We report on coherent manipulation of electron spins in an antiferromagnetically coupled spin triangle ${{\mathrm{Cu}}_{3}\mathrm{\text{\ensuremath{-}}}X}$ ($X=\mathrm{As}$, Sb) impregnated in freestanding nanoporous silicon (NS) by using 240 GHz microwave pulses. Rabi oscillations are observed and the spin coherence time is found to be ${T}_{2}=1066\text{ }\text{ }\mathrm{ns}$ at 1.5 K. This demonstrates that the ${{\mathrm{Cu}}_{3}\mathrm{\text{\ensuremath{-}}}X}\mathrm{\text{:}}\mathrm{NS}$ hybrid material provides a promising scheme for implementing spin-based quantum gates. By measuring the spin relaxation times of samples with different symmetries and environments we give evidence that a spin chirality is the main decoherence source of spin triangle molecules.