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The crystal structure of monoclinic HfO2 was determined using Weissenberg techniques. Data were obtained from a needlelike single crystal which was grown from a lithium molybdate melt. The crystal was rotated about the α axis, and reflection data were obtained for nine levels. A three‐dimensional least‐squares refinement confirms that monoclinic hafnia is isomorphous with monoclinic zirconia. The atomic coordinates in the structures agree within one standard deviation. Thus, the fractional coordinates for the metal atom differ by less than 0.0005 and those for the oxygen atoms by no more than 0.01. Whereas three of the seven Hf–O distances are larger than the corresponding Zr–O distances, the average value is approximately 0.01 Å smaller. The average metal‐metal distance is approximately 0.02 Å less in HfO2 than in ZrO2.

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The structure of the synthetic deoxydodecamer d(C-G-C-I-A-A-T-T-A-G-C-G) has been determined by single crystal X-ray diffraction techniques at 2.5A resolution. The refinement converged with a crystallographic residual, R = 0.19 and the location of 64 solvent molecules. The sequence crystallises as a B-DNA helix with 10 Watson-Crick base-pairs (4 A.T. and 6 G.C) and 2 inosine.adenine (I.A) pairs. The present work shows that in the purine.purine base-pairs the adenine adopts syn orientation with respect to the furanose moiety while the inosine is in the trans (anti) orientation. Two hydrogen bonds link the I.A. base-pair, one between N-1(I) and N-7(A), the other between O-6(I) and N-6(A). This bulky purine.purine base-pair is incorporated in the double helix at two positions with little distortion of either local or global conformation. The pairing observed in this study is presented as a model for I.A base-pairs in RNA codon-anticodon interactions and may help explain the thermodynamic stability of inosine containing base-pairs. Conformational parameters and base stacking interactions are presented and where appropriate compared with those of the native compound, d(C-G-C-G-A-A-T-T-C-G-C-G) and with other studies of oligonucleotides containing purine.purine base-pairs.

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