Fig. 1. Known structurally characterized homoleptic TMCCs without strong contacts to counterions. 14 VE: [M(CO)₂]^+/2+ Ag⁺, Hg²⁺; 16 VE: [M(CO)₄]^+/2+ Rh⁺, Pd²⁺, Pt²⁺; 17 VE: [M(CO)₄]⁺˙ Ni⁺; [M(CO)₅]⁺˙ Fe⁺ [M(CO)₆]⁺˙ Cr⁺, Mo⁺, W⁺; 18 VE: [M(CO)₄]⁺ Cu⁺; [M(CO)₅]⁺ Co⁺; [M(CO)₆]^{+/2+/3 +} Mn⁺, Tc⁺, Re⁺, Fe²⁺, Ru²⁺, Os²⁺, Ir³⁺; [M(CO)₇]⁺ Nb⁺, Ta⁺; 50 VE: [M₃(CO)₁₄]²⁺ {Ru₃}²⁺, {Os₃}²⁺.