Thermochemical study of adducts of methylurea with zinc, cadmium, and mercury halides

Abstract

CLAUDIO AIROLDI, AECIO P. CHAGAS, and FRANCISCO P. A s s u~q i o .Can. J. Chem. 60,2132Chem. 60, (1982. The adducts Zn(mu),X, (X = CI, Br), M(mu)X, (M = Cd, Hg and X = CI, Br) have been characterized. The CO and NH stretching frequencies indicate that methylurea (mu) is bound to metals through oxygen. Enthalpies of dissolution of the adducts in ethanol or methanol have been measured calorimetrically. Combination with the enthalpies of solution of metal halides and ligand in the same solvents at 298.15 K yielded the standard enthalpy (AH,e/kJ mol-I) for the reaction: MX,(s) + nmu(s) -t M(mu),,X, (s):Zn(mu),Cl,, (-36.27k0.51); Zn(mu),Br,, (-37.52k0.97); Cd(mu)CI,, (-22.78k0.26); Cd(mu)Br,, (-9.58k0.26); Hg(mu)Cl,, (-13.91k 0.41); and Hg(mu)Br,, (-13.29k0.48). The standard enthalpies of formation of theadducts in the same sequence as above, AH,e (s, 298.15 K): -1024, -938, -70 1, -612, -524, and -470 kJ mol-', were determined from these values, the standard enthalpy of the ligand (-285k 15 kJ mol-I) being obtained via combustion calorimetry, and literature values of the standard enthalpies of metal halides being used. With the determination of the standard enthalpy of sublimation of the ligand (78.2 kJ mol-I) it was possible to determine the standard enthalpies of the reactions MX,(g)The enthalpies of metal-oxygen bonds were also estimated. Introductioninfrared studies methylurea has a nearly planar Our interest in the thermochemistry of adducts configuration of the N-C(ObN moiety with the of halides of the zinc family with urea derivatives as C-N bonds possessing appreciable double bond ligand is now focused on methylurea (mu). The character and a tendency to form hydrogen bonds determinations of crystallographic parameters for (4). It can act as a ligand utilizing either nitrogen or Cd(mu),,X, (X = C1, Br, I and n = 1, 2) and Oxygen as the d~n o r atomZn(rnu),Br, were the pioneer studies involvingFrom the results on thermal decomposition of methylurea as a ligand (1,2). Moreover, a complete CdLC1, (L = urea, and N,N'-di-X-ray diffraction pattern for Cd(mu)Cl, illustrates methylurea) adducts by therm~~ravimetric analyan interesting structure (3) where the metal is sis in air and vacuum, the following order of octahedrally coordinated, with the participation of stability was established: urea > methylurea > methylurea as a monodentate ligand. This polymer N,Nf-dimethylurea (6). his sequence clearly instructure shows one site of coordination occupied dicates an influence of ligand substituents on stabilby oxygen of the ligand carbonyl with the other ity. This is the only thermochemical datum dealing positions being occupied by chloride bridges.with the methylurea ligand. The coordination characteristic of methylurea is In Our study, the Zn(mu)*X, (X = C 1 j Br) and expected to be the same as that of N,N'-M(mu)X, (M = Cd, Hg and X = C1, Br) adducts dimethylurea (dmu) where both molecules resem-were synthesized and characterized, with special ble the urea molecule (4, 5 ) in structure. prom concern being devoted to ...

The solid state structure and reactivity of NbCl5·(N,N′-dicyclohexylurea) in solution: evidence for co-ordinated urea dehydration to the relevant carbodiimide

“…Ureas may act as ligands to transition metal systems 10 through the O-or the N-atoms: the h 1 -O, h 1 -N and h 2 -N,N¢ modes of bonding 11 have been demonstrated. [15][16][17] The renovated interest in metal complexes (Mn II , Co II , Ni II , Cu II , Zn II , lanthanides) with N,N¢-dimethylurea-DMU, O-bonded to the metal, was due to their ability to form supramolecular 2D structures. Metal complexes containing 2, 4, 6 molecules of urea itself, 10,12 either O-or N-bonded have been described and a rare example of a chelate h 2 -N,N¢ mode of bonding has recently been described.…”

“…13 Metal complexes in which urea bridges two metal centres have also been characterized 14 and substituted ureas or thioureas have intensively been studied. [15][16][17] The renovated interest in metal complexes (Mn II , Co II , Ni II , Cu II , Zn II , lanthanides) with N,N¢-dimethylurea-DMU, O-bonded to the metal, was due to their ability to form supramolecular 2D structures. 18 Despite such abundance of cases, very rare studies on the reactivity of co-ordinated ureas are available in the literature: Ti-urea complexes have been thermally decomposed to afford nanoparticles of TiO 2 , 19 while Ni II -urea complexes have been reported to show an urease-like action.…”

Síntese e termoquímica de adutos de brometos de metais bivalentes com aminas hetrocíclicas

“…A variação entálpica padrão de reação na fase gasosa é determinada por meio da seguinte reação: Não é possível se determinar a variação entálpica de sublimação dos adutos devido à que eles se decompõem por aquecimento [94]. Foi considerada a aproximação em que a variação entálpica de sublimação do aduto é igual à média das variações entálpicas de sublimação dos brometos metálicos e do ligante [93,95].…”