Dynamics, cation conformation and rotamers in guanidinium ionic liquids with ether groups

•Novel ionic liquids based on the guanidinium cation are synthesized.•Structure-property relations are investigated in detail.•Ether side chain leads to higher melting point but accelerated dynamics.•Different conformations in solid and liquid state are found for ether and alkyl side chain.•Ether coordination increases the rotational barrier around the C-N bond of the guanidinium cation.