4-aminopyridinium Cations Research Articles

Three new thiocyanato-bridged complexes of cadmium(II): syntheses, X-ray crystal structures and thermal properties

Three new thiocyanato-bridged polymers of cadmium(II), [Cd(me4dpt)(SCN)2] n (1) [me4dpt = 3,3′-iminobis(N,N-dimethylpropylamine], [Cd(me2tn)(SCN)2] n (2) (me2tn = N,N′-dimethyl-1,3-propanediamine) and [{amphyH} {Cd(SCN)3}] n (3) (ampyH = 4-aminopyridinium cation), have been synthesized and their molecular structures determined through X-ray crystallography. In Complex 1 each square pyramidal mononuclear fragment is H-bonded (N − H…S) to form a 1D supramolecular chain. Complex 2 is a 1D coordination polymer in which each distorted octahedral cadmium(II) ion is linked with the four bridging thiocyanates and one diamine. The structure of 3 reveals anionic [Cd(SCN)3]− zigzag chains arranged in an approximately hexagonal array with the 4-aminopyridinum cations occupying triangular channels. Each chain is H-bonded (N−H…N) to form a 2D supramolecular network. Upon heating, 1 and 2 melt and transform to transparent solid masses at ambient temperature over a few days. On scratching, these turn to a fine powder. This phenomenon is repeatable. Complex 3 upon heating loses a 4-aminopyridine molecule and transforms to [H][Cd(SCN)3] at ˜ 195°C.

Crystal Structure, Hydrogen Bonding, and 81Br NQR of Low-Temperature Phase of 4-Aminopyridinium Tetrabromoantimonate(III)

Abstract The crystal structure of the low-temperature phase (LTP) of the title compound was determined at 220 K (monoclinic, P21⁄c). The 4-aminopyridinium cations (4-NH2C5H4NH+) were found to be ordered in LTP, while being severely disordered in the room-temperature phase (monoclinic, C2⁄c). The tetrabromoantimonate anions (SbBr4−) were incorporated into the infinite polyanion chains of irregular SbBr6 octahedra with two-edges sharing. The trans-Br–Sb–Br moiety in the SbBr4− anion was approximately symmetric differing from the asymmetric Br–Sb···Br moiety found in LTP of pyridinium tetrabromoantimonate(III). The N–H moieties in both of the pyridine ring and the amino (–NH2) group participate in the formation of N–H···Br hydrogen bonds. It was shown that the 81Br NQR spectrum of LTP is closely related to the anion structure and the hydrogen bonds. The distinctive anion structures, as well as the different types of phase transitions, exhibited by the PyH and 4-APyH salts, seemed to be attributable to the difference in the hydrogen bond scheme between them.

Ferroelectric properties of[4−NH2C5H4NH][SbCl4]

A ferroelectric crystal $[4\ensuremath{-}{\mathrm{NH}}_{2}{\mathrm{C}}_{5}{\mathrm{H}}_{4}\mathrm{NH}][{\mathrm{SbCl}}_{4}]$ has been synthesized. The x-ray diffraction studies indicate that it is made of polyanionic chains of $({\mathrm{SbCl}}_{4}^{\ensuremath{-}}{)}_{n}$ forming a tunnel-like structure and the 4-aminopyridinium cations connected via weak hydrogen bonds to the chlorine atoms. The x-ray and differential scanning calorimetry studies show that the crystal undergoes a complex sequence of phase transitions: ${P2}_{1}/c\stackrel{240/245\mathrm{K}}{\ensuremath{\leftrightarrow}}(\mathrm{Cc})\mathrm{CcC}2/cC2/c.$ The pyroelectric measurements reveal that $[4\ensuremath{-}{\mathrm{NH}}_{2}{\mathrm{C}}_{5}{\mathrm{H}}_{4}\mathrm{NH}][{\mathrm{SbCl}}_{4}]$ becomes ferroelectric below 270.5 K with the spontaneous polarization of the order of 3.5 ${\mathrm{m}\mathrm{C}/\mathrm{m}}^{2}$ measured along the [102] direction. The dielectric results confirm the order-disorder nature of the paraelectric-ferroelectric phase transition. The dynamics of the 4-aminopyridinium cations plays an essential role in the ferroelectric phase transition mechanism.

Spontaneous magnetization below 7.7 K based on an extended 3-D H-bonding network material: synthesis, crystal structure and magnetic properties

The structure of the complex [4-aminopyridinium][Ni(mnt)2], as determined by X-ray single crystal analysis, consists of 4-aminopyridinium cations and [Ni(mnt)2]− anions. The interactions between anions and cations via the bifurcated N(Py)–H⋯NC H-bonds give rise to a 1-D zigzag chain of alternating cations and anions, and a 3-D H-bonding network through further N(NH2)–H⋯NC interactions. χdc and χac have been measured down to 1.8 K and analysed, indicating the existence of a spin canting phenomenon. Below the critical temperature (around 7.7 K), the sample spontaneously magnetizes, and the hysteresis loop was observed at 1.85 K, corresponding parameters are as follows: Hc = 150 Oe and Mr = 7.9 emu mol−1. The pathway of the exchange interaction in this complex via H-bonding is discussed in light of the crystal structure analysis.

Potentiometric studies of cationic heteroconjugation equilibria in systems involving free and protonated pyridine derivatives in dimethyl sulfoxide

Cationic standard heteroconjugation constantsKfo (BHB1) have been determined by potentiometric titration in systems formed by 4-aminopyridinium and 4-methylpyridinium cations with 4-methylpyridine, 2-methylpyridine, and pyridine in dimethyl sulfoxide. The constants, expressed as lgKfo (BHB1), varied between 1.45 and 3.20. The most stable heterocomplex, with Kfo(BHB1) = 3.20, was formed between protonated 4-methylpyridine and pyridine. A closer scrutiny of the constant values has shown that in systems with proton donors of enhanced basicity, the constants increased with declining basicity of the proton donor at a fixed proton acceptor. Before the determination of the heteroconjugation constants, acid dissociation constants were determined for the pyridinium ion and a variety of protonated pyridine derivatives in dimethyl sulfoxide. Their pKao (BH +) values fell in the range 0.05 to 8.48 and were one to two factors of 10 lower than the corresponding pKao (BH +) values in water. Further, it was found that cationic homoconjugation equilibria were not established in the systems involving pyridine derivatives in dimethyl sulfoxide.

Organoammonium diphosphopentamolybdates(VI): influence of organic cations and anion protonation on crystal packing and geometrical features of polyanion

Four organoammonium diphosphopentamolybdate(VI) with the formulae (C 5H 7N 2) 6[P 2Mo 5O 23]·5H 2O ( 1), (C 2H 10N 2) 3[P 2Mo 5O 23]·6H 2O ( 2), Al(C 4H 15N 3) 4[HP 2Mo 5O 23] 2Cl·10H 2O ( 3) and (C 4H 12N) 4[H 2P 2Mo 5O 23]·5H 2O ( 4) have been synthesized. The crystal structures have been determined by means of single crystal X-ray diffraction data. The geometrical characteristics of the [H n P 2Mo 5O 23] (6− n)− heteropolyanions have been compared with those described in the literature for other salts. Several relationships between the protonated state and topological changes in the heteropolyanions have been found. The crystal structure in compound 1 is stabilized by electrostatic forces, an extensive network of hydrogen contacts involving anions, cations and water molecules and π–π interactions among 4-aminopyridinium cations. The anions of compound 2 are arranged in layers perpendicular to the [ 1 ̄ 10] direction. The interactions between anions are established through hydrogen contacts which involve water molecules and ethylenediammonium cations. The monohydrogendiphosphopentamolybdate(VI) anions in the crystal structure of compound 3 are joined along the [010] direction by means of strong O–H⋯O interactions ( d(O⋯O)=2.529(10) Å) which lead to a polymeric structure of [HP 2Mo 5O 23] 5− polyanions. Likewise, a similar anion polymeric arrangement is found in compound 4 in which the diprotonated polyanions are held together by means of two strong hydrogen bonds ( d(O⋯O)=2.591(6) and 2.596(6) Å).

Syntheses and chemical, spectroscopic and structural study of 4-aminopyridinium salts of dithiooxalate ligand complexes, [M(S 2C 2O 2) 2] 2− (M = Ni II, Pd II or Pt II)

The synthesis conditions, the solid state characterization and the crystal structures of three 4-aminopyridinium salts of planar inorganic dithiooxalato anions, (C 5H 7N 2) 2[M(S 2C 2O 2) 2].2H 2O where M = Ni(II), Pd(II) and Pt(II) (hereafter abbreviated as NIDT4AP, PDDT4AP, and PTDT4AP, respectively), are described. The compounds have been prepared by reaction of 4-aminopyridinium hydrochloride and the corresponding K 2[M(S 2C 2O 2) 2] in aqueous solution, and then recrystallized in N,N-dimethylformamide. The compounds have been identified by using IR, thermoanalytical, and X-ray diffraction techniques. X-ray diffraction analyses of these compounds show that all of them are isostructural and crystallize in monoclinic system, space group C2/m, Z = 2. The crystal and molecular structure of compound PDDT4AP was determined: a = 10.462(1), b = 12.020(4), c = 9.207(1) A ̊ , β = 114.44(5)°, V = 1054.1(6) A ̊ 3 , Z = 2, F(000) = 576, μ = 12.866 cm −1, M = 572.98, D o = 1.80(1), D x = 1.81 Mg· m −3, and λ( MoKα) = 0.71069 A ̊ . Final refinement led to R = 0.025 and wR = 0.030 for 1542 observed reflections with I > 3 σ(I). The unit cell is made up of bis(dithiooxalato)palladate(II) anions and 4-aminopyridinium cations forming layers, and the water molecules occupy the space among them. In the crystal structure there are some significant π-π interactions between the aromatic cations and also d z2-π interactions between the metal ion of the complex anion and the planar cations. There is also an extensive hydrogen bond network. All these types of interactions ensure the lattice cohesiveness and give to the compound a tridimensional character.