Pure and mixed {Nd/Yb} carborane-based metal–organic frameworks integrating slow magnetic relaxation, magnetocaloric effect and NIR emission

Abstract

Multi-lanthanide metal–organic frameworks (MOFs) offer a flexible route for designing multifunctional materials. Here we report a carborane-based isostructural series of MOFs of formula {[(Nd_yYb_1−y)₃(mCB-L)₄(NO₃)(DMF)_x]_n·Solv}, including the homometallic Nd (y = 1) and Yb (y = 0) compounds and a mixed Nd/Yb analogue (y = 0.44). Magnetic, magnetocaloric and near-infrared (NIR) optical properties were investigated by dc/ac magnetometry, X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD), and photoluminescence. Nd³⁺ and Yb³⁺ yield MOFs combining slow relaxation of the magnetization (U/k_B ∼ 19 K), cryogenic magnetocaloric response (−ΔS_m ∼ 1.6 R at 5 T, 1.8 K) and ion-centered NIR luminescence. Notably, the mixed Nd/Yb MOF further extends this multifunctionality by exhibiting dual NIR emission at 998 nm and 1060 nm arising from partial Nd → Yb energy transfer. These results underscore carborane ligands as effective blocks for engineering multi-lanthanide frameworks, and highlight {Nd/Yb} MOFs as multifunctional materials for quantum technologies, optical communication, and cryogenic cooling.