  The massive infrared dark cloud G0.253+0.016 projected 45pc from the Galactic
centre contains ~10^5Msun of dense gas whilst being mostly devoid of observed
star-formation tracers. To scrutinise the physical properties, dynamics and
structure of this cloud with reference to its star-forming potential, we have
carried out a concerted SMA and IRAM 30m study of this cloud in dust continuum,
CO isotopologues, shock tracing molecules, as well as H$_2$CO to trace the gas
temperature. We detect and characterise the dust cores within G0.253+0.016 at
~1.3 mm and find that the kinetic temperature of the gas is >320K on
size-scales of ~0.15 pc. Analysis of the position-velocity diagrams of our
observed lines show broad linewidths and strong shock emission in the south of
the cloud, indicating that G0.253+0.016 is colliding with another cloud at
v(LSR)~70 km/s. We confirm via an analysis of the observed dynamics in the CMZ
that it is an elongated structure, orientated with Sgr B2 closer to the Sun
than Sgr A*, however our results suggest that the actual geometry may be more
complex than an elliptical ring. We find that the column density PDF of
G0.253+0.016 is log-normal with no discernible power-law tail, consistent with
little star formation, and that its width can be explained in the framework of
theory predicting the density structure of clouds created by supersonic,
magnetised turbulence. We also present the delta-variance spectrum of this
region, and show it is consistent with that expected for clouds with no star
formation. Using G0.253+0.016 as a test-bed of the conditions required for star
formation in a different physical environment to that of nearby clouds, we also
conclude that there is not one column density threshold for star formation, but
instead this value is dependant on the local physical conditions. [Abbrv.]
