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Hyperpolarized orthohydrogen (o‐H₂) is a frequent product of parahydrogen‐based hyperpolarization approaches like signal amplification by reversible exchange (SABRE), where the hyperpolarizedo‐H₂signal is usually absorptive. We describe a novel manifestation of this effect wherein large antiphaseo‐H₂signals are observed, with¹H enhancements up to ≈500‐fold (effective polarizationP_H≈1.6 %). This anomalous effect is attained only when using an intact heterogeneous catalyst constructed using a metal–organic framework (MOF) and is qualitatively independent of substrate nature. This seemingly paradoxical observation is analogous to the “partial negative line” (PNL) effect recently explained in the context of Parahydrogen Induced Polarization (PHIP) by Ivanov and co‐workers. The two‐spin order of theo‐H₂resonance is manifested by a two‐fold higher Rabi frequency, and the lifetime of the antiphase HPo‐H₂resonance is extended by several‐fold.

Hyperpolarized orthohydrogen (o‐H₂) is a frequent product of parahydrogen‐based hyperpolarization approaches like signal amplification by reversible exchange (SABRE), where the hyperpolarizedo‐H₂signal is usually absorptive. We describe a novel manifestation of this effect wherein large antiphaseo‐H₂signals are observed, with¹H enhancements up to ≈500‐fold (effective polarizationP_H≈1.6 %). This anomalous effect is attained only when using an intact heterogeneous catalyst constructed using a metal–organic framework (MOF) and is qualitatively independent of substrate nature. This seemingly paradoxical observation is analogous to the “partial negative line” (PNL) effect recently explained in the context of Parahydrogen Induced Polarization (PHIP) by Ivanov and co‐workers. The two‐spin order of theo‐H₂resonance is manifested by a two‐fold higher Rabi frequency, and the lifetime of the antiphase HPo‐H₂resonance is extended by several‐fold.