Single-crystal neutron refinement of creatine monohydrate at 20 K and 123 K

Abstract

The molecular structure and bonding of guanidine and related compounds have been a source of considerable interest for theoretical chemists over the past 30 years. Here we present a study of one such compound, creatine monohydrate, using low-temperature pulsed neutron diffraction data to refine the known X-ray crystal structure. The molecule crystallises in space group P2 ₁ /c with a=12.492(4), b=4.967(1), c=12.051(4) Å, β=109.10(2)° at 20 K and a=12.489(7), b=4.987(1), c=12.075(6) Å, β=108.86(3)° at 123 K, Z=4. The final refinements included anisotropic temperature factors on all atoms and converged to wR(F)=0.055 at 20 K and 0.045 at 123 K (190 parameters). The extensive network of hydrogen bonds is now well defined, and a thermal parameter analysis reveals significant torsional motion of the methyl group at both temperatures.