Ion pairs in the crystal structure of potassium ethyl viologen hexacyanometallates(II) (original) (raw)
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The colours of simple salts of the violurate anion
Spectrochimica Acta Part A: Molecular Spectroscopy, 1991
Salts of the violurate anion with the alkali and alkaline earth metals, the d" ions Zn*' and Cd'+, Mn'+, Pb2+, Ag+ and the lanthanides show a variety of spectacular colours in the solid state. The metal ions have no intrinsic absorption in the visible region (apart from the weak spin-forbidden bands of Mn2+) and do not normally show charge-transfer absorption. The colours are ascribed to the n-& transition of the violurate anion. As confirmation of this assignment the visible absorption of the K+ salt is shown to be polarized perpendicular to the plane of the violurate anion. Low temperature (-20 K) absorption spectra of the Na+, K+ and Rb+ salts are reported. INTRODUC~ON THE violurate anion ([Hzva]-) forms compounds with a large number of metal ions. These include many transition metals, the alkali metals, the alkaline earth metals, the lanthanide elements and a number of heavyp-block elements. One of the most dramatic features of violurate ion compounds is their colour: although an aqueous solution of [Hzva]-is pale pink, compounds containing the [H,va]-ion, including compounds of alkali and alkaline earth ions, show a variety of different colours ranging from blue, through red, to yellow (Table 1). The colours and electronic spectra of the [Hzva]-transition met& complexes present no problems; they reflect a combination of the ddd transitions of the metal ion, chargetransfer transitions and the electronic spectrum of [H,va]-itself. Unexpectedly, however, many simple salts of [H,va]-, including those of the s-block elements, the lanthanides, some of the p-block elements and Mn2+ and Zn'+, are also highly coloured and this does require an explanation. The ions have no d-electrons (apart from Mn" where the d+d transitions are spin forbidden and therefore very weak) and are not easily oxidized or reduced and so are not expected to show charge-transfer spectra. An initial conclusion is therefore that the colours originate in some way from the violurate ion itself. The crystal structure of violuric acid has been determined [ 11, as have those of a few of its compounds including [N&][Fe(Hzva)3].4Hz0 [2], [Cu(Hzva)$4Hz0 [3], K(H*va)-4Hz0 [4], Rb(H2va).4H20 [4] and Sr(H,va)z-4Hz0 [S]. The structures of the IV, Rb*+ and S? compounds show, as expected, that the violuric acid has lost its oxime proton. There is no evidence from these structures that the [H,va]-ion has a geometry or coordination chemistry which would account for the colours nor, of course, can there be any charge-transfer in such complexes. The closest contacts between the metal ion and the [H2va]-are in the range 2.5-3.0 A.
Crystal structures and Raman spectroscopic study of croconate violet salts with alkaline earth ions
Vibrational Spectroscopy, 2010
In this work are described the crystal structures of two alkaline earth salts as well the vibrational spectra of three alkaline earth salts of 3,5-bis-(dicyanomethylene)cyclopentane-1,2,4-trionate (known as croconate violet -CV 2− ). The compounds obtained are a mixed salt of potassium and magnesium [MgK 2 (CV) 2 ], beyond of calcium and barium salts (CaCV and BaCV, respectively). The structures of MgK 2 (CV) 2 and BaCV have been confirmed by single crystal X-ray diffraction and spectroscopic analysis. These compounds crystallize in monoclinic P2 1 /n space group, showing four and five water molecules for MgK 2 (CV) 2 and BaCV, respectively. The dianionic units [MgK 2 (CV) 2 (H 2 O) 4 ] adopt a slight distorted octahedral geometry in which the metallic center is coordinated by six oxygen atoms (four from CV 2− and two from water molecules). These units are connected through intermolecular hydrogen bonding giving rise to a supramolecular array in a two-dimensional arrangement (2D). The potassium ion shows monodentate coordination, whereas the magnesium ion presents a chelate coordination in the MgK 2 (CV) 2 salt and for the BaCV, the coordination geometry of metal site is monodentate and chelate coordination; it is straightforward to mention that the barium compound is the only pure divalent salt obtained until now in the literature. In the vibrational spectra, the most important vibrational markers for croconate violet ion are the (C N) and (C O) modes, which present different behavior due to the modification of chemical. In general way, the bands assigned to (C N) and (C O) in MgK 2 (CV) 2 , CaCV and BaCV present small wavenumber shifts, which can be associated to the different interionic interactions between anion and cations.
Inorganica Chimica Acta, 2010
The vibrational spectra and crystal structures of four lanthanide and potassium salts of 3,5-bis(dicyanomethylene)cyclopentane-1,2,4-trionate (C 1 1N 4 O 2À 3 ), known as croconate violet (CV), are described in this work. All LnKC 22 N 8 O 6 (Ln = La +3 , Nd +3 , Gd +3 and Ho +3 ) compounds are isostructural, crystallizing in the triclinic P 1 space group. In each compound the lanthanide ion is acting as both monodentate and chelate metal sites, whereas the potassium presents only monodentate coordination. The crystal structure shows the formation of a periodic 2D structure extended by K-N bonds parallel to the crystallographic [0 0 1] direction; these 2D sheets form hydrogen bonds with water molecules giving rise to a 3D extended arrangement. It is not possible to observe any type of p-interaction and the main forces responsible to stabilize the structures are the hydrogen bonds. The vibrational spectra of all the compounds are very similar, and the most important vibrational markers for the croconate violet ion, namely the m(C"N) and m(C@O) modes, behave differently: the m(C"N) modes are not shifted by the presence of the lanthanide ion species, only showing small band intensity differences, whereas the m(C@O) bands are shifted to higher wavenumbers, due to their coordination to the metal sites.
Structure and Electronic Spectra of Purine−Methyl Viologen Charge Transfer Complexes
The structure and properties of the electron donor− acceptor complexes formed between methyl viologen and purine nucleosides and nucleotides in water and the solid state have been investigated using a combination of experimental and theoretical methods. Solution studies were performed using UV−vis and 1H NMR spectroscopy. Theoretical calculations were performed within the framework of density functional theory (DFT). Energy decomposition analysis indicates that dispersion and induction (charge-transfer) interactions dominate the total binding energy, whereas electrostatic interactions are largely repulsive. The appearance of charge transfer bands in the absorption spectra of the complexes are well-described by time-dependent DFT and are further explained in terms of the redox properties of purine monomers and solvation effects. Crystal structures are reported for complexes of methyl viologen with the purines 2′- deoxyguanosine 3′-monophosphate (DAD′DAD′ type) and 7-deazaguanosine (DAD′ADAD′ type). Comparison of the structures determined in the solid state and by theoretical methods in solution provides valuable insights into the nature of charge-transfer interactions involving purine bases as electron donors.
Inorganica Chimica Acta, 2006
The crystal structures and vibrational spectra of two alkaline salts of 3,5-bis-(dicyanomethylene)cyclopentane-1,2,4-trionate ðC 11 N 4 O 3 2À Þ, known as croconate violet, are described: 1-rubidium and potassium croconate violet (RbKCV), and 2-rubidium croconate violet (Rb 2 CV). These compounds are isostructural and crystallize in triclinic P 1 space group. The stoichiometries of the salts show two water molecules to each M 2 C 11 N 4 O 3 unit. The anions are displayed in layers linked to water molecules by hydrogen bonds, therefore forming an extended structure with two-dimensional arrangement (2D). Crystal structure shows two different metal sites (M1 and M2) that present different types of coordination: monodentate, quelate and bidentate in M1; and monodentate and bidentate in M2. In RbKCV the rubidium cation is predominant in M1 and M2 sites, presenting total occupation of 70% and the molecular formula of this salt is Rb 1.4 K 0.6 C 11 N 4 O 3 AE 2H 2 O. Vibrational spectra of RbKCV and Rb 2 CV are similar to the spectra of potassium croconate violet (K 2 CV). In the Raman spectrum of RbKCV some small wavenumber shifts are observed when compared K 2 CV and Rb 2 CV spectra. The structural difference in RbKCV salt is due to the interionic interactions between CV anion and potassium and rubidium cations; this effect could be responsible to spectral differences observed in RbKCV Raman spectra. However, the exchange between potassium and rubidium ions in the solid state structure does not alter croconate violet anion crystal packing, which can be observed in the vibrational spectra.
Electronic spectra and crystal field analysis of
Chemical Physics Letters, 2007
The 10 K electronic absorption spectrum of Cs 2 NaTmF 6 together with the 355 nm and 455 nm excited luminescence spectra of Cs 2 NaYF 6 :Tm 3+ (1 and 10 at.% Tm 3+ ) have been recorded and assigned in detail. Vibrational structure in the sidebands of the electronic transitions is analogous to that in the spectra of the hexachloroelpasolite systems except that the phonon dispersion is greater. The resulting 4f 12 energy level dataset has been analyzed by a crystal field model including the configuration interaction with the ligand to metal charge transfer configuration. The previously published spectra of Rb 2 NaTmF 6 and Rb 2 NaYF 6 :Tm 3+ have been reinterpreted and shown to be consistent with the present results.
Inorganic Chemistry, 1991
The effects of zero-point energy and counterion on the rate of intramolecular electron transfer in mixed-valence biferrocenium salts are investigated. All asymmetrically substituted biferrocenium triiodide salts, where the substituent is either 1'-ethyl (9), 1'-butyl (IO), I'-acctyl (ll), 1'-butyryl (12), or 1'-ethyl 6'-propyl (13), are found to be localized on the Miwsbauer, EPR, and IR time scales. In 300 K Miwsbauer spectra they each show two doublets, one for Fe" metallocene and the other for Fell' metallocene (electron-transfer rates less than -IO7 s-'). The cation in each of compounds e 1 3 is not symmetric; that is, the two irons are not in equivalent environments. This asymmetry induces a nonzero zero-point energy barrier for intramolecular electron transfer. The effects on the rate of electron transfer of replacing 13by picrate (14), IBrF (IS), and PF6-(16) in 2 are also examined. Replacing 13by picrate and IBr, leads to a decrease in the rate of electron transfer. The Miwsbauer spectrum taken at 300 K for 14 consists of two doublets. In other words, the electron-transfer rate of 14 is less than -lo7 s-l. In the case of 15, the variable-temperature (100-275 K) Miwsbauer spectra exhibit a localized electronic structure. The PFC salt is converted from valence trapped at low temperatures to valence detrapped above 280 K. The difference in electron-transfer rates can be explained by the magnitude of the energy barrier of charge oscillation in anions and cation-anion interactions. Hendrickson, D. N.; Oh, S. M.; Dong, T.-Y.; Kambara, T.; Cohn, M. J.; Moore. M. F. Comments Inorg. Chem. 1985, 4 (6), 329. Dong, T.-Y.; Cohn, M. J.; Hendrickson, D. N.; Pierpont, C. G. J. Am. Chem. Soc. 1985, 107, 4777. Cohn, M. J.; Dong, T.-Y.; Hendrickson, D. N.; Geib, S. J.; Rheingold, A. L. J . Chem. SOC., Chem. Commun. 1985. 1095. Dong, T.-Y.; Hendrickson, D. N.; Iwai, K.; Cohn, M. J.; Geib, S. J.; Rheingold, A. L.; Sano, H.; Motoyama, 1.; Nakashima, S . J. Am. Chem. SOC. 1985. 107, 7996. Iijima, S.; Saida, R.; Motoyama, 1.; Sano, H. Bull. Chem. SOC. Jpn. 1981, 54, 1375. Nakashima. S.; Masuda, Y.; Motoyama, I.; Sano, H. Bull. Chem. Soc. Jpn. 1981, 60, 1673. Nakashima, S.; Katada. M.; Motoyama, I.; Sano, H. BUN. Chem. Soc. The binding structures of enantiomeric and racemic [M(phen)J2+ (M = Ru, Fe; phen = ],IO-phenanthroline) complexes with