Ingrid Svoboda

Alkalicyamelurates, M3[C6N7O3].xH2O, M = Li, Na, K, Rb, Cs: UV-luminescent and thermally very stable ionic tri-s-triazine derivatives.

Cyamelurates are salts of cyameluric acid, a derivative of tri-s-triazine (1,3,4,6,7,9-hexaazacyclo[3.3.3]azine or s-heptazine). These compounds are thermally very stable and possess interesting structural and optical properties. Only very few tri-s-triazine derivatives have been reported in the literature. The water-soluble alkali cyamelurates were extensively characterized using NMR, FTIR, Raman, UV, luminescence spectroscopy and elemental analysis. In addition, the single crystal X-ray structure analyses of the four hydrates of lithium, sodium, potassium and rubidium cyamelurates (Li(3)[C(6)N(7)O(3)].6H(2)O; Na(3)[C(6)N(7)O(3)].4.5H(2)O; K(3)[C(6)N(7)O(3)].3H(2)O; Rb(3)[C(6)N(7)O(3)].3H(2)O) are presented. Thermogravimetric analysis shows that the dehydrated salts start to decompose at temperatures above 500 degrees C. The thermal stability does not depend on the cations which is in contrast to the analogous s-triazine salts, i.e. the alkali cyanurates M(3)[C(3)N(3)O(3)]. The photoluminescence spectra indicate a very strong solid state UV-emission with maxima between 280 and 400 nm.

Potassium melonate, K3[C6N7(NCN)3]·5H2O, and its potential use for the synthesis of graphite-like C3N4 materials

Melonates, Mx3/x[C6N7(NCN)3], contain the aromatic and planar tricyanamino-s-heptazine anion. Only one example, the potassium derivative, has been isolated in pure form so far, but it has never been characterised comprehensively. Potassium melonate is obtained from a reaction of the polymer melon, [C6N9H3]n, with KSCN. 13C NMR, FTIR, Raman, UV-vis and luminescence spectroscopy support the proposed molecular structure. The crystal structure of the hydrate K3[C6N7(NCN)3]·5H2O was determined by single crystal X-ray analysis (MoKα: Pbca (no. 161), a = 6.538(2), b = 24.033(6), c = 23.684(6) A and Z = 8). Thermogravimetric analysis shows that the dehydrated salt starts to decompose at temperatures above 500 °C. The [C6N7(NCN)3] unit is an ideal molecular building block for carbon(IV) nitrides, especially s-heptazine based graphite-like C3N4 networks.

Synthesis, reactivity and magnetochemical studies on copper(II) complexes derived from N-salicylidenearoylhydrazines. X-ray structure of [mononitratoOO( -1) (N-salicylidenatobenzoylhydrazine) - ONO( -1)]copper(II) monohydrate

Abstract A series of new mononuclear and binuclear copper(II) complexes derived from N-salicylidenearoylhydrazines (H2L) of the types K2[{Cu(L)(OH)}2]·nH2O, [Cu(HL)Cl·H2O]·nH2O, [{Cu(HL)Cl}2], [Cu(HL)NO2]·H2O, [{Cu(HL)}2]·2NO3, [{Cu(HL)H2O}2]·2NO3·nH2O and [Cu(HL)NCS]·H2O have been prepared and characterized. The X-ray crystal and molecular structure of [Cu(HSBzh)NO3]·H2O, where HSBzh refers to the mononegative N-salicylidenebenzoylhydrazine anion, has been determined. The complex is monomeric with the copper(II) adopting a (4+1) distorted square pyramidal coordination, with the ONO aroylhydrazone tridentate anion and an oxygen atom of the unsymmetric bidentate nitrate ion occupying the basal plane. The fifth coordination site is occupied by the other oxygen of the nitrate ion. The magnetic susceptibilities of both mononuclear and binuclear complexes were measured within the temperature range 4.2–298 K. All binuclear copper(II) complexes show strong antiferromagnetic interactions, and the singlet–triplet separation (−2J) recorded for μ-dihydroxy bridged complexes K2[{Cu(L)OH}2}]·nH2O are within the range 172–276 cm−1, while (−2J) for binuclear complexes [{Cu(HL)Cl}2], [{Cu(HL)}2]·2NO3 and [{Cu(HL)H2O}2]·2NO3·nH2O are respectively within the range 400–460, ca. 340 and ca. 390 cm−1. There are no appreciable exchange interactions between copper(II) ions in the monomeric complexes [Cu(HL)Cl·H2O]·nH2O, [Cu(HL)NO2]·H2O and [Cu(HL)NCS]·H2O. The IR spectra of the prepared complexes are also discussed.

Synthesis, magnetochemical studies and X-ray molecular structures of some mononuclear copper(II)–1H-pyrazole adducts and mono(μ-pyrazolate) bridged dicopper(II) complexes derived from N-salicylidenearoylhydrazines

Abstract 1H-Pyrazole complexes, [Cu(HL)HPz Cl] nH2O and [Cu(L)HPz] nH2O were prepared and characterized, where HL and L, respectively, refer to the mononegative and dinegative N-salicylidenearoylhydrazine anions. The X-ray crystal and molecular structure of [monochloro(N-salicylidenebenzoylhydrazinato)ONO(−1)monopyrazole] copper(II) monohydrate, [Cu(HSBzh)HPz Cl] H2O, and [(N-salicylidenebenzoylhydrazinato)ONO(−2)monopyrazole] copper(II) hemihydrate, [Cu(SBzh)HPz] 1/2H2O, were determined. The Cu(II) in [Cu(HSBzh)HPz Cl] H2O is in a distorted square pyramidal environment and is bound in the equatorial plane with the mononegative tridentate aroylhydrazone anion and pyrazole nitrogen, the axial fifth coordination site is occupied by a chloride ion. On the other hand, the complex [Cu(SBzh)HPz] 1/2H2O consists of two monomeric crystallographically independent but chemically similar molecules. In each molecule, the Cu(II) is in a distorted square planar geometry and is coordinated to the dinegative tridentate aroylhydrazone via the phenoxy oxygen, azomethine nitrogen and enolimide oxygen, and the fourth coordination site is occupied by the pyrazole nitrogen. The mono(μ-pyrazolate) dicopper(II) complexes, K[Cu2(L)2Pz] nH2O, were also prepared and the X-ray molecular structure of K2[Cu4(SBzh)4(Pz)2] 2H2O 1/2CH3OH was determined. In this complex, two copper(II) atoms are bridged by only one pyrazolate anion forming a dicopper mono(μ-pyrazolate) unit. Each two units are connected together by a five coordinate K+ cation forming a tetranuclear assembly. These tetranuclear assemblies are connected together by another K+ cation forming a supramolecular structure. Variable temperature magnetic studies on these pyrazolate complexes indicated antiferromagnetic behaviour with −2J values varying from 25 to 36 cm−1.

Some new NiZn heterodinuclear complexes: square-pyramidal nickel(II) coordination

A new series of heterodinuclear nickel(II)zinc(II) complexes, [NiL·ZnCl 2 ·4-picoline] ( 1 ), [NiLDM·ZnCl 2 ·4-picoline] ( 2 ), [NiL·ZnBr 2 ·4-picoline] ( 3 ), [NiLDM·ZnBr 2 ·4-picoline] ( 4 ), [NiLDM·ZnBr 2 ·3-picoline] ( 5 ), [NiLDM·ZnBr 2 ·3,5-lutidine] ( 6 ) and [NiL·ZnI 2 ·4-picoline] ( 7 ), where L is N , N ′-bis(salicylidene)-1,3-diaminopropane dianion and LDM is N , N ′-bis(salicylidene)-2,2′-dimethyl-1,3-diaminopropane dianion, were prepared. The complexes were characterized by elemental analysis, thermogravimetric analysis and IR spectroscopy. X-ray crystallographic analysis of complexes 1 , 2 and 4 revealed that nickel(II) ion in heteronuclear complexes had a square-pyramidal coordination sphere. It is concluded that formation of square-pyramidal nickel(II) coordination depends strongly on the concentration of methyl pyridine present in the medium and occurs when methyl pyridine/Ni ratio is below 1.5.

Synthesis, characterization and magnetochemical studies of some imidazole and imidazolate copper(II) ternary complexes derived from N-salicylidenearoylhydrazines. X-ray crystal and molecular structures of [(N-salicylidene-p-chlorobenzoylhydrazine)ONO(−2)imidazole]copper(II) monohydrate and dimeric [(N-salicylidene-p-methylbenzoylhydrazine)ONO(−2)imidazole]copper(II) hemihydrate

Abstract The reactions of imidazole (Him) with N-salicylidenearoylhydrazine copper(II) complexes have been studied and a number of ternary copper(II) complexes, [Cu(L)Him]·nH2O, [Cu(HL)X·Him]·nH2O and [{Cu(L)}2Im]·nH2O, have been prepared and characterized (HL and L refer, respectively, to mono- and dinegative N-salicylidenearoylhydrazine anions and X is a mononegative monodentate ligand). The X-ray crystal and molecular structure of [(N-salicylidene-p-chlorobenzoylhydrazine)imidazole]copper(II) monohydrate, [Cu(Sp-ClBzh)Him]·H2O, and [(N-salicylidene-p-methylbenzoylhydrazine)imidazole]copper(II) hemihydrate, [Cu(Sp-CH3Bzh)Him]·1/2H2O, were measured. The p-chloro complex [Cu(Sp-ClBzh)Him]·H2O is monomeric with the Cu(II) in a distorted square planar environment and is coordinated to the tridentate hydrazone via phenoxy oxygen, azomethine nitrogen and enolimide oxygen, the fourth coordination site is occupied by the imidazole nitrogen. The p-methyl complex [Cu(Sp-CH3Bzh)Him]·1/2H2O was found to be a centrosymmetric dimer, the monomeric unit being bridged through the phenoxy oxygen. The Cu(II) is in a square pyramidal environment and is bounded in the equatorial plane with the enolimide oxygen, azomethine nitrogen and phenoxy oxygen of the hydrazone ligand while the fourth site is occupied by the symmetry related phenoxy oxygen of the other unit; the axial fifth coordination site is occupied by the imidazole nitrogen. The magnetic susceptibility measurements at different temperatures (5–298 K) have been recorded and are discussed. The binuclear imidazolate complexes show antiferromagnetic exchange coupling interactions, the measured −J values are within the range 17.0–20.0 cm−1, while the imidazole complexes do not show any appreciable exchange interactions.

Spectroscopic and magnetic properties and structure of a five-coordinate, O2-binding cobalt(II) Schiff base complex and of the copper(II) analogue

Abstract The cobalt(II) complex CoL and the copper(II) complex CuL of the pentadentate O 2 N 2 N′ Salen-type Schiff base ligand H 2 L = N, N ′-bis(3-t-butyl-2-hydroxy-5-methylbenzyliden)-1, 7-diamino-4-methyl-4-azaheptane were prepared, characterized and subjected to single crystal X-ray analysis. The {MO 2 N 2 N′} coordination core forms a trigonal bipyramid differing in the degree of distortion, as expressed by the O-M-O angles 138.62(8)° [O-Co-O] and 155.21(7)° [O-Cu-O]. The distances between the metal and the aliphatic tertiary nitrogen atoms N′ are markedly different, 2.123(2) [Co-N′] and 2.300(2)A[Cu-N′]. In contrast to normal Salen complexes the imine nitrogen atoms are located trans to each other. Solution room temperature electron spectra show a broad absorption in the near-IR range at 6350 (CoL) and 8200 (CuL) cm −1 . The temperature dependence of the effective magnetic moment for high-spin CoL ( S =3/2) shows a maximum at 50 K, which is reproduced by the following set of magnetic parameters, reflecting the zero-field splitting; g 1 = 1.68, g 1 = 1.89, g = 3.21, D/hc = −38.9cm −1 , E/hc = 1.7cm −1 , α 110 = 0, zJ/hc = −1.00cm −1 . Variable temperature electron paramagnetic resonance experiments prove that CoL, dissolved in toluene, N, N -dimethylformamide or pyridine, binds dioxygen reversibly.

Crystal structure and spin crossover studies on bis(2,6-bis(benzimidazol-2-yl)pyridine) iron(II) perchlorate

Abstract The structure of the [Fe(bzimpy) 2 ](ClO 4 ) 2 · x H 2 O system ( x = 0.25) was determined by single crystal X-ray structure analysis. The Fe(II) ion is hexacoordinated by six donor nitrogen atoms. The magnetic properties of the complex were investigated by powder magnetic susceptibility measurements and ESR. The freshly prepared sample does not show any traces of iron(III) impurities but these are formed as a function of time. After 1 year the sample contains 8.2% iron(III) as shown by UV spectroscopy and indicated by g eff = 4.3 and 2.0 in its ESR spectrum. This explains the recorded ξ versus T behaviour at low temperature: with increasing temperature the ξ value decreases according to the Curie-Weiss law for a S = 5/2 system having an effective g = 4.3. Above 220 K a continuous increase in the ξ value is observed and a spin crossover applies. The spin transition is not complete at room temperature. A pronounced hysteresis is observed upon heating/cooling the sample between 220 and 414 K on the basis of magnetic data and infrared spectra.

Cyanamidonitrate–copper(II) complexes of imidazole ligands: X-ray crystallography and physical investigation

Abstract New cyanamidonitrate–copper(II) complexes [Cu(NO2NCN)2Ln] (L=imidazole (iz), n=2; L=iz, 1-, 2- or 4-methylimidazole (meiz), n=4) have been isolated and characterised by IR, electronic and ESR spectroscopy. The crystal structures of 1- and 4-meiz complexes have been determined by X-ray crystallography; the structure of [Cu(NO2NCN)2(iz)2] is known (J. Kožisek, J.G. Diaz, M. Hvastijova, L. Jager, Acta Crystallogr., Sect. C 53 (1997) 703). The crystal structure of the first two compounds consists of [Cu(NO2NCN)2L4] units, in which the central CuII atoms are pseudo-octahedrally coordinated by six nitrogen atoms. Four of them, in equatorial planes, originate from meiz molecules and two, in axial positions, are nitrile nitrogens from the NO2NCN− anions. Influence of hydrogen bonds on equatorial–axial bond length correlation was ascertained. In the ESR spectra of the [Cu(NO2NCN)2L4] compounds copper hyperfine splitting is resolved. For all complexes, weak lines corresponding to the ΔMs=2 transitions appear. The spectrum of [Cu(NO2NCN)2(iz)4] in frozen methanolic solution shows 16-fold nitrogen splitting of the perpendicular band.

The spectroscopic and structural properties of copper(II) complexes of the novel tridentate (ONO) pyridine N-oxide ligand Hpoxap

Abstract A tridentate ligand (Hpoxap=2-(o-hydroxyphenyliminomethyl)pyridine N-oxide) has been synthesised by the Schiff condensation of 2-pyridinecarboxaldehyde N-oxide with 2-aminophenol. A series of copper(II) complexes with this ONO-donor ligand has been prepared and their spectroscopic properties (electron, vibration, ESR) were studied. The structures for two complexes have been determined by X-ray analysis. The structure of [Cu(poxap)(OAc)] consists of isolated neutral molecules in which the copper(II) atom is situated in a slightly distorted square-planar surrounding. The structure of [Cu(poxap)(H2O)(NO3)] consists of neutral molecules which are interconnected by hydrogen bonds giving rise to a ladder structure of copper(II) ions with two different Cu⋯Cu distances of 5.27 and 7.41 A. The copper atoms are in a slightly distorted square-pyramidal environment with the tridentate ligand poxap− and the water molecule in the basal plane; the apical position being occupied by an oxygen atom of the nitrate anion. Magnetic susceptibility studies were undertaken and these confirm predominantly a dimeric character of the complex.