Manganese complexes with substituted bisphosphonates useful as imaging and therapeutic agents

A compound useful as a magnetic resonance imaging (MRI) contrast agent and a therapeutic agent, said compound having a structure represented by:

• Y—X—Z
• wherein,
• X is Mn(II), and Y and Z are each independently a bisphosphonate of the formula:
• wherein:
• R1 is —OH,
• R2, R3, R4, R5 and R6 are each independently H, alkyl, or -LR′, wherein at least one of R2, R3, R4, R5 and R6 is -LR′,
• wherein each L is present or absent and when present is a linking group, and
• wherein each R′ is independently a therapeutic agent,
• or a pharmaceutically acceptable hydrate thereof,
• wherein said compound has a stoichiometry of 1:2 (Mn(II):
• bisphosphonate),
• wherein said compound is a salt comprising at least one alkali metal and at least one alkaline earth metal, and
• wherein the contrast agent has a molecular weight of less than 2,000 daltons.