On the temperature dependence of the hydrogen bond order in squaric acid: neutron diffraction studies at four different temperatures1
Abstract
The crystal structure of squaric acid [3,4-dihydroxy-3-cyclobutene-1,2-dione, H2C4O4, M = 114.1] has been determined from neutron diffraction data at 15 K, Tc − 21 K, Tc − 13 K and Tc + 5 K below and above the phase transition at 374 K. The space group of the material is monoclinic P21/m from 15 K and up to Tc and tetragonal I4/m above. After corrections for absorption and thermal diffuse scattering, least-squares refinements were carried out with 69 variable parameters in the model below Tc and 25 above Tc. The analysis of difference vibrational parameters along the C–O internuclear direction strongly suggest that the high-temperature structure has a disordered C4O4 unit. In agreement with previous findings, the protons are distributed on two principal positions 0.53 Å apart along the O … O hydrogen bond above Tc. In the low-temperature phase, an increasing amount of disorder with increasing temperature is found, particularly in the protonic positions. However, the protons in the two different hydrogen bonds show distinctly different behavior, and hence immediately below Tc different degrees of order are found along the x- and z-directions. These structural findings are discussed in the light of the 1-D correlations observed in the material.
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Artikel in diesem Heft
- Beta-succinic acid, a crystal of extreme elastic anisotropy
- Coordination sequences for lattices
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- The crystal structure of In7Br9
- The crystal structure of EuZnGe and its relation with EuGe2
- Synthesis, structure and thermal behavior of benzyltrimethylammonium trihydrogen selenite
- On the temperature dependence of the hydrogen bond order in squaric acid: neutron diffraction studies at four different temperatures1
- Structure of the 1,7-bis(dimethylamino)heptamethinium dye in crystals of the picrate salt
- A monoclinic polymorph of tris(1,3-diphenylpropane-1,3-dionato)-cobalt(III)
- Crystal structure of potassium aluminium fluoride phosphate, KAlFPO4
- Crystal structure of yttrium carbide iodide (10-4-18), [Y10(C2)2]I18
- Crystal structure of caesium yttrium carbide iodide (1-10-4-18), Cs[Y10(C2)2]I18
- Crystal structure of dipotassium lithium diarsenidoindate, K2LiInAs2
- Crystal structure of 1-(1-adamantyl)-1-methylethoxycarbonyl-L-proline, C19H29NO4
- Crystal structure of dichlorobis(triphenylphosphine)nitridotechnetium(V), TcNCl2((C6H5)3P)2
- Crystal structure of 5-hydroxymethyl-5-methyl-2-thiophenyl-1,3,2-dioxa-phosphorinane-2-one, C11H15O4PS
- Crystal structure of μ-iodo-bis[(3,3′-trimethylenedinitrilo-bis-(2-butanoneoximato)-difluoroborate)copper(II)] perchlorate bis-(methonal), ((C3H6N2(C4H6NO)2BF2)Cu)2I ClO4(CH3OH)2
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- Crystal structure of scandium cadmium, ScCd7
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- Complete Minimal Surfaces of Finite Total Curvature. Mathematics and its applications. Vol. 294.
- Handbook on the Physics and Chemistry of Rare Earths. Vol. 17: Lanthanides/Actinides: Physics-1.
- Crystallographic Computing 6. A Window on Modern Crystallography.
- Crystal Structure Analysis for Chemists and Biologists.
