The results of the crystal structure analyses of an entirely organic compound and four transition metal derivatives are reported and the development of an interactive crystallographic computer graphics system as an aid to the interpretation and presentation of both preliminary and final structural data is discussed. The crystal structure of C₆H₅CCo₃(CO)₆C₇H₈, a product of the direct reaction of C₆H₅CCo₃(CO)₉with cycloheptatriene, has been determined by a three-dimensional X-ray analysis of data collected by counter methods. The crystals are triclinic, space group P1 with a = 8.816(3) Å, b = 8.214(2) Å, c = 13.583 Å, a= 90.69(2)º, Å= 87.43(2), β = 98.47(2)ºand z = 2. The structure was solved by conventional Patterson and Fourier methods and refinement by full-matrix least squares methods led to R = 0.062 for the 2303 reflections for which |F’|^2 > 4.5β(|F’|^2). The molecular structure is derived from the parent compound C₆H₅CCo₃(CO)₉ by the replacement of three axial carbonyl groups by one cycloheptatriene molecule so that the cycloheptatriene mean plane is approximately parallel to the Co₃ plane of the central CCo₃ tetrahedral core. Each Co atom is clearly associated with one double bond of the cycloheptatriene moiety and the mean of the associated Co-C distances is 2.18 Å. The reaction of (C₆H₅₂)PCH₂P(C₆H₅)₂ (denoted as dpm) with the compound Pd(CO)Br yields a crystalline compound (Pd(dpm)Br)₂, the structure of which has been determined by three-dimensional X-ray analysis of counter data. The crystals are monoclinic, P2â‚ /c, with a = 13.661(4) Å, b = 16.726(4) Å, c = 21.442(6) Å and Å= 106.00(4) Å and z = 4. The structure was solved by conventional Patterson and Fourier methods and refinement by full-matrix least squares led to R = 0.078 for the 1495 reflections for which |Fâ‚’]² > 3σ([Fâ‚’]²). The molecular structure of (Pd(dpm)Br)₂ is based upon an approximately linear Br,Pd,Pd,Br chain which contains a direct Pd-Pd bond of 0 2.699(5) Å bridged by two dpm ligands. An idealised square planar environment is observed about each Pd atom but there is a pronounced twist about the Pd-Pd bond resulting in an angle of 39º between the pair of P,Pd,P,Pd mean planes containing P atoms which belong to different dpm ligands but which are bonded to a common Pd atom. The crystal structure of Feâ‚‚ (CO₂(C₇H)₂, a product of the application of the olefin metathesis catalyst WC1₆-Câ‚‚H₅OH-Câ‚‚H₅AlClâ‚‚ to the compound Fe(CO)₃ cycloheptatriene, has been determined by a three-dimensional X-ray analysis. The crystals are orthorhombic, space group Cmcm, with a= 10.180(2) Å, b = 8.278(2) Å, c = 19.128(3) Å and Z = 4. Crystallographic 2mm symmetry (C2v) is imposed upon a single molecule with the asymmetric unit consisting of one quarter of a molecule. The structure was solved by conventional Patterson and Fourier methods and full-matrix least squares refinement led to R = 0.083 for the 366 counter-collected reflections for which |F‚’ > 3([F‚’]²). The molecular structure consists of a F(CO)â‚„ core which contains an Fe-Fe bund of 2.588(6) Å, two bridging carbonyl groups and two terminal carbonyl groups. Each iron atom is also bonded to a cycloheptadienyl ligand which co-ordinates in a penta-hapto fashion via a pentadienyl moiety. The reaction of the compound Fe(CO)₃ cyclo-octatetraene with the olefin metathesis catalyst described above yields a crystalline product Feâ‚‚ (CO)₆C‚ ₆H‚ ₆ , the structure of which has been determined by a three-dimensional X-ray analysis of counter data. The crystals are orthorhombic, space group Pbc2 (a non-standard setting of Pca2‚ ), with a= 6.369(1) Å, b 22.888(4) Å, c = 13.185(2) Å and Z = 4. The structure was solved by conventional Patterson and Fourier methods and full-matrix least squares refinement led to R = 0.053 for the 1538 reflections for which |F‚’] > 3([’]). The molecular structure which contains a pseudo C symmetry axis consists two Fe(CO) groups each bonded to 1,3-diene moieties in a pentacyclo|9.5.0.0.0.0| ring system. The reaction of 3-isopropenyl-3-methylcyclohexan-1-one with boron trifluoride-dichloromethane under cyclisation reaction conditions yields a minor crystalline product C₃ The crystals are monoclinic, P2‚ /c, with a= 12.619(2) Å, b = 12.971(2) Å, c = 11.692(2) Å, Å= 108.07(1)º and Z = 4. A three-dimensional X-ray analysis using counter data was solved by symbolic addition and Fourier methods and full-matrix least squares refinement led to R 0.070 for the 1327 reflections for which |F‚’] > 3([F‚’]). The molecule consists of two bicyclo|3.2.1| ring systems which are linked by both a carbon-carbon single bond and an intramolecular hydrogen bond which is formed from an alcohol function and the oxygen atom of an ether linkage.