Strong piezoelectricity in [H-β-(2-pyridyl)-Ala-OH][BF₄] and [H-β-(2-pyridyl)-Ala-OH][ClO₄] – new amino acid based hybrid crystals

Abstract

New amino acid based crystals were synthesized and their structure and functional piezoelectric properties were determined. PFM measurements revealed that the piezoelectric coefficient, d15eff, of the [H-β-(2-pyridyl)-Ala-OH][BF4] crystal is more than twice that in LiNbO3.

Crystal Structure and Strong Piezoelectricity of New Amino Acid Based Hybrid Crystals: [H-β-(3-Pyridyl)-Ala-OH][ClO4] and [H-β-(4-Pyridyl)-Ala-OH][ClO4]

“…The geometrical parameters (bond lengths and angles) for two organic molecules in the crystals are very similar and are in good agreement with those reported for the related compounds, such as [2PyAla]­[ClO 4 ] and [2PyAla]­[BF 4 ] , corroborating the protonation of both the amine and pyridine nitrogen atoms. One of the C–H groups of the pyridinium ring forms an intramolecular C–H···O hydrogen bond with O atom of the carboxyl group as a result of tilting the latter group toward the pyridinium ring (Figure a,b).…”

“…The corresponding O–ClO angles are within 108.97(11)–110.31(11)° for the former and 108.68(12)–110.24(14)° range for the latter compound, respectively. It is worthy of note that another amino acid–inorganic acid hybrid salt [2PyAla]­[ClO 4 ] may be characterized by very similar values of these angles, whereas the Cl–O bonds are slightly shorter …”

“…It should be emphasized that the IP signal is several times higher than the OOP one as it was in the case of [3PyAla]­[ClO 4 ] crystals. It is worthy of note that the concretion of crystals was present also in H-β-(2-pyridyl)-Ala-OH and [2PyAla]­[ClO 4 ] . Most probably the way of preparation of the sample on the substrate (see Experimental Section) may lead to the growth of nonuniform microcrystals.…”

“…It is interesting to compare the studied crystals [3PyAla]­[ClO 4 ] and [4PyAla]­[ClO 4 ] with [2PyAla]­[ClO 4 ] (i.e., the perchlorate derivative of 2-pyridyl alanine crystal, ref ). Table illustrates selected properties of these crystals (symmetry, piezoelectric properties).…”

“…Recently, we have widened the research of amino acids into the organic–inorganic materials by synthesizing hybrid salts of selected, voluminous amino acid and simple, small inorganic acids (HClO 4 , HBF 4 , etc.) derivatives . It has been shown that the tetrafluoroborate derivative of 2-pyridyl alanine exhibits piezoelectric constants higher than those of lithium niobate.…”