A Complete 3 × 3 Metal × Halogen Isostructural Matrix: Opposing Ni/Pd/Pt and Cl/Br/I Trends in Hal···O(SO2) Halogen Bonds

Abstract

Isostructural exchange is a cornerstone of crystal engineering, yet systematic substitution has remained almost entirely one-dimensional; the sole two-axis study reported to date reached only 2 × 2 (Pd/Pt × Br/I) scope. Here we report the first complete two-axis 3 × 3 metal × halogen isostructural exchange: nine isomorphous Group 10 MII (Ni, Pd, Pt) sulfonamide-modified dithiocarbamate complexes bearing Cl, Br, or I (pairwise RMSD < 0.17 Å), all assembling into one architecture sustained by directional C−Hal···O(SO2) halogen bonds. Uniquely, the two axes drive opposing trends in the same contact: Cl → Br → I shortens and linearizes it, whereas Ni → Pd → Pt elongates it despite rising metal electronegativity. Held by a structurally invariant {MIINS3} anchor, the matrix separates the metal-driven and halogen-driven contributions to the contact geometry within one crystalline family. MEP, QTAIM/NCIPlot, EDA, and NBO analyses rationalize the metal-driven paradox: an LP(O) → σ*(C−Hal) charge transfer that grows from Cl to I yet attenuates along Ni → Pd → Pt, consistent with electron withdrawal through the M−N−SO2 linkage depleting sulfonyl-oxygen nucleophilicity. The {MIINS3} fragment thus behaves as a supramolecular equivalent in two independent dimensions, extending “metal identity masking” into a two-dimensional framework and defining a transferable blueprint for exchanges beyond 3 × 3.