Non-covalent interatomic interactions, particularly hydrogen bonds, have been studied through systematic analysis of published crystallographic data, and through the determination of novel crystal structures. Chapters 1-3 give relevant background on crystal structure analysis and describe the available crystallographic databases.

Chapters 4 and 5 utilise the Cambridge Structural Database to examine the hydrogen bond acceptor abilities of nitrogen and sulphur. Chapter 4 examines non bonded N---H interactions in the Csp$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$-NR$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ fragment and, specifically, hydrogen bond formation during the Nsp$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$➔Nsp$\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$ transition. Chapter 5 investigates the hydrogen bonds formed by 'univalent' (i.e C=S) and 'divalent' (i.e -S-) sulphur, and compares the results with data for their oxygen analogues.

Chapter 6 describes a novel method (NIPMAT) for representing non-bonded interactions in crystal structures. The shortest contacts for each atom in the asymmetric unit to atoms in neighbouring molecules are generated and displayed in a matrix form. A computational method is developed for visually representing and comparing the non-bonded contacts in two different crystal structures. A comparison of pairs of polymorphic structures is used to show how the method is more informative than standard visual or numerical comparisons.

Chapter 7 describes eight crystal structures: A sixteen-membered aluminium ring compound, [C$\mathrm{<mrow\; data-mjx-texclass="ORD">33</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">40</mrow>}$AI$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$N$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$O$\mathrm{<mrow\; data-mjx-texclass="ORD">8</mrow>}$], a chiral amidolithium tetrahydrofuran complex, [C$\mathrm{<mrow\; data-mjx-texclass="ORD">40</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">52</mrow>}$LI$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$N$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$O$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$], a hydrogen bonded primary amine-phosphine oxide adduct, [C$\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">27</mrow>}$N4O4PS], an organic phosphus oxide, [C$\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">38</mrow>}$NO$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$P], an aqua magnesium complex, [C$\mathrm{<mrow\; data-mjx-texclass="ORD">26</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">50</mrow>}$MgN$\mathrm{<mrow\; data-mjx-texclass="ORD">14</mrow>}$O$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$P$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$S$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$], a tetrameric lithium complex, [C$\mathrm{<mrow\; data-mjx-texclass="ORD">60</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">72</mrow>}$Li$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$N$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$O$\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}$], lithium dithioato tetramethylethylene diamine [C$\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">23</mrow>}$LiN$\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$S$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$], l,4-dimethoxy-2-(pyrazol-3-yl)-benzene, [C$\mathrm{<mrow\; data-mjx-texclass="ORD">11</mrow>}$H$\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}$N$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$O$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$].