Compounds and compositions comprising specific metal salts of bicyclo[2.2.1]heptane dicarboxylate salts in order to provide highly desirable properties within polyolefin articles are provided. The inventive salts and derivatives thereof are useful as nucleating and/or clarifying agents for such polyolefin, provide excellent crystallization temperatures, stiffness, and calcium stearate compatibility within target polyolefin. Also, such compounds exhibit very low hygroscopicity and therefore excellent shelf stability as powdered or granular formulations. Polyolefin additive compositions and methods of producing polyolefin with such compounds are also contemplated within this invention.