Using ab initio electronic structure calculations, we study a cluster-assembled form of carbon which is based on C28 units arranged in a diamond crystal (hyperdiamond). We investigate how the charge density and electronic spectrum of an isolated C28 unit is altered in the infinite lattice. We analyze the nature of electronic states near the Fermi level of both an isolated C28 cluster and its solid form. A tight binding model, with parameters fitted to reproduce energy eigenvalues calculated from first principles, provides insight on how the states of hyperdiamond are derived from those of C28.491284468453