  We present new X-ray temperatures and improved X-ray luminosity estimates for
15 new and archival XMM-Newton observations of galaxy clusters at intermediate
redshift with mass and luminosities near the galaxy group/cluster division
(M2500 < $2.4\times 10^{14} h_{70}^{-1} M_\odot$, L < $2\times 10^{44}$ erg
$s^{-1}$, 0.3< z < 0.6). These clusters have weak-lensing mass measurements
based on Hubble Space Telescope observations of clusters representative of an
X-ray selected sample (the ROSAT 160SD survey). The angular resolution of
XMM-Newton allows us to disentangle the emission of these galaxy clusters from
nearby point sources, which significantly contaminated previous X-ray
luminosity estimates for six of the fifteen clusters. We extend cluster scaling
relations between X-ray luminosity, temperature, and weak-lensing mass for
low-mass, X-ray-selected clusters out to redshift $\approx$0.45. These
relations are important for cosmology and the astrophysics of feedback in
galaxy groups and clusters. Our joint analysis with a sample of 50 clusters in
a similar redshift range but with larger masses (M500 < $21.9 \times 10^{14}
M_\odot$, $0.15 \leq z \leq 0.55$) from the Canadian Cluster Comparison Project
finds that within r2500, $M \propto L^{0.44 +/- 0.05}$, $T \propto L^{0.23 +/-
0.02}$, and $M \propto T^{1.9 +/- 0.2}$. The estimated intrinsic scatter in the
M-L relation for the combined sample is reduced to ${\sigma}_{log(M|L)}=0.10$,
from ${\sigma}_{log(M|L)}=0.26$ with the original ROSAT measurements. We also
find an intrinsic scatter for the T-L relation, ${\sigma}_{log(T|L)}=0.07 +/-
0.01$.
