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Self-healing crystals and polymorphism in nickel(II) complex with glycinamide

Complexes of essential metals and amino acids and their derivatives are often investigated as model systems for metal-protein interactions [1], and also for their biological activity, due to bioavailability and non-toxicity of amino acids [2]. Amino acids are also interesting compounds for investigation in crystal engineering since they are capable of forming various types of noncovalent interactions [3]. Glycinamide is the simplest amino acid amide, but it is poorly investigated in the solid state. As part of our research of glycinamide (glyam) complexes of essential metals, we have prepared complex [Ni(H2O)2(glyam)2]I2 (1). Two polymorphs of the complex were obtained – room temperature, 1RT, and low temperature polymorph, 1LT, stable at temperature < 200K. 1RT crystallizes in the orthorombic crystal system, space group Pnma, while 1LT crystallizes in monoclinic crystals system, space group I2/a. When a crystal of 1RT is cooled down, below 200 K, it transforms into 1LT and breaks into two sets of differently oriented domains, hence some diffraction maxima are split into two and new ones appear in the diffraction images after transition (Figure 1). The process is reversible so when crystals of 1LT are heated back over the transition temperature a single crystal of 1RT is obtained again. This transition will be discussed in more details.

polymorphism, glycinamide, nickel(II) complexes, reversible phase transition, self-healing crystal

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