Hydrogen terminal-bridging

There is a marked difference in chemical reactivity between bridging and terminal hydrogens. Terminally bonded hydrogens readily react in a similar manner to that observed for mononuclear hydrides. Thus reactions with chlorinated hydrocarbons such as carbon tetrachloride yield the chloro cluster complexes and chloroform. In contrast, bridging hydrides are stable and may be studied in chlorinated sol-... 

Of the atoms within the carboranes, the bridge hydrogens (rule 2) are in the most alien environments (as compared to the common one-coordinate terminal hydrogens). Most bridge hydrogens are 100% over their normal coordination environment (two-coordinate), whereas some are 200% over normal (three-coordinate). 

The compound Ru4(jt-H)4(CO)12 is obtained as a yellow air-stable powder, which is soluble in most organic solvents, but insoluble in water. The IR spectrum contains v(CO) bands at 2081 (s), 2067 (vs), 2030 (m), 2024(s), and 2009(w)cm-1 (cyclohexane solution) the HNMR spectrum has a resonance at <5 — 17.98 (CDC13 solution). The molecular structure of Ru4(/i-H)4(CO)12 has been determined by X-ray diffraction the four hydrogen atoms bridge the edges of the tetrahedral Ru4 core in a D2d arrangement, while three CO ligands are terminally bonded to each ruthenium.8 The deuterated complex Ru4(/i-D)4(CO)12 can be prepared in the same way if D2 is used in place of H2.6... 

The other ligands in a hydrido compound also influence the polarity of the M — H bond. The hydrogen atom may be bound as a terminal, bridging, or ligand ... 

Considering each boron-terminal hydrogen group p to supply a pair of electrons for the other bonds in the structure, there are p pairs of electrons available. One pair is necessary for each boron-boron-boron, three-center bond t and for each boron-boron, two-center bond y. One electron (half a pair) is necessary for each boron-hydrogen-boron, bridge bond 5- and for each extra terminal hydrogen x beyond the one already assumed on each boron. 

C5H5 = cyclopentadienyl Ht = terminal hydrogen, H = bridging hydrogen. 

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