exciton interactions between electric dipole allowed transitions of two pyromellitdiimide chromophores in compounds 2-5, provide reliable and useful information concerning the conformation and absolute configuration of these molecules, which may be extrapolated to other oligoimide systems

Chiroptical Properties, Structure, And Absolute Configuration Of Heterosubstituted 2( 5H)-furanones

Chiroptical properties of a series of 3 and/or 4-heterosubstituted 2(5H)-furanones were investigated with respect to correlation with absolute configuration. The n −pi* and pi − pi* Cotton effects have been assigned on the basis of comparison with the UV spectra in solvents of varying polarity. It is demonstrated that the n − pi* transition in 4-amino substituted 2(5H)-furanones appears at shorter wavelength with respect to the pi − pi* transition. With the exception of 4-pyrrolidino and 4-benzylamino substituted 2(5H)-furanones, other heterosubstituted 2(5H)-furanones follow the butenolide con-figurational rule (Gawronski et al. J. Org. Chem. 61:1513–1515, 1996). Absolute configu-ration of 2(5H)-furanone derivatives can also be assigned according to the sign of the Cotton effect (of unknown origin) at 200–230 nm. The structure of four representative sulfur and nitrogen substituted 2(5H)-furanones has been analyzed by X-ray diffraction. The results indicate planarity of the furanone ring and extended conjugation in 4-amino substituted 2(5H)-furanones.