The flexibility of the bicyclo[2.2.1]heptane-based tricyclic bridged system in longifolene is analysed based on x-ray structural data. In this context, the molecular structure of three differently substituted longifolenes has been analysed. The highly substituentdependent conformation provides scope for the synthesis of a variety of commercially oriented products.

MULTAN is the most widely used package for structure determination. However, there are situations where even after utilizing all possible built-in routes the solution is not reached and these become “difficult structures”. If such a structure (a) has one or more heavy atoms, (b) is “chicken-wire” with predominant aromatic character, (c) has weak diffraction data, the new approaches discussed will lead to a unique structure solution by introducing simple, economic and time saving ideas into the MULTAN package.

The crystal structure of C₁₂OH₂₀ (lR-6R-4R-2 R-3,7,7-trimethyl-4-(2-hydroxyethyl) bicyclo [4.1.0] hept-2-ene) has been determined by X-ray diffraction. The compound crystallizes in space group P2₁2₁2₁ witha = 5.893(1),b = 22.572(2), c = 26.164(3) Å,V = 3480.3 Å₃, Z= 12. The structure was solved by modified direct methods and refined to anR value of 0.081 for 607 unique reflections. Each asymmetric unit has three molecules which are held together through intermolecular hydrogen bonds resulting in a novel spiral-type arrangement of molecules. The six-membered ring has a half-chair conformation.

Room temperature reactions of [Fe₂(CO)₆(μ -Se₂)] with the diacetylenes, RC≡ CC≡ CH(R = Me, n-Bu) yield the products, [(CO)₆Fe₂{μ-SeCC(H)C(R)SeCSe}]; X-ray analysis of the R = Me compound has been carried out and reveals an unusual cyclisation of the diacetylene with incorporation of a selenium atom to form a cyclic C₄Se ligand attached to the Fe₂(CO)₆Se₂ core.