Step 1: Apply the vector formula.
\[
\vec{AB} = (x_2 - x_1)\hat{i} + (y_2 - y_1)\hat{j} + (z_2 - z_1)\hat{k}
\]
Substituting values \( A(2, -3, 5) \) and \( B(3, -4, 7) \):
\[
\vec{AB} = (2 - 3)\hat{i} + (-3 + 4)\hat{j} + (5 - 7)\hat{k}
\]
Step 2: Simplify the components.
\[
\vec{AB} = -\hat{i} - \hat{j} - 2\hat{k}
\]
Final Answer:
\[
\boxed{-\hat{i} - \hat{j} - 2\hat{k}}
\]