Which of the following best describes an "improper bond" in the context of chemistry or materials science?
A) A bond formed between atoms with mismatched electron configurations.
B) A bond between two different types of molecules that is too weak to be stable.
C) A bond that occurs when atoms do not adhere to the ideal bond angles or lengths, leading to structural issues.
D) A bond where atoms share electrons unevenly, leading to a polar covalent bond.