We demonstrate flexible multidimensional modulation formats, polarization multiplexed k-symbol check quadrature phase shift keying (PM-kSC-QPSK), based on PM-QPSK constellations for elastic optical networks. The experimental results show a significant optical signal noise ratio (OSNR) tolerance improvement for PM-2SC-QPSK and PM-4SC-QPSK over PM-QPSK in both back-to-back and 500 km transmission scenarios at the expense of spectral efficiency reduction. This flexible modulation method can be used in elastic optical networks to provide a trade-off between the spectral efficiency and OSNR tolerance.