The Crystal Structures of Nickel(II) and Cobalt(II) 2,6-Naphthalenedicarboxylate Tetrahydrate

Researchers at BP Chemicals and Searle have used computational chemistry techniques to understand the crystal structures of nickel(II) and cobalt(II) 2,6-naphthalenedicarboxylate tetrahydrate, by-products in the production of dimethyl 2,6-naphthalenedicarboxylate (NDC), a new chemical intermediate that leads to high performance polyesters.

Understanding the nature of these solids will aid in determining the causes of their formation, and thus yield process improvements.

Dimethyl 2,6-naphthalenedicarboxylate (NDC) is an important chemical intermediate that leads to high-performance polyesters. For example, NDC can be hydrolyzed to produce naphthalenedicarboxylic acid, a higher performing substitute for terephthalic acid in liquid-crystal polyester applications. Polybutylene naphthalate, a homopolymer alternative to polybutylene terephthalate with improved chemical and thermal resistance and higher tensile strength, can be produced from NDC.

Commercial NDC is manufactured from 2,6-dimethylnaphthalene which undergoes catalytic homogeneous oxidation to produce naphthalenedicarboxylic acid (NDA). The NDA produced is then esterified to yield NDC. Carboxylate salts of catalyst and corrosion metals are occasionally recovered from the process. An understanding of the crystal structures of these carboxylate salts would give an insight in to their formation and hence inhibition.

James A. Kaduk of BP Chemicals and Jason A. Hanko of Searle have used computational chemistry techniques to gain such an understanding. The scientists first prepared fine-powder samples of the nickel(II) and cobalt(II) 2,6-naphthalenedicarboxylate tetrahydrate salts. Powder patterns revealed the two compounds to be isostructural. The NDA dianion was built and optimized using the COMPASS forcefield. The model structure was derived using the Powder Solve method (available in Reflex Plus) and then refined using standard Rietveld techniques on laboratory powder diffraction data. Quantum mechanical optimization using CASTEP located the water molecule hydrogen atoms. Hydrogen bonds are important features of the crystal structure and also determine the conformation of the coordinated anion.

Dr James Kaduk, Research Associate Chemist, BP Chemicals, comments, "Computational chemistry techniques gave us valuable insight in to the crystal structures of the two salts that would have been difficult to obtain by conventional methods that only give partial structural information." Kaduk continues "Knowing the crystal structures helped us understand how such compounds form in our processes and gave us ideas on how to inhibit their formation."

Reference

1. J. A. Kaduk and J. A. Hanko, 'Salts of Aromatic Carboxylates: The Crystal Structures of Nickel(II) and Cobalt(II) 2,6-Naphthalenedicarboxylate Tetrahydrate', J. Appl. Crystallogr., 2001, 34, 720-714.