The development of low-carbon binders has been recognized as a means of reducing the carbon footprint of the Portland cement industry, in response to growing global concerns over CO2 emissions from the construction sector. This paper reviews recent progress in the three most attractive low-carbon binders: alkali-activated, carbonate, and belite-ye'elimite-based binders. Alkali-activated binders/materials were reviewed at the past two ICCC congresses, so this paper focuses on some key developments of alkali-activated binders/materials since the last keynote paper was published in 2015. Recent progress on carbonate and belite-ye'elimite-based binders are also reviewed and discussed, as they are attracting more and more attention as essential alternative low-carbon cementitious materials. These classes of binders have a clear role to play in providing a sustainable future for global construction, as part of the available toolkit of cements.

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Two triosmium complexes of 1,4-bis(ferrocenyl)-1,3-butadiyne, Os 3 (CO) 10 (µ 3 -FcC 4 Fc) (2) and Os 3 -(CO) 11 (µ 3 -FcC 4 Fc) (3) (Fc ) (C 5 H 5 )Fe(C 5 H 4 )), have been prepared and structurally characterized. In 2 one of the triple bonds of the butadiyne grouping is coordinated as a triple bridge to a triangle of three osmium atoms. In 3 the triosmium cluster is opened and is coordinated as a linear chain to both triple bonds. The electronic communication measured via redox potentials of the ferrocenyl groups indicates that the metal atoms increase the electronic communication in 3 and decrease it in 2.

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