Kitaev interactions through extended superexchange pathways in the $${j}_{{\mathsf{eff}}}=1/2$$ Ru3+ honeycomb magnet RuP3SiO11

Magnetic materials are composed of the simple building blocks of magnetic moments on a crystal lattice that interact via magnetic exchange. Yet from this simplicity emerges a remarkable diversity of magnetic states. Some reveal the deep quantum mechanical origins of magnetism, for example, quantum spin liquid (QSL) states in which magnetic moments remain disordered at low temperatures despite being strongly correlated through quantum entanglement. A promising theoretical model of a QSL is the Kitaev model, composed of unusual bond-dependent exchange interactions, but experimentally, this model is challenging to realise. Here we show that the material requirements for the Kitaev QSL survive an extended pseudo-edge-sharing superexchange pathway of Ru³⁺ octahedra within the honeycomb layers of the inorganic framework solid, RuP₃SiO₁₁. We confirm the requisite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mrow><mml:mi>j</mml:mi></mml:mrow> <mml:mrow><mml:mi>eff</mml:mi></mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mfrac><mml:mrow><mml:mn>1</mml:mn></mml:mrow> <mml:mrow><mml:mn>2</mml:mn></mml:mrow> </mml:mfrac> </mml:math> state of Ru³⁺ in RuP₃SiO₁₁ and resolve the hierarchy of exchange interactions that provide experimental access to an unexplored region of the Kitaev model.