Preheat the oven to 375°. On a baking sheet, toast the bread for 8 minutes, until golden. Brush the toasts with olive oil and rub them all over with the whole garlic clove. Put 1 toast in the bottom of each of 4 bowls.
In a deep skillet, heat the 1/4 cup of oil. Add the smashed garlic and the chiles and cook over moderate heat for 2 minutes. Add the wine and cook over moderately high heat for 2 minutes. Add the clam juice and bring to a boil. Add the clams and tomatoes, cover and cook for 2 minutes. Stir in the mussels and scallops, cover and cook over high heat until the clams and mussels open and the scallops are just cooked, 3 minutes. With a slotted spoon, transfer the seafood to the bowls. Boil the broth for 1 minute, until slightly reduced. Add the basil, season lightly with salt and pour the broth into the bowls. Drizzle with oil and serve.