  We present a new detailed multiband study of the merging cluster A3562, in
the core of the Shapley Concentration Supercluster. We analyzed new, low
frequency radio data performed at 240 MHz, 332 MHz and 610 MHz with the Giant
Metrewave Radio Telescope (GMRT). The new GMRT data allowed us to carry out a
detailed study of the radio halo at the centre of A3562, as well as of the
head--tail radio galaxy J1333--3141 embedded in it, and of the extended
emission around the peripheral cluster galaxy J1332--3146a. Thanks to the
present observations we could derive the integrated spectrum of the radio halo
with five data points in the frequency range 240 MHz -- 1.4 GHz. Our data show
a clear steepening of the total spectrum in this frequency range. Furthermore,
by comparing the GMRT 332 MHz image with a previously published VLA 1.4 GHz
image, we produced an image of the halo spectral index distribution. The image
shows a very complex structure, with an average value of
$\alpha^{1.4GHz}_{332MHz} \sim 1.5$ and a number of knots steepening up to
$\sim 2$. We performed a combined morphological and statistical analysis using
the radio images and the quantities derived from XMM--Newton and {\it Chandra}
observations. We discuss our results in the light of particle re--acceleration
processes in galaxy clusters. In particular, we outline an overall picture,
consistent with the available radio and X-ray data, in which the cluster merger
kinematics, the injection of turbulence and B--amplification induced by the
merger between A 3562 and SC 1329--313 are jointly taken into account.
