[{"from": "human", "value": "Generate a molecule based on the given description. The molecule appears as a whitish to gray crystalline solid. Denser than water. Contact may irritate skin, eyes and mucous membranes. Used to make other chemicals."}, {"from": "gpt", "value": "[C][=C][C][=C-1][C][=C][Ring1][=Branch1].[C][=C][C][=C-1][C][=C][Ring1][=Branch1].[Mg+2]"}]