Impact of Metal Heterogeneity on Multivariate and High-Entropy MOF SBUs.
Abstract
In chemically complex multimetal systems, how local coordination asymmetry emerges and propagates to define the bulk structural behavior remains fundamentally unresolved. In high-entropy metal-organic frameworks (MOFs), long-range crystallographic order coexists with intrinsic chemical disorder, yet a quantitative relationship among metal identity, local coordination geometry, and lattice-scale response has not been established. Here, we demonstrate that metal heterogeneity induces well-defined, composition-dependent distortions within trinuclear secondary building units (SBUs), which propagate coherently to produce measurable lattice-level structural changes. Using a porphyrinic TCPP framework with conserved topology, metal identity was varied across mono-, bi-, tri-, and five-metal compositions containing Fe, Co, Ni, Cu, and Zn. Nearly 20 compositions and ∼50 element-specific extended X-ray absorption fine structure (EXAFS) measurements provide metal-dependent bond-distance references across the full series. Single- and bimetallic references resolve M-O, M-C, and M-M distances, showing that heterometal substitution generates asymmetric, occupancy-dependent node distortions. In tri- and five-metal compositions, EXAFS signatures remain distributed rather than collapsing to a single averaged geometry, indicating persistent local heterogeneity within the conserved framework. These local distortions correlate with reproducible, composition-dependent lattice-parameter shifts while retaining long-range order. Time-resolved X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS) further reveal dynamic, metal-dependent incorporation during framework formation, while molecular dynamics (MD) simulations identify metal-nitrate binding and precursor lability as descriptors that rationalize early incorporation and late substitution trends. Together, these results provide an experimentally anchored framework for connecting metal identity, local coordination asymmetry, lattice response, and time-dependent incorporation in multivariate and high-entropy MOFs.