which provides a way of constraining the Heisenberg exchange through fitting the high temperature susceptibility. Figure plots the inverse of the magnetic susceptibility where a fit of the data for T > 100 K (in the high temperature paramagnetic regime) affords Θ 𝐶𝐶𝐶𝐶 = -18.5 K ≡ -12.89 cm -1 , which fixes the sum 𝐽𝐽 rr + 𝐽𝐽 CR in our analysis discussed below with regards to the parameterization of the magnetic Hamiltonian. We note that this implies, based on the sign of the sum of the exchange constants, that the dominant exchange is antiferromagnetic.