Evaluation of the Solid State Dipole Moment and Pyroelectric Coefficient of Phosphangulene by Multipolar Modeling of X-ray Structure Factors

Abstract

The electron density distribution of the molecular pyroelectric material phosphangulene has been studied by multipolar modeling of X-ray diffraction data. The “in-crystal” molecular dipole moment has been evaluated to 4.7 D corresponding to a 42% dipole moment enhancement compared with the dipole moment measured in a chloroform solution. It is substantiated that the estimated standard deviation of the dipole moment is about 0.8 D. The standard uncertainty (s.u.) of the derived dipole moment has been derived by splitting the dataset into three independent datasets. A novel method for obtaining pyroelectric coefficients has been introduced by combining the derived dipole moment with temperature-dependent measurements of the unit cell volume. The derived pyroelectric coefficient of 3.8(7)×10−6 C m−2 K−1 is in very good agreement with the measured pyroelectric coefficient of p=3±1×10−6 C m−2 K−1. This method for obtaining the pyroelectric coefficient uses information from the X-ray diffraction experiment alone and can be applied to much smaller crystals than traditional methods. Elektrontæthedsfordelingen i det molekylære pyroelektriske materiale phosphangulen er blevet undersøgt ved multipolmodelering af røntgendiffraktionsdata. Det molekylære dipolmoment i fastfase er blevet evalueret til 4.7 D, hvilket svarer til en 42 % forøgelse af dipolmomentet sammenlignet med dipolmomentet målt i en kloroformopløsning. Det er godtgjort, at den estimerede standardafvigelse på dipolmomentet er omkring 0.8 D. Det udledte dipolmoment er blevet kombineret med temperaturafhængige målinger af enhedscellevolumet til beregning af den pyroelektriske koefficient. Den herved beregnede værdi på 3.8(7)×10−6 C m−2 K−1 viser en meget god overensstemmelse med den målte pyroelektriske koefficient på p=3±1×10−6 C m−2 K−1. Denne metode til udledelse af den pyroelektriske koefficient bygger alene på information opnået fra røntgendiffraktionseksperimentet og kan anvendes på meget mindre krystaller end traditionelle metoder behøver. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2000/f1964_s.pdf or from the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.