High-throughput methods have been employed to study the system Co2+/(H2O3PCH2)(2)NCH2C6H4COOH/NaOH in detail, The use of the phosphonocarboxylic acid (H2O3PCH2)(2)NCH2C6H4COOH has led to several new cobalt carboxyaryl phosphonates under hydrothermal conditions. In addition to the effect of the pH of the starting mixture, the influence of the counterions of the cobalt salts on the product formation was investigated, Thus, reaction trends as well as fields of formation could be identified. Four new compounds Co-2[(O3PCH2)(2)NCH2C6H4COOH]center dot H2O (1), Co[(O3PCH2)(OCH)NCH2C6H4COOH]center dot H2O (2), Co[H-2(O3PCH2)(2)NCH2C6H4COOH] (3), and [CO2(O3PCH2)(2)NCH(2)C(6)Hr COOH]center dot 3.5H(2)O (4) were obtained, and compounds 1 and 2 could be isolated as single crystals suitable for singlecrystal X-ray diffraction. The counterions of the cobalt salts have an influence on the structure of the resulting compounds. This is due to the effect on the initial pH as well as the possibility of the counterions to take part in redox reactions. Compounds 1 and 4 are formed under more basic conditions, and the phosphonic acid group is fully deprotonated. The structure of I is a rare example of the family of inorganic-organic hybrid materials with iminobis(methylphosphonic acid) units wherein the nitrogen coordinates to the metal center. Compound 2 is the result of an in situ oxidation of one of the P-C bonds; the organic building unit is stabilized by complexation of the cobalt ion. On the basis of spectroscopic, thermogravimetric, elemental chemical analysis, and EDX-analysis data, compound 3 has been characterized as CO[H-2(O3PCH2)(2)NCH2C6H4COOH] and compound 4 as [Co-2(O3PCH2)(2)NCH2C6H4COOH]center dot 3.5H(2)O. X-ray powder diffraction and IR-spectroscopic studies show that thermal treatment of 4 leads to the title compound 1. This transformation is accompanied by a change of color from pink to deep blue.