An overview of the electronic structure in trigonal bipyramidal clusters of main elements or mixed with transition metals

A Bonding Quandary—or—A Demonstration of the Fact That Scientists Are Not Born With Logic

“…We construct elsewhere a general relation between equatorial, apical and interaxial bonding in TBP compounds formed by main group elements alone, or containing three equatorial metals, over a wide range of skeletal electron counts. [22] Here, I only wish to remark how interaxial and skeletal bonding may correlate for a given electronic structure of the M 3 X 2 skeleton. In the context of Figure 3 and 6, we see that in Ni 3 S 2 compounds the 2e'' level is invariably depopulated.…”

“…The dramatic shortening of the S‐S distance to 2.26 Å confirms how prone these TBP frameworks are to various internal or external redox processes involving coupling (or decoupling) between all the vertices. We construct elsewhere a general relation between equatorial, apical and interaxial bonding in TBP compounds formed by main group elements alone, or containing three equatorial metals, over a wide range of skeletal electron counts 22. Here, I only wish to remark how interaxial and skeletal bonding may correlate for a given electronic structure of the M 3 X 2 skeleton.…”

Electronic Stabilization of Trigonal Bipyramidal Clusters: the Role of the Sn(II) Ions in [Pt5(CO)5{Cl2Sn(μ-OR)SnCl2}3]3– (R = H, Me, Et, iPr)

“…In previous studies, we examined the MO architecture of TBP clusters, either formed only by main group elements (e.g., B 5 H 5 2– ) or mixed with metals (e.g., M 3 S 2 species) . In particular, B 5 H 5 2– had raised divergent opinions about equatorial vs apical redistribution of the skeletal electron pairs. , Our analysis indicated how, from one σ hybrid and two p π orbitals per vertex, 15 basic MOs are constructed, of which only six are edge-bonding and populated (see Figure 1 of ref ). Among mixed M 3 S 2 TBPs, numerous L x M 3 S 2 structures ( x = 2, 3) were rationalized in terms of isolobal analogy and their variable TEC values (47–53), which normally induce loss of either M–S or M–M edge bonding .…”

“…Nine M–M TBP connectivities do not necessarily imply that, with respect to the PSEPT model, three additional electron pairs participate in skeletal bonding . Importantly, PSEPT is an extension of the Wade rules for main group TBPs such as B 5 H 5 2– (i.e., n vertexes + 1 = 6 skeletal electron pairs, which are remarkably the same as in C 4 H 4 tetrahedrane). In the M 5 clusters, the metals have generally additional electrons available, which may contribute to skeletal bonding.…”

“…For this reason, the Pt 5 Sn 6 system is comparable to main group TBPs, such as B 5 H 5 2– , which has six bonding electron pairs over nine edges. In other words, the PSEPT extension of the Wade rule , to metal clusters seems to be appropriate for these unusual Pt 5 clusters.…”