Rhodium bulk properties

In search for a model giving a concise description of all these observed sterical effects, the concept of the accessible molecular surface (AMS) of the rhodium center within the flexible [(P2)Rh] fragment has been developed for the catalyst system of type 13. It has been demonstrated how the shape and the size of the open cavity is determined not only by the P-Rh-P angle and the steric bulk of the groups R at phosphorus, but also by the flexibility of R and by possible internal movements within the chelate ring. All relevant parameters for the description of the intrinsic steric properties of the [(P2)Rh] fragment is reflected by the cavity. 

Crystalline-state photochromism usually proceeds with considerably lower interconversion ratios of less than 15% because the light penetration into the bulk crystal is prohibited by the absorption of the photo-generated isomer (inner-filter effects) [3,4]. The fully reversible crystalline-state photochromism of 1 can be partly attributed to its photochromic property. The rhodium dithionite complex 1 belongs to a unique class of photochromic compounds, which exhibits a unimolecular type T inverse photochromism [13]. The type T inverse photochromism means that the back reaction occurs thermally and the A.max of the absorption spectrum of 1 is longer than that of 2. If the back reaction occurs photochemically and the XmaK of the initial absorption spectrum is shorter than that of the photo-generated isomer, it is called type P positive photochromism and is known as a common photochromic system. 

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