We show that the electronic structures of the title compounds predicted by density functional theory are well described by tight binding models. We determine the frustration ratio, J 0 =J, of the Heisenberg model on the anisotropic triangular lattice, which describes the spin degrees of freedom in the Mott insulating phase for a range of PdðdmitÞ 2 salts. All of the antiferromagnetic materials studied have J 0 =J & 0:5 or J 0 =J * 0:9, and all salts with 0:5 & J 0 =J & 0:9 are known, experimentally, to be charge ordered valencebond solids or spin liquids. DOI: 10.1103/PhysRevLett.109.097206 PACS numbers: 75.10.Kt, 71.15.Mb, 74.70.Kn, 75.10.Jm The interplay of geometrical frustration and electronic correlations produces a wide range of exotic phenomena [1,2] in the organic charge transfer salts Me 4Àn Et n Pn½PdðdmitÞ 2 2 (henceforth Pn-n) [3]. At ambient pressure and low temperature, these materials are Mott insulators, many of which are driven superconducting by the application of hydrostatic pressure or uniaxial stress. Most salts display antiferromagnetic (AFM) order, but recent experiments [1,2] suggest that Me 3 EtP½PdðdmitÞ 2 2 (P-1) is a valence-bond solid (VBS), and Me 3 EtSb½PdðdmitÞ 2 2 (Sb-1) is a type II spin liquid (SL) [2], with a singlet gap but no triplet gap [4].In this Letter, we report density functional theory (DFT) calculations of the electronic structures of Sb-1 and P-1. We parametrize these results in terms of tight binding models and report the parameters found for a number of PdðdmitÞ 2 salts with AFM or charge ordered (CO) ground states. The simplest model that has been proposed for the insulating phases of the PdðdmitÞ 2 salts is the Heisenberg model on the anisotropic triangular lattice [1,2,5]. In this model, each site represents a PdðdmitÞ 2 dimer, J is the exchange coupling around the sides of square, and J 0 is the exchange interaction along one diagonal. We find that those materials that display long-range AFM order lie in the parameter regimes J 0 =J & 0:5 or J 0 =J * 1 where many-body theories predict long-range magnetic order. Further, all of the materials with CO, SL, or VBS ground states lie in the parameter regime 0:5 & J 0 =J & 0:9 where the low energy physics remains controversial because there are a number of competing states. We argue that this means that other terms in the Hamiltonian may be crucial for determining the ground state.The Heisenberg model on the anisotropic triangular lattice has been studied by a range of theoretical methods including linear spin-wave theory [6] [19]. Collectively, these studies suggest that Néel (, ) order is realized for J 0 =J & 0:5, and incommensurate (q, q) long-range AFM order is realized for J 0 =J $ 1 (in the special case J 0 =J ¼ 1, the 120 state with q ¼ 2=3 is realized). However, the ground state for 0:6 & J 0 =J & 0:9 remains controversial.Many PdðdmitÞ 2 salts undergo a Mott transition under hydrostatic pressure and/or uniaxial strain [1,2]. Therefore, it is possible that the Heisenberg model misses some essential physi...