Exxon Mobil Corp. said Tuesday that it was buying land in the much sought after Permian Basin region from the Bass family for $5.6 billion in stock and up to $1 billion in contingent cash payments. Exxon Mobil is buying companies owned by the oil family closely associated with Fort Worth, Texas, that have an estimated potential for 3.4 billion barrels of oil equivalent production, including in New Mexico’s Delaware Basin, an area…