Synthesis, structure, and bonding of weakly coordinating anions based on CN adducts.

The addition of alkali or silver salts of dicyanoamide (dca), tricyanomethanide (tcm) and tetracyanoborate (tcb) to a solution of B(C6F5)3 in diethyl ether affords salts containing very voluminous B(C6F5)3 adduct anions of the type [E(CN)n−]·[ B(C6F5)3]n: E = N (dca_nb with n = 1, 2; b = B(C6F5)3); E = C (tcm_nb with n = 1, 2, 3), and E = B (tcb_nb with n = 1, 2, 3, 4). Salts bearing these anions such as B[(CN)·B(C6F5)3]4− (= [B(CN)4−]·[ B(C6F5)3]4), C[(CN)·B(C6F5)3]3− (= [C(CN)3−]·[ B(C6F5)3]3), and N[(CN)·B(C6F5)3]2− (=[N(CN)2−]·[ B(C6F5)3]2) can be prepared in good yields. They are thermally stable up to over 200 °C and dissolve in polar organic solvents. Depending on the stoichiometry mono-, di-, tri-, or tetraadduct formation is observed. The solid state structures of dca_2b, tcm_3b and tcb_4b salts show only long cation···anion contacts and thereby weak interactions, large anion volumes and only small distortions of the dca, tcm or tcb core enwrapped between B(C6F5)3 groups. That is why these anions...