Both would be important nutrients to try and get into his diet. Breast milk does not supply adequate amounts of either. Try to add to his diet a vitamin C fortified juice or fruit puree, or add kiwi, oranges, or ripe melon. Also high in vitamin C are red peppers and broccoli. He should be eating an iron fortified baby cereal or getting iron drops if he refuses the cereal.
Iron contributes to proper cognitive development, and helps with appetite.
You may want to try and get him to take a child's multivitamin in order to assure the proper intake of vitamins until he is further along in eating solids. Do not concentrate on any one food to the exclusion of another, but you do want to keep the bulk of his diet low. That means include nutrient and calorically dense foods. Because he is so little, he won't be able to eat a large volume of food so has to get his nutrition in a small package. Higher fat foods like peanut butter, meat, eggs, and cheese are good choices.