Polymorphism of 2‑Adamantanone

Abstract

The polymorphism of 2-adamantanone (C₁₀H₁₄O) has been investigated by means of X-ray diffraction and high-pressure thermal analysis. The intricate behavior of the low-temperature crystalline phases has been disentangled. The stable phase has been found to be orthorhombic (<i>Cmc2</i>₁, <i>Z</i> = 4), fully ordered, with lattice parameters <i>a</i> = 6.8884(18) Å, <i>b</i> = 10.830(3) Å, <i>c</i> = 10.658(3) Å, and <i>V</i>/<i>Z</i> = 198.8(1) ų. The metastable phase was determined to be monoclinic (<i>P</i>2₁/<i>c</i>, <i>Z</i> = 4) with lattice parameters <i>a</i> = 6.5920(17) Å, <i>b</i> = 11.118(3) Å, <i>c</i> = 12.589(3) Å, β= 118.869(11) ^o, and <i>V</i>/<i>Z</i> = 202.0(1) ų. The pressure–temperature phase diagram irrefutably shows the stability relation between both phases and, accordingly, the long-time unknown polymorphic behavior is now revealed and gives coherent physical explanation of the literature published so far