= Solution
A suitable structure is a triangular Ti$_3$ <metal cluster> with one <1,2-Bis(dimethylphosphino)ethane> chelate and one terminal <chloride> at each <titanium>, and one <bridging ligand> $\mu$-Cl spanning each edge. Include a direct Ti–Ti single <metal-metal bond> along each edge. The last panel distinguishes these direct bonds from the <chloride> bridges.
The six chlorides have total formal charge $-6$, so equivalent centers are \b[Ti(II), $d^2$]. At each <titanium> the two <phosphorus> donors supply four <electrons>, the terminal <chloride> supplies two, and the two incident <chloride> bridges each donate a pair in ionic <electron counting>. Two incident Ti–Ti single bonds supply another two <electrons>:
$$
\boxed{\mathrm{VE(Ti)}=2_d+4_{\mathrm{P,P}}+2_{\mathrm{Cl}}+2(2)_{\mu\mathrm{-Cl}}+2_{\mathrm{Ti-Ti}}=14.}
$$
Each $d^2$ center can contribute one <electron> to each of its two edge bonds, making three bonds from six <metal> <electrons> overall. \b[This is a 14-<electron> early-<metal cluster>, not an 18-<electron> complex.] Forcing the <18-electron rule> here would invent excessive bond orders. <chloride> bridges donate to more than one center, so summing local counts is not the same as counting distinct <electrons> of the whole cluster.
Back to article page
