## 1 Introduction  
Carbon monoxide releasing molecules (CORMs) are drugs that are examined to explicitly convey carbon monoxide (CO) to unhealthy or aggravated tissues to start and advance remedial impacts at the site of disease. In several mammalian tissues, carbon monoxide mitigates important physiologically effects embracing antiproliferative, anti-inflammatory, and anticoagulative responses [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]. Metal carbonyl complexes have been dominatingly assessed as CORMs. There are currently various models available in the literature, with CORM-2 and CORM-3 (Figure 1) being the best-known complexes of this class of pharmaceutical compounds. The molecules are known to reverse the inhibition of mitochondrial biogenesis [11; 12; 13; 14; 15] and prevent doxorubicin-induced cardiac cell death [16; 17]. CORM-2 and CORM-3, e.g., exert in vivo a positive effect in doxorubicin (Dox)-induced cardiomyopathy. CORM-2 protects the myocardium from Dox exposure by decreasing apoptosis and oxidative stress, while CORM-3, in a rat model of Dox-induced cardiomyopathy, induces a positive inotropic effect by increasing systolic pressure of the heart [17]. CORMs have also recently been evaluated as anticancer compounds [18],and their liberated CO plays an important role in vascular functions with concentration-dependent pro-angiogenic [19; 20; 21; 22; 23] and anti-angiogenic [24] effects [25]. Our contribution to the field was the introduction of 17-electron Re complexes [26; 27; 28] (Figure 1) showing cardioprotective [13] and anticoagulative [6] effects. Because of their unique signatures, vibrational spectroscopy is the most commonly used structural technique for the characterization of such chemical systems. Metal carbonyl complexes are recognized for their distinctive infrared (IR) properties. They exhibit energetically segregated vibrations in a segment of the electromagnetic spectrum (characteristically in the 2100-1800 cm\({}^{-1}\) region) amiable to rapid interpretation. This characteristic has allowed, e.g., for the IR mapping of several metal carbonyl-based drugs in live cells [29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39]. In recent years, macromolecular systems have also begun to be exploited as CORM carriers in an attempt to improve the pharmacokinetic properties of the molecules [40; 41; 42]. To date micelles [43; 44], magnetic iron oxide particles [45], porous coordination polymers [46], polymer matrices [47; 48; 49] and nanoparticles [50; 51; 52; 53], have been described. Permeable silica-based materials are especially appealing for drug-delivery applications because of their biocompatibility and degradability, in addition to their thermal and chemical stability. However, their synthesis is expensive, tedious and habitually requires poisonous substances. In 1999, [PERSON] proposed the utilization of natural diatoms as an option in contrast to manufactured silica-based materials for bio-applications [54]. Diatoms are unicellular organisms flourishing in all aquatic and wet environments. These creatures have the remarkable element of being encased inside a cell wall made of hydrated silicon dioxide called a frustule. The hereditarily controlled design of the frustule of these creatures surpasses the current human designing abilities and, because of their abundance, various shapes, and physical-chemical properties, they can be very useful in material chemistry, biology, and medicine. Effective frustule encapsulation has been accounted for several medications [55; 56; 57; 58; 59; 60], but the key for the further development of these composite materials is also a thorough comprehension of the drug distribution in the same. Within the context above, we have decided to functionalize via standard chemisorption techniques _Coscinodiscus_ diatoms frustules with the promising CO releasing drug _cis_-[Re(CO)\({}_{2}\)Br\({}_{4}\)]\({}^{2-}\) (ReCORM-2) and B\({}_{12}\)-ReCORM-2 (Figure 1).