We report the results of a search for serendipitous C ii 157.74 m emitters at z 4.4-4.7 using the Atacama Large Millimeter/submillimeter Array (ALMA). The search exploits the AS2UDS continuum survey, which covers ∼50 arcmin2 of the sky toward 695 luminous (S870 1 mJy) submillimeter galaxies (SMGs), selected from the SCUBA-2 Cosmology Legacy Survey 0.96 deg2 Ultra Deep Survey (UDS) field. We detect 10 candidate line emitters, with an expected false detection rate of 10%. All of these line emitters correspond to 870 m continuum-detected sources in AS2UDS. The emission lines in two emitters appear to be high-J CO, but the remainder have multi-wavelength properties consistent with C ii from z 4.5 galaxies. Using our sample, we place a lower limit of on the space density of luminous (LIR 1013 ) SMGs at z = 4.40-4.66, suggesting % of SMGs with mJy lie at 4 < z < 5. From stacking the high-resolution (∼0 15 full-width half maximum) ALMA 870 m imaging, we show that the C ii line emission is more extended than the continuum dust emission, with an average effective radius for the C ii of kpc, compared to re = 1.0 0.1 kpc for the continuum (rest-frame 160 m). By fitting the far-infrared photometry for these galaxies from 100 to 870 m, we show that SMGs at z ∼ 4.5 have a median dust temperature of Td = 55 4 K. This is systematically warmer than 870 m selected SMGs at z 2, which typically have temperatures around 35 K. These z 4.5 SMGs display a steeper trend in the luminosity-temperature plane than z ≤ 2 SMGs. We discuss the implications of this result in terms of the selection biases of high-redshift starbursts in far-infrared/submillimeter surveys.