One-quadrupole-phonon states of vibrational nuclei have been observed throughout the nuclear chart. Collective quadrupole excitations of symmetric and mixed-symmetric character allow for investigating the underlying microscopic nuclear structure as well as the effective proton-neutron interaction. Isovector valence-shell excitations are distinct especially near shell closures. The N = 80 isotones around the doubly-magic nucleus Sn-132 and the region around the doubly-magic nucleus Pb-208 are of particular interest. Projectile Coulomb-excitation experiments on the radioactive nucleus Sm-142 and the stable nuclei Hg-202 and Hg-204 were performed in order to further our understanding of nuclear structure in these regions. The decay strength of the first excited state of Sm-142 is determined to B(E2;2_1^+ -> 0_1^+) = 32 (4) W.u. It is a foundation for the investigation of a possible restoration of shell stabilization in N = 80 isotones above the Z = 58 subshell closure. The 2_1,ms^+ state of Po-212 has recently been identified. The nucleus Hg-204 is the particle-hole conjugate to Po-212 with respect to the doubly-magic nucleus Pb-208. Hg-204 was investigated together with its neighboring even-even isotope Hg-202 for comparison to the situation in Po-212. One quadrupole-phonon mixed-symmetry states are identified in both nuclei, with transition strengths of B(M1;2_7^+ -> 2_1^+) = 0.16 (7) µ_N^2 in Hg-202 and B(M1;2_2^+ -> 2_1^+) = 0.20 (2)µ_N^2 in Hg-204. This is the first time, that isovector valence-shell excitations have been identified in this mass region, using complete sets of decay strengths.