The physico-chemical properties and thermal stability in air of Cu(II) 2,3- , 3,5- and 2,6-dimethoxybenzoates were compared and the influence of the position of -OCH3 substituent on their thermal stability was investigated. The complexes are crystalline, hydrated salts with blue colour. The carboxylate ion is a bidentate chelating or bridging group. The thermal stability of analysed Cu(II) dimethoxybenzoates was studied in the temperature range of 293-1173 K. The positions of methoxy- groups in benzene ring influence the thermal properties of studied complexes. Their different thermal properties are markedly connected with the various influence of inductive, mesomeric and steric effects of -OCH3 substituent on the electron density in benzene ring. The magnetic susceptibilities of the complexes were measured over the range of 76-300 K and the magnetic moments were calculated. The results show that they form dimers.

Os anions complexos do ácido 2,6-dimetóxibenzóico com ions de Co(II), Ni(II) e Cu(II) foram sintetizados como sólidos policristalinos e caracterizados por análise elementar, espectroscopia, estudos magnéticos e também por medidas de difratometria de raios X e termogravimetria. Os complexos analisados apresentaram a seguinte coloração: rosa para os compostos deCo(II), verde para os compostos de Ni(II) e azul para os compostos de Cu(II). O grupo carboxilato se liga como monodentado, bidentado em ponte e ligantes quelatos. No aquecimento ao ar até 1173 K os complexos se decompõem em quatro, três ou duas etapas. Inicialmente, eles se desidratam para sais anidros em uma ou duas etapas, decompondo-se em seguida para os respectivos óxidos metálicos. A solubilidade em água a 293 K dos dimetoxibenzoatos analisados é em torno de 10-2 mol/dm3. Seus momentos magnéticos foram determinados no intervalo de temperatures entre 76-303 K. Os resultados mostraram que os compostos de Co(II) e Ni(II) são complex-os de spin elevado e que os compostos de Cu(II) formam dímeros.

The complexes of 2,6-dimethoxybenzoic acid anion with ions of Co(II), Ni(II), and Cu(II) have been synthesized as polycrystalline solids, and characterized by elemental analysis, spectroscopy, magnetic studies, and also by X-ray diffraction and thermogravimetric measurements. The analysed complexes have following colours: pink for Co(II), green for Ni(II), and blue for Cu(II) compounds. The carboxylate group binds as monodentate, and bidentate bridging and chelating ligands. On heating in air to 1173 K the complexes decompose in four, three or two steps. At first, they dehydrate in one or two steps to anhydrous salts, that next decompose to oxides of the respective metals. The solubility of the investigated dimethoxybenzoates in water at 293 K is of the order of 10-2 mol/dm3. Their magnetic moments were determined in the temperature range of 76-303 K. The results reveal the compounds of Co(II) and Ni(II) to be high-spin complexes and that of Cu(II) to form dimer.