Cuneane

Abstract: [reaction: see text] This study is a multinational, multidisciplinary contribution to the thermochemistry of dimethyl1,4-cubanedicarboxylate and the corresponding isomeric, cuneane derivative and provides both structural and thermochemical information regarding the rearrangement of dimethyl 1,4-cubanedicarboxylate to dimethyl 2,6-cuneanedicarboxylate. The enthalpies of formation in the condensed phase at T = 298.15 K of dimethyl 1,4-cubanedicarboxylate (dimethyl pentacyclo[4.2.0.0.(2,5)0.(3,8)0(4,7)]octane-1,4-dicarboxylate) and dimethyl 2,6-cuneanedicarboxylate (dimethyl pentacyclo[3.3.0.0.(2,4)0.(3,7)0(6,8)]octane-2,6-dicarboxylate) have been determined by combustion calorimetry, delta(f) H(o)m (cr)/kJ x mol(-1) = -232.62 +/- 5.84 and -413.02 +/- 5.16, respectively. The enthalpies of sublimation have been evaluated by combining vaporization enthalpies evaluated by correlation-gas chromatography and fusion enthalpies measured by differential scanning calorimetry and adjusted to T = 298.15 K, delta(cr) (g)Hm (298.15 K)/kJ x mol(-1) = 117.2 +/- 3.9 and 106.8 +/- 3.0, respectively. Combination of these two enthalpies resulted in delta(f) H(o)m (g., 298.15 K)/kJ x mol(-1) of -115.4 +/- 7.0 for dimethyl 1,4-cubanedicarboxylate and -306.2 +/- 6.0 for dimethyl 2,6-cuneanedicarboxylate. These measurements, accompanied by quantum chemical calculations, resulted in values of delta(f) Hm (g, 298.15 K) = 613.0 +/- 9.5 kJ x mol(-1) for cubane and 436.4 +/- 8.8 kJ x mol(-1) for cuneane. From these enthalpies of formation, strain enthalpies of 681.0 +/- 9.8 and 504.4 +/- 9.1 kJ x mol(-1) were calculated for cubane and cuneane by means of isodesmic reactions, respectively. Crystals of dimethyl 2,6-cuneanedicarboxylate are disordered; the substitution pattern and structure have been confirmed by determination of the X-ray crystal structure of the corresponding diacid.

Abstract: Phosphorus is known to form a wide range of homoatomic clusters. Known examples that contain the P 8 nucleus are the substituted and anionic clusters P 8 R 4 , P 8 R 6 , and P 8 6- . Although the neutral P 8 naked cluster has never been prepared, there has been theoretical interest in this molecule in recent years. Neutral P 8 would be isoelectronic with (CH) 8 hydrocarbons for wich at least 13 structural isomers have been prepared. We report the results of geometry optimized ab initio SCF MO calculations with 4-31G * and 6-31G * basis sets for P 8 in the cubane, octabisvalene, and cuneane isomeric forms

Abstract: The octanuclear coordination cage [Ni8(L14Naph)12](BF4)16 has the core structure of a ‘cuneane’ - a toplogical isomer of a cube - with a metal ion at each of the eight vertices and bridging ligand spanning each of the twelve edges; this is the only possible 8-vertex polyhedron other than a cube that will form a cage in which each metal is connected to three others.